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Solar heat

Posted: Sat Mar 19, 2016 1:43 pm
by KathyLauren
We are installing a solar thermal system on our house. Weather permitting, the installers will be here next week.

The house is actually not bad for passive solar, but, even after a sunny day, the furnace (oil-burning) comes on at night. Since the heating system is radiant in-floor hot water, and the house has a steep south-facing roof that is not shaded by trees, it is a good candidate for a solar heating system. It will provide all our domestic hot water as well as storing additional hot water for the in-floor heating.

There will be a bypass switch so that, on a sunny day, we can start circulating heat directly from the collectors into the concrete floor slab in the late afternoon, to pre-heat it while the sun is still shining without drawing down the stored heat.

Based on our experience in a previous house, where a one-panel solar hot water system would collect significant solar energy even on bright overcast days, this system should be able to keep the furnace off most nights.

Looked at purely economically, it is probably an extravagance. I figure that the payback time will be more than ten years. But I really like the idea of not burning oil. Granted the stuff is cheap at the moment, but that will change soon enough. Cheap or not, it's fossil fuel CO2 that I'd rather not send up the flue.

Re: Solar heat

Posted: Sat Mar 19, 2016 8:18 pm
by Green Aura
KeithBC wrote:Looked at purely economically, it is probably an extravagance. I figure that the payback time will be more than ten years. But I really like the idea of not burning oil. Granted the stuff is cheap at the moment, but that will change soon enough. Cheap or not, it's fossil fuel CO2 that I'd rather not send up the flue.


Sometimes it's not down to finance, is it.

We're just waiting on quotes to get our roof done - if we can afford it our flat roof will have sufficient pitch to house solar pv panels. The thermal store we had installed a couple of years ago has ports (?) for solar pv. With us it's not so much a case of pay back but when can we pay in. Once the roof is done we'll have to save for the panels - our nice government has pretty much scrapped any help. :(

Re: Solar heat

Posted: Sun Mar 20, 2016 9:07 am
by Flo
You are both right - doing the green thing isn't always cheaper but that often goes with doing the right thing.

Re: Solar heat

Posted: Tue Mar 22, 2016 7:04 pm
by KathyLauren
Image
The installers are here. Four panels up, one more to go.

Re: Solar heat

Posted: Tue Mar 22, 2016 9:03 pm
by Green Aura
Slight panel envy.

Re: Solar heat

Posted: Sat Apr 23, 2016 12:47 am
by KathyLauren
Well, the solar heating system has been operational for a couple of weeks. It is providing all the hot water we can use, at a higher temperature than the boiler provides. The more hot water we use, the more efficient it is, since unused hot water is kept hot by burning oil, whereas used hot water is replaced from the solar pre-heat.

The space heating is a bit trickier, since it only provides preheated water to the radiant floor heating system if the solar water is hotter than the return flow coming back to the boiler from the floor loops. I have had to turn down the temperature of the boiler to run the floor heat cooler and give the solar a chance to come on. It's a bit of a balancing act.

We had one operational problem that required the crew to come back out and fix it. The heat exchanger loop on the space heating tank developed an air lock. I didn't know that; I only knew that that tank wasn't getting as much heat as the other one. There is a switch to select which tank's sensor controls the flow of coolant to the panels on the roof. Not wanting the system to shut off until the tank was hot, I selected the sensor on the cooler tank. Of course, it was a bright, sunny day, so it just kept pumping more and more heat into the one tank that was accepting it, and none into the tank with the sensor that would have shut the system down. You can probably guess where this is going... The temperature/pressure relief valve on the hot tank finally blew, flooding the basement with hot water and steam.

When we got them out to look at the problem, the crew diagnosed the air lock and bled the lines. It's working fine now. They also plumbed in a line from the relief valves to the basement drain, so a repeat performance will not flood the place.

I eventually want to instrument the system so that I can tell how much the solar heat is contributing. The oil-fired boiler will still run, but it should run later, less often, and for a shorter time than it used to. We are definitely noticing that it runs less (It sounds like a jet aircraft taking off, so it's easy to monitor!), but we aren't sure how much of that is due to the solar and how much is due to the outdoor temperature warming up as spring arrives.

I figured that this would be an appropriate post with which to observe Earth Day. :sunny:

Re: Solar heat

Posted: Tue Apr 26, 2016 6:50 am
by Flo
So you won't really know till this time next year about the success of your investment? But with oil fired heating, it has to be a good one doesn't it (or do I mean a necessary one?). Oil fired heating is what keeps me down in the valleys instead of in the wide open uplands that are so much nicer in the county.