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Thread: alpha pump flow rate not enough for some rads

  1. #1
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    Default alpha pump flow rate not enough for some rads

    I have 20 rads, HR92 on all of them, alpha2-50/60 pump. viessman 26kw boiler. sealed system. Alpha pump needs to be set on PP3 mode for noise avoidance (Avoid the usual very noisy / resonance behaviour with when call for heat level is just 1 rad open a tiny bit). Due to a catastrophic leak in the ground-floor screed-buried CH piping when we went to sealed about 6 years back, there is a set of 4 ground floor rads that are on a really long and convoluted run from upstairs with drops from the ceiling inside cupboards etc. I've recently got into homeassistant/esphome monitoring of everything, temperature probes everywhere, and confirmed my suspicions , that particular group of 4 will not warm up in any reasonable time, if more than a couple of the other rads are on - the flow simply prefers not to go that way until its got no other options. but I can get the flow to go that way if I whack the pump up to speed III. which is not a long term solution due to the aforementioned noise ....

    ideas
    1. if there is such a thing, find a pump that is by default variable speed like the alpha, but can be forced to go "max" with an external trigger input of some kind. doesn't need to be fully automated.. human button press is fine, but needs to revert to the variable setting once the trigger is unset.
    2. go up to alpha 2-80 pump, hoping that the increased head will help
    3. split the system with a LLH/buffer, putting the "slow" group on a separate pump to the rest. There'd then have be 3 pumps - one primary side, 2 secondary side. The slow group has T off point on the flow and return sides so perfectly do-able to re-plumb it. But how do I control multiple pumps from evohome? "if zones 3 and 7 calling for heat then power up relay X", doesn't exist as an output option.
    4. as previous but don't separate the pump controls - rely on alpha pump's standby mode to stop , if there is no open rad in that zone.
    5. spend a stupendous amount of time trying to "balance" - if that is even possible with evohome (read many recommendations to suggest that its not worth the effort)



    thoughts?
    Ian

  2. #2
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    Do you have Evohome or any other TRV zoned valve. If so may be adjust the schedule so that those 4 radiators are heated up first before any of the others.

  3. #3
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    evohome HR92 on all the rads. I've played with doing it by scheduling, not feasible. the rooms in question tend to be used later in the day than others - our tv room/snug and sitting room - but if the hall or kitchen are on, then they take the flow.

  4. #4
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    Sounds like the system just hasn't been balanced properly, if at all. Regardless of the convoluted pipe run for those radiators, provided they heat up normally when they are the only radiators in use (showing that the pump is producing enough head) you should still be able to balance the system via adjusting the lockshield valves so that all radiators heat up together without these ones being starved.

    Balancing is adjusting the flow resistance of each branch of the pipe network to be roughly equal as seen at the pump so that when all radiators are open at once they all receive roughly equal flows. Pipes that are longer or skinnier have higher flow resistance than those that are shorter or fatter, so the lockshield valves on radiators with short/thick pipe runs need to be partially closed to increase their flow resistance to match those of radiators with longer/skinnier pipes.

    Normally the runs with the worst flow (your radiators with convoluted pipes) should have their lockshield valves completely open and all other radiators should have the lockshield valves partially closed to varying degrees - with those radiators with the easiest runs which heat up the fastest closed the most.

    Most of my house is 8mm microbore (so fairly high flow resistance) and one room in particular has a very long run of 8mm back to the main manifold - the lockshield for that radiator is fully open while many of the others are significantly closed to achieve balance. And while it's not perfect (I think there is a kink in one of the pipes to that radiator under the floor as well) it certainly doesn't get starved during initial warm up when all other radiators are on as well.

    Fitting a larger pump won't help if you have a radiator on a short easy flow section of the pipe network that is not balanced - if that radiator has its lockshield fully open then when that HR92 is open it will reduce the differential pressure to the point where there just isn't enough differential pressure to serve the radiators with the convoluted pipe run.

    Properly balancing a system while not fundamentally complicated or difficult (you can do it yourself if you know the right method) can be a long laborious process that can't be done quickly - hence its pretty common for heating engineers (who have to charge by the hour...) to simply not bother to do it at all unless there is an obvious issue as they can't easily do it properly during a single call out. To do a good job of it you need to allow all radiators to cool down for an hour or two then test all radiators heating simultaneously during initial warm up - compare the rate that each radiator heats up, make adjustments and repeat the process, so many hours to a day or two due to the necessary cool down times between each test.


    Regarding the radiator noise if you turn the pump up - is there an automatic bypass valve fitted? I'm not familiar with that pump - are you using it in a constant speed mode or a load sensing mode? I have a Grundfos Alpha UPS2 15-50/60 which has 3 load sensing modes and 3 fixed speed modes, and I ended up using it in the middle fixed speed mode with an automatic bypass valve, because I don't think load sensing pumps work very well on systems with high flow resistance like mine. (it just refused to ramp up the pump speed due to the high flow resistance)

    If your pump is indeed in a fixed speed mode and you don't have an automatic bypass valve that will be why your radiators can get noisy if only one is open - due to excessive differential pressure. This won't happen with a properly adjusted automatic bypass valve which acts as a different pressure regulator and thus sets an upper limit on the differential pressure.

    To me it sounds like your system needs an automatic bypass valve if it doesn't already have one fitted (which will allow the differential pressure to be better regulated as radiator demand varies, allowing you to set the pump speed a bit higher without noisy radiators) and the radiators all need to be properly balanced.

    There can be quite a bit of interaction between the pump speed, automatic bypass valve adjustment and lockshield valve adjustment on individual radiators, so a little bit of experimentation can be needed to find the right balance and the right technique needs to be used.
    Last edited by DBMandrake; 6th May 2021 at 09:58 AM.

  5. #5
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    hi, I would agree on the lack of balancing, I know its not been done.. Just that with 20-odd rads, that is a right **** of a job. I have a 22mm 3 zone distribution from a central point, with 15mm loops off each of those 3 zones distributions nearer to the rads. One of the zones (upstairs) is unchanged since the house build (1970's). The other 2 serve downstairs, not planned that way for any particular reason other than achieving a usable route between rads without putting a pipe in a stupid place back when we had to replace the connections to every single ground floor rad . In fact I have one evhome "zone" (the hall) that contains 3 rads that ended up on two different distribution flows.

    My pump is the same as yours - grundfos alpha2 50/60. I run it in the PP3 mode. The noise problem is not flow noise, its resonance. in my system, if we have a rad on just a little bit, large sections of the house's pipework sings , its like someone is playing a really big church organ on your pipework, its very very loud. Its caused by the tiny gap on the HR92 acting as a reed, initiating the resonating waves, as I understand it. With a pump at fixed speed, this resonance will come on and stays on - for minutes at a time (until the HR92 on that rad changes state, either closes fully or opens a bit more). the higher the fixed speed, the worse it is. But with the variable mode on the pump, it senses the resonance as a pressure wave, the pumps logic makes it adjust its flow rate / head, changing the resonant frequency of the system, and the noise goes away after a second or so. So the PP3 mode is completely necessary on my system as the long-term mode to avoid us being regularly deafened! This resonance happens at minimal heat demand levels and minimal pump flow rates - so relying on the ABV to open to take the resonance away doesn't work, because it won't open - if set it low enough to open at that level, it'd be open all the time when running with more pressure.
    I do have an ABV, in fact I just replaced it because the previous one was bust (couldn't turn). been experimenting with the setting level.
    cheers
    Ian

    cheers
    Ian

  6. #6
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    I have the same pump but because I have a bypass valve I run the pump at a fixed speed to stop the ABV from fighting with the variable flow rate. My house is very old and has 22 radiators and I have actually no idea where the pipes actually run. Five years ago I took all the radiators off in rotation and took them outside to blast them clean with a hosepipe. It worked. Over the years, I've tried balancing by a number of supposed standard but it was pretty impossible to measure radiator in-flow and out-flow temperatures. Eventually, I did it ('it' being all the radiators being hot in the morning) by setting all the lockshield radiator valves quarter turn from closed. Then opening up each COLDER radiator by a further quarter turn at a time until they warm up. Mark the top of the valves with a line so you can keep a record of where the valves are. I found this a pretty straightforward and have never had to fiddle with them again. This approach has the benefit of forcing hot water towards the under-performing radiators. I used to think my boiler was underpowered but it wasn't.

  7. #7
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    Quote Originally Posted by sandyman View Post
    hi, I would agree on the lack of balancing, I know its not been done.. Just that with 20-odd rads, that is a right **** of a job.
    It's not that difficult but it is very time consuming. But if you're willing to do it yourself it can be done over a couple of days in amongst other activities... I did my 9 radiator system in a day, with the limiting factor being the cool down periods between each iteration.

    There are a couple of different methods, both use an IR temperature gun.

    The most common method I've seen described is to adjust the balancing to achieve a certain target temperature differential from one side of each radiator to the other, however I have not found this method to work well and have some fundamental disagreements with the reasoning behind this approach. For a start, for an equal flow rate a long radiator will have an increased temperature drop than a short radiator - it can be nearly impossible to achieve the desired temperature drop across a short radiator. Also if the pump speed is set too high blindly following the temperature differential approach would cause you to close all of the lockshields too much.

    The approach I use is to equalise the warm up rate of the radiators from a cold start - with the objective being that all radiators - when turned up full blast starting from cold radiators and boiler, heat up at about the same rate with none significantly far ahead or (more importantly) none lagging behind.

    Start with the lockshield valves all fully open, radiators and boiler cold after a couple of hours cool down with the system off, then set all zones to a relatively high temperature at once in the 25-30 degree range. (The custom mode is handy for doing this to all zones at once)

    Then as the radiators start to warm up keep walking quickly around the house with an IR temperature gun from radiator to radiator, aiming the gun at the top middle of each radiator taking mental notes of their temperatures every few minutes, from this you can quickly establish a ranked list of fastest heating radiator to slowest heating radiator.

    Once the radiators are all up to temperature turn the system off for a few hours to cool down and make an initial adjustment to the lockshields - any radiators that are very slow or don't heat up at all, leave their lockshields fully open.

    Those that are very quick to heat up close them down to about 2 turns from fully closed, those that are neither fast or slow to warm up set to them to about 3 turns from closed.

    Then repeat - you should start to see the slow heating radiators speed up a bit and the fast heating ones slowing down. Rank the radiators in heat up rate order again and make a smaller adjustment this time - leave the slow ones alone and close the fast/medium heating ones by about half a turn.

    A few rounds of this and it should be possible to get it right. The main thing is there should always be at least one radiator whose lockshield remains fully open so that there is no unnecessary flow resistance in the system, and no lockshield should be set to less than about 1/2 to 1 turn.

    My pump is the same as yours - grundfos alpha2 50/60. I run it in the PP3 mode. The noise problem is not flow noise, its resonance. in my system, if we have a rad on just a little bit, large sections of the house's pipework sings , its like someone is playing a really big church organ on your pipework, its very very loud. Its caused by the tiny gap on the HR92 acting as a reed, initiating the resonating waves, as I understand it. With a pump at fixed speed, this resonance will come on and stays on - for minutes at a time (until the HR92 on that rad changes state, either closes fully or opens a bit more). the higher the fixed speed, the worse it is.
    That sounds like a classic case of water hammer resonance due to a one way TRV valve body being installed on the wrong side of the radiator.

    We had this issue in a flat we live in and I fixed it by swapping the TRV valve body to the correct side of the radiator. Check the valve body for a flow direction arrow - unless it has a dual arrow pointing both ways it is a single way valve and is only designed to be installed on the return side of the radiator. It's a very common error for these to be installed on the wrong side, and they will give exactly the sound you describe - a loud reed like vibration in the pipe work at a very specific valve opening.

    It's worse with an HR92 than a conventional TRV because once an HR92 finds equilibrium will tend to hold the exact same position - and if that happens to cause a resonance in the pipe it will last for minutes at a time, whereas a wax pellet TRV is never entirely "still", it is always varying slightly so passes quickly through any points of resonance.

    It should be noted that even modern "bidirectional" TRV valve bodies can suffer from this vibration under exceptional circumstances - so its still preferable to install them on the return side so there is no chance of vibration.

    Some TRV valve bodies are also "noisier" in terms of water flow (due to turbulence) than others and may provoke resonances in the pipe work where other valve bodies wouldn't, due to less turbulent flow.

    Although I changed them for other reasons (sticking) the Peggler Bulldog valves I used to have were MUCH noisier in partial opening states than the Honeywell Valencia I have now. The following picture shows just how different they are inside:



    The peggler bulldog is in the middle and you can see that the hole drilled in the side port is a lot smaller, also the diameter of the active plunger in the valve is a lot smaller, and has a different geometry - this causes this valve to have a lot more turbulence and generates a very audible hiss that the new valves don't have.

    If you have older one way valves and any are installed on the wrong side I would definitely consider swapping them to the correct side. If they are already bidirectional valves then you might want to consider replacing them with a different type.

    You don't need to live with this pipe resonance.
    Last edited by DBMandrake; 7th May 2021 at 09:19 PM.

  8. #8
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    thanks both. my valves are already honeywell valencia two-ways everywhere, but I don't know which side they are fitted off the top of my head, I will have to go round and check. balancing may well have to be a project for this summer. whilst there's ample PV I'll use the HW tank as a heat exchanger to warm up a slug of primary water and then run that round the rads to avoid gas wastage. with the windows open so we don't cook!
    I've never been sure about this exact temp drop across radiator approach either - with modulating boilers and evohome it seems non-feasible - so long as your rads all get warm when you want them to, I figure the modulation + evohome will take care of the rest. I've got an IR gun and a seek mini thermal camera for my phone - better than the IR gun for metallic surfaces, and has already found some sneaky insulation gaps / draughts.

  9. #9
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    Are there any long runs of pipe with no mechanical support, long enough to allow a resonance to occur? If so perhaps some additional support brackets would help.

  10. #10
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    Quote Originally Posted by DBMandrake View Post
    It should be noted that even modern "bidirectional" TRV valve bodies can suffer from this vibration under exceptional circumstances - so its still preferable to install them on the return side so there is no chance of vibration.
    Just a minor correction to make to what is a great post: problematic valves (whether unidirectional or some bidirectional as you say) should be fitted on the *flow* side whenever possible. The reason for this is that in doing so the flow direction maintains a constant pressure against the valve jumper in the open direction and hence is always working against the valve keeping everything stable. If fitted on the return then as soon as the valve gets *almost* closed a loose jumper will prematurely slam against the valve seat momentarily decreasing the pressure differential causing it to open back up again before the cycle repeats itself causing chattering until the TRV head has positively closed the valve itself.

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