Heat dumping using the central heating pump

Deepwell · 13-08-2012 10:36pm #1

I’d like to use the central heating circulating pump to dump heat from the cylinder rather than diverting to the existing heat dump radiator. My rationale is that this is provides a better way of cooling the system particularly when away on holidays and also dissipates the heat more evenly rather than in one section of the house. Reading some of the other threads this seems to be a valid approach but I just wanted to check if anyone can confirm it would be ok to wire a switching relay in parallel with the pump output on a Potterton Suprima 100 boiler. I presume it just uses an electromechanical relay to switch the pump and I would prefer not to interrupt its output with an inline relay. The relay will be powered from the boiler spur. Anyone foresee any issues??

quentingargan · 23-08-2012 12:40am

Just a few...

You need to be sure that nobody later fits a zoning valve which prevents the flow from the top coil of the cylinder.

You need to be sure that the flow can cope with the production of the solar panels. If there are TRVs on all the rads, that may not be the case.

In terms of electricity consumption, you will now be using two pumps instead of one. So slightly more power consumption.

Be careful with the wiring. If you are using your solar controller to switch on the pump and its power comes from a different MCB to the heating system, you may be paralelling two MCBs if they both switch at the same time for some reason.

I am considering reverting to this system - I have a heat dump on the solar circuit, but my reasons are more complex as I also have a wind turbine that dumps surplus energy into the cylinder and I need to be sure of clearing that heat.

Deepwell · 23-08-2012 2:50pm

Quentin – thanks for your comments. To clarify, I don’t intend to disconnect or bypass the existing heat dump. My idea was to turn on the circulating pump at a temperature somewhere between the store max (65C as we have hard water) and the collector max (currently set to 85C). That way I’m hoping to avoid the solar system going into heat dump while also continuing to cycle heat into the lower part of the cylinder (once the actual temp is lower than the store max). As it stands I’ve noticed that on hot days the heat dump kicks in while the lower part of the cylinder is relatively cool (due to usage) because the store max and collector max temps are exceeded.

I take your point about the TRV’s. I don’t have any yet but do plan to add them along with a zone switch to allow me to switch off heating to the first floor but there will always be at least one bathroom radiator on – besides the heat dump can still kick in as an added precaution. The second pump is valid point but it will only be used occasionally unless our climate improves for a sustained period :rolleyes:

Any guess as to how long the pump is likely to run to drop the temp say by 1c? I know its dependant on a lot of variables but I’m guessing its minutes rather than hours even with a 300L tank and worst case only one radiator on (and usually several).

I’m planning to use my home automation system to control this loop so it will measure the tank temperatures independently and wirelessly switch the heating pump so the switch and pump will be on the same spur and MCB. The only think holding me back is checking I can switch the pump in parallel without damaging the Potterton pump output (and of course some sustained sunshine to test it

). I guess I should probably post this also in the plumbing & heating section to see if anyone is familiar with the Potterton output switch.

quentingargan · 23-08-2012 3:38pm

Hi Deepwell. You highlight one important flaw in many controllers - the second relay operating the heat dump is based on the top of the cylinder, not the bottom. So if you use water and the top is still at 65 degrees, the dump operates.

You can improve this somewhat by setting the hysteresis very low. Switch the dump on at 65 and off at 64.5. Usually when you use water there is a bit of movement in the cylinder.

Deepwell · 23-08-2012 4:23pm

I'll try that anyway. I'm using a Deltasol BS/3 (layout 3). Is the DT O parameter I change? Its currently set to 6.0 while DT F is 3.5.

quentingargan · 23-08-2012 4:36pm

Deepwell wrote: »

I'll try that anyway. I'm using a Deltasol BS/3 (layout 3). Is the DT O parameter I change? Its currently set to 6.0 while DT F is 3.5.

No - DT o and DT f are the temperature differentials that operate your solar pump. The item you are looking for used to be near the end of the menu and called AH (for after heat) but more modern controllers may call them something else. There was AH O for on and AH F for off. You want AH O set to 65 and AH F set to 64.

That said, if I had limescale in the water I would keep things closer to 60 to prevent the coil getting limed over.

Q

Deepwell · 23-08-2012 5:39pm

Looking at the Deltasol manual, it appears the AH O/F parameters are not available when the system layout 3 is used.

I'll drop the store max to 60 or so as suggested although I thought I had read someware that a stainless steel tank didn't suffer from limescale the same way as copper did?

quentingargan · 23-08-2012 7:39pm

Yes - I have the old unit, but I think there is no reason why you can't change that to system 2, use AHo and AHf to control the heat dump. If you are doing that, you would need to set the max store temperature higher. Say 65 for Smax to knock everything off if the heat dump fails to do the trick for any reason.

But if you are keeping the other heat dump in place, you are going to have to do this differently anyhow - use a thermostat on the tank to control the central heating pump and leave the rest of the system as-is perhaps, but with Smax a bit higher than the stat.

Q

garyh3 · 20-02-2014 5:04pm

quentingargan wrote: »

Just a few...

You need to be sure that nobody later fits a zoning valve which prevents the flow from the top coil of the cylinder.

Ok That's what's happened to me need to upgrade the boiler and controls, and the solar need to be setup with a Rad heat dump. what's the ball park for fitting a heat dump in the attic? Current has a circulation pump as a dump.

dathi · 22-02-2014 12:20pm

you can put a electrical relay on the zoning valve that will open it when the heat dump is active thats whats on mine

garyh3 · 22-02-2014 3:02pm

Cheers for that will pass that onto the Plumber, should save a few Euros

garyh3 · 22-02-2014 10:04pm

Ok he says that the relays are designed for volt free.

We cant wire the system like that as the relays are designed for volt free contact. The way the motorised valves work is when they open up it sends a signal to the boiler and in return the boiler fires up. There is no other way of installing this heat dump with controls.

dathi · 23-02-2014 3:03pm

not talking about the existing relays in the solar controller am talking about putting a couple of 8 pin 220v relays wired to the valve and pump when the solar controller heat dump turns on the 220 relays opens the valve but prevent the boiler from firing you need an electrician not a plumber to install the relays

garyh3 · 25-02-2014 1:27pm

Cheers for that ... He agrees or his Electrician says that ok to do

Just saved a bunch.....

Heat dumping using the central heating pump

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