UFH ASHP - Getting finer temp control

[Adam2]

I'm really happy with my system - Cool Energy ASHP, UFH in a liquid screed, 300L hot water tank, Salus auto-balancing actuators and Wunda controls.

 

All works as it should, running at about 35 degrees on the UFH.

 

My only issue is the Wunda controls. I have the control units (x10 - it's a big house) in my plant room and temp sensors in the walls with a mesh type wall mounted panel. I've calibrated the Wunda controllers so they are pretty accurate to room temp. BUT, the control units have a min temp trigger 0.5 degrees above / below target temp. So this means if target is 22 degrees, the actuator(s) will be opened/pumps triggered at 21.5 degrees and stay this way until 22.5 - this doesn't sound bad but the reality is that the temp will then carry on increasing for at least another 0.5-1 degree due to the continuing heat coming from the screed.

 

What are the best options? Things I can think of:

 

1) Replace all (or some) controllers with more sensitive ones. Ideally just cutting out at the target temp would be a big improvement

 

2) Use a lower UFH temp, the Wunda provided manifold I don't think goes much below 35 degrees

 

3) Anyway to get my Wunda controllers to stop heating at the target temp and not go on for another 0.5 degrees

 

Nothing sounds cheap or easy apart from 3 but that may not be possible

 

 

 

 

[dpmiller]

put a calibration  offset on the stat so it reads a wee bit high might help

 

or if it's happening in all the rooms, reduce the flow temperature a degree or two yes. Is the heatpump controlling on flow or return btw? And what DeltaT is the heatpump seeing?

[joth]

7 hours ago, Adam2 said:

2) Use a lower UFH temp, the Wunda provided manifold I don't think goes much below 35 degrees

Does the cool energy ASHP have any control over it's flow temperature?

Ideally you want load compensation: turn down the flow temp as the building temperature starts to approach target. 

This way the manifold is just a safety backstop rather than being the main control of UFH loops, and you might squeeze a better cop out of the ASHP too

[dpmiller]

@joth Yes we can set variable flow or return temps, schedule temperature changes by time, run WC, choose the DeltaT etc etc. That's why I queried whether the OP was in flow or return control and what the PWM pump was up to...

 

the CE inverter pumps might be "cheaper" than the big brand stuff, but lack none of the functionality.

[Adam2]

HI thanks for comments @joth @dpmiller

 

I should have maybe said the ASHP feeds a buffer. We have 4 manifolds, 1 per floor (we're on a hill), flooring is all porcelain laid on 55mm liquid screed with insulation beneath (pretty standard)

ASHP set temp is 40 and it starts to heat (from memory) when buffer temp drops to 36 and stops at something like 43 - it was a bit arbitrary choosing the range 

The manifold for the largest floor was at 35 but I put down to the lowest on the blender which looks like 30 but is not marked - I guess as they lose accuracy maybe that low

 

Increasing the temp slightly on the thermostat doesn't really help I think as the issue with the thermostat is that it triggers a call for heat when 0.5 below target temp and only stops when 0.5 above target temp which doesn't sound like it should be an issue but to fine tune things I'd rather have it stop sooner. By lowering the temp at the manifold

 

May experiment next week with the ASHP temp being set to 30 (with something like a range of 26 to 34) - I suppose an issue then may be that by the time a thermostat calls for heat it will then take somewhat longer for the eventual temp change but maybe that won't be noticable.

 

[Conor]

I run mine totally differently and it works well. Flow temp set to 35c (with weather comp) to a 60l buffer. Feeds three manifolds, and 6-8 loops per manifold. Flow rates set as required. No individual room stats or actuators. Each manifold is it's own zone with single stat. No blending valves are need with a low temp setup. Works well. 

 

[dpmiller]

@Adam2 so have you the probe in the buffer tank, and you're controlling the heat pump on it, and the UFH is completely separate?

 

Are you using the time and temp scheduling, and what fan mode are you in?

 

I'd tighten the temperature difference setting a little so there's less chance of the flow going cooler than optimal, and make sure there's a bit of overshoot (this is the area where there is most modulation- it ramps down approaching setpoint, and then ramps down further in an attempt to keep the unit on and running even tho you've achieved temperature...

[Adam2]

@dpmiller yes the ashp only "sees" the buffer and the temp from that goes to the control module.

 

No time/temp based scheduling - my thinking in a well insulated fairly air-tight house was to pretty much always be at 22 degrees but it could be interesting to reconsider this by having the unit off overnight when it is coldest and on say 5am so when we get up there will be warm floors. Could be quicker to do this on the ashp vs changing all the thermostats

 

Fan mode is low speed

 

OK thanks have made some tweaks to the temp settings

[dpmiller]

1 hour ago, Adam2 said:

Fan mode is low speed

 

 

careful... that means weather compensation is turned on so your setpoint will be all over the place, also you may not get full power when you want it. You might try setting it to high speed to begin with until you get a feel for how the system responds and can tune the WC in.

[Adam2]

Ahhh thanks @dpmiller I was going to investigate why that was the case 🙂

 

Is there some additional manual that has this kind of info as I can see a lot of settings on the app under UserMask that are hard to interpret the meaning of?

 

Also, is there any need to get the password for other settings to be adjusted?

Edited February 3, 2023 by Adam2
pressed save too early

[dpmiller]

There's a bit more description of some things in the "original" manual, see attached. The installer password will let you make a real mess of things if you want, but you should be able to do 95% of what you need in user and timezone masks.

I find the scheduler is good, you can have it on 24/7 but use temperature changes to "prioritise" heating, if you will...

 

 

sprsun-user-manual-for-dc-inverter.pdf

[Conor]

12 minutes ago, dpmiller said:

There's a bit more description of some things in the "original" manual, see attached. The installer password will let you make a real mess of things if you want, but you should be able to do 95% of what you need in user and timezone masks.

I find the scheduler is good, you can have it on 24/7 but use temperature changes to "prioritise" heating, if you will...

 

 

sprsun-user-manual-for-dc-inverter.pdf 1.87 MB · 0 downloads

 

9 months after installing mine, this is the first time I've looked at the manual!  

[Bramco]

24 minutes ago, dpmiller said:

There's a bit more description of some things in the "original" manual, see attached. The installer password will let you make a real mess of things if you want, but you should be able to do 95% of what you need in user and timezone masks.

I find the scheduler is good, you can have it on 24/7 but use temperature changes to "prioritise" heating, if you will...

 

 

sprsun-user-manual-for-dc-inverter.pdf 1.87 MB · 1 download

That looks like the manual that can be downloaded from their web page.

 

Also, what's the installer password - that's something I've not been able to get out of them...

 

Simon

[dpmiller]

5 minutes ago, Bramco said:

Also, what's the installer password

there are two that I know of- one for the Carel display, and one within the App. Send me a PM if there's something you think you need to change in the nether...

[Bramco]

We run ours differently as well.  And our system is slightly different - a larger buffer tank and no auto-balancing actuators (there's a recent thread on whether these are actually useful for ASHPs with UFH).

 

The other main difference is that our UFH loops are incorporated in the insulated slab - so probably our system is slower to heat up and cool down than UFH in screed.

 

We have 12 loops and 3 zones with Tado thermostats - and just like you @Adam2 the thermostats tend to cycle on and off which means the ASHP cycles too much.

 

We've solved this more by chance than good management.  We're on Octopus Go, so we scheduled the thermostats to 22 degs from 00:30 to 04:30 on the 7p tariff.  This was fine in the autumn and I could see from some monitoring of the various temperatures that the ASHP runs continuously for 4 hours and the slab is loaded with heat.  As things got colder, I added another scheduled period from 15:00 to 19:00 again at 22 deg.  This didn't cause cycling most of the time - the exceptions were on sunny days where we get a lot of heat into the house from the large south facing windows.   Obviously also, when it's really cold the HP goes through it's defrost cycles, so doesn't run continuously.   When the thermostats aren't scheduled for 22 degs, they're in frost protection, so no chance that there will be a call for heat.  I should add that we use solar PV and the 7p tariff for DHW, so the ASHP is on Heating only.

 

So basically, we've almost got round the fact that the thermostats are less than ideal with a HP through scheduling things.  I would really like though to have a much wider window between the call for heat and the thermostats saying they are up to heat.

 

One idea from another forum would be to use the wiring to the thermostats as the wiring for DS18B20 temperature sensors hooked up to a suitable microcontroller and have that switch the call for heat to the wiring centre.   It could even be done with wireless temperature sensors like the Sonoff ones (there are plenty of other makes) which are pretty cheap.  Obviously this isn't an off the shelf solution but should be quite easy to implement.

 

Simon

 

 

[Bramco]

On 01/02/2023 at 23:45, Adam2 said:

What are the best options? Things I can think of:

 

1) Replace all (or some) controllers with more sensitive ones. Ideally just cutting out at the target temp would be a big improvement

 

2) Use a lower UFH temp, the Wunda provided manifold I don't think goes much below 35 degrees

 

3) Anyway to get my Wunda controllers to stop heating at the target temp and not go on for another 0.5 degrees

 

Nothing sounds cheap or easy apart from 3 but that may not be possible

 

Another option Adam that I've considered is to add a delay timer into the thermostat circuits. These are the kind of things that keep a bathroom fan running when you've turned off the light.

 

Although we've mostly overcome the cycling caused by the thermostats turning on and off too much/quickly with the way we're scheduling them if we had a delay time in the circuit, then it would prevent the call for heat being switched off by the thermostat after a few minutes.   For your situation, you could maybe lower the target temperature  and make sure with the delay that the ASHP runs for at least say 30 minutes.  So ensuring the HP runs more efficiently.

 

Simon

[ProDave]

On 01/02/2023 at 23:45, Adam2 said:

BUT, the control units have a min temp trigger 0.5 degrees above / below target temp. So this means if target is 22 degrees, the actuator(s) will be opened/pumps triggered at 21.5 degrees and stay this way until 22.5 - this doesn't sound bad but the reality is that the temp will then carry on increasing for at least another 0.5-1 degree due to the continuing heat coming from the screed.

This is a symptom of the UFH being too hot so the room is warming too quickly, and the excess heat in the slab continues warming the room.

 

If you have reached they physical stop on the blending valve and it won't go any lower, try removing the knob and seeing if the splined shaft will rotate a little more beyond what the stop (usually part of the knob mechanism) will allow to get the temperature lower.

[dpmiller]

33 minutes ago, Bramco said:

Although we've mostly overcome the cycling caused by the thermostats turning on and off too much/quickly with the way we're scheduling them if we had a delay time in the circuit, then it would prevent the call for heat being switched off by the thermostat after a few minutes.   For your situation, you could maybe lower the target temperature  and make sure with the delay that the ASHP runs for at least say 30 minutes.  So ensuring the HP runs more efficiently.

  worth noting that the minimum cycle times on, and off, are configurable in the installer menu and if you ensure there's plenty of turn off overshoot, then you can have a gently tailing off heating period each time. Or you could try playing with the PID settings...

[Adam2]

great thanks, so much useful info

 

Yes I do have the regular manual - only query was the existence of something else that would, for example, have explained that putting the fan mode into Low Speed would have an impact on the temp setpoints as this is not logical (to me at least)

 

Have changed fan mode to Day and brought down the heating set point and increased the overshoot as suggested. Essentially the blending valves won't be doing much unless there's an issue with the ashp overheating the buffer

 

With the buffer tank and my smallest zone being 35m then I don't think we have a high probability for any short-cycle issue but not sure how to easily monitor that aside from watching what happens on the app for a while

[Bramco]

6 hours ago, dpmiller said:

worth noting that the minimum cycle times on, and off, are configurable in the installer menu and if you ensure there's plenty of turn off overshoot, then you can have a gently tailing off heating period each time. Or you could try playing with the PID settings...

Thanks - will look into this to see if I can force longer runs on the odd occasion that the thermostats take over control!

 

Simon

[JohnMo]

10 hours ago, Bramco said:

would really like though to have a much wider window between the call for heat and the thermostats saying they are up to heat

Turn down the flow temp of your heat pump? Better CoP at the same time

[HughF]

Ideally you’d ditch the buffer and allow the heat pump to run direct into the ufh circuit, gaining considerable efficiency there. The industry is moving away from the buffer/llh/plate installation scheme and moving towards direct installations, as a drive to increase efficiency. Plenty of articles from Brendon Uys on LinkedIn about this (and the renewable heating forum)

 

You then wouldn’t have a disconnect between the heat generator and the heat consumer. The issue now present is that unfortunately the Cool Energy unit doesn’t have any idea of room temperature and thus cannot do load compensation.

 

You could however use the room stats to drive the call-for-heat input on the heat pump, and use them as hi-limit stats. Once the weather comp is set correctly then the internal Temperature should stay consistent. The high limit stats would take care of any solar gain.
 

Remember, not many heat pumps actually have load compensation, for some reason. LG and Mitsubishi are the only two that I remember.

 

tl;dr - your weather comp is set too high.

 

[HughF]

As an aside, I’ve been leaning on the developers of Homely ( a smart temperature controller for heat pumps) to try and get them to add support for the modbus registers in the Cool Energy/SPRSUN units. Then you could have automatic weather comp tuning and load compensation.

 

They haven’t got back to me yet so I might knock something up myself.

[markocosic]

Why not use slab temperature control instead of air temperature control?

 

Output from slab is proportional to difference between floor temp and air temp.

 

Compensate the slab temperature proportionally to the weather above the desired setpoint.

 

You should be able to do this by weather compensating the heat pump output down BUT might find that this isn't discriminating enough between rooms.

 

Air temperature based control is always going to fail on a high mass slab I think.

[HughF]

An update on the high-mass slab…. I pump 27 degree flow around it for 18hrs a day at 3ltrs/min, the house stays at 21 ish, all good. The ufh pump is on a plug top at the moment, the heatpump scheduler turns the ashp on at 05:00 and off at 23:30. I’m running without a thermostat.

 

Will add a timeclock to the ufh pump so I have some sort of automatic control.