Heat Pump Sizing?

michaels

The level of detail available on cop by air vs flow temp seems to vary a lot by manufacturer.

Also the gap does not seem to be linear percentage with flow temp 35 vs 54 at -7 may be different to 35 vs 45 at +10. 
This matters as obviously with a weather comp curve I will only be running the highest flow temp at the lowest outside temp.

Does anyone know what proportion of typical overall usage is done at different external temps - for example -3 is probably pretty rare but will require lots of energy input, +10 is probably much more common but requires much less energy per hour when it does happen.

matt_drummer

I have said this before.

Why don't you just look at heatpumpmonitor.org


There are more than a hundred heat pumps to look at in varying sizes from most manufacturers.

You can see what happens to heat pumps in real life, not from a test in a warehouse somewhere.

You can look at data in 10 second intervals, you'll see heat output, flow and return temperature, flow rates plus indoor and outdoor temperatures. You can see the size of the house and the heat loss amongst other things.

I don't understand why you keep asking here when you have access to fully certified real life data?

michaels

matt_drummer said:

I have said this before.

Why don't you just look at heatpumpmonitor.org


There are more than a hundred heat pumps to look at in varying sizes from most manufacturers.

You can see what happens to heat pumps in real life, not from a test in a warehouse somewhere.

You can look at data in 10 second intervals, you'll see heat output, flow and return temperature, flow rates plus indoor and outdoor temperatures. You can see the size of the house and the heat loss amongst other things.

I don't understand why you keep asking here when you have access to fully certified real life data?

Thanks, there is indeed lots of data, trying to collate it in a way that included installations comparable to what ours might look like in terms of heat loss, local climate, heat pump brand and model, heat usage pattern, etc etc may well mean looking at individual entries in which case the data could be unrepresentative due to some individual installation factor I am not even aware of.

I would have thought rather than trying to crunch the whole dataset I could also ask for input from people with experience who may have come across some 'rule of thumb' examples such as 5 degree flow temp reduction at lowest modelled temp typically equates to an x% reduction in input energy (for space heating) in the SE.

matt_drummer

I do understand.

You'll have to do the work yourself or find an installer you trust.

Expecting some random strangers on the internet to help you find a suitable heat pump and design a heating system without seeing your house is not very wise in my opinion.

There are so many variables with heat pumps that it will be virtually impossible to advise you.

You have some unique demands.

You want it installed on a flat roof, that means you need to find an installer willing to do that and that may restrict your choice of heat pump to something they are familiar with.

You need lots of hot water which means you will need a bigger heat pump than your heat loss requires, it will cause some issues, maybe minor but you will have to have a bigger heat pump than somebody else might get away with in your house.

Increasing radiator sizes sounds limited.

And you don't want to spend too much money on it, which I get, but it seems like it clouds your judgement on choice of heat pump. You like Viessman but not the price?

I am sure everybody would like to help you but there are not many heat pump experts on this forum.

I don't think you'll get any further here than you have done.


Did any installer offer you a 12kW Vaillant?


If I was you, based upon what I know from your posts, that is the heat pump I would choose.

matt_drummer

And if you can, get a Heat Geek installer.

They will guarantee to make it work at a decent efficiency and if it doesn't they will fix it as part of the guarantee.

You can't lose.

The only downside is that it probably won't be the cheapest installation.

The choice is yours and yours alone.

matt_drummer

Or convince Octopus to install a 16kW Daikin if you want a cheap installation.

Their installs are really good and I think the 16kW Daikin would be great.

It will modulate down to 3.5 to 4kW

I have an 8kW Daikin and only have a heat loss of about 4.5kW at -3c

I only ever go down to about 2kW of heat output and I am very happy with one of the best performing systems on heatpumpmonitor.org

Just make a choice and go for it!

FreeBear

matt_drummer said: You want it installed on a flat roof, that means you need to find an installer willing to do that and that may restrict your choice of heat pump to something they are familiar with.

You need lots of hot water which means you will need a bigger heat pump than your heat loss requires, it will cause some issues, maybe minor but you will have to have a bigger heat pump than somebody else might get away with in your house.

A flat roof will act like a sound board, so the noise from a HP running may be intolerable. Yes, I know they are installed with isolation blocks, but some sound will still get through to the roof.

The alternative to a single big HP is two units. One for heating, the other for DHW. It would increase installation costs, and require planning permission, but might be more efficient to run than just one big pump. Or go for a hybrid system with gas on the DHW side, and the HP for heating. You wouldn't get the BUS grant, so that will also increase the cost, but it does mean you don't have to jump through the MCS hoops.

matt_drummer

FreeBear said:

matt_drummer said: You want it installed on a flat roof, that means you need to find an installer willing to do that and that may restrict your choice of heat pump to something they are familiar with.

You need lots of hot water which means you will need a bigger heat pump than your heat loss requires, it will cause some issues, maybe minor but you will have to have a bigger heat pump than somebody else might get away with in your house.

A flat roof will act like a sound board, so the noise from a HP running may be intolerable. Yes, I know they are installed with isolation blocks, but some sound will still get through to the roof.

The alternative to a single big HP is two units. One for heating, the other for DHW. It would increase installation costs, and require planning permission, but might be more efficient to run than just one big pump. Or go for a hybrid system with gas on the DHW side, and the HP for heating. You wouldn't get the BUS grant, so that will also increase the cost, but it does mean you don't have to jump through the MSC hoops.

It's MCS - Microgeneration Certificate Scheme.

Not being pedantic but anybody looking for MSC will find a shipping company rather than anything to do with heat pumps!

I think all of that is beyond @michaels budget if you remember his posts?

Reed_Richards

FreeBear said:

... but it does mean you don't have to jump through the MSC hoops.

I know some of the MCS conditions seem onerous but it's no bad thing to end up with a system that is MCS certified.

Before I bought my heat pump I was warned-off by a neighbour who had got one about a decade earlier and ended up cold but with huge electricity bills.  I don't know what his problem had been, but my guess is that he got a heat pump as a drop-in replacement for a boiler without changing the radiators.  The MCS certification for heat pumps was an attempt to impose standards and stop that sort of thing from happening.  Maybe some of those standards are too rigorous but a lot of them are there for your benefit and protection.    

michaels

FreeBear said:

matt_drummer said: You want it installed on a flat roof, that means you need to find an installer willing to do that and that may restrict your choice of heat pump to something they are familiar with.

You need lots of hot water which means you will need a bigger heat pump than your heat loss requires, it will cause some issues, maybe minor but you will have to have a bigger heat pump than somebody else might get away with in your house.

A flat roof will act like a sound board, so the noise from a HP running may be intolerable. Yes, I know they are installed with isolation blocks, but some sound will still get through to the roof.

The alternative to a single big HP is two units. One for heating, the other for DHW. It would increase installation costs, and require planning permission, but might be more efficient to run than just one big pump. Or go for a hybrid system with gas on the DHW side, and the HP for heating. You wouldn't get the BUS grant, so that will also increase the cost, but it does mean you don't have to jump through the MCS hoops.

Thanks

The flat roof is over a garage so hopefully the sound would not be a problem but at least one installer said they would look to use wall brackets rather than mount on the flat roof to avoid the vibration casing issues with the roof.

Part of me thinks that we are due an announcement form a review on heat pump regulations and we have a new probably more favourable government in place so I should wait to see what happens - mitigating against this is that currently my gas boiler is not working and the repair cost is unknown so I was hoping to go to heat pump before the winter....