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Old 08-19-16, 12:52 PM   #8
Steve Hull
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
Posts: 829
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Yes, I will incorporate solar water heating for both domestic use and for radiant. I will also tie in the existing water to air GTHP desuperheater into this. A separate water to water GTHP (to be installed), existing hot water solar panels and existing water to air GTHP will all supply a separate 50 gallon (200 L) preheat water tank. In the summer, my existing three solar drain back panels (total ~100 sq ft; ~ 3 sq meters) provides FAR more hot water than I can use for domestic use (dishwasher, showers, sinks, etc).

All this can be done. I am already preheating my domestic water with the drain back panels and the water to air GTHP desuperheater. The problem is winter when it gets VERY cold. Oklahoma is not in the deep south of the USA, but in the middle area where we get little winter sunshine (drain back solar panels don't provide much hot water) and the desuperheater on the water to air GTHP also does little. I will have to employ another way to heat the water for the PEX radiant system. By far, the cheapest way to do this is with a water to water GTHP as it has a COP of ~ 4. But it is also very expensive to put in.

In the winter, the majority of the radiant water (90%?) will have to come from a source other than my solar drain back panels and the desuperheater GTHP. The cheapest installation is to use a 10 kW tankless water heater, but it is by FAR the highest in yearly operating costs. Next is propane, but it is almost as expensive as electricity.

So, my real question, "is it all worth it"? I can do it, but the cost to do so is expensive with such a short winter.

An alternative is to put down radiant electric resistant mats in the concrete (insulated below) in bathrooms and areas where my wife complains about "cold" floors. Cheap to install, expensive to operate . . . Mind, you, the floors are not cold, but probably about 18C (65F), but because we don't have rugs (allergy issues), the foot "feels" cold due to conduction.

Wife was in a home (in cold Michigan) a few winters ago, where they had radiant floors and she fell in love with them.

The issue may all be settled - happy wife, happy life; I may just end up putting in a very expensive system for a 10 week winter . . . . .

consulting on geothermal heating/cooling & rational energy use since 1990
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