Thanks for your reply and I am trying to learn as I go, along with the contractor. I think hybrid systems are fairly new to this area as 3 out of the 4 contractors I had come out said that they had heard of heat pumps but weren't familar with them. The contractor I hired has the most experience in this area with heat pumps but is still learning. The Evolution thermostat does not calculate the best balance point but has a lot of other nice features as far as I can tell being a newcomer to this field. I will see if I can track down the LoadCalc software.
Originally Posted by arc8
Last edited by adamsdp; 11-14-2007 at 09:08 PM.
Under the advanced settings there is a selection where you can choose a heat pump lockout temperature. I think it is under Advanced/Settings/Hybrid Heat. If you can't find it let me know and I will try it again at home and reply.
My default setting was none which I think means the heat pump would run as long as it could keep up with heating demands and then switch to the furnace if it could not keep up. I have set mine for 28 deg for now.
Originally Posted by wormie1205
My contractor spoke with the local Bryant rep and he said that there are two schools of thought on the balance point for this area - SE Michigan. One is that you have no heat pump lockout temp selected and let the heat pump run as much as possible until it can't keep up and then the furnace will take over as the heat pump will be cheaper to run than the furnace at any outdoor temperature that the heat pump can provide heat for. The other school is that the defrost cycle uses a good amount of electricity and also to save wear and tear on the heat pump, a balance point of 28-30 is a good setting. My contractor said they don't have a long history of information to go on in this area about the wear and tear/defrost cycle but he is going to look for software to provide more guidance.
Since I am a BRyant rep please go to page 2 and read my reply. you are way overthinking this decision. I think a good train of thought for you is to lower it until it in not able to keep you comfortable and then move it up a couple of degrees.
If not please set it at 20 and go from there
You write that:
Originally Posted by stopro1
"when the heat pump's COP is at .95 "
The factor that you have not consideed in your analysis is the Cost of Power.
However, the Conversion of Power (COP) is only one factor in the equation.
At lower temps the Heat Pump COP becomes very low - you sited 0.95.
If raw energy cost (BTU cost) from electricty is 2X the NG cost, the cross over point for the cost of home heating will not be the heat pump COP number.
Neither of those consider the "comfort factor" of having blowing hot air, and that is homeowner subjective.
C.O.P. = Coeffficient Of Performance
Originally Posted by aaCharley
It's Not Rocket Science, But It is SCIENCE
with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
Thanks for the correction and the useful link to the proper definition.
The coefficient of performance, or COP (sometimes CP), of a heat pump is the ratio of the output heat to the supplied work . . . .
Conversion of Power is not correct - just the way I think of it.
That COP number is variable, depending upon the outside air temp. The Wikipedia example uses a geothermal source which would have very little variability.