solar water temp

[boatie]

I'm installing a solar system in an off grid house and would like to limit the temp through the taps without resorting to a pricy thermostatic or automated valve (as there is no mains power).
I just need one temperature limiting device for the whole system ideally. Any ideas?

Thanks

Ben

 

[PaulAH]

Not wishing to discourage but.... What is this solar heating system you have that, in the UK, can push the HW temperature up to a point where it needs limiting?

 

[boatie]

Hmmm, another unbeliever!

The water inside a panel can in certain situations reach 200 degrees and flash to steam, so temperature can certainly be a problem. Practically speaking it reaches around 60 degrees fairly easily, and as the problem I'm trying to solve is in an off grid house with no boiler/mains electric/mains water I wanted to avoid using a powered mixer valve.

Can anyone help?

Ben

 

[oilman]

You can use a thermostatic mixer valve used in many combi boilers, but you will need a cold supply to mix it with. If you have a 200 litre tank, to get the temperature to 60 degs, you must have some pretty big panels.

I'm an unbeliever too, I've had 1/2 litre up to 75 Celcius, with a 1 sq m reflector, and it took an hour in bright sunshine. When the coluds covered the sun, that was that.

 

[croydoncorgi]

You identified a different problem yourself.... if the temperature of the collector exceeds boiling point (of whatever fluid you're using) that's a serious problem in itself.

I'm no expert but I'd have thought you'd need a heatsink arrangement to dump excess heat once the water is hot enough.

Also, it sounds like you're planning a single circuit, with tap water flowing through the collector. Otherside you'll presumably need a circulating pump to move water from a hot water cylinder up to the collector (gravity won't work unless the hot water tank is ABOVE the collector!). If you do use a single circuit, there are (insurmountable?) Water Byelaw issues and anyway the collector will get limescaled and lose efficiency within months.

 

[boatie]

OK, thanks for your help...

When I said that they can reach 200 deg and flash to steam I only meant theoretically in a worst case scenario with no safety measures...that would be a pressurised system left to stagnate ie: the pump broke and water was failing to circulate to the tank and nothing in place to relieve the temp/pressure. I certainly won't be doing that...The system will stop working at 60 degrees, but this is still too hot when the elderly/children may be accessing the taps. I guess I will have to only have a feed from the tank and not from the solar circuit directly.

For the unbelievers, 60 deg is definitely possible, even on a cloudy day with a single panel.

The system I will be using is powered by a variable solar pump, ( the tank will be lower than the panel ) but as the house will be run on 12volts I imagined that it would be difficult to source a powered mixer valve. Are thermostatic valves the only solution? I have only seen very expensive ones, but could I source one from the inside of a combi boiler going to scrap?

thanks again

 

[oilman]

........could I source one from the inside of a combi boiler going to scrap?

Not a good idea if you are worrying about elderly children using the taps. A new one would cost between £25 and £50 depending what features and size you want.

 

[boatie]

thanks for your help oilman

 

[billy bob]

You need a blending valve, these are availiable from any plumbers merchant, they are a manuel valve that you adjust yourself until the desired temp is acheived

What solar system are you using, I fit a lot of solar mainly pressurized systems. but I fail to see how you will control the temp of the cylinder without a controller