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Old 01-21-11, 07:32 PM   #1
Drake
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Default Summer active heating control?

Passive summer heating control is pretty easy to understand - shading. And domestic water heating is needed all year. But how is summer overheating controlled in other active collector systems?

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Old 01-21-11, 09:30 PM   #2
strider3700
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for my hot water system when the tank is up to full temp I'll just turn the pump off basically stopping the collection and stagnating the collectors. They will be metal and glass so they'll be just fine. You could do the same if you just didn't want any heat from them. For air collectors and others that can't be stagnated I've seen people pack them up and put them away for the summers or cover them with something to keep the sun off.
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Old 01-23-11, 12:15 PM   #3
Ryland
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With solar hot water systems you can not simply turn the pump off or you will damage the system, every time I've worked on a solar hot water system that had a pump fail we had other parts of the system fail as well, it also damages the glycol anti-freeze that is in the panels as the glycol is only good for 240F or so before it starts to brake down.
One call that we go was because the solar panel that ran the pump had been shaded for a few minutes the pump stopped running and the glycol got hot enough that it softened the PEX enough that combined with the build up in pressure in the panels from the water glycol mix turning to steam burst the PEX tubing and sent a gush of 250+F steem/water/anti-freeze in to the air, lucky enough no one was around to be hurt by this and this was on a day that was -10F outside so I had the joy of making repairs with freezing fingers.

When you have as much domestic hot water as you want and your house is as hot as you want you have to dump the heat, most people install a ground dump loop, one house I worked on they heated a deep sand bet (7 feet down under their floor) others heat hot tubs or ponds, but however you do it you need to get rid of that heat some people simply shade all but the last of their panels in the summer, it is part of the reason why people angle their hot water panels for the ideal winter angle as that is the time that they need the most heat.
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Old 01-23-11, 01:28 PM   #4
strider3700
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IT depends on the system, mine is going to be a drain back system using pure water. Turn off the pump and the collectors go empty. Any tiny amount of remaining water in them will steam off pretty quickly. The collectors are copper, aluminum and glass with a wood frame. my only concern is if they get hot enough to melt the isocyanurate insulation on the backs of them when stagnated. I'll be going with more of a winter angle, probably 65-69 degrees on the collectors to help with summer overheating as well. Watching the datalog of temperatures will be important to make sure they don't melt before I throw a sheet on them if it comes to it.
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Old 01-29-11, 11:22 AM   #5
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Another method, especially on drain back systems would be to install the panels vertically, so the sun does not tend to overheat them in the summer. An overhang might also be useful. Sustainable By Design :: tools
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Old 02-06-11, 03:16 PM   #6
mohsinkhalid
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RYLAND I had the same situation.With solar hot water systems you can not simply turn the pump off or you will damage the system, every time I've worked on a solar hot water system that had a pump fail we had other parts of the system fail as well, it also damages the glycol anti-freeze that is in the panels as the glycol is only good for 240F or so before it starts to brake down.
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Old 02-06-11, 03:57 PM   #7
Drake
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If whole fluid system only held 10 gls glycol mix would it be expensive to drain/fill each winter(only want to use for space heating)?
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Old 02-07-11, 12:00 AM   #8
Ryland
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Quote:
Originally Posted by Drake View Post
If whole fluid system only held 10 gls glycol mix would it be expensive to drain/fill each winter(only want to use for space heating)?
You still risk damage to the panels, that is one risk with buying used panels is you need to check that they have not over heated as it can melt the solder joints if they were soldered instead of welded or brazed, if they have wood frames the wood can be scorched, the rubber seals brake down faster when the panels over heat, all in all I don't see it worth draining them, you would be better off shading them in the summer.
But to answer your question, the last system that I worked on (A number of years ago) I think was around 5 3x10 foot panels, had loops heating 1,900 sf of cement slab and a 300 foot dump loop, I think they had around 60 gallons of glycol mix in there, but you should be able to get specs on how much a panel in your system holds, how much the heat exchanger holds, how much tubing you have and from that figure out how much fluid you will have, but if you did want to drain it you might as well get an empty storage tank and pump it in there in the summer, or shade your panels if you don't want to have a dump loop and don't need hot water in the summer.
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Old 02-07-11, 02:50 AM   #9
Solar Mike
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I have 8.5 sqm DIY solar hot water panels on the roof feeding a 300 liter cylinder, in summer there is a large excess of heat to get rid of. This is to get max heating in the winter months.
The controller opens a bypass valve when it detects the water in the bottom of the cylinder exceeds 80 Celsius, this diverts the returning hot water from the panels through a zig zag run of copper tubing clamped between 2 sheets of mini corrugate aluminum sheet mounted sideways under the floor, painted mat black, this acts as a heat sink having a total surface area of 2 sqm and effectively cools down the water prior to entering the cylinder. The system is self regulating and works well especially when away on holiday with no hot water draw off.
There is a backup circuit, a 12 volt DC solenoid valve opens and dumps hot water down the drain should the water temp exceed 90 c, this draws cold water into the bottom of the cylinder which gets pumped to the panels thus lowering their temp. We have really good water, so potable water circulates though the system.

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Old 02-07-11, 12:42 PM   #10
Drake
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What would "shading" be aside from tree or overhang? A cover?

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