3.7.6.5 Electric Heat Pump

90.1-2016 BM

Electric Heat Pump Heating Capacity

Applicability

All heat pumps

Definition

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

Units

Btu/h

Input Restrictions

As designed

Baseline Rules

Autosize and use an oversizing factor of 25% (let the software determine heating capacity based on the building loads). The equipment capacity may need to be increased to ensure that the number of unmet load hours do not exceed 300.

Electric Heat Pump Supplemental Heating Source

Applicability

All heat pumps

Definition

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

• Electric resistance
• Gas furnace
• Oil furnace
• Hot water
• Other

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

Baseline electric air-source heat pumps shall be modeled with electric auxiliary heat and an outdoor air thermostat. The systems shall be controlled to energize auxiliary heat only when the outdoor air temperature is less than 40°F. The air-source heat pump shall be modeled to continue to operate while auxiliary heat is energized.

Electric Heat Pump Heating Efficiency

Applicability

All heat pumps

Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). The ARI ratings include the energy of the supply air fan. For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

When COP47 is given

(Equation 3.7.6-4)

$$COP_{nfheating}=1.48\times 10^{-7}\cdot COP_{47} \cdot Q +1.062 \cdot COP_{47}$$When HSPF is given

(Equation 3.7.6-5)

$$COP_{nfheating}=-0.0296\cdot HSPF^{2} + 0.7134 \cdot HSPF$$

where

 COPnfheating The heat pump efficiency adjusted to exclude the fan COP47 The COP of the heat pump determined at an outdoor temperature of 47 °F Q The ARI rated heating capacity in Btu/h BHPsupply The supply fan brake horsepower (bhp).

Units

Unitless

Input Restrictions

As designed

Baseline Rules

The heat pump efficiency for baseline systems 2 and 4 shall be determined from the data below.

 Size (based on cooling capacity) Outdoor Conditions Efficiency Test Procedure <65,000 Btu/h n.a. 6.6 HSPF ARI 210/240 ≥65,000 Btu/h and <135,000 Btu/h 47 °F db, 43 °F wb 3.2 COP ARI 340/360 17 °F db, 15 °F wb 2.2 COP ≥135,000 Btu/h 47 °F db, 43 °F wb 3.1 COP 17 °F db, 15 °F wb 2.0 COP

Electric Heat Pump Heating Capacity Adjustment Curve(s)

Applicability

All heat pumps

Definition

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

(Equation 3.7.6-6)

$$Q_{available} = CAP\_FT \times Q_{rated}$$

For air-cooled heat pumps:

(Equation 3.7.6-7)

$$CAP\_FT = a+b \cdot t_{odb} + c \cdot t_{odb}^{2} + c \cdot t_{odb}^{3}$$

For water-cooled heat pumps:

(Equation 3.7.6-8)

$$CAP\_FT = a + b \cdot t_{db} + d \cdot t_{wt}$$

where

 Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h) tdb The entering coil dry-bulb temperature (°F) twt The water supply temperature (°F) todb The outside-air dry-bulb temperature (°F) Qrated Rated capacity at ARI conditions (in kBtu/h a, b, c, d Coefficients taken from Appendix H

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.

Baseline Rules

Use default curves.

Electric Heat Pump Heating Efficiency Adjustment Curve(s)

Applicability

All heat pumps

Definition

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

(Equation 3.7.6-9)

$$PLR - \frac{Q_{operating}}{Q_{available, (t_{db},t_{odb/wt})}}$$

(Equation 3.7.6-10)

$$EIR\_FPLR = a + b \cdot PLR + c \cdot PLR^{2}+ d \cdot PLR^{3}$$

Air Source Heat Pumps:

(Equation 3.7.6-11)

$$EIR\_FT = a + b \cdot t_{odb} + c \cdot t_{odb}^{2}+ d \cdot t_{odb}^{3}$$

Water Source Heat Pumps:

(Equation 3.7.6-12)

$$EIR\_FT = a + b \cdot t_{wt} + d \cdot t_{db}$$

(Equation 3.7.6-13)

$$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT$$

where

 PLR Part load ratio based on available capacity (not rated capacity) EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature Qoperating Present load on heat pump (Btu/h) Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h). tdb The entering coil dry-bulb temperature (°F) twt The water supply temperature (°F) todb The outside air dry-bulb temperature (°F) Prated Rated power draw at ARI conditions (kW) Poperating Power draw at specified operating conditions (kW) a, b, c, d Coefficients from Appendix H

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, documentation shall be provided.

Baseline Rules

Use default curves

Electric Heat Pump Supplemental Heating Capacity

Applicability

All heat pumps

Definition

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

Units

Btu/h

Input Restrictions

As designed

Baseline Rules

Autosize

Electric Supplemental Heating Control Temp

Applicability

All heat pumps

Definition

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

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Default to 40°F

Baseline Rules

The space is required to be controlled with multistage space thermostats and an outdoor air thermostat which would energize the auxiliary heat on the last thermostat stage and when the outdoor air temperature is less than 40°F

Coil Defrost

Applicability

Air-cooled electric heat pump

Definition

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

• Hot-gas defrost, on-demand
• Hot-gas defrost, timed 3.5 minute cycle
• Electric resistance defrost, on-demand
• Electric resistance defrost, timed 3.5 minute cycle

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

Units

List (see above)

Input Restrictions

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

Baseline Rules

The baseline building uses the default.

Coil Defrost kW

Applicability

Heat pumps with electric resistance defrost

Definition

The capacity of the electric resistance defrost heater

Units

Kilowatts (kW)

Input Restrictions

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

Baseline Rules

Not applicable.

Crank Case Heater kW

Applicability

All heat pumps

Definition

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

Units

Kilowatts (kW)

Input Restrictions

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

Baseline Rules

Zero (0)

Crank Case Heater Shutoff Temperature

Applicability

All heat pumps

Definition

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

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. This descriptor defaults to 50°F.

Baseline Rules

50°F