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Old 02-19-10, 08:45 AM   #1
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Default Solar hot water and electric tankless


I install solar pool heaters, solar domestic hot water and PV

I don't have a lot of practical experience with domestic hot water, I have only installed 4 systems, but one of the systems is in my house, and I have taken factory training from several different manufacturers. I have seen the many different ways that companies deal with the heat exchange from gycol to domestic hot water.

I always want to try to make things work better. On my system at home I have a tank with an internal heat exchanger at the bottom of the tank and an electric element at the top. The problem I see with this is the solar has to heat the whole tank higher than the temperature that the top element is set at to stop that element from coming on. You also want to put the solar hot water at the top of the tank so it can be used first.

The conclusion I have come to is that the best system would be like the one "Enerworks" uses where they have an external heat exchanger that uses convection to draw the cool water from the bottom of the tank and put the then heated water into the top of the tank, where it can be used first.

(I just want to add a side note here. Enerworks has two systems, a US one and a Canadain one. The US one uses one tank and seems much more efficient. The Canadian one uses a second tank as a pre-heat tank, then goes into the existing water heater. I always thought that was dumb, your solar heated water has to work it's way through your existing water heater where it is going to cool. I asked the tech guy and he told me the Canadian government made them do it that way. So things are not always done with the highest efficiency in mind)

The second idea I have to improve efficiency if you are using electricity to heat water is to use an electric tankless water heater, for obvious reasons.

I have some other opinions as well, just didn't want to make too long a post

Last edited by Heynow999; 02-19-10 at 08:49 AM..
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