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 15: System #1 Description

System Description:

Packaged Terminal Air Conditioner (#1)

Supply Fan Power:

N/A (fan power integral to unit efficiency), ventilation provided naturally through operable windows

Supply Fan Control:

Constant volume

Min Supply Temp:

50 < T < 60   DEFAULT:  20°F below return air temperature

Cooling System:

Direct expansion (DX)

Cooling Efficiency:

Minimum seasonal energy efficiency ratio (SEER) or energy efficiency ratio (EER) based on equipment type and output capacity of standard design unit(s). Adjusted EER is calculated to account for supply fan energy.

Maximum Supply Temp:

85 < T < 110   DEFAULT:  100

Heating System:

Gas furnace (#3) or heat pump (#4)

Heating Efficiency:

Minimum annual fuel utilization efficiency (AFUE), thermal efficiency, coeffience of performance (COP) or heating season performance factor (HSPF) based on equipment type and output capacity of standard design unit(s).

Economizer:

None

Ducts:

N/A (unducted)

Table 16: System #2 Description

System Description:

Four-Pipe Fan Coil (#2)

Supply Fan Power:

0.35 W/cfm

Supply Fan Control:

Cycles with load

Min Supply Temp:

50 < T < 60   DEFAULT:  20°F below return air temperature

Space Temp Control:

SAT is fixed at 55°F. Fan cycles to meet the load.

Cooling System:

Chilled water

Cooling Efficiency:

Minimum kW/ton and IPLV per Path B chiller requirements in Title 24 Section110.2

Maximum Supply Temp:

85 < T < 110   DEFAULT:  100

Heating System:

Boiler

Heating Efficiency:

Minimum AFUE, thermal efficiency per Section 110.2 of Title 24 Part 6 for the applicable heating capacity

Economizer:

None

Ducts:

N/A (unducted)

Table 17: System #3 Description

System Description:

Packaged Single Zone with Gas Furnace/Electric Air Conditioning (#3)

Supply Fan Power:

See Section 5.7.3

Supply Fan Control:

Constant volume

Min Supply Temp:

50 < T < 60   DEFAULT:  20°F below return air temperature

Cooling System:

Direct expansion (DX)

Cooling Efficiency:

Minimum SEER or EER based on equipment type and output capacity of standard design unit(s). Adjusted EER is calculated to account for supply fan energy.

Maximum Supply Temp:

85 < T < 110   DEFAULT:  100

Heating System:

Gas furnace (#3)

Heating Efficiency:

Minimum AFUE, Thermal Efficiency, COP or HSPF based on equipment type and output capacity of standard design unit(s)

Economizer:

Integrated economizer with differential dry-bulb high limit, when mechanical cooling output capacity of the standard design as modeled in the compliance run by the compliance software is over 54,000 Btu/hr

Ducts:

For ducts installed in unconditioned buffer spaces or outdoors as specified in §140.4(l), the duct system efficiency shall be as modified by accounting for duct leakage rate

 

Table 18: System #5 Description

System Description:

Packaged VAV with Boiler and Reheat

Supply Fan Power:

See Section 5.7.3

Supply Fan Control:

VAV - variable speed drive

Relief Fan Control:

See fan section

Minimum Supply Temp:

50 < T < 60    DEFAULT:  20°F below return air temperature

Cooling System:

Direct expansion (DX)

Cooling Efficiency:

Minimum efficiency based on average standard design  output capacity of equipment unit(s)

Maximum Supply Temp:

90 < T < 110    DEFAULT:  105

Heating System:

Gas boiler

Hot Water Pumping System

Variable flow (two-way valves) riding the pump curve

Heating Efficiency:

Minimum efficiency based on average standard design output capacity of equipment unit(s)

Economizer:

Integrated dry bulb economizer with differential dry-bulb limit

 

Table 19: System #6 Description

System Description:

Chilled Water VAV with Reheat

Supply Fan Power:

See Section 5.7.3

Supply Fan Control:

VAV - variable speed drive

Return Fan Control:

Same as supply fan

Minimum Supply Temp:

50 < T < 60    DEFAULT:  20°F below return air temperature

Cooling System:

Chilled water

Chilled Water Pumping System

Variable flow (two-way valves) with a variable speed drive (VSD) on the pump if three or more fan coils or air handlers; constant volume flow with water temperature reset control if less than three fan coils or air handlers; reset supply pressure by demand if standard system has DDC controls

Cooling Efficiency:

Minimum efficiency based on standard design output capacity of equipment unit(s)

Maximum Supply Temp:

90 < T < 110    DEFAULT:  105

Heating System:

Gas boiler

Hot Water Pumping System

Variable flow (two-way valves) riding the pump curve if three or more fan coils or air handlers; constant volume flow with water temperature reset control if less than three fan coils or air handlers;  reset supply pressure by demand

Heating Efficiency:

Minimum efficiency based on standard design output capacity of equipment unit(s)

Economizer:

Integrated dry bulb economizer with differential dry-bulb limit

 

Table 20: System #7 Description

System Description:

Single-Zone VAV System

Supply Fan Power:

See Section 5.7.3

Supply Fan Control

Variable-speed drive

Minimum Supply Temp:

50 < T < 60    DEFAULT:  20°F below return air temperature

Supply Temp Control:

Supply air temperature setpoint shall be linearly reset from minimum at 50 percent cooling load and above to maximum at 0 percent cooling load. Fan volume shall be linearly reset from 100 percent air flow at 100 percent cooling load to minimum air flow at 50 percent cooling load and below. Minimum fan volume setpoint shall be 50 percent. (This is effectively an “airflow first” sequence.)

Cooling System:

Direct expansion

Cooling Efficiency:

Minimum efficiency based on the standard output capacity of specific equipment unit(s)

Compressor Stages:

Two to four (See minimum unloading ratio requirement)

Maximum Supply Temp:

90 < T < 110    DEFAULT:  100

Heating System:

Gas furnace

Hot Water Pumping System

Variable flow (two-way valves) riding the pump curve if three or more fan coils; constant volume flow with water temperature reset control if less than three fan coils; reset supply pressure by demand if standard system has DDC controls

Heating Efficiency:

Minimum efficiency based on the standard output capacity of specific equipment unit(s)

Economizer:

Integrated dry bulb economizer with differential dry-bulb high limit

Table 21: System #9 Description

System Description:

Heating and ventilation only system

Supply Fan Power:

See fan power details

Supply Fan Control

Constant volume

Minimum Supply Temp:

N/A

Cooling System:

None

Cooling Efficiency:

N/A

Maximum Supply Temp:

90 < T < 110    DEFAULT:  100

Heating System:

Gas furnace

Hot Water Pumping System

N/A

Heating Efficiency:

Minimum efficiency based on the standard output capacity of specific equipment unit(s)

Economizer:

TBD

Table 22: System #10 Description

System Description:

Computer Room Air Handler (CRAH)

Supply Fan Power:

0.49 W/cfm at design air flow where economizer is required, 0.39 W/cfm where economized is not required;

Supply Fan Control

variable speed drive; fan power part-load curve is for “VSD with static pressure reset”

Minimum Supply Temp:

60 F

Cooling System:

Single zone VAV with chilled water cooling source

Cooling Efficiency:

Same as System #6 (Built-up VAV)

Maximum Supply Temp:

80°F

Heating System:

None

Economizer:

Integrated 100 percent outside air economizer with differential dry-bulb limit

Supply Temp Control:

VAV: Supply air temperature setpoint shall be reset between 60 °F and 80°F; fan volume shall be reset between 100 percent and 50 percent flow, depending on cooling load; minimum fan volume setpoint shall be 50 percent

Table 23: System #11 Description

System Description:

Computer Room Air Conditioner (CRAC)

Supply Fan Power:

0.49 W/cfm at design flow (see equipment sizing) where economizer is required; 0.39 W/cfm whereeconomizer is not required

Supply Fan Control

Constant speed if the computer room receptacle load is less than 17.5 kW; otherwise, variable speed drive. Fan power curve for VSD is ‘VSD with static pressure reset‘.

Relief  Fan Control:

No relief fan

Minimum Supply Temp:

60°F

Cooling System:

Single zone Air-cooled DX

Cooling Capacity:

Equipment design CFM and cooling capacity sized at 115 percent of the capacities generated from a system sizing run; one system per zone

Cooling Efficiency:

Appliance Standards Table C-9

Maximum Supply Temp:

80°F

Heating System:

None

Economizer:

Integrated 100 percent outside air economizer with differential dry-bulb limit if the net cooling capacity is greater than 54,000 Btu/h

Supply Temp Control:

VAV: Supply air temperature setpoint shall be between 60 F and 80 F; fan supply air volume shall be reset between 100 percent and 50 percent of the rated fan condition, depending on the cooling load; minimum fan volume setpoint shall be 50 percent
CV: supply air temperature setpoint modulates to meet the load

Table 24: System #12 Description

System Description:

Laboratory HVAC System

Supply Fan Power:

See supply fan static pressure, supply fan efficiency, and supply fan motor efficiency for standard design specifications

Supply Fan Control

Variable-speed drive

Return Fan Control:

No return fans

Exhaust Fan Control:

Variable volume, variable-speed drive if total building laboratory exhaust air flow rate is greater than 2,000 cfm and 10 ACH or greater; constant volume otherwise.

Ventilation:

Same as proposed but subject to a minimum 6 ACH; system is 100 percent outside air

Minimum Supply Temp:

55°F

Cooling System:

PVAV with air-cooled DX if  total lab floor area <150,000 ft2; water-cooled chiller if greater than  150,000 ft2 floor area

Cooling Capacity:

Equipment fan CFM and cooling capacity sized at 115 percent of the capacities determined using a sizing run; one laboratory system per floor when total building laboratory floor area is 10,000 ft2 or greater, otherwise one laboratory system per zone

Cooling Efficiency:

Minimum efficiency requirements per Section 110.2

Maximum Supply Temp:

95

Heating System:

Gas furnace if building total floor area is 10,000 ft2 or less; hot water coils/boiler if greater than 10,000 ft2

Economizer:

integrated 100 percent outside air economizer with differential dry-bulb limit

Supply Temp Control:

VAV: Supply air temperature setpoint shall be reset upwards by 5 F based on warmest zone; fan volume shall be reset between100 percent and 50 percent flow, depending on cooling load; minimum fan volume setpoint shall be 50 percent

CV: supply air temperature setpoint modulates to meet the load

 

Table 25: System #13 Description

System Description:

Kitchen HVAC system

Supply Fan Power:

Fixed supply fan static pressure, see Section 5.7.3

Supply Fan Control

Constant speed if total exhaust airflow rate is greater than or equal to 2,000 cfm; otherwise, variable speed drive; fan power ratio at part load is determined by the part load ratio and the static pressure reset system curve

Return Fan Control:

No return fans

Exhaust Fan Control:

Variable volume, variable-speed drive if total exhaust air flow rate > 5,000 cfm; constant volume otherwise

Minimum Supply Temp:

20°F below space temperature setpoint

Cooling System:

PVAV with air-cooled DX if floor area < 50,000 ft2; water-cooled chiller if greater 50,000 ft2 floor area

Cooling Capacity:

Cooling capacity sized at 115 percent of the calculated room load; fan airflow sizing based on exhaust airflow requirements; one fan system per room

Cooling Efficiency:

Minimum efficiency requirements per Section 110.2

Maximum Supply Temp:

95°F

Heating System:

Gas furnace if building total floor area is 10,000 ft2 or less; hot water coils/boiler if greater than 10,000 ft2

Economizer:

None

Supply Temp Control:

VAV: Supply air temperature setpoint shall be linearly reset from minimum at 50 percent cooling load and

above to maximum at 0 percent cooling load; fan volume shall be linearly reset from 100 percent air flow at 100 percent cooling load to minimum air flow at 50 percent cooling load and below; minimum fan volume setpoint shall be 50 percent (effectively an “airflow first” sequence)

CV: supply air temperature modulates to meet the load

5.7.1    Basic System Information

 

HVAC System Name

Applicability

All system types

Definition

A unique descriptor for each HVAC system

Units

Text, unique

Input Restrictions

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

Standard Design

None

Standard Design:

Existing Buildings

 

 

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

     Fan configuration for multiple deck systems

Units

List from the choices below

Input Restrictions

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

SPVAC – Single package vertical air conditioner (minimum efficiency defined in Section 110.2)

SPVHP – Single package vertical heat pump (minimum efficiency defined in Section 110.2)

* 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 Table 4); baseline system types are shown in Table 27

Standard Design:

Existing Buildings

 

Table 26: Baseline Building System Type

Baseline Building System Type

System 1 – PTAC

System 2 – FPFC

System 3 – PSZ-AC

System 5 – Packaged VAV with Reheat

System 6 – VAV with Reheat

System 7 – PSZ-SZVAV

System 9 – Heating and Ventilation

System 10 – CRAC Unit

System 11 – CRAH Unit

System 12 – LAB

System 13 – Kitchen

 

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

Standard Design:

Existing Buildings

 

 

Thermal zone List

Applicability

All system types

Definition

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

Units

None

Input Restrictions

As designed

Standard Design

Same as the proposed design

Standard Design:

Existing Buildings

 

 

Total Cooling Capacity

Applicability

All system types

Definition

The installed cooling capacity of the project.

This includes all:

     Chillers

     Built-up DX

     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 percent. If the number of unmet load hours exceeds 150, increase the cooling capacity according to the procedures in Chapter 2

Standard Design:

Existing Buildings

 

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 multi-zone 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

     Optimal start

Units

None

Input Restrictions

List one of the following inputs:

Direct digital control (DDC) control to the zone level – DDC 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

Standard Design:

Existing Buildings

 

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 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

Standard Design:

Existing Buildings

 

 

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.

Standard Design

Same as the proposed design

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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 when the HVAC schedule indicates the building is occupied. (See night cycle control input for fan operation during unoccupied hours.) 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 all other systems, fixed at continuous.

Standard Design

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

Standard Design:

Existing Buildings

 

 

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

Fixed at yes if control system type is DDC to the zone level; otherwise, as designed

Standard Design

Fixed at yes, if control system type is DDC to the zone level

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

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

15°F below the space temperature setpoint for interior zones that are served by multiple zone systems; for all other zones, 20°F below the space temperature setpoint

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

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 9):

     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 11: 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

Standard Design:

Existing Buildings

 

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

Standard Design:

Existing Buildings

 

 

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; 60°F for multiple zone systems; no heating for data centers and computer rooms

Standard Design:

Existing Buildings

 

 

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, instead it 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)

Standard Design:

Existing Buildings

 

 

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 10):

     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 12: SAT Heating Setpoint Reset Based on Outdoor Air Temperature (OAT)

Units

Degrees Fahrenheit (F°)

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design: Existing Buildings

 

5.7.3    Fan and Duct Systems

5.7.3.1  Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See Section 5.7.1, Table 27 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 one of 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.

Standard Design:

Existing Buildings

 

 

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 percent point for the fan part-load curve.

Units

CFM (ft3/min)

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°F 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 system airflow rate that satisfies that coincident peak of all thermal zones at the design supply air temperature (55°F).

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

Table 27: Baseline Building Fan Control Method

Baseline building System

Fan Control Method

System 1 – PTAC

Constant volume, cycling 

System 2 – FPFC

Constant volume, cycling

System 3 – PSZ-AC

Constant volume

 

 

System 5 – Packaged VAV with Reheat

Variable-flow, variable speed drive (VSD)

System 6 – VAV with Reheat

Variable-flow, variable speed drive (VSD)

System 7 – PSZ, Single Zone VAV

Variable-flow, variable-speed drive (VSD)

 

 

System 9 – Heating and Ventilation

Constant volume

System 10 – CRAH Units

Variable-flow, variable speed drive (VSD)*

System 11 – CRAC Units

Variable-flow, variable speed drive (VSD)*

* For CRAH Units, fan volume shall be linearly reset from 100 percent air flow at 100 percent cooling load to minimum airflow at 50 percent 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 maximum of the user entered bhp and 95 percent of the next smaller motor horsepower:

Proposed bhp = max(user bhp, 95 percent ×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 percent of the next smaller motor horsepower is 19.

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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: choose from 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

The brake horsepower for the supply fan is this value times the supply fan ratio (see above).

Standard Design:

Existing Buildings

 

 

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:

Airflow

Single zone, six stories or less

Multiple zone, less than six stories

Multiple zone, greater than six stories

<2000 cfm

2.5”

3.0”

3.5”

2000 cfm – 10,000 cfm

3.0”

3.5”

4.0”

>10,000 cfm

3.5”

4.0”

4.5”

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.

Standard Design:

Existing Buildings

 

 

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 percent if the design supply air flow is less than 2000 cfm; 60 percent if the design supply air flow is between 2000 cfm and 10,000 cfm; or 62 percent if the design supply airflow is greater than 10,000 cfm.

Not applicable for the four-pipe fan coil system.

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

Table 28: Minimum Nominal Efficiency for Electric Motors (Percent)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Motor Horse Power

 

 

1

85.5

1.5

86.5

2

86.5

3

89.5

5

89.5

7.5

91.7

10

91.7

15

92.4

20

93.0

25

93.6

30

93.6

40

94.1

50

94.5

60

95.0

75

95.4

100

95.4

125

95.4

150

95.8

200

96.2

250

96.2

300

96.2

350

96.2

400

96.2

450

96.2

500

96.2

 

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

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

Fan Part-Flow Power Curve

Applicability

All variable flow fan systems

Definition

A part-load power curve that 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 3 and Table 30 for the type of fan specified in the proposed design.

Where:

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

Minimum fan power ratio

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

Constants from the table below

 

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.

Standard Design:

Existing Buildings

 

 

 

Percent

Powermin

Fan Type – Control Type

0.1631

1.5901

-0.8817

0.1281

70%

AF or BI riding the curvea

0.9977

-0.659

0.9547

-0.2936

50%

AF or BI with inlet vanes or discharge dampersa

0.1224

0.612

0.5983

-0.3334

50%

FC riding the curvea

0.3038

-0.7608

2.2729

-0.8169

50%

FC with inlet vanesa

0.1639

-0.4016

1.9909

-0.7541

40%

Vane-axial with variable pitch bladesa

0.070428852

0.385330201

-0.460864118

1.00920344

10%

Any fan with VSD

0.040759894

0.08804497

-0.07292612

0.943739823

10%

VSD with static pressure reset

 

 

 

 

 

a: Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500-03-082 A-11, 2007

 

Supply Fan Power Index

Applicability

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

Definition

The supply fan power (at the motor) per unit of flow

Units

W/cfm

Input Restrictions

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

Standard Design

For FPFC systems, 0.35 W/cfm; for other systems, not applicable.

Standard Design:

Existing Buildings

 

 

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 zero. Special documentation is required to claim any credit for filtration in excess of 1 inch wc. 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 inch wc

Standard Design:

Existing Buildings

 

 

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

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

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

Standard Design:

Existing Buildings

 

 

Return Air Path

Applicability

Any system with return ducts or return air plenum

Definition

Describes the return path for air.

Can be 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.

Standard Design:

Existing Buildings

 

 

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 percent fan flow point for the part-load curve (see below).

Units

Cfm

Input Restrictions

As designed

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.

Standard Design:

Existing Buildings

 

 

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 percent 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.

Standard Design

Standard design systems with an economizer shall use relief fans and shall use the static pressure and fan efficiency method.

Standard Design:

Existing Buildings

 

 

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 choose from 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

The brake horsepower for the supply fan is this value times the supply fan ratio (see above).

Standard Design:

Existing Buildings

 

 

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”.

Standard Design:

Existing Buildings

 

 

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 percent. For design airflow 10,000 cfm or greater, 50 percent.

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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 3 and Table 30 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.

Standard Design:

Existing Buildings

 

 

5.7.3.4  Exhaust Fan Systems

The standard design shall track the proposed design exempt process exhaust flow rate up to the prescribed outside air ventilation rate by space type (see Appendix 5.4A for the baseline maximum exhaust rate). Exempt process exhaust includes exhaust from toilets, break rooms, copy rooms and kitchens. 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. For the standard design, total outside air ventilation supply airflow may need to be adjusted so that the design supply airflow for each floor of the building matches the total design exhaust airflow for that floor.

If an exhaust fan system is used in the proposed design as a ventilation system, then an equivalent baseline exhaust fan system is NOT defined, since the baseline has its own specification of a ventilation system that is independent of the proposed.

 

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. However, if the user has specified an exhaust system as the ventilation system an equivalent baseline system will not be modeled since the baseline has its own definition for ventilation systems. The name can be identical to that used for the proposed design or some other appropriate name may be used.

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

Exhaust Fan Design Airflow

Applicability

All exhaust fan systems

Definition

The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100 percent flow point of 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 total design exhaust flow capacity for building (conditioned space) shall not exceed the sum of building minimum ventilation (outdoor) air flow. Exhaust makeup can be transferred from other zones in the building provided that the total building exhaust rate does not exceed the total minimum outside air flow rate.

Standard Design

Same as proposed design, but with the same limitations described under input restrictions. The design supply air ventilation rate for zone(s) may need to be adjusted by the software, so that the total design outside air ventilation rate supplied to all zones on a floor equals the total exhaust fan design airflow for all zones on the floor.

Standard Design:

Existing Buildings

 

 

Exhaust 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)

Units

List (see above)

Input Restrictions

As designed, 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 to 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.

For exhaust fans serving laboratory spaces, the fan control method is variable-flow, variable speed drive when the exhaust flow is 10 ACH or less. If the lab exhaust flow is greater than 10 ACH, the control method is constant volume.

Standard Design:

Existing Buildings

 

 

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 lab spaces, the schedule is defined in Appendix 5.4B.

Standard Design

Specified in Appendix 5.4B for the specified occupancy.

Standard Design:

Existing Buildings

 

 

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

Standard Design

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 percent 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

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.

Standard Design:

Existing Buildings

 

 

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 - choose from 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

Standard Design:

Existing Buildings

 

 

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” wc. For lab exhaust, 4” if six stories or less; or 4.5” if greater than six stories.

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

Standard Design:

Existing Buildings

 

 

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 percent.

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 percent, while for lab exhaust it is 62 percent. 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).

Standard Design:

Existing Buildings

 

 

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

For exempt process fans other than lab, kitchen, and garage exhaust fans, same as proposed. For process fans, the value is taken. Otherwise, from Table 30.

Standard Design:

Existing Buildings

 

 

Fan Part-Flow Power Curve

Applicability

All variable flow exhaust fan systems

Definition

A part-load power curve that 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 3 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 3 and Table 30 for the type of fan specified in the proposed design.

Standard Design:

Existing Buildings

 

 

Exhaust Fan Power Index

Applicability

Exhaust systems serving high-rise residential units and hotel/motel guestrooms

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

W/cfm

Input Restrictions

As designed

Standard Design

For high-rise residential units and hotel/motel guestrooms, 0.58 W/cfm

Standard Design:

Existing Buildings

 

 

5.7.3.5  Garage Exhaust Fan Systems

When garage exhaust fan systems are modeled the 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.

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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 or 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 percent of the design fan power.

Standard Design

Same as proposed

Standard Design:

Existing Buildings

 

5.7.3.6  Duct Systems in Unconditioned Space

The details of these modeling rule requirements are under development.

 

Duct Leakage Rate

Applicability

Any single-zone systems with ducts in unconditioned space serving zones of 5,000 ft2 or less

Definition

The leakage rate from the duct system into unconditioned space.

All leakage is assumed to occur to unconditioned space (not to outdoors).

Units

Percentage of design airflow (%)

Input Restrictions

For new systems: If duct leakage testing is performed as per instructions in the Reference Appendices and certified by a Home Energy Rating System (HERS) rater as designed. If not tested, 15 percent.

For existing, altered systems: 15 percent if tested and verified by the HERS procedures in Reference Appendix NA2. If untested or if failed test, 20 percent.

Standard Design

6 percent for new construction

15 percent for existing, altered systems

Standard Design:

Existing Buildings

 

 

Duct Location

Applicability

Single zone, constant volume systems with ducts in unconditioned space, serving 5000 ft2

Definition

The duct location is the fraction that is in unconditioned space, in conditioned space, and outdoors

Units

Three unitless fractions

Input Restrictions

All in unconditioned space

Standard Design

All in unconditioned space

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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 percent outside air, with ventilation rates as specified by the user, but not less than 6 ACH.

See ventilation control method at the zone level.

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

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., 75°F).

     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 percent 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 percent 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 and when the standard design cooling system is not a computer room air handling unit (CRAH). 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.

Standard Design:

Existing Buildings

 

 

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 (see above)

Input Restrictions

List non-integrated or integrated

Standard Design

Integrated for systems above capacity 54,000 Btu/h at Air-Conditioning, Heating, and Refrigeration Institute (AHRI) conditions

Standard Design:

Existing Buildings

 

 

Economizer High Temperature Lockout

Applicability

Systems with fixed dry-bulb economizer

Definition

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

Standard Design:

Existing Buildings

 

 

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 applicable

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

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; either chilled water, direct expansion (DX), or other

Units

List (see above)

Input Restrictions

As designed

Standard Design

The baseline building cooling source is shown in Table 33

Standard Design:

Existing Buildings

 

 

Table 29: Cooling Source for Baseline Building System

Baseline building System

Cooling Source

Syst-em 1 – PTAC

Direct expansion (DX)

System 2 – FPFC

Chilled water

System 3 – PSZ-AC

Direct expansion (DX)

System 5 – Packaged VAV with Reheat

Direct expansion (DX)

System 6 – VAV with Reheat

Chilled water

System 7 – PSZ, Single Zone VAV

Direct expansion (DX)

System 9 – Heating and Ventilation

None

System 10 – CRAH Unit for Data Centers

Chilled water

System 11 – CRAC Unit for Data Centers

Direct expansion (DX)

 

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

NOT A USER INPUT

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:

Where:

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

The AHRI rated total cooling capacity of a packaged unit (Btu/h) Qfan,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 4:

Equation 4 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 UMLH 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 determined from the standard design net cooling capacity, and from applying the fan power rules above for adjusting for fan heat.

Standard Design:

Existing Buildings

 

 

Gross Total 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.

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:

Where:

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

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

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 UMLH 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 percent. Sizing calculations shall be based on 0.5 percent design dry-bulb and mean coincident wet-bulb.

Standard Design:

Existing Buildings

 

 

Gross Total Cooling Capacity

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:

For air-cooled direct expansion:

For water-cooled direct expansion:

For chilled water coils:

 

Where:

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

Adjusted capacity at AHRI conditions (Btu/h)

A multiplier to adjust Qt,adj

The entering coil wet-bulb temperature (°F)

The entering coil dry-bulb temperature (°F)

The water supply temperature (°F)

The outside air dry-bulb temperature (°F)

Note: If an air-cooled unit employs an evaporative condenser,  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.

 

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

Standard Design:

Existing Buildings

 

 

Table 30: Cooling Capacity Curve Coefficients

Coefficient

Air-Cooled Direct Expansion

Water-Cooled Direct Expansion

Chilled Water Coils

Air-Source
(PTAC)

Air-Source
(Other DX)

Water-Source
(Heat Pump)

Water-Source
(Other DX)

Fan-Coil

Other Chilled Water

a

1.1839345

0.8740302

-0.2780377

0.9452633

0.5038866

2.5882585

b

-0.0081087

-0.0011416

0.0248307

-0.0094199

-0.0869176

-0.2305879

c

0.0002110

0.0001711

-0.0000095

0.0002270

0.0016847

0.0038359

d

-0.0061435

-0.0029570

-0.0032731

0.0004805

0.0336304

0.1025812

e

0.0000016

0.0000102

0.0000070

-0.0000045

0.0002478

0.0005984

f

-0.0000030

-0.0000592

-0.0000272

-0.0000599

-0.0010297

-0.0028721

Note: These curves are the DOE-2.1E defaults, except for Water-Source (Other DX), which is taken from the “ECB Compliance Supplement”, public review draft prepared by the SSPC 90.1 ECB Panel, Version 1.2, March 1996.

 

 

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

Standard Design:

Existing Buildings

 

 

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.

Standard Design

Defaults

Standard Design:

Existing Buildings

 

Table 31: Default Coil Bypass Factors

System Type

Default Bypass Factor

Packaged Terminal Air Conditioner and Heat Pumps

0.241

Other Packaged Equipment

0.190

Multi-Zone Systems

0.078

All Other

0.037

 

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:

Where:

The coil bypass factor at AHRI rating conditions

The coil bypass factor adjusted for airflow and coil conditions

The ratio of airflow to design airflow

A multiplier on the rated coil bypass factor to account for variation in air flow across the coil (take coefficients from Table 34)

A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients from Table 35)

A multiplier on the rated coil bypass factor to account for the part load ratio (take coefficients from Table 36)

The entering coil wet-bulb temperature (F)

The entering coil dry-bulb temperature (F)

Part load ratio

Standard Design

Defaults

Standard Design:

Existing Buildings

 

Table 32: Coil Bypass Factor Airflow Adjustment Factor

Coefficient

COIL-BF-FFLOW (PTAC)

COIL-BF-FFLOW (HP)

COIL-BF-FFLOW (PSZ/other)

a

-2.277

-0.8281602

-0.2542341

b

5.21140

14.3179150

1.2182558

c

-1.93440

-21.8894405

0.0359784

d

 

9.3996897

 

Table 33: Coil Bypass Factor Temperature Adjustment Factor

Coefficient

COIL-BF-FT (PTAC)

COIL-BF-FT (HP)

COIL-BF-FT (PSZ, other)

a

-1.5713691

-29.9391098

1.0660053

b

0.0469633

0.8753455

-0.0005170

c

0.0003125

-0.0057055

0.0000567

d

-0.0065347

0.1614450

-0.0129181

e

0.0001105

0.0002907

-0.0000017

f

-0.0003719

-0.0031523

0.0001503

Table 34: Coil Bypass Factor Part Load Adjustment Factor

Coefficient

COIL-BF-FPLR (All Systems)

a

0.00

b

1.00

 

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:

Where:

The ratio of airflow to design airflow

A multiplier on the rated coil capacity to account for variation in air flow across the coil (take coefficients from Table 33)

A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients from Table 34)

The curve takes the form:

With the following coefficients:

Coefficient

0.47278589

1.2433415

-1.0387055

0.32257813

 

Standard Design

Use defaults as described above

Standard Design:

Existing Buildings

 

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 Energy Efficiency Ratio (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:

Where:

The adjusted EER for simulation purposes

The rated EER

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

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:

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 standards.

Standard Design:

Existing Buildings

 

 

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 EER or the 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 2015 Appliance Efficiency Standards.

Standard Design:

Existing Buildings

 

 

Integrated Energy Efficiency Ratio

Applicability

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

Definition

Integrated Energy Efficiency Ratio

This is a SEER that is a composite rating for a range of part-load conditions and different ambient conditions. The rating is determined according to AHRI procedures. Equipment with this rating is subject to mandatory minimum requirements.

This input is currently only used for mandatory minimum efficiency checks.

Units

Btu/h-W

Input Restrictions

As designed

If the IEER rating is below mandatory minimum required levels specified in Section 110.2 of the standards, the compliance run shall fail.

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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.

For air-cooled DX systems:

For water-cooled DX systems:

Where:

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

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

The entering coil wet-bulb temperature (F)

The water supply temperature (F)

The outside-air dry-bulb temperature (F)

Rated power draw at AHRI conditions (kW)

Power draw at specified operating conditions (kW)

 

 

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 DX 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. The software generates the equipment performance curve based on the pre-defined performance curves specified in Appendix 5.7.

Standard Design:

Existing Buildings

 

Table 35: Cooling System Coefficients for EIR-FT

Coefficient

Water-Source (Heat Pump)

Water-Source (Other)

Air-Source (PTAC)

Air-Source (PSZ with Cool Cap <=65,000 Btu/h)

Air-Source (Other)

a

2.0280385

-1.8394760

-0.6550461

n/a (see Standard Design)

-1.0639310

b

-0.0423091

0.0751363

0.0388910

n/a

0.0306584

c

0.0003054

-0.0005686

-0.0001925

n/a

-0.0001269

d

0.0149672

0.0047090

0.0013046

n/a

0.0154213

e

0.0000244

0.0000901

0.0001352

n/a

0.0000497

f

-0.0001640

-0.0001218

-0.0002247

n/a

-0.0002096

 

Direct Expansion Part-Load Efficiency Adjustment Curve

Applicability

Packaged systems with 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) :

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

Note: 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. Where:

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

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

The entering coil wet-bulb temperature (°F)

The water supply temperature (°F)

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

Present load on heat pump (Btu/h)

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

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.

Standard Design:

Existing Buildings

 

 

Table 36: Cooling System Coefficients for EIR-FPLR

Coefficient

Water-Source
(Heat Pump)

Water-Source
(Other)

Air-Source (PTAC)

Air-Source (PSZ with Cap  <65,000 Btu/h)

Air-Source (Other)

a

0.1250000

0.2012301

0.1250000

0

0.2012301

b

0.8750000

-0.0312175

0.8750000

1

-0.0312175

c

0.0000000

1.9504979

0.0000000

0

1.9504979

d

0.0000000

-1.1205105

0.0000000

0

-1.1205105

Table 37: Cooling System Coefficients for Part-Load Factor
(PLF) Correlation (EnergyPlus)

Coefficient

Water-Source
(Heat Pump)

Water-Source
(Other)

Air-Source (PTAC)

Air-Source (PSZ with Cap <65,000 Btu/h)

Air-Source (Other)

a

0.85

0

0.85

1

0

b

0.15

5.1091

0.15

0

5.1091

c

0

-8.5515

0

0

-8.5515

d

0

4.4744

0

0

4.4744

 

Number of Cooling Stages

Applicability

Single zone VAV systems and DX systems with multiple stages

Definition

This applies to single zone VAV and any 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 standard design shall be two for the single zone VAV baseline and packaged VAV baseline.

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

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 °F

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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

Not applicable

Standard Design:

Existing Buildings

 

 

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 °F

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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.

Standard Design:

Existing Buildings

 

 

Supply Fan Low Power Ratio

Applicability

Single sone 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.

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

Minimum Hot-Gas Bypass 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

Standard Design:

Existing Buildings

 

 

Condenser Type

Applicability

All direct expansion systems including heat pumps

Definition

The type of condenser for a 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 in section 5.7.1. Air-cooled for systems 1 (PTAC), 3, (PSZ), 5 (PVAV) and 11 (CRAC). Not applicable for other standard design systems.

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

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 - 55°F

Supply air temperature control - fixed

Design heating supply air temperature - 105°F

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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 percent 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

Standard Design:

Existing Buildings

 

 

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 (Section 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

Standard Design: Existing Buildings

 

 

Direct Stage Effectiveness

Applicability

Systems with evaporative cooling

Definition

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

Where:

The direct stage effectiveness

The entering air dry-bulb temperature

The entering air wet-bulb temperature

The direct stage leaving dry-bulb temperature

 

Units

Numeric (0 EFF 1)

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

Indirect Stage Effectiveness

Applicability

Systems with evaporative cooling

Definition

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

Where:

The indirect stage effectiveness

The entering air dry-bulb temperature

The entering air wet-bulb temperature

The indirect stage leaving dry-bulb temperature

 

Units

Numeric (0 EFF 1)

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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:

Where:

Part load ratio of airflow based on design airflow

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

Operating primary air stream airflow (cfm)

Design primary air stream airflow (cfm)

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 applicable

Standard Design:

Existing Buildings

 

 

Table 38: Part-Load Curve Coefficients-
Evaporative Cooler Effectiveness

Coefficient

Direct

Indirect

A

1.1833000

1.0970000

B

-0.2575300

-0.1650600

C

0.0742450

0.0680690

 

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

Standard Design:

Existing Buildings

 

 

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

Standard Design:

Existing Buildings

 

 

5.7.5.4  Western Cooling Challenge Equipment

A special credit is available in the ACM Reference Manual for equipment (including evaporative equipment) that meets efficiency and water use requirements of the Western Cooling Challenge (WCC), 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 for more information.

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). 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.

 

Building Descriptor

Section

Proposed Input

System Type

5.7.1

PSZ-AC and PSZVAV-AC only

Cooling Supply Air Temperature

5.7.2.2

20°F below return air temperature

Cooling Supply Air Temperature Control

5.7.2.2

Fixed (single zone system)

Heating Supply Air temperature

5.7.2.3

105°F

Heating Supply Air Temperature Control

5.7.2.3

Fixed (constant)

Supply Fan Design Air Rated Capacity

5.7.3

400 cfm/ton

Fan Control Method

5.7.3

Constant Volume

Supply Fan Power Index

5.7.3.2

0.365 W/cfm

Maximum Outside Air Ratio

5.7.4.1

1

Design Outside Air Flow

5.7.4.1

(as designed)

Economizer Control Type

5.7.4.2

Differential dry-bulb

Economizer Integration Level

5.7.4.2

Integrated

Economizer High Temperature Lockout

5.7.4.2

n/a

Economizer low temperature lockout

5.7.4.2

n/a

Cooling Source

5.7.5

DX

Total Cooling Capacity

5.7.5

As designed

(NOTE: If there are UMLH, the user will have to enter a larger capacity system, or add a supplemental DX unit with standard efficiency (EER~11) to meet cooling load.)

Sensible Cooling Capacity

5.7.5

As designed

Cooling Capacity Adjustment Curves

5.7.5

Use air-cooled DX defaults

Coil Bypass Factor (if used)

5.7.5

0.190

Direct Expansion Cooling Efficiency

5.7.5.2

As designed

(User enters EER from WCC test and software makes adjustment for EER, removing fan power from efficiency as needed.)

Seasonal Energy Efficiency Ratio

5.7.5.2

n/a

Direct Expansion Cooling Efficiency Temperature Adjustment Curve

5.7.5.2

Use default curve

Direct Expansion Part-Load Efficiency Adjustment Curve

5.7.5.2

Use default curve

Refrigerant Charge Factor

5.7.5.2

1

Airflow Adjustment Factor

5.7.5.2

1

Duct Leakage Rate

5.7.5.2

As designed (for qualifying spaces)

Minimum Unloading Ratio

5.7.5.2

0.25 (units > 240 kBtu/h)

0.35 (units >= 65 kBtu/h and < 120 kBtu/h)

Cooling Setpoint Schedule

5.4

Use default schedule for space type (this will be 75°F when occupied, in most cases)

Heating

 

 

Heating Source

5.7.6.1

As designed (but heat pump not allowed)

Preheat Coil

5.7.6.2

No preheat coil

Heating Coil Capacity

5.7.6.3

As designed

Furnace Capacity

5.7.6.4

As designed

Furnace Fuel Heating Efficiency

5.7.6.3

As designed

Furnace Fuel Heating Part Load Efficiency Curve

5.7.6.4

Fixed default curve

Furnace Fuel Heating Pilot

5.7.6.4

0

Furnace Fuel Heating Fan/Auxiliary

5.7.6.4

n/a

Heat recovery

5.7.6.6

Not allowed for this credit

Humidity Controls and Devices

5.7.7

None

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; includes any pump(s) and/or fans that are part of the precooling unit

Units

Watts

Input Restrictions

As designed

Standard Design

Not applicable

Standard Design:

Existing Buildings

 

 

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:

Where:

The direct stage effectiveness

The outside air dry-bulb temperature