GSHP COP with and without backup boiler
Good morning,
I have recently had a GSHP installed (Vaillant Flexotherm) including separate electric meters for the GSHP and GSHP Backup boiler. I also have a Sontex heat meter installed.
I have been monitoring the COP of the system daily to try and improve efficiency. The problem is that the efficiency increase greatly on the days the backup boiler is turned on once per week (for legionella) which I'm struggling to understand?? As far as I'm aware the backup boiler roughly produces 1kw of heat per 1kw electric input.
I'm calculating COP as follows. Heat Kw/ (GSHP Electric + Backup boiler Electic)
For example on the days the backup boiler is not on I'm averaging ~3.8 COP
The days the backup boiler is on I'm averaging ~4.2 COP
Any ideas will be greatly appreciated.
Happy to provide more info if needed?
That does sound surprising!
I expect that you're right - the backup heater is likely to be an inline immersion somewhere.
How do you measure the electrical energy? How well are the Sontex temperature probes attached (perhaps a photo?).
Which Flexotherm unit is it - I think they come in 5/8/11kW. So far as I can see, the units are simple on/off gshp ones with impressive COP, not inverter units(correct me if I'm wrong!).
If you run the unit continuously for (eg) an hour (make sure your thermostat is high) without backup heater, what heat energy do you get, and what Electrical does it take?
Ditto, but now with the heater on - what heat and electrical energy?
Thanks for the reply.
The electrical energy is measured via separate electrical meters, one for renewable (i.e. GSHP) and one for non renewable (i.e. backup boiler). I have attached a photo of this and the heat meters. Also the photo of where the sensors are connected.
It is a Flexotherm 11kw. It is sold as having a COP of 4.73 @ 35c flow temp. I'm unsure about whether it has an inverter.
I've run the pump with and without the backup boiler on.
26/01 - Backup boiler off - Electric 44.38kw; Heat 170kw; COP 3.83
30/01 - Backup boiler on - Electric 46.1kw (of which 5.24kw backup boiler); Heat 219kw; COP 4.75
One thought I had was that the DHW when being run by the GSHP was killing the efficiency/COP somehow? Maybe flow temps too high??
I don't think it's an inverter model - this says not:
https://www.toptenuk.org/consumer/product/view/VaillantGmbHflexoTHERMexclusiveVWF874
Perhaps you're right, and it's a "marginal COP" thing due to the DHW temperature. It seems very surprising. How hot does it run to for DHW?
Can you separate out hot water and heating? I assume that you have a hot water tank - does it have it's own immersion heater that you could use for a while, and stop the GSHP trying to heat it. Then run the experiment again - measure Heat and Elec both with and without the backup heater ?
Yes we have a hot water tank so I will try your suggestion of using the immersion to isolate the Heating and DHW.
The flow temps get up to 60c when the DHW is on. Looking at the 'Marginal COP idea' that could make sense if the flow temps are so high its actually less efficient.
I'll let you know how I get on.
- 26 Forums
- 2,171 Topics
- 47.8 K Posts
- 44 Online
- 5,744 Members
Join Us!
Podcast Picks
Latest Posts
-
RE: MCS certificate SCOP vs real-world performance
MCS:3.65 Reported by Vaillant: 3.96 (heating only); 3....
By JamesPa , 23 minutes ago
-
I think, based on what others have said here, that the ...
By JamesPa , 35 minutes ago
-
RE: Big Changes Coming to Our Heat Pump System
I'm intrigued by this exercise, so far you haven't repo...
By JamesPa , 38 minutes ago
-
RE: Mitsu PAR-WT60R Wireless Controller - options
@abernyte Thank you for passing on your experience and ...
By DavidAlgarve , 2 hours ago
-
RE: Powerwall 3 or Myenergi or something else?
Yes I was thinking of outdoor, IP65 batteries with buil...
By Temperature_Gradient , 3 hours ago
-
RE: Help me keep the faith with my air source heat pump installation
Water pump will certainly make a hum (which could conce...
By JamesPa , 6 hours ago
-
@jamespa Thanks. Yeah any adjustments Ive made at pr...
By cliffhanger , 6 hours ago
-
RE: How to choose Towel Rails for an ASHP
@rob-nezard yes absolutely. Here is the link and a pho...
By GrahamF , 2 days ago
-
@mixergy Thanks for the update, I would appreciate some...
By bontwoody , 2 days ago
-
RE: Is Your Broadband Router the Weak Link in Your High-Tech Home?
Unfortunately I'm not that well connected 😂 ...
By Scalextrix , 2 days ago
-
RE: A Customer's Lessons Learnt from a Heat Pump Installation in a Large House
It is interesting to see what our new Grant Aerona 290 ...
By GrahamF , 2 days ago
-
RE: Testing new controls/monitoring for Midea Clone ASHP
I've never physically seen it, but I seem to recall som...
By cathodeRay , 2 days ago
-
RE: Midea ASHP – how to set weather compensation
I noticed that too and thought the same thing, but then...
By cathodeRay , 3 days ago
-
RE: Ya can’t win! It is S*d’s Law!
@old_scientist If IOF is still running next late spring...
By Toodles , 3 days ago
-
RE: Electricity price predictions
Those of you on Agile will do well tomorrow; there are ...
By Toodles , 3 days ago
-
RE: Who’s Caved and Switched the Heating On Already?
We've been running our Ecodan system, installed in June...
By Sheriff Fatman , 3 days ago
-
Ok. Two schools of thought. The first is to run the ...
By JamesPa , 4 days ago
-
@drei Willing as I am to help, I don't think I'm yet ...
By JamesPa , 4 days ago
-
Selling 5 year old ASHP & Gas Combi Boiler - £590
Selling a 5-year-old Daikin Altherma Hybrid Air Source ...
By Paul G , 4 days ago