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Author Topic: Heat pump CoP check, something seems off?  (Read 5697 times)
Stig
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« Reply #15 on: April 03, 2018, 10:18:18 AM »

The house meter measures the actual power by multiplying the voltage and current together.  Your clamp is only measuring the current and doesn't know its phase wrt the voltage.

Checking your clamp-on meter vs. your house meter will give you an idea of the total power factor of your house, you'd need to switch everything else off except the heat pump to do the test for just the heat pump's power factor.  That might be inconvenient...
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marshman
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« Reply #16 on: April 03, 2018, 10:39:49 AM »

Agree on the power factor thing BUT The figures from Kensas own datasheets do not add up. The ones on my Thermia Duo data sheet do..  I/p x COP = O/p 

Even assuming a power factor of 0.8 (it shouldn't be worse than this really) it is still consuming 2.1 kW (assuming indicated 2.6kW on power meter).  Something doesn't add up in my opinion, or the measured input power is way off for other reasons (such as assuming 240V input when the mains voltage is much lower at  say 226V) That coupled with the power factor could make the numbers work (just) - but still doesn't answer the spec. sheet difference.

Roger
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geoheated
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« Reply #17 on: April 03, 2018, 08:40:48 PM »

Did 4 tests measuring the apparent power factor between the house meter and the heat pump clamp-on meter.

Its coming it quite reliably at 0.77 each time. Seems a bit lower than expected, but that does factor in the clamp-on meter accuracy as well as an overall correction/power factor.


So that now corrects my initial results to:

When measuring 2.65kW, actual was closer to 2.65*0.77 = 2.04kW

For B6/W35 (actual conditions) the datasheet stated output is 7.9kW with a CoP = 4.77.

I am however still only getting:

7.9 / 2.04 = CoP 3.87

Gettting there, needs more investigating yet... I still agree with Roger that the datasheet isnt clear.


Noticed near the top of the datasheet, it also states "power consumption" at 2.1 with no units (assume this is kW) for B0W35, with a CoP of 4.13, so you would assume that the output would therfor be 2.1*4.13 = 8.67kW ?

But the other page of the same datasheet says B0W35 for the heat pump gives 6.5kW output and CoP = 4.13. So you would assume that meant input power of 6.5/4.13 = 1.57kW.

Go figure? Maybe time to ask Kensa :-)







« Last Edit: April 03, 2018, 08:53:49 PM by geoheated » Logged
geoheated
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« Reply #18 on: October 23, 2019, 01:13:40 PM »

Soon i hope to update this thread, never understood the figures from Kensa....

So i am installing a Kamstrup 403 heat meter soon and have some good monitoring / data logging kit from https://openenergymonitor.org/

Seeing the run cycles of a fixed speed compressor with warm ground return temperatures at this time of year (12 degC), the nominal 6kW (B0W35) is giving out  9+kW (see last attachment), great, but not if your fixed speed and cycling a lot.
Even at the predicted 9+Kw output, it is pulling 2.4kW, so COP <4.0. Data sheet states >5.2 (Data only published upto 10 degC ground return). So what is up ?

The UFH cannot dissipate anywhere near that so lots of start/stops, the buffer helps but...

Example of initial log:
HP controller setup to stop heating at return Temp = 32, (typically giving a flow out of 37 degC)
Delta 2 (Start heating again at 30 degC return temp).

As is very clear, the heating flow temp only spends 4 minutes > 35 deg C, then 24 minutes with a flow temperature falling from 35 down to 30.

So actually the floor only operates at 35+ water flow for 14% of the time.
Doesn't seem like the best way to operate. An inverter driven pump would modulate to near constant 35 water out and would give a lot more heat capacity from the floors over this time.

Just the start of my logging experience to answer this, will share the results once fully setup.

Data for reference:

Kensa state here that at 2.1kW consuption (B0W35) the COP =4.13.
https://www.kensaheatpumps.com/wp-content/uploads/2014/03/TI-Compact-Single-%E2%80%93-11.pdf

That would assume a thermal output for (B0W35) of 2.1 x 4.13 = 8.67kW.
However the other data sheet (below, attached as image as since deleted from their website) states that at (B0W35) output = 6.5kW, which seems more likely for a 6kW HP. So the 4.13 COP cannot be true, or the 2.1kW consumption figure is wrong. but from measurements it is not!
So the COP is more like 6.5/2.1 = 3.1 and i intend to prove this.

 

Also sharing the 10 deg C return temperature data, which is closest to where i am operating currently.



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geoheated
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« Reply #19 on: October 23, 2019, 02:55:42 PM »

Where as, take the Kensa Evo Series. The numbers do add up.

1.7kW consumption on 7kW model data sheet.
https://www.kensaheatpumps.com/wp-content/uploads/2017/02/TI-Evo.pdf

From the output sheet. As you would expect.
7.72kW output (B0W35)
4.52 COP
=7.72/4.52 = 1.7kW
https://www.kensaheatpumps.com/wp-content/uploads/2015/09/TI-Actual-Thermal-Outputs-1.pdf

So what changes between performance measurement of the Compact to the Evo? Both were evaluated to EN14511.


« Last Edit: October 23, 2019, 04:17:23 PM by geoheated » Logged
nowty
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« Reply #20 on: October 23, 2019, 03:22:12 PM »

Welcome to the real world and not the manufactures datasheets based upon impossible to achieve assumptions and do they include the water pumps power use ?

See the report written by the energy saving trust on heatpumps.
https://www.energysavingtrust.org.uk/sites/default/files/reports/TheHeatisOnweb%281%29.pdf

The ground source heat pump installations they measured, the COPs varied between 1.6 and 3.8 with an average of 2.8. So yours sounds about right.

Example, my heatpump has a COP spec of about 4.7, but that's based on a ground return of 15 degrees and a water flow rates I can only get half off. So I get a working COP of about 3 which I am happy enough with.
« Last Edit: October 23, 2019, 09:15:13 PM by nowty » Logged

12kW+ of PV installed and 60+ MWh's generated.
Home battery storage of 40+ kWh's.
Hot water storage of 15+ kWh's.
Heat storage of 15+ kWh's.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
290,000+ litres of water harvested from underground river.
geoheated
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« Reply #21 on: October 23, 2019, 04:20:56 PM »

Welcome to the real world and not the manufactures datasheets based upon impossible to achieve assumptions and do they include the water pumps power use ?

See the report written by the energy saving trust on heatpumps.
https://www.energysavingtrust.org.uk/sites/default/files/reports/TheHeatisOnweb%281%29.pdf

The ground source heat pump installations they measured, the COPs varied between 1.6 and 3.8 with an average of 2.8. So yours sounds about right.

Example, my heatpump has a COP spec of about 5, but that's based on a ground return of 15 degrees and a water flow rates I can only get half off. So I get a working COP of about 3 which I am happy enough with.

Thanks, interesting article, i will be reading it with interest!

What i am surprised is that at specific quoted temperatures, the electric consumption is greater than advertised. This is not excusable.

The water pumps will be included as they come off the single supply to the heat pump and are build into it.
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Countrypaul
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« Reply #22 on: October 23, 2019, 04:50:05 PM »

The PDF you linked to where the power is given as 2.1  also gives the typical runing current at 10.4A based on 220-240V, whihc would suggest a figure somehwat higher than 2.1kW to me.
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geoheated
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« Reply #23 on: October 23, 2019, 06:45:50 PM »

Ah yes, i fell into that trap earlier on in this thread.

We think its the inductive load power factor. Typically 0.8.
Brings it much closer to the 2.1kW on the same data sheet.

I am logging true power from a meter now so i will log that against the heat output with a Kamstrup and see what the true COP is.

At the same temperatures on their data sheet there should be very little variation. But early indications are far from that.
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nowty
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« Reply #24 on: October 23, 2019, 07:03:43 PM »

What i am surprised is that at specific quoted temperatures, the electric consumption is greater than advertised. This is not excusable.

The water pumps will be included as they come off the single supply to the heat pump and are build into it.

But they are also quoted at specific design water flow rates which may be unachievable and you have not mentioned whether you have measured the flow rates or not. If your flow rates are lower than the design rates, then you will get a larger difference between your water flow temp and the compressor gas temp so the gas temp will be higher and therefore won't be as efficient as the datasheet values.

Just because the water pumps are built in does not necessarily mean they are included in the datasheet figures. I mean the pump power consumption of them will depend on the viscosity of the fluid (different antifreeze concentrations) and the resistance of your pipework.
« Last Edit: October 23, 2019, 08:19:45 PM by nowty » Logged

12kW+ of PV installed and 60+ MWh's generated.
Home battery storage of 40+ kWh's.
Hot water storage of 15+ kWh's.
Heat storage of 15+ kWh's.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
290,000+ litres of water harvested from underground river.
marshman
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« Reply #25 on: October 23, 2019, 08:35:40 PM »

When you are measuring the power input are you recording the actual output water temperature or just what the cut off is set to? Also as Nowty said have you checked flow rates and temperature difference between flow and return on the brine side?

This document illustrates the quite dramatic effect input and output temperatures have on the COP.

When I had mine installed I was told you need a flow rate of around 3 litres/min per 1 kW heat output. My system (10kW) has four loops flowing 8 litres/min so actually 3.2 litres/min.  Also was told to ensure temperature difference flow to return was around 3 deg C.

This Kensa document is quite good:

https://www.kensaheatpumps.com/the-unbendable-rules-of-ground-arrays/

Note also the comment on the power taken by the ground loop pump.  As Nowty says the viscosity of the fluid also makes a big difference - is the antifreeze mix correct, too much antifreeze will make the liquid too viscous for efficient circulation.

In terms of a non modulated compressor cycling on and off and maintaining 35 deg for the  UFH.  It has been mentioned on here before that if you have a heatpump it is far more efficient to run it for longer periods at lower temperatures than to run it like a Gas or oil boiler where it is heating for a few hours in the morning and late afternoon/early evening.  My system actually runs 24/7 during the heating season.  The heatpump will come on and heat the UFH water including the small buffer tank  upto target temp then switch off for a variable period of time. The water then slowly cools down before the next heatpump heating cycle. What I have observed is that the controller aims for a long term average temperature. In my case it seems to be in the low to mid 20's. As this is circulating 24/7 it essentially just balances the heat loss from the house. When it is really cold (really cold for here is only -2 or -3 deg),  the pump will fire up for at most 20mins once an hour, never seen it do more than that. More typically it is on for 10 to 15 mins every 1.5 to 2 hours.  So it is the average you are looking at and not the instantaneous UFH temperature.  If I feel the flow pipe to the UFH, unless the heatpump has just switched off, you can hardly feel it is warm yet the house stays a nice stable 20 deg C in the living areas, bedrooms are a bit cooler, and it never varies.

As others have said I doubt you are going to get a real world COP of much more than 3, less if you are regularly using it for DHW as well.

Is your actual electricity bill a lot higher than you think it should be?  I can monitor the instantaneous power consumption of my pump and at certain times - near the end of a DHW cycle - and the input power can be over 4kW for a short time. If your bills arn't excessive and all your flow rates and temps are correct I wouldn't worry too much.

Roger
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geoheated
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« Reply #26 on: October 24, 2019, 08:42:45 AM »

Roger, Nowty,

Thanks you both for the input here.

I dont have an accurate setup yet so a lot of your concerns will be answered when i have it, until i get the Kamstrup with its ultrasonic flow measurement, i wont have accurate heat flows etc.
I did some quick checks some time ago, taking the rough flow rates from the UFH manifold and it was 22l/min, the KENSA datasheet states design flow is ~18, so i dont think i will be far off and unlikely to be lower.
When taking data i keep all UFH circuits open to fix ensure constant flow.

I will have to look back but when commissioning the ground loops i did a timed flow test between two water butts, i will dig that out for interest. The glycol was mixed precisely, i have no concerns around flow rates and i agree it can effect performance if too low, so i will be evaluating any final data with flow for validity.

The main point i seek to prove in all this is that if the data sheets for the Kensa Single Compact do not add up, and the COP is the over-stated value.
Even in principle with perfect conditions, the COP, kW-Draw and kW-Heat do not calculate out.

I take your point about pump draw. I cant imagine their data sheet for the heatpump would not include it in the kW draw figures as the pumps are fed off the single supply so they would be mis-leading any electrical installer, however, even if so, those two pumps only draw 200watts at operating condition (i have the pump curves), so they dont explain the missing 530 watts (6.5kW @ 4.13 COP = 1.57kW draw, but stated and measured is 2.1kW+).

However, going to their latest EVO heatpump, the datasheet figures do add up, as expected.

My Single Compact 6kW: (B0W35) states:
2.1kW draw
COP 4.13
6.5kW Heat output. (INCORRECT 2.1x4.13=8.7kW, over 2kW out, and no way this HP puts out 8.7kW at B0W35! COP has to be 3.1)

EVO 7kW: (B0W35) states:
1.7kW draw
COP 4.52
7.72kW Heat Output (CORRECT for 1.7x4.52=7.7kW )

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geoheated
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« Reply #27 on: October 24, 2019, 09:01:48 AM »

What i am surprised is that at specific quoted temperatures, the electric consumption is greater than advertised. This is not excusable.

The water pumps will be included as they come off the single supply to the heat pump and are build into it.

But they are also quoted at specific design water flow rates which may be unachievable and you have not mentioned whether you have measured the flow rates or not. If your flow rates are lower than the design rates, then you will get a larger difference between your water flow temp and the compressor gas temp so the gas temp will be higher and therefore won't be as efficient as the datasheet values.

Just because the water pumps are built in does not necessarily mean they are included in the datasheet figures. I mean the pump power consumption of them will depend on the viscosity of the fluid (different antifreeze concentrations) and the resistance of your pipework.

To conclude the concern of pump power. The datasheet of the the HP is for the entire unit, they couldn't (Shouldn't) state the power consumption of just one component inside (compressor) the unit and not others (2 pumps).

With regards to flow rate effecting pump power drawn. Kensa state 19.2 kg/min design flow for the ground loop. The density of the glycol/water mix is 1100kg/m3 (+/-4kg/m3 with temperature). =  1.047m3/h

Take the pump cure, that's right on about 150watts.

If the flow was to double or halve, it would only be +/- 20 watts, no influence on the 2.1kW overall.

So im not worried about pump influences on electric consumption or this assessment. 





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geoheated
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« Reply #28 on: October 24, 2019, 09:51:30 AM »

When you are measuring the power input are you recording the actual output water temperature or just what the cut off is set to? Actual temperatures, see my early log chart a few posts up. I have flow and return of both sides.
Also as Nowty said have you checked flow rates and temperature difference between flow and return on the brine side? Yes

This document illustrates the quite dramatic effect input and output temperatures have on the COP.

When I had mine installed I was told you need a flow rate of around 3 litres/min per 1 kW heat output. My system (10kW) has four loops flowing 8 litres/min so actually 3.2 litres/min.  Also was told to ensure temperature difference flow to return was around 3 deg C. Interesting rule of thumb, i have an estimated (TBC) heating flow of 22l/min = 22/3 = 7.2kW for my 6kW HP, sounds good.

This Kensa document is quite good:

https://www.kensaheatpumps.com/the-unbendable-rules-of-ground-arrays/

Note also the comment on the power taken by the ground loop pump.  As Nowty says the viscosity of the fluid also makes a big difference - is the antifreeze mix correct, too much antifreeze will make the liquid too viscous for efficient circulation. Mix is correct at 25%, low delta across ground flow/return suggests good flow is still being achieved.

In terms of a non modulated compressor cycling on and off and maintaining 35 deg for the  UFH.  It has been mentioned on here before that if you have a heatpump it is far more efficient to run it for longer periods at lower temperatures than to run it like a Gas or oil boiler where it is heating for a few hours in the morning and late afternoon/early evening.  Agree! My system actually runs 24/7 during the heating season.  The heatpump will come on and heat the UFH water including the small buffer tank  upto target temp then switch off for a variable period of time. The water then slowly cools down before the next heatpump heating cycle. What I have observed is that the controller aims for a long term average temperature. Which controller do you have out of interest? In my case it seems to be in the low to mid 20's My UFH is designed for 35 degC flow, if i ran it in the 20's i would never achieve the heat input required to replace my losses, i have peak losses at -2.1 degC outdoor temp of 4.9kW, so expect my 6.5kW HP to run at least 75% of the time. . As this is circulating 24/7 it essentially just balances the heat loss from the house. When it is really cold (really cold for here is only -2 or -3 deg),  the pump will fire up for at most 20mins once an hour So approx 1/3 x 10kW heat pump, on all day, so your heat loss < 3.3kW for the whole house? Sounds very good!  , never seen it do more than that. More typically it is on for 10 to 15 mins every 1.5 to 2 hours That would =~ 0.125 x 10kW = 1.25kW heat loss being replaced by the HP, is that right?.  So it is the average you are looking at and not the instantaneous UFH temperature.  If I feel the flow pipe to the UFH, unless the heatpump has just switched off, you can hardly feel it is warm yet the house stays a nice stable 20 deg C in the living areas, bedrooms are a bit cooler, and it never varies.

As others have said I doubt you are going to get a real world COP of much more than 3, less if you are regularly using it for DHW as well.

Is your actual electricity bill a lot higher than you think it should be?  I can monitor the instantaneous power consumption of my pump and at certain times - near the end of a DHW cycle - and the input power can be over 4kW for a short time. If your bills arn't excessive and all your flow rates and temps are correct I wouldn't worry too much.

Roger
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marshman
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« Reply #29 on: October 24, 2019, 10:42:00 AM »

The controller is built into the heatpump. It monitors the outside temperature and that is all. There is no temperature sensor in the house. The controller "simply" looks at the heat being taken by the system, I assume by the rate of decrease in temperature of the circulating water, and decides when it needs a "boost". There is a "heat curve" which you can adjust, nudge it down a bit if the house is too warm and up a bit if it is too cold. I spent the first heating season after the system was installed tweaking this and have not touched it since. Brilliant system as it just works.

Pretty sure the figures/timings I quoted are correct.  Heating is usually active from end of October through to end of April - give or take a week or so. Last heating season the heatpump (including all circulating pumps) used 1264 kWh for heating and DHW. This equates to approx 7kWh per day (1264kWh/180days).  Highest daily consumption recorded last year was 13kWh (inc. DHW).  House an old detached 5 bedroom Farmhouse in an exposed spot near the English Channel, approx 240 sqm. Living rooms sit at 20 degC 24/7, bedrooms a bit cooler. There are no zone valves in the UFH at all, I have just spent time balancing the flow round the loops to get the various room temps where I wanted them. There is one circulating pump for the whole house and this runs on its lowest setting consuming < 10W.

Roger
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