Mitsubishi compensation curve, wet UFH, thermostats, and rads
I’ve “inherited” an Ecodan/Zubodan ASHP, wet undefloor heating+rads downstairs, and rads only upstairs system and have many questions. I’ve been running the system with limited success over the last year and a half but with a newborn and a cold winter about to hit I want to make sure I’ve got everything efficient, cost effective, and working properly. I’ve read most of the threads here but still unclear on exactly what I should be doing for our situation and very conscious a small change could massively change the temperature in the house.
Our current set up is:
- 2x zones. Downstairs is 8 UFH loops + 2 rads, and upstairs is 3 rads + a towel rail. Both zones supplied by the same temp from ASHP.
- Every room downstairs has 1x UFH loop aside from the lounge and the hallway. Those two have 2x loops *and* a radiator with a TRV.
- Every room is thermostatically controlled. When temp is reached TRV & ufh circuit actuator shuts off for that room. These are also on a schedule (19 at night, 20 during the day for some rooms, 2 unused rooms are static at 17.5 and things like the lounge vary wildly).
- DHW comes on between 3am and 6am, heats to 48 degrees, with a max temp drop of 6 degrees. When this happens I can see the house temp plummet.
- ASHP not set to compensation mode but static temp of 49 degrees.
- All UFH loops in the manifold are balanced.
I know this isn’t the right way to set the system up but the previous owners were treating the ASHP and UFH like a combi and messed with all the settings (among other things - we found the immersion was on 24/7 for about 2 months after moving in during the summer!) so I’ve been spending the last year during periods of colder weather fixing it back to the recommended settings slowly, tracking the difference, and learning bits as I go along. Last winter though we were spending about £30/day on electricity which doesn’t feel right at all.
My plan is to move to weather compensation curve but my brain can’t get away from combi boiler type thinking with regards to the schedules and the rads upstairs.
So I guess my questions are: Should each room in zone 2 (UFH+rads) be set to a static temp all day, with no schedule, and the TRVs (lounge & hall) be set to a middle of the road setting. Further to this, should the upstairs TRVs be set to fully open and dial them back if it’s too warm until it’s a constant temp for a few days or should these run on a schedule? Conscious if we move to compensation curve these radiators won’t be warm before bed like they are now on their schedule (for example 6am - 10am 20 degrees, 18 during the day and then 20 degrees from 9pm until 1am or so).
Caveats (not sure if these affect anything):
- The kitchen thermostat is pretty twitchy when the cooker/hob is used and spikes (therefore shutting the thermostat off at its current setting.
- I have an ecodan FTC-6, but not a mitsubishi tank and the stats are all danfoss in each room.
- We have a log burner in the lounge which, similar to cooker, is picked up by the room stat and effectively turns off that room.
- We have a semi-draughty house in places. I’ve been plugging most of the gaps as I go along, but I’m aware there’s bits that aren’t ideal.
- We have a newborn so messing with heating and it being cold for extended periods isn’t really a fun idea.
A further fun complication is the company that installed the system want nothing to do with servicing it - seems they wanted that sweet government grant money but care not to maintain it moving forward so I’m on plums trying to get them to give me any sort of documentation or training session - hence coming here for help.
I feel like the solution is obvious if I sit back and think about it but messing with heating always gives me analysis paralysis. Any help or pointers would be awesome.
