New Heat Pump Installation

[AnRam]

I have recently had an LG Therma V monoblock 16KW Heat Pump installed. It has been fitted with a Honeywell T3R thermostat. It appears this thermostat has a cycle 'feature'
When the room temperature is within 1.5 degrees of the demanded temperature the thermostat goes into a boiler cycle mode. In this mode it cycles the boiler on and off a preset number of times per hour. When installed, the setting was 6 which means the boiler is on for 5 mins then off for 5 mins (6 times/hour) On this heat pump this serves no purpose as the pump takes more than 5 mins to start hence power is wasted while running the circulating pump to no effect. If the thermostat cycle time is set to 1, as described in the installation booklet, then the boiler is on for 30 mins and off for 30. This at least allows the heat pump to start and run but due to the slow warm up has little effect before it is switched off again. I can see the cycle time might work for a gas or oil boiler to maintain a background heat level, but with a heat pump all it seems to do is waste energy!
When the room temperature is more than 1.5 degrees below the demanded temperature the thermostat switches on in the normal manner until the demanded temperature - 1.5 degrees is achieved.

In practice this means that the thermostat temperature has to be set 1.5 degrees above that desired as the cycling of the thermostat largely achieves nothing except wasting energy.
Has anybody any suggestions for a 'non cycling' programmable wireless thermostat or will the HP accept a modulating thermostat?
 

[IanR]

1 hour ago, AnRam said:

It has been fitted with a Honeywell T3R thermostat. It appears this thermostat has a cycle 'feature'
When the room temperature is within 1.5 degrees of the demanded temperature the thermostat goes into a boiler cycle mode. In this mode it cycles the boiler on and off a preset number of times per hour. When installed, the setting was 6 which means the boiler is on for 5 mins then off for 5 mins (6 times/hour) 

Really? It's an unsuitable thermostat for a Heat Pump then, since HPs should not be short-cycled, otherwise the compressors expire before they should. Keep it set to "1" until you've fully understood it, and replace if your analysis proves to be correct.

Setting it to 1.5 degrees higher than desired may get your house to the temp you want, but the HP is still cycling every 30 mins (which is not terrible occasionally, but that's not how you want it all the time).

 Is there any chance it's a "priority" thing? ie. the ASHP space heating is being disabled to allow the hot water cylinder to be recharged. Then, you would hope, if there's not a call to recharge the HWC, the ASHP will remain in space heating mode until the desired temp is reached.

[dpmiller]

Is there not a buffer tank?

[ProDave]

The manual is here https://livewell.honeywellhome.com/honeywell_wp/wp-content/uploads/Resideo_T3R_manual.pdf

 

It makes no mention of this "feature"

 

It says this on the Honeywell website

 

"

Energy Saving

Utilizes an advanced, self-learning algorithm for intelligent heating control, ensuring more efficient boiler control than ever before. Boiler plus compliant."

 

If it is some silly self learning function that you cannot turn off, I would just change it for an alternative "dumb" thermostat.

[Bramco]

10 minutes ago, ProDave said:

If it is some silly self learning function that you cannot turn off, I would just change it for an alternative "dumb" thermostat.

 

A lot of 'intelligent' thermostats are unsuitable unless you've got the right type of system.  The Nest thermostat was designed for the US market and I'd be surprised if the intelligence works with our systems.

 

But then, our heating regs make you put a central thermostat AND trvs on radiators.   So the radiators will slowly turn themselves down as the room gets up to temperature - but if the room where the central thermostat is gets too hot (sunny day) they might open up to accept more heat but it won't be forthcoming because the central one has turned the system off.  Madness.

 

Simon

[MJNewton]

9 hours ago, AnRam said:

It has been fitted with a Honeywell T3R thermostat. It appears this thermostat has a cycle 'feature'
 

 

Yes, and it is absolutely superb at providing pseudo-modulating demand functionality where only an on/off heat demand boiler input exists. When well below target temperature it'll run flat out ('100% demand') but as it nears/reaches the target it'll switch it a pulse width modulation to avoid overshoot such that if it calculates that it only require '80% demand') it'll apply a 80:20 on:off ration. With a cycle rate of 6 (times an hour) that means it'll call for heat for 8 minutes and remain off for 2 minutes, every 10 minutes. The cycle rate and minimum on time can be tweaked but only within certain limits. Great for gas boilers and gives rock solid temperatyre control but absolutely no use for heat pumps given what you've described regarding the futility of short burn times.

 

Many other 'intelligent' thermostats that aim to minimise/eliminate under/overshoot will operate in a similar way so if looking for an alternative avoid any that described some variation of TPI (Time Proportional & Integral) or Pulse Width Modulation etc.

Edited October 19, 2021 by MJNewton

[dpmiller]

^ yep, some have a choice of (IIRC) 6 or 10 cycles/hr.

[AnRam]

Thank you all for your comments. I am very concerned that my Heat Pump Supplier is providing this unsuitable type of Thermostat. I have asked them why, but have not had a response. I have thought out a simple 'defeat' mechanism for the existing thermostat which consists of a delay timer that has a delay slightly longer than the 'on' cycle time. (the cycle time can be set to 12/hr so the delay can be as short as 6 mins) The delay timer will switch on the heat pump so when the thermostat is more than 1.5 degrees below demanded temperature (on continuously) the HP will be run after 6 mins. Once the thermostat is within the 1.5 degree limit the delay timer will prevent the HP being run at all. To make this practical the thermostat will need to be set 1.5 degrees hotter than is actually required. A crude solution, but it will make more sense till I can fix it properly!

15 hours ago, ProDave said:

The manual is here https://livewell.honeywellhome.com/honeywell_wp/wp-content/uploads/Resideo_T3R_manual.pdf

 

It makes no mention of this "feature"

 

It says this on the Honeywell website

 

"

Energy Saving

Utilizes an advanced, self-learning algorithm for intelligent heating control, ensuring more efficient boiler control than ever before. Boiler plus compliant."

 

If it is some silly self learning function that you cannot turn off, I would just change it for an alternative "dumb" thermostat.

 

 In answer to your comment, ProDave, I agree that Honeywell make no useful reference to the 'feature' but if you look at the Quick Installation Guide under 4, Parameters, you will see listed a setting 2CR which is the cycle rate with no other information about its use! I have spoken to Honeywell who agree this feature exists and cannot be disabled. Helpful Huh!

 

I am amazed that professional installers appear not to be aware of this issue and that there is no obvious Heat Pump friendly thermostats. If anybody knows of a suitable Programmable, Wireless, 'Dumb' thermostat I would love to know. 

[MJNewton]

11 minutes ago, AnRam said:

I am amazed that professional installers appear not to be aware of this issue and that there is no obvious Heat Pump friendly thermostats. If anybody knows of a suitable Programmable, Wireless, 'Dumb' thermostat I would love to know. 

 

Are you after just a thermostat (temperature control only, timings dealt by a dedicated timer) or a programmer* (combined temperature and timing control allowing different temperatures for different times of day/night)? And wire or wireless?

 

*Which might nowadays sometimes go by the name of a smart thermostat if there is some form of app control too

Edited October 20, 2021 by MJNewton

[AnRam]

4 minutes ago, MJNewton said:

 

Are you after just a thermostat (temperature control only, timings dealt by a dedicated timer) or a programmer (combined temperature and timing control allowing different temperatures for different times of day/night)? And wire or wireless?

 

I would prefer a combined temperature and timing control, wireless device.

Thanks

[MJNewton]

13 minutes ago, AnRam said:

 

I would prefer a combined temperature and timing control, wireless device.

Thanks

 

Makes sense, and its a powerful combination.

 

Unfortunately I'm not in a position to make personal recommendations as I always use Honeywell (and they all (at least those I've had) have the TPI control that doesn't suit your needs). However, if I didn't want TPI I'd perhaps take a look at the Heatmiser neoAir v2-M Wireless Smart Thermostat with Two Channel Wireless Receiver - Heatmiser RF Switch as it implements a basic switching algorithm based around an adjustable differential e.g. if set to 1C then it'll switch on when at least 1C below target and off at target. It also has an 'output delay' setting to delay a call for heat for x minutes following being turned off. They do have 'smart' versions available to if you want app control and whatever features might also come with that (e.g. geofencing).

Edited October 20, 2021 by MJNewton

[AnRam]

Thanks MJNewton, I will take a look.

[dpmiller]

You might be sending the ASHP a demand signal, but surely it'll only be running based on water temperature anyway?

[AnRam]

On 21/10/2021 at 08:00, dpmiller said:

You might be sending the ASHP a demand signal, but surely it'll only be running based on water temperature anyway?

 

True, but the water temperature is always low because the pump is being cycled on and off, it never fully heats up

[dpmiller]

Did you say whether it's underfloor or rads?

[AnRam]

19 hours ago, dpmiller said:

Did you say whether it's underfloor or rads?

 

Rads

[AnRam]

On 20/10/2021 at 10:22, AnRam said:

I have thought out a simple 'defeat' mechanism for the existing thermostat which consists of a delay timer that has a delay slightly longer than the 'on' cycle time. (the cycle time can be set to 12/hr so the delay can be as short as 6 mins) The delay timer will switch on the heat pump so when the thermostat is more than 1.5 degrees below demanded temperature (on continuously) the HP will be run after 6 mins. Once the thermostat is within the 1.5 degree limit the delay timer will prevent the HP being run at all. To make this practical the thermostat will need to be set 1.5 degrees hotter than is actually required. A crude solution, but it will make more sense till I can fix it properly!

I have now fitted the delay timer as described above. It does what I require, but the thermostat effectively has no hysteresis, so is a little enthusiastic to turn the HP on and off to maintain an exact temperature. I am continuing to look at alternative thermostats.