Originally posted by bruce_miranda
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New home, mammoth Evohome install
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Originally posted by bruce_miranda View PostI think it must have something to do with TDI. The BDR91 does TDI on its own depending on the Heat Demand sent by the Controller. It could be that the Heat Pump needs to be switched on/off differently than a traditional boiler or zone.
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The Cycle Rate and Minimum On Time settings affect all BDRs in the system (and I wish it didn't). But its not the controller that is actually switching the BDR91 on and off each time. The controller just passes the setting information to the BDR91 once. Then on an ongoing basis it passes the Heat Demand required and the BDR91 then decides how to turn on and off to best meet that Heat Demand using the Cycle Rate and On Time settings.
So my guess is that when the BDR91T is set up as a Heat Pump relay, it must have a different algorithm that it follows for it's on off cycle, to fulfil the Heat Demand requested by the controller.
In fact it's a shame we cannot use this Heat Pump setting for the Zone Valve etc because I use my BDR91 to control an UFH pump and I could do with keeping that on longer. Rather than the BDR91 just doing TPI on that, like it would do with the boiler.Last edited by bruce_miranda; 25 November 2020, 09:02 AM.
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I've attached two graphs which might explain how a normal BDR91 works.
The first step graph is the Heat Demand the controller is sending the BDR91. Notice how the Heat Demand required, doesn't switch on and off, it goes from 100% down to 0% in stages.
The second graph is actually tracking the time the BDR91 stays on and off. I have a Cycle Rate set to 6 per hour. Notice how the amount of time the BDR91 stays on within a particular hour reduces as the Heat Demand required reduces.
My guess is that it's this part that must differently when it's paired as a Heat Pump Relay.
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Originally posted by bruce_miranda View PostI've attached two graphs which might explain how a normal BDR91 works.
The first step graph is the Heat Demand the controller is sending the BDR91. Notice how the Heat Demand required, doesn't switch on and off, it goes from 100% down to 0% in stages.
The second graph is actually tracking the time the BDR91 stays on and off. I have a Cycle Rate set to 6 per hour. Notice how the amount of time the BDR91 stays on within a particular hour reduces as the Heat Demand required reduces.
My guess is that it's this part that must differently when it's paired as a Heat Pump Relay.
Ok, that explains a lot. Curious how you can catch the signal send from Evohome to the BDR91Last edited by Fmb; 25 November 2020, 08:47 PM.
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Turns out I have odd twin pipe manual micrometric valves (flow+return+single rad pipe) for 2 thin vertical panel radiators, that I can’t fit HR91s to, for my 4 towel rad circuit.
I don’t want those rads heating with the UFH, so no point replacing their NC zone valve with NO.
So I’m thinking of connecting a BDR91 to the NC zone valve, so I can schedule when that zone is heating.
But what should I use for the sensor? I guess I can’t bind one of the HR91s as a zone valve sensor.
Can you double bind a DTS92? Can I bind one of the UFH DTS92s, where the rads are, as an HCC80 UFH zone sensor and also as the towel rads BDR91 zone sensor?
Or can I use my second Evotouch DHW zone, without a cylinder sensor, just to heat the towel rads for a short time twice per day?Last edited by kevinsmart; 12 December 2020, 11:37 AM.
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Originally posted by kevinsmart View PostJust placed a huge order with the EvoHome Shop for my new house, after getting to grips with the existing set up (Danfoss controls).
Comprises of:
16 x DTS92E Room Thermostats (I chose these as they will cover removed Danfoss thermostats better than T87RF)
4 x HCC80R UFH Controllers
1 x HCS80 Extension Module
1 x HR914 Radiator Multi Zone Kit (Kieran recommended these over HR92s for towel rads)
2 x ATF600 Wall Mount Kits
1 x Evohome Connected Modulation Pack
1 x Evohome Connected Thermostat Pack
1 x ATF500 Hot Water Kit
1 x Honeywell High Limit Pipe Thermostat
2 x Honeywell 28mm N/O Motorised Zone Valves
Going to have 2 controllers handling 23 zones: 19 UFH via 4 manifolds, 4 towel rads. OpenTherm with weather compensation implemented by my custom firmware on an OpenTherm monitor, reading external temperature sensor.
DHW priority, closing N/O valves on UFH and radiator circuits.
Removing existing Thermostatic Mixing Valve, which was set at 75C when I moved in (!) as I will limit the max OpenTherm flow temperature. Install a High Limit Pipe Thermostat to cut the UFH pump on over temperature, just in case.
I learned from Kieran at the EvoHome shop that the controller was updated this year, requiring a different wall mount kit, ATF600 vs. ATF300 before.
Looking forward to having Evohome again!
I'd always wondered what Evo could control other than radiator TRVs, motorised zone valves, etc. Sounds a fun install, has this all been completed now?
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Originally posted by MrBoy View PostHey Kevin how are you setting up zones across dual controllers? THere's no clever trickery available right, you just have two distinct systems?
I'd always wondered what Evo could control other than radiator TRVs, motorised zone valves, etc. Sounds a fun install, has this all been completed now?
I still have an open question above in terms of how to best handle my radiator circuit where I can't fit HR91s to two of the rads.
Hopefully he will be able to fit me in later this week.
The 2 controllers will bind to the same OpenTherm gateway, which I think will map their highest percentage demand to a flow temperature.
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Unfortunately my installer got sick one day into the install, so not done yet, but I decided to help by pre-binding everything.
So it turns out you can use an unmounted HR91 as a zone valve sensor.
Also if you now order the HCC80R UFH controller, you’ll find an HCE80R with an external HRA80 antenna in the box. Apparently due to component supply issues.
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That's the install completed, and I've updated my OTGW weather compensation firmware.
My inherited Vokera boiler has some limitations versus the Intergas I had before. Its minimum flow temperature is 40C unless switched with a jumper to an underfloor heating mode. On the other hand, it does report back the return water temperature, the Intergas HRE did not, so there is maybe some further optimisation I can do with that.
Independent of Evohome, in OpenTherm mode, it also appears to briefly fire once per hour to heat to 40C.
To determine that DHW is heating I had to fit a relay which open circuits the outside temperature sensor when the DHW BDR91 closes. When DHW is heating the OpenTherm outside temperature read request is invalid.
So the changes I made to the OTGW firmware.
Report the Max CH water setpoint as 60C rather than 80C reported by the boiler.
Report the Max CH setpoint boundaries as 40-60C, rather than 40-80C. Evohome appears to ignore the lower bound, I see control setpoints in the 20Cs, but it limits its requests to within the max setpoint (100%->60C).
Implemented a simple UFH weather compensation heating curve, TMax = 50C-outside temperature, capped at 60C. So at -10C: 60C, 0C: 50C, 10C: 40C.
If the control setpoint is below the calculated TMax, it is not modified.
When DHW heating is detected, increase the control setpoint from 60C to 70C.
I now have a DHW priority setup. The UFH pump which receives demand from the 4 HCE80s is stopped and the NO UFH 2-port valve is closed.
I'll continue to monitor, but it's all working great so far.Last edited by kevinsmart; 25 January 2021, 07:45 PM.
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Some observations from monitoring.
This is apparently how the OpenTherm bridge converts a % demand into a Control Setpoint temperature:
Control Setpoint = 20 + % x (Max CH Setpoint - 20)/100 Celsius
I have two Evotouch controllers. The % demand converted is the highest of the two controllers.
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