Solar Hot Water Systems - PV vs delta T control [RE-wrenches]

[David Blittersdorf]

Question:

We are in Vermont which gets real cold in the winter and SHW systems are antifreeze 
loop types. I have a Heliodyne system with AC pumps and a differential temperature 
sensor controller. I am looking at the trade-offs of going to the PV powered pump 
system vs the delta T control. I like the temperature sensor system as it will not turn on 
the pump when the stored hot water is warmer than the collector temperature. I have 
noticed in the very cold winter months that the pumps cycle on and off to make sure the 
incoming collector water is at a higher temperature than the tank.

I can forsee a problem with the PV powered pump happly pumping cold water into a hot 
tank because the PV panel is very efficiently running the pump (cold temp.) but the 
collectors are not warm yet. I also notice that my PV panels shed snow quicker than my 
hot water collectors. 

Any experience out there?

Thanks,

David Blittersdorf
NRG Systems, Inc.
110 Commerce Street
Hinesburg, VT 05461 USA
Tel: 802-482-2255
Fax: 802-482-2272
email: davidb at nrgsystems.com
Web:http://www.nrgsystems.com

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