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olpjeb
Registered Users
New Member
Posts:58
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| 05/30/2009 3:35 PM |
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I want to install two 30-evacuated tube panels with a closed loop glycol system. The heated glycol from the panels will provide heat to a basement with in-floor radiant tubes. My design options are:
1) Pipe the hot glycol from the solar panel into an indirect fired water heater (tank with internal coil), and then have the controller pump the hot glycol (or water) in the tank into the basement tubes. My solar differential controller has two relays so it can activate two separate pumps, and it can separately measure the bulk fluid temperature in the tank to activate a second pump.
2) The other option is to use a small plate & frame exchanger so that whenever the differential solar controller calls for the pump to run, it will also activate a second pump which heats the floor's radiant tubes.
In either case I am not wanting to control the floor or living space temperature. My primary purpose is to dump heat into the slab during the winter and summer. I estimate that the basement's heat loss will be greater than what the solar panels can provide, but all I want is to keep the basement at greater than 50F.
Any opinions?
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Dana1
Registered Users
Advanced Member
Posts:702
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| 06/05/2009 10:16 AM |
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If it's always in heat dump mode, there's no need for the separate thermal storage you'd get using an indirect as your heat exchanger. The amount of head the pump is working against may differ though, if that's your concern (in which case you can look up the specs.) The slab itself will have many times the thermal-mass of even a pretty big indirect.
It's also not clear why you need the isolation of heat exchangers & dual pumps unless you're planning on having other thermal inputs into the radiant loop water(?). Are you looking at dramatically different flow rates in normal operation? You have only one load, and one source- if well designed it should only take one pump, and one measured delta-T.
You don't say where you are located, but an insulated reasonably well sealed basement with an insulated slab & conditioned space above it will generally stay over 50F year round in most populated regions of N. America. And if it's not already an insulated slab in a well sealed & insulated basement you're wasting your money on the solar equipment. First rule of solar: Reduce the loads to the minimum-practical level. Good old low-tech low-maintenance insulation & air sealing is where you need to go first.
Also if you're only running 70F-80F water into the slab, that's sufficiently cool to get decent efficiency out of less expensive flat-panel collectors even when it's 10F out. Even if it's commonly colder than that there during peak winter sun, the lower efficiency of the panels under those conditions may be compensated for with more collector area and far higher annual performance for the same cash outlay in solar collectors. This isn't a DHW application where you need 120F water, by any means. The colder you run the collectors, the higher the net efficiency. |
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