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.
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