ufh heat recovery

[gravelrash]

Sounds insane but here we go..

I have planned UFH system going in slab 122m2 floor with plenty of solar gain to south and west. Heat load at -4 is just above 3000w with flow design temp at 30c and slab temp at 21c, using single zone initially till we see how it performs. Due to limited UFH volume of 42lt and using small gas Combi we are sourcing a 80lt 4 port buffer tank with an upper coil installed. Idea is to load tank to 40c in upper 2/3 and also pre heat DHW through top coil before entering boiler. Idea being the tank is heated at max condensing efficiency where HW is not, so a slight gain.

That parts pretty straight forward....but I would like the system to reverse cycle during summer months to remove some heat from slab and dump it in buffer tank. I know it will not produce high temps but any preheat to mains water at 10c on HW side is beneficial and will help cooling.

Any thoughts? 

Is there a circulation pump that will reverse flow? or am I looking at second pump and diverter valve?

any one know of a heat/cool thermostatic programmer that work with slab sensor?

Any recommendations for Buffer specialist supplier

 

[JohnMo]

Just commissioned a system quite similar to you are talking about.

 

Combi boiler - Atag can take pre heated water

Thermal store, DHW Coil feeding into combi

Combi central heating circuit, heating TS via sealed coil at bottom of TS.

Water within store connected to UFH pump and let down to 30 degrees via mixer at manifold.

 

Thermal store temp set at 45 degrees.  Boiler central heating flow temp is a 50 degree curve.

 

The only difference is my immersion is connected to PV diverter.  So what you want I cannot do, but you can.

 

UFH pump is running when a thermostat has a heat demand, boiler only runs when the thermal store asks for heat.

 

Summer

Turn thermostat down in summer so there is always a call for heat, but ensure the central heating demand is switched off in summer, so thermal store is cold.  UFH heating will circulate back to store - no need to reverse.  Heat at top of store will be consumed by cold  water passing through upper coil prior to being heated for DHW. But you need the separation of UFH and boiler, but running through coils within the tank gives you this

 

[SteamyTea]

Would an exhaust air heat pump be easier.

I think @Gone West had one in his old place.

Edited October 21, 2021 by SteamyTea

[gravelrash]

Looking at using what I actually will need rather than what I would like...but using it in the most effective way, so no expensive heat pump.

I looked at TS but cant get small ones and large one would just be heating water for the sake of it. I like the idea of turning boiler to summer mode.. makes good sense, possibly electric valve to stop any thermal flow through boiler would be a cheap benefit during summer

Edited October 21, 2021 by gravelrash

[JohnMo]

I just heat the top half of the store, thermostat about half up store set to 45 degrees.  I am using wood stove connection at top of store as my UFH take off

[gravelrash]

Was going to do similar with heating programmer wired via temp sensor on tank controlling boiler heating. once boiler switches off the heating pump will still circulate ufh until temp drops in tank.

[SteamyTea]

@JohnMo

Is that multifoil insulating the area?

Have you ever checked the thermal losses from your combination cylinder?

[gravelrash]

Johnmo,

where did you get your Atag boiler? which model are you running? how did you find cost of it?

[JohnMo]

No its not a multi foil.  That's the vapour control airtight layer.  There is spray foam insulation inside the roof structure.

 

Thermal losses not accessed, but at 40 degrees in the top half only isn't worth while assessing.  The plastic cap on the top of cylinder is cool to touch.  The water in the expansion tank, feels warm, but not hot.  The room not much hotter than the rest of the house.  The top of the room is being extracted to MVHR, so being recycled.

 

The boiler came from Wolseley, it's an A325ECX, cost me £950 (including VAT,)  including a standard flue.  For one of the highest efficiency boiler you can get pretty good price.  The main reason I chose it was it build out of the box to take solar preheated water.

[gravelrash]

anyone else got any input?

[gravelrash]

bump