Posted by: @technogeek

↑

Hi All,

 

I have had my ASHP (Samsung HT Quiet) fitted about 2 months ago and slowly getting to know its functionality. Currently it is used to just heat the hot water in my old cylinder (170 litre solar tank with 2 coils, upper coil is used by the ASHP) which it manages to get from 36C to 55C in approx 30mins on average. The COP is working out to be about 2 for this. The hotwater cylinder is getting upgraded in October to a modern tank more compatibile with ASHP's.

I am wondering what COP other owners are getting for DHW generation to see if mine is OK or bad and if the new tank upgrade is going to make an improvement?

 

Cheers

TechnoGeek

Just over 2 for me too but that's for a whole year. Ecodan with new 250l tank. 

These are mine for the last week- legionella cycle is on a Monday hence the dip in average COP. Weather has been 15-17 C most days this week. 180L tank and 46C desired temp (60 C for legionella cycle)- not sure on its coil size yet. The installer is going back to his designer though as they reckon they can improve on it. Haven’t got winter figures yet. 

We heat our 10yr old solar tank with a gshp.  It used to just heat the top coil with up to 55C flow, getting the water tank to ‘maybe’ 43C.  In the Nov freeze one of our solar thermals bust, so I’ve retired this system and replumbed the tank - now the gshp still does the top coil(0.4m2) and also is seriesed into the lower ‘solar’ coil (1.6m2).  I’m pleased with the result - we get 50C dhw now, with the same flow temp.  43 was a bit marginal for Mrs Robl, and she’s now happy!  I also prefer to run the gshp system throughout the year - best not to find any faults only when it gets cold.  Weekly 65C achieved with an immersion, after the gshp is done with it, all times to be Octopus Go time.

I think our mean dhw COP is 2.5, hugely influenced by the push to get to the upper temperatures.

The pic maybe attached shows COP versus Tflow heating (orange) and dhw(blue) during the heating season.  There’s a lot of blue dots at over 50C flow - the last bit is hard work, so actually makes a big difference to the COP.  Pipe losses increase markedly at over 50C, and the gshp is only 2.5kW.

I also have a Samsung HTQ 14kw, now it's working for 7 days only for DHW and my COP is also about 2.

Why its so bad?

150L Tank 45-50C outside 15-26C

Posted by: @kocta

↑

I also have a Samsung HTQ 14kw, now it's working for 7 days only for DHW and my COP is also about 2.

Why its so bad?

150L Tank 45-50C outside 15-26C

Whilst a COP of 2 may not be brilliant, it is certainly not bad. If the DHW was heated via an immersion heater then the COP would be 1.

@kocta Hi please to meet you!

That is interesting to know. I assume your COP is acheived with a modern DHW tank?

At the moment to heat the tank (50% of a 170L solar tank) from 36C to 55C my ASHP uses approx 2.8Kwh a day (50% at 9.5p / Kwh and 50% 31p / Kwh) costing 56.7p a day.

My oil boiler uses 1.1 litres a day (I have an inline oil meter) to do the same job costing 70.5p based on the oil price I paid in June, so I am happy it is costing less even with a COP = 2. If there is a way to improve on this even further I am willing to try, hence having a new unvented cylinder fitted in October which is specifically designed for ASHP's. If it improves great, as a minimum I will save the electricity running the shower pumps as I will no longer need them! 🙂

@TechnoGeek Hi nice to meet you too!

I have my old tank from 2018

I just was expecting little bit more than COP of 2, from a new Samsung Heat Pump in the summer. But maybe there's a way to optimize the pump.

But if you say you have simmulare results

Posted by: @derek-m

↑

Posted by: @kocta

↑

I also have a Samsung HTQ 14kw, now it's working for 7 days only for DHW and my COP is also about 2.

Why its so bad?

150L Tank 45-50C outside 15-26C

Whilst a COP of 2 may not be brilliant, it is certainly not bad. If the DHW was heated via an immersion heater then the COP would be 1.

 

What you also need to remember is that when the heating is off, all the fixed overheads of keeping the ASHP on standby, running the controllers and all the pumps, etc., are (for proper COP calculations at least) included in the energy consumed number used to work out the HW COP. That's not the case when the heating is on for all or most of the day

I've a HQT and get a COP around 3 on hotwater (trusting the samsung heatoutput and electricity input reported values, I've no glycol so the heat ouput is likely over estimated). 
It does default to a strange mode where the immersion is used as well as the HP which will kill the COP. To get out of this you need to use 'economic' mode, but that also only heats to 5deg below your set point unless you go messing in the installer menus to remove the offset

@kocta Being the curious engineer that I am, I decided to do a little experiment with my metered oil boiler and heat pump and got some further questions to be answered!

Heating the same volume of water from approx 38 C to 55 C I found the following:

Oil boiler consumed 0.56 litres and has an efficiency according to manufactures data for DHW generation of 59.1%

So: 0.56ltr x 10.1 Kw/ltr x 0.591 efficiency = 3.34 Kw heat energy to heat hot water to 55C

Heat Pump used 1.1Kw and registered 2.2 Kw heat generation @ambient temp 20C, flow temp of 66C on the controller to do the same job giving a supposed efficiency of 2.2Kw / 1.1kw = 2.0

At an ambient temp of 20C and flow of 66C the minimum efficiency should be about 3.2

If the oil boiler generated 3.34Kw heat to generate the hot water why has the HP supposedly only needed 2.2Kw of heat to do the same job, where has the extra 1.1Kw disappeared to?

So using the oil boiler output of 3.34Kw / 1.1Kw HP Elect = HP efficiency of 3.03 ( approx correct with Samsung datasheet for the environmental conditions)

That has left me unsure whether to believe or am I misunderstanding the energy generated figure supplied by the controller? Is it generated heat + input power = total output power?

Hopefully someone can clear up the mystery!

As I understand it, which a dangerous start to any internet fora post, what we refer to as the COP in an ASHP is actually the measure of how efficient a heat pump is at turning electrical energy into usable heat.  So the energy out divided by the energy in = COP which is this case is 2.2kW/1.1kW = 2. So if that is correct then the problem lies in the assumptions made in calculating the efficiency of the oil boiler.  It would appear that the efficiency of your oil boiler is only 35%

I bet that I have this totally wrong!