He lives in New hampshire, has baseboard hot water and an oil fired boiler. He told us that. They don't use heat pumps or electric heat in New Hampshire!
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16 years ago
Heat - when to set back
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16 years ago
Maybe not, in a high-conductance house with a low thermal mass and a long setback and high-capacity resistance heaters. In the example below, a low- capacity heat pump barely returns the house to 70 F on a cold day, running through almost the whole setback time. Heat pumping alone uses 19% more energy as it slowly raises the house temp from 60 to 70 F with a higher average setback temp than the same heat pump with a final 8 minute goose from resistance heaters, just before 5 PM.
20 G=1200'house conductance (Btu/h-F) 30 C=2400'house capacitance (Btu/F) 40 TH=70'normal house temp (F) 50 TS=60'min setback temp (F) 60 SBT=12'setback time (hours) 70 TA=40'outdoor temp (F) 80 RC=C/G'time constant (hours) 90 TC=-RC*LOG((TS-TA)/(TH-TA))'cooling time (hours) 100 TWP=SBT-TC'heat pump warming time (hours) 110 THP=(TH-TS*EXP(-TWP/RC))/(1-EXP(-TWP/RC))'equiv. heat pump temp (F) 120 HPC=(THP-TA)*G'heat pump capacity (Btu/h) 130 COP=3'heat pump COP 140 HPE=HPC*TWP/COP'heat pump energy (Btu elec.) 150 RHC=5*HPC'resistance heat capacity (Btu/h) 160 THR=TA+(RHC+HPC)/G'equiv. resistance + heat pump temp (F) 170 TWR=-RC*LOG((THR-TH)/(THR-TS))'resistance + HP warming time (hours) 180 REE=RHC*TWR'resistance heater energy (Btu elec.) 190 HPA=(TS-TA)*G*(SBT-TC-TWR)'heat pump setback energy (Btu) 200 HPW=HPC*TWR'heat pump warming energy (Btu) 210 HPT=(HPA+HPW)/COP'heat pump total energy (Btu elec.) 220 RET=REE+HPT'total energy with res. assist (Btu elec.) 230 PRINT SBT,TC,TWP,TWR 240 PRINT HPC,RHC,HPE,RET,HPE/RETsetback cooling heat pump warming hours hours hours hours
12 .8109303 11.18907 .1288909heat pump resistance Heat pump HP+res HP alone/ Btu/h Btu/h alone Btu Btu (HP+res) Btu
36044.78 180223.9 134435.9 113259.3 1.186974Nick