Some may remember that at the beginning of my project I was asking about ASHPs. In the end I decided just to install one for ufh on the ground floor (new oil boiler for 1st and 2nd floor rads).
My plumber installed a 6kW Grant unit. The makeup of the ground floor is roughly 100sqm limecrete with 2-300mm foamed glass under that. Walls are mostly 60mm woodfibre with lime on 5-600mm brick walls. All windows are currently single glazed and I still have some draft proofing to do around the front door.
It has now been running constantly for a month and has only managed to get up to around 18-19C room temp but more like 16-17 on the coldest days. I was concerned before it was installed that we should have gone for the 10kW but he was sure it would be enough. I will be installing wood burners for the colder months as I have a good supply of my own wood but I would prefer if it could cope on its own if needed. How does this sound to those with experience? I I guess I should do some of my own calcs. Is there a site where you can input data to do this fairly quickly?

Posted By: Tomasz_PIs there a site where you can input data to do this fairly quickly?

If you want a site to do u value heat loss calcs. look at
https://www.ubakus.com/en/r-value-calculator/
use the demo version

Posted By: Tomasz_PMaybe I am approaching it the wrong way and I should use my heat pump capacity as an incentive to improve insulation and draught proofing but don't want to be running it flat out if it is inefficient to do so!

+1
e.g. single pane glass has a u value of about 5.7 put that with a few draughts and you have a recipe for heat loss

What temperatures are the water at, flowing from the ASHP to the UFH, and returning back from the UFH to the ASHP?

That would help work out whether the ASHP is the weak link, or whether the UFH pipes are too fully loaded.

The ASHP will have a setting for the target water temperature, you need to find if the ASHP is easily meeting its target water temperature most of the time (in which case you could increase it).

It would be surprising if 100m² of floor would be able to emit any more than 6kW of heat, unless the UFH pipes are very close together and the flow temperature is very high.

Edit: Other things to consider are whether you are running the heating 24/7 (better) or only at certain times of day. And what is the floor finish, tiles (better), wood, carpet (worse)?

Is there a thermostat blending valve in the UFH manifold (try turning it up a bit).

Is the upstairs heated and warm, or is the heat from the ground floor all rising up the house and displacing cold air back downstairs?

Great advice guys, thank you. Flow/return is currently at 30/24 (taken from the dials at the manifold) which sounds pretty low but the heat is definitely going into the floor. The blending valve has been set to max already. I am not sure what would constitute an ideal install and I can't remember the pipe spacing but I could check. At the moment we have some tiles and the rest is still bare limecrete.

I have been running it 24/7.

Posted By: Tomasz_PAt the moment we have some tiles and the rest is still bare limecrete.

What is under the limecrete ?

Hi Tomasz,
The MCS-021 guidelines suggest that a tiled floor with UFH supplied at 30degC could emit 30-50 W/m², so that would add up to 3-5kW capacity across your 100m². As you still have single glazing and draft-stopping work to do, that might not be enough to keep up with the heat loss from the building yet, but might be enough when your work is complete?

If you stand next to the heat pump for half an hour, does it sound like it is running flat out hard all the time to reach 30degC, or is it modulating down? Did you find what target temperature its control is trying to reach? The installer should set up a weather compensation curve so it runs at enough target temperature on cold days for the UFH and ASHP capacity to match each other, maybe that can be adjusted.

To increase the heat emissions to 50-80W/m², the MCS guide suggested a flow temperature should be 35-40degC, perhaps by changing out the blending valve or removing it?

No point in fitting a bigger heat pump of any bigger capacity than the floor can emit.

For our old house we were looking at retrofitting UFH but had the same issue that, to get many W/m² out of it, we needed a higher flow temperature. Alternatively, with that higher flow temperature we could use (larger) radiators, or maybe a mix of UFH plus radiators.

Edit to add: very roughly, the floor surface should be +1degC hotter than the room air temperature for every 10W/m² of heating. So if the 100m² floor was giving out 6kW, it would be 6deg warmer than the air temperature. If you want the room at 22degC, the floor surface would be 22+6=28 degC. The heating flow and return temperatures would both be warmer than that, because some temperature is needed to drive heat through the screed and tiles.

Hi all,

Thank you for your really helpful information. It is useful hearing some of the info from the MCS guidelines.

The pipes are all set into the limecrete. I do believe that the pipe install is good in that sense and checked at various point around the ground floor and the temp hovers around 21 (I found and attached a picture before the limecrete went down). The range is about 20-22 but mostly somewhere around 21. That ties in with the room temp today of 16-17, so the hp should be outputting around 5kW.

Over the past week I have been monitoring room temps in the morning and they have have ranged from around 15-17 but it has been sub 0 every night, which is not that common here in Norfolk.

I can see that the blending valve has already been set to max so there is nothing more that can be done there. I can ask the plumber about weather compensation as the next port of call. I would need quite a hike in floor temps to reach the set room temp though!

One side note. 16-17 room temp sounds bad but actually is generally fine unless you are sitting still for quite a while. I guess that is the nature of the way the heat is delivered.

I will report back with the plumbers suggestions and continue working on the heat loss for now!

Posted By: Tomasz_POver the past week I have been monitoring room temps in the morning and they have have ranged from around 15-17 but it has been sub 0 every night, which is not that common here in Norfolk.

One thing it might be worth bearing in mind is that it isn't necessary to use the same heating system in all external conditions. That is, you can use some supplementary heating if external conditions are very cold. Adding some direct electric heaters (radiant probably) would be a cheap way to boost heating power for a few days per year.

Tomasz - Did you do any heat loss calcs. from the link at the top of this thread. Going through this exercise should give an indication if the system you have could ever provide enough heat after the draft proofing has been done. You should do a calc.for what you have and after various works, this should (could) give a clue as to where to put your (first) efforts

Unless you monitor and measure, from what I have seen, it is very easy to not setup a Heat Pump efficiently. In years to come this will become a major factor where folk 'trust' the plumber (who really has no incentive after it is fitted to ensure it works efficiently).

I read various stuff on this dark art even though I do not have (the pleasure?) of a HP yet.

For instance https://community.openenergymonitor.org/t/heat-pump-experiment-review-after-two-years/18402

High levels of efficiency, require very good data and high levels of control (IMHO).

Posted By: WillInAberdeenI think remote configuration updates over the internet will be next.

Aargh! Doctor, doctor, my heating doesn't work 'cos my internet's down