Solar Heat Dumps - more than one option

youtheman

Folks, I've read with interest several threads which discuss the option of a 'heat dump'. I've come across the following very useful article (http://www.kingspansolar.com/pdf/20527_ks-technical-thermo.pdf) which describes two options (see pages 39 & 40). I've also 'dreamed up' a third option which I would like to put forward for comment.

Option A : the one commonly discussed here. Put a radiator of the solar side with a 3 way diverter valve. Assuming you controller has a temp sensor and output for the diverter valve then you obviously need a additional radiator and 3 way valve.

Option B : use a radiator on the central heating side (as shown in the above referenced link). Not an option I've seen before. But as a variation on this I was thinking could you use the output from your controller to just switch on your central heating pump. Assuming you don't have an actuated valve (closed) on the circuit then all your central heating radiators would act as a heat dump. The advantage of this is that you don't need any additional hardware (3 way valves or radiators).

Option C : similar to Option A, but instead of using a 3-way valve to circulate through a dedicated radiator, use the actuated valve on the supply out of the cylinder to just dump the contents of the cylinder down the drain. The cylinder will then be replenished with cold water which will allow the solar side to cool down. The advantage of this is that you don't need a dedicated radiator in the attic.

Of the above I think that the option of just running your central heating pump seems to be the easiest. What do you think (Quentin, are you out there?).

kevymoss

provided no zoning on the heating system, just use the central heating pump. If there is zoning by pass the valves and use a pump

quentingargan

Yes, I have seen systems using the domestic heating system as a heat dump. There are just two downsides to this;

1) You are now running two pumps and doubling your electricity useage (though only for a very short time)
2) You have to be sure that the system will always work in such a way that this succeeds in dumping the heat. For example if a subsequent householder installed TRVs on all the radiators, or implemented flow control, then the system would no longer work.

I would always encourage householders to put a motorised valve on the feed from the boiler to the cylinder, and people are being encouraged to introduce zones where they don't currently exist.

Lastly, if you do decide to use the central heating pump, and are feeding this using your solar controller, you need to ensure that either
1) they both are on the same fused circuit (otherwise if they both switch on the pump at once, you are parallelling two fuses and sometimes one will be working on an ELCB while the other isn't) or
2) Use a relay.

Q

quentingargan

Oh - and the only thing wrong with dumping water from the cylinder is that it is, of course, wasting water. May not matter in some situations (ours comes under gravity from a mountain spring, and the more we use, the better the drainage in our top fields) but generally we need to conserver water... Q