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Thread: alpha pump flow rate not enough for some rads

  1. #11
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    Quote Originally Posted by sandyman View Post
    I've got an IR gun and a seek mini thermal camera for my phone - better than the IR gun for metallic surfaces
    Note that you can't reliably read the temperature of a metallic (reflective) surface with an IR sensor as its emissivity will be way short of (and lacking consistency with) the near-perfect body that is assumed. Put a small square of black insulation tape on first as this has an emissivity of ~0.95 which is likely what the gun has been calibrated for. Also make sure you hold the sensor right up to the surface - they essentially average across an imaginary 'cone' of IR input and hence the further away you are the more background radiation you'll pick up (lowering the apparent temperature).
    Last edited by MJNewton; 12th May 2021 at 04:21 PM.

  2. #12
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    yes absolutely. I was using the close-up IR gun technique for ages - had black insulating tape everywhere - until I got the thermal camera. its proving extremely useful.

  3. #13
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    Yes, useful tools to have. I see that if you're an Octopus energy customer you can borrow them which is a great idea/service (for free too I think!).

  4. #14
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    Hmmm this is interesting, new user here and just seen this thread, I also have a Grundfos Alpha2 pump like this, also a Viessmann 26kw boiler, except mine is y-plan open vented, and I have 13 radiators. I also have struggled with the pump settings, for years I have fiddled with the different settings and found that the middle fixed speed setting "II" (pump shows around 20w consumption) is the only one that provides a satisfactory amount of heat with an acceptable level of noise.

    I just recently had another play, reading the instructions it suggests that auto-adapt or PP2 are the best settings for a system like mine, and I would love for the pump to auto-adjust based on how many TRVs are open, but with both settings the pump only draws between 5-8w and the boiler will shut down after a few minutes because the flow temperature overshoots the set point, you can see the flow temp slowly drop as the pump continues to run until eventually the boiler fires and overheats the water again and so on - I end up waking up to a cold house in the mornings. I think the water simply isn't moving fast enough through the hex. I tried CP2 as well with similar results, it's just not running fast enough. On fixed speed 2 everything runs fine, the boiler stays lit and the flow temp stabilises around 68-69 degrees.

    It's a shame there isn't a way to adjust these PP settings, because I have this fancy pump with all this "intelligence" built in but end up ignoring all that and just running it like a standard fixed speed pump. There is a slight noise from some of the radiator return valves but it's bearable, what makes more noise are the motors in the HR92, the one in our bedroom wakes me up, but that's another topic!

  5. #15
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    Quote Originally Posted by MJNewton View Post
    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.
    You're right - depending on the orientation of the valve. An old unidirectional valve should always be fitted so that the flow follows the direction of the arrow. This could be on the flow or return side depending on whether the radiator is attached to the side or bottom port of the valve...

  6. #16
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    Quote Originally Posted by MJNewton View Post
    Note that you can't reliably read the temperature of a metallic (reflective) surface with an IR sensor as its emissivity will be way short of (and lacking consistency with) the near-perfect body that is assumed. Put a small square of black insulation tape on first as this has an emissivity of ~0.95 which is likely what the gun has been calibrated for.
    Your point about reflective metallic surfaces is correct, however most modern radiators are painted and therefore don't have reflective metallic surfaces... Paint makes a good black body radiator and the kind used on radiators has an emissivity fairly close to 0.95. For any painted radiator there is no need to add tape, and tape will slow down the response time of the reading as tape after all is a fairly good insulator. You don't really want the added thermal lag of the tape when you're trying to quickly compare the surface temperatures of many radiators as they are heating up.

    The only time you might need to do something like this would be an unpainted antique cast iron radiator - but even then an oxidised surface still has a very high emissivity compared to polished metal.
    Also make sure you hold the sensor right up to the surface - they essentially average across an imaginary 'cone' of IR input and hence the further away you are the more background radiation you'll pick up (lowering the apparent temperature).
    Good point which I should have made - hold the gun about an inch away from the panel to ensure that its field of view doesn't pick up parts of the wall etc or the reading will be artificially low.

  7. #17
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    Quote Originally Posted by therealfronty View Post
    Hmmm this is interesting, new user here and just seen this thread, I also have a Grundfos Alpha2 pump like this, also a Viessmann 26kw boiler, except mine is y-plan open vented, and I have 13 radiators. I also have struggled with the pump settings, for years I have fiddled with the different settings and found that the middle fixed speed setting "II" (pump shows around 20w consumption) is the only one that provides a satisfactory amount of heat with an acceptable level of noise.

    I just recently had another play, reading the instructions it suggests that auto-adapt or PP2 are the best settings for a system like mine, and I would love for the pump to auto-adjust based on how many TRVs are open, but with both settings the pump only draws between 5-8w and the boiler will shut down after a few minutes because the flow temperature overshoots the set point, you can see the flow temp slowly drop as the pump continues to run until eventually the boiler fires and overheats the water again and so on - I end up waking up to a cold house in the mornings. I think the water simply isn't moving fast enough through the hex. I tried CP2 as well with similar results, it's just not running fast enough. On fixed speed 2 everything runs fine, the boiler stays lit and the flow temp stabilises around 68-69 degrees.

    It's a shame there isn't a way to adjust these PP settings, because I have this fancy pump with all this "intelligence" built in but end up ignoring all that and just running it like a standard fixed speed pump. There is a slight noise from some of the radiator return valves but it's bearable, what makes more noise are the motors in the HR92, the one in our bedroom wakes me up, but that's another topic!
    Yes this is exactly what happened to me when I tried to use the variable speed modes on my pump - all three variable modes were completely useless on my system because the pump would slow right down to a trickle even with all radiators open, let alone with only a few open.

    There is too much flow resistance in my system (consisting of about a 3 metre run of a 28mm manifold which then branches off to long runs of mostly 8mm microbore) for the load sensing pump to operate properly. When all my radiators are open it thinks most of them are closed and throttles right down! Needless to say my boiler isn't happy.

    So I use it in either slow or medium fixed speed modes. Slow is enough for all but the depths of winter and saves a bit of power while I use Medium in the winter to squeeze that last bit of performance out.

  8. #18
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    Quote Originally Posted by therealfronty View Post
    Hmmm this is interesting, new user here and just seen this thread, I also have a Grundfos Alpha2 pump like this, also a Viessmann 26kw boiler, except mine is y-plan open vented, and I have 13 radiators. I also have struggled with the pump settings, for years I have fiddled with the different settings and found that the middle fixed speed setting "II" (pump shows around 20w consumption) is the only one that provides a satisfactory amount of heat with an acceptable level of noise.

    I just recently had another play, reading the instructions it suggests that auto-adapt or PP2 are the best settings for a system like mine, and I would love for the pump to auto-adjust based on how many TRVs are open, but with both settings the pump only draws between 5-8w and the boiler will shut down after a few minutes because the flow temperature overshoots the set point, you can see the flow temp slowly drop as the pump continues to run until eventually the boiler fires and overheats the water again and so on - I end up waking up to a cold house in the mornings. I think the water simply isn't moving fast enough through the hex. I tried CP2 as well with similar results, it's just not running fast enough. On fixed speed 2 everything runs fine, the boiler stays lit and the flow temp stabilises around 68-69 degrees.

    It's a shame there isn't a way to adjust these PP settings, because I have this fancy pump with all this "intelligence" built in but end up ignoring all that and just running it like a standard fixed speed pump. There is a slight noise from some of the radiator return valves but it's bearable, what makes more noise are the motors in the HR92, the one in our bedroom wakes me up, but that's another topic!
    I've been playing with my settings after replacing my bypass valve, which was bust. with the bypass set to a high value, pump in PP3 mode, warm up times are really slow, pump stays at low speed, boiler takes a long time to warm up. similar to you. whereas III is much quicker and gets the job done. Interestingly if I drop the bypass pressure, this allows some short-circuiting , the warm up time in PP3 mode improves. For these tests I am only running a single heat destination , my DHW cylinder, so the resistance of the rest of the circuit is a constant.
    what I notice happening is that the pump speed in PP3 mode seems to be proportional to water temp as well. this fits with some of the grundfos documentation. With the partial short circuit of a bypass open a bit, the return temp to the boiler goes up more quickly , so the boiler has to increase flow temp to keep the delta-T correct so burns a bit harder, then the pump speeds up some more, then its a positive feedback loop until we end up with a properly hot flow circuit at the target temp, boiler modulating to keep it there, and the pump running quite fast (still in PP3 mode). It does appear to me that cold-start is the problem - assuming you have an ABV, maybe you could try a bit of short-circuit?
    what would be ideal would be for them to make a pump with a "boost mode" relay (that you could trigger on a timer or some IOT cleverness) or even better a linkage to evohome. so based on a large call for heat, cold system in the morning or whatever, the system would set the pump to mode III to get things warmed up as fast as poss, and then for tickover it could run it on Auto/PP/CP mode saving on noise and circulating pump power.

    In my case, I will persevere with balancing and check my TRV locations as others have suggested, but I suspect I will need to keep to a PP mode for noise reasons. I am considering splitting the system with a buffer, will allow introduction of ASHP as well, in which case it will allow a fixed speed on the primary side and a variable on the secondary.

  9. #19
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    Quote Originally Posted by DBMandrake View Post
    Your point about reflective metallic surfaces is correct, however most modern radiators are painted and therefore don't have reflective metallic surfaces... Paint makes a good black body radiator and the kind used on radiators has an emissivity fairly close to 0.95. For any painted radiator there is no need to add tape, and tape will slow down the response time of the reading as tape after all is a fairly good insulator. You don't really want the added thermal lag of the tape when you're trying to quickly compare the surface temperatures of many radiators as they are heating up.
    It is usual practice to measure the pipes or valve tails, not the radiator itself, in order to ensure consistency. It is after all the flow and return temperatures you are trying to measure. Paint is almost certainly going to have variable emissivity depending on colour, pigment and compound. A piece of tape won't introduce any thermal lag whatsoever (it is too thin; indeed thinner than paint - but neither will make any difference anyway as the lag is already in the order of minutes due to the thermal mass of the metal component parts) but will significantly improve accuracy. Black PVC tape is very consistent in emissivity hence why it is the go-to surface for accurate IR temperature readings - most non-contact thermometer instructions will specify its use if they pass any comment at all.

    There are numerous lookup tables for emissivity figures - such as this one - where'll you see black insulating tape always ranked right up at the top. Interestingly this particular table includes something called 3M Black Velvet Coating 9560 with an emissivity of 1.00 and whilst unnecessary and likely an expensive specialist product you would likely need to adjust your thermometer to use that accurately as it will almost not have been calibrated to assume such a perfect black body surface.
    Last edited by MJNewton; 16th May 2021 at 12:29 AM.

  10. #20
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    Quote Originally Posted by sandyman View Post
    With the partial short circuit of a bypass open a bit, the return temp to the boiler goes up more quickly , so the boiler has to increase flow temp to keep the delta-T correct so burns a bit harder
    Was this through observation? I would expect the opposite. The boiler should be trying to maintain the set target temperature and whether it's tracking the flow, return or both if the return temperature is increasing it should be modulating down to try and meet the target. That's one of the purposes of the bypass - it is effectively signalling to the boiler (in a rather crude, but nevertheless effective, way) that the boiler's heat supply is exceeding the demand (or sink capacity, if lower) and so needs to reduce the heat output (eventually to the point of cycling if it can't modulate low enough). This is why if the bypass is opening too soon (wrongly set, stuck open etc) then heat-up times will be extended and overall output lowered as the boiler is always having to hold itself back.

    I suspect the reason you saw the heat-up time improve with a partially opened bypass was down to the increased flow this allowed through the boiler hence greater dissipation of heat being produced - even if it was just around whatever length of pipework you have between the boiler and bypass because, if I understand your test setup correctly, this will contribute a relatively high additional flow path when compared to just the coil in your cylinder. You would be better off including some radiators in any such tests as it'll balance out the heat source:sink ratio and minimise the impact of what should otherwise be subtle influencing factors.
    Last edited by MJNewton; 16th May 2021 at 12:27 AM.

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