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Creative trials on Night-time Setbacks to @ faster recovery, improved comfort and even greater energy reductions.

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I would certainly agree that the heat pump operation is causing an increase in defrost cycles and also a reduction in efficiency.

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Topic starter  

Definition of setback.

we have tried different set back temperatures to see what fits our Low mass building. In other words our house warms up quickly but it also cools down relatively quickly. We also have radiators rather than a high mass slow release slab of under floor heating so efficiency is somewhat curtailed by the properties of our house. So we are having to try and make the most of what we have.

We are operating a setback from daytime 21c back to 17c between the hours of 9pm and 4am. The ramp up in the morning starts at 4am and is achieved in 1c increments with 1.5 hours between each 1c rise taking our set temperature up to 20c. The incremental rises are designed to keep the Auto Adaptive controller operating at a minimal output so that the feedback loop doesn’t see large temperature rise targets. The 21c room temp is achieved by Auto Adaptive always over running the target by half or one degC.

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There have been several observations about how the system works along the way to finding the best setting for the widest outside temperature ranges. If ever there was a system which didn’t want to be controlled it would be the Heat Pump.

Nonetheless we have persevered and found several ‘unknown unknowns’ and turned many into ‘known unknowns’. 

Perhaps the most surprising of these has been to understand ‘Freeze Stat Function.’

Just when you think you have everything under control Freeze Stat Function decides to switch on at 2am and operate right through to the morning ramp up.

CAUTION (with our Ecodan)

Freeze Stat Function takes Operational Priority over scheduled temperature changes. In other words the HP continues operating at minimal output instead of responding to Auto Adaptive Set Temperature asking for temperature rise!? As yet I haven found a way of prioritising AA set temp over Freeze Stat.

Stuck in Freeze Stat instead of starting the morning ramp up at 4am

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Meanwhile 3 hours later the HP starts the ramp up playing catch-up with the AA target room temperature 

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Nothing's ever simple.

Here you might be able to see Freeze Stat stopping room temperature from rising until later in the morning.

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Derek M reacted
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Topic starter  

In summary the purpose of these trials have been to see if there are any energy savings in having an automated setback over a 7 hour period of night time, while still guaranteeing a comfortable room temperature of 20.5c between the hours of 8.00am or earlier and 10.30pm. 

Here is a 24 hour chart of operation of a typical day with a setback which closely follows the set temperature using Auto Adaptive room temperature control.

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Here is a comparison of a recent continuous operation chart showing the same even target room temperature of 20c with the same over run of More or less 1c. So it’s quite difficult to get an exact 21c constant room temperature.

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The attached scatter graph shows all the daily energy our heat pump has consumed for December (pink crosses) January and February (green crosses)

Can anybody identify the 4 days when the heat pump operated for 24 hours continuously?

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The debate is : Is there any energy saved by operating the heat pump with a setback compared to operating continuously? With the proviso that a minimum room temperature of 20.5c must be attained between the hours of 8.00am and 10.30pm.

who can improve on @cathoderay s guess he has identified one of the 24 hour days.

there are clues in the previous page of this thread.

and @cathoderay identified the pink cross correctly.....


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Topic starter  

The results of our trials:  There were 4 continuous 24 hour trials which coincided with 4 different outside ambient temperatures. These temperatures were:

  • 12c Ambient
  • 8c Ambient
  • 7c Ambient
  • 5c Ambient

These tests coincided with clusters of set back trials done at the same Ambient temperatures and the 24 hour energy consumption of all trials were recorded.

The attached scatter graph shows the 4 continuous operation energy consumption outputs linked by the blue pencil line while the clusters of the equivalent setbacks done on the same Ambient temperature days are shown in their location.

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It can be seen that in all cases, except one, energy consumption was higher in the continuous operation day than all of the 18 setback trials. It can also be seen that the trials were well clustered. The actual difference between the 24 hour trial and the mean average of the equivalent ambient temperature was as follows:

  • 12c Ambient, for continuous operation =2.9kwh above mean consumption
  • 8c Ambient, for continuous operation = 3.5kwh above mean consumption  
  • 7c Ambient for continuous operation = 8.2kwh above mean consumption
  • 5c Ambient for continuous operation = 2.42kwh above mean consumption

(mean consumption refers to the aggregated consumption of the setback trials clustered at same Ambient temperature divided by the number of trials.)

exceptions: there appears to be a considerable difference at the 7c Ambient which may be attributable to the notion that my December ambient observations were not so rigorously well refined as January and February data.

NB I have removed neighbouring trials outside the ambient ranges as they may only serve to distract.

however I attached all the data of the scatter graph in the spreadsheet below. It’s  important to remember that these are not just dots on a graph.... each cross represents an entire 24 hour period with recorded events through each day.

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Obviously I would like to have done some colder day comparisons to see what the differential might be during defrosts and freeze stat function over the night time without the setback but perhaps February might yet deliver such a day.

Tim441 reacted
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