That’s a good schedule comparison, did you get a bit of undershoot on the target temp, Im getting about 4000 degree hours below set point? But it’s still doing well hitting ~20.2C on the coldest days:
Interestingly if I adjust Kp and Ki to reduce degree hours below set point to ~2200, I no longer get a saving and now the intermittent mode uses 3.6% more electric!
Alternatively it looks like running 20.2C continuous (the max temp actually reached by the first intermittent example) saves about the same amount as the intermittent schedule on a fixed tariff..
Managed to get an 8% saving with your morning and evening schedule (peak temps of 20C in the schedule) with setback increased to 17C to help meet the peak time setpoint and Ki adjusted up a little.
Moving the start time of the evening schedule from 4pm earlier to 1pm increased the saving - presumably as the heat up happens at warmer midday temperatures. Starting the morning schedule at 5am rather than 6am has the opposite effect (decreases the saving)..
Simulation examples attempting to reproduce poorly configured heat pumps:
Vaillant 5kW with weather comp curve set way too high or fixed flow temp set 50-60C. Simulated with compressor set to fixed speed 80%: 37% more electric consumption than well optimised continous heating:
On/off 3rd party stat, weather comp far too high or fixed flow temp ~60C, continuous heating to 20C- 120L system volume
3.37
9022
2678
£696
£514
On/off 3rd party stat, weather comp far too high or fixed flow temp ~60C, intermittent heating (on 20C 6-9, 16-22, off in-between) – 120L system volume
3.11
7630
2453
£638
£602
On/off 3rd party stat, weather comp far too high or fixed flow temp ~60C, intermittent heating (on 20C 6-9, 16-22, off in-between) – 60L system volume
2.94
7509
2556
£664
£621
On/off 3rd party stat, weather comp far too high or fixed flow temp ~60C, intermittent heating (on 20C 6-9, 16-22, 17C set back) – 60L system volume
3
7695
2564
£667
£604
Load compensation (lowest possible flow temps and modulation), 20C continuous, 60L system volume
4.09
8659
2117
£550
£407
Load compensation (lowest possible flow temps and modulation), 20C continuous, 120L system volume
4.1
8660
2113
£550
£407
Load compensation intermittent heating (on 20C 6-9, 16-22, 17C set back) – 120L system volume
3.43
6980
2034
£529
£489
Load compensation intermittent heating (on 20C 6-9, 16-22, off in-between) – 120L system volume
3.33
7108
2137
£556
£524
Load compensation intermittent heating (on 20C 13-22, 17 in-between) – 120L system volume
3.54
6795
1920
£499
£434
Load compensation, gradual heat up from 17C overnight starting 10am, 20C by 5-6pm
3.71
6686
1801
£468
£439
Load compensation 20C all day apart from boost to 21C at 1pm and blocked off off period 4-7pm (agile peak), indoor temp drops to 18C by 7pm (3C drop)
3.99
8396
2102
£546
£361
Winner so far on fixed tariff is 17C setback, gradual heat up starting 10am reaching 20C by 5-6pm. I think with a better control algorithm that slowly ramps up the compressor over this 7-8 hour period the savings on this schedule could be a bit higher still.
Winner on agile is turning heat pump off between 4-7pm of course.
Continuous 20C on agile is still just over 10% cheaper than the cheapest fixed tariff scenario (assuming 26p/kWh on a fixed tariff).
Have you implemented Vaillant’s Active mode? When recovering from an off period it calculates the difference between current room.temperature and target setpoint temperature, then adds that to the setpoint temperature and uses the resulting value to select the flow temperature from the set weather curve. In my personal experience, it was taking hours to recover even a 1 K setback. I soon abandoned that…
If the room temperature is above the setpoint, whether through solar gain, cooking, lots of people in the room where the thermostat is, whatever, Active uses the same approach to reduce heating power. However if the room temperature is above target you don’t want any heating power at all, which is what Expanded mode adds to Active: in that scenario, the pump is simply shut down.
Thanks Dan, the simulator does not implement Vaillant control algorithms per se, it just uses a simple PID algorithm to adjust the heat output to try and match the target temperature. It’s probably more like the Ecodan auto-adapt control algorithm but even then it’s not exactly the same - as the exact algorithms that manufacturers use are sadly proprietary.
I feel there could be an opportunity here for a collaborative effort to build a more comprehensive tool and do welcome help on this!
Just playing around with the responsiveness of the simulation PI control algorithm, and actually contrary to what I initially wrote in my reply to your post above @Dan_Grey it actually has less impact than I thought. E.g if the control algorithm does hit the target temperature setpoints, how fast it does so results in savings variations in the ±2% range.
I didn’t list the full conditions to reproduce the “Load compensation, gradual heat up from 17C overnight starting 10am, 20C by 5-6pm” example. I now with slightly different parameters get slightly lower cost difference between running continuous and intermittent with the agile tariff.
3.4 kW heat loss
7.4 kW of DT50 radiators
250W internal gains
30% minimum modulation on the Vaillant 5kW (max output 8.5 kW)
Then an interesting result is that if I increase the radiator capacity from 7.4 kW to 15 kW corresponding to a design flow temperature of 38C. I can now achieve a financial saving of 18% with fixed tariff intermittent heating and even a 2% saving with this intermittent schedule coupled with agile!
Potentially the savings could be similar with well implemented weather comp with parallel shift I think.. I do wonder if load comp could be implemented effectively if that might just be a better solution. Maybe load comp with a user settable response time that defaults to slow response in order to minimise the flow temp and compressor modulation elevation?
