navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Heat pump CoP check, something seems off?  (Read 2815 times)
geoheated
Newbie
*
Offline Offline

Posts: 29


« 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.







« Last Edit: April 02, 2018, 02:03:24 PM by geoheated » Logged
DonL
Hero Member
*****
Offline Offline

Posts: 560


« Reply #1 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
Logged

Schuco solar hot water - 3300kWh/annum, 16 BP 4175N PV panels - 2.8kWp, log burner and back boiler and 18 Ying Li 235 PV panels - 4.2kWp, 42kW ground mount PV, 9kW Panasonic ASHP
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1429


« Reply #2 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.
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #3 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
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #4 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
Logged
brackwell
Hero Member
*****
Offline Offline

Posts: 2959


« Reply #5 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.
Logged
Mikel
Full Member
***
Offline Offline

Posts: 134


« Reply #6 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.
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #7 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).
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #8 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
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #9 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
Logged
marshman
Hero Member
*****
Offline Offline

Posts: 914


WWW
« Reply #10 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
Logged

3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #11 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
Logged
Stig
Sr. Member
****
Offline Offline

Posts: 452


« Reply #12 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
Logged
Mikel
Full Member
***
Offline Offline

Posts: 134


« Reply #13 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/

 
Logged
geoheated
Newbie
*
Offline Offline

Posts: 29


« Reply #14 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

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
Logged
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!