Hi there, My brother had a Solar hot water system installed on his house a few months ago. So far it hasnt saved him much $. I had a few thoughts on it and figured I’d throw them out there.
The system has the panels on the roof and then it pipes the Glycol to a storage tank. The storage tank is an electric hot water heater that doesnt have the electric coil or anythng and is just a holding tank. The Glycol heats the water and the tank holds the water hot. It does get very hot and holds it for quite a while.
Where the problem lies I think is that he stil has two gas fired freestanding hot water heaters. (two family house) When you use the hot water it will then take water from these heaters which will then take water from the solar holding tank. The heater does not fire often when using hot water as it is taking in heated water from the solar. My thinking though is that they still fire during the day when they have cooled off. There is no circulation between the holding tank and the heaters when not using hot water. It seemed to me there shoudl be some sort of circulating pump to keep the hot water heaters hot while not in use.
I hope I explained this right and was just hoping for some thoughts from those in the know about these things. His plan is that when it is time to replace the existing hot water heaters to go with tankless.
Thanks
Dana
Replies
I believe you're correct.
I believe you're correct. Tankless would solve the heat loss problem with keeping all that hot water on standby. Energy in those things goes right up the vent all the time.
I wonder if there is any way to circulate between the two in the meantime before he changes the hot wter heaters?
Why not tie the thermostat in the gas fired heater to a sensor at the solar hot water heater storage tank? The solar heater would still refresh the water in the gas heated storage tank and but the burner wouln't kick in until necessary. In a sense, what your heaters are now doing is short cycling, which is inefficient. Even lowering the temperature they kick in at would help, I believe, since the solar will refresh and reheat as needed, except maybe when it's cloudy. Radiant heating systems use outside sensors to solve this particular problem. I was talking to a solar guy about something else awhile back and he mentioned that he regularly puts a sensor on the outside of pipes and calibrates accordingly so I think redoing the firing mechanism would be easy to do.
This is a case where tankless might make sense. You could install a circulation system, but likely the losses would just about offset the gains, unless the water heaters and storage tank were very closely coupled.
The other option would be to change out the gas heaters for better-insulated ones, or even for electrics.
Thanks Dan, yeah he plans on switching ot tankless but the ones there now are less than 5 years old. When they blow he will put in Tankless. I was just hoping there was a way for him to make it more worthwhile until then. He is wishing he just put in the tankless rather than the solar I think. He got a good deal with tax credits and incentives from the gas company on the solar. The installer promised him a better savings than what he's getting now which isn't much.
Thnaks Again
Dana
It would be worth a shot installing one of the circulating pump systems that is thermostatically controlled. Would work best if the water heater and storage tank are side-by-side, worse if they're some distance apart.
You could go tankless, but the system you described should still be saving energy. I have the same setup in my house, no circulator. The solar tank keeps hot water warm pretty long, so the gas fired heaters only have to raise the water temp from their temp to the setpoint of say 140 degrees. Even if the solar didnt do anything, just having the water sit in the solar tank would probably help, since the water comes into the house at around 45 degrees and just sitting in the tank would probably get it to about 70 degrees, the inside house temp. In my house, even in winter the tank temp is aroun100 degrees, so the gas heater is only raising the water about 40 degrees (140 - 100) instead of the 95 degrees (140 - 45) that it would have to do otherwise. The fact that the solar tank is probably around 120 gallons also means it will be harder to run out of hot water since even the solar water would be tolerable for a shower.
A lot of systems have valves to bypass the gas fired heaters in the summer, where you can get practically free hot water from the solar tank alone, but usually there is a backup electrical element in the solar tank in case of a bunch of cloudy days in a row. YOurs may not have this, but in the summer the solar tank may be over 140 degrees all by itself, so the gas heater would only fire to get by standby losses, but not when water is in use.
>>since the water comes into
>>since the water comes into the house at around 45 degrees and just sitting in the tank would probably get it to about 70 degrees, the inside house temp
During heating season this is just causing the heating system to run more, to heat the water in the tank. There probably isn't any energy savings.
You are correct that, without something to push heat from the solar tank to the water heater, the water heater will fire to replace heat lost in standby mode and the solar system won't be doing anything to lessen that.
We installed a system somewhat similar to what you describe, although it has a drainback tank between the panels and the storage tank, and the water heater is a well-insulated electric unit rather than a gas unit. The standby losses from the electric heater are absolutely minimal, in fact the loss from the storage tank and the electric heater together are minimal.... they're in a small closet that doesn't get hot even when the solar tank has 130 or 140 degree water in it.
In your situation a small pump to circulate water from the storage tank thru the water heater might make sense. A tiny cartridge circulator and an aquastat would be more than enough to do it. Who designed the system? Are they willing/able to address this question?
Or... replace the gas units with electric units or at least something with less standby loss.