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

matt_drummer

If the pipework is a deal breaker then it's not actually an option for you.

In the nicest possible way, if one option is not really an option then there is no real point asking anybody what they would choose with any expectation that it would influence your decision.

You could get it installed and then reroute the pipework later at your own cost.

I would assume that anything done for free would be to a high enough standard to work properly but probably won't be the same as if you were paying yourself, they will take the path of least resistance to achieve the aims of the scheme.

I honestly would go for the better heat pump.

I can see the heat loss as averaging 8.5kW. Have they been more specific?

What is your heat loss at the lowest expected outside temperatures?

How big is your house?

Not that big judging by the number of radiators? 

How many square meters?

Pec123

matt_drummer said:

If the pipework is a deal breaker then it's not actually an option for you.

In the nicest possible way, if one option is not really an option then there is no real point asking anybody what they would choose with any expectation that it would influence your decision.

You could get it installed and then reroute the pipework later at your own cost.

I would assume that anything done for free would be to a high enough standard to work properly but probably won't be the same as if you were paying yourself, they will take the path of least resistance to achieve the aims of the scheme.

I honestly would go for the better heat pump.

I can see the heat loss as averaging 8.5kW. Have they been more specific?

What is your heat loss at the lowest expected outside temperatures?

How big is your house?

Not that big judging by the number of radiators? 

How many square meters?

Thank-you we have looked at it again and agree with you.
116m/2. I have to enquire about: Have they been more specific? What is your heat loss at the lowest expected outside temperatures?

matt_drummer

Pec123 said:

matt_drummer said:

If the pipework is a deal breaker then it's not actually an option for you.

In the nicest possible way, if one option is not really an option then there is no real point asking anybody what they would choose with any expectation that it would influence your decision.

You could get it installed and then reroute the pipework later at your own cost.

I would assume that anything done for free would be to a high enough standard to work properly but probably won't be the same as if you were paying yourself, they will take the path of least resistance to achieve the aims of the scheme.

I honestly would go for the better heat pump.

I can see the heat loss as averaging 8.5kW. Have they been more specific?

What is your heat loss at the lowest expected outside temperatures?

How big is your house?

Not that big judging by the number of radiators? 

How many square meters?

Thank-you we have looked at it again and agree with you.
116m/2. I have to enquire about: Have they been more specific? What is your heat loss at the lowest expected outside temperatures?

My heat loss is about 6.50kWh at 21c indoors and -3c outside but that includes a conservatory.

My house is about the same size as yours and I have 13 radiators in total.

I have a 9kW Daikin heat pump and I think it is too big.

It gets a bit complicated and I have quite sophisticated monitoring on my heat pump.

The heat produced at its lowest output is more than my house needs at current outdoor temperatures.

You live in Scotland so it may be colder than it is here for more of the time.

Even so, a 14kW heat pump seems quite large for that house.

I don't know what radiator sizes they intend to fit but unless they are really massive then I would imagine you would need to run at higher flow temperatures than is ideal.

Maybe you have a schedule of radiator types and sizes?

The heat output of radiators fall the closer the mean (average) flow temperature is to the room temperature.

As an example the heat output from a radiator with a mean flow temperature of 30c and a room temperature of 20c is about 13% of the same radiator with a mean flow temperature of 70c (typical with a gas or oil boiler) and a room temperature of 20c.

If the radiators are too small and the heat pump is too big there won't be enough capacity to disapate the heat output of the heat pump.


I know that all sounds a bit complicated and it is. The key to a successful heat pump installation is in the planning.

Slapping in a great big heat pump sounds great, but it really isn't, too big is almost as much of a problem as too small. If it is too big it may not turn down enough for your house which means you won't get long efficient runs. If it is too small your house won't get hot enough on the coldest days. They really need to be just the right size.

The heat pump will still work pretty well even if its a bit too big, it is just that it probably won't be as efficient as it could be.


I would ask more about the heat loss, you need to know what it is at the minimum average temperatures you experience and at what room temperatures.

It should be something like 8.5kWh at 20c inside and -5c outside - that's just an example

Both the heat pumps you have been quoted for perform well so you should get good results.

Just double check the size.

Also read some forums, don't just take my word for it. I know a bit but I'm not an expert or a heating engineer.

I am just passing on a lot of the information and knowledge that has been passed to me in the last couple of weeks in respect of my under performing heat pump.

matt_drummer

Also have a look here.

HeatpumpMonitor.org

You can view various heat pumps from different manufacturers installed all over the country in different sized houses.

You can look at many of the heat pump's performance in detail.

You will be able to see things like heat produced, electricity consumed, flow rates and temperatures.

You will see varying levels of performance from SCOPs of 2.50 to over 5.00.

Some heat pumps are over 500% over the course of  a year. Those over 4.00 are doing really well.

You will see Mitsubishis and Grants there

Pec123

I have misread and quoted wrong thing. It is actually 8.5KW but range can go to 14KW. Sorry learning all the time!

Radiator Information
dining room 725 700x1600 k2 centre rad 1.9 (HEG) 1682 1682 100%

kitchen 824 700x800 k2 centre rad 1.9 (HEG) 831 831 100%

bedroom 1 490 400x1400 p+ 1.9 (HEG) 760 760 100%

lounge 822 400x1400 k2 krad 1.9 (HEG) 982 982 100%

hall 253 600x1000 k1 centre rad 1.9 (HEG) 499 499 100%

bathroom 663 600x1000 p+ centre rad 1.9 (HEG) 704 704 100%

bedroom 2 404 600x1000 k1 krad 1.9 (HEG) 500 500 100%

bedroom 3 587 600x1600 k2 centre rad 1.9 (HEG) 1488 1488 100%

New Renewable System Informaon

Type of System Air Source Heat Pump * This calculator is not designed to be used for Solar Assisted Heat Pumps

Manufacturer Name mitsubishi

Manufacturer Model puz-WM85VAAMCS Cerficaon Number -037-0033-20-03-3.48 * Available from the MCS Product Directory

Flow Temperature 55 °C * Determined by the temp. of the water leaving the HP when supplying space heang at the external design temp.

MCS SCOP Heang 55 * SCoP - Seasonal Coefficient of Performance. This value is based on the MCS HP SCoP Table below

MCS SCOP Hot Water 1.75 * If providing space heang and DHW, default value from SAP2012. IF DHW only see methodology in MIS3005

Renewable System Provides Heang and Hot Water

Hot Water Immersion Use Once per week * based on 50°C up to 60°C, 3kW

Size of Hot Water Cylinder 200 ltr

matt_drummer

You have 7.50 kW of radiators and I would assume that is based on their performance at a delta t of 30 - 50c mean flow temperature and 20c room temperature. It looks like they are designing on 55c incoming flow from the heat pump. It will cost a fortune to run like that.

Those radiators will put out about 3.75kW at a delta t of 15c - that would be with a flow temperature of 35c and a room temperature of 20c

Your average heat loss is 8.5kW but you say up to 14.5kW

I predict you will be cold with those radiators on the coldest days and on others you will be running a high flow temperature just to keep warm. You have no chance of keeping warm with those at low flow temperatures if the heat loss is correct.

7.50kW of heat can't replace 14.5kW of heat loss.

I would say that they are nowhere near big enough.

I would check with somebody else.


I have 9kW of radiators at a delta t of 30c and my heat loss is only 6.5kW.

And I don't think my radiators are big enough, they are OK but if I want to run lower temperatures when it is really cold mine need to be bigger.

Reed_Richards

I have not really been following this thread but it looks as if your design is for a flow temperature of 55 C for central heating.  In my opinion this is too high.  My heat pump system was designed around a flow temperature of 50 C and with hindsight I wish I had got larger area radiators and made the target flow temperature 45 C.  The lower this temperature is, the more efficiently your heat pump will run and so the lower will be your running costs.  

If (this is a guess) the first figure is the actual calculated heat loss for the room then the radiators in the dining room and bedroom 3 are greatly oversized for the required heat output, the one in the hall is quite large and but the one in the kitchen falls a bit short.

k2 radiators are a bit fatter than k1 or p+ types but have a higher heat output.  If you used k2 radiators throughout you might be able to use a lower design flow temperature and save yourself some running costs.  But the one in the lounge would need to be physically larger.  Or there are k3 radiators which are really fat but give out even more heat.

Also , they don't tell you what SCOP to expect for heating (or "heang" as they call it).  This is a serious omission.  You should be looking for a figure of at least 3, in my opinion.   

Reed_Richards

By the way, my guess is that the number 1.9 represents a divisor on the Delta T = 50 heat output value for each radiator.  So that would probably mean they assume a flow of 55 C and a return of 50 C, the 5 C difference being standard for a heat pump.  So if your rooms temperatures are 21 C that would make your actual delta T 31.5 C.  That's about right for divide by 1.9.

I see @matt_drummer replied whilst I was still writing my previous comment and he agrees with me that the 55 C flow temperature is too high. 

matt_drummer

Pec123 said:

I have misread and quoted wrong thing. It is actually 8.5KW but range can go to 14KW. Sorry learning all the time!

Radiator Information
dining room 725 700x1600 k2 centre rad 1.9 (HEG) 1682 1682 100%

kitchen 824 700x800 k2 centre rad 1.9 (HEG) 831 831 100%

bedroom 1 490 400x1400 p+ 1.9 (HEG) 760 760 100%

lounge 822 400x1400 k2 krad 1.9 (HEG) 982 982 100%

hall 253 600x1000 k1 centre rad 1.9 (HEG) 499 499 100%

bathroom 663 600x1000 p+ centre rad 1.9 (HEG) 704 704 100%

bedroom 2 404 600x1000 k1 krad 1.9 (HEG) 500 500 100%

bedroom 3 587 600x1600 k2 centre rad 1.9 (HEG) 1488 1488 100%

If the first figure in the radiator sizes was the heat loss of the room then your total heat loss is only 4.768kW.

Is that what this figure represents?

If that is correct where does the heat loss of 14.5kW come from?

Also if your heat loss is only 4.768kW then a 14+kW heat pump is way too big.

Under this scheme are they improving your insulation? Maybe the heat loss is currently 14.5kW and once improvements have been made it falls to 4.768kW

Is this how this information has been presented to you or are you copying it in some way.?

It would be more helpful if you posted the actual documents.

shinytop

matt_drummer said:

Pec123 said:

I have misread and quoted wrong thing. It is actually 8.5KW but range can go to 14KW. Sorry learning all the time!

Radiator Information
dining room 725 700x1600 k2 centre rad 1.9 (HEG) 1682 1682 100%

kitchen 824 700x800 k2 centre rad 1.9 (HEG) 831 831 100%

bedroom 1 490 400x1400 p+ 1.9 (HEG) 760 760 100%

lounge 822 400x1400 k2 krad 1.9 (HEG) 982 982 100%

hall 253 600x1000 k1 centre rad 1.9 (HEG) 499 499 100%

bathroom 663 600x1000 p+ centre rad 1.9 (HEG) 704 704 100%

bedroom 2 404 600x1000 k1 krad 1.9 (HEG) 500 500 100%

bedroom 3 587 600x1600 k2 centre rad 1.9 (HEG) 1488 1488 100%

If the first figure in the radiator sizes was the heat loss of the room then your total heat loss is only 4.768kW.

Is that what this figure represents?

If that is correct where does the heat loss of 14.5kW come from?

Also if your heat loss is only 4.768kW then a 14+kW heat pump is way too big.

Under this scheme are they improving your insulation? Maybe the heat loss is currently 14.5kW and once improvements have been made it falls to 4.768kW

Is this how this information has been presented to you or are you copying it in some way.?

It would be more helpful if you posted the actual documents.

@Pec123 has been quoted for an 8.5kW Ecodan.  If you read their posts, the 14kW refers to the maximum output from the Ecodan range, not their specific quote.  That sounds about right for the house described. 

I agree about the design flow temp being too high.  Having said that, remember that it will only use 55 deg when it's -3 deg or whatever.  Most of the time it will be much lower.