As my electricity tariff provides very cheap electricity overnight, I though I would experiment with running my heat pump at night (until 5.30am) as a sort of setback/preheat. My reasoning was that it should reduce the amount of energy needed when I start my heat pump as normal at 8am.
I expected that when looking at my heat pump graph I would see that the area under the electricity curve would be smaller at 8am. However looking at the graphs (this one is typical), the area under the graph is pretty much the same at 3am as at 8am. To me this seems as though Im not achieving anything with the preheat?
Am I missing something?
Addendum: Actually I think ive just worked it out myself, All i am seeing is the electricity needed to bring the flow temperature up to speed. I really need to see a graph of room temperature, superimposed on the one above to see what effect the preheat is having. Please feel free to ignore this post!
House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60
So I do have a stand alone thermometer in the lounge and it looks like the preheat just stops the drop in temperature and leaves it slightly higher than it started. I would estimate by eye it probably raises the room temperature by about 1 degree C compared to just leaving the room unheated overnight, in this mild weather.
House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60
I'm just starting an experimental week with setbacks but I don't have the monitoring capabilities nor do I have a night time tariff. I'm on Octopus Tracker.
I'm just looking at the Kwhs used per day (on the Octopus app) + OAT - purely to see if it saves any £s.
What surprised me this past week was that heating the water with my Daikin seems to use the same KWHs no matter what the temperature of the water pre-heating. 🤔
@lucia is it possible that your DHW is on for a constant time rather than to reach a set temperature?Otherwise it doesn’t make sense.
On set-back as you probably realise from other strings on here is depends on the house, and it is contentious. In our case at present temperatures it is worthwhile allowing for the higher electric consumption in the morning we save about 4hours of nominal rate heating for an 8hour setback. But when external temperature is below freezing I expect the saving to be less and the time to re-heat in the morning to be too long for comfort. We’ll see.
2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC
As my electricity tariff provides very cheap electricity overnight, I though I would experiment with running my heat pump at night (until 5.30am) as a sort of setback/preheat. My reasoning was that it should reduce the amount of energy needed when I start my heat pump as normal at 8am.
This is exactly what the smart heat pump controllers like Homely, Passiv, Havenwise and Adia claim to do, taking into account weather forecasts, future electricity prices, house temperature and doubtless other factors to judge the amount of pre-loading/set back to apply and the flow temperature required. Adia goes one step further and controls the radiators as well.
It makes sense and also helps with grid balancing. Since grid balancing is going to become increasingly vital as we electrify (unless we want to spend vastly more than we need to on infrastructure), it seems to me that smart manipulation of heat pumps (which is really just using the house fabric as a battery) is going to be increasingly important. I'm guessing that energy suppliers might well offer the service in return for reduced prices (and of course all of your data). It would seem natural for Octopus to do this as they are already well into the space.
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.
@bontwoody Is your Samsung internet connected? Looking at your OEM graph, you would need to increase the flow temperature overnight to really make use of the cheap overnight tariff. Just having it run on normal WC will help, but the effect will be small.
(FYI I'm the founder of HavenWise which James refers to above)
@hcas If you mean via the MIM-B19N board, then no. I just use the Samsung controller so Im stuck with my normal WC curve. I suppose the good news is that due to it being cooler overnight I will get an increased flow temperature naturally.
One problem that occurs to me with having the heat pump on overnight (and perhaps with higher flow temperature) is that the bedroom will get too hot unless I use the TRV which then affects the flow volume. If you have a lot of bedrooms that might be an issue without a volumiser.
House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60
@judith I think you are right. My installer set it to come on at 5am for an hour. I assumed it would reach the set point and stop.
I can't find (yet) how to check this but for now I have cut the timing window in half to half an hour. So thanks for the suggestion.
But I guess the energy used is the same as if I had a huge heating set-back - the heat pump revs itself up to get going. In that case timing possibly won't make much difference.
I expected that when looking at my heat pump graph I would see that the area under the electricity curve would be smaller at 8am. However looking at the graphs (this one is typical), the area under the graph is pretty much the same at 3am as at 8am. To me this seems as though Im not achieving anything with the preheat?
Am I missing something?
I think there is at least one thing that isn't right in that chart, the sudden precipitous drop in flow temp when the heat pump turns off. That doesn't happen, it cools more slowly, at least on my system. I've also always been inclined to take the COPs on these charts with a pinch of salt - 5.82 after it has been going flat out? Possible, but unlikely. I think I am right in saying you are totally dependent on Samsung's compressor-gate black box determination of the energy in and out values, which in my book suggests the need for healthy scepticism! Furthermore, as you say the boosts in energy in and out look similar at 0300 and 0800 (and similar ones can be seen after the other two starts) but what is causing them? Perhaps internally Samsung pumps are programmed to apply a boost when there is a large difference between the actual flow temp and set (from the weather comp curve) flow temp? If so, then you would expect the areas under the electricity curves to be similar, because the difference between the actual flow temp and (presumed, it is not actually on the chart- perhaps you can add it?) set flow temp at the 0300 and 0800 start ups are similar. Since all the start ups on this chart have similar boosts applied, this appears to be normal Samsung behaviour, based on what can be seen on this chart, which you say is typical. It would also be useful to have the IAT on the same chart.
The other slightly odd thing is the continued rise of the flow and return temp after the initial meteoric rise, seen most clearly after the 0800 start up, but also visible after the other start ups. Again, it would be very useful to have the set flow temp on the chart, to see where the actual flow temp is in relation to the set flow temp.
Lastly, a comment: that chart shows classic on/off running as in a fossil fuel boiler, albeit done for different reasons and at different times.It would be interesting to compare costs for this type of on/off running with conventional steady Eddie running first looking at energy used (kWh, ie not taking into account time of use tariff effects) and then factor in the tariff effects and compare the hole in our pocket costs (£££). The question here as I understand it is, can you deposit heat in the house during cheap tariff periods and then withdraw it when when the tariff is high? An appealing idea, one that might even get me thinking about a time of use tariff, but only if it really works, and it doesn't provide the wrong heat at the wrong times. I don't want to sweat all night only to have a chilly breakfast. I do note from your separate IAT chart that the IAT is is somewhat volatile, ranging between ~19 and 23 degrees over a 24 hour period, with one of the nadirs at around breakfast time.
None of this is easy, I know only too well from my own efforts to make sense of what my heating system does. Here is my chart for the last 48 hours, running with a six hour setback overnight. The post setback boost is at least partly controlled by an external script I have which boosts the LWT when the actual IAT is more than a degree below the desired IAT, 19 degrees in my case. The big middle of the day spikes are DHW heating periods, and the very evident cycling is OK, the actual frequency being once or twice and hour, and the average actual LWT is not far from the set LWT. Note that the energy in and out are calculated by me from basic parameters (amps x volts, and flow rate x LWT/RWT delta t and circulating fluid specific heat) and I am also inclined to take the more extreme COPs with a large pinch of salt!):
Midea 14kW (for now...) ASHP heating both building and DHW
I think there is at least one thing that isn't right in that chart, the sudden precipitous drop in flow temp when the heat pump turns off. That doesn't happen, it cools more slowly, at least on my system.
The flow and return temperatures are measured by inline temperature probes from my heat meter, so Im pretty sure they are giving an accurate picture.
I've also always been inclined to take the COPs on these charts with a pinch of salt - 5.82 after it has been going flat out? Possible, but unlikely. I think I am right in saying you are totally dependent on Samsung's compressor-gate black box determination of the energy in and out values, which in my book suggests the need for healthy scepticism!
Im measuring the electricity usage via my open energy monitor via a CT clamp, so its not MID approved, but my COP is in line with Glyn Hudsons who does have MID monitoring and identical setup. Also im not heating my DHW via my heatpump so that helps COP :-). Its been 5.1 over the last 3 months and 4 over the last year but Im expecting that to improve after some changes to the house.
Regarding changes to the graph, I think I should be able to add some more information but at the moment I havent cracked how. I dont monitor IAT via OEM but its something on my list 🙂 I cant think of any way of adding the set flow temperature but it is very close to the measured stable flow temperauture.
Lastly, a comment: that chart shows classic on/off running as in a fossil fuel boiler, albeit done for different reasons and at different times.It would be interesting to compare costs for this type of on/off running with conventional steady Eddie running first looking at energy used (kWh, ie not taking into account time of use tariff effects) and then factor in the tariff effects and compare the hole in our pocket costs (£££). The question here as I understand it is, can you deposit heat in the house during cheap tariff periods and then withdraw it when when the tariff is high? An appealing idea, one that might even get me thinking about a time of use tariff, but only if it really works, and it doesn't provide the wrong heat at the wrong times. I don't want to sweat all night only to have a chilly breakfast. I do note from your separate IAT chart that the IAT is is somewhat volatile, ranging between ~19 and 23 degrees over a 24 hour period, with one of the nadirs at around breakfast time.
The on/off running is partially due to me using the Samsung controller as a thermostat in the living room. I cant lower the flow temperature any more without cycling badly so as a last resort the HP goes off. I might play with raising the setback temperature as suggested by @hcas and see if I can limit bedroom temperature with the TRVs.
House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60
The flow and return temperatures are measured by inline temperature probes from my heat meter, so Im pretty sure they are giving an accurate picture.
Inline probes should be accurate, but at the same time such a precipitous drop seems most unlikely, given there is warm water still in the system, the temperature should fall off a cliff as it appears to do. What happens if you zoom in? I wonder if it is something to do with how the charting works. Otherwise, I would still want an explanation if I saw that on my system, as it would make me question the inline probes' accuracy.
If you are willing to use modbus, there are very affordable room temperature and humidity sensors that can be hooked into the system, and will give you IAT. I have an MD02 sensor, and it has worked flawlessly since I added it over a year ago.
Midea 14kW (for now...) ASHP heating both building and DHW
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