Going from Coal to Air Heat Source Pump and PV's using ECO4 grant scheme

Pec123

QrizB said:

You should be able to tinker with flow rates.

You can certainly ask the installer what flow temperature they have designed for, and (if you don't like the answer) ask if they could size radiators for a lower one. However, if you set it up correctly, your system will only need the max flow temp on really hard winter weather.

I've got gas (not a heat pump yet) and I suspect my system was designed for an 80C flow temp. But it's rare that I need more than 50-55C.

The above post has images of documents for a flow temperature of 45C

Pec123

Reed_Richards said:

It would be a very bad thing if the Eco4 scheme rules do permit a 55 C flow temperature from the ASHP.  That will give you a system that has a lower SCOP than for a 50 C flow temperature and so a higher running cost.  And this scheme is for people with low incomes and/or are on benefits, the last thing they need is a heating system that costs more to run than it might do.

45 C is not too low; it's really good but it might be more difficult to find suitable radiators in rooms where there is limited space to fit one.

Here's an example of a radiator scheme that would work at 45 C flow, a bit less actually

Room	Heat loss?	H x L	Type	Manufacturer		Divisor	Output	% of required
dining room	725	700x1600	k2	centre rad	3195	3.0 (HEG)	1065	147%
kitchen	824	700x1600	k2	centre rad	3195	3.0 (HEG)	1065	129%
bedroom 1	490	450x1400	k2	centre rad	1954	3.0 (HEG)	651	133%
lounge	822	700x1600	k2	centre rad	3195	3.0 (HEG)	1065	130%
hall	253	600x1000	k1	centre rad	949	3.0 (HEG)	316	125%
bathroom	663	700x1000	k2	centre rad	1982	3.0 (HEG)	661	100%
bedroom 2	404	600x900	k2	centre rad	1575	3.0 (HEG)	525	130%
bedroom 3	587	600x1600	k2	centre rad	2828	3.0 (HEG)	943	161%
	Total						Total
	4768						6291

I have changed every radiator except the ones in the dining room, the hall and in bedroom 3.  The figure in the new 5th column is the radiator output at a delta T of 50 C, taken from the CenterRad Compact leaflet on the Wolsey website.  I have divided this number by 3, rather than 1.9, which corresponds to a Delta T of about 22 C.

To get enough heat output in the kitchen and the lounge I have used the same large radiator as was suggested for the dining room and you would have to look and see if there is actually room for a radiator that big, particularly in your kitchen as kitchens rarely have much blank wall space.  The actual power consumed by all these radiators combined is less (by over 1 kW) than in the scheme that was suggested because they are running at a lower temperature.  The radiator in the bathroom is the least powerful compared to the actual requirement so there's room for improvement there, perhaps a smaller radiator and also a heated towel rail?

Please note that this is all based on guesswork that I am correctly interpreting the figures given to you.

The above post has images of documents for a flow temperature of 45C

Reed_Richards

The good news is that those revised radiator sizes are much better (more similar to the ones I suggested).  They'll give you a much lower heating flow temperature requirement so much lower running costs.  Great.  Now get a tape measure and check in each room that you have enough free wall space to fit those radiators.

You have also gained a study that was not there in the previous version.  Do you have any other rooms not accounted for?

Slightly bad news, there is a glaring error in the table of flow temperature and SCOP.  The figure given for 45 C just repeats the 55 C figure, it should be somewhere in between the 44 C figure (4.07) and the 46 C figure (4.21), so it should be 4.14, near enough.  If you point this out to Broad Oak I'm sure they will correct it.

I think this mistake is carried over to the data on the first page so the quoted SCOP for heating is much lower than should be.  I guess the problem is that these pages are churned out by a computer program and nobody looks at them too carefully so an obvious mistake like this is not spotted.

I haven't figured out why the quoted SCOP for hot water is so low; I'll look for clues.

   

Reed_Richards

Okay so the heat pump will heat your hot water to 50 C.  Once a week your immersion heater will come on and take the cylinder temperature to 60 C and hold it there for one hour as a precaution against Legionella.  That's normal.  Your figures indicate that the immersion heater will use 156 kWh of electricity per year to do that.  That's 3 kWh per week, probably an overestimate because the immersion heater should turn off once it reaches the 60 C set temperature and I think it should manage that in less than an hour.

However the data says that your immersion heater will consume 1514 kWh per year.  I don't understand why they think this but because you are predicted to be using your immersion heater quite a lot I presume this is why the quoted SCOP for water heating is so low.  I'm afraid it makes not sense to me.  I never use my immersion heater except for the weekly Legionella cycle.        

Reed_Richards

Anybody else care to comment?  I am contending:

1. The SCOP figure for 45 C operation is obviously wrong.
2. The SCOP figure for hot water is probably low because it is envisaged that the immersion heater will be used a lot. 

Heat supplied by immersion heater (kWh/yr) 1514

As a result, the calculated average SCOP for heating and hot water is only 2.52.  It would be a lot better if the correct SCOP for 45 C flow was used and the immersion heater was not used except for Legionella.  Could this be a "vampire load" issue for which the hot water is taking the blame?

{"Vampire Load" - my LG heat pump uses about 10 W when it's in "standby" doing nothing but a few heat pumps have an internal heater that pushes this up to 100 W or more and makes a heat pump unnecessarily expensive to run in summer when you only need it for hot water.  This has been termed "Vampire Load"]

    
 

QrizB

Reed_Richards said:

Your figures indicate that the immersion heater will use 156 kWh of electricity per year to do that.  That's 3 kWh per week, probably an overestimate because the immersion heater should turn off once it reaches the 60 C set temperature and I think it should manage that in less than an hour.

How big is the hot water tank?

Heating 200 litres of water by 10 degrees C will take 2.33kWh, per Omnicalculator.

https://www.omnicalculator.com/physics/water-heating

Reed_Richards

QrizB said:

How big is the hot water tank?

Heating 200 litres of water by 10 degrees C will take 2.33kWh, per Omnicalculator.

https://www.omnicalculator.com/physics/water-heating

You guessed/remembered correctly; it's a 200 litre tank, according to the first page of the screenshot pictures posted by the OP.  In which case the assumed 3 kWh per Legionella cycle isn't too far off.

QrizB

More luck than judgement really - the pictures are hard to view legibly on my phone

Pec123

Thank-you for your help so far I am most grateful.

Going forward how do I attach documents rather than images, it does not seem to give the option.

Reed_Richards

I don't think it's possible to add documents as such, but if it's a document on your device it might be possible to copy the contents and past those into the message (that's what I did for the radiator size table).

@Pec123, please check with your suppliers that that the documentation need to be amended for the larger SCOP (4.14)  that goes with the 45 C flow temperature.  And please ask them why they think you will be using the immersion heater so much.