5.8 HVAC Primary Systems

5.8.1 Boilers

Boiler Name
Applicability	All boilers
Definition	A unique descriptor for each boiler, heat pump, central heating heat-exchanger, or heat recovery device
Units	None
Input Restrictions	User entry Where applicable, this should match the tags that are used on the plans for the proposed design.
Standard Design	Boilers are only designated in the baseline model if the baseline system type uses hot water for space heating.
Standard Design: Existing Buildings

Boiler Fuel Source

Applicability

All boilers

Definition

The fuel source for the central heating equipment

The choices are:

• Gas

• Oil

• Electricity

Units

List (see above)

Input Restrictions

As designed

This input is restricted, based on the choice of boiler type, according to the following rules:

	Electricity	Gas	Steam
Steam Boiler			Allowed
Hot Water Boiler		Allowed

Standard Design

Gas

Standard Design:

Existing Buildings

Boiler Type
Applicability	All boilers
Definition	The fuel source for the central heating equipment The choices are: • Gas • Oil • Electricity
Units	List (see above)
Input Restrictions	As designed
Standard Design	Hot water boiler
Standard Design: Existing Buildings

Boiler Draft Type
Applicability	All boilers
Definition	How combustion airflow is drawn through the boiler. The choices are natural (sometimes called atmospheric) or mechanical. Natural draft boilers use natural convection to draw air for combustion through the boiler. Natural draft boilers are subject to outside air conditions and the temperature of the flue gases. Mechanical draft boilers enhance the air flow in one of three ways: 1) induced draft, which uses ambient air, a steam jet, or a fan to induce a negative pressure which pulls flow through the exhaust stack; 2) forced draft, which uses a fan and ductwork to create a positive pressure that forces air into the furnace, or 3) balanced draft, which uses both induced draft and forced draft methods to bring air through the furnace, usually keeping the pressure slightly below atmospheric.
Units	List (see above)
Input Restrictions	As designed
Standard Design	Mechanical (forced)
Standard Design: Existing Buildings

Number of Identical Boiler Units
Applicability	All boilers
Definition	The number of identical units for staging
Units	Numeric: integer
Input Restrictions	As designed; default is 1
Standard Design	The baseline building shall have one boiler for a when the baseline plant serves a conditioned floor area of 15,000 ft² or less and have two equally size boilers for plants serving more than 15,000 ft².
Standard Design: Existing Buildings

Boiler Design Capacity
Applicability	All boilers
Definition	The heating capacity at design conditions
Units	Btu/h
Input Restrictions	As designed If unmet load hours exceed 150, the user may need to manually adjust boiler design capacity
Standard Design	The boiler is sized to be 25 percent larger than the peak loads of the baseline building. Baseline boilers shall be sized using weather files containing 99.6 percent heating design temperatures and 0.5 percent dry-bulb and 1 percent wet-bulb cooling design temperatures.
Standard Design: Existing Buildings

Boiler Efficiency Type
Applicability	All boilers
Definition	The full load efficiency of a boiler is expressed as one of the following: • Annual fuel utilization efficiency (AFUE) is a measure of the boiler’s efficiency over a predefined heating season. • Thermal efficiency (E_t) is the ratio of the heat transferred to the water divided by the heat input of the fuel. • Combustion efficiency (E_c) is the measure of how much energy is extracted from the fuel and is the ratio of heat transferred to the combustion air divided by the heat input of the fuel.
Units	List (see above)
Input Restrictions	None
Standard Design	AFUE for all gas and oil-fired boilers with less than 300,000 Btu/h capacity. Thermal efficiency (E_t)for all gas and oil-fired boilers with capacities between 225,000 and 2,500,000 Btu/h. Combustion efficiency (E_c), for all gas and oil-fired boilers with capacities above 2,500,000 Btu/h.
Standard Design: Existing Buildings

Boiler Efficiency

Applicability

All boilers

Definition-

The full load efficiency of a boiler at rated conditions (see efficiency type above) expressed as a dimensionless ratio of output over input. The software must accommodate input in either thermal efficiency (E_t), combustion efficiency (E_c), or AFUE. The software shall make appropriate conversions to thermal efficiency if either AFUE or combustion efficiency is entered as the rated efficiency.

Where AFUE is provided, E_t shall be calculated as follows:

If combustion efficiency is entered, the compliance software shall convert the efficiency to thermal efficiency by the relation:

All electric boilers will have an efficiency of 98 percent.

Units

Ratio

Input Restrictions

As designed

Standard Design

Boilers for the baseline design are assumed to have the minimum efficiency as listed in Table E-4 of the 2009 Appliance Efficiency Standards.

Standard Design:

Existing Buildings

Boiler Part-Load Performance Curve

Applicability

All boilers

Definition

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

Where:

	The fuel heating part-load efficiency curve
	The fuel consumption at part-load conditions (Btu/h)
	The fuel consumption at design conditions (Btu/h)
	The boiler capacity at part-load conditions (Btu/h)
	The boiler capacity at design conditions (Btu/h)
	Constant
	Constant
	Constant

Units

Ratio

Input Restrictions

Prescribed to the part-load performance curve in the ACM Appendix 5.7, based on the boiler draft type.

Standard Design

The baseline building uses the mechanical draft fan curve in Appendix 5.7.

Standard Design:

Existing Buildings

Boiler Forced Draft Fan Power
Applicability	All mechanical draft boilers
Definition	The fan power of the mechanical draft fan at design conditions.
Units	Nameplate horsepower
Input Restrictions	As designed The software shall convert the user entry of motor horsepower to fan power in watts by the following equation:
Standard Design	Sized for an energy input ratio of 0.001018 (0.2984 W per kBtu/h heat input)
Standard Design: Existing Buildings

Boiler Minimum Unloading Ratio
Applicability	All boilers
Definition	The minimum unloading capacity of a boiler expressed as a percentage of the rated capacity. Below this level, the boiler must cycle to meet the load.
Units	Percent (%)
Input Restrictions	As designed If the user does not use the default value, the software must indicate that supporting documentation is required on the output forms. Fixed at 1 percent (this accounts for jacket losses and start/stop losses).
Standard Design	1 percent
Standard Design: Existing Buildings

Boiler Minimum Flow Rate
Applicability	All boilers
Definition	The minimum flow rate recommended by the boiler manufacturer for stable and reliable operation of the boiler
Units	Gpm
Input Restrictions	As designed If the boiler(s) is piped in a primary only configuration in a variable flow system then the software shall assume there is a minimum flow bypass valve that allows the hot water pump to bypass water from the boiler outlet back to the boiler inlet to maintain the minimum flow rate when boiler is enabled. Note: The boiler entering water temperature must accurately reflect the mixed temperature (colder water returning from the coil(s) and hotter bypass water) to accurately model boiler efficiency as a function of boiler entering water temperature.
Standard Design	0 gpm
Standard Design: Existing Buildings

Hot Water Supply Temperature
Applicability	All boilers
Definition	The temperature of the water produced by the boiler and supplied to the hot water loop
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Standard Design	Use 180°F for baseline boiler
Standard Design: Existing Buildings

Hot Water Return Temperature
Applicability	All boilers
Definition	The temperature of the water returning to the boiler from the hot water loop
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed.
Standard Design	Use 140°F for baseline boiler design
Standard Design: Existing Buildings

Hot Water Supply Temperature Reset
Applicability	All boilers
Definition	Variation of the hot water supply temperature with outdoor air temperature
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed (not allowed for non-condensing boilers)
Standard Design	The hot water supply temperature should vary according to the following: • 180°F when outside air is < 20°F • Ramp linearly between 180°F and 150°F when outdoor air is between 20°F and 50°F • 150°F when outdoor air is > 50°F
Standard Design: Existing Buildings

5.8.2 Chillers

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry; where applicable, this should match the tags that are used on the plans
Standard Design	Chillers are only designated when the baseline system uses chilled water
Standard Design: Existing Buildings

Chiller Type
Applicability	All chillers
Definition	The type of chiller, either a vapor-compression chiller or an absorption chiller. Vapor compression chillers operate on the reverse Rankine cycle, using mechanical energy to compress the refrigerant, and include: Reciprocating* Scroll* Screw* Centrifugal – uses rotating impeller blades to compress the air and impart velocity Direct-Fired Single Effect Absorption – uses a single generator and condenser Direct-Fired Double Effect Absorption – uses two generators/ concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect but it must use a higher temperature heat source. Indirect-Fired Double Effect Absorption Gas Engine-Driven *Positive displacement – includes reciprocating (piston-style), scroll and screw compressors
Units	List (see above). The software shall support all chiller types listed above.
Input Restrictions	As designed
Standard Design	The baseline building chiller is based on the design capacity of the standard design (baseline) as follows:
Standard Design: Existing Buildings

Table 43: Type and Number of Chillers

Building Peak Cooling Load	Number and type of chiller(s)
≤ 300 tons	One water-cooled screw chiller
300 < Load < 600	Two water-cooled screw chillers, sized equally
≥ 600 tons	A minimum of two water-cooled centrifugal chillers, sized to keep the unit size below 800 tons

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging
Units	None
Input Restrictions	As designed; default is 1
Standard Design	From Table 43 above
Standard Design: Existing Buildings

Number of Identical Chiller Units

Applicability

All chillers

Definition

The fuel source for the chiller

The choices are:

Electricity (for all vapor-compression chillers)

Gas (absorption units only, designated as direct-fired units)

Hot water (absorption units only, designated as indirect-fired units)

Steam (absorption units only, designated as indirect-fired units)

Units

List (see above)

Input Restrictions

As designed

This input is restricted, based on the choice of chiller type, according to the following rules:

	Electricity	Gas	Hot Water	Steam
Reciprocating	Allowed
Scroll	Allowed
Screw	Allowed
Centrifugal	Allowed
Single Effect Absorption		Allowed	Allowed	Allowed
Direct-Fired Double Effect Absorption		Allowed	Allowed	Allowed
Indirect-Fired Absorption		Allowed	Allowed	Allowed

Standard Design

Electricity

Standard Design:

Existing Buildings

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions
Units	Btu/h or tons
Input Restrictions	As designed The user may need to manually adjust the capacity if the number of unmet load hours exceeds 150.
Standard Design	Determine loads for baseline building and oversize by 15 percent
Standard Design: Existing Buildings

Chiller Rated Efficiency
Applicability	All chillers
Definition	The efficiency of the chiller (EER for air-cooled chillers, kW/ton for water-cooled electric chillers, and COP for fuel-fired and heat-driven chillers) at AHRI 550/590 rated full-load conditions
Units	Ratio (kW/ton, COP, EER, depending on chiller type and condenser type) Water-cooled electric chiller - kW/ton Air-cooled or evaporatively-cooled electric chiller - EER All non-electric chillers – COP
Input Restrictions	As designed Must meet the minimum requirements of Table 110.2-D.
Standard Design	Use the minimum efficiency requirements from Tables 110.2-D Path B. If chiller type is reciprocating, scroll, or screw, use the efficiency for positive displacement chillers from Table 110.2-D.
Standard Design: Existing Buildings

Integrated Part-Load Value
Applicability	All chillers
Definition	The part-load efficiency of a chiller developed from a weighted average of four rating conditions, according to AHRI Standard 550
Units	Ratio (kW/ton, COP, EER, depending on chiller type and condenser type) Water-cooled electric chiller - kW/ton Air-cooled or evaporatively-cooled electric chiller - EER All non-electric chillers – COP
Input Restrictions	As designed; must meet the minimum requirements of Table 110.2-D
Standard Design	Not used When the standard design system has a chiller, the standard design will always use Path B performance curves.
Standard Design: Existing Buildings

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity

Below this level the chiller must either cycle to meet the load or false-load the compressor (such as with hot gas bypass).

Table 44: Default Minimum Unloading Ratios

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed but constrained to a minimum value of 10 percent. If the user does not employ the default values, supporting documentation is required.

Standard Design

Use defaults listed above

Standard Design:

Existing Buildings

Chiller Minimum Part Load Ratio
Applicability	All chillers
Definition	The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity Below this level the chiller must cycle to meet the load. If the chiller minimum part-load ratio (PLR) is less than the chiller minimum unloading ratio, then the compliance software shall assume hot gas bypass operation between the minimum PLR and the minimum unloading ratio.
Units	Percent (%)
Input Restrictions	As designed, but constrained to a minimum value of 10 percent. If the user does not employ the default values, supporting documentation is required.
Standard Design	When the standard design has a screw chiller, the minimum PLR is 15 percent. When the standard design has a centrifugal chiller, the minimum PLR is 10 percent.
Standard Design: Existing Buildings

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as:

For air-cooled chillers:

For water-cooled chillers:

Where:

	Available cooling capacity at present evaporator and condenser conditions (MBH)
	The chilled water supply temperature (°F)
	The condenser water supply temperature (°F)
	The outside air dry-bulb temperature (°F)
	Rated capacity at AHRI conditions (MBH)

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

Separate curves are provided for Path A and Path B chillers in Appendix 5.7.

Units

Data structure

Input Restrictions

Prescribed curves are provided in Appendix 5.7 for the proposed design chiller type and the compliance path (A or B). If the default curves are overridden, supporting documentation is required.

Standard Design

Use prescribed curve for Path B chiller as applicable to the standard design chiller type.

Standard Design:

Existing Buildings

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio.

Note: For variable-speed chillers, the part-load cooling efficiency curve is a function of both part-load ratio and leaving condenser water temperature. The default curves are given as:

Variable Speed:

Air-Cooled:

Water-Cooled:

Where:

	Part-load ratio based on available capacity (not rated capacity)
	Present load on chiller (Btu/h)
	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
	The chilled water supply temperature (°F)
	The condenser 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)

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

Units

Data structure

Input Restrictions

Curves are prescribed in Appendix 5.7 given the chiller capacity and type. A separate set of curves are provided for Path A chillers and Path B chillers. The path is determined by comparing software inputs of full-load efficiency and integrated part-load value with the requirements of standards Table 110.2-D.

Standard Design

Use Path B curves specified in Appendix 5.7

Standard Design:

Existing Buildings

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:

Default curves for steam-driven single and double effect absorption chillers:

Default curves for direct-fired double effect absorption chillers:

The default curves for engine driven chillers are the same format as those for the steam-driven single and double effect absorption chillers but there are three sets of curves for different ranges of operation based on the engine speed.

Where:

	Part-load ratio based on available capacity (not rated capacity)
	A multiplier on the fuel input ratio (FIR) to account for part-load conditions
	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
	A multiplier on the capacity of the chiller (Equation 45)
	Present load on chiller (in Btu/h)
	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
	The chilled water supply temperature (in °F)
	The condenser water supply temperature (in °F)
	The outside air dry-bulb temperature (°F)
	Rated fuel consumption at AHRI conditions (in Btu/h)
	Fuel consumption at specified operating conditions (in Btu/h)

Units

Data structure

Input Restrictions

Restricted to curves specified in Appendix 5.7

Standard Design

Use prescribed curves specified in Appendix 5.7

Standard Design:

Existing Buildings

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Standard Design	The baseline chilled water supply temperature is set to 44°F.
Standard Design: Existing Buildings

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Standard Design	The standard design chilled water return temperature is set to 64°F.
Standard Design: Existing Buildings

Chilled Water Supply Temperature Control Type
Applicability	All chillers
Definition	The method by which the chilled water setpoint temperature is reset The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	List none, outside air-based reset, or demand-based reset
Input Restrictions	As designed
Standard Design	Outside air-based reset
Standard Design: Existing Buildings

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Standard Design	10°F from design chilled water supply temperature The chilled water supply temperature reset follows an outside air reset scheme, where the setpoint is 44°F at outside air conditions of 80°F dry-bulb and above; the setpoint is 54°F at outside air conditions of 60°F dry-bulb and below; and ramps linearly from 44°F to 54°F as the outside air dry-bulb temperature varies between 80°F and 60°F.
Standard Design: Existing Buildings

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller The choices are: Air-cooled Water-cooled Evaporatively-cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except a water mist is used to cool the condenser coil, making them more efficient.
Units	List (see above)
Input Restrictions	As designed
Standard Design	The baseline chiller is always assumed to have a water-cooled condenser, although the chiller type will change depending on the design capacity.
Standard Design: Existing Buildings

5.8.3 Cooling Towers

Standard Design Summary. Standard design system 6 has one or more cooling towers. One tower is assumed to be matched to each standard design chiller. Each standard design chiller has its own condenser water pump that operates when the chiller is brought into service. The range between the condenser water return (CWR) and condenser water supply (CWS) is 10°F. The baseline building condenser pumping energy is assumed to be 12 W/gpm. The cooling tower is assumed to have a variable-speed fan that is controlled to provide a CWS equal to the design wet-bulb temperature when weather permits. The design approach shall be 10°F.

Cooling Tower Name
Applicability	All cooling towers
Definition	A unique descriptor for each cooling tower
Units	Text, unique
Input Restrictions	User entry; where applicable, this should match the tags that are used on the plans
Standard Design	Descriptive name that keys the baseline building plant
Standard Design: Existing Buildings

Cooling Tower Type
Applicability	All cooling towers
Definition	Type of cooling tower employed. The choices are: • Open tower, centrifugal fan • Open tower, axial fan Open cooling towers collect the cooled water from the tower and pump it directly back to the cooling system. Closed towers circulate the evaporated water over a heat exchanger to indirectly cool the system fluid.
Units	List (see above)
Input Restrictions	As designed
Standard Design	The baseline cooling tower is an open tower axial fan device
Standard Design: Existing Buildings

Cooling Tower Capacity
Applicability	All cooling towers
Definition	The tower thermal capacity per cell adjusted to Cooling Technology Institute (CTI) rated conditions of 95°F condenser water return, 85°F condenser water supply, and 78°F wet-bulb with a 3 gpm/nominal ton water flow. The default cooling tower curves below are at unity at these conditions.
Units	Btu/h
Input Restrictions	As designed
Standard Design	The baseline building chiller is autosized and increased by 15 percent. The tower is sized to supply 85°F condenser water at design conditions for the oversized chiller.
Standard Design: Existing Buildings

Cooling Tower Number of Cells
Applicability	All cooling towers
Definition	The number of cells in the cooling tower Each cell will be modeled as equal size. Cells are subdivisions in cooling towers into individual cells, each with their own fan and water flow, that allow the cooling system to respond more efficiently to lower load conditions.
Units	Numeric: integer
Input Restrictions	As designed
Standard Design	One cell per tower and one tower per chiller
Standard Design: Existing Buildings

Cooling Tower Total Fan Horse Power
Applicability	All cooling towers
Definition	The sum of the nameplate rated horsepower (hp) of all fan motors on the cooling tower. Pony motors should not be included.
Units	Gpm/hp or unitless if energy input ratio (EIR) is specified (if the nominal tons but not the condenser water flow is specified, the condenser design water flow shall be 3.0 gpm per nominal cooling ton).
Input Restrictions	As designed, but the cooling towers shall meet minimum performance requirements in Table 110.2-G
Standard Design	The cooling tower fan horsepower is 60 gpm/hp
Standard Design: Existing Buildings

Cooling Tower Design Wet-Bulb
Applicability	All cooling towers
Definition	The design wet-bulb temperature that was used for selection and sizing of the cooling tower
Units	Degrees Fahrenheit (°F)
Input Restrictions	Specified from design wet-bulb conditions from Reference Appendix JA2 for the city where the building is located, or the city closest to where the building is located
Standard Design	Specified from design wet-bulb conditions from Reference Appendix JA2 for the city where the building is located, or from the city closest to where the building is located
Standard Design: Existing Buildings

Cooling Tower Design Entering Water Temperature
Applicability	All cooling towers
Definition	The design condenser water supply temperature (leaving tower) that was used for selection and sizing of the cooling tower
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed; default to 85°F
Standard Design	85°F or 10°F above the design wet-bulb temperature, whichever is lower
Standard Design: Existing Buildings

Cooling Tower Design Return Water Temperature
Applicability	All cooling towers
Definition	The design condenser water return temperature (entering tower) that was used for selection and sizing of the cooling tower
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed; default to 95°F
Standard Design	Set to a range of 10°F (10°F above the cooling tower design entering water temperature)
Standard Design: Existing Buildings

Cooling Tower Capacity Adjustment Curve
Applicability	All cooling towers
Definition	A curve or group of curves that represent the available total cooling capacity as a function of outdoor air wet-bulb, condenser water supply, and condenser water return temperatures. The default curves are given as follows: Approach = Coeff(1) + Coeff(2)•FRair + Coeff(3)•(FRair)2 +Coeff(4)•(FRair)3 + Coeff(5)•FRwater + Coeff(6)•FRair•FRwater + Coeff(7)•(FRair)2•FRwater + Coeff(8)•(FRwater)2 + Coeff(9)•FRair•(FRwater)2 + Coeff(10)•(FRwater)3 + Coeff(11)•Twb + Coeff(12)•FRair•Twb + Coeff(13)•(FRair)2•Twb + Coeff(14)•FRwater•Twb + Coeff(15)•FRair•FRwater•Twb + Coeff(16)•(FRwater)2•Twb + Coeff(17)•(Twb)2 + Coeff(18)•FRair•(Twb)2 + Coeff(19)•FRwater•(Twb)2 + Coeff(20)•(Twb)3 + Coeff(21)•Tr + Coeff(22)•FRair•Tr + Coeff(23)•FRair•FRair•Tr + Coeff(24)•FRwater•Tr + Coeff(25)•FRair•FRwater•Tr + Coeff(26)•(FRwater)2•Tr + Coeff(27)•Twb•Tr + Coeff(28)•FRair•Twb•Tr + Coeff(29)•FRwater•Twb•Tr + Coeff(30)•(Twb)2•Tr + Coeff(31)•(Tr)2 + Coeff(32)•FRair•(Tr)2 + Coeff(33)•FRwater•(Tr)2 + Coeff(34)•Twb•(Tr)2 + Coeff(35)•(Tr)3 Where: FRair – ratio of airflow to airflow at design conditions FRwater – ratio of water flow to water flow at design conditions Tr – tower range (°F) Twb – wet-bulb temperature Coefficients for this performance curve are provided in Appendix 5.7.
Units	Data structure
Input Restrictions	User must use one of the prescribed curves defined in Appendix 5.7
Standard Design	Use one of the prescribed curves defined in Appendix 5.7
Standard Design: Existing Buildings

Cooling Tower Set Point Control
Applicability	All cooling towers
Definition	The type of control for the condenser water supply. The choices are fixed or wet-bulb reset. A fixed control will modulate the tower fans to provide the design condenser water supply temperature at all times when possible. A wet-bulb reset control will reset the condenser water setpoint to a fixed approach to outside air wet-bulb temperature. The approach defaults to 10°F. A lower approach may be used with appropriate documentation.
Units	List (see above)
Input Restrictions	As designed; default to 95°F
Standard Design	Fixed at the 0.4 percent design wet-bulb temperature, which is prescribed and specified for each of the 86 weather data files
Standard Design: Existing Buildings

Cooling Tower Capacity Control
Applicability	All cooling towers
Definition	Describes the modulation control employed in the cooling tower. Choices include: • Fluid Bypass provides a parallel path to divert some of the condenser water around the cooling tower at part-load conditions. • Fan Cycling is a simple method of capacity control where the tower fan is cycled on and off. This is often used on multiple-cell installations. • Two-Speed Fan/Pony Motor are the same from an energy perspective. A lower horsepower pony motor is an alternative to a two-speed motor. The pony motor runs at part-load conditions (instead of the full-sized motor) and saves fan energy when the tower load is reduced. Additional building descriptors are triggered when this method of capacity control is selected. • Variable-Speed Fan is a variable frequency drive is installed for the tower fan so that the speed can be modulated.
Units	List (see above)
Input Restrictions	As designed
Standard Design	Variable-speed fan
Standard Design: Existing Buildings

Cooling Tower Low-Speed Airflow Ratio
Applicability	All cooling towers with two-speed or pony motors
Definition	The percentage full-load airflow that the tower has at low speed or with the pony motor operating; equivalent to the percentage full-load capacity when operating at low speed
Units	Ratio
Input Restrictions	As designed
Standard Design	Not applicable
Standard Design: Existing Buildings

Cooling Tower Low-Speed kW Ratio
Applicability	All cooling towers with two-speed or pony motors
Definition	The percentage full-load power that the tower fans draw at low speed or with the pony motor operating
Units	Ratio
Input Restrictions	Calculated, using the as-designed flow ratio and the cooling tower power adjustment curve below
Standard Design	Not applicable
Standard Design: Existing Buildings

Cooling Tower Power Adjustment Curve

Applicability

All cooling towers with VSD control

Definition

A curve that varies the cooling tower fan energy usage as a function of part-load ratio for cooling towers with variable speed fan control. The default curve is given as:

Where:

	Part-load ratio based on available capacity (not rated capacity)
	Present load on tower (in Btu/h)
	Tower available capacity at present range, approach, and outside wet-bulb conditions (in Btu/h)
	The outside air wet-bulb temperature (°F)
	The tower range (°F)
	The tower approach (°F)
	Rated power draw at CTI conditions (kW)
	Power draw at specified operating conditions (kW)

Table 45: Default Efficiency TWR_Fan-FPLR Coefficients - VSD on Cooling Tower Fan

Coefficient
	0.33162901
	-0.88567609
	0.60556507
	0.9484823

Units

Data structure

Input Restrictions

User shall use only default curves

Standard Design

Use default curves given above

Standard Design:

Existing Buildings

Cooling Tower Minimum Speed
Applicability	All cooling towers with a VSD control
Definition	The minimum fan speed setting of a VSD controlling a cooling tower fan expressed as a ratio of full load speed
Units	Ratio
Input Restrictions	As designed; default is 0.50
Standard Design	0.5
Standard Design: Existing Buildings

5.8.4 Water-side Economizers

Baseline Building Summary - None of the baseline building systems use a water-side economizer.

Water-Side Economizer Name
Applicability	All water-side economizers
Definition	The name of a water-side economizer for a cooling system
Units	Text, unique
Input Restrictions	Descriptive reference to the construction documents; default is no water-side economizer
Standard Design	No water economizer
Standard Design: Existing Buildings

Water Economizer Type
Applicability	All water-side economizers
Definition	The type of water-side economizer. Choices include: • None • Heat exchanger in parallel with chillers. This would be used with an open cooling tower and is often referred to as a non-integrated economizer because the chillers are locked out when the plant is in economizer mode. • Heat exchanger in series with chillers. This would be used with an open cooling tower and is often referred to as integrated because the chillers can operate simultaneously with water economizer operation. • Direct water economizer. This would be used with a closed cooling tower. In this case, a heat exchanger is not needed. This type works only as a non-integrated economizer (also known as strainer-cycle).
Units	List (see above)
Input Restrictions	As designed
Standard Design	No water economizer
Standard Design: Existing Buildings

Water-Side Economizer HX Effectiveness

Applicability

Water-side economizers with an open cooling tower

Definition

The effectiveness of a water-side heat exchanger at design conditions

This is defined as:

Where:

	The maximum load that the economizer can handle
	The chilled water flow rate
	The chilled water specific heat
	The chilled water return temperature
	The condenser water supply temperature
WSEeff	The effectiveness of the water-side economizer coil
tea	The entering coil air dry-bulb temperature (°F)
tla	The leaving coil air dry-bulb temperature (°F)
tea	The entering coil water temperature (°F)

Units

Ratio

Input Restrictions

As designed; default is 60 percent

Standard Design

No water economizer

Standard Design:

Existing Buildings

Water-Side Economizer Heat Exchanger Heat Transfer Coefficient Value
Applicability	Water-side economizers with an open cooling tower
Definition	The heat transfer coefficient of the plate-and-frame heat exchanger with the waterside economizer
Units	Btu/h-°F
Input Restrictions	As designed
Standard Design	Not applicable
Standard Design: Existing Buildings

Water-Side Economizer Approach
Applicability	All water-side economizers
Definition	The design temperature difference between the chilled water temperature leaving the heat exchanger and the condenser water inlet to the heat exchanger
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed; default is 3°F
Standard Design	No water economizer
Standard Design: Existing Buildings

Water-Side Economizer Maximum CWS
Applicability	All water-side economizers
Definition	The control temperature (condenser water supply temperature) above which the water-side economizer is disabled
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed; default is 50°F
Standard Design	No water economizer
Standard Design: Existing Buildings

Water-Side Economizer Availability Schedule
Applicability	All water-side economizers
Definition	A schedule which represents the availability of the water-side economizer
Units	Data structure: schedule, on/off
Input Restrictions	As designed
Standard Design	No water economizer
Standard Design: Existing Buildings

Water-Side Economizer Auxiliary kW
Applicability	Water-side economizers with an open tower
Definition	The electrical input (pumps and auxiliaries) for a dedicated pump for the chilled water side of the heat exchanger This power is in excess of the condenser water pumps and cooling tower fans for the system during water-side economizer operation.
Units	KW or kW/ton
Input Restrictions	As designed
Standard Design	No water economizer
Standard Design: Existing Buildings

5.8.5 Pumps

Baseline Building Summary - Hot water pumping in the baseline building shall be modeled as a variable flow, primary only system. Two-way valves are assumed at the heating coils.

Chilled water pumping in the baseline building (system 6) is a primary system. Each chiller has its own primary and condenser water pumps that operate when the chiller is activated.

General Notes - The building descriptors in this section are repeated for each pumping system. See the pump service building descriptor for a list of common pump services.

Pump Name
Applicability	All pumps
Definition	A unique descriptor for each pump
Units	Text, unique
Input Restrictions	User entry; were applicable, should match the tags that are used on the plans
Standard Design	Same as proposed design If there is no equivalent in the proposed design, assign a sequential tag to each piece of equipment. The sequential tags should indicate the pump service as part of the descriptor (e.g., CW for condenser water, CHW for chilled water, or HHW for heating hot water).
Standard Design: Existing Buildings

Pump Service
Applicability	All pumps
Definition	The service for each pump. Choices include: • Chilled water • Chilled water (primary) • Chilled water (secondary) • Heating water • Heating water (primary) • Heating water (secondary) • Service hot water • Condenser water • Loop water (for hydronic heat pumps)
Units	List (see above)
Input Restrictions	As designed
Standard Design	As needed by the baseline building system
Standard Design: Existing Buildings

Number of Pumps
Applicability	All pumps
Definition	The number of identical pumps in service in a particular loop, e.g., the heating hot water loop, chilled water loop, or condenser water loop
Units	Numeric: integer
Input Restrictions	As designed
Standard Design	There will be one heating hot water pump for each boiler, one chilled water pump, and one condenser water pump for each chiller.
Standard Design: Existing Buildings

Water Loop Design
Applicability	All pumps
Definition	The heating and cooling delivery systems can consist of a simple primary loop system, or more complicated primary/secondary loops or primary/secondary/tertiary loops
Units	List (see above)
Input Restrictions	As designed
Standard Design	Assume primary loops only for heating hot water; for chilled water loops, a primary loop design is assumed.
Standard Design: Existing Buildings

Pump Motor Modeling Method
Applicability	All pumps
Definition	Software commonly models pumps in one of two ways. The simple method is for the user to enter the electric power per unit of flow (W/gpm). This method is commonly used for smaller systems. A more detailed method requires a specification of the pump head, design flow, impeller, and motor efficiency.
Units	List power-per-unit-flow or detailed
Input Restrictions	Detailed
Standard Design	Detailed for chilled water and condenser water pumps; power-per-unit-flow for heating hot water and service hot water pumps
Standard Design: Existing Buildings

Pump Motor Power-Per-Unit-Flow
Applicability	All proposed design pumps that use the power-per-unit-flow method
Definition	The electric power of the pump divided by the flow at design conditions
Units	W/gpm
Input Restrictions	As designed
Standard Design	Not applicable for chilled water and condenser water pumps; 19 W/gpm for heating hot water and service hot water pumps
Standard Design: Existing Buildings

Pump Motor Horsepower
Applicability	All pumps
Definition	The nameplate motor horsepower
Units	Horsepower (hp)
Input Restrictions	Constrained to be a value from the following 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
Standard Design	Not applicable
Standard Design: Existing Buildings

Pump Design Head

Applicability

All baseline building pumps and proposed design pumps that use the detailed method

Definition

The head of the pump at design flow conditions

Units

ft of wc

Input Restrictions

As designed but subject to an input restriction. The user inputs of pump design head, impeller efficiency, cooling tower design entering water temperature, and cooling tower design return water temperature shall be used to calculate the proposed brake horsepower. This shall be compared to the pump motor horsepower for the next smaller motor size (MHPi-1) than the one specified by the user (MHPi).

The proposed design for the pump design head shall be constrained so that the resulting brake horsepower is no smaller than 95 percent of the next smaller motor size:

Where:

	The brake horsepower used in the simulation
	The brake horsepower resulting from the user input of design head
	The pump motor horsepower specified by the user
	The index into the standard motor size table for the user motor horsepower
	The motor horsepower for the next smaller motor size. For example, if the user-specified pump motor horsepower is 25, the next smaller motor size in the table above is 20

Since all other user inputs that affect the proposed design brake horsepower are not modified, the proposed design pump design head is adjusted in the same proportion as the pump brake horsepower in the equation above. If the user-entered pump design head results in a brake horsepower that is at least 95 percent of the horsepower of the next smaller motor size, no modification of the user input is required.

Standard Design

For chilled water pumps:

(40 ft) + (0.03 ft/ton) x [chiller plant nominal capacity (tons)]

(not to exceed 100 ft)

For condenser water pumps:

45 ft

Standard Design:

Existing Buildings

Impeller Efficiency
Applicability	All pumps in proposed design that use the detailed modeling method
Definition	The full load efficiency of the impeller
Units	Ratio
Input Restrictions	As designed
Standard Design	Not applicable
Standard Design: Existing Buildings

70%

Motor Efficiency
Applicability	All pumps in proposed design that use the detailed modeling method
Definition	The full load efficiency of the pump motor
Units	Ratio
Input Restrictions	As designed
Standard Design	The motor efficiency is taken from Table 29, using the next larger motor size than the calculated standard design brake horsepower
Standard Design: Existing Buildings

Pump Minimum Speed
Applicability	All two-speed or variable-speed pumps
Definition	The minimum pump speed for a two-speed for variable-speed pump. For two-speed pumps this is typically 0.67 or 0.5. Note: The pump minimum speed is not necessarily the same as the minimum flow ratio, since the system head may change.
Units	Ratio
Input Restrictions	As designed
Standard Design	0.10
Standard Design: Existing Buildings

Pump Minimum Flow Ratio
Applicability	Primary chilled water pumps
Definition	The minimum fraction of design flow when the pump is operating at its minimum speed. The pump minimum speed is not necessarily the same as the minimum flow ratio, since the system head may change.
Units	Ratio
Input Restrictions	As designed For compliance software that cannot model intermittent pump operation, the minimum flow ratio is set to 0 and the minimum power per the part-load performance curve is fixed at 0.103.
Standard Design	For compliance software that cannot model intermittent pump operation, the minimum flow ratio is set to 0 and the minimum power per the part-load performance curve is fixed at 0.103.
Standard Design: Existing Buildings

Pump Design Flow (GPM)
Applicability	All pumps
Definition	The flow rate of the pump at design conditions; derived from the load, and the design supply and return temperatures
Units	gpm or gpm/ton for condenser and primary chilled water pumps
Input Restrictions	Not a user input
Standard Design	The temperature change on the evaporator side of the chillers is 20°F (64°F less 44°F) and this equates to a flow of 1.2 gpm/ton. The temperature change on the condenser side of the chillers is 12°F, which equates to a flow of 2.0 gpm/cooling ton. A VSD is required for heating pumps when the service area is greater than or equal to 120,000 ft². For hot water pumps servicing boilers, the flow rate in gpm shall correspond to a loop temperature drop of 40°F.
Standard Design: Existing Buildings

Pump Control Type
Applicability	All pumps
Definition	The type of control for the pump Choices are: • Fixed speed, fixed flow • Fixed speed, variable flow (the default, with flow control via a valve) • Two-speed • Variable speed, variable flow
Units	List, see above
Input Restrictions	As designed; default is “fixed speed, variable flow”, which models the action of a constant speed pump riding the curve against two-way control valves
Standard Design	The chilled water pumps shall be modeled as variable-speed, variable flow, and the condenser water pumps shall be modeled as fixed speed. The hot water pumps shall be modeled as fixed-speed, variable flow, riding the curve.
Standard Design: Existing Buildings

Pump Operation
Applicability	All pumps
Definition	The type of pump operation can be either on-demand, standby, or scheduled. On-demand operation means the pumps are only pumping when their associated equipment is cycling. Chiller and condenser pumps are on when the chiller is on and the heating hot water pump operates when its associated boiler is cycling. Standby operation allows hot or chilled water to circulate through the primary loop of a primary/secondary loop system or through a reduced portion of a primary-only system, assuming the system has appropriate three-way valves. Scheduled operation means that the pumps and their associated equipment are turned completely off according to occupancy schedules, time of year, or outside conditions. Under scheduled operation, when the systems are on they are assumed to be in on-demand mode.
Units	List (see above)
Input Restrictions	As designed
Standard Design	The baseline system pumps are assumed to operate in on-demand mode. The chilled water and condenser pumps are tied to the chiller operation, cycling on and off with the chiller, and the heating hot water pumps are tied to the boiler operation.
Standard Design: Existing Buildings

Pump Part-Load Curve

Applicability

All pumps

Definition

A part-load power curve for the pump:

Where:

	Part-load ratio (the ratio of operating flow rate in gpm to design flow rate in gpm)
	Pump power draw at part-load conditions (W)
	Pump power draw at design conditions (W)

Coefficient	Default (No Reset)	DP Reset
A	0	0
B	0.5726	0.0205
C	-0.301	0.4101
D	0.7347	0.5753

Units

Data structure

Input Restrictions

Default is “Default (No Reset)”. The Differential Pressure (DP) reset curve may only be selected if the DDC control type building descriptor indicates that the building has DDC controls.

Standard Design

DP Reset curve for chilled water pumps; heating hot water pump power is assumed to be constant even though the pump is riding the curve.

Standard Design:

Existing Buildings

5.8.6 Plant Management

Plant management is a method of sequencing equipment. Separate plant management schemes may be entered for chilled water systems, hot water systems, etc. The following building descriptors are specified for each load range, e.g., when the cooling load is below 300 tons, between 300 tons and 800 tons, and greater than 800 tons.

Equipment Type Managed
Applicability	All plant systems
Definition	The type of equipment under a plant management control scheme Choices include: • Chilled water cooling • Hot water space heating • Condenser water heat rejection • Service water heating • Electrical generation
Units	None
Input Restrictions	As designed
Standard Design	Same as the proposed design
Standard Design: Existing Buildings

Equipment Schedule
Applicability	All plant equipment
Definition	A schedule that identifies when the equipment is in service
Units	Data structure
Input Restrictions	As designed
Standard Design	Operation staging when multiple equipment is used
Standard Design: Existing Buildings

Equipment Operation
Applicability	All plant equipment
Definition	Equipment operation can be either on-demand or always-on. On-demand operation means the equipment cycles on when it is scheduled to be in service and when it is needed to meet building loads. Otherwise it is off. Always-on means that equipment runs continuously when it scheduled to be in service. For the purpose of the compliance model, always-on is used for equipment such as chillers that are base-loaded, and on-demand equipment is scheduled to be on only when the base-loaded equipment (one or more) cannot meet the load.
Units	None
Input Restrictions	As designed; default is on-demand
Standard Design	Assume on-demand operation
Standard Design: Existing Buildings

Equipment Staging Sequence
Applicability	All plant equipment
Definition	The staging sequence for plant equipment (chillers and boilers) indicates how multiple pieces of equipment will be staged on and off when a single piece of equipment is unable to meet the load. In both the proposed design and baseline design, the compliance software uses the optimal sequence to determine plant staging based on part-load performance. This descriptor is used to identify sequencing when the plant contains unequal equipment, where the order in which the plant equipment is enabled affects plant energy use.
Units	Structure – an array, where each element includes a) the load range, in minimum tons and maximum tons; and b) a list of equipment that is enabled to operate. The equipment will run in the priority matching the order of the equipment listed.
Input Restrictions	As designed; user may specify load ranges for staging each plant equipment.
Standard Design	Not applicable The standard design chiller and boiler plant each consist of one or more equal chillers or boilers, so the loading order is not applicable.
Standard Design: Existing Buildings

5.8.7 Thermal Energy Storage

The compliance model inputs below document the requirements to model a chilled water thermal energy storage system with compliance software. Some systems (ice storage, eutectic salts) cannot be modeled with compliance software.

Thermal Energy Storage Systems Name
Applicability	All thermal energy storage systems
Definition	A unique descriptor for thermal energy storage systems
Units	Text, unique
Input Restrictions	Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Standard Design	Not applicable

Thermal Energy Storage Systems Type
Applicability	All thermal energy storage systems
Definition	The type of thermal energy storage system being used. Chilled water storage system is the only currently supported option.
Units	List chilled water
Input Restrictions	As designed
Standard Design	Not applicable

Discharge Priority
Applicability	All thermal energy storage systems
Definition	A descriptor determines whether the storage system or a chiller will operate first to meet cooling loads during the discharge period. Storage priority will normally provide larger demand charge savings but requires a larger storage system. Chiller priority allows use of a significantly smaller storage system but demand reduction will be smaller.
Units	List storage or chiller
Input Restrictions	As designed
Standard Design	Not applicable

Operation Mode Schedule
Applicability	All thermal energy storage systems
Definition	A schedule which controls operating mode of the thermal energy storage system. A thermal energy storage system can be discharging (supplying chilled water to meet cooling loads), charging (receiving chilled water to be stored for later use), or off. The operation mode schedule specifies one of these modes for each of the 8,760 hours in a year.
Units	Data structure - thermal energy storage mode schedule, specifies charging, discharging, or off on an hourly basis
Input Restrictions	As designed
Standard Design	Not applicable

Rated Capacity
Applicability	All thermal energy storage systems
Definition	The design cooling capacity of the thermal energy storage system. The rated cooling capacity of the thermal energy storage system is determined by design flow rate of the thermal energy storage system and the temperature difference between the fluid system supply and return water temperature during discharging.
Units	Btu/hr
Input Restrictions	As designed
Standard Design	Not applicable

Tank Location
Applicability	All thermal energy storage systems
Definition	The location of the heat pump water heater for determining losses and heat energy interaction with the surroundings
Units	List zone, outdoors, or underground
Input Restrictions	As designed
Standard Design	Not applicable

Tank Shape
Applicability	All thermal energy storage systems
Definition	The shape of the energy storage system tank used to calculate surface area of the tank for heat gain/loss calculations
Units	List: Vertical cylinder, Horizontal cylinder, or rectangular
Input Restrictions	As designed
Standard Design	Not applicable

Tank Volume
Applicability	All thermal energy storage systems
Definition	The volume of water held in the thermal energy storage system tank. The tank volume and the rated capacity will determine how long the storage system can meet the load.
Units	Gallons
Input Restrictions	As designed
Standard Design	Not applicable

Tank Height
Applicability	All thermal energy storage systems
Definition	For vertical cylinder or rectangular tank, the height will be the maximum internal height of water held in the upright storage tank. For horizontal cylinder tank, the height of the storage tank will be the inner diameter of the storage tank.
Units	Feet
Input Restrictions	As designed
Standard Design	Not applicable

Tank Length to Width Ratio
Applicability	All thermal energy storage systems
Definition	The length to width ratio of a rectangular storage tank in plan view. It is required only if tank shape is rectangular. If the tank is square, the length to width ratio is one. For a rectangular tank, the ratio will be greater than one since the length of the tank is always greater than the width of the tank. This is used to determine the surface area of the tank.
Units	Unitless ratio
Input Restrictions	As designed
Standard Design	Not applicable

Tank R-Value
Applicability	All thermal energy storage systems
Definition	The insulation applied to the tank used in calculating the tank U-factor
Units	R-value (h-ft²-F/Btu)
Input Restrictions	As designed
Standard Design	Not applicable