@derek-mThey checked my WC curves a few years back in Urology when I had cancer of the prostate. Post-Radiotherapy, I now have ‘short cycling’ - but at least I’m alive (I think?). Regards, Toodles.
Toodles, he heats his home with cold draughts and cooks his food with magnets.
@jamespa - I've decided to keep the raw minute data as it is, all corrections (the 1.18 for all derived/calculated energy in kWh and COP values) will be done only in the hourly and 24 hourly data csv files, meaning I can post the minute data as it is:
To maintain comparability, and increase accuracy, any calculations to do with energy in should be increased by the 1.18 correction factor. Personally, I do this for the kWh values when calculating them from amps x volts, then any subsequent calculations eg COPs will have the correction already baked in.
...
Thanks for the data.
I have taken this and plotted various adjustments. Here are the key results. Each point is one noon-noon measurement. I have excluded the data at the beginning when there was little or no heating and the last day which was partial. In each case I am plotting energy to house (from flow temp and deltaT) vs degree minutes.
Raw data
As above with energy to house adjusted by -17000Wh*change in IAT -2000Wh*change in OAT (accounting for history stored in the fabric)
As above but instead of degree minutes being measured actual IAT-OAT they are measured 15.5-OAT
The middle of these shows the best correlation, and significantly better than the first ('unadjusted') result.
I think this shows that adjusting for the energy flow to and from the fabric is a (very probably) valid technique and can significantly reduce the noise on the correlation between OAT and energy use.
A couple of interesting things to ponder though (ideas invited)
-17000 * change in IAT is pretty easy to explain. Basically it says that the fabric has a heat capacity of about 17kWh/C. this is in the same order, but not the same value, as that estimated by @derek-m using a wholly different technique.
-2000 * change in OAT is not so easy to explain quantitatively, although not surprising qualitatively. As the OAT changes the temperature gradient through the fabric changes and that will change the stored energy. This effect, in a tolerably well insulated house, should be smaller than the effect of IAT which is indeed what we observe. I haven't worked out yet how to 'predict' what the value will be, -2000 is simply the figure which gives best correlation.
The intercept is positive on the energy axis. This is the most surprising as one would expect it to be negative, on the basis that there are other sources of heat. Its about 4kWh/day, so not a large positive number, but positive all the same. Would it be wild speculation to suggest that this because we are actually measuring the primary circuit (from heat pump to PHE) not the secondary circuit (from PHE to emitters)?
The slope is also worth thinking about. Its 6.5Wh/degree minute. Based on this figure alone the capacity required at -2 (a randomly picked design temperature) for heating alone with no margin and based on a design IAT of 20 is 6.5*60*22 = 8.6kW. I think that's rather less than the actual capacity of the pump which @cathoderay I think reports underperforms, so there is a bit of reconciliation to do here too. However given the strength of the correlation it cant be ignored. It could of course be down to systematic errors in the spreadsheet, or in the flow rate measurement, neither of which are impossible, or indeed to other reasons.
I have uploaded the spreadsheet as well in case anyone wants to look at the data but I think the key take-away is that, if you are attempting to correlate energy use with OAT (or work backwards from OAT to energy use) then accounting for any change in IAT and thus energy stored in the fabric is likely significantly to improve the correlation. Frankly this is not a surprise, but its interesting (at least to me) to demonstrate that it does work and get some figures out of it which might have other uses.
This post was modified 1 year ago 4 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@cathoderay Slightly different take on this: during the colder period the delta-T looks like it was around 8 for a lot of the time, and (for my Ecodan) that would have a huge impact on cost, typically it runs just over 4. In the later period, your delta-T is lower, hence the need for less power.
Clearly the issue of the defrosts and the pump then trying to recover is closely linked to delta T but I did wonder if anything done to close that delta, e.g. higher pump speed, might mitigate the cost. My Delta-t recovers a lot faster than yours, I don't know why that would be - chart from a couple of days ago. You can see the delta-T reducing is what drives down the energy usage.
-- Attachment is not available --
Probably a good analogy is volts and amps for flowrate and DT. For the same amount of power, if you increase the volts then the amps will fall.
The limiting factor is often how much thermal energy can the heat emitters dissipate, at the average water temperature going through them.
On your displayed chart, LWT is slightly higher, the heat loss is higher, so more energy is being dissipated by the heat emitters. If more thermal energy is being taken out of the heat emitters, but the water flowrate remains the same, then the DT will increase. The heat pump controller senses this increasing DT and puts more thermal energy into the water, which in turn draws more electrical energy from the supply.
If you wish to reduce energy consumption then try to improve the building's insulation. Fitting larger heat emitters may also help by causing the heat pump to run at lower LWT's.
fascinating graph esp to see the kw used to restart heating after defrost. I can’t get that overlay on my graphs. However there is a correlation of our deltaT with yours.... when looking at one heating cycle. We also get a high DT (7 or 8) after a defrost. Followed by a readjustment down to DT5 or a bit less.
Here is our hourly chart of a defrost cycle
However we have also noticed in a normal heating cycle that the Ecodan can modulate even lower once the set temperature is met. It doesn’t just switch off it appears to adjust to try to add just enough heat to match the room losses. Shown in Auto Adaptive operation.
Here is a chart of our place today exactly as it reached set temperature of 19C at 12.40pm. Having reached the target room temperature, It appears to modulate down to DT3 for a further 30 minutes.
Ive become more and more impressed with these Ecodan abilities to modulate. Especially since they don’t have an internal circulation pump. It seems to cope with a wide ranging flow rate and still achieve a DT5 I have set ours at 14lpm, 16lpm, and 19lpm and still the HP has kept to a DT of 5. This I think is a strength where circulation pump speed adjustments are not required.
@cathoderay Slightly different take on this: during the colder period the delta-T looks like it was around 8 for a lot of the time, and (for my Ecodan) that would have a huge impact on cost, typically it runs just over 4. In the later period, your delta-T is lower, hence the need for less power.
Clearly the issue of the defrosts and the pump then trying to recover is closely linked to delta T but I did wonder if anything done to close that delta, e.g. higher pump speed, might mitigate the cost. My Delta-t recovers a lot faster than yours, I don't know why that would be - chart from a couple of days ago. You can see the delta-T reducing is what drives down the energy usage.
-- Attachment is not available --
Probably a good analogy is volts and amps for flowrate and DT. For the same amount of power, if you increase the volts then the amps will fall.
The limiting factor is often how much thermal energy can the heat emitters dissipate, at the average water temperature going through them.
On your displayed chart, LWT is slightly higher, the heat loss is higher, so more energy is being dissipated by the heat emitters. If more thermal energy is being taken out of the heat emitters, but the water flowrate remains the same, then the DT will increase. The heat pump controller senses this increasing DT and puts more thermal energy into the water, which in turn draws more electrical energy from the supply.
If you wish to reduce energy consumption then try to improve the building's insulation. Fitting larger heat emitters may also help by causing the heat pump to run at lower LWT's.
fascinating graph esp to see the kw used to restart heating after defrost. I can’t get that overlay on my graphs. However there is a correlation of our deltaT with yours.... when looking at one heating cycle. We also get a high DT (7 or 8) after a defrost. Followed by a readjustment down to DT5 or a bit less.
Here is our hourly chart of a defrost cycle
However we have also noticed in a normal heating cycle that the Ecodan can modulate even lower once the set temperature is met. It doesn’t just switch off it appears to adjust to try to add just enough heat to match the room losses. Shown in Auto Adaptive operation.
Here is a chart of our place today exactly as it reached set temperature of 19C at 12.40pm. Having reached the target room temperature, It appears to modulate down to DT3 for a further 30 minutes.
Ive become more and more impressed with these Ecodan abilities to modulate. Especially since they don’t have an internal circulation pump. It seems to cope with a wide ranging flow rate and still achieve a DT5 I have set ours at 14lpm, 16lpm, and 19lpm and still the HP has kept to a DT of 5. This I think is a strength where circulation pump speed adjustments are not required.
I can explain what I believe is happening if anyone is interested.
@jamespa - very interesting. The degree of correlation in your second chart is impressive. I think I get the idea, the fabric of the house acts like a storage heater (or flywheel, for another analogy) absorbing heat (energy) when heat (energy) is flowing into the building, and returning it when heat (energy) is not flowing into the building.
The slope is also worth thinking about. Its 6.5Wh/degree minute. Based on this figure alone the capacity required at -2 (a randomly picked design temperature) for heating alone with no margin and based on a design IAT of 20 is 6.5*60*22 = 8.6kW. I think that's rather less than the actual capacity of the pump which @cathoderay I think reports underperforms, so there is a bit of reconciliation to do here too. However given the strength of the correlation it cant be ignored. It could of course be down to systematic errors in the spreadsheet, or in the flow rate measurement, neither of which are impossible, or indeed to other reasons.
I do think the heat loss at -2 is more than 8.6kW, and closer to the design calculations value of 12.4kW. The evidence for this is the heat pump starts to struggle when the OAT gets down to zero and below, at which point according to the Midea Engineering Data it will be putting out around 11.3kW. This point, around zero OAT / 11.3kW is the break even point, above which the heat pump can cope, and below which it can't quite cope. At around this point, the heat pump's output just about manages to equal the building heat loss, giving us an estimate of the heat loss at that OAT. Put another way, if the heat loss really is only 8.6kW at -2, then the heat pump wouldn't shows evidence of struggling at around zero. See recent charts for periods when the OAT was around zero, and the IAT had fallen below design IAT, even with continuous no setback running.
If these conclusions are correct ie the loss at -2 OAT is close to 12.4kW, then a predicted heat loss of 8.6kW does need some reconciliation.
Midea 14kW (for now...) ASHP heating both building and DHW
This chart shows the heat pump not quite meeting demand on the left hand side where the OAT is around zero, leaving the IAT below design IAT (19 degrees), nadir 17.3 degrees, and then recovering as the OAT rises, with the IAT rising to meet the desired IAT (had got to 18.6 degrees by noon today):
If I understand the graph correctly the 60min average energy out seems to be around 8kW.
Is this right?
Yes, on the left hand side it peaks at just under 8kWh (which is 8kW over that hour, unless I've totally lost the plot). Clearly this is much closer to your figure, but how do we reconcile that with the Midea Engineering Data, and the fact the for whatever reason (though presumed to be inadequate heat supply) the actual IAT has fallen below the desired IAT. If the heat pump has some reserve, why doesn't it use it?
Midea 14kW (for now...) ASHP heating both building and DHW
@cathoderay Slightly different take on this: during the colder period the delta-T looks like it was around 8 for a lot of the time, and (for my Ecodan) that would have a huge impact on cost, typically it runs just over 4. In the later period, your delta-T is lower, hence the need for less power.
Clearly the issue of the defrosts and the pump then trying to recover is closely linked to delta T but I did wonder if anything done to close that delta, e.g. higher pump speed, might mitigate the cost. My Delta-t recovers a lot faster than yours, I don't know why that would be - chart from a couple of days ago. You can see the delta-T reducing is what drives down the energy usage.
-- Attachment is not available --
Probably a good analogy is volts and amps for flowrate and DT. For the same amount of power, if you increase the volts then the amps will fall.
The limiting factor is often how much thermal energy can the heat emitters dissipate, at the average water temperature going through them.
On your displayed chart, LWT is slightly higher, the heat loss is higher, so more energy is being dissipated by the heat emitters. If more thermal energy is being taken out of the heat emitters, but the water flowrate remains the same, then the DT will increase. The heat pump controller senses this increasing DT and puts more thermal energy into the water, which in turn draws more electrical energy from the supply.
If you wish to reduce energy consumption then try to improve the building's insulation. Fitting larger heat emitters may also help by causing the heat pump to run at lower LWT's.
fascinating graph esp to see the kw used to restart heating after defrost. I can’t get that overlay on my graphs. However there is a correlation of our deltaT with yours.... when looking at one heating cycle. We also get a high DT (7 or 8) after a defrost. Followed by a readjustment down to DT5 or a bit less.
Here is our hourly chart of a defrost cycle
However we have also noticed in a normal heating cycle that the Ecodan can modulate even lower once the set temperature is met. It doesn’t just switch off it appears to adjust to try to add just enough heat to match the room losses. Shown in Auto Adaptive operation.
Here is a chart of our place today exactly as it reached set temperature of 19C at 12.40pm. Having reached the target room temperature, It appears to modulate down to DT3 for a further 30 minutes.
Ive become more and more impressed with these Ecodan abilities to modulate. Especially since they don’t have an internal circulation pump. It seems to cope with a wide ranging flow rate and still achieve a DT5 I have set ours at 14lpm, 16lpm, and 19lpm and still the HP has kept to a DT of 5. This I think is a strength where circulation pump speed adjustments are not required.
I can explain what I believe is happening if anyone is interested.
Of course... I’m sure it will be enlightening....
btw ive attached the following hourly chart showing the modulated operation for 56 minutes (not 30 minutes as stated) before stopping for a brief period. If it’s of any interest....
I have to admit that I have not had the time to look at your results, or indeed the underlying raw data.
One thing that I noticed, when I was analysing the previous raw data kindly supplied by CathodeRay, was that care must be taken when extracting the 'meat' from the minute by minute data. This is because the heat pump is either cycling or carrying out defrost cycles.
Does your method use all the one minute data, or just the one minute data for the periods when the heat pump was actually producing thermal energy?
As CathodeRay has correctly stated, the maximum thermal energy output that the heat pump can produce in the 0C to -2C OAT range, is in the order of 11.5kW, but since the heat pump is not producing thermal energy output for 100% of the time, and if defrosting, it is actually grabbing some of this thermal energy back, The average thermal energy input to the home during the viewed period may be much lower than 11.5kW.
Does your method use all the one minute data, or just the one minute data for the periods when the heat pump was actually producing thermal energy?
It uses all the one minute data positive and negative except if the diverter is set to dhw.. Energy for defrost comes from the house so should be and is subtracted from the energy delivered to the house.
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