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Do setbacks save energy without compromising comfort?

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cathodeRay
(@cathoderay)
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@derek-m - I think you need to restart the meds, right now!

Midea 14kW (for now...) ASHP heating both building and DHW


   
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 Rod
(@rod)
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@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.

image

   
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(@newhouse87)
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So was away in Scotland since Thursday and was shocked at my usage on app. Saturday morning i was pulling 7kw at 7am, seems BUH was running, is that part of defrosts? Had setback house a bit but wasnt expecting this cold whilei was away and house went below 18.5 few mornings so heavy usage as heat pupcame on out of timed schedule. Anyway checked my cop last night after few hours running @1.5deg OAT, shockingly low 2.0. Took derek and james advice and left running all night. I lowered flow temp to 29, cop for last 12hours 3.8, which is pretty good at them temps i think. Only used 15kwh last 12 whereas at full throttle at 8pm last night at32 flow it used 6kw so my opinion has changed and in lower oat, 24/7 running is only way. Also noticed OAT increases when outside fan dialed down so dereks theory of lower oat being caused by fan seems correct. Approx 1deg i think.


   
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cathodeRay
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Posted by: @rod

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.

Good points, but I think, at least on a Midea unit, that behaviour is hard wired into the controller. I don't think there is (and am not surprised that there isn't) a way to alter defrost behaviour. Nor have I found any way to change the pump speed, it seems to be set permanently (or rather almost permanently, because there are what look like brief random variations) at a flow rate around 1.4 m^3/h when it does run. 

Midea 14kW (for now...) ASHP heating both building and DHW


   
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cathodeRay
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Having boldly stated my heat pump flow rate is effectively fixed, I thought I had better actually check! It seems it pretty much is, most of the time. Here is a scatter plot of the last 5000 minute by minute values, plotted in ascending order:

image

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@derek-m)
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Posted by: @rod

@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.

image

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.

 


   
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(@derek-m)
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Posted by: @cathoderay

@derek-m - I think you need to restart the meds, right now!

You may be correct, but at least I have a sense of humour. 😋 

 


   
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cathodeRay
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@derek-m - only the madman judges his own sense of humour. You really do need to take those meds. 

This post was modified 3 months ago by cathodeRay

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@derek-m)
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Posted by: @cathoderay

@derek-m - only the madman judges his own sense of humour. You really do need to take those meds. 

Thanks for the medical advice. How's your heat pump running?

 


   
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Toodles
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@derek-m One needs a very good sense of humour with today’s energy prices!

Toodles, 76 years young and hoping to see 100 and make some ROI on my renewable energy investment!


   
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Toodles
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@derek-m I’ve just had a day in the CCU of our local hospital to have a CT scan of my pump, all seems to be well but they wish to do a further scan of an emitter, the liver as there is s slight pressure increase in one right hand heart valve - perhaps it is the glycol… (Seriously though, I seem to be a medical mystery but they are still investigating.) Regards, Toodles.

Toodles, 76 years young and hoping to see 100 and make some ROI on my renewable energy investment!


   
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(@derek-m)
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Posted by: @toodles

@derek-m I’ve just had a day in the CCU of our local hospital to have a CT scan of my pump, all seems to be well but they wish to do a further scan of an emitter, the liver as there is s slight pressure increase in one right hand heart valve - perhaps it is the glycol… (Seriously though, I seem to be a medical mystery but they are still investigating.) Regards, Toodles.

Did they check your WC curve settings?

Or is it just on the ladies that they check the 'curves'?

This post was modified 3 months ago by Derek M

   
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