I’ve just had my new heating system installed and commissioned -
Mitsubishi Ecodan Air source heat pump
Underfloor heating system with Salus controls
So I effectively have two thermostats - the heatpump has its room thermostat, and the UFH has a thermostat. The hot water cylinder and heatpump controller are located in the loft, as I do not need regular access to these and it saves space. However, I didn’t initially realise that the heatpump had its own thermostat control for room temperature, so as it was left by the installer I had the following scenario:
Heatpump thermostat in loft (where there is no heating) set to 20 deg.
UFH thermostat in room set to 18 deg.
My understanding is that the heatpump would be trying to satisfy both of these demands - 1. is effectively impossible as there is no heating in the loft. So initially the energy demands were rather higher than expected…
I have since set 1. to its lowest temperature setting (10 deg), so my understanding is that the system will now be solely controlled by the UFH thermostat (which will eventually be added to my Home Assistant config).
The heatpump is now behaving more as I would expect, but just wondering if I am understanding the situation correctly and if anyone has any better advice.
The EcoDan controller can be used in 3 main modes:
room temperature auto adapt
fixed flow temperature
With the EcoDan controller up in the loft, the most efficient way to run this (without moving the controller) is to set it to weather compensation and adjust the weather compensation to match your system design.
To begin with set the UFH thermostat 1-2 degrees above the temperature that you would like to target and keep adjusting the weather compensation settings on the main controller until the system essentially achieves the target temperature that you are after just by running the water temperature in the system at the right temperature.
You want to use the UFH thermostat more like an overheat cut off rather than your main source of temperature control. If you get the weather compensation right that should keep your house at a nice even temperature with the lowest flow temperatures possible - ensuring efficient operation.
Personally though I would get the main controller moved to your main living space so that you can more easily adjust the settings rather than having to go up to the loft. You could then experiment with using the auto adapt setting and all the scheduling options build into the Ecodan controls - which may help you tweak the system for better performance.
Do you have multiple UFH thermostats and zones? or is it just the single thermostat turning all circuits on/off?
Do you know what flow temperature your system was designed to require at the minimum outside design temperature? Many systems seem to be designed to work at around 45C when it’s around -3C outside, though the lower the better of course with heat pumps.
Do you have radiators in the house as well as the underfloor?
Does the underfloor have a mixing valve? if it does do you know what setting it is on? it might be worth sharing a picture of your manifold if you dont mind.
Thanks for the detailed response Trystan - although I think I may be more confused now than when I started…
There are two UFH zones each with thermostats, one for the bathroom and one for everywhere else. The advantage of the Salus control for the bathroom is that I can independently warm the floor regardless of the air temperature.
I can control the ecodan via the Mel cloud app but of course with the controller in the loft, its temperature sensor is also in the loft. I don’t know what effect that will have on the efficiency of the system.
Basically, I don’t really understand the difference between the heatpump thermostat and the UFH thermostats. When I request a target temperature for a UFH zone - what is it asking the heat pump to do? And what effect does the Heatpump’s thermostat have?
Thanks. Typically with your setup the installer should have configured the ecodan controller for weather compensation mode (this effectively disables the thermostat in the indoor controller which in your case is in the loft).
Weather compensation means that your system flow temperature will vary depending on the outside temperature. So as an example, the flow temperature might be 45C when it’s -3C outside and 35C when its 8C outside.
Technically if that’s setup correctly you could set your zone thermostats to 25C so that they are always on and the system would just run to keep your house at around 20C. If with the zone thermostats are up at 25C and your indoor temperature keeps climbing - this means that your weather compensation curve is set too hot or your controller is perhaps trying to run hot in order to heat an un-heatable loft…
Out of interest, did your installer go through any of this during commissioning? Are you able to get them round to check the settings on the system?
No, it was quite complicated because it was a complete renovation involving solid wall and floor insulation in addition to UFH. The UFH was handled separately and was installed before the details of the heatpump installation were known.
Ideally I’d prefer to be able to use the Salus controls as these are zigbee enabled and I can integrate them with Home Assistant - one thing I’ll probably want to be able to do is have a lower temperature during the night so it’s easier to sleep.
Thanks for the pointers, and I’ll have a look at the videos and try and get my head round the weather compensation feature.
@TrystanLea It was actually set in Weather Compensation mode, but the MEL cloud app was displaying something different. I am not sure if using the app overrides the local controller? Something else I need to investigate.
I have set it to Flow temp [email protected] deg and [email protected] deg. I have set the UFH thermostats to 25 deg. I will leave it like this for 24 hours and report back - unless it becomes intolerably warm!
One further question though - how do I reduce the temperature overnight - use the UFH thermostats?
Great, that’s a good starting point, it would be worthwhile checking for system cycling as you reduce the flow temperature. Are you monitoring electricity consumption, logging to emoncms or home assistant?
It is possible to nudge the curve ±a few degrees on the main controller but im not sure if that’s automatable. Several folk here are automating control via melcloud so may be able to advise further @MyForest@Timbones any ideas?
It’s worth checking the setting on that blending valve, you really want that to be set to max so as to minimise blending, you want to have your heat pump reduce the water temperature not the blending valve.
The UFH is in screed, which is covered in tile in the bathroom and hardwood in the remainder of the floor.
Initially the bathroom stat was set at max, the idea being I assume to ensure the floor stayed warm regardless of the air temp. I expect this was what was responsible for the initial high energy usage.
I’m sorry, I’ve not seen a way to automate altering the weather compensation curve, I re-implemented the logic in my code and then enhanced it. As a result I just keep setting the target flow every two minutes from my code.