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Mr Matt
join:2008-01-29
Eustis, FL

Mr Matt to pandora

Member

to pandora

Re: Anyone have a suggestion for standby whole home generator?

Pandora, I was not able to find a comment in this thread regarding how various heat pumps operate while in the defrost mode. In my case when each heat pump goes into the defrost mode the compressor and heat strip operate together. My condensers and air handler fans draws a total of 41 and 45 Amps respectively at 240 Volts when in the defrost mode. The heat strip in each system is rated at 4.8 KW or 20 Amps at 240 Volts. A generator powering my 30,000 BTU heat pump in the defrost mode would have to supply 41 Amps or 9840 Watts and my 42,000 heat pump 45 Amps or 10,800 Watts. That total requirement would exceed the capacity of a 20,000 Watt generator which is why a load management system is required to use a 20,000 generator in my home. That is probably why one Generac dealer recommended a 36Kw generator for my home if I stayed all electric.

I agree with nunya that if you can use propane rather than electric heat strips for back up heat you can use a smaller generator and in my opinion your system will probably provide better quality heat. The key facts that one has to review is the total capital investment in you appliances for an all electric solution and the total capital investment for a propane/electric solution, along with the yearly operating cost and how long you plan to remain in this house. If the difference in cost is significant, I would also consider the convenience factor for the two different systems, to determine if the more expensive solution is better.

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO
·Charter

nunya

MVM

Defrost mode is a big problem. In theory, you could defeat the electric strips to keep them from running at the same time as the heatpump. You don't want your heatpump to skip defrost mode, especially when it's cold outside. It will literally (in Chris Traeger style) turn into a block of ice.
I've had this happen (bad defrost timer), and it's always in the coldest part of the year (murphy's law).

I'm fortunate that where I'm at now is NG, but I plan on moving to the country soon, and I'm afraid heatpumps may be in my future. I will still probably have propane backup (and for other heating appliances).
pandora
Premium Member
join:2001-06-01
Outland

pandora to Mr Matt

Premium Member

to Mr Matt
said by Mr Matt:

Pandora, I was not able to find a comment in this thread regarding how various heat pumps operate while in the defrost mode. In my case when each heat pump goes into the defrost mode the compressor and heat strip operate together. My condensers and air handler fans draws a total of 41 and 45 Amps respectively at 240 Volts when in the defrost mode. The heat strip in each system is rated at 4.8 KW or 20 Amps at 240 Volts. A generator powering my 30,000 BTU heat pump in the defrost mode would have to supply 41 Amps or 9840 Watts and my 42,000 heat pump 45 Amps or 10,800 Watts. That total requirement would exceed the capacity of a 20,000 Watt generator which is why a load management system is required to use a 20,000 generator in my home. That is probably why one Generac dealer recommended a 36Kw generator for my home if I stayed all electric.

I agree with nunya that if you can use propane rather than electric heat strips for back up heat you can use a smaller generator and in my opinion your system will probably provide better quality heat. The key facts that one has to review is the total capital investment in you appliances for an all electric solution and the total capital investment for a propane/electric solution, along with the yearly operating cost and how long you plan to remain in this house. If the difference in cost is significant, I would also consider the convenience factor for the two different systems, to determine if the more expensive solution is better.

Good point, DLM will turn off any large appliance that draws too much off the generator. My understanding is I have 83 amps more or less stable from a 20KW generator.

We shall see what happens. It'll be interesting.

As to propane auxiliary heat, not going to happen, unless the electric bill is extremely high.
Mr Matt
join:2008-01-29
Eustis, FL

Mr Matt

Member

There is one other work around that would be more expensive then heat strips but less expensive then separate gas hot air furnaces. I saw this system in operation and it is very effective. The method below is the only method I could use to heat my home with propane because the air handlers are in half closets on the second floor and the building codes do not permit installation of a gas furnace in that location.

I am aware that you already replaced your hot water system, if you did not the cost of the installation would be lower. You can provide auxiliary heat and hot water with a 75 Gallon quick recovery propane fueled hot water heater (75,000 Btu burner). The hot water output of the water heater would be connected to two potable water circulating pumps to circulate hot water, to a water to air heat exchanger in each air handler of the heat pumps and a tempering valve set at 125 degrees to provide domestic hot water. The auxiliary heat relay in the heat pump would turn on the circulating pump feeding the heat exchanger when auxiliary heat is required. In order to provide sufficient heat the water heater would have to be set between 160 and 180 degrees when heat is required. In order to prevent scalding the tempering valve is used to reduce 160 to 180 degree hot water to 125 degrees for domestic use. During the summer the water heater can be set to 125 degrees and only set in the 160 to 180 range in the winter while heat is required.

This method is very cost effective if replacing the hot water heater, because the only extra cost is the tempering valve, circulating pumps, heat exchangers and the cost of installation.