@gary 

i can see a blending valve on the manifold though. Whats that set too? 

and here is my floor ticking over at 27ish degrees 

@davidnolan22 good spot, that should probably be ideally removed not needed for a heat pump.

Needs to be set so it doesn't do anything if possible.

What size HP do you have I can't get mine that low just cycles constantly.

@gary 11.2kw for 260m2 house.  its tight on the heat loss at the cold end, but in mild and a bit cold weather, works well

@davidnolan22 Nice out of interest do you know how much power it pulls at that temp at 32C my 8.5KW unit pulls about 800W

@gary yeah, more than that. about 1000-1200w, ive never really seen it go below that. and that's with the compressor bumbling around 30hz,

@jamespa

 Thanks very much. I appreciate you’re probably sick of newbies coming along and asking questions but I’m genuinely trying to educate myself because I want this to work as well as it can.  

Seeing energy usage spiral upwards daily this week has been a bit scary so I know I need to put the effort in.

I’ve currently got all the thermostats running at 26 degrees and the flow temperature is 38. it’s 7 degrees outside.

Every room achieves different temperatures but generally, using this, the upstairs rooms are currently at a temperature we can enjoy but the lower level (concrete slab), which is always a colder zone, is struggling to get past 21 degrees… which is mostly warm enough anyway… but it’s not overheating the rooms. 

The fact that we’re getting decent temperatures from this at such a low temperature is astonishing me. 

When we had an oil boiler we ran it more like traditional heating because having UFH seemed to just swallow oil. The only way we could get a comfortable temperature was by having the manifold flow temperature at 50 to 53 degrees  

Thanks for finding the Polypipe manifold information too. I’ll take a look. 

So going forward; best practice is to leave the thermostats on a much higher temperature so the ASHP runs continuously on a lower flow temperature..?

In that case though, how would most people regulate temperatures in rooms? Such as bedrooms if you want them cooler and bathrooms being warmer? We’re currently doing this with the thermostats. I can see how you’d do it with radiators but would adjusting the manifold be the only way in the case of UFH?

Posted by: @davidnolan22

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I have a lot of UFH, and depends on the design and pipe spacing, but if you run it 24/7, you'll be surprised at how cool you can run it.  I rarely ever need the flow above 33. 

We’ve been relying on people doing heat loss evaluations to size the heat pump and two different ones came back with similar suggestions so we were hoping it was right.

Its not a perfectly insulated house and we have a lot of big windows some of which need replacing but its not draughty.  

If it is oversized, is that likely to cause serious headaches down the line?

At the moment, with current OAT, I’m finding 38 is the sweet spot for keeping the house continually warm (around 21 degrees).

Posted by: @sandman1600

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So going forward; best practice is to leave the thermostats on a much higher temperature so the ASHP runs continuously on a lower flow temperature..?

 

Yes absolutely.

Posted by: @sandman1600

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In that case though, how would most people regulate temperatures in rooms? Such as bedrooms if you want them cooler and bathrooms being warmer? We’re currently doing this with the thermostats. I can see how you’d do it with radiators but would adjusting the manifold be the only way in the case of UFH?

Exactly, the manifold has the equivalent of a radiator LSV and a radiator TRV (the actuator) together.  With a radiator you adjust the LSV and leave the TRV on max or heads removed.  You can leave one or two on in rooms that suffer large swings, (eg due to solar gain).

Some houses do need a bit of room influence (eg Ecodan Autoadjust mode or whatever they call it) on top of the weather compensation, but many do not.  If the house has a long thermal time constant (it takes a long time to cool) then room influence can make things less stable than with pure WC.  The underlying control problem is that the room temperature is a 'rear view mirror' view of whats happening, whereas the OAT tells the heat pump in advance whats going to happen to the building.  Control loops based on rear view mirrors are inherently tricky, particularly when the response time of the system (ie the house) is longer than the timescale for changes in the conditions that drive things (ie the weather).  There is a whole branch of engineering devoted to this type of problem (control theory) but the bottom line is that for many houses pure weather compensation delivers the most stable, lowest cost and most comfortable result. 

Incidentally weather compensation exists for boilers too, and is mandatory in some countries.  The UK didn't mandate it which means that, for the past 20 years, our gas bills have been 10% more than they needed to be.

I strongly reccommed you read this introduction, it will helpo cement the thoughts https://renewableheatinghub.co.uk/the-abcs-of-ashps-a-jargon-free-introduction-to-heat-pump-basics

Posted by: @gary

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@sandman1600 

Do you have the wireless adaptor and Melcloud app once you have it running consistently the hourly temperature plots under reports are useful to see the last 24 hours of temps and whether its cycling or not.

Thanks for the info. That manifold mod might be a good option.

I discovered the reporting this morning and that is useful. At least I can track what’s happening when using Weather Compensation. 

Posted by: @sandman1600

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At the moment, with current OAT, I’m finding 38 is the sweet spot for keeping the house continually warm (around 21 degrees).

 

That sounds high for UFH.  Strongly recommend you follow the procedure I outlined upthread and report back.  You should hopefully be looking at a flow temp  of 35C or less when its -2 outside!

@jamespa Thanks again. That’s such a helpful response.

I’ve read the guide twice now and I’m referring back to it constantly to help cement the knowledge. 

It’s all starting to become clearer. Slowly. 

@sandman1600 

Hi, this is all tricky. 

One thing I wold say is to give the house time. When running the heating very low and slow, it can take days to heat the floor, walls, bricks to a consistent temperature. When I ran mine more on/off, my rooms were at 19/20, my floor at 23-25 but my walls were at 18/19 degrees (yes I do measure them.... my wife thinks i'm really odd). When running more constant the walls and structure of the house gets warmer (21-22 for a floor surface temp 23-25) and can act as a heat sink (depending on thermal mass of walls etc).   you'll be be able to go lower than 38 at these temps I'd be fairly sure.  Your problem will be the minimum output of the 14kw heat pump might be not far from your heat loss in cold weather, but that's another matter.  If that's the case, then you may need a change is strategy.  

As for heat and rooms. Run it for a while to get a feeling of it.  If there are room that are getting too hot too then you can reduce the flow of water to that room by turning the valve on your manifold.  This can take a long time to really understand and get a feel for, and you can't restrict too much as you need flow around the system.  Also, once your house it reasonably well balanced, then you could ask Haven wise to take control of the pump. But you need to be happy that you've got an open loop system with all the rooms where you want them.