Low temp differential stats for UFH?

[Adam2]

Hi - UFH has been in and working great. Only issue is that the UFH is in liquid screed (50-75mm thick) and the Wunda stats only have a 0.5 min temp differential meaning if I set 22 degrees UFH will come on at 21.5 and stay on until 22.5. SAs we're running low temp ~32 degrees by the time the UFH comes on and we notice a difference it could be 3hrs later by which time it is much below 21.5. And of course the stat will stop UFH flow at 22.5 and then there is a lot of heat still in the slab so we overshoot desired temp.

 

This is of course not a big deal in the scheme of things but I am wondering if I could swap out some of the stats for more sensitive controllers - I called Wunda and they say the ones I have can't be adjusted to be more sensitive (I already read the manual but hoped there may be a trick as the temp reading is per 0.1 degree granularity). I have 1-0 of these but at least hey are all in the plant room so swapping one out to test is quite easy.   Other aspects to consider ASHP and wired temp probes in walls within a vented panel. I do have a home automation system running (Hubitat/Zwave) which I could possibly start to use to support this and maybe could have saved money by not having the stats/temp probes in the first place but I like the idea of the UFH being modular and just left to do its own thing without extra integrations.

 

Thanks for any suggestions. 

[JohnMo]

Computherm Q7RF, Amazon was the best price I found. Works pretty well for heating and cooling.

 

If you are getting big overshoot turn the flow temp down a degree or so.

[Adam2]

4 hours ago, JohnMo said:

If you are getting big overshoot turn the flow temp down a degree or so.

yes will try that also.

 

I see the same co does a simpler version which looks like a good replacement for my Wunda which has 0.2 degree differential vs Wunda 0.5. Will get one to test on 26 quid

[Adam2]

OK so seems the simpler model does not allow external temp probe - which I need. Issue is the larger one does not fit a standard back box - which I need.

 

So....still looking for a low temp differential (0.1 or 0.2 degrees) simple timer that allows an external temp probe and fits a regular UK single back box - let me know if you have any....am continuing to Google of course but nothing yet

[JohnMo]

Are you trying to make things more complex than they need to be. It looks like your flow temp is too high and the system needs balancing. 

 

What are the external probes bringing to the party?

[Adam2]

Well, maybe. The aim is to KISS 🙂

The ASHP / Buffer config is a setpoint of 34 degrees (thought was 32 as per original post) with a 3 degree differential. Meaning the UFH should be getting water in the range 31 to 37 degrees. I'll take the setpoint down to 30 and see how we get on. My concern with going lower is really just the time for the UFH to start having an impact. 

 

The room stats are all in the plant room so have remote probes in vented wall mounts

 

Balancing - using self-balancing actuators so think this should be OK unless there is some other balancing you have in mind.

Edited October 20, 2023 by Adam2

[JohnMo]

KISS, is really a single thermostat, no actuators, no manifold pump or mixer and no buffer. Then run the whole lot on either WC, or a modified version for batch charging the floor etc.

 

But if you are keeping the zones, have a look at at Salus SQ610, fits a standard wall box, they look nice and lots of good fuctionality for UFH. It has built in control algorithm for UFH so it learns how to stop and start the heating to keep things stable. It needs the Salus ZigBee unit to function, but once commissioned there is no need to be internet connected but you can be if you want.

[John Carroll]

On 18/10/2023 at 11:36, Adam2 said:

Hi - UFH has been in and working great. Only issue is that the UFH is in liquid screed (50-75mm thick) and the Wunda stats only have a 0.5 min temp differential meaning if I set 22 degrees UFH will come on at 21.5 and stay on until 22.5. SAs we're running low temp ~32 degrees by the time the UFH comes on and we notice a difference it could be 3hrs later by which time it is much below 21.5. And of course the stat will stop UFH flow at 22.5 and then there is a lot of heat still in the slab so we overshoot desired temp.

 

This is of course not a big deal in the scheme of things but I am wondering if I could swap out some of the stats for more sensitive controllers - I called Wunda and they say the ones I have can't be adjusted to be more sensitive (I already read the manual but hoped there may be a trick as the temp reading is per 0.1 degree granularity). I have 1-0 of these but at least hey are all in the plant room so swapping one out to test is quite easy.   Other aspects to consider ASHP and wired temp probes in walls within a vented panel. I do have a home automation system running (Hubitat/Zwave) which I could possibly start to use to support this and maybe could have saved money by not having the stats/temp probes in the first place but I like the idea of the UFH being modular and just left to do its own thing without extra integrations.

 

Thanks for any suggestions. 

Are you sure the Wunda stat is working correctly? A setpoint temp of 22.0C with a switching differential of 0.5C should mean a switch on at 21.5C and switch off at 22C.

[JohnMo]

1 hour ago, John Carroll said:

Are you sure the Wunda stat is working correctly? A setpoint temp of 22.0C with a switching differential of 0.5C should mean a switch on at 21.5C and switch off at 22C.

If the hysterisis is 0.5 the switch off, is 22.5 not 22. The control point is 22 the hysterisis on the thermostat is actually +/-0.5.

A 0.1 deg hysterisis thermostat works at +/-0.1 from the control point.

Edited October 24, 2023 by JohnMo

[John Carroll]

36 minutes ago, JohnMo said:

If the hysterisis is 0.5 the switch off, is 22.5 not 22. The control point is 22 the hysterisis on the thermostat is actually +/-0.5.

A 0.1 deg hysterisis thermostat works at +/-0.1 from the control point.

So, if it states on a stat that the differential is 0.5C does that differ from a stat that states its hysteresis is  0.5C or does it mean the same thing?

 

it's interesting because I have a simple digital stat set to its lowest differential setting of 0.3C, as soon as the stat switches off, you then have to increase its SP by 0.3C to get it to switch in again, it will then switch off at its SP temperature but after a few cycles it will switch OFF/ON at SP +/-1.5C. Its FantiCosmi stat.

 

 

 

Edited October 24, 2023 by John Carroll

[JohnMo]

18 minutes ago, John Carroll said:

So, if it states on a stat that the differential is 0.5C does that differ from a stat that states its hysteresis is  0.5C or does it mean the same thing?

As far as I tell it's the same thing.