Solar heat dump alternative

knx

Hi,

I have a solar kit that I bought from the UK and self installed. Knew nothing about heat dumps when I bought it and having read some posts on here have decided I want to put some kind of protection in place. There is no connection on the controller for a valve (is this necessary for the heat dump or is there a mechanical device available). I have however come up with a plan and would like some advice on whether it would work or not.

If I turned on the heating circulating pump and opened all zones would this remove enough heat from the system. I have about 12 rads, 2 towel rails and a solid fuel stove as well as an oil burner. I could circulate the water through the two boilers as obviously the aim here is to get rid of heat. So as the solar coil was heating the tank the CH coil would be circulating cold water and removing heat. Achieving this would just mean a programming change on the heating system already in place so I just need to know if in theory this would serve as a heat dump (of sorts).

heinbloed

Why should it not work?
Meassure the results (temperatures) and you'll see.

homer911

I would have thought that it depends on the positioning of the coils in the cylinder.

What will you do when you go on holiday (in the summer) when overheating is more likely?

quentingargan

Yes, this will work. Some solar installers actually do this. The boiler coil is usually at the top of the cylinder, and the solar coil at the bottom, so the boiler coil can easily dissipate this heat.

You could put a stat near the BOTTOM of the cylinder to switch on this pump. The temperature you do this at depends on the hardness of your water, and whether or not you have a thermostatic mixing valve. If you have soft water (no limescale in the kettle for example) and a mixing valve on your hot water outlet, it is safe enough to let this cylinder go to 85 degrees. Set the maximum temperature on your solar controller to 85 degrees, and set the stat a little lower than this - say 80 degrees. If, for some reason, the pump doesn't get rid of the heat, the temperature will continue to rise and the solar panel will shut down and go into stagnation.

The only reason why I personally frown on this system is because later on, someone may put in zoning valves which would have the effect of leaving the pump running against a shut valve.

Also, be careful that the stat is fed by the same fused circuit that is running the pump from the central heating side. Otherwise, if for some reason the central heating, and the solar dump both switch on the pump, you will have two fuses in parallel, making one 40A fuse instead of two 20A ones. Also, one might be via the ELCB while the other isn't. So just watch out for that.

knx

heinbloed wrote: »

Why should it not work?

Exactly what I thought but wanted the opinion of somebody in the know.

homer911 wrote: »

What will you do when you go on holiday (in the summer) when overheating is more likely?

Thats exactly when I want this function to occur. It will be an automatic response to a set temperature.

quentingargan wrote: »

Yes, this will work.

Exactly what I wanted to hear from the very fellow I wanted to hear it from. It was your comments on various other threads that got me thinking about this in the first place.

I was actually goin to rely on a stat positioned on the centre of the tank set to 65 or 70c. I have a thermostatic mixing valve. The heating system is controlled with knx. (an actual control sytem as well as my user name) Everything can be switched independantly and binary inputs will give me valve and stat positions. I have two mechanical stats, one on the cylinder and one on the flow to the stove. I intend to use this cylinder stat to control both the heating of the cylinder when the boilers are in use, and cool the cylinder when just the solar panels are heating it. Depending on which stat activates first the system will know what to do by way of some logic.

quentingargan

knx wrote: »

I was actually goin to rely on a stat positioned on the centre of the tank set to 65 or 70c. I have a thermostatic mixing valve. The heating system is controlled with knx. (an actual control sytem as well as my user name) Everything can be switched independantly and binary inputs will give me valve and stat positions. I have two mechanical stats, one on the cylinder and one on the flow to the stove. I intend to use this cylinder stat to control both the heating of the cylinder when the boilers are in use, and cool the cylinder when just the solar panels are heating it. Depending on which stat activates first the system will know what to do by way of some logic.

That all sounds good to me. Just make sure that the solar controller is going to allow the cylinder to go up to about 75 or 80 degrees so that it doesn't shut the system down before your other stat has cut in.

Good on ya! QG