May 16, 2010 04:58 pm
Re: SHW & Existing Oil-fired Boiler w/storage tank
I am over in Northern NH (RT2) and I agree that a 20 watt panel is too small to run the PV pump. The 20 watt panel that came with AET kit would only run the pump about 3 hours per day and the flid got real hot when it wasnt running. I had an old 48 watts panel that has some degradation and it works fine. A 30 watt panel would probably work but they seem to be rare. The other thing to look at is a DC pump controller. There are times in the morning and evening where even though the sun is out and the pump wants to run that the water being circulated is colder than the storage tank, and therefore it cools down the storage. I installed an Art Tech controller after the original installation and it is set up so that the pump only runs when the water in the collector is warmer than the SHW tank.
I have the same plumbing setup but do have a bypass around the oil fired storage tank for summer when I normally shut down the furnace. I also have a thermal switch on the output of my SHW tank that locks out the oil fired storage tank when the SHW is hot enough during spring and fall. Unfortunately that means that without a bypass, the nice hot water from the SHW tank has to go through the now cold Oil heated storage tank unless I have a bypass. The alternative is to install a recirculation pump between the tanks, but that is more complication. I have the parts but not the motivation to automate the bypass, but currently I just go turn two valves.