GSHP, UFH & Buffer Tank/Thermal Store

[adh]

Hi all,

Hopefully someone with a little knowledge of this setup can advise on my best course of action. Currently our plumber is about to start the first fix. Our system is a little unusual compared to the normal and I would appreciate some advice on the best setup for what we want to achieve. First a basic rundown of the system:

Danfoss Diplomat 8ES GSHP 8.1kw with integral 180L DHW tank (unvented)
NuHeat underfloor heating on all three floors.

To enable more efficient running of the heat pump we require a buffer tank which will be situated in the loft. This is to reduce cycling of the heat pump and has been recommended by Danfoss. I would also like additional DHW capacity and therefore propose to have a thermal store for this purpose. The question is whether to have a combined thermal store and buffer tank or two separate tanks. Due to space issues, I would prefer a combined unit. The plumber says he can do either but didn't really say which was better as he says either method is workable. However I'm confused about how the combined unit operates as both a thermal store and buffer tank. Can anyone explain how this works? Can anyone recommend a good manufacturer to approach or have any specific models they would recommend?

Our plumber has also suggested running the downstairs bathrooms off the DHW tank integrated with the GSHP and running the upstairs two bathrooms with the tank in the loft. Has anyone any thoughts on this arrangement?

I'm also tempted to have heated towel rails in the bathrooms but due to our heating being fed at 45 degrees, the rails would have to be fed via the DHW system which entails a separate circulation system and special towel rails which will not corrode or rust - NuHeat have a specific range of towel rails for this and a specific circulation system. Our plumber has suggested it might be more efficient to have the towel rails running off the heating system but boosted to the required temperature with electric elements. Anyone any thoughts on these two methods?

Thanks for any advice and feedback from those who already have a system installed like this would be most appreciated.

 

[Cds]

From your post this is my understanding of what you will have:

1) GSHP with integral DHW cylinder. This will be heated by the GSHP and then topped up with direct electricity (heating element).

2) UFH from Nuheat

3) A buffer vessel to improve GSHP efficiency.

The use of a buffer tank will ensure that the GSHP runs without short cycling and will work well with UFH. However the ideal temperature to run the buffer tank at will be about 45ºC which is not hot enough for DHW.

If you try to use a thermal store then you will have to increase the temperature to at least 60ºC which will make the GSHP inefficient.

If you do need more DHW then I would have another DHW cylinder with heating elements or look at some of the specialist equipment for use with heat pumps. Consider having solar panels which will work well with a direct cylinder.

Check with Danfoss for possible solutions.

 

[adh]

Thanks for the advice. It seems what I was thinking was correct. It would make sense to have two separate tanks, one for buffer and one for extra DHW.

I've emailed Danfoss and will see what they come back with.

Many Thanks.