Are you sure the DHW pump is over-running? It would quickly be pumping the cold water that was entering the cylinder low down as hot water was drawn off up into the hotter water above and you would have a tepid tankful in short order. Is it the fact that it is hot that makes you think this? I find the cylinder side loop of the PHE gets hot and remains very warm even several hours after the HW cycle has run – a lumpy run of metallic bends, valves and the pump itself all just leaking heat out of the cylinder! I think it is too hot all the way down this loop just to be the copper conducting heat, there must be a continuous slow circulation of water cooling in the pipework and flowing down into the bottom of the tank. I was disappointed by the apparent heat loss of the cylinder after installation – I think I have partly improved it by painstakingly insulating the pipework. My installers insulated most of straighter pipes leading up to the cylinder (though not well enough for my liking) but left bare the mess of copper that comes attached to the front of the packaged unit. I have managed to closely insulate a lot of it but circular pump housings just have a loose blanket of rockwool-type stuff.
I think the cylinder pipework is a compromised design as it has been laid out for compactness but at the expense of some practicality. The clips for the thermistors, the return in particular, are on pipes that are awkward to access and insulate properly. Given that accurate temperatures are required for the FTC to do its job most effectively I would have thought proper pockets should have been provided.
I am certain that the DHW pump is running as I have managed to get my ear onto the casing (unless I am hearing other pumps through the pipework)....I think I should go back up in the loft and hold my ear there and adjust the speed to see if i can tell the difference. I have checked the freeze stat in the service menu and that is disabled as it shows **.
I have to agree about the packaged cylinder arrangement, mine is the slimline and is probably more condensed, I have just managed to nip the thermistor clips with great difficulty because mine were not fitted in the clip very well and not insulated, it is so easy to catch the cable and dislodge them when insulating in the locality.
Just an update that my system is now returning respectable COP which I am sure was mainly down to the thermistors not being correctly positioned and insulated.
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
I've also been trailing room temp versus weather comp - so far my findings reflect yours. i.e. more cycling/energy consumption in weather comp mode at milder temperatures. Once ambient temps get to around zero the cycling stops and I get constant running (just a defrost cycle interrupts things).
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
My understanding is that when operating in WC mode, the controller compares the outside air temperature to the WC curve and calculates the required LWT.
When operating in Auto Adaptation (AA) mode, it still calculates the LWT using the above method, but then slightly modifies the actual required LWT if the 'room' temperatures has varied from the setpoint.
So in AA mode the controller uses both the outside air temperature thermistor and the room temperature thermistor to calculate the required LWT.
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
I've also been trailing room temp versus weather comp - so far my findings reflect yours. i.e. more cycling/energy consumption in weather comp mode at milder temperatures. Once ambient temps get to around zero the cycling stops and I get constant running (just a defrost cycle interrupts things).
Cycling will occur in milder weather conditions when the controller cannot lower the water pump speed any more. Cycling could also occur if the WC curve is set too high at the warmer end of the curve, what are the settings of your WC curve?
Also to add on AA mode. It also overshoots, and undershoots the target LWT by +5 and -5 degrees (hence less cycling in this mode). The + - values are configurable via the 'themo diff adjust' values in the attached. I currently have mine at +3 and -3 (also tried -9 which gives a longer 'off' period).
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
I've also been trailing room temp versus weather comp - so far my findings reflect yours. i.e. more cycling/energy consumption in weather comp mode at milder temperatures. Once ambient temps get to around zero the cycling stops and I get constant running (just a defrost cycle interrupts things).
Cycling will occur in milder weather conditions when the controller cannot lower the water pump speed any more. Cycling could also occur if the WC curve is set too high at the warmer end of the curve, what are the settings of your WC curve?
Hi. The curve was at 36c at -3 and 26c at +15 which was resulting in the attached at +5 degrees (4 cycles per hour
). Second attachment was also at +5 ambient temps but in AA mode (2 cycles per hour).
[Edit] the attachments got added in the wrong order.
Also to add on AA mode. It also overshoots, and undershoots the target LWT by +5 and -5 degrees (hence less cycling in this mode). The + - values are configurable via the 'themo diff adjust' values in the attached. I currently have mine at +3 and -3 (also tried -9 which gives a longer 'off' period).
What are the settings of the Room temp. control 'mode' and 'interval'?
What are the settings of the Room temp. control 'mode' and 'interval'?
I'm still at the default of 10 mins. I'm all rads so a 10 min time collection interval seemed reasonable to me. I did change it to 30 mins as a test but did not notice any difference (I think it's more for those with UFH as the slab will be slow to react?). Mode is at ' Normal'.
On a final note do you use Room temperature control (Auto Adapt) or Weather Compensation?.............I have trialed both and the conclusion I am coming to is that weather comp seems to be a bit more costly to run and the pump cycles a bit more frequently.
I've also been trailing room temp versus weather comp - so far my findings reflect yours. i.e. more cycling/energy consumption in weather comp mode at milder temperatures. Once ambient temps get to around zero the cycling stops and I get constant running (just a defrost cycle interrupts things).
Cycling will occur in milder weather conditions when the controller cannot lower the water pump speed any more. Cycling could also occur if the WC curve is set too high at the warmer end of the curve, what are the settings of your WC curve?
Hi. The curve was at 36c at -3 and 26c at +15 which was resulting in the attached at +5 degrees (4 cycles per hour
). Second attachment was also at +5 ambient temps but in AA mode (2 cycles per hour).
[Edit] the attachments got added in the wrong order.
If you system only requires a LWT of 36C at -3C, then that would indicate that you home is well insulated and that you have correctly sized heat emitters. Whilst that is good news in colder weather conditions, it of course can lead to cycling during milder weather.
Unfortunately the graphs don't include the indoor temperature and outside temperature, which makes like for like comparison more difficult.
The other thing that I noted was that the AA test was performed at 08:00, whilst the WC one was at 15:00. This can make quite a difference, even if the actual outside air temperature reading is the same. Overnight the fabric of your home will lose heat energy, because the outside air temperature often falls, and also because there is a lack of solar thermal energy to help warm the building fabric, or at least reduce the rate of heat loss. At 08:00, the external fabric can still be quite cold from the overnight temperature drop, which will present more heat loss to internals of the building. At 15:00, the external fabric of the building will probably be much warmer, even on cloudy days, so the probable heat loss will have reduced.
The two graphs show that your heat pump was producing more heat energy than that being lost from your home, so it can be expected that both the internal temperature, and that of the water flowing around your heating system, will start to increase. Under normal operating conditions the speed of the compressor would be controlled to regulate the LWT, and the speed of the water pump would be controlled to provide the required DeltaT between LWT and RWT.
It is difficult to be certain what is actually happening within your system. It could be that the controller has reduced the compressor to its minimum operating speed, and it can no longer prevent the LWT from increasing, it therefore reaches the setting when the controller stops the compressor, until the LWT falls to the lower setting and the compressor is once more started. If the settings of the WC curve are higher than required at the warmer end of the curve, this may also cause the heat supply to exceed the heat demand, and hence cause the heat pump to be stopped for a period of time.
Without closely monitoring the various parameters, over a period of time, it is difficult to identify the root cause. You could try lowering the WC curve and see if this makes any difference.
What are the settings of the Room temp. control 'mode' and 'interval'?
I'm still at the default of 10 mins. I'm all rads so a 10 min time collection interval seemed reasonable to me. I did change it to 30 mins as a test but did not notice any difference (I think it's more for those with UFH as the slab will be slow to react?). Mode is at ' Normal'.
Try changing the 'Interval' to 60 minutes for at least a full day and see if that reduces the cycling frequency.
If you system only requires a LWT of 36C at -3C, then that would indicate that you home is well insulated and that you have correctly sized heat emitters. Whilst that is good news in colder weather conditions, it of course can lead to cycling during milder weather.
Unfortunately the graphs don't include the indoor temperature and outside temperature, which makes like for like comparison more difficult.
The other thing that I noted was that the AA test was performed at 08:00, whilst the WC one was at 15:00. This can make quite a difference, even if the actual outside air temperature reading is the same. Overnight the fabric of your home will lose heat energy, because the outside air temperature often falls, and also because there is a lack of solar thermal energy to help warm the building fabric, or at least reduce the rate of heat loss. At 08:00, the external fabric can still be quite cold from the overnight temperature drop, which will present more heat loss to internals of the building. At 15:00, the external fabric of the building will probably be much warmer, even on cloudy days, so the probable heat loss will have reduced.
The two graphs show that your heat pump was producing more heat energy than that being lost from your home, so it can be expected that both the internal temperature, and that of the water flowing around your heating system, will start to increase. Under normal operating conditions the speed of the compressor would be controlled to regulate the LWT, and the speed of the water pump would be controlled to provide the required DeltaT between LWT and RWT.
It is difficult to be certain what is actually happening within your system. It could be that the controller has reduced the compressor to its minimum operating speed, and it can no longer prevent the LWT from increasing, it therefore reaches the setting when the controller stops the compressor, until the LWT falls to the lower setting and the compressor is once more started. If the settings of the WC curve are higher than required at the warmer end of the curve, this may also cause the heat supply to exceed the heat demand, and hence cause the heat pump to be stopped for a period of time.
Without closely monitoring the various parameters, over a period of time, it is difficult to identify the root cause. You could try lowering the WC curve and see if this makes any difference.
Firstly, thanks for the detailed response. Appreciated.
I have read a fair number of older posts where you've described much of the above (in detail, and in a way that's understandable, thanks) so I was already wondering if the compressor is reducing to it's minimum operating speed then having to stop to allow LWT to reduce. I'm not sure if I'm looking at the right parameter but do you know if code 016 (I think that is compressor frequency) will give a clue as to if it's running close to minimum (the couple of times I've checked in heating mode the number has been 36)? Indeed, is there any way of checking?
Appreciate what you say around the testing/graph times. AA seems to take a day or two to settle back down so I had to get the graphs at as near same indoor/outdoor temps as I could. Nominally, outdoor temps were 5c, indoor 18c.
Generally, it is only the 6kW unit (and the heat loss survey come up with 5.8kW heat loss estimates, so appears to be right sized) and it does seem to be providing the required heat with relative ease. I've been comparing my stats versus Heat Geeks graphs on their open monitor - I near matched their COP when temps were at or below zero, as soon as it gets much above that they race ahead (and that milder range is likely where the efficiencies save the most money).
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