UFH - EvoHome and reluctant plumber

[kevinsmart]

I think the key difference is that I am only heating our UFH zone in the evening. In an experiment, running 24/7, Evohome could maintain a stable temperature when the set point was set to the current temperature.

It doesn’t matter if the temperature differential is 3 degrees or only 0.5 degrees when heating starts, by 9pm when optimum stop kicks in the zone is 1 degree above the set point.

[mtmcgavock]

I think the key difference is that I am only heating our UFH zone in the evening. In an experiment, running 24/7, Evohome could maintain a stable temperature when the set point was set to the current temperature.

It doesn’t matter if the temperature differential is 3 degrees or only 0.5 degrees when heating starts, by 9pm when optimum stop kicks in the zone is 1 degree above the set point.

Why are you only running it in the evening? You aren't meant to run UFH for short periods otherwise you won't get the correct heat out of it. In effect you are heating a big surface area that holds it's heat. Heating it for short periods you are never going to get the correct temperatures. You can't operate it like radiators.

[kevinsmart]

Why are you only running it in the evening? You aren't meant to run UFH for short periods otherwise you won't get the correct heat out of it. In effect you are heating a big surface area that holds it's heat. Heating it for short periods you are never going to get the correct temperatures. You can't operate it like radiators.

I don’t see that as the issue. Evohome should be able to balance any heat loss for any zone when the set point is reached. As it stands, at set point, the zone still has a 50% heating demand leading to the overshoot. At 1 degree over there is still a 20% demand, which doesn’t make sense considering the heat retention. It should learn that much less energy is needed when the room is up to temperature, but it isn’t doing a good job and is wasting energy.

I expected much better temperature control from Evohome. It copes well with HR92 zones, but is unable to adapt to my UFH zone. I could program a Raspberry Pi to do a better job. 😀

[Neamac]

Hope you don't mind me carrying on with the BDR91 vs HCC80 theme. I am about to add UFH to my existing Evohome system that has 11 Rads with HR92s fitted and it works well. I have a 4 port manifold for UFH for a kitchen and utility room, 3 pipe runs for kitchen (72m, 80m, 81m) & Utility 67m. I was thinking about using 1 BDR91 running the 4 ports as 1 zone with a UFH pump and a mixer valve. There is no motorized zone valve or actuators other than manual adjuster on the manifold.
If I wired the BDR to switch on the UFH pump for all the ports on the manifold and control the temperature with a Y87RF thermostat would this work ok? Thanks in advance - I hope I haven't hijacked the thread!

[kevinsmart]

I have a single zone twin loop UFH setup controlled via Y87RF and BDR91 in my new well insulated extension. BDR91 activates the pump and manifold valves are left open.

As it’s in combination with 26 rads, there is a thermostatic mixing valve to reduce the flow temperature. Boiler is Intergas HRE40 SB with OpenTherm module, and an outdoor sensor (unfortunately weather compensation doesn’t work with Evohome OpenTherm support though).

I’m not happy with the UFH setup for a few reasons:

1. The mixing valve intermittently emits a high pitched whine, appears to be when the flow temperature matches its set point.
2. Wife complains about 1!
3. Poor temperature control. Evohome indicates a 40-60% demand for the zone even when the set point is reached, as a result there is an overshoot. Optimum start typically pre-heats for 1.5 hours, temperature increases to more than 1 degree above the set point after a few more hours, still with <20% demand, then optimum stop kicks in 1 hour before set back. I’ve tried reducing the mixing valve set point temperature but Evohome seems unable to adapt.

Primarily because of 2, I’m going to replace with an HM80 controlled rotary actuator and flow temperature sensor. I hope this will work better with OpenTherm and provide more accurate temperature control.

It took a while (largely due to lack of support for this in the UK) but I now have the HM80 controlled solution for my single-zone UFH in place. And it works great, I no longer see the 1 degree overshoot, the set temperature is reached and maintained within around 0.1 degrees over several hours.

It's entertaining watching the controller make quiet regular small adjustments to the rotary valve to maintain temperature.

One interesting observation was this freezing morning with a 15C setback temperature and 15.5C measured temperature, the controller decided to run the pump, with Evohome indicating a 0% heating demand (but other zones heating). This appeared to stop further heat loss in the zone.

[kimber.kimber]

Hope you don’t mind me piggy backing on this, but I have wet UFH as a single zone, two loops controlled using a zone valve set up. It’s in conjunction with the rest of the house on radiators. The system runs on optimum start.

My question is about scheduling. With the temp drop over the last few days, it’s taken a while on warm up. Normal temp is 20degs, with a setback to 17degs when we’re not using the room. Last night it didn’t hit its set temp, only getting to 19degs.

Is it best to have the schedule adjusted to get this the sole priority when warming up? My feeling is that it shouldn’t matter as the water temps are significantly lower than to the rest of the system. Or do you think it’s the optimum start that’s causing the issue, because of the large lag with the heat cycle?

Cheers,

Ian

[kevinsmart]

Hope you don’t mind me piggy backing on this, but I have wet UFH as a single zone, two loops controlled using a zone valve set up. It’s in conjunction with the rest of the house on radiators. The system runs on optimum start.

My question is about scheduling. With the temp drop over the last few days, it’s taken a while on warm up. Normal temp is 20degs, with a setback to 17degs when we’re not using the room. Last night it didn’t hit its set temp, only getting to 19degs.

Is it best to have the schedule adjusted to get this the sole priority when warming up? My feeling is that it shouldn’t matter as the water temps are significantly lower than to the rest of the system. Or do you think it’s the optimum start that’s causing the issue, because of the large lag with the heat cycle?

Cheers,

Ian

Ian, you can configure how many hours optimum start will pre-heat, maybe you need to increase that parameter.

[kimber.kimber]

Ian, you can configure how many hours optimum start will pre-heat, maybe you need to increase that parameter.

Thanks Kevin, I had forgotten about that. I'll see how it goes over the next couple of days and adjust that if required.

I'm assuming even when you add a new zone, the learning still takes place, and it is continually learning, taking into account the conditions?

[kevinsmart]

I'm assuming even when you add a new zone, the learning still takes place, and it is continually learning, taking into account the conditions?

Yes, that should be the case.

[BuxtonJim]

I started out with my wet UFH plumbed into a radiator circuit but was never completely happy with its controllability. I know in theory that it should be independent and fine if all rads have HR92s fitted, it seems to behave perfectly now it's plumbed back directly to the boiler. Temperatures are maintained to +/- 0.5 and optimum start and stop set to 1hr work really well. The ufh zone is flagged so there's real opportunity for overshoot but the optimised stop seems to handle this.