Honeywell Evohome and ASHP
Discussion
Currently got an Evohome setup with a heating-only system oil boiler. No diverter valve, so the Evohome boiler relay just switches the boiler mains supply on and off. Vented immersion is completely separate.
The oil system needs replacing, so we are going for an ASHP for the same price. Mitsubishi EcoDan, plus an unvented hot water system.
Any ideas how to get the Evohome system working to control the ASHP?
I appreciate that the ASHP will need to run for longer periods, but I'd still like to have the individual room/zone temperature control that Evohome allows - lower temps in some rooms when not in use, overnight setback, etc.
We don't use much hot water (electric showers, no bath), so I'm happy to just heat the tank on a simple timer overnight.
The oil system needs replacing, so we are going for an ASHP for the same price. Mitsubishi EcoDan, plus an unvented hot water system.
Any ideas how to get the Evohome system working to control the ASHP?
I appreciate that the ASHP will need to run for longer periods, but I'd still like to have the individual room/zone temperature control that Evohome allows - lower temps in some rooms when not in use, overnight setback, etc.
We don't use much hot water (electric showers, no bath), so I'm happy to just heat the tank on a simple timer overnight.
"Do not use the evohome controller to call for heat from the heat pump. The "call for heat" output of the BDR goes nowhere (bear with me).
Instead, Use the heat pumps own controller / thermostat, placed in a suitable living space. make sure that this will be calling for heat 99% of the time. (thus you don't need the BDR to activate the HP).
Take the TRV heads off ALL the radiators in the downstairs rooms, and the circulation spaces. So they are always on.
The same with your UFH, run it always on.
Leave the TRV heads on in the bedrooms if you prefer cooler rooms for sleeping. Use the evohome controller only to set those as you require.
Tune the flow temperature (via the weather compensation settings), and balance the radiators (and UFH flow rates), so that all rooms stay at a stable comfort temperature all the time. This will take a LOT of iterations and is where the hard work is (but also the reward - get it right you get a stable efficient system).
(doesn't relate directly to evohome) Install something that monitors in real time your heat pumps usage and gives historical tracking. It will really help you with seeing the effect of any tuning you do. plenty of discussion on this on other threads (I don't know what daikin has natively)
as for weather comp : 45c@0c and 35c@15c vs 43c@-10c and 25c@15c . the former implies a higher water temp for the same outdoor temp. Its just a line on a graph, fairly easy to understand if you draw it. The former will therefore use more energy. you want to have your weather comp set to the lowest possible water temp, that keeps your house at a constant temperature with all the radiators on and the heat pump running at a steady output (ref point 6)."
https://renewableheatinghub.co.uk/forums/renewable...
Instead, Use the heat pumps own controller / thermostat, placed in a suitable living space. make sure that this will be calling for heat 99% of the time. (thus you don't need the BDR to activate the HP).
Take the TRV heads off ALL the radiators in the downstairs rooms, and the circulation spaces. So they are always on.
The same with your UFH, run it always on.
Leave the TRV heads on in the bedrooms if you prefer cooler rooms for sleeping. Use the evohome controller only to set those as you require.
Tune the flow temperature (via the weather compensation settings), and balance the radiators (and UFH flow rates), so that all rooms stay at a stable comfort temperature all the time. This will take a LOT of iterations and is where the hard work is (but also the reward - get it right you get a stable efficient system).
(doesn't relate directly to evohome) Install something that monitors in real time your heat pumps usage and gives historical tracking. It will really help you with seeing the effect of any tuning you do. plenty of discussion on this on other threads (I don't know what daikin has natively)
as for weather comp : 45c@0c and 35c@15c vs 43c@-10c and 25c@15c . the former implies a higher water temp for the same outdoor temp. Its just a line on a graph, fairly easy to understand if you draw it. The former will therefore use more energy. you want to have your weather comp set to the lowest possible water temp, that keeps your house at a constant temperature with all the radiators on and the heat pump running at a steady output (ref point 6)."
https://renewableheatinghub.co.uk/forums/renewable...
dmsims said:
"Do not use the evohome controller to call for heat from the heat pump. The "call for heat" output of the BDR goes nowhere (bear with me).
Instead, Use the heat pumps own controller / thermostat, placed in a suitable living space. make sure that this will be calling for heat 99% of the time. (thus you don't need the BDR to activate the HP).
Take the TRV heads off ALL the radiators in the downstairs rooms, and the circulation spaces. So they are always on.
The same with your UFH, run it always on.
Leave the TRV heads on in the bedrooms if you prefer cooler rooms for sleeping. Use the evohome controller only to set those as you require.
Tune the flow temperature (via the weather compensation settings), and balance the radiators (and UFH flow rates), so that all rooms stay at a stable comfort temperature all the time. This will take a LOT of iterations and is where the hard work is (but also the reward - get it right you get a stable efficient system).
(doesn't relate directly to evohome) Install something that monitors in real time your heat pumps usage and gives historical tracking. It will really help you with seeing the effect of any tuning you do. plenty of discussion on this on other threads (I don't know what daikin has natively)
as for weather comp : 45c@0c and 35c@15c vs 43c@-10c and 25c@15c . the former implies a higher water temp for the same outdoor temp. Its just a line on a graph, fairly easy to understand if you draw it. The former will therefore use more energy. you want to have your weather comp set to the lowest possible water temp, that keeps your house at a constant temperature with all the radiators on and the heat pump running at a steady output (ref point 6)."
https://renewableheatinghub.co.uk/forums/renewable...
That makes sense, I think.Instead, Use the heat pumps own controller / thermostat, placed in a suitable living space. make sure that this will be calling for heat 99% of the time. (thus you don't need the BDR to activate the HP).
Take the TRV heads off ALL the radiators in the downstairs rooms, and the circulation spaces. So they are always on.
The same with your UFH, run it always on.
Leave the TRV heads on in the bedrooms if you prefer cooler rooms for sleeping. Use the evohome controller only to set those as you require.
Tune the flow temperature (via the weather compensation settings), and balance the radiators (and UFH flow rates), so that all rooms stay at a stable comfort temperature all the time. This will take a LOT of iterations and is where the hard work is (but also the reward - get it right you get a stable efficient system).
(doesn't relate directly to evohome) Install something that monitors in real time your heat pumps usage and gives historical tracking. It will really help you with seeing the effect of any tuning you do. plenty of discussion on this on other threads (I don't know what daikin has natively)
as for weather comp : 45c@0c and 35c@15c vs 43c@-10c and 25c@15c . the former implies a higher water temp for the same outdoor temp. Its just a line on a graph, fairly easy to understand if you draw it. The former will therefore use more energy. you want to have your weather comp set to the lowest possible water temp, that keeps your house at a constant temperature with all the radiators on and the heat pump running at a steady output (ref point 6)."
https://renewableheatinghub.co.uk/forums/renewable...
Basically use the heat pump's own control system to set the base line temperatures in the main living areas, with a smaller overnight setback to minimise the morning warm-up time.
Makes sense to use off-peak rates to keep the system ticking over.
Leave the boiler relay powered, but don't physically connect it to the boiler.
Use the Evohome setup purely to control the radiator valves in the bedrooms and the lounge, maybe the main bathroom too, where heating is only really needed in the evening.
No need for Evohome to "call for heat", as the ASHP is already running to keep the common areas warm.
The Evohome gear will just be used as fancy TRVs.
Does that sound right?
Presumably the unvented water system will have its own controls, so it will only heat up during the off-peak period (Octopus Go)? Our immersion heater currently just runs for an hour overnight. Gives us enough hot water for the day.
Apparently the latest Evohome firmware allows you to bind a BDR91T (boiler relay) as a heat pump - allowing much longer cycle settings than you get with the standard BDR91
https://www.bolasystems.com/wireless-relay-unit-ho...
“ The Honeywell Home BDR91T Wireless Relay Box is the new 2021 updated BDR91 that allows extra functionality for the control of heat pumps when paired to the Honeywell Home evohome Controller. This is denoted by the house symbol on the front cover (BDR91’s without the house symbol cannot control heat pumps)”
https://www.bolasystems.com/wireless-relay-unit-ho...
“ The Honeywell Home BDR91T Wireless Relay Box is the new 2021 updated BDR91 that allows extra functionality for the control of heat pumps when paired to the Honeywell Home evohome Controller. This is denoted by the house symbol on the front cover (BDR91’s without the house symbol cannot control heat pumps)”
Edited by essayer on Tuesday 19th November 21:03
essayer said:
Apparently the latest Evohome firmware allows you to bind a BDR91T (boiler relay) as a heat pump - allowing much longer cycle settings than you get with the standard BDR91
https://www.bolasystems.com/wireless-relay-unit-ho...
“ The Honeywell Home BDR91T Wireless Relay Box is the new 2021 updated BDR91 that allows extra functionality for the control of heat pumps when paired to the Honeywell Home evohome Controller. This is denoted by the house symbol on the front cover (BDR91’s without the house symbol cannot control heat pumps)”
I saw the updated BDR91T. Seen quite a few posts about it apparently not working - minimum cycle still showing as "3". https://www.bolasystems.com/wireless-relay-unit-ho...
“ The Honeywell Home BDR91T Wireless Relay Box is the new 2021 updated BDR91 that allows extra functionality for the control of heat pumps when paired to the Honeywell Home evohome Controller. This is denoted by the house symbol on the front cover (BDR91’s without the house symbol cannot control heat pumps)”
Edited by essayer on Tuesday 19th November 21:03
I think I'll try just using the Evohome to control some of the TRVs, leaving the ASHP controls to call for heat.
Presumably it's OK to use normal "dumb" TRVs with a heat pump - just have to leave more of the heating circuit "open" than with a normal boiler?
We don't have UFH, just radiators.
ASHP installation is going live today. Plumbing is all done, electrician is finishing off and commissioning this afternoon.
He is going to fit the Honeywell boiler relay, rather than the Mitsubishi wireless stat and receiver. He assures me that it will all be fine - as long as I leave a couple of the rads "open".
Apparently it was an issue a few years ago, but they have got around it by fitting a "low loss header" on new installations. Acts as a bypass, so the heatpump doesn't throw up circulation errors if all the rads are closed.
Not exactly sure how it works, but it's a length of 38mm copper pipe with several connections, a second 2 port valve, and a second pump.
He is going to fit the Honeywell boiler relay, rather than the Mitsubishi wireless stat and receiver. He assures me that it will all be fine - as long as I leave a couple of the rads "open".
Apparently it was an issue a few years ago, but they have got around it by fitting a "low loss header" on new installations. Acts as a bypass, so the heatpump doesn't throw up circulation errors if all the rads are closed.
Not exactly sure how it works, but it's a length of 38mm copper pipe with several connections, a second 2 port valve, and a second pump.
clockworks said:
ASHP installation is going live today. Plumbing is all done, electrician is finishing off and commissioning this afternoon.
He is going to fit the Honeywell boiler relay, rather than the Mitsubishi wireless stat and receiver. He assures me that it will all be fine - as long as I leave a couple of the rads "open".
Apparently it was an issue a few years ago, but they have got around it by fitting a "low loss header" on new installations. Acts as a bypass, so the heatpump doesn't throw up circulation errors if all the rads are closed.
Not exactly sure how it works, but it's a length of 38mm copper pipe with several connections, a second 2 port valve, and a second pump.
How have you got on for the past few weeks? We are in exactly the same position, old oil boiler, invented system etc and considering an ashp....would love to know your experience? If you've got an old slightly drafty house that would be even better 😀He is going to fit the Honeywell boiler relay, rather than the Mitsubishi wireless stat and receiver. He assures me that it will all be fine - as long as I leave a couple of the rads "open".
Apparently it was an issue a few years ago, but they have got around it by fitting a "low loss header" on new installations. Acts as a bypass, so the heatpump doesn't throw up circulation errors if all the rads are closed.
Not exactly sure how it works, but it's a length of 38mm copper pipe with several connections, a second 2 port valve, and a second pump.
PugwasHDJ80 said:
How have you got on for the past few weeks? We are in exactly the same position, old oil boiler, invented system etc and considering an ashp....would love to know your experience? If you've got an old slightly drafty house that would be even better ??
Apart from a leak on "day 2" (failed solder joint on a drain point), it has all gone pretty smoothly.We did have issues with cold spots on some of the radiators. Turned out to be the old water/inhibitor mixture not mixing with the new water/glycol mixture.
Glycol mix is heavier than water, so it can remain "stratified" in the radiator. The glycol circulates and gets hot, the old water just stays there, cold.
Took a fair bit of time to bleed off the old water.
Although the system was all working by day 3, some tweaking is helping to balance temperatures against running cost. The parameters used by the installer are really a "best guess for the location".
Scheduling to make the most of cheap periods (Octopus Go) looks like it'll save at least £25 a month.
I've fitted a Shelly energy monitor to the supply, so that I can see exactly how much electricity the ASHP and associated gubbins is using. Around £3 a day. Not that much more than I was spending on oil.
Difference is the whole house is now comfortable, rather than just heating a few rooms properly.
The Evohome gear is working properly, but I've reduced the "zoning" so that all rooms are a nice temperature.
House could probably benefit from a bit more insulation, and a couple of windows are draughty - hinges failing. It was rated "D" when the EPC was done to get the grant.
Any updates on this?
I still don’t get why you wouldn’t run an EvoHome style setup for demand… if after all there is no demand from occupants, why run?
I appreciate the paradigm is low and slow so setting cooler nights and hot evenings etc won’t work and the ASHP won’t work like that.
Ina previous home we had a Honeywell zone control per room running UFH on all three floors, with a manifold per floor, and a gas combi boiler.
It all worked fine largely set to 17-18 degC constant, but some rooms hotter like bathroom, some cooler like pantry. Iirc I did run some rooms cooler on a night but only a degree or so otherwise the slab cooled making the ‘saving’ pointless.
It’d even sensibly not heat the lounge when the fire was lit, which a whole house single thermostat ASHP setup would.
So what is the issue? Just that some people try use EvoHome type configs and have demand flapping on and off all the time?
Again, in recent experience, single controls are just as rubbish. Ie, If they’re on a wall the sun hits at certain times, it breaks, ie low sun in winter on a cold day sneaking in.
Surely it’s all pros and cons and it’s more about setting a sensible correction curve and sensible demand duty cycle?
I still don’t get why you wouldn’t run an EvoHome style setup for demand… if after all there is no demand from occupants, why run?
I appreciate the paradigm is low and slow so setting cooler nights and hot evenings etc won’t work and the ASHP won’t work like that.
Ina previous home we had a Honeywell zone control per room running UFH on all three floors, with a manifold per floor, and a gas combi boiler.
It all worked fine largely set to 17-18 degC constant, but some rooms hotter like bathroom, some cooler like pantry. Iirc I did run some rooms cooler on a night but only a degree or so otherwise the slab cooled making the ‘saving’ pointless.
It’d even sensibly not heat the lounge when the fire was lit, which a whole house single thermostat ASHP setup would.
So what is the issue? Just that some people try use EvoHome type configs and have demand flapping on and off all the time?
Again, in recent experience, single controls are just as rubbish. Ie, If they’re on a wall the sun hits at certain times, it breaks, ie low sun in winter on a cold day sneaking in.
Surely it’s all pros and cons and it’s more about setting a sensible correction curve and sensible demand duty cycle?
Mr Whippy said:
Any updates on this?
I still don t get why you wouldn t run an EvoHome style setup for demand if after all there is no demand from occupants, why run?
I appreciate the paradigm is low and slow so setting cooler nights and hot evenings etc won t work and the ASHP won t work like that.
Ina previous home we had a Honeywell zone control per room running UFH on all three floors, with a manifold per floor, and a gas combi boiler.
It all worked fine largely set to 17-18 degC constant, but some rooms hotter like bathroom, some cooler like pantry. Iirc I did run some rooms cooler on a night but only a degree or so otherwise the slab cooled making the saving pointless.
It d even sensibly not heat the lounge when the fire was lit, which a whole house single thermostat ASHP setup would.
So what is the issue? Just that some people try use EvoHome type configs and have demand flapping on and off all the time?
Again, in recent experience, single controls are just as rubbish. Ie, If they re on a wall the sun hits at certain times, it breaks, ie low sun in winter on a cold day sneaking in.
Surely it s all pros and cons and it s more about setting a sensible correction curve and sensible demand duty cycle?
I've got everything working how I want it, rooms at the right temps, running costs are little cheaper than oil, house more comfortable.I still don t get why you wouldn t run an EvoHome style setup for demand if after all there is no demand from occupants, why run?
I appreciate the paradigm is low and slow so setting cooler nights and hot evenings etc won t work and the ASHP won t work like that.
Ina previous home we had a Honeywell zone control per room running UFH on all three floors, with a manifold per floor, and a gas combi boiler.
It all worked fine largely set to 17-18 degC constant, but some rooms hotter like bathroom, some cooler like pantry. Iirc I did run some rooms cooler on a night but only a degree or so otherwise the slab cooled making the saving pointless.
It d even sensibly not heat the lounge when the fire was lit, which a whole house single thermostat ASHP setup would.
So what is the issue? Just that some people try use EvoHome type configs and have demand flapping on and off all the time?
Again, in recent experience, single controls are just as rubbish. Ie, If they re on a wall the sun hits at certain times, it breaks, ie low sun in winter on a cold day sneaking in.
Surely it s all pros and cons and it s more about setting a sensible correction curve and sensible demand duty cycle?
I ended up not using the Evohome "call for heat" - disabled the Honeywell boiler relay with a bypass switch so it can still be used if I want to, rather than completely disconnecting it from the heatpump controller.
The Evohome TRVs are now acting as programmable TRVs - some rooms off in the evenings, one off during the day. They also act as limiters on the rooms that I want a bit cooler (main bedroom) or that can get a lot of solar gain.
The inner hallway (where the heatpump remote stat is located) has no TRV.
The weather compensation curve is set, rads balanced, so the heatpump is effectively on for 20 hours a day, without hitting the limit on on the hallway stat.
It is set to come on as soon as the Octopus Intelligent cheap period starts, and goes off at 19:30. Seems to be the cheapest way to do it.
The only manual intervention required is on sunny days when the heating is on. The conservatory gets very warm, so we take advantage of the free heat by opening the door into the kitchen diner, and turn down the heatpump remote so it goes off.
Heating is currently running overnight, then manually turned off with the stat as soon as the conservatory gets to over 25 degrees. This is costing about 40p a day including hot water.
The most expensive day so far (zero degrees all day) cost £6.
Looking at the HDD numbers locally, and projecting for a full year, I reckon £600 for heating and hot water. This is pretty much what we were paying for oil for heating only (DHW was immersion heater).
TLDR:
Disabling the Evohome boiler relay "call for heat" made everything work properly.
Mr Whippy said:
Any updates on this?
I still don t get why you wouldn t run an EvoHome style setup for demand if after all there is no demand from occupants, why run?....?
I think fundamentally it comes down to response time.I still don t get why you wouldn t run an EvoHome style setup for demand if after all there is no demand from occupants, why run?....?
You can't always get acceptable results by waiting for 'demand from occupants'. You have to heat some houses ahead of when you want them warm
The cheap power in the middle of the night changes the game too.
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