Solid Fuel CH System Design

[fidom]

I am installing an Aga type solid fuel cooker with boiler + rads and indirect cylinder. I want it to be pumped CH and gravity DHW. At first I was going to try and manage without any motorised valves but it looks like this could result in a circulation of water through the rads and indirect coil without going through the boiler! I would like the pump on the return as it gives it a bit lower operating temperature. I wondered about a 2 port valve on the DHW coil circuit, connected to the pump. It would need to shut off the DHW coil when energised and open again by spring action in the event of a power cut. Does such a valve exist? The ones I have seen appear to be open when energised.

The alternative seems to be a 3 port diverter valve used instead of a tee on the return pipe to the boiler. Again when energised by the CH it would divert the pumped return into the boiler instead of the gravity return from the cylinder. I could have a pipe stat on the flow pipe from the boiler so that the CH cuts in above a certain boiler temperature. I have done quite a bit of plumbing over the years but have never used motorised valves so am not really sure what they can and can't do.

 

[cross thread]

if you go with the gravity hot water set up pump on the return fit anti gravity valve on the heating pipe

 

[fidom]

Sorry but what is an anti gravity valve?

 

[cross thread]

exactly what is says a valve fitted on the heating flow that is spring loaded so only opens on pump pressure.

 

[Nige F]

Can you post a drawing of what you propose.

 

[fidom]

Thanks but do you mean as well as the motorised valve or instead? I am not bothered if some or all rads get hot when the pump is not going as the fuel is being burned anyway and the stove will only be used in cold weather. I have a gas cooker for use in summer and the cylinder has an electric immersion heater. Could the anti gravity valve be used as an anti pumped valve to shut off the DHW coil? I can see how that could avoid the need for a motorised valve.

 

[Mechanical Matt]

Which Rayburn model are you looking to install?

What will the rayburn be heating?
How many convectors?
How many bathrooms, Hw outlets do you have?
Are you looking to have pressurised hot water? (Hw)

Mech Matt

 

[Corgigrouch]

Depending on the appliance, you may well find that it has two flow and two return tappings so you can have gravity hot water and pumped heating....However, you will still need a "Normally open" motorised valve on the heating so that the water in the boiler can be controlled to prevent back end rot

 

[fidom]

This is the stove, I bought it secondhand so I don't know a make or model, only that it was made in Slovenia:

It only has 2 tappings, hence the need to tee the CH and DHW circuits together. I think I am just going to go with what I think should work and modify it if it gives trouble. On the flow side I will just tee the 2 circuits together. On the return I will feed the pump into the centre branch of a 3 port diverter valve and hard wire the valve to the pump. The pump control will be a pipe stat on the flow pipe out of the boiler so that the CH comes on above a certain boiler temperature. This can then be adjusted to get a good balance between heating and hot water. The fire will often be on low for periods of the day so the water should get chance to heat up at such times. The gravity hot water is being used as the safety heat sink in the event of a power cut so I need to make sure the valve is configured to revert to straight through flow by spring action when not energised.

 

[Nige F]

This is the stove, I bought it secondhand so I don't know a make or model, only that it was made in Slovenia:

It only has 2 tappings, hence the need to tee the CH and DHW circuits together. I think I am just going to go with what I think should work and modify it if it gives trouble. not

Well as long as you have an open vent with no valves in it terminating over a metal feed/expansion cistern. You can do what you like

 

[Mechanical Matt]

Your proposed system layout could give you hydraulic problems. As you are installing a batch fed appliance I would recommend you utilise a thermal store cylinder, minimum 200ltrs. This can be connected off the 2 tap ins on the Aga with 28mm flow and return as gravity only (make sure the cold feed is on the return, and open vent on flow). This will connect onto one side of the thermal, the other side you can install a pump and motorised valve as you would a normal s plan heating system with the motorised valve controlled via a programmable room stat. I would also suggest you use a 3 way mixing valve before the heating pump to drop the flow temp down to about 70d/c. There are numerous safety devices you must install to comply with HETAS and building regs. A 28mm normally open valve must be installed close to the thermal store on the return controlled via a low limit stat set to at least 60 d/c. Unless you would like to replace the Aga in 12months time?