UFH to be connected to ASHP ?

[nowty]

I think the Valiant modulates, i.e. can reduce down to lower power with inverter technology whereas the Samsung cannot as far as I can see.

[robl]

I’ve heard the 3.5kW Vaillant arotherm plus is a software limited version of the 5kW. If so, you’d have the same low power level, just a limited maximum compressor speed ie power, so lower modulation effectively. I’m not sure of an engineering reason to make two models out of one piece of hardware, I’d guess it’s marketing. I’d be going for the 5kW, even if 3.5 was sufficient.

Bit of Googling to confirm and saw this:
https://www.reddit.com/r/heatpumps/comm ... nfo_costs/

[url=https://postimg.cc/sQkbCx6R][img]

[Stinsy]

R290 HPs don’t seem to lose power output in low temps compared with R32. Hard to know for sure, not seen real world data, just looking at manufacturer figures.

I wouldn’t recommend running the HP hard for space heating unless you have UFH beneath a 200mm slab. Comfort levels will be poor due to the temperature fluctuation. Better to run the HP low-and-slow 24/7 even if that means paying for peak electric.

Our UFH is in a minimum of 150mm of screed on top of 100mm of concrete.
The concrete is sitting on 300mm of EPS.
It can store a lot of heat - I just don't really know if it's enough

In which case you could crank the HP in the cheap period. However your ability to transfer heat from the pipes to the concrete becomes your limiting factor. Eg if you’re pumping 25c water through the pipes, the concrete right next to the pipes would quickly heat up to 25c and not take any more heat out of the water. It take hours and hours for that heat to migrate through the concrete.

[newtoallthis]

R290 HPs don’t seem to lose power output in low temps compared with R32. Hard to know for sure, not seen real world data, just looking at manufacturer figures.

I wouldn’t recommend running the HP hard for space heating unless you have UFH beneath a 200mm slab. Comfort levels will be poor due to the temperature fluctuation. Better to run the HP low-and-slow 24/7 even if that means paying for peak electric.

Our UFH is in a minimum of 150mm of screed on top of 100mm of concrete.
The concrete is sitting on 300mm of EPS.
It can store a lot of heat - I just don't really know if it's enough

In which case you could crank the HP in the cheap period. However your ability to transfer heat from the pipes to the concrete becomes your limiting factor. Eg if you’re pumping 25c water through the pipes, the concrete right next to the pipes would quickly heat up to 25c and not take any more heat out of the water. It take hours and hours for that heat to migrate through the concrete.

Yes, a thick slab could be a blessing or a curse - I'll just have to play with the set points and flowrates to try and make it work for our lifestyle.

[Fintray]

I was under the impression that delivering a dT of 5C was required in order to minimise cycling of the heat pump - is this not the case ?

I probably does and I could possibly get away with a smaller heat pump in all but the coldest weather. My heat pump ran for over 300hrs without cycling once during last month and up to 11:00hrs today has been running 60hrs without cycling (0.1C avg. temp. and cop of 3.78), SCOP since March 9th 2024 4.12.
The flow through my heat pump is usually 33l/min which I intend to reduce to see the effect it has on DT and cycling.

[sharpener]

I was under the impression that delivering a dT of 5C was required in order to minimise cycling of the heat pump - is this not the case ?

I probably does and I could possibly get away with a smaller heat pump in all but the coldest weather. My heat pump ran for over 300hrs without cycling once during last month and up to 11:00hrs today has been running 60hrs without cycling (0.1C avg. temp. and cop of 3.78), SCOP since March 9th 2024 4.12.
The flow through my heat pump is usually 33l/min which I intend to reduce to see the effect it has on DT and cycling.

Unlike many other mrfs Vaillant run their HPs with constant flow rate, and modulation therefore results in variable DT. If you force the flow rate down it will raise the DT. Most ppl on this FB forum https://www.facebook.com/groups/488794632317506/ seem to think this will make the efficiency worse and leaving it in Auto is best in most circs.

[Fintray]

I was under the impression that delivering a dT of 5C was required in order to minimise cycling of the heat pump - is this not the case ?

I probably does and I could possibly get away with a smaller heat pump in all but the coldest weather. My heat pump ran for over 300hrs without cycling once during last month and up to 11:00hrs today has been running 60hrs without cycling (0.1C avg. temp. and cop of 3.78), SCOP since March 9th 2024 4.12.
The flow through my heat pump is usually 33l/min which I intend to reduce to see the effect it has on DT and cycling.

Unlike many other mrfs Vaillant run their HPs with constant flow rate, and modulation therefore results in variable DT. If you force the flow rate down it will raise the DT. Most ppl on this FB forum https://www.facebook.com/groups/488794632317506/ seem to think this will make the efficiency worse and leaving it in Auto is best in most circs.

I'll report back once I alter the flow rate which won't be till mid March as that gives me a full year of data at the current flow rate.

[Moxi]

https://heatpumps.co.uk/heating/simulator.html

Can you model it on this simulator to get an idea Fintray ? I note the flow rate doesn't go high enough to reflect your system at present but maybe its good enough to draw parallels ?

Moxi

[Fintray]

Thanks Moxi, I gave it a try to see how to get the DT up and I would need to reduce the flow, what that will do to the overall COP I'll have to wait and see.

[Moxi]

Don’t you want the delta T to go down so the heat pump isn’t working so hard ? Obviously you need a certain temperature differential to drive heat in to the house.

Moxi