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Thread: new to evoHome - existing Honeywell wireless room thermostat

  1. #41
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    Quote Originally Posted by bruce_miranda View Post
    Interesting and very useful. So looks like a rewiring is needed or a normally open head. Wiring from the pump is a bit difficult for me because the pump is wired directly from the boiler and not my wiring box. But will look into this. Or i could just go back to my S plan configuration. Trouble is that I witnessed several instances where the boiler fired up under the direction of the OT bridge, with no zone valve open. I didn't like all the heat simply cycling through my bypass valve.
    I have the same 'issue' here - I had currently latched the valve open and would now prefer to connect to the pump as suggested but my pump is internal to a Vaillant system boiler and I'm not entirely sure the best way to connect it. If you figure it out please let us know! I don't want to go back to the S plan since I had the same as you - on numerous occasions the OT bridge fired the boiler with no zone valve open which inevitably resulted with the bypass overheating and the boiler cycling...

  2. #42
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    Quote Originally Posted by mart1711 View Post
    I'm finally making progress and have the first two HR92s installed. One thing that I have noted is that it takes a long time (~1 minute) for the controller to operate the BDR91. If for example I switch all heating to "OFF" from the user interfae, the BDR91 only clicks off after a minute.

    If I turn the heating back on, it equally takes around 1 minute for the BDR91 to turn on. Is this to be expected?
    Yes.

    If you change the set points from the controller (or via the Phone apps) then it takes anywhere up to about 4 minutes for the set point change to be sent to the HR92's - this is because set point changes are not sent from the controller to HR92's immediately, but on a regular 4 minute repeating schedule.

    So depending on where you currently are in that 4 minute schedule when you make a change it might take anywhere from a few seconds to 4 minutes to take effect.

    This is done to conserve battery life on the HR92's so the batteries can last 2 years - they only wake up once every 4 minutes to receive new commands from the controller, check the room temperature, adjust the valve (if necessary) and send a new heat demand back to the controller then go to sleep for another 4 minutes.

    If you adjust the temperature from the knob on the top of the HR92 then this up to 4 minute delay is bypassed because you are directly controlling the device and waking it up immediately by turning the knob.

    However there is an additional delay that always applies - when you adjust the set point, if that results in the valve having to turn it will wait until after the valve has finished turning before it sends an updated heat demand back to the controller. It can take up to 30 seconds for the valve to go from fully closed to fully open so this is an additional delay that applies regardless of where you change the set point from. If the valve only has to turn a small amount due to a small set point change the delay might be only a few seconds.

    Once a new heat demand has been sent back to the controller it forwards it on to the boiler relay within a few seconds.

    I wouldn't worry too much about how long reaction to set point changes takes - it does take a few minutes when done from the controller, that's just the way the system works, so turning your heating off and on from the controller is not instant like a conventional wall stat or timer due to the delay sending set point changes to the HR92's and then waiting for them to adjust their valve position and send a heat demand back.
    Last edited by DBMandrake; 4th November 2016 at 01:43 AM.

  3. #43
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    Quote Originally Posted by Bluestraw View Post
    I have the same 'issue' here - I had currently latched the valve open and would now prefer to connect to the pump as suggested but my pump is internal to a Vaillant system boiler and I'm not entirely sure the best way to connect it. If you figure it out please let us know! I don't want to go back to the S plan since I had the same as you - on numerous occasions the OT bridge fired the boiler with no zone valve open which inevitably resulted with the bypass overheating and the boiler cycling...
    I am lucky, in that the electrician who installed the wiring used a 5 core cable for the boiler and there is one spare wire going between boiler pcb and the wiring box. I don't have a Vaillant system boiler but my external pump is driven from the Vaillant boiler pcb which will be exactly how the system boiler will be wired. I just need to use the Live feed of the pump to also open the zone valve. This is actually quite a good suggestion because now my valve also stays open for pump over run but does not stay open forever and risk getting seized.

  4. #44
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    Quote Originally Posted by bruce_miranda View Post
    I am lucky, in that the electrician who installed the wiring used a 5 core cable for the boiler and there is one spare wire going between boiler pcb and the wiring box. I don't have a Vaillant system boiler but my external pump is driven from the Vaillant boiler pcb which will be exactly how the system boiler will be wired. I just need to use the Live feed of the pump to also open the zone valve. This is actually quite a good suggestion because now my valve also stays open for pump over run but does not stay open forever and risk getting seized.
    I didn't think of the anti-sticking benefit, I just didn't like the idea of the valve being energised 24/7 even when the heating is off, and if there is only a point to it being open if the pump is circulating it seems logical to power it from the pump supply if you want the valve "bypassed" without actually physically removing the valve.

    It's interesting to note that with boiler relay control using TPI, since I moved from heating only control to S-Plan and added the two zone valves (I had no zone valves at all before) I've noticed quite an improvement in the ability of the system to regulate room temperatures when demand is low.

    I have a long pump overrun time so previously when TPI cycles the boiler off the radiators all keep flowing for quite a while (under the control of individual HR92's of course) which causes the flow to be more or less constantly on but the flow temperature drops down quite low since the radiators dissipate the heat...which sounds like what you want to happen. (Poor mans Opentherm)

    But I found that it didn't maintain a steady flow temperature under light load conditions with the flow temperature dropping really low then going back up fairly high, so room temperatures did fluctuate above and below the set points quite a bit (maybe a degree at most) during light load conditions when only a small amount of heat was needed to keep the room temperature topped up.

    Since I added the heating zone valve TPI now also cycles the heating zone valve closed as well as cycling the boiler off in each cycle. Initially I didn't like the idea of that because that would then shunt my boilers flow entirely through the ABV in each TPI off period, so I came up with a circuit using an MRT16-REM/VF timer to effectively give me "heating zone valve overrun" that was active only when the hot water zone valve was closed. However because that's another 30 for the timer and I'd already spent a lot on my S-Plan conversion I decided to give it a chance without that to see how the system behaved with the zone valve opening and closing with TPI.

    Much to my surprise the temperature regulation under very light loads (mild weather outside) is much better than it was without the heating zone valve. My hallway and living room zones - both which use remote sensors so are pretty accurately measured now look like almost perfect flat lines on my temperature graphs with no oscillations, with the living room maintaining the room within about +/- 0.2 degrees all evening versus about +/- 0.5 to +/- 1 degree previously depending on conditions.

    I puzzled over this for a while and then realised what it probably is - with no zone valve the water keeps circulating and TPI tries to control the average flow temperature, but the temperature you actually get varies all over the place and isn't directly proportional to the TPI duty cycle, so it's constantly having to make corrections due to this random variability thus both the flow temperature and room temperature keep varying.

    With the heating zone valve what seems to happen is that the zone valve closing tends to cause the boiler to come up to its regulated flow temperature (65 at the moment) even with low loads due to latent heat in the boiler and the small automatic bypass loop. So each time the heating zone valve does open the temperature is about the same regardless of how long the valve is open, because when it opens and the temperature starts to fall the boiler comes on to maintain the flow temperature. When it goes off and the heating zone valve turns off the bypass loop maintains the temperature it was just before the boiler switched off, which is pretty close to the set flow temperature.

    So what you have is a more or less constant flow temperature available at the boiler but the actual flow time through the radiators is controlled by the heating valve and that is directly proportional to valve open time. That means the total amount of heat going into the radiators is more or less directly proportional to the heating zone valve open time in each cycle, thus it has much better control. Genius!

    It's probably not quite as efficient as there will be some heat loss through the bypass loop in the closed periods but watching the flow temperature its not much as it barely drops 1-2 degrees during the closed part of the cycle. Also if it was a condensing boiler it might not condense as well so maybe not quite as efficient there.

    So my conclusion is that if you use a boiler relay and TPI that a heating zone valve may reduce the total efficiency slightly but increases accuracy of room temperature control under light loads quite significantly, perhaps almost to the point you would get with OpenTherm, as I'm very impressed with just how flat my temperature graphs are in those rooms now that previously were not like that.

    On the other hand if you use OpenTherm which does give the system precise control over flow temperature, it seems like it would better for the heating zone valve to remain open all the time that there is heating demand and let OpenTherm just modulate the flow temperature to control total heat going to the radiators, which it can do far more accurately than TPI. The only exception might be that you would want the heating zone valve TPI modulated if there was also a simultaneous hot water demand, as the hot water demand may push your flow temperature sky high while it is reheating the water which would cause a temperature overshoot in all the active rooms.

    Something like my zone valve overrun timer which only functions when there is no hot water demand might be just right for that.
    Last edited by DBMandrake; 4th November 2016 at 10:39 AM.

  5. #45
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    Or you use a single bdr91 but with HW priority that just closes the CH valve anytime there is HW demand. But on other times it is open.
    Apparently the normal motorised zone valve were never designed to stay open for long durations and hence many don't recommend that they are used for UFH purposes. There are other valves that are designed for that. Problem is most plumbers and electricians swear by the Honeywell valves so will only ever use that. The compromise I guess is to make sure the valves open and close regularly so that they don't seize.

  6. #46
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    Quote Originally Posted by bruce_miranda View Post
    Or you use a single bdr91 but with HW priority that just closes the CH valve anytime there is HW demand. But on other times it is open.
    Yeah you could do that very easily. But in my case a full cylinder reheat from completely cold is about 25 minutes so I'd have no heating for that time, so I don't really want full hot water priority. I have a balancing valve for the indirect loop that means both radiators and hot water cylinder each get a pretty fair share of the flow when both are demanding heat, but if I was to add a simple overrun timer to the heating zone valve then when it was trying to modulate the heating at say 20% but there was also hot water demand not only would the flow temperature be boosted for hot water reheat, the heating zone valve would remain open when it thought it was controlling it to 20% so there would be a major overshoot in radiator temperatures.

    I figured that if I dropped back to TPI control of the heating zone valve when hot water demand was present (by disabling the overrun when hot water is on) this would avoid this. But I don't think I'll do any of this as I quite like the better temperature control I'm seeing from just letting the heating zone valve do its thing.
    Apparently the normal motorised zone valve were never designed to stay open for long durations and hence many don't recommend that they are used for UFH purposes. There are other valves that are designed for that. Problem is most plumbers and electricians swear by the Honeywell valves so will only ever use that. The compromise I guess is to make sure the valves open and close regularly so that they don't seize.
    I've actually wondered the reverse - I would have though the two port zone valves were designed decades ago with non-TPI systems in mind - where your heating zone valve would cycle maybe once per hour or so at most. On a TPI system your heating zone valve is cycling on and off every 10 minutes - that seems like a lot of cycling and I do have to wonder whether they are up to all that extra opening and closing over a period of years or whether it will wear them out prematurely...has TPI been in wide use for long enough for this to be determined yet ? What is the average life expectancy of a heating zone valve with and without TPI control ??
    Last edited by DBMandrake; 4th November 2016 at 11:08 AM.

  7. #47
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    Quote Originally Posted by DBMandrake View Post
    has TPI been in wide use for long enough for this to be determined yet ?
    First references I can find to TPI are 2008, but knowing Honeywell it was around before that, just called something else!

    P.

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    Quote Originally Posted by paulockenden View Post
    First references I can find to TPI are 2008, but knowing Honeywell it was around before that, just called something else!
    Right, so we don't really have enough historical data yet to see how two port zone valves hold up under constant TPI operation and what that might do to their lifespan.

    I decided to spend a little bit extra and go for the Honeywell valves since everyone seems to say they're the most reliable... the irony is if you shop carefully on ebay and/or amazon you can actually find new unopened V4043's for not much more than a lot of the cheaper brands...

  9. #49
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    Infact a plumber recently almost forced me to change a Vaillant supplied valve to a Honeywell one, because he said it was a ticking time bomb. Since I supplied the valve, he didn't even charge me anything to replace it, that is how strongly he felt about it. And yes, I agree, if you shop around there are some good prices to be had on them.

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    Quote Originally Posted by bruce_miranda View Post
    Infact a plumber recently almost forced me to change a Vaillant supplied valve to a Honeywell one, because he said it was a ticking time bomb. Since I supplied the valve, he didn't even charge me anything to replace it, that is how strongly he felt about it. And yes, I agree, if you shop around there are some good prices to be had on them.
    For something so critical to the operation of your heating that you can't easily replace without draining the system down, (well you can replace the motor head without a drain down, or you could install gate valves on either side but I don't have the room to do that) I figure that you don't cut corners. Anything that needs a full drain down to replace I don't cut corners on.

    I found one on Ebay for 35 new and unopened including shipping, ordered that to do a C Plan conversion (just adding it to the gravity loop) and then changed my mind a few days later and wanted to go the whole hog and do an S-Plan conversion, so I needed a second one - went back to the same seller and they were now sold out! Found another one from someone else on ebay for 45 including shipping also new and still boxed and still a lot cheaper than list price. Both are absolutely new and genuine Honeywell units.

    Check the listings carefully on Ebay - there are a lot of similar looking valves that say they are V4043 compatible, but they are not actually Honeywell valves when you read closely...
    Last edited by DBMandrake; 4th November 2016 at 03:47 PM.

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