Recommended temperature setback with dual fuel and solar power

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Old 10-09-19, 08:55 AM
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Recommended temperature setback with dual fuel and solar power

Hey guys, I'm just looking for your recommendations on how much I should set back my thermostat at night (first floor zone only) and/or while we are at work during the day (both first and second floor zones).

We have a dual fuel system with a 5 ton Bosch inverter heat pump, an Amana 100k btu 80% natural gas furnace, 2 Ecobee4 thermostats, and a Honeywell HZ432 dual fuel zone board. We are located in NY (climate zone 5).

We are running on solar power and have excess energy but we do not want to use our excess inefficiently as we will have more electricity demands in the near future. We currently pay $1/therm.

I'm thinking the best options are to either leave the thermostat alone all winter and burn through extra energy at night when the temp drops, or set the temp back 5 degrees at night and during work hours and allow the furnace to recover an hour before we get home. Then allow the heat pump to maintain the temp.

Our thermostat is currently configured to lockout heat pump below 5 degrees, lock out furnace above 35 degrees, and to initiate furnace with a 2 degree drop or 90 minute run time.

We also have a steam humidifier so I'm not sure if too big of a temp drop would cause condensation issues.


Your recommendations are greatly appreciated!
 
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Old 10-09-19, 09:45 AM
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A lot depends on where you are located and how well your house is insulated. Two things we don't know. Generally the more poorly sealed and insulated I think you get more benefit from setting back. But, if your house is modern, tight and well insulated then I would tend towards picking a temp and leaving it.
 
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Old 10-09-19, 10:20 AM
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The house is 18 years old. A blower door test revealed that it is relatively tight. We are in NY, about 60 miles north of Manhattan.
 

Last edited by diynewb105; 10-09-19 at 11:40 AM.
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Old 10-09-19, 12:14 PM
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It can be hard to come up with a solid figure but it comes down to which is more efficient and less costly to run.... the heat pump or the gas furnace.

Here where I am in NJ..... natural gas is the clear winner. I have a gas furnace with a split A/C system. I set back my temps 4 at night.

You know when your heat pump can't keep as it shuts down and the gas furnace takes over..... or should.... so you should know your heat pump recovery rate.
 
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Old 10-09-19, 01:09 PM
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It's more of a question as to what's more wasteful I guess? Maintaining a set temp with the heat pump using the excess solar energy we created and thereby increasing our rate of heat loss.

Or

Minimizing the use of the heat pump overnight by setting the thermostat back and paying for the natural gas furnace to recover the temp.

The heat pump will be able to maintain the temp in the house down to about 5-10 degrees.
 
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Old 10-09-19, 01:10 PM
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Guys The Bosh heat pump uses a Mitsubishi compressor and is inverter drive just like ductless. Here in VA they say no back up heat is needed with them. Bit colder in his location but the heat pump is really efficient. LOOks like the OP is wanting to know what is best for electric consumption. IMO because of the solar Id put the gas on at 20 with a 4 degree set back at night and away.
 
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Old 10-09-19, 02:41 PM
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Thanks for your help! So even though we have a surplus of kwh you would still opt to use the gas furnace to recover from the 4 degree setback?

The Bosch is supposed to still put out decent btus down to 5 degrees apparently.
 

Last edited by diynewb105; 10-09-19 at 03:13 PM.
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Old 10-09-19, 03:50 PM
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Would you make more money selling the electric back then the gas would cost ?
 
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Old 10-09-19, 04:01 PM
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In NY we bank the extra kwh vs getting paid for them but it would cost 2-3x more to heat the home with electric vs natural gas if I were buying it from the grid.

I was kind of thinking setting it back 4 to 5 degrees, letting the heat pump recover the difference down to 30 degrees and then let the furnace recover anything below 30. Notnsure of that's less efficient than no setback at all though.
 

Last edited by diynewb105; 10-09-19 at 05:28 PM.
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Old 10-10-19, 08:25 AM
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which is more efficient and less costly to run.... the heat pump or the gas furnace
Efficient vs cost?

I cant speak to the efficiency difference but gas heat is always cheaper than electric heat.
 
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Old 10-10-19, 10:15 AM
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gas heat is always cheaper than electric heat.
It typically is for resistance heating but not always with a heat pump.
We've had some members post some extremely low electric rates.
 
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