Central Heating - Multiple heat sources

[clivejo]

My current system works well but I wish to install a new condensing oil boiler and allow a Solar array to be fitting in the near future.  At the moment I have an oil fired range and a wood burner both plumbed to the same coil in the hot water cylinder.  The system transfers the heat via gravity feed and also heats the first floor radiators too without the pump switched on.  When I power up the pump it forces the water to circulate around the down stairs radiators, however this tends to disrupt the gravity siphon and makes water flow places I dont want it to!! (ie the other heat source).  I could install automatic values, but I want to keep things as simple as possible.

I have a new duel coil cylinder available and was thinking of re-plumbing the system.  My first priority is a tank of hot water, then heating.  I want to be able to use any of the three heat sources (range, log burner or condensing boiler), maybe even 2 or more at the same time with little or no electrical input.  I was thinking of using the current hot water cylinder as a buffer/heat store, and running the down stairs heating from the coil in this(this would be the only pumped part of the system), do you think it would work?

I also need the return to the new condensing boiler to be as cool as possible.

[Richard Owen]

It might work.

Sounds complicated.

What you need is a neutral point in the system for all the heat sources to combine without interfering with each other.

I'd do that using a thermal store with a solar coil at the bottom.

It you already have a twin coil system available to you, I'd mount a Dunsley Baker Neutraliser under the new tank and plumb all the heating sources into that.

The wood burner, being an uncontrolled source, will need to also be connected to a heat dump (usually a radiator.)

Connect the output from the neutraliser to the upper coil on the tank and the solar to the lower coil.

Connect the heating to the neutraliser.

[clivejo]

The wood burner, being an uncontrolled source, will need to also be connected to a heat dump (usually a radiator.)

Connect the output from the neutraliser to the upper coil on the tank and the solar to the lower coil.

Connect the heating to the neutraliser.

Could my upstairs heating be used as the heat dump? 

Does a neutraliser need electrical power?

[dhaslam]

You really need a decent sized cylinder that can handle everything  without boiling or  running out of hot water.    That is in theory but having the space to put it is another  problem.   

[Richard Owen]

Could my upstairs heating be used as the heat dump? 

Yes, as long as you could demonstrate that at least one radiator was always on (you couldn't, for example, have a TRV on every radiator)

Does a neutraliser need electrical power?

No,

[clivejo]

The bathroom towel rail and three radiators in wardrobes are always on and on the upstairs circuit.

[Tigger]

Remember that your heat dump radiator for the wood burner needs to be on the gravity circuit between the wood burner and the neutraliser so it effectively becomes isolated from the normal 'central heating' circuit.  If you're using any other heat source to provide central heating and the wood burner is not fired up, the radiator(s) being used as the heat dump for the log burner will not get any heat to it (them).

I've used a Dunsley Neutraliser to hook up a wood burner and an oil fired boiler and I've used the single radiator on the landing as the heat dump since we can live without heat on the landing if the wood burner isn't in use.

It all depends on which of your heat sources is your primary source, if it's the wood burner then you could get away with having the upstairs circuit as the heat dump but then you'd never heat the upstairs via the other heat sources.

Hope that makes sense.......

[clivejo]

So an update...

About a week ago I turned on my central heating pump as the weather is getting cooler and I have discovered that the coil in my old copper cylinder has burst inside.  i.e. the water from heating system is mixing with the DHW!  So I sat down and had a think of how to get all heat sources to work with a dual coil solar cylinder,  without a nest of wires and values or an expensive Neutraliser!  It hurt my head and I decided it wasn't do-able.  So I acquired a triple coil, 350l copper cylinder.  My plan is to use the cylinder as a heat store.  There are two main coils and a solar coil in the bottom.  I just wanted to run a few questions by you guys.

If I plumb all the heat sources together to one coil, relying on gravity feed/thermo-siphon, this will require no external power (i.e. pumps or electric valves).  Then connect the second coil to the CH via a pump, with a safety thermostat on the return of the heat source coil to activate the CH pump, to act as a heat dump if required. 

Can I do without a physical dump radiator on the thermo-siphon circuit?
Maybe a small pump connected to the top and bottom of the heat store, to circulate the cold water from the bottom to the top and cool things down a bit, if the safety thermostat is activated?
I also want to fit a small electrical immersion heater between the top and bottom of the tank as a dump load for if my batteries get over limit, is this a good idea?

All thoughts and ideas are most welcome!

[clivejo]

Anyone able to answer my question "Can I do without a physical dump radiator on the thermo-siphon circuit?"

[Richard Owen]

Anyone able to answer my question "Can I do without a physical dump radiator on the thermo-siphon circuit?"

No.

[Richard Owen]

So I acquired a triple coil, 350l copper cylinder.  My plan is to use the cylinder as a heat store.  There are two main coils and a solar coil in the bottom. 

Since you have three heat sources and three coils, the simplest thing to do it put one heat source per coil and use it as a traditional hot water tank.

If you want to use it as a heat store, one of the coils is going to need to be close to the top of the tank or your DHW performance will be rubbish.

Let's assume that the three coils are stacked one on top of the other.

If I were using this as a thermal store, I'd connect the solar to the solar coil. I'd connect the other two heat sources to a neutral point and then connect that to the top and bottom of the tank.

I would then connect the upper coil to the DHW system and the middle coil to the CH.

The downside of this arrangement is that you might not have enough DHW to meet your needs as only the top of the tank accessible by the top coil is available. Probably not an issue for the gas boiler as it can replenish as it's used, but the solid fuel might struggle.

If the two non-solar coils are nested together in the lower part of the tank, it isn't going to work at all well as a thermal store.

[clivejo]

I have three main heat sources

1) Oil fired burner - controlled
2) Condensing boiler - controlled
3) WB boiler - uncontrolled

I want to keep the solar coil for install of an array sometime in the near furture.

Can I just have the heat dump radiator on the WB boiler leg of the circuit so I'm not wasting heat when using the other sources?  Could the radiator be located in a cupboard i.e. airing cupboard where my old cylinder used to be?

[Richard Owen]

Can I just have the heat dump radiator on the WB boiler leg of the circuit so I'm not wasting heat when using the other sources? 

Yes.

Could the radiator be located in a cupboard i.e. airing cupboard where my old cylinder used to be?

Yes, I believe so.