Heat pump and UFH mixing setup

[bissoejosh]

About ready to lay my screed. Worked out heating requirements and pipe spacing. Pipe and 6 point manifold ordered from Wunda - 3 loops in the same room, very similar lengths being run as one zone so nice and simple (hopefully!).

 

When I spoke to Wunda prior to ordering they mentioned not ordering one of their complete kits as the pump / mixer arrangement isn't ideal for a heat pump. The bloke did try to explain but to be honest I didn't fully understand and at this point really just want to get the floor down.

 

Is there anything else I need to consider at this stage or can I figure the rest out as and when a heat pump is purchased? Does anyone have a quick explanation for an UFH luddite about the mixer /pump issue? I've searched site and previously found reference to something similar but can't find again annoyingly..

 

System is likely to be heat pump serving UFH and DHW with UVC.

 

Many thanks

Edited May 2, 2019 by bissoejosh
additional info

[joe90]

I bought a manifold kit from Wunda fir an ASHP and it did not have a pump and the wrong connections, when I called them they assumed the pump in the ASHP would be sufficient. Our ASHP does not have a pump and because we are using a buffer tank two pumps are required, one for the UFH ccts on the manifold and one for the buffer tank and DHW and ASHP cct.

[bissoejosh]

2 hours ago, joe90 said:

I bought a manifold kit from Wunda fir an ASHP and it did not have a pump and the wrong connections, when I called them they assumed the pump in the ASHP would be sufficient. Our ASHP does not have a pump and because we are using a buffer tank two pumps are required, one for the UFH ccts on the manifold and one for the buffer tank and DHW and ASHP cct.

 

Certainly sounds like it's worth holding off until I have a heat pump sourced and know exactly what I need - also gives me some extra homework time. I'll fit the pipes, keep the manifold safe and get the floor down I think. I believe I'll need a buffer tank also so will likely end up with a similar set up to yours.

[joe90]

1 hour ago, bissoejosh said:

I believe I'll need a buffer tank also so will likely end up with a similar set up to yours.

 

I was advised to use a buffer tank to stop the ASHP from short cycling but others have not installed one and theirs seem to work ok ?

[SteamyTea]

4 hours ago, joe90 said:

I was advised to use a buffer tank to stop the ASHP from short cycling but others have not installed one and theirs seem to work ok

I suspect that you can get away without a buffer tank if the heat pump is a little undersized.  There may well bit a bit of a hit on the CoP though as the internal heater may kick in more often and the risk of frosting.  I am starting to think that the frosting risk may be overstated a bit, but not seen any data to confirm it.

6 hours ago, bissoejosh said:

Certainly sounds like it's worth holding off until I have a heat pump sourced and know exactly what I need

Are you going for a CO₂ heat pump, the old refrigerants are being phased out fairly soon I think.  CO₂ HPs can also run up to a higher temp, that may mean you do need a buffer.

[ProDave]

5 minutes ago, SteamyTea said:

I suspect that you can get away without a buffer tank if the heat pump is a little undersized.  There may well bit a bit of a hit on the CoP though as the internal heater may kick in more often and the risk of frosting.  I am starting to think that the frosting risk may be overstated a bit, but not seen any data to confirm it.

 

My heat pump is not under sized (5KW HP and max demand a little over 2Kw) and it copes well with being directly linked to the UFH without a buffer.  It just moduates down and runs at a very low power.

 

The only time it ever seems to defrost is when working harder to heat the DHW, and then not very often.  It is around or just above 0 on a damp day that it is most likely to need to defrost.

[bissoejosh]

10 hours ago, SteamyTea said:

I suspect that you can get away without a buffer tank if the heat pump is a little undersized.  There may well bit a bit of a hit on the CoP though as the internal heater may kick in more often and the risk of frosting.  I am starting to think that the frosting risk may be overstated a bit, but not seen any data to confirm it.

Are you going for a CO₂ heat pump, the old refrigerants are being phased out fairly soon I think.  CO₂ HPs can also run up to a higher temp, that may mean you do need a buffer.

No idea at this time. I'm hoping to seek out an eBay / Gumtree cheapie but depends what pops up!