Using ResStock 2.2.4, OpenStudio 2.9.0, and EnergyPlus 9.2
I'm finding that a single-speed ASHP expends less energy for heating and cooling compared to a two-speed ASHP with HIGHER SEER&HSPF and a MSHP with the same SEER and HSPF. Why is this so?
I'd imagine that MSHP's, without duct work, would be more efficient than that of an ASHP. And furthermore, a two-speed ASHP with larger SEER and HSPF values, should, by definition, expend less energy than that of a single-speed ASHP with the lower efficiencies.
Is there something I'm missing in how ResStock models these types of heat pumps? I also noticed the kwh's used for the fans are noticeably larger for the single-speed ASHP -- does electricity_heating_kwh and electricity_cooling_kwh not take into account the energy expended for fans?
Details of my results and relevant information is below:
Climate Zone: IECC Zone 6
Sizing: All heat pumps' cooling and heating capacities were sized to meet unit_final.Heat_Load. This was done by altering hvac_sizing.rb
Simulation Output Report Values:
Average electricity_cooling_kwh for 100 buildings using identical weather file and seed:
- ASHP, single-speed: 849
- ASHP, two-speed: 1164
- MSHP: 898
Average electricity_heating_kwh for 100 buildings using identical weather file and seed:
- ASHP, single-speed: 9273
- ASHP, two-speed: 10650
- MSHP: 9571
Average electricity_cooling_fans_kwh for 100 buildings using identical weather file and seed:
- ASHP, single-speed: 117
- ASHP, two-speed: 26
- MSHP: 0.9
Average electricity_heating_fans_kwh for 100 buildings using identical weather file and seed:
- ASHP, single-speed: 1655
- ASHP, two-speed: 884
- MSHP: 177
Characteristics of the single-speed ASHP
seer=15.0 hspf=8.5 eer=12.5 cop=3.5 shr=0.73 fan_power_rated=0.365 fan_power_installed=0.5 min_temp=0.0 crankcase_capacity=0.02 crankcase_temp=55.0 eer_capacity_derate_1ton=1.0 eer_capacity_derate_2ton=1.0 eer_capacity_derate_3ton=1.0 eer_capacity_derate_4ton=1.0 eer_capacity_derate_5ton=1.0 cop_capacity_derate_1ton=1.0 cop_capacity_derate_2ton=1.0 cop_capacity_derate_3ton=1.0 cop_capacity_derate_4ton=1.0 cop_capacity_derate_5ton=1.0 heat_pump_capacity=autosize supplemental_efficiency=1.0 supplemental_capacity=autosize dse=NA
Characteristics of two-speed ASHP
seer=18.0 hspf=9.6 eer=13.6 eer2=12.5 cop=4.2 cop2=3.7 shr=0.71 shr2=0.725 capacity_ratio=0.72 capacity_ratio2=1.0 fan_speed_ratio_cooling=0.86 fan_speed_ratio_cooling2=1.0 fan_speed_ratio_heating=0.8 fan_speed_ratio_heating2=1.0 fan_power_rated=0.14 fan_power_installed=0.3 min_temp=0.0 crankcase_capacity=0.02 crankcase_temp=55.0 eer_capacity_derate_1ton=1.0 eer_capacity_derate_2ton=1.0 eer_capacity_derate_3ton=1.0 eer_capacity_derate_4ton=0.93 eer_capacity_derate_5ton=0.9 cop_capacity_derate_1ton=1.0 cop_capacity_derate_2ton=1.0 cop_capacity_derate_3ton=1.0 cop_capacity_derate_4ton=1.0 cop_capacity_derate_5ton=1.0 heat_pump_capacity=autosize supplemental_efficiency=1.0 supplemental_capacity=autosize dse=NA
Characteristics of MSHP
seer=15.0 min_cooling_capacity=0.4 max_cooling_capacity=1.2 shr=0.73 min_cooling_airflow_rate=200 max_cooling_airflow_rate=425 hspf=8.5 heating_capacity_offset=2300 min_heating_capacity=0.3 max_heating_capacity=1.2 min_heating_airflow_rate=200 max_heating_airflow_rate=400 cap_retention_frac=0.25 cap_retention_temp=-5 pan_heater_power=0 fan_power=0.07 is_ducted=false heat_pump_capacity=autosize supplemental_efficiency=1.0 supplemental_capacity=autosize dse=NA
