ASHP heating design help.

[Dam0]

Hi all,

 

First post here but have been lurking for a while now. I need to gather your vast collective knowledge to make sure I'm doing the right thing when it comes to heat pumps.

 

I'm due to install my ashp within the next few weeks and need help with what will work out the most efficient method of heating circuit design. Currently I have UFH downstairs and radiators upstairs. The UFH has it's own blending valve, pump and actuators and is connected to the heating circuit via a couple of stats and a 3 port valve (paired to upstairs radiators) Radiators are on their own stats with TRV's. All pipework is 22mm with 15mm to the radiator valves only. 

 

The new ashp cylinder has two zones with individual pumps connected from a buffer tank.

 

This is my plan... if im being simple please let me know...

 

I plan to remove the UFH pump, actuators and blending valve and run the UFH completely open loop, connected to pump 1 on the buffer tank. I will then use weather compensation only to control this and aim to have it continuously heat at a low temperature. 

 

I will then use pump 2 on the buffer tank to pipe to the upstairs radiator. I will then be able to control these with the upstairs stat as and when we need a boost in warmth ( I can set timing profiles of the stat or just leave it open if needed).

 

My thinking is that I will then have the main heating (UFH) running constantly and providing warmth downstairs without having to run the upstairs radiators upstairs all the time. I can then remove alot of the compexity of the system with essentially two loops (with the returns meeting just before the cylinder).

 

I'd like to add that for the past few years using our thermal store we haven't needed the upstairs radiators on much other than a towel rail. The log burner, ufh and electric UFH in the bathroom has always provided enough heat throughout the year.

 

My thoughts:

 

If I am running the heat pump set to UFH temperatures, I can imagine that the upstairs radiators will barely be warm to the touch when they are switched on. I am happy to upgrade the radiator sizes if needed but they are fairly well specced anyway due to the thermal store in the property.

 

Would it better to not remove the blending valve + ufh pump and instead run the heat pump at a higher temperature - blending it down for the UFH and have hotter water for the upstairs rads? If this was the case then I could then utilise just the one buffer tank pump and control the radiator demand via a 3 port valve. I feel this would add complexity however and mean I have two pumps running whenever the UFH is on.

 

Or do I run everything open loop on 1 pump and just use weather compensation for the whole circuit? I feel I may stuggle to get the flow through the UFH in this case without really restricting the radiators in this case... 

 

Help!

 

 

[JohnMo]

Keep as simple as possible.

 

Blending valve, buffer and all additional pumps delete. Run direct from heat pump circulation pump.

 

Tee rads in upstream of the UFH manifold and the return after the manifold. Run all as a single zone. Have radiator valves to control bedroom temps. Upgrade rads if needed. Run Weather Compensation (WC).

 

Set the flow rates for the UFH at the manifold and then heat pump circulation pump, if not a modulating circulation pump, set the speed to get the correct flow through the radiators. If modulating circulation pump it will sort itself.

 

I have a similar set up, getting a CoP for heating at 9 degrees outside of just under 6. Mine system consists of an ASHP, fan coil, UFH manifold, 3 port diverter valve and a cylinder.

[IGP]

46 minutes ago, JohnMo said:

Keep as simple as possible.

 

Blending valve, buffer and all additional pumps delete. Run direct from heat pump circulation pump.

 

Tee rads in upstream of the UFH manifold and the return after the manifold. Run all as a single zone. Have radiator valves to control bedroom temps. Upgrade rads if needed. Run Weather Compensation (WC).

 

Set the flow rates for the UFH at the manifold and then heat pump circulation pump, if not a modulating circulation pump, set the speed to get the correct flow through the radiators. If modulating circulation pump it will sort itself.

 

I have a similar set up, getting a CoP for heating at 9 degrees outside of just under 6. Mine system consists of an ASHP, fan coil, UFH manifold, 3 port diverter valve and a cylinder.

This. 

[JoeBano]

Just check your radiators are sized correctly, 40c flow temperature on Ufh might exceed 27c floor temperature limit on most floor coverings. So if you want 1 circuit design you will need to take this in consideration. 

[dpmiller]

could put them in series, UFH on the return from the rads

[Dam0]

Thanks for replies with this. I'm going to do exactly that and bypass the buffer tank in the combi cylinder.

 

Do you think I'll need check valves on the return if I tee the rads in up stream and the return after the UFH manifold? Or will this not be a issue as its just a single zone?

 

Thanks again

[JohnMo]

On a single zone it shouldn't be an issue as there will always be (or it's all off) flow through the UFH and radiators, so you cannot get reverse flow.

[Dam0]

On 13/09/2024 at 11:47, JohnMo said:

On a single zone it shouldn't be an issue as there will always be (or it's all off) flow through the UFH and radiators, so you cannot get reverse flow.

Many thanks