Buffer tank or no buffer tank for UFH

[joe90]

As some of you will know we have UFH in our new build and it was completed (almost) about 8 months ago. On advise from this forum I was advised to have a 90ltr buffer tank to stop the ASHP short cycling. I wired it so that the buffer tank was heated whenever the buffer tank stat called for heat, the reasoning being if the house required heat as called for by a room stat we would not have to wait fir the buffer to be heated then the slab which could be a long time. 

 

Now that it’s summer, the house is not calling for heat at all (well not on the last few weeks) but I have noticed the buffer periodically calls for heat. The tank is well insulated as is the pipework but there are small losses. Others on this forum have no buffer and theirs appears to run ok. I am tempted to remove the buffer tank. I suppose I could seasonally turn the buffer tank stat off (disconnected) but could suffer if we had a cold spell.

 

I have no data to prove the costs of heating the buffer during the summer, plan B is to go E7 as the house holds heat well (a heavy house) and I could use timers for both heating and DHW.

 

All comments welcome.

[BotusBuild]

Joe,

How is the buffer tank plumbed in? In the HP/UFH/buffer tank installations I have been involved with the buffer tank has always had 4 pipes - H and C from the HP, and H and C to the UFH. This minimizes the volume of liquid the HP has to heat up, and evens out the flow to the UFH. Each section of UFH should be thermostatically controlled, and the thermostat that controls the UFH should be linked to the buffer tank.

If the buffer tank thermostat calls for heat .... well you get the idea.

HTH

Stuart

[joe90]

Hi @BotusBuild, the buffer tank is plumbed with its contents connected to the flow and return on the manifold, the ASHP is plumbed with its flow and return heating a large coil within the tank, this limits the amount of fluid requiring anti freeze. The tank stat controls the heat of the contents of the tank, not the coil. We have one zone, downstairs and the pump on the manifold is controlled by a room stat in the hallway. To vary heat slightly between areas the flow rate is adjusted (i,e, lounge slightly warmer as that is where we sit rather than working/walking).

15 minutes ago, BotusBuild said:

If the buffer tank thermostat calls for heat 

 

The ASHP heats the buffer but the heat is not sent to the manifold unless the room stat calls for heat.

 

 

[BotusBuild]

@joe90

That's not strictly a buffer tank - that's a hot water tank. A buffer tank has no coil inside it.

There could be two reason for the intermittent HP working, one you have already identified as the potential small heat losses. The other could be some feature of your ASHP that makes it cycle occasionally for "maintenance" reasons - might be worth a conversation with the manufacturer directly rather than the installer.

 

Regards

Stuart

[ProDave]

I would say put the whole operation under the control of a conventional central heating programmer as I have done, that is something everyone understands and easily allows you to turn the heating off completely in the sumner.

[Fraser Lamont]

2 hours ago, jack said:

 

You'll get a wider range of responses if you post this as a new thread. Let me know if you want me to move it to its own thread.

 

[Fraser Lamont]

Subject moved to it's own thread. Nick from Wales, could you repost your last image to the new thread? I came up with a plan that could be similar to yours. TIA

[PeterW]

@Fraser Lamont I’ve added all the comments to a new thread for you

[PeterW]

All here

 

[Fraser Lamont]

Thread moved here. Thanks all!!

[Fraser Lamont]

32 minutes ago, PeterW said:

@Fraser Lamont I’ve added all the comments to a new thread for you

Thanks so much.