5.7   HVAC Secondary Systems    

This group of building descriptors relate to the secondary HVAC systems. There is not a one-to-one relationship between secondary HVAC system components in the proposed design and the baseline building since the baseline building system is determined from building type, size and number of floors. Where the Standard Design for a building descriptor varies with the standard design HVAC system selection, the baseline is specified as a table with the applicable value for each of the 11 baseline systems.

The HVAC standard design (baseline) systems are described in the summary tables below for reference. The details of individual building descriptor definitions can be found in section 5.7.1 and in subsections under 5.7.

Table 16 – System #1 Description

Table 17 – System #2 Description

Table 18 – System #3 Description

Table 19 – System #5 Description

Table 20 – System #6 Description

Table 22 – System #9 Description

Table 23 – System #10 Description

Table 24 – System #11 Description

Table 25 – System #12 Description

Table 26 – System #13 Description

5.7.1  Basic System Information

HVAC System Name

Applicability

All system types

A unique descriptor for each HVAC System

Units

Text, unique

Input Restrictions

When applicable, this input should match the tags that are used on the plans.

Standard Design

None

System Type

Applicability

All system types

Definition

A unique descriptor which identifies the following attributes of an HVAC System:

•      Number of air decks (one to three);

•      Constant or variable air flow;

•      Type of terminal device; and

•      Fan configuration for multiple deck systems.

Units

List from the choices below

Input Restrictions

List

PTAC – Packaged Terminal Air Conditioner

PTHP – Packaged Terminal Heat Pump

PSZ-AC – Packaged Single Zone

PSZ-HP – Packaged Single Zone Heat Pump

PVAV – Packaged VAV with Reheat

VAV* – VAV with Reheat

PSZVAV* – Single Zone VAV

PSZVAVHP – Single Zone VAV Heat Pump

HV – Heating and Ventilation Only

CRAC – Computer Room Air Conditioner

CRAH – Computer Room Air Handler

FPFC – Four-pipe fan coil

DFDD – Dual-fan dual duct

RADFLR – Radiant floor heating and cooling

WSHP – water-source heat pump

* Choice includes series and parallel fan-powered boxes as zone terminal units

Standard Design

Based on the prescribed system type in the HVAC system map (see Section 5.1.2). The baseline system types are shown in the table below.

Table 27 – Baseline Building System Type

Air Distribution Type

Applicability

All system types

Definition

Type of air distribution system that is coupled with the HVAC system.  The choices are (overhead) mixing ventilation system, underfloor air distribution system (UFAD), and displacement ventilation system (DV).

Units

List:  Mixing, UFAD, DV

Input Restrictions

As designed

Standard Design

Mixing

Thermal zone List

Applicability

All system types      

Definition

Comprehensive list of all thermal zones served by a given HVAC system.

Units

None

Standard Design

Same as the proposed design

Input Restrictions

As designed

Total Cooling Capacity

Applicability

All system types

Definition

The installed cooling capacity of the project. This includes all:

•      Chillers;

•      Built-up DX; and,

•      Packaged cooling units.

Units

Cooling tons (12,000 Btu/h per ton)

Input Restrictions

As designed.

Standard Design

Autosize. The cooling capacity shall be oversized by 15%. If the number of unmet load hours exceeds 150, increase the cooling capacity according to the procedures in Chapter 2.

5.7.2 System Controls    

5.7.2.1 Control System Type

Control System Type

Applicability

All HVAC systems that serve more than one control zone, as well as the hydronic systems that serve building HVAC systems.

Definition

The type of control system for multizone HVAC systems and their related equipment. This input affects the proposed design system specification for zone level controls, supply air temperature reset controls, ventilation controls and fan and pump static pressure part-load curves. See the following building descriptors:

Ventilation Control Method

Terminal Heating Control Type

Pump Part-Load Curve

Fan Part-load Curve

Units

None

Input Restrictions

List: can be one of the following inputs

DDC Control to the Zone Level – direct digital control systems with control to the zone level

Other – other control systems, including pneumatic and DDC systems without control to the zone level

Standard Design

DDC Control to the Zone Level

5.7.2.2 Schedules

Cooling Schedule

Applicability

All cooling systems

Definition

A schedule that represents the availability of cooling

Units

Data structure: schedule, on/off

Input Restrictions

Schedule Group is prescribed in Appendix 5.4A and schedule values are prescribed in Appendix 5.4B. See Section 2.3.3 Considerations on how software shall assign schedules when the spaces served by the system are assigned to different schedule groups in Appendix 5.4A.

Standard Design

Same as the proposed design

Heating Schedule

Applicability

All systems

Definition

A schedule that represents the availability of heating

Units

Data structure: schedule, on/off

Input Restrictions

Schedule Group is prescribed in Appendix 5.4A and schedule values are prescribed in Appendix 5.4B. See Section 2.3.3 on how software shall assign schedules when the spaces served by the system are assigned to different schedule groups in Appendix 5.4A.

Same as the proposed design

Air-Handler Schedule

Applicability

All systems that do not cycle with loads

Definition

A schedule that indicates when the air handler operates continuously

Units

Data structure: schedule, on/off

Input Restrictions

Schedule Group is prescribed in Appendix 5.4A and schedule values are prescribed in Appendix 5.4B. See Section 2.3.3 on how software shall assign schedules when the spaces served by the system are assigned to different schedule groups in Appendix 5.4A.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.

Standard Design

Same as the proposed design

Air Handler Fan Cycling

Applicability

All fan systems

Definition

This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.

Units

List: Continuous or Cycles with loads

Input Restrictions

For four-pipe fan coil systems, As Designed.if the HVAC system serving the spaces includes a dedicated outside air source for ventilation; otherwise, fixed at Continuous.

For mechanical ventilation systems with operable windows, As Designed if the system includes interlocks or automatic window controls to prevent simultaneous operation; otherwise the proposed design input is fixed at Continuous.

For all other systems, fixed at Continuous.

Standard Design

 Cycles with loads for PTAC or FPFC systems; Continuous for all other standard design system types.

Optimal Start Control

Applicability

Systems with the control capability for flexible scheduling of system start time based on building loads.

Definition

Optimal start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.

Units

Boolean (Yes/No)

Input Restrictions

No (not allowed)

Standard Design

Not Not applicable

Night-Cycle HVAC Fan Control

Applicability

All systems

Definition

The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal zones during periods when the heating, cooling and fan systems are scheduled to be off. For this control, the space is controlled to the setback or setup temperature only; this control is not equivalent to a night purge control. The choices are:

•      Cycle on call from any zone

•      Cycle on call from the primary control zone

•      Stay off

•      Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.

Units

None

Input Restrictions

Cycle on call from any zone, except for systems with fan-powered boxes, where either Cycle on call from any zone or Cycle zone fans only is allowed.

Standard Design

Cycle on call from any zone

5.7.2.3 Cooling Control    

Cooling Supply Air Temperature

Applicability

Applicable to all systems

Definition

The supply air temperature setpoint at design cooling conditions

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

15F below the space temperature setpoint for interior zones; for all other zones,

20°F below the space temperature setpoint

Cooling Supply Air Temperature Control

Applicability

Any cooling system

Definition

The method of controlling the supply air temperature. Choices are:

•      No control – for this scheme the cooling coils are energized whenever there is a call for cooling

•      Fixed (constant)

•      Reset by warmest zone, airflow first

•      Reset by warmest zone, temperature first

•      Reset by outside air dry-bulb temperature

•      Scheduled setpoint

•      Staged setpoint  (for Single Zone VAV and DX with multiple stages)

Units

List (see above)

Input Restrictions

As designed

Standard Design

For baseline building systems 1 through 4, the SAT control is fixed. For systems 5 through 8,10 and 11, the SAT control shall be reset by warmest zone, airflow first. For system 9 (heating and ventilation) this input is not applicable.

Cooling Reset Schedule by OSA

Applicability

When the proposed design resets SAT by outside air dry-bulb temperature

Definition

A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 10):

•      The coldest cooling supply air temperature

•      The corresponding (hot) outdoor air dry-bulb setpoint

•      The warmest cooling supply air temperature

•      The corresponding (cool) outdoor air dry-bulb setpoint

Figure 10 – SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT)

Units

Data structure (two matched pairs of SAT and OAT, see above)

Input Restrictions

As Designed.

Standard Design

Not applicable

5.7.2.4 Heating Control

Preheat Setpoint

Applicability

Systems with a preheat coil located in the outside air stream

Definition

The control temperature leaving the preheat coil

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

Not Applicable

Heating Supply Air Temperature

Applicability

All systems

Definition

The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

95°F for system types 1-4; 70°F for multiple zone systems; no heating for data centers and computer rooms

Heating Supply Air Temperature Control

Applicability

Systems with the capability to vary heating SAT

Definition

The method of controlling heating SAT. Choices are:

•      No control – the heating coil is energized on a call for heating, but the supply air temperature is not directly controlled, but instead is dependent on the entering air temperature, the heating capacity and the airflow rate.

•      Fixed (constant)

•      Reset by coldest zone, airflow first

•      Reset by coldest zone, temperature first

•      Reset by outside air dry-bulb temperature

•      Staged Setpoint

•      Scheduled setpoint

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

Fixed (constant)

Heating Reset Schedule by OSA

Applicability

Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)

Definition

A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 11):

•      The hottest heating supply air temperature

•      The corresponding (cold) outdoor air dry-bulb threshold

•      The coolest heating supply air temperature

•      The corresponding (mild) outdoor air dry-bulb threshold

Figure 11 – Example of SAT heating setpoint reset based on outdoor air temperature (OAT).

Units

Data structure (°F)

Input Restrictions

As designed

Standard Design

Not applicable

5.7.3 Fan Systems    

5.7.3.1 Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See Section 5.7, Table 5 for the HVAC baseline building system mapping.

When the proposed design has exhaust fans (toilets or kitchens), or fume hood exhaust systems, the baseline building has the same systems.

5.7.3.2 Supply Fans    

Fan System Modeling Method

Applicability

All fan systems

Definition

Software commonly models fans in three ways. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.

Units

List: power-per-unit-flow, static pressure or brake horsepower

Input Restrictions

As designed. Either the static pressure or brake horsepower method shall be used.  The user is required to enter the brake horsepower and motor horsepower of all fans.

Standard Design

The baseline building shall use the static pressure method for all HVAC systems except the four-pipe fan coil system, which shall use the power-per-unit-flow method.

Supply Fan Design Airflow

Applicability

All fan systems

Definition

The air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.

Units

cfm

Input Restrictions

As designed. For multiple deck systems, a separate entry should be made for each deck.

Standard Design

The program shall automatically size the air flow at each thermal zone to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air  20°F temperature differential between the supply air and the return air for exterior zones and a 15°F temperature differential for interior zones served by multiple zone systems. The design supply air flow rate is the larger of the flow rate required to meet space conditioning requirements and the required ventilation flow rate. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal zones served by the fan system.

Fan Control Method

Applicability

All fan systems

Definition

A description of how the supply (and return/relief) fan(s) are controlled. The options include:

•      Constant volume

•      Variable-flow, inlet or discharge dampers

•      Variable-flow, inlet guide vanes

•      Variable-flow, variable speed drive (VSD)

•      Variable-flow, variable pitch blades

•      Variable-flow, other

•      Two-speed

•      Constant volume, cycling (fan cycles with heating and cooling)

Units

List (see above)

Input Restrictions

As designed

Standard Design

Applicable to variable air volume systems

Based on the prescribed system type. Refer to the HVAC System Map in 5.1.2

Table 28 – Baseline Building Fan Control Method

* For CRAH Units, fan volume shall be linearly reset from 100% air flow at 100% cooling load to minimum airflow at 50% cooling load and below.

Supply Fan Brake Horsepower

Applicability

All fan systems, except those specified using the power-per-unit-flow method

Definition

The design shaft brake horsepower of each supply fan. This input does not need to be supplied if the Supply Fan kW is supplied.

Units

Horsepower (hp)

Input Restrictions

As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.

The compliance software shall apply the following rule to specify the proposed design bhp, based on user input:

A Standard Motor Size table (hp) is defined as: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

The user-entered brake horsepower for the proposed design is compared against the next smaller motor size from the user-entered Supply Fan Motor Horsepower.  The proposed design Supply Fan Brake Horsepower (bhp) is set to the minimum of the user-entered bhp and 95% of the next smaller motor horsepower:

Proposed bhp = max(User bhp, 95% x MHPi-1)

Where User bhp is the user-entered supply fan brake horsepower,

MHPi is the proposed (nameplate) motor horsepower

MHPi-1 is the next smaller motor horsepower from the Standard Motor Size table above.  For example, if the proposed motor horsepower is 25, the next smaller motor horsepower from the table above is 20, and 95% of the next smaller motor horsepower is 19..

Standard Design

Not applicable

Supply Fan Motor Horsepower

Applicability

All fan systems, except those specified using the power-per-unit-flow method

Definition

The motor nameplate horsepower of the supply fan

Units

List: chosen from a list of standard motor sizes: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

Input Restrictions

As designed. This building descriptor is required for the static pressure or the brake horsepower methods

Standard Design

Not applicableThe brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).

Supply Fan Static Pressure

Applicability

All fan systems using the static pressure method

Definition

The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.

Units

Inches of water column (in. H₂0)

Input Restrictions

As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.

Standard Design

The standard design for all systems except four-pipe fan coil (FPFC) and PTAC is defined by the following table:

An additional pressure drop allowance is available for special filtration requirements only for specific processes such as clean rooms.  See Process and Filtration Pressure Drop for details.

Not applicable for the four-pipe fan coil system.

Supply Fan Efficiency

Applicability

All fan systems using the static pressure method

Definition

The efficiency of the fan at design conditions; this is the static efficiency and does not include motor losses.

Units

Unitless

Input Restrictions

As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.

Standard Design

For all standard design systems except the four-pipe fan coil:

The baseline Supply Fan Efficiency shall be 50% if the design supply air flow is less than 2000 cfm, 60% if the design supply air flow is between 2000 cfm and 10,000 cfm, or 62% if the design supply airflow is greater than 10,000 cfm.

For the four-pipe fan coil system, not applicable.

Supply Motor Efficiency

Applicability

All supply fans, except those specified using the power-per-unit-flow method

Definition

The full-load efficiency of the motor serving the supply fan

Units

Unitless

Input Restrictions

As designed. Not applicable when the power-per-unit-flow method is used.

Standard Design

The motor efficiency is determined from Table 29 for the next motor size greater than the bhp.

Table 29 – Minimum Nominal Efficiency for Electric Motors (%)

Fan Position

Applicability

All supply fans

Definition

The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).

Units

List (see above)

Input Restrictions

As designed.

Standard Design

Draw through

Motor Position

Applicability

All supply fans

Definition

The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.

Units

List (see above)

Input Restrictions

As designed.

Standard Design

In the air stream

Fan Part-Flow Power Curve

Applicability

All variable flow fan systems

Definition

A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.

Units

Unitless ratio

Input Restrictions

As designed. The user shall not be able to select VSD with Static Pressure Reset if the building does not have DDC controls to the zone level. The default fan curve shall be selected from Equation (4) and Table 30 for the type of fan specified in the proposed design.

where

PLR Ratio of fan power at part load conditions to full load fan power

PowerMin     Minimum fan power ratio

FanRatio      Ratio of cfm at part-load to full-load cfm

a, b, c and d Constants from Table 30 below

Table 30 – Fan Curve Default Values

Standard Design

Not applicable for baseline building systems constant volume systems. The curve VSD with static pressure reset fans shall be used for variable volume systems.

Supply Fan Power Index

Applicability

Fan systems that use the power-per-unit-flow method

Definition

The supply fan power per unit of flow.

Units

kW/cfm

Input Restrictions

As designed or specified in the manufacturers’ literature. May only be used for four-pipe fan coil systems.

Standard Design

Not applicable for all systems except the four-pipe fan coil (FPFC).

For the FPFC system, the standard design is 0.35 W/cfm.

Process and Filtration Pressure Drop

Applicability

Any system with special requirements for filtration or other process requirements

Definition

Additional system pressure drop related to application-specific filtration requirements or other process requirements. Special documentation requirements may apply.

Units

List

Input Restrictions

As designed. Default is 0.  Special documentation is required to claim any credit for filtration in excess of 1” w.g. Filtration shall be associated with process requirements (such as clean room or hospital areas).

Standard Design

Same as proposed, but subject to a maximum of 1” w.g.

5.7.3.3 Return/Relief Fans

The baseline building has no return fan. The standard design system has a relief fan only if the standard design system has an economizer.

Plenum Zone

Applicability

Any system with return ducts or return air plenum

Definition

A reference to the thermal zone that serves as return plenum or where the return ducts are located

Units

Text, unique

Input Restrictions

As designed

Standard Design

Not applicable

Return Air Path

Applicability

Any system with return ducts or return air plenum

Definition

Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.

Units

List (see above)

Input Restrictions

As designed

Standard Design

Applicable when the baseline building has a relief fan. For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 11 the baseline building shall be ducted return.

Return/Relief Fan Design Airflow

Applicability

All systems with a return or relief fan

Definition

The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).

Units

cfm

Input Restrictions

For a return fan, the Return/Relief Fan Design Airflow is set equal to the Proposed Design Supply Fan Design Airflow minus the Proposed Design Exhaust Fan Design Airflow and minus 0.05 cfm/ft2 for pressurization.

For relief fans, the Return/Relief Fan Design Airflow is set equal to the Proposed Design outside air ventilation rate minus the Proposed Design Exhaust Fan Design Airflow and minus 0.05 cfm/ft2 for pressurization.

Standard Design

The Relief Design Airflow is equal to the design outside airflow minus the exhaust design air flow rate and minus 0.05 cfm/ft2 for pressurization.

Return/Relief Fan Brake Horsepower

Applicability

Any system with return or relief fans that uses the brake horsepower method

Definition

The design shaft brake horsepower of the return/relief fan(s)

Units

Brake horsepower (bhp)

Input Restrictions

As designed.

The compliance software shall apply the following pre-processing rule to specify the proposed design Return/Relief Fan Brake Horsepower, based on user input:

A Standard Motor Size table (hp) is defined as: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

The return/relief fan brake horsepower is determined from user inputs of brake horsepower and motor horsepower for the proposed design, in the same manner as the Supply Fan Brake Horsepower.

Proposed bhp = min (user bhp, 95% x MHPi-1)

Where Proposed bhp is the Return/Relief Fan Brake Horsepower used in the simulation,

User bhp is the actual fan bhp as entered by the user, and

MHPi-1 is the motor horsepower of the next smaller motor size from the Standard Motor Size Table above; MHPi is the motor size that the user enters for the return/relief fan

See the Supply Fan Brake Horsepower descriptor for further details.

1. If the user-entered proposed bhp <= 95% of the next larger standard motor size, then proposed design Supply Fan Brake Horsepower = 95% (Next Larger Motor Size).

        a. For example, if the user bhp=18 and the next larger motor size is 20 from the table above, sine 18< 95% (20), Proposed Supply Fan Brake Horsepower = 95%(20)= 19 hp.

2. If the user-entered proposed bhp>95% of the next larger motor size, then the Proposed Return/Relief Fan Brake Horsepower = 95% of the next larger motor size.

        For example, if the user-entered proposed bhp=19.2 and the next larger motor size is 20, since 19.2>95%(20), the Proposed Return/Relief Fan Brake Horsepower = 95%(25) = 23.75 hp, where 25 is the next larger motor size after 20 hp in the table.

Standard Design

Applicable when the baseline building has a return fan. The bhp of the return fan shall be the fan system brake horsepower (see Table 5 times the return fan ratio. Not applicable. Standard Design systems with an economizer shall use relief fans and shall use the static pressure and fan efficiency method.

Return/Relief Fan Motor Horsepower

Applicability

All fan systems, except those specified using the power-per-unit-flow method

Definition

The motor nameplate horsepower of the supply fan

Units

List: chosen from a list of standard motor sizes: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

Input Restrictions

As designed. This building descriptor is required for the static pressure or the brake horsepower methods

Standard Design

Not applicableThe brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).

Return/Relief Design Static Pressure

Applicability

Any system with return or relief fans that uses the static pressure method

Definition

The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.

Units

Inches of water column (in. H20 gauge)

Input Restrictions

As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.

Standard Design

For fans with design airflow less than 10,000 cfm, the static pressure is 0.75”.

For fans with design airflow rate 10,000 cfm or greater, the static pressure is 1.0”

Return/Relief Fan Efficiency

Applicability

Any system with return or relief fans that uses the static pressure method

Definition

The efficiency of the fan at design conditions; this is the static efficiency and does not include the efficiency loss of the motor.

Units

Unitless

Input Restrictions

As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.

Standard Design

For design airflow less than 10,000 cfm, 40%. For design airflow 10,000 cfm or greater, 50%.

Return/Relief Motor Efficiency

Applicability

All return fans, except those specified using the power-per-unit-flow method

Definition

The full-load efficiency of the motor serving the supply fan

Units

Unitless

Input Restrictions

As designed. Not applicable when the power-per-unit-flow method is used.

Standard Design

From ACM Table 29

Motor Position

Applicability

All return fans

Definition

The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.

Units

List (see above)

Input Restrictions

As designed.

Standard Design

In the air stream

Fan Part-Flow Power Curve

Applicability

All return fans for variable flow fan systems.

Definition

A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.

Units

Unitless ratio

Input Restrictions

As designed. The default fan curve shall be selected from Equation (4) and Table30 for the type of fan specified in the proposed design.

Standard Design

Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems that have a return/relief fan.

5.7.3.4 Exhaust Fan Systems    

The Standard Design shall track the Proposed Design exempt process exhaust flow rate and fan power up to the maximum allowed by space type (see Appendix 5.4A for the baseline maximum exhaust rate). Exempt process exhaust includes exhaust from toilets, break rooms, and copy rooms and kitchens with less than 5,000 cfm of exhaust. If the proposed exempt process exhaust exceeds the maximum allowed then the baseline exempt process exhaust shall equal the maximum allowed and the baseline fan power shall be prorated based on flow rate (e.g. if the proposed exempt process exhaust for a given space is 10,000 cfm and 10 BHP and the maximum allowed in the baseline is 5,000 cfm then the baseline exempt process exhaust fan power for that space shall be 5 BHP).

Covered process exhaust includes garage ventilation, lab exhaust and exhaust from kitchens with over 5,000 cfm of exhaust. Rules for the baseline covered process exhaust rate and fan power are discussed in the following sections.

Exhaust fan flow is specified and scheduled for each thermal zone. An exhaust fan system may serve multiple thermal zones.

Exhaust Fan Name

Applicability

All exhaust systems serving multiple thermal zones

Definition

A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal zone level refer to this name.

Units                                                    

Text, unique

Input Restrictions

Where applicable, this should match the tags that are used on the plans.

Standard Design

The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.

Exhaust Fan System Modeling Method

Applicability

All exhaust fan systems

Definition

Compliance software can model fans in three ways. See definition for supply system modeling method.

Units

List: power-per-unit-flow, static pressure or brake horsepower

Input Restrictions

As designed

Standard Design

The baseline building shall use the static pressure method.

Exhaust Fan Design Airflow

Applicability

All exhaust systems

Definition

The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal zone, as modified by the schedule for each thermal zone.

Units

cfm

Input Restrictions

As designed. The exhaust flow capacity for a zone shall not exceed the supply flow capacity plus transfer flow capacity, i.e. exhaust makeup can be transferred from other zones in the building provided that the total building exhaust rate in any hour does not exceed the total outside air flow rate plus total infiltration rate.

Standard Design

Same as proposed design, but with the same limitations described under Input Restrictions.

Fan Control Method

Applicability

All exhaust fan systems

Definition

A description of how the exhaust fan(s) are controlled. The options include:

•      Constant volume

•      Variable-flow, variable speed drive (VSD)

•      Variable-flow, constant speed

Units

List (see above)

Input Restrictions

As designed, however, when exhaust fan flow at the thermal zone level is varied through a schedule, one of the variable-flow options shall be specified.

Standard Design

The baseline building exhaust fan control shall be the same as the proposed design, but subject the conditions described above.

For exhaust fans serving kitchen spaces, the fan control method is constant volume for fans with flow rate 5,000 cfm and below, and variable flow, variable speed drive for fans with flow rate greater than 5,000 cfm.

Exhaust Fan Schedule

Applicability

All exhaust fan systems

Definition

A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal zone level.

Units

Data structure: schedule, on/off

Input Restrictions

For exhaust fans not serving kitchen and lab spaces, the schedule is fixed to match the HVAC availability schedule for the specified occupancy in Appendix 5.4B. For kitchen and la spaces, the schedule is defined in Appendix 5.4B.

Standard Design

Specified in Appendix 5.4B for the specified occupancy.

Exhaust Fan Brake Horsepower

Applicability

All exhaust fan systems

Definition

The design shaft brake horsepower of the exhaust fan(s).

Units

Brake horsepower (bhp)

Input Restrictions

As designed

The Compliance Software implements a pre-processing rule to specify the proposed design Exhaust Fan Brake Horsepower (bhp), based on user input:

A Standard Motor Size table (hp) is defined as: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

The exhaust fan brake horsepower is determined from user inputs of brake horsepower and motor horsepower for the proposed design, in the same manner as the Supply Fan Brake Horsepower.

Proposed bhp = max (user bhp, 95% x MHPi-1)

Where Proposed bhp is the Return/Relief Fan Brake Horsepower used in the simulation,

        User bhp is the actual fan bhp as entered by the user, and

        MHPi-1 is the motor horsepower of the next smaller motor size from the Standard Motor Size Table above; MHPi is the motor size that the user enters for the exhaust fan

See the Supply Fan Brake Horsepower descriptor for further details.

1. If the user-entered proposed bhp <= 95% of the next larger standard motor size, then proposed design Supply Fan Brake Horsepower = 95% (Next Larger Motor Size).

        a. For example, if the user bhp=18 and the next larger motor size is 20 from the table above, sine 18< 95% (20), Proposed Supply Fan Brake Horsepower = 95%(20)= 19 hp.

2. If the user-entered proposed bhp>95% of the next larger motor size, then the Proposed Supply Fan Brake Horsepower = 95% of the next larger motor size.

        For example, if the user-entered proposed bhp=19.2 and the next larger motor size is 20, since 19.2>95%(20), the Proposed Supply Fan Brake Horsepower = 95%(25) = 23.75 hp, where 25 is the next larger motor size after 20 hp in the table.

Standard Design

Not applicable

Exhaust Fan Motor Horsepower

Applicability

All fan systems, except those specified using the power-per-unit-flow method

Definition

The motor nameplate horsepower of the supply fan

Units

List: chosen from a list of standard motor sizes: 1/12, 1/8, ¼, ½, ¾, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200

Input Restrictions

As designed. This building descriptor is required for the static pressure or the brake horsepower methods

Standard Design

Not applicable. The brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).

Exhaust Fan Design Static Pressure

Applicability

Any system with return or relief fans that uses the static pressure method

Definition

The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.

Units

Inches of water column (in. H20)

Input Restrictions

As designed for exhaust fans not serving kitchens. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.

Standard Design

For kitchen exhaust fans, the static pressure is fixed at 2.5” w.c.

For lab exhaust, 4” if 6 stories or less, or 4.5” if greater than 6 stories.

For all other exhaust fans, the standard design fan W/cfm shall be the same as the proposed design W/cfm.

Exhaust Fan Efficiency

Applicability

Any exhaust fan system that uses the static pressure method

Definition

The efficiency of the exhaust fan at rated capacity; this is the static efficiency and does not include losses through the motor.

Units

Unitless

Input Restrictions

For kitchen exhaust fans, the fan efficiency is prescribed at 50%.

For all other exhaust fans, as designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.

Standard Design

For kitchen exhaust fans, the fan efficiency is 50%.

For lab exhaust: 62%

For all other exhaust fans, the standard design efficiency (and resulting W/cfm) shall be the same as the proposed design efficiency (and resulting W/cfm).

Exhaust Fan Motor Efficiency

Applicability

All exhaust fan systems

Definition

The full-load efficiency of the motor serving the exhaust fan

Units

Unitless

Input Restrictions

As designed

Standard Design

From Table 30

Fan Part-Flow Power Curve

Applicability

All variable flow exhaust fan systems

Definition

A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.

Units

Unitless ratio

Input Restrictions

As designed. The default fan curve shall be selected from Equation (4) and Table 30  for the type of fan specified in the proposed design.

Standard Design

The baseline building fan curve shall be selected from Equation (4) and Table 30 for the type of fan specified in the proposed design.

Exhaust Fan Power Index

Applicability

All exhaust systems

Definition

The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.

Units

kW/cfm

Input Restrictions

As designed.

Standard Design

Not applicable

5.7.3.5 Garage Exhaust Fan Systems

Garage exhaust fan systems shall be modeled and included as part of regulated building energy use. These fans shall be modeled as constant volume fans, with the fan power determined by whether or not the fan has CO controls.

Garage Exhaust Fan Name

Applicability

All garage exhaust systems

Definition

A unique descriptor for each garage exhaust fan or fan system. Fans with equivalent efficiency and motor efficiencies may be combined and modeled as one fan.

Units

Text, unique

Input Restrictions

Where applicable, this should match the tags that are used on the plans.

Standard Design

The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.

Garage Exhaust Fan System Modeling Method

Applicability

All exhaust fan systems

Definition

Software commonly models fans in three ways. See definition for supply system modeling method.

Units

List: power-per-unit-flow, static pressure or brake horsepower

Input Restrictions

brake horsepower method (fixed value)

Standard Design

The baseline building shall use the power-per-unit-flow method.

Garage Exhaust Fan Rated Capacity

Applicability

All exhaust systems

Definition

The rated design air flow rate of the garage exhaust fan system.

Units

cfm

Input Restrictions

As designed

Standard Design

Same as proposed design

Garage Exhaust Fan Control Method

Applicability

All exhaust fan systems

Definition

The control method for the garage exhaust fan.  This input determines the fan power for the exhaust fan; no other fan inputs are required.

Units

List:  Constant Volume, CO Control

Input Restrictions

For systems with fan capacity below 10,000 cfm, either Constant Volume or CO Control

For systems with fan capacity above 10,000 cfm, CO Control

If Constant Volume is selected, proposed fan power is as designed

If CO Control is selected, proposed fan power is 12.5% of the design fan power

Standard Design

For garage fans with a supply air flowrate below 10,000 cfm, the baseline fan power is 0.35 W/cfm.

For garage fans with a design supply air flowrate of 10,000 cfm and above, the baseline fan power is 0.044 W/cfm.

5.7.4 Outdoor Air Controls and Economizers    

5.7.4.1 Outside Air Controls

Maximum Outside Air Ratio

Applicability

All systems with modulating outside air dampers

Definition

The descriptor is used to limit the maximum amount of outside air that a system can provide as a percentage of the design supply air. It is used where the installation has a restricted intake capacity.

Units

Ratio

Input Restrictions

For systems with capacity under 54,000 Btu/h without FDD, the maximum allowed value is 0.9.

For all other systems the maximum allowed value is 1.

Standard Design

1.0 for all systems above 54,000 Btu/h cooling capacity; 0.9 for other systems

Design Outside Air Flow

Applicability

All systems with outside air dampers

Definition

The rate of outside air that needs to be delivered by the system at design conditions. This input may be derived from the sum of the design outside air flow for each of the zones served by the system.

Units

cfm

Input Restrictions

As designed, but no lower than the ventilation rate of the standard design.

Standard Design

Minimum ventilation requirements specified by Standard 120(b)2 as the greater of 15 cfm/person and the minimum ventilation rates specified in Appendix 5.4

For systems serving laboratory spaces, the system shall be 100% outside air, with ventilation rates of 6 ACH.

See ventilation control method at the zone level.

Outdoor Air Control Method

Applicability

All HVAC systems that deliver outside air to zones

Definition

The method of determining the amount of outside air that needs to be delivered by the system. Each of the zones served by the system report their outside air requirements on an hourly basis. The options for determining the outside air at the zone level are discussed above. This control method addresses how the system responds to this information on an hourly basis. Options include:

•      Average Flow. The outside air delivered by the system is the sum of the outside air requirement for each zone, without taking into account the position of the VAV damper in each zone. The assumption is that there is mixing between zones through the return air path.

•      Critical Zone. The critical zone is the zone with the highest ratio of outside air to supply air. The assumption is that there is no mixing between zones. This method will provide greater outside air than the average flow method because when the critical zone sets the outside air fraction at the system, the other zones are getting greater outside air than required.

Units

List (see above)

Input Restrictions

As designed

Standard Design

Average Flow

5.7.4.2 Air Side Economizers

Economizer Control Type

Applicability

All systems with an air-side economizer

Definition

An air-side economizer increases outside air ventilation during periods when refrigeration loads can be reduced from increased outside air flow. The control types include:

•      No economizer

•      Fixed dry-bulb. The economizer is enabled when the temperature of the outside air is equal to or lower than temperature fixed setpoint (e.g., 75F).

•      Differential dry-bulb. The economizer is enabled when the temperature of the outside air is lower than the return air temperature.

•      Differential enthalpy. The economizer is enabled when the enthalpy of the outside air is lower than the return air enthalpy.

•      Differential dry-bulb and enthalpy. The system shifts to 100% outside air, or the maximum outside air position needed to maintain the cooling SAT setpoint, when the outside air dry-bulb is less than the return air dry-bulb AND the outside air enthalpy is less than the return air enthalpy. This control option requires additional sensors.

•      Fixed or dry-bulb enthalpy. The economizer is enabled when the outside air dry-bulb and enthalpy are both below the fixed setpoints for the return air.

•      Fixed dewpoint and dry-bulb. The system shifts to 100% outside air, or the maximum outside air position needed to maintain the SAT setpoint, when the dewpoint of the air and dry-bulb are below the specified setpoints.

Units

List (see above)

Input Restrictions

As designed

Standard Design

The control should be no economizer when the baseline cooling capacity < 54,000 Btu/h. Otherwise the baseline building shall assume an integrated differential dry-bulb economizer.

An exception is that economizers shall NOT be modeled for systems serving high-rise residential or hotel/motel guestroom occupancies.

Economizer Integration Level

Applicability

Airside economizers

Definition

This input specifies whether or not the economizer is integrated with mechanical cooling. It is up to the modeling software to translate this into software-specific inputs to model this feature. The input could take the following values:

•      Non-integrated. The system runs the economizer as the first stage of cooling. When the economizer is unable to meet the load, the economizer returns the outside air damper to the minimum position and the compressor turns on as the second stage of cooling.

•      Integrated. The system can operate with the economizer fully open to outside air and mechanical cooling active (compressor running) simultaneously, even on the lowest cooling stage.

Units

List

Input Restrictions

List: Non-integrated, Integrated

Standard Design

Integrated for systems above capacity 54,000 Btu/h at AHRI conditions

Economizer High Temperature Lockout

Applicability

Systems with fixed dry-bulb economizer

Definition

It is the outside air setpoint temperature above which the economizer will return to minimum position.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

Not Applicable

Not applicable

N

Economizer Low Temperature Lockout

Applicability

Systems with air-side economizers

Definition

A feature that permits the lockout of economizer operation (return to minimum outside air position) when the outside air temperature is below the lockout setpoint.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

Not used

Economizer High Enthalpy Lockout

Applicability

Systems with differential enthalpy economizers

Definition

The outside air enthalpy above which the economizer will return to minimum position

Units

Btu/lb

Input Restrictions

As designed. The default is 28 Btu/lb.(High altitude locations may require different setpoints.)  The compliance software shall apply a fixed offset and add 2 Btu/lb to the user-entered value.

Standard Design

No lockout limit

5.7.5 Cooling Systems    

5.7.5.1 General

This group of building descriptors applies to all cooling systems.

Cooling Source

Applicability

All systems

Definition

The source of cooling for the system. The choices are:

•      Chilled water

•      Direct expansion (DX)

•      Other

Units

List (see above)

Input Restrictions

As designed

Standard Design

The baseline building cooling source is shown in Table 31. See Section 5.1.2 for HVAC system mapping.

Table 31 – Cooling Source for Baseline Building System

Gross Total Cooling Capacity

Applicability

All cooling systems

Definition

The total gross cooling capacity (both sensible and latent) of a cooling coil or packaged DX system at AHRI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Units

Btu/h

Input Restrictions

As designed. For packaged equipment that has the fan motor in the air stream such that it adds heat to the cooled air, the software shall calculate the net total cooling capacity as follows:

                                                                 (6)

where

Q_t,net,rated         The net total cooling capacity of a packaged unit as rated by AHRI (Btu/h)

Q_{t,gross,rated}      The AHRI rated total cooling capacity of a packaged unit (Btu/h)

Q_fan,rated                    The heat generated by the fan and fan motor (if fan motor is in airstream) at AHRI rated conditions

If the gross and net total cooling capacities at AHRI conditions are known, the fan heat at rated conditions is the difference between the two values. If the either the gross or net total cooling capacity is unknown, the fan heat at rated conditions shall be accounted for by using equation (7):

                                                                     (7)

This equation 7 is based on an AHRI rated fan power of 0.365 W/cfm, and a cooling airflow of 400 cfm/ton.

If the number of unmet load hours in the proposed design exceeds 150, the software shall warn the user to resize the equipment.

Standard Design

The gross total cooling capacity of the systems in the baseline building is autosized by the compliance software, and then oversized by 15%.. Sizing calculations shall be based on 0.5% design dry-bulb and mean coincident wet-bulb.

Gross Sensible Cooling Capacity

Applicability

All cooling systems

Definition

The gross sensible cooling capacity of the coil or packaged equipment at AHRI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should be adjusted to calculate the net sensible cooling capacity, which includes the effect of fan motor heat.

Note that the sensible heat ratio (SHR) used by some energy simulation tools can be calculated from the sensible cooling capacity and total cooling capacity:

SHR = Sensible Cooling Capacity / Total Cooling Capacity

Units

Btu/h

Input Restrictions

As designed.

For packaged equipment, the compliance software adjusts the user input of gross sensible cooling capacity to account for the effect of fan motor heat as follows:

                    (8)

where

Q_s,net,rated        The AHRI rated (from manufacturers’ literature) or net sensible cooling capacity of a packaged unit (Btu/h)

Q_{s,gross,rated}      The AHRI rated (from manufacturers’ literature) or gross sensible cooling capacity of a packaged unit  (Btu/h)

Q_fan,rated          The heat generated by the fan and fan motor (if fan motor is in air stream) at AHRI rated or hourly conditions (Btu/h). See Gross Total Cooling Capacity building descriptor.

If the number of unmet load hours in the proposed design exceeds 150, the software shall warn the user to resize the equipment.

Standard Design

The gross total cooling capacity of the systems serving the baseline building is autosized by the compliance software, and then oversized by 15%. Sizing calculations shall be based on 0.5% design dry-bulb and mean coincident wet-bulb.

Cooling Capacity Adjustment Curves

Applicability

All cooling systems

Definition

A curve that represents the available total cooling capacity as a function of cooling coil and/or condenser conditions. The common form of these curves is given as follows:

(5)

For air cooled direct expansion

(6)

For water cooled direct expansion

(7)

For chilled water coils

(8)

where

Q_t,available         Available cooling capacity at specified evaporator and/or condenser conditions (MBH)

Q_t,adj  Adjusted capacity at AHRI conditions (Btu/h) (see Equation Error! Reference Source Not Found

CAP_FT       A multiplier to adjust Qt,adj  

t_wb    The entering coil wet-bulb temperature (°F)

t_db     The entering coil dry-bulb temperature (°F)

t_wt     The water supply temperature (°F)

t_odb    The outside-air dry-bulb temperature (°F)

Note: if an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Software may represent the relationship between cooling capacity and temperature in ways other than the equations given above.

Table 32 –Cooling Capacity Curve Coefficients

Units

Data structure

Input Restrictions

As designed. The equations and coefficients given above are the default.

Standard Design

Use the default curves or equivalent data for other models.

Coil Latent Modeling Method

Applicability

All DX cooling systems

Definition

The method of modeling coil latent performance at part-load conditions.

Units

List

Input Restrictions

One of the following values:

Bypass factor – used by DOE-2 based programs

NTU-effectiveness – used by EnergyPlus

Standard Design

Same as proposed

Coil Bypass Factor

Applicability

All DX cooling systems using the bypass factor Coil Latent Modeling Method

Definition

The ratio of air that bypasses the cooling coil at design conditions to the total system airflow.

Units

Ratio

Input Restrictions

Prescribed values as shown in Table 33.

Table 33 – Default Coil Bypass Factors

Standard Design

Defaults

Coil Bypass Factor Adjustment Curve

Applicability

All DX cooling systems using the bypass factor Coil Latent Modeling Method

Definition

Adjustments for the amount of coil bypass due to the following factors:

•      Coil airflow rate as a percentage of rated system airflow

•      Entering air wet-bulb temperature

•      Entering air dry-bulb temperature

•      Part load ratio

Units

Data structure

Input Restrictions

Where applicable, prescribed (fixed) simulation engine defaults based on HVAC system type. The following default values shall be used for the adjustment curves:

(9)

(10)

(11)

(12)

where

CBF_rated         The coil bypass factor at AHRI rating conditions

CBF_adj           The coil bypass factor adjusted for airflow and coil conditions

CFMR                      The ratio of airflow to design airflow

COIL-BF-FFLOW       A multiplier on the rated coil bypass factor to account for variation in air flow across the coil (take coefficients fromTable 34)

COIL-BF-FTA            multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients fromTable 35)

COIL-BF-FPLR          A multiplier on the rated coil bypass factor to account for the part load ratio (take coefficients fromTable 36)

T_wb   The entering coil wet-bulb temperature (°F)

T_db    The entering coil dry-bulb temperature (°F)

PLR Part load ratio

And the coefficients are 'listed in the tables below.

Table 34 – Coil Bypass Factor Airflow Adjustment Factor

Table 35 – Coil Bypass Factor Temperature Adjustment Factor

Table 36 – Coil Bypass Factor Part Load Adjustment Factor

Standard Design

Use defaults as described above.

Cooling Capacity Airflow Adjustment Curve

Applicability

All DX cooling systems using the NTU Effectiveness Coil Latent Modeling Method

Definition

Normalized curve that varies cooling capacity as a function of airflow, which affects system latent capacity

Units

Data structure

Input Restrictions

Where applicable, prescribed (fixed) simulation engine defaults based on HVAC system type. The following default values shall be used for the adjustment curves:

(13)

(14)

where

CFMR                       The ratio of airflow to design airflow

COOL-CAP-FFLOW   A multiplier on the rated coil capacity to account for variation in air flow across the coil (take coefficients from Table 34)

COOL-CAP-FT          A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients fromTable 35)

The curve takes the form:

COOL-CAP-FFLOW = a + b x CFMR + c x CFMR² + d x CFMR³

And the coefficients are 'listed in the tables below.

Table 37 – Cooling Capacity Airflow Adjustment Factor

Standard Design

Use defaults as described above.

5.7.5.2 Direct Expansion

Direct Expansion Cooling Efficiency

Applicability

Packaged DX equipment

Definition

The cooling efficiency of a direct expansion (DX) cooling system at AHRI rated conditions as a ratio of output over input in Btu/h per W, excluding fan energy. The abbreviation used for this full-load efficiency is EER.

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the EER shall be adjusted as follows:

(15)

where

EER_adj          The adjusted Energy Efficiency Ratio for simulation purposes

EER             The rated Energy Efficiency Ratio

Qt,_gross,rated     The AHRI rated total gross cooling capacity of a packaged unit (kBtu/h)

Qfan,rated    The AHRI rated fan energy, specified in equation (7) for the Gross Total Cooling Capacity building descriptor

Units

Btu/h-W

Input Restrictions

As designed, except that the user-entered value must meet mandatory minimum requirements of Table 110.2-A, Table 110.2-B or Table 110.2-C for the applicable equipment type.. When possible, specify the SEER and EER for packaged equipment with cooling capacity less than 65,000 Btu/h from manufacturer’s literature. For equipment with capacity above 65,000 Btu/h, specify EER.

When EER is not available for packaged equipment with SEER ratings (AHRI cooling capacity of 65,000 Btu/h or smaller), it shall be calculated as follows:

 (16)

EER = MIN(-0.0194 x SEER² +1.0864 x SEER,13)

The default EER shall be calculated by the equation above, but constrained to be no greater than 13.

Evaporative cooling systems that pass the requirements of the Western Cooling Challenge may be modeled with an EER as if the equipment were packaged unitary equipment. See section 5.7.5.4.

Standard Design

Use the minimum cooling efficiency (EER) from tables in Tables 110.2-A, 110.2-B and 110.2-E in Section 110.2 of the Standard.

Seasonal Energy Efficiency Ratio

Applicability

Packaged DX equipment with AHRI cooling capacity of 65,000 Btu/h or smaller

Definition

The seasonal cooling efficiency of a direct expansion (DX) cooling system at AHRI rated conditions as a ratio of output over input in Btu/h per W, excluding fan energy. The software must accommodate user input in terms of either the Energy Efficiency Ratio (EER) or the Seasonal Energy Efficiency Ratio (SEER). For equipment with SEER ratings, EER shall be taken from manufacturers’ data when it is available.

Units

Btu/h-W

Input Restrictions

As designed. This input is required for small DX systems.  The Direct Expansion Cooling Efficiency input is optional for these systems.

Standard Design

Use the minimum SEER from the 2009 Appliance Efficiency Standards.

Direct Expansion Cooling Efficiency Temperature Adjustment Curve

Applicability

Packaged DX equipment

Definition

A curve that varies the cooling efficiency of a direct expansion (DX) coil as a function of evaporator conditions, condenser conditions, and for small packaged equipment, part-load ratio.

(17)

For air-cooled DX systems:

(18)

For water-cooled DX systems:

(19)

where

PLR Part load ratio based on available capacity (not rated capacity)

EIR-FT          A multiplier on the EIR to account for the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature

Q_operating         Present load on heat pump (Btu/h)

Q_available          Heat pump available capacity at present evaporator and condenser conditions (in Btu/h).

t_wb    The entering coil wet-bulb temperature (°F)

t_wt     The water supply temperature (°F)

t_odb    The outside-air dry-bulb temperature (°F)

P_rated   Rated power draw at AHRI conditions (kW)

P_operating       Power draw at specified operating conditions (kW)

Note: if an air-cooled unit employs an evaporative condenser, todb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Table 38 – Cooling System Coefficients for EIR-FT

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, the software must indicate that supporting documentation is required on the output forms.

For direct-expansion equipment with a capacity greater than 65,000 Btu/h, the user may not enter data on the temperature dependent equipment performance. However, the ACM compliance software vendor may work with manufacturers to collect such data and build this data into the ACM compliance software. The user may either select equipment for which the ACM compliance software vendor has collected or use the defaults.

Standard Design

For all systems except packaged DX units with cooling capacity <= 65,000 Btu/h, use default curves from Appendix 5.7.  For packaged DX units with cooling capacity less than or equal to 65,000 Btu/h that have SEER ratings, the user inputs EER and SEER, and the software generates the equipment performance curve based on the pre-defined performance curves specified in Appendix 5.7.

Direct Expansion Part-Load Efficiency Adjustment Curve

Applicability

Packaged systems with direct expansion (DX) cooling

Definition

A normalized performance adjustment curve to the rated efficiency (Energy Input Ratio) that describes how the efficiency varies at part-load conditions. At a value of 1 (full load), the normalized efficiency is 1 (same as part-load conditions).

The default curves are given as follows as adjustments to the energy input ratio (EIR):

(20)

(21)

This curve may take the form of a part-load factor (PLF) or EIR-FLPR, which is the fraction of time the unit must run to meet the part-load for that hour. For example, at 40% of full load, the equipment might need to run 50% of the hour (for cycling losses).

Note that for small packaged equipment with SEER ratings (<65,000 Btu/h), the part-load efficiency curve is set to no degradation, since the part-load degradation is built-into the Direct Expansion Cooling Efficiency Temperature Adjustment Curve.

Default curves are provided for the different major classes of equipment.

Units

Coefficients (three for a quadratic, or up to four for a cubic)

Input Restrictions

The coefficients should sum to 1 (within a small tolerance). This corresponds to a curve output of 1 for an input of 1.

Standard Design

The baseline part-load efficiency adjustment curves are shown in the tables below.

Table 39 – Cooling System Coefficients for EIR-FPLR

Table 40 – Cooling System Coefficients for Part-Load Factor (PLF) Correlation (EnergyPlus)

Number of Cooling Stages

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

This applies to Single Zone VAV HVAC systems with multiple compressors or multiple discrete stages of cooling.  This system is a packaged unit with multiple compressors and a two-speed or variable-speed fan. Systems with unequally sized compressors may have additional cooling stages.

Units

None (Integer)

Input Restrictions

As Designed

Standard Design

The default shall be 2 for the Single Zone VAV baseline.

Total Cooling Capacity by Stage

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

This provides the total cooling capacity of each cooling stage, at AHRI rated conditions. The capacity is expressed as an array, with each entry a fraction of the total rated cooling capacity for the unit.  For example, if the stage cooling capacity is 4 tons (48,000 Btu/h) and the total cooling capacity is 8 tons (96,000 Btu/h), the capacity is expressed as “0.50” for that stage.

Units

Array of fractions

Input Restrictions

As Designed

Standard Design

The default shall be (0.50, 1) for the Single Zone VAV baseline.

Sensible Cooling Capacity by Stage

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

This provides the sensible cooling capacity of each cooling stage, at AHRI rated conditions. The capacity is expressed as an array, with each entry a fraction of the total rated sensible cooling capacity for the unit.  For example, if the stage sensible cooling capacity is 3.5 tons (42,000 Btu/h) and the total sensible cooling capacity is 7 tons (72,000 Btu/h), the capacity is expressed as "0.5" for that stage.

Units

Array of fractions

Input Restrictions

As Designed

Standard Design

The default shall be (0.50, 1) for the Single Zone VAV baseline.

Supply Air Temperature Reset by Stage

Applicability

Single Zone VAV Systems with Supply Air Temperature Control Method set to Staged Control

Definition

This provides the cooling supply air temperature setpoint deviation from the cooling design supply air temperature, specified in the building descriptor Cooling Supply Air Temperature.

The temperature reset is expressed as an array, with each entry a deviation from the design supply air temperature.  For example, an entry of “5” for a stage would indicate a 5°F reset (for example, 60°F from 55°F).

Units

Array of temperature differences, in degrees F

Input Restrictions

As Designed

Standard Design

N/A

Number of Heating Stages

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

The number of heating stages provided by the system. Multiple stages could be provided via a heat pump or via a multiple-stage gas furnace.

Units

Integer

Input Restrictions

As Designed

Standard Design

1

Heating Capacity by Stage

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

This provides the total heating capacity of each heating stage, at AHRI rated conditions. The capacity is expressed as an array, with each entry a fraction of the total rated cooling capacity for the unit.  For example, if the stage heating capacity is 48,000 Btu/h and the heating capacity is 96,000 Btu/h, the capacity is expressed as “0.50” for that stage.

Units

Array of fractions

Input Restrictions

As Designed

Standard Design

N/A

Heating Supply Air Temperature by Stage

Applicability

Single Zone VAV Systems and DX systems with multiple stages

Definition

This provides the heating supply air temperature setpoint deviation from the design heating supply air temperature, specified in the building descriptor Heating Supply Air Temperature.

The temperature reset is expressed as an array, with each entry a deviation from the design supply air temperature.  For example, an entry of “-10” for a stage would indicate a 10°F reset (for example, 95°F from 105°F).

Units

Array of temperature differences, in degrees F

Input Restrictions

As Designed

Standard Design

N/A

Supply Fan Low Speed Ratio

Applicability

Single Zone VAV Systems and DX systems with multiple stages and two-speed fans

Definition

This specifies the low fan speed setting on a Single Zone VAV system or DX system with multiple cooling stages.

Units

None (fraction)

Input Restrictions

As Designed

Standard Design

The default shall be the greater of 0.50 or the minimum outside air fraction for the Single Zone VAV baseline.

Supply Fan Low Power Ratio

Applicability

Single Zone VAV Systems and DX systems with multiple stages and two-speed fans

Definition

This specifies the fraction of full load fan power corresponding to low fan speed operation on a Single Zone VAV system or DX system with multiple cooling stages.

Units

None (fraction)

Input Restrictions

As Designed

Standard Design

The default shall be 0.30, or the minimum power ratio calculated by applying the minimum outside air fraction to the “Any Fan with VSD” curve, for the Single Zone VAV baseline.

Minimum Unloading Ratio

Applicability

Packaged DX systems

Definition

The fraction of total cooling capacity below which compressor(s) must cycle on and off to meet the cooling load. Below the minimum unloading ratio, part-load efficiency is reduced.  Also, below the minimum unloading ratio, the economizer will not operate in a fully integrated mode with compressor cooling.

Units

Ratio

Input Restrictions

As designed. The user must enter this descriptor for each DX cooling system. If hot-gas bypass is not employed, a value of 0 may be entered.

Standard Design

0.25 for units with a peak total cooling capacity greater than or equal to 240 kBtu/h; 0.35 for units with a peak cooling capacity greater than or equal to 65 kBtu/h and less than 240 kBtu/h

Minimum HGB Ratio

Applicability

Packaged systems which use hot-gas bypass during low load conditions

Definition

The lower end of the hot-gas bypass operating range. The percentage of peak cooling capacity below which hot-gas bypass will no longer operate (i.e. the compressor will cycle).

Units

Ratio

Input Restrictions

0

Standard Design

0

Condenser Type

Applicability:

All direct expansion systems including heat pumps

Definition

The type of condenser for a direct expansion (DX) cooling system. The choices are:

•      Air-Cooled

•      Water-Cooled

•      Air-Cooled with Evaporative Pre-cooler

Units

List (see above)

Input Restrictions

As designed

Standard Design

Based on the prescribed system type. Refer to the HVAC System Map section 5.7.1. Air-cooled for Systems 1 (PTAC), 3, (PSZ), 5 (PVAV) and 11 (CRAC). Not applicable for other standard design systems.

Condenser Flow Type

Applicability:

All direct expansion systems including heat pumps

Definition

Describes water flow control for a water-cooled condenser. The choices are:

•      Fixed Flow

•      Two-position

•      Variable Flow

Units

List (see above)

Input Restrictions

Default to fixed flow. If the variable-flow is selected, the software must indicate that supporting documentation is required on the output forms.

Standard Design

Two-position

Supplementary DX Cooling Unit

Applicability

Required when user-defined natural ventilation or evaporative cooling systems have excessive unmet load hours

Definition

The specification of a supplementary DX cooling system that must be used when the user-defined cooling system results in unmet load hours exceeding 150 for any zone

Units

List

Input Restrictions

The user shall input the following system characteristics, with one unit for each zone:

Total Cooling Capacity (Btu/h)

Total Heating Capacity (Btu/h)

The compliance software shall define the following prescribed system characteristics:

Efficiency: Minimum efficiency from Table 110.2-A, based on cooling capacity

System Airflow: 350 cfm/ton cooling

Economizer: None

Design Supply Air Temperature: 55F

Supply Air Temperature Control: Fixed

Design Heating Supply Air Temperature: 105F

Standard Design

Not Applicable

5.7.5.3 Evaporative Cooler

This is equipment that pre-cools the outside air that is brought into the building. It may be used with any type of cooling system that brings in outside air. This equipment is not applicable for the baseline building.

Evaporative Cooling Type

Applicability

Systems with evaporative cooling

Definition

The type of evaporative pre-cooler, including:

•      None

•      Non-Integrated Direct

•      Non-Integrated Indirect

•      Non-Integrated Direct/Indirect

•      Integrated Direct

•      Integrated Indirect

•      Integrated Direct/Indirect

An integrated cooler can operate together with compressor or CHW cooling. A non-integrated cooler will shut down the evaporative cooling whenever it is unable to provide 100% of the cooling required.

Direct evaporative cooling can only be applied to the outside air.  Indirect evaporative cooling can be applied to outside air or return air.

Units

None

Input Restrictions

As designed

Standard Design

Not applicable

Evaporative Cooling System Capacity

Applicability

Systems with evaporative cooling

Definition

The total sensible cooling capacity of the evaporative cooling system at design outdoor dry-bulb conditions. This value may be derived from other inputs of Supply Fan Design Air Rated Capacity (5.7.3), Direct Stage Effectiveness, Indirect Stage Effectiveness and design outdoor conditions.

Units

None

Input Restrictions

Not applicable. Derived input.  If there are excessive unmet load hours in any zone served by the evaporative cooling system, a Supplementary DX Cooling Unit must be defined by the user. See Section 5.7.5.2.

Standard Design

Not applicable

Direct Stage Effectiveness

Applicability

Systems with evaporative cooling

Definition

The effectiveness of the direct stage of an evaporative cooling system. Effectiveness is defined as follows:

(22)

where

DirectEFF     The direct stage effectiveness

T_db    The entering air dry-bulb temperature

T_wb   The entering air wet-bulb temperature

T_direct The direct stage leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Standard Design

Not applicable

Indirect Stage Effectiveness

Applicability

Systems with evaporative cooling

Definition

The effectiveness of the indirect stage of an evaporative cooling system. Effectiveness is defined as follows:

(23)

where

IndEFF         The indirect stage effectiveness

T_db    The entering air dry-bulb temperature of the supply air

T_wb   The entering air wet-bulb temperature of the “scavenger air”

T_ind   The supply air leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Standard Design

Not applicable

Evaporative Cooling Performance Curves

Applicability

Systems with evaporative cooling

Definition

A curve that varies the evaporative cooling effectiveness as a function of primary air stream airflow. The default curves are given as follows:

(24)

where

PLR             Part load ratio of airflow based on design airflow

EFF-FFLOW A multiplier on the evaporative cooler effectiveness to account for variations in part load

CFM_operating     Operating primary air stream airflow (cfm)

CFM_design       Design primary air stream airflow (cfm)

Table 41 – Part Load Curve Coefficients – Evaporative Cooler Effectiveness

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, the software must indicate that supporting documentation is required on the output forms.

Standard Design

Not used.

Auxiliary Evaporative Cooling Power

Applicability

Systems with evaporative cooling

Definition

The auxiliary energy of the indirect evaporative cooler fan, and the pumps for both direct and indirect stages

Units

Watts

Input Restrictions

As designed

Standard Design

Not applicable

Evaporative Cooling Scavenger Air Source

Applicability

Systems with evaporative cooling

Definition

The source of scavenger air for an indirect section of an evaporative cooler. Options include:

•      Return Air

•      Outside Air

Units

List (see above)

Input Restrictions

As designed

Standard Design

Not applicable

5.7.5.4 Western Cooling Challenge (WCC) Equipment

A special credit is available in the 2013 ACM for equipment (including evaporative equipment) that meets efficiency and water use requirements of the Western Cooling Challenge, a program of the Western Cooling Efficiency Center.  This compliance option triggers an Exceptional Condition and documentation requirements – see Chapter 3 of the ACM Reference Manual.

This equipment is modeled as high-efficiency DX equipment, with a constant volume fan, integrated economizer and fixed performance curve. Unlike the input model for a packaged DX equipment, the WCC equipment has many building descriptor inputs fixed (prescribed); therefore, rather than listing the WCC input restrictions as an option within each building descriptor, all requirements for WCC equipment are contained in this section.

Heating equipment must be specified separately, as the WCC test procedure does not include heating conditions.  The heating system may be any system other than a heat pump.

5.7.5.5 Evaporative Condenser

Evaporative Condenser Power

Applicability

Direct expansion systems with an evaporatively cooled condenser

Definition

The power of the evaporative precooling unit. This includes any pump(s) and/or fans that are part of the precooling unit.

Units

Watts

Input Restrictions

As designed

Standard Design

Not applicable

Evaporative Condenser Effectiveness

Applicability

Direct expansion systems with an evaporatively cooled condenser

Definition

The effectiveness of the evaporative precooling unit for a condenser. Effectiveness is defined as follows:

(25)

where

DirectEFF     The direct stage effectiveness

Tdb              The outside air dry-bulb temperature

Twb              The outside air wet-bulb temperature

Tdirect          The direct stage leaving dry-bulb temperature (at the condenser inlet)

Units

Ratio

Input Restrictions

As designed

Standard Design

Not applicable

Evaporative Condenser Operation Range

Applicability

Direct expansion systems with an evaporatively cooled condenser.

Definition

The temperature range within which the evaporative condenser operates. Two values are provided:

T_maximum         The threshold outside air dry-bulb temperature below which evaporative condenser operates.

T_minimum          The threshold outside air dry-bulb temperature above which evaporative condenser operates.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed

Standard Design

Not applicable

5.7.5.6 Four-Pipe Fan Coil Systems

This section contains building descriptors required to model four-pipe fan coil systems. Note that this system requires an outside air ventilation source to serve the zones and that an airside economizer is not available.

The fan coil fans shall be modeled with the power-per-unit-flow method.  The standard design fan power shall be 0.35 W/cfm when the four-pipe fan coil is the standard design system. See the supply fan ACM section 6.1.3.2 for details.

Supply air flow rates are set at the zone level. Chilled water flow rates are set according to the rules in 6.2.5, Pumps.

Note that additional HVAC components (chiller, boiler, pumps) are needed to fully define this system. If a water-side economizer is specified with this system, refer to section 6.2.4 for a list of applicable building descriptors.

Capacity Control Method

Applicability

Four-pipe fan coil systems

Definition

The control method for the fan coil unit at the zone. The following choices are available:

ConstantFanVariableFlow

CyclingFan

VariableFanConstantFlow

VariableFanVariableFlow

Units

List (with choices above)

Input Restrictions

Not a User Input – Derived from building descriptors for fan control and chiller loop flow control

Standard Design

Cycling Fan

5.7.5.7 Radiant Cooling

This section describes a floor-based radiant cooling system and the inputs required for Title 24 compliance evaluation.

Hydronic Tubing Length

Applicability

Floor-based radiant cooling systems

Definition

The length of the hydronic tubing in the slab

Units

ft

Input Restrictions

As designed

Standard Design

Not applicable

Hydronic Tubing Inside Diameter

Applicability

Floor-based radiant cooling systems

Definition

The inside diameter of the hydronic tubing in the slab

Units

ft

Input Restrictions

As designed, between a minimum of ½” and a maximum of ¾”

Standard Design

Not applicable

Temperature Control Type

Applicability

Floor-based radiant cooling systems

Definition

The temperature used for control (operative temperature, mean air temperature, mean radiant temperature, ODB, OWB

Units

None

Input Restrictions

Fixed at Mean Air Temperature for compliance calculations

Standard Design

Not applicable

Cooling Control Temperature

Applicability

Variable Flow Systems

Definition

The temperature used for control (operative temperature, mean air temperature, mean radiant temperature, ODB, OWB

Units

None

Input Restrictions

Fixed at Mean Air Temperature for compliance calculations

Standard Design

Not applicable

Condensation Control Type

Applicability

Floor-based radiant cooling systems

Definition

The temperature used for control (operative temperature, mean air temperature, mean radiant temperature, ODB, OWB

Units

None

Input Restrictions

Fixed at Mean Air Temperature for compliance calculations

Standard Design

Not applicable

Condensation Control Dewpoint Offset

Applicability

Floor-based radiant cooling systems

Definition

The temperature difference above dewpoint that is the minimum cold water supply temperature

Units

None

Input Restrictions

Fixed at 2°F above dewpoint

Standard Design

Not applicable

Rated Pump Power Consumption

Applicability

Floor-based radiant cooling systems

Definition

The rated pump power at design conditions

Units

Watts

Input Restrictions

As Designed

Standard Design

Not applicable

Motor Efficiency

Applicability

Floor-based radiant cooling systems

Definition

The pump motor efficiency

Units

Decimal fraction

Input Restrictions

As Designed

Standard Design

Default motor efficiency from Table N2-20 (Table numbering may change) based on motor nameplate hp

Fraction of Motor Heat to Fluid

Applicability

Floor-based radiant cooling systems

Definition

Fraction of the heat from the motor inefficiencies that enters the fluid stream

Units

none

Input Restrictions

As designed. Default is 0.

Standard Design

Not applicable

Cooling High Water Temperature

Applicability

Floor-based radiant cooling systems

Definition

The high temperature used for control. If the water temperature is above the high temperature, the control temperature is set to the low control temperature.

Units

Deg F

Input Restrictions

As Designed

Standard Design

Not applicable

Cooling Low Water Temperature

Applicability

Floor-based radiant cooling systems

Definition

The temperature used for control of the water temperature.  If the water temperature of the radiant cooling is below this temperature, cooling is disabled.

Units

Deg F

Input Restrictions

Fixed at 55°F

Standard Design

Not applicable

Condensation Control Type

Applicability

Floor-based radiant cooling systems

Definition

The simulation program may have a means of detecting when condensation is likely to occur on floor surfaces in the space.  When this occurs, the simulation can shut off the system to prevent condensation from occurring.

Units

List: None, Simple, Variable

Input Restrictions

As designed

Standard Design

Not applicable

5.7.5.8 Chilled Beams

Reserved. Building descriptors will be added to define how chilled beams can be modeled for the proposed design. Chilled beams are not applicable to the standard design system.

5.7.5.9 Ground-Source Heat Pumps

Reserved. Building descriptors will be added to define how ground-source heat pumps (GSHP) can be modeled for the proposed design. GSHP are not applicable to the standard design system.

5.7.5.10 Variable Refrigerant Flow

Reserved. Building descriptors will be added to define how VRF systems can be modeled for the proposed design. VRF are not applicable to the standard design system.

5.7.5.11 Underfloor Air Distribution

Reserved. Building descriptors will be added to define how UFAD systems can be modeled for the proposed design. UFAD systems are not applicable to the standard design system.

5.7.6 Heating Systems    

5.7.6.1 General

Heating Source

Applicability

All systems that provide heating

Definition

The source of heating for the heating and preheat coils. The choices are:

•      Hot water

•      Steam

•      Electric resistance

•      Electric heat pump

•      Gas furnace

•      Gas heat pump (optional feature)

•      Oil furnace

•      Heat recovery

Units

List (see above)

Input Restrictions

As designed

Standard Design

Based on the prescribed system type. Refer to the HVAC System Map in Section5.1.2.

Table 42 – Heating Source for Baseline Building

5.7.6.2 Preheat Coil

Preheat Coil Capacity

Applicability

Systems with a preheat coil located in the outside air stream

Definition

The heating capacity of a preheating coil at design conditions.

Units

Btu/h

Input Restrictions

As designed

Standard Design

not applicable

Preheat Coil Efficiency

Applicability

Systems with a preheat coil with gas heating

Definition

The heating efficiency of a preheating coil at design conditions.

Units

Percentage

Input Restrictions

As designed. Default is 80%.

Standard Design

Not applicable

5.7.6.3 Hydronic/Steam Heating Coils

Systems with boilers have heating coils, including baseline building systems with hot water heating.

Heating Coil Capacity

Applicability

All systems with a heating coil

Definition

The heating capacity of a heating coil at AHRI conditions

Units

Btu/h

Input Restrictions

As designed. The user may need to manually adjust the capacity if the number of unmet load hours exceeds 150.

Standard Design

Autosize with a heating oversizing factor of 25%. If the number of unmet load hours for the baseline exceeds, reduce the heating coil capacity as indicated in Section2.6.2|topic=2.6.2 Sizing Equipment in the Standard Design.

5.7.6.4 Furnace

Furnace Capacity

Applicability

Systems with a furnace

Definition

The full load heating capacity of the unit

Units

Btu/h

Input Restrictions

As designed. The user must adjust the capacity if the number of unmet load hours exceeds 150.

Standard Design

Autosize with an oversizing factor of 25% (let the software determine heating capacity based on the building loads). If the number of unmet load hours for the baseline exceeds 150, reduce the furnace capacity as indicated in Figure 2 and 2.6.2

Furnace Fuel Heating Efficiency

Applicability

Systems with a furnace

Definition

The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (E_t) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(26)

E_t = 0.005163 x AFUE + 0.4033

where

AFUE           The annual fuel utilization efficiency (%)

E_t     The thermal efficiency (fraction)

Units

Fraction

Input Restrictions

As designed

Standard Design

Look up the requirement from the equipment efficiency tables in Table 6.8.1E of the Standard. The baseline efficiency requirement is located in Table E-3 or Table E-4 of the 2010 Appliance Efficiency Standards.  Use the heating input of the standard design system to determine the size category.

Furnace Fuel Heating Part Load Efficiency Curve

Applicability

Systems with furnaces

Definition

An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(27)

(28)

where

F_HeatPLC                   The Fuel Heating Part Load Efficiency Curve

F_uelpartload                 The fuel consumption at part load conditions (Btu/h)

F_uelrated                    The fuel consumption at full load (Btu/h)

Q_partload                   The capacity at part load conditions (Btu/h)

Q_rated                      The capacity at rated conditions (Btu/h)

Table 43 – Furnace Efficiency Curve Coefficients

Units

Data structure

Input Restrictions

Fixed

Standard Design

Fixed

Furnace Fuel Heating Pilot

Applicability

Systems that use a furnace for heating

Definition

The fuel input for a pilot light on a furnace

Units

Btu/h

Input Restrictions

As designed

Standard Design

Zero (pilotless ignition)

Furnace Fuel Heating Fan/Auxiliary

Applicability

Systems that use a furnace for heating

Definition

The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps

Units

Kilowatts (kW)

Input Restrictions

As designed

Standard Design

Not applicable

5.7.6.5 Electric Heat Pump

Electric Heat Pump Heating Capacity

Applicability

All heat pumps

Definition

The full load heating capacity of the unit, excluding supplemental heating capacity at AHRI rated conditions

Units

Btu/h

Input Restrictions

As designed

Standard Design

Autosize and use an oversizing factor of 25% (let the software determine heating capacity based on the building loads).

Electric Heat Pump Supplemental Heating Source

Applicability

All heat pumps

Definition

The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:

•      Electric resistance

•      Gas furnace

•      Oil furnace

•      Hot water

•      Other

Units

List (see above)

Input Restrictions

As designed

Standard Design

Electric resistance

Electric Heat Pump Heating Efficiency

Applicability

All heat pumps

Definition

The heating efficiency of a heat pump at AHRI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(29)

COP = 0.2778 x HSPF + 0.9667

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(30)

where

COP_adj          The adjusted coefficient of performance for simulation purposes

COP The AHRI rated coefficient of performance

HCAP_rated      The AHRI rated heating capacity of a packaged unit (kBtu/h)

Qfan,rated    ARI rated fan power, equal to the gross rated cooling capacity times 0.040.

Units

Unitless

Input Restrictions

As designed

Standard Design

Not applicable

Electric Heat Pump Heating Capacity Adjustment Curve(s)

Applicability

All heat pumps

Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(31)

(32)

For air-cooled heat pumps:

(33)

For water-cooled heat pumps:

where

Q_available                      Available heating capacity at present evaporator and condenser conditions (kBtu/h)

t_db                             The entering coil dry-bulb temperature (°F)

t_wt                             The water supply temperature (°F)

t_odb                            The outside-air dry-bulb temperature (°F)

Q_rated                         Rated capacity at AHRI conditions (in kBtu/h)

Table 44 – Heat Pump Capacity Adjustment Curves (CAP-FT)

Units

Data structure

Input Restrictions

Fixed – Use curves in Table 45 for water-source or air-source heat pumps as appropriate.

Standard Design

Not applicable.

Electric Heat Pump Heating Efficiency Adjustment Curve(s)

Applicability

All heat pumps

Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(34)

(35)

Air Source Heat Pumps:

 (36)

Water Source Heat Pumps:

 (37)

(38)

where

PLR             Part load ratio based on available capacity (not rated capacity)

EIR-FPLR     A multiplier on the EIR of the heat pump as a function of part load ratio

EIR-FT          A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature

Q_operating         Present load on heat pump (Btu/h)

Q_available          Heat pump available capacity at present evaporator and condenser conditions (Btu/h) .

t_db     The entering coil dry-bulb temperature (°F)

t_wt     The water supply temperature (°F)

t_odb    The outside air dry-bulb temperature (°F)

P_rated             Rated power draw at AHRI conditions (kW)

P_operating         Power draw at specified operating conditions (kW)

Table 45 – Heat Pump Heating Efficiency Adjustment Curves

Units

None

Input Restrictions

Fixed – use appropriate curve from Table 46

Standard Design

Not applicable

Electric Heat Pump Supplemental Heating Capacity

Applicability

All heat pumps

Definition

The design heating capacity of a heat pump supplemental heating coil at AHRI conditions

Units

Btu/h

Input Restrictions

As designed

Standard Design

Not applicable

Electric Supplemental Heating Control Temp

Applicability

All heat pumps

Definition

The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Default to 40°F  

Standard Design

Not applicable

Heat Pump Compressor Minimum Operating Temp

Applicability

All heat pumps

Definition

The outside dry-bulb temperature below which the heat pump compressor is disabled

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed.

Standard Design

Not applicable

Coil Defrost

Applicability

Air-cooled electric heat pump

Definition

The defrost control mechanism for an air-cooled heat pump. The choices are:

•      Hot-gas defrost, on-demand

•      Hot-gas defrost, timed 3.5 minute cycle

•      Electric resistance defrost, on-demand

•      Electric resistance defrost, timed 3.5 minute cycle

Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.

Units

List (see above)

Input Restrictions

Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.

Standard Design

Not applicable

Coil Defrost kW

Applicability

Heat pumps with electric resistance defrost

Definition

The capacity of the electric resistance defrost heater

Units

Kilowatts (kW)

Input Restrictions

As designed. This descriptor defaults to 0 if nothing is entered.

Standard Design

Not applicable.

Crank Case Heater kW

Applicability

All heat pumps

Definition

The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.

Units

Kilowatts (kW)

Input Restrictions

As designed. This descriptor defaults to 0.1 if nothing is entered.

Standard Design

Not applicable

Crank Case Heater Shutoff Temperature

Applicability

All heat pumps

Definition

The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. This descriptor defaults to 50°F.

Standard Design

Not applicable

5.7.6.6 Heat Recovery

Exhaust Air Sensible Heat Recovery Effectiveness

Applicability

Any system with outside air heat recovery

Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(39)

where

HREFF         The air-to-air heat exchanger effectiveness

EEAdb         The exhaust air dry-bulb temperature entering the heat exchanger

ELAdb         The exhaust air dry-bulb temperature leaving the heat exchanger

OSAdb         The outside air dry-bulb temperature

Units

Ratio between 0 and 1

Input Restrictions

As designed

Standard Design

Not applicable

Exhaust Air Latent Heat Recovery Effectiveness

Applicability

Any system with outside air enthalpy heat recovery

Definition

The latent heat recovery effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(40)

where

HREFF         The air-to-air heat exchanger effectiveness

EEAw           The exhaust air humidity ratio (fraction of mass of moisture in air to mass of dry air) entering the heat exchanger

ELAdb         The exhaust air humidity ratio leaving the heat exchanger

OSAdb         The outside air humidity ratio

Note that for sensible heat exchangers this term is not applicable.

Units

Ratio between 0 and 1

Input Restrictions

As designed

Standard Design

Not applicable

Condenser Heat Recovery Effectiveness

Applicability

Systems that use recover heat from a condenser

Definition

The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.

Units

Percent (%)

Input Restrictions

As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.

Standard Design

Not applicable

Heat Recovery Use

Applicability

Systems that use heat recovery

Definition

The end use of the heat recovered from a DX or heat pump unit. The choices are:

•      Reheat coils

•      Water heating

Units

List (see above)

Input Restrictions

As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.

Standard Design

Not applicable for most conditions. The end use will be water heating if required for 24-hour facility operation. Not applicable

5.7.7 Humidity Controls and Devices

5.7.7.1 General

Humidifier Type

Applicability

Optional humidifier

Definition

The type of humidifier employed. Choices include:

•      Hot-Water

•      Steam

•      Electric

•      Evaporative Humidification

Units

List (see above)

Input Restrictions

As designed

Standard Design

Not applicable

Humidistat Maximum Setting

Applicability

Systems with humidity control

Definition

The control setpoint for dehumidification

Units

Percent (%)

Input Restrictions

As designed

Standard Design

Not applicable

Humidistat Minimum Setting

Applicability

Systems with humidity control

Definition

The control setpoint for humidification

Units

Percent (%)

Input Restrictions

As designed

Standard Design

Not applicable

5.7.7.2 Desiccant

Desiccant Type

Applicability

Systems with desiccant dehumidification

Definition

Describes the configuration of desiccant cooling equipment

The following configurations for desiccant systems are allowed:

•      LIQ-VENT-AIR1 – a liquid desiccant dehumidifying unit

•      LIQ-VENT-AIR2 – a liquid desiccant dehumidifying unit combined with a gas-fired absorption chiller

•      SOL-VENT-AIR1 – a solid desiccant dehumidifying unit

•      NO-DESICCANT – the default, which indicates that no desiccant system is present

Units

List (see above)

Input Restrictions

As designed

Standard Design

Not applicable

Desiccant Control Mode

Applicability

Systems with desiccant dehumidification

Definition

The method of controlling the operation of the desiccant unit. For liquid-based systems this can be either:

•      Dry-bulb – the desiccant unit is turned on whenever the outside air dry-bulb exceeds a set limit.

•      Evaporative cooling– cycles the desiccant unit on when an evaporative cooler is on to maintain a dewpoint setpoint.

•      Dewpoint – cycles the desiccant unit on and off to maintain the dewpoint temperature of the supply air.

For solid-based systems the following configurations are possible:

•      Dehumidification only – the desiccant unit cycles on and off to maintain indoor humidity levels

•      Sensible heat exchanger plus regeneration – the desiccant unit includes a sensible heat exchanger to precool the hot, dry air leaving the desiccant unit. The air leaving the exhaust side of the heat exchanger is directed to the desiccant unit

•      Sensible heat exchanger – the desiccant unit includes a heat exchanger, but the air leaving the exhaust side of the heat exchanger is exhausted to the outdoors

Units

List (see above)

Input Restrictions

As designed

Standard Design

Not applicable

Desiccant Air Fraction

Applicability

Systems with desiccant dehumidification

Definition

The fraction of the supply air that passes through the desiccant unit. Typically either the minimum outside air fraction or all of the air passes through the desiccant system.

Units

Ratio

Input Restrictions

As designed

Standard Design

Not applicable

Desiccant Heat Source

Applicability

Systems with desiccant dehumidification

Definition

The source of heat that is used to dry out the desiccant. This can be either:

•      Gas – Hydronic – the regeneration heat load is met with a gas-fired heater

•      Hot water – the heat load is met with hot water from the plant

Units

List (see above)

Input Restrictions

As designed

Standard Design

Not applicable

Liquid Desiccant Performance Curves

Applicability

Systems with liquid-based desiccant dehumidification

Definition

A set of performance curves that apply to liquid desiccant systems.

(41)

•     

•      (42)

•     

•      (43)

•     

•      (44)

•     

where

DESC-T-FTW            dry-bulb temperature leaving desiccant unit

DESC-W-FTW           humidity ratio leaving desiccant unit

DESC-Gas-FTW        Gas usage of desiccant unit

DESC-kW-FTW         Electric usage of desiccant unit

T      entering air temperature

w     entering humidity ratio

Table 46 – Liquid Desiccant Unit Performance Curves

Units

Data structure

Input Restrictions

As designed, default to values in Table 46

Standard Design

Not applicable

Desiccant Dewpoint Temperature Setpoint

Applicability

Systems with desiccant dehumidification

Definition

The setpoint dewpoint temperature of the air leaving the desiccant system

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Defaults to 50°F.

Standard Design

Not applicable

Desiccant Heat Exchanger Effectiveness

Applicability

Systems with desiccant dehumidification

Definition

The effectiveness of a sensible heat exchanger used with a desiccant system

Units

Ratio

Input Restrictions

As designed

Standard Design

Not applicable

Desiccant Heat Exchanger Pressure Drop

Applicability

Systems with desiccant dehumidification

Definition

The pressure drop across a sensible heat exchanger used with a desiccant system

Units

in. H2O

Input Restrictions

As designed. Defaults to 1.0 in. H₂O

Standard Design

Not applicable