Solar thermal system and collector choices
I’m renovating a house in the Seattle area. Part of the renovation includes changing the roof lines for good solar exposure. Heating will be hydronic radiant upper floor (1900 ft2) and hydronic wall panels in finished daylight basement (1400 ft2). Floors will be connected with an open staircase. Air sealing and high levels of insulation are being incorporated. Being on Puget Sound, we’re sacrificing insulated west walls for an expansive view of the Sound using a lot of Serious windows. Very efficient windows but windows none the less. On the rare Western Washington sunny winter afternoon, they’ll help in heating the house.
Energy system involves the following:
PV (2 arrays)
Solar thermal (liquid)
Daikin Altherma air-water heat pump with Daikin DHW tank.
I’ve been presented an extensive energy package proposal. The solar thermal system proposed is a closed loop pressurized propylene glycol system. It comprises (8) Buderus SKS 4.0 collectors and a 200 gallon PL750/2S Buderus storage tank. This integrates with the Daikin Altherma system with the Daikin hot water tank. After doing some reading and calculating the relatively small amount of DHW I might use per day (sometimes 15-20 over a couple weeks), I broached the subject of a heat dump. It took some coaxing but it was finally agreed that a heat dump system was required. The number of panels may be reduced as well. After doing more reading and research, I really like the idea of a closed loop drainback system. With care taken for proper drainage, overtemp, freezing, and power failure problems are resolved.
The company I’m working with is relatively new and comprised of 3 persons from different backgrounds. Radiant system installer and controls engineer, electrician with extensive PV experience, and a structural engineer. They’re good to work with and are open to other ideas. Some of the engineering is being done by a distributor for Buderus so the proposal is probably skewed. I think they’re open to building the best system possible and that’s what I’m after.
With all this said, I need help in selecting the best type of collector (plate or tube) and if a drainback system is better than a pressurized glycol system. Any other advice is appreciated as well.
Thanks to all in advance.
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