Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: geoheated on April 02, 2018, 01:56:04 PM



Title: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 01:56:04 PM
So i installed a Kensa 6kW GSHP last summer and its done well heating our house over the winter.

I installed a clamp-on energy meter (cheap but seems accurate enough when referenced to my house meter readings), to the HP Supply.

I am reading 2.65kW running current.

Looking over the datasheet, i get to the following conclusion:

@6C Return temps, which i currently have, the stated Output is 7.9kW, CoP = 4.77.

4.77 CoP * 2.65kW = 12.64kW (Clearly something wrong there)

Looking at it the other way:
7.9kw / 4.7 CoP = 1.68kW (Why am i seeing 2.65kW measured?)

So i looked at the published operating power, the datasheet states:
Typical running current @ B0/W35 amps = 10.4 Amps
Well, 10.4A x 240v = 2.496kW  (Not far off what i am measuring!)

The datasheet also states for B0/W35 = 6.5kW @ CoP = 4.13
But 6.5kW / 4.13 CoP = 1.57kW (Which would be equal to 1.57kW / 240V = 6.54 Amps)

Do you see my confusion here?

Data for reference below.

Look forward to other opinion's on this.


(https://s7.postimg.org/5n5aybqzr/kensa_data_compact_6kw.jpg) (https://postimg.org/image/5n5aybqzr/)

(https://s7.postimg.org/dfvyqcmp3/COP_0c.jpg) (https://postimg.org/image/dfvyqcmp3/)

(https://s7.postimg.org/q7a4wvrc7/COP_6c.jpg) (https://postimg.org/image/q7a4wvrc7/)


Title: Re: Heat pump CoP check, something seems off?
Post by: DonL on April 02, 2018, 03:50:13 PM
You don't mention your water temperature on the heating side of your pump. The COP of 4.77 is for a water exit temperature of 35C.
Don


Title: Re: Heat pump CoP check, something seems off?
Post by: Countrypaul on April 02, 2018, 04:17:26 PM
I'm not an electrician so may be looking completely in the wrong direction.

As far as I know the HP will not be a resistive device but an inductive one, therefore the power factor maybe significantly less than 1. From what I have read about the power meters previously they are generally not very good with purely inductive loads as they often assume a PF of 1.

You might be better off runing he HP for an hour and checking how much energy the Mains meter registers assumign there is nothing else significant running.


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 04:45:15 PM
You don't mention your water temperature on the heating side of your pump. The COP of 4.77 is for a water exit temperature of 35C.
Don

Hi,

Thanks for looking at this.

My output is between 35 and 37. So i read off the 35 column.

James


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 04:50:18 PM
I'm not an electrician so may be looking completely in the wrong direction.

As far as I know the HP will not be a resistive device but an inductive one, therefore the power factor maybe significantly less than 1. From what I have read about the power meters previously they are generally not very good with purely inductive loads as they often assume a PF of 1.

You might be better off runing he HP for an hour and checking how much energy the Mains meter registers assumign there is nothing else significant running.

Interesting note, thank you. I will investigate that more.

James


Title: Re: Heat pump CoP check, something seems off?
Post by: brackwell on April 02, 2018, 05:33:28 PM
It says typical running current 10.4 amps  =  2.496kW. Whats the problem ? Perhaps i am not understanding but you are quoting COP and others which i dont see on the spec sheets.


Title: Re: Heat pump CoP check, something seems off?
Post by: Mikel on April 02, 2018, 05:39:59 PM
Our Kensa GSHP displays a return temp which is set at 5 degrees below the output temp. Might be worth checking your manual to see whether it is the same.

Also, your electricity meter will read the total consumption for the GSHP and that includes the pumps for the ground loop and the central heating and hot water tank heating. Best to think of the quoted CoP as similar to car official consumption figures, I.e. not likely to be achieved in practice.


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 05:46:54 PM
Our Kensa GSHP displays a return temp which is set at 5 degrees below the output temp. Might be worth checking your manual to see whether it is the same.

Also, your electricity meter will read the total consumption for the GSHP and that includes the pumps for the ground loop and the central heating and hot water tank heating. Best to think of the quoted CoP as similar to car official consumption figures, I.e. not likely to be achieved in practice.

I have been through the settings in great detail over the winter and its set as follows:

Return Temp 32 Deg C (Which gives a rough output of 37 Deg C)
Differential 3 Deg C. (This is the amount the return temp must drop below 32 Deg C once the pump has stopped heating before it will start heating again, not to be confused with the "estimated/typical" 5 deg C differential between inlet and outlet while heating).


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 05:58:39 PM
It says typical running current 10.4 amps  =  2.496kW. Whats the problem ? Perhaps i am not understanding but you are quoting COP and others which i dont see on the spec sheets.

What i am saying is they quote two consumption figures, Current (Amps) and Power (kW). The power figure is tied to a CoP.

The power and current should somewhat correspond when you multiply voltage, but they dont.

They state B0/W35 Amps = 10.4 Amps, which equates to 10.4A x 240v = 2.496kW

However, they also state for the same conditions B0/W35, Power = 6.5kW @ CoP = 4.13
But 6.5kW / 4.13 CoP = 1.57kW

Why the huge difference?

I am measuring 2.65kW into the heat pump, at B6W35.
The datasheet states for B6W35 i would see 7.9kW @ CoP = 4.77 out of the heat pump.

But again, 7.9/2.65 = CoP actual of 2.98. Not the 4.77 stated.

All figures are on the datasheets in the first post.

Thanks


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 06:03:59 PM

Also, your electricity meter will read the total consumption for the GSHP and that includes the pumps for the ground loop and the central heating and hot water tank heating. Best to think of the quoted CoP as similar to car official consumption figures, I.e. not likely to be achieved in practice.

I would expect their published figures to include all power consumption for the unit. So the compressor, electronics and two pumps inside the unit. To clarify, i am measuring the power to the heat pump, no aux pumps i have installed.

I would agree you may / may not achieve the exact figures, but im 60% short of the expected CoP.
Hopefully its explainable.

James


Title: Re: Heat pump CoP check, something seems off?
Post by: marshman on April 02, 2018, 06:16:32 PM
I understand where you are coming from. I have a Thermia Duo G2. When running the heating, according to my power meter, it uses around 2.5kW (give or take), it does slowly increase when heating the hot water above 45 deg. Mine is a 10kW unit.  Looking at Thermia figures on their data sheet they add up like you expect. i.e. @ BW035 (inc circ pumps) elec input 2.2kW,  Heat output 9.4kW,  COP 4.24.  This matches closely what I get.  Their 6kW unit quotes:  elec input 1.3kW,  Heat Output 5.55kW, COP 4.04 - which is close to what you say you are expecting.

I would try to determine that the power figure you are seeing is what is actually being used - as others have said check against the electric supply meter - mu heatpump installer put a meter in on the GSHP supply. You only have to watch it count for a short time - count the flashes of the red LED and work from there.  If that tallies with your power meter reading then give Kensa a call and ask them to explain. Kensa are a respected make so I suspect we are missing something in respect of the figures on their datasheets.

I disagree with Mikel - the quoted figures for BOW35  are actual test figures and are achievable in real life if you have a properly designed and installed system. Its easy to verify (just measure temps in and out and power consumption) so therefore quite hard to cheat! Also the figures given by Thermia closely match what my system has actually achieved since install in late 2016, including over the recent cold snap.

Roger


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 02, 2018, 06:54:00 PM
I understand where you are coming from. I have a Thermia Duo G2. When running the heating, according to my power meter, it uses around 2.5kW (give or take), it does slowly increase when heating the hot water above 45 deg. Mine is a 10kW unit.  Looking at Thermia figures on their data sheet they add up like you expect. i.e. @ BW035 (inc circ pumps) elec input 2.2kW,  Heat output 9.4kW,  COP 4.24.  This matches closely what I get.  Their 6kW unit quotes:  elec input 1.3kW,  Heat Output 5.55kW, COP 4.04 - which is close to what you say you are expecting.

I would try to determine that the power figure you are seeing is what is actually being used - as others have said check against the electric supply meter - mu heatpump installer put a meter in on the GSHP supply. You only have to watch it count for a short time - count the flashes of the red LED and work from there.  If that tallies with your power meter reading then give Kensa a call and ask them to explain. Kensa are a respected make so I suspect we are missing something in respect of the figures on their datasheets.

I disagree with Mikel - the quoted figures for BOW35  are actual test figures and are achievable in real life if you have a properly designed and installed system. Its easy to verify (just measure temps in and out and power consumption) so therefore quite hard to cheat! Also the figures given by Thermia closely match what my system has actually achieved since install in late 2016, including over the recent cold snap.

Roger

Roger,

Great info, thanks for joining in.

I have just started a test, my DHW tank was down to 14 Deg C, so doing a full heat up. Logging the house meter v.s the clamp on HP meter.
I also have a clamp on meter for the whole house supply, so i can see how much the house is using to deduct that from the total and hopefully end up with an accurate estimate of the HP meter performance!

James


Title: Re: Heat pump CoP check, something seems off?
Post by: Stig on April 03, 2018, 07:42:38 AM
What I am saying is they quote two consumption figures, Current (Amps) and Power (kW). The power figure is tied to a CoP.

The power and current should somewhat correspond when you multiply voltage, but they don't.

That's because you don't know what the power factor is.


They state B0/W35 Amps = 10.4 Amps, which equates to 10.4A x 240v = 2.496kW

No, not necessarily...

https://en.wikipedia.org/wiki/Power_factor (https://en.wikipedia.org/wiki/Power_factor)


Title: Re: Heat pump CoP check, something seems off?
Post by: Mikel on April 03, 2018, 09:19:17 AM
Roger,

Re: Cop test conditions vs. actual installed conditions. I agree with you that a well designed system will perform more towards the CoP achieved under test conditions. The Energy Saving trust conducted a couple of studies years ago and found a wide variation of performance for ASHP and GSHP and hopefully the lessons learned have been put into practice. BTW, I was not suggesting that there was any cheating over the CoP tests.

For me, the most important measure is the SPF, Seasonal Performance Factor and this is the average CoP over the heating season.

For anyone interested: http://www.yougen.co.uk/blog-entry/2866/How+do+you+assess+the+efficiency+of+a+ground+source+heat+pump%273F/

 


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated on April 03, 2018, 09:23:08 AM
What I am saying is they quote two consumption figures, Current (Amps) and Power (kW). The power figure is tied to a CoP.

The power and current should somewhat correspond when you multiply voltage, but they don't.

That's because you don't know what the power factor is.


They state B0/W35 Amps = 10.4 Amps, which equates to 10.4A x 240v = 2.496kW

No, not necessarily...

https://en.wikipedia.org/wiki/Power_factor (https://en.wikipedia.org/wiki/Power_factor)

Thanks for this, seems you and Countrypaul are both highlighting most of my error in the readings i am taking.

So now i am running a 24hr test to see how my clamp-on meter measures compared to my main house meter.

Out of interest, does anyone know how the house meter compensates for the potential PF errors, i assume it wont have the same issue as the clamp-on??

I have learnt something from this experiment, great forum!
James


Title: Re: Heat pump CoP check, something seems off?
Post by: Stig 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...


Title: Re: Heat pump CoP check, something seems off?
Post by: marshman 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


Title: Re: Heat pump CoP check, something seems off?
Post by: geoheated 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 :-)