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Thermal store adviceAnybody got any experience / recommendations about using thermal stores for electric/solar/wood input - mains press hot water / underfloor heating output? The advice we're getting from tank suppliers varies wildly. Especially on a couple of points - is it acceptable to have a pumped circuit for the woodstove back boiler? And do we need seperate coils for the boiler, the uf heatng etc (as chelmer suggest) or use the same tank water for everything except solar in and domestic hot water out (consolar). A recommendation for an adviser / installer covering west Devon would be appreciated.
I think it's considered good practice to have a separate coil for each in and each out. However, we have also been told that it would be fine to have the woodburner directly connected to an in at the bottom of the tank and an out at the top.
If you have a look at the forums at navitron.org.uk there are loads of helpful guys who will probably be able to recommend local installers.
Hope this helps,
hi dee - first off if you are talking to chelmer heating - they are very well respected within the industry so you should get some good advice from them.
It would not be normal to have a separte coil for the boiler and the ufh - i.e. the same water would normally flow through both.
Common practice would be to have a separate coil for the wood stove - being classed as an uncontrolled heat sourced it will have to be vented to an f&e tank in the loft. The coils would also have to be rated for for the stove so might limit the stove to 5kw.
A better way to my way of thinking is to use an neutraliser valve which will allow you to connect the boiler and the wood burning stove directly to the water in the thermal store -
normally - no you cant pump a wood burner to a thermal store because it has to be an open circuit - in the event of a power failure the pump wouldn't operate and would be a restriction in this circuit. However the neutraliser valve will allow you to connect multiple inputs from the boiler and stove etc and combine them as one output to heat store. In this case you can keep one open circuit to the wood stove and have one pumped circuit vastly improving the efficiency of the system.
I have a designed a system for exactly this if you are interested.
This also has the advatage that you can still use the cylinder coil for a solar system.
Re: Thermal store advice
|Dee J wrote: |
|Anybody got any experience / recommendations about using thermal stores for electric/solar/wood input - mains press hot water / underfloor heating output? |
And is there another boiler?
There are different ways of using electricity for heating.
You might simply have an immersion heater in the tank. Or you might use electricity to run a heat pump, whether ground or water sourced heat. And there are "electric boilers".
A heat pump is a very good match for an underfloor system - without involving a store (tank). The temperature for underfloor can be produced efficiently by a heat pump. The higher the temperature output, the lower the efficiency (CoP) of the heat pump.
Using underfloor in a large thermal mass floorslab, allows heat from off-peak electricity to be buffered - its a ginormous storage radiator.
Different people advocate and sell different systems. With different merits and demerits, and prices.
|The advice we're getting from tank suppliers varies wildly. Especially on a couple of points - is it acceptable to have a pumped circuit for the woodstove back boiler? |
As explained above, during any electricity cut, a gas or oil boiler would produce no new heat, so the pump failing then isn't a problem.
But a woodburner keeps on producing heat during a powercut, which would make for problems if one was reliant on a non-working pump to shift the heat and prevent boiling.
There are two ways of doing mains pressure hot water (apart from a combi boiler!) One involves a coil/heat exchanger carrying the water to the taps - it is heated as it passes through.
The second involves the water filling the tank going to the taps (this means the tank is pressurised - and more expensive).
The first method uses heat exchangers that may need occasional descaling, but it does afford the possibility of having the tank water on a direct thermo syphon circuit going through the woodburner. So no woodburner coil.
What is this boiler?
|And do we need seperate coils for the boiler, the uf heatng etc (as chelmer suggest) or use the same tank water for everything except solar in and domestic hot water out (consolar). |
Underfloor wants water at about 30/35C. Hot taps want 55C. The hotter your store gets, the more heat you are storing.
To deliver fixed temperature hot water from a variable heat store, you'd have hot/cold blending valves. (Similarly if you are trying to run underfloor from a hot store.)
I'd suggest that hot water from a heat exchanger in a vented (ie unpressurised) tank directly heated by the woodburner, with a solar coil in the tank - and an (E7 or E10) immersion heater for (inter-season) backup - and kept separate from the underfloor heating run from a heat pump, sounds like the most straightforward route. (Economy 10 would likely be the best tariff scheme for the heat pump, so I'd expect you could have the immersion on that too.)