I have a 2700 foot home in the high sierras, 5 ton ground source heat pump, hydronic heating, 5Kw solar electric (with a 1700 amp hour battery bank), 2 4x10 solar hot water panels preheating my domestic hot water system via a drainback heat exchanger. Everything in the house runs off the solar electric except for the ground source heat pump (it takes a 35Kw surge just to start it). The power goes off here on a pretty regular basis and when it does, so does my heating (ground source heat pump). We have a gas fireplace and it starts to take the chill off, but it isn't efficient to really heat the home up hotter than 50F when it is bone chilling cold outside.It would be nice to have some other form of back up for the hydronic heating when the ground source power source is off. My plumbing friend suggested hooking a flat plate exchanger up to my hot water heater, where- when there is a black out, I could manually open some valves from the ground source hydronic loop and direct the hydronic flow into a flat plate panel located next to my existing domestic hot water heater and then the domestic hot water heater could help take the chill off- but probably not run the house at temps we are accustomed to.
Last night I got in the internet and started looking at the combi boilers- the ones that are either tank or tankless and run solar hot water, a radiant loop and domestic hot water through them. Has anyone had any experience with them? The way my solar hot water system is set up, the panels circulate the hot water into a loop that has a heat exchanger on it. I have a used unheated solar hot water tank in my basement where the cold water from my well comes in the cold water side. When the solar loop gets hot enough, a pump turns on and circulates the standing cold water from that tank past the heat exchanger at the panels and back into that downstairs tank. During the day, I also have a pump system which circulates the hot domestic water from that tank in a loop throughout the house to ensure instant hot water when turning on a tap. My main conventional hot water heater tank is located upstairs in the mechanical room in the living space. The cold water line-in draws from the 80 gal solar heated tank downstairs, so in most cases throughout the day, the cold water coming into the conventional hot water heater upstairs may be as hot as 120F.
What would be the most cost effective solution for having a back up heating for my hydronic system? A remote flat plate connected to my existing hot water heater? A combi tank system? A combi instantaneous hot water heater? How are the efficiencies compared to conventional systems? I assume the combis don't draw much power, so the solar system could probably run them. The incidence of power black outs doesn't happen that often, but when it does, it is usually during full on snow storms where having a warm house is a benefit. Would any of the combi systems have issues with hot solar heated water coming into them from the cold water in? Are they much more efficient than traditional tank water heaters? I recognize the combis are quite expensive, but is there a long term advantage through higher efficiency (of the device of not using as much propane- or perhaps thermal efficiency)? My current conventional hot water heater is probably 5 years old and seems to be working fine.
Comments?
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