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Heat pumps and on/off working - starting to quantify it

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(@jamespa)
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@newhouse87 if you have a cop of 6 and you are consuming 2kW, then you are apparently delivering 12kW somewhere.  That's enough that something must be getting very hot or alternatively is able to lose heat very quickly.  It doesn't make sense.

 

Whats the calculated house heat loss, what's the house indoor temp, is  there anywhere a large amount of heat could be lost to the outside?


   
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(@derek-m)
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Posted by: @newhouse87

With last week of heating, if my daikin is correct im getting cop of 6, which is Great, however im using 2kwh per hour usage or close to it, this is lwt27/28deg and mild weather 10degrees. I know lots of factors but it still seems excessive. That is when its flowing through all loops at34l/min. Now the house is nice and warm but at that usage, no way would i run continuously, im better off heating for 6 hours maybe in cold weather and if my produced energy at cop 6 is correct, that should keep house warm. Just wondering are some heat pumps set up to use lot of energy but also produce alot in shorter period of time?

I'm afraid your figures just don't add up.

To supply 12kW of thermal energy at a LWT of 28C, you would require heat emitters with a total capacity of 275kW.

Please provide photo's of all your screen displays with the system running, along with details of the heat loss calculations for your home.

 


   
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(@fazel)
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Posted by: @derek-m

Posted by: @newhouse87

With last week of heating, if my daikin is correct im getting cop of 6, which is Great, however im using 2kwh per hour usage or close to it, this is lwt27/28deg and mild weather 10degrees. I know lots of factors but it still seems excessive. That is when its flowing through all loops at34l/min. Now the house is nice and warm but at that usage, no way would i run continuously, im better off heating for 6 hours maybe in cold weather and if my produced energy at cop 6 is correct, that should keep house warm. Just wondering are some heat pumps set up to use lot of energy but also produce alot in shorter period of time?

I'm afraid your figures just don't add up.

To supply 12kW of thermal energy at a LWT of 28C, you would require heat emitters with a total capacity of 275kW.

Please provide photo's of all your screen displays with the system running, along with details of the heat loss calculations for your home.

 

https://emoncms.org/app/view?name=MyHeatpump&readkey=e27db14ae1b516ab45ab87475d9b9789

New Ecodan 11kW UFH, similar data.

image

 


   
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(@derek-m)
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@fazel

Your chart appears to show a low, but increasing, indoor temperature, is that correct?


   
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cathodeRay
(@cathoderay)
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Those emoncms charts continue not to impress (at least for me). The colours are hard to distinguish (and I am not colour blind so far as I know) but even worse, I have no idea what the multiple Y axes refer to. I guess (have to guess, as there are no labels) the right hand one of the three is 'heat', whatever that is, as the numbers in the popup seem in the right range, despite the fact at the top it says Heat 0w (maybe that is a current reading, who knows), and, without the popup, which i guess isn't always visible, we wouldn't even know this is historical data from 16th Oct (this year? last year?) as the X axis has only time, no date. Beyond that I am lost. The middle Y axis does not start at zero, always a warning sign that someone is trying to impress (gee-whizz charts). Nor is there any context. Was there some event just before 1100 that we should know about? Has the room temp gone from around 12 to 14 unspecified units? Or from around 7.5 to 10 unspecified units? It is impossible to tell...and I am none the wiser.

Sometimes a picture is worth a thousand words, other times it can sew a thousand confusions. 

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


   
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(@newhouse87)
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Thanks lads, house stays warm when up to temp so dont think i have massive heatloss. Attached is ber cert i got for house, think heat loss calc is in there somewhere, im not offay with it. I will attach screenshots of running conditions soon. House is approx 20deg and have heating on since 930am. Just upped offset to make it 29deg lwt. Obviously that cop of 6 is wrong but that's what unit is telling me most days. Its new house with good insulation so not understanding this. Could setting be wrong like the issue i had with unit with frost protection enabled leaving the factory.


   
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(@derek-m)
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Posted by: @newhouse87

 

Thanks lads, house stays warm when up to temp so dont think i have massive heatloss. Attached is ber cert i got for house, think heat loss calc is in there somewhere, im not offay with it. I will attach screenshots of running conditions soon. House is approx 20deg and have heating on since 930am. Just upped offset to make it 29deg lwt. Obviously that cop of 6 is wrong but that's what unit is telling me most days. Its new house with good insulation so not understanding this. Could setting be wrong like the issue i had with unit with frost protection enabled leaving the factory.

Do you have a Smart meter? If so, how much electricity does it say that your heat pump is using? What other home devices are using electrical energy?

 


   
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(@newhouse87)
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IMG 20231029 WA0006
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IMG 20231029 WA0009
IMG 20231029 WA0011

 

@derek-m Yes i have meter for heat pump in fuse box and smart meter outdoors, they pretty similar for past hour usage. No nothing else that would use much energy. Just calculated heating/dhw is 72% total usage since i moved in. Like is 1.7kwh an hour as today v high usage @9deg, lwt 29/30 for 242sqm house. 


   
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(@derek-m)
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@newhouse87

According to the readings on your screen display, at the time your heat pump was producing approximately 8.2kW of thermal energy. If the heat pump is drawing 1.7kW of electrical energy, then it is operating at a COP of 4.8, which most people would think to be quite good.

Was the heat pump running continuously or starting and stopping? Is the heat pump drawing 1.7kW whilst running, or 1.7kWh of energy over a 1 hour period?

What was the indoor temperature at the time?

I notice that you have MVHR (Mechanical Ventilation Heat Recovery). Is this running continuously? I would suggest stopping the MVHR for a few hours and see if it makes any difference.


   
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(@newhouse87)
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@derek-m How did you work out what thermal energy i was producing from them screen? actually no cycling at all, flow modulating abit at times but not shutting off. Its approx 1.7kwh per hour. I Have been running continuously since 930am, was off most of the previous day. Its due to shut off at 930pm and come on again at6am. Yes i have mvhr, why would i turn that off, to save electric? Thats on all year round and doesn't seem to use much at all. IAT in my kitchen 22,living room 21 and bedrooms @20 except gym room at 18, only 1 loop in there with big sliding door so doesn't heat as good but i don't mind that. I just read about some peoples usage and cant understand how mine is so much more.


   
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(@derek-m)
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Posted by: @newhouse87

@derek-m How did you work out what thermal energy i was producing from them screen? actually no cycling at all, flow modulating abit at times but not shutting off. Its approx 1.7kwh per hour. I Have been running continuously since 930am, was off most of the previous day. Its due to shut off at 930pm and come on again at6am. Yes i have mvhr, why would i turn that off, to save electric? Thats on all year round and doesn't seem to use much at all. IAT in my kitchen 22,living room 21 and bedrooms @20 except gym room at 18, only 1 loop in there with big sliding door so doesn't heat as good but i don't mind that. I just read about some peoples usage and cant understand how mine is so much more.

The quantity of thermal energy being produced by the heat pump is given by the following:-

Flow Rate (lpm) x 60 = 21.8 x 60 = 1308 lph

Hourly Flow Rate x Energy required to increase 1 litre of water by 1C (1.16W) = 1308 x 1.16 = 1517W

Water temperature increase by heat pump = LWT - RWT = 29 - 23.6 = 5.4C

Thermal Energy produced by heat pump = 1517 x 5.4 = 8193W

The fact that you are not running your heat pump continuously throughout the whole day, means that it has to put sufficient thermal energy into your home in say 12 hours, to keep your home warm for 24 hours. So today, in 12 hours your heat pump may use 20.4kWh of electrical energy to produce 98kWh of thermal energy. If you spread those values over a 24 hour period, then 0.85kWh of electrical energy is on average producing 4.1kWh of thermal energy. I think that many, with the same size home, would be quite happy with those values.

Your MVHR is stated to be 90% efficient, so it is losing 10% of the thermal energy being exhausted from the system. Dependent upon the air flow rate this will add up over a 24 hour period.

 


   
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(@newhouse87)
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@derek-m Thanks man, feel more optimistic in my hp now. Also the flow rate is often above 30 it modulates a bit. I just don't get the continuous conclusion though. If i kept my current curve and ran for another 12hours it would uses twice the energy or would it modulate down and start shutting off abit more thus reducing energy consumption for some parts of the day?. The heat pump doesn't know im going to shut it off at a  certain time. The amount of energy produced and my usage for my home is ok so and nothing untoward going on in your opinion or should my house be roasting with that level being sent in? I can stop asking questions then hopefully.

The mvhr is important to prevent condensation im told as i had bit last year in real cold weather.

 

When i divide my energy produced by kwh meter im getting cop near 6 so its bit off compared to your calc but not too bad. Edit at 30l/min flow using your formula it would be near 6 like unit.


   
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