The Efficient Home Forum

Hi,

I have a air source heat pump, downstairs is all underfloor heating and controlled by individual room thermostats. I am happy with this setup and can control this centrally (although not a Honeywell system). For hot water I have a simple honeywell st9100c controller and a schedule with an over ride option, again no plans to upgrade this (unless the proposed system could replace it).

Upstairs is where I would like to focus my efforts! I have 8 radiators, all in a single zone with a Honeywell CM707 controlling it, this is located on the landing and the landing radiator is the only one without a TRV. My proposal at the moment is to replace the TRVs on the radiators with smart ones, however, I am not sure what to do about the 707, presumably this is what "calls for heat" for the whole of the upstairs?

At the moment I think I have a few options,

- replace the 707 with something that can be called by any of the smart TRVs (and add a smart TRV to the landing rad)
- replace the 707 with a smart room thermostat, allow the TRVs to call for heat and not add a TRV to the landing rad
- setup a schedule on the existing 707 and only allow the TRVs to call for heat during this time
- replace the 707 with a smart switch / relay and get the smart TRVs to switch the heat circuit on when they need heat

Is there anything else I could do? What products would I need to create this setup? What (if anything) is a direct replacement for the CM707.

At the moment I am leaning towards option 4... It seems to be the simplest solution?

The second you mentioned an ASHP and wanting to 'micro-zone' (as some installers are calling it), it brings me to want to discuss this fully but sadly without the time in the day to do so.

In a nut shell, gas and oil boilers are very different from an ASHP and you have to be really careful with the design of the ASHP system to cope with this situation. ASHP's require much larger flow rates and if you start hindering this flow rate (essentially by the use of smart TRV's on all radiators), you can dramatically affect the efficiency of the ASHP.

More on this can be found here (https://youtu.be/zpTVIeUh04E).

I'm not saying its not possible, you just have to invest in the design to make this situation work.

Hi @Evohomeshop

I have installed a Daikin ASHP (Daikin R32 16kW low temperature hydro-split) of late and am awaiting its commissioning.
From your experience, is it possible to use the Evohome controller to control the system? I am open to managing it in whatever way possible but would like to understand what hardware changes I might require.
I have 6 UFH zones downstairs and can maintain all of these on the same schedules/dropbacks etc.
I have 5 * HR924UK upstairs, all of these rooms are in use so again, wouldn't look to tinker too much with this.

The current list of hardware is as follows:
HR924UK
ATP921R3100
HCC80R
T87RF2033
HR92UK
ATF500DHW

Can you please advise if I need to add anything to enable the compatibility of Evohome with ASHP?
Do you know of any guidance available, here or elsewhere, on how Evohome can/should be set up with ASHP. I have been running Evohome for 4/5 years now with OFH and have been extremely happy with its performance so would prefer to hot have to discard it at this point if possible.

Thanks
Ken

kenm wrote:Hi @Evohomeshop

I have installed a Daikin ASHP (Daikin R32 16kW low temperature hydro-split) of late and am awaiting its commissioning.
From your experience, is it possible to use the Evohome controller to control the system? I am open to managing it in whatever way possible but would like to understand what hardware changes I might require.
I have 6 UFH zones downstairs and can maintain all of these on the same schedules/dropbacks etc.
I have 5 * HR924UK upstairs, all of these rooms are in use so again, wouldn't look to tinker too much with this.

The current list of hardware is as follows:
HR924UK
ATP921R3100
HCC80R
T87RF2033
HR92UK
ATF500DHW

Can you please advise if I need to add anything to enable the compatibility of Evohome with ASHP?
Do you know of any guidance available, here or elsewhere, on how Evohome can/should be set up with ASHP. I have been running Evohome for 4/5 years now with OFH and have been extremely happy with its performance so would prefer to hot have to discard it at this point if possible.

Thanks
Ken

Hi Ken,

Firstly only ATC928G3000 models with minimum 19.33 firmware and a BDR91T (https://theevohomeshop.co.uk/product/ho ... dr91t1004/) can handle any kind of 'Heat Pump' control. The cycle rate for heat pumps must be set to 1 cycle per hour and minimum on time set as long as possible. A 16kW heat pump running at DT5 would need a system capable of flowing 2742 litres per hour, so I really hope your heating installer has done the maths correctly!?!

Thanks @evohomeshop for your response.
Apologies for the delayed reply, I have only finally had my space heating commissioned within the past 2 weeks as I had difficulty getting the plumber back to complete.

Just wanted to clarify one point, I have a buffer tank within my system, does this negate the need for a BDR91T? Also, application firmware is currently 02.00.17.03, does that need to be updated to handle my system setup? I have contacted Resideo to see if they can push the most recent update to my ATC928G3000 in any case.
I currently have the BDR91A set to 3 cycle per hour and minimum on time of 5 minutes.
Heat pump was commissioned with a DT of 8c so not sure what flow rates should be for this but assuming it was considered and calculated correctly.

Thanks
Ken