Hi @mona,

As a question, why do you need a rating down to -7? I am sure central London has rarely seen those kind of temperatures.

Hi @batalto

Good question, you are right, for London, the weather rarely is below -2 C. Just considering the worst-case scenario based on manufacturer range and comparing COPs for different brands. As some of the manufacturers have been provided a specific COP for -7 to -2 rang for example.

@mona honestly I wouldn't worry about the extremes. Honestly there might be 1-2 days a year where its very very cold. That said, you should treat any COP from a manufacturer much like MPG from a car company. Its always going to be in the best possible circumstances.

Do you have radiators or underfloor heating? You'll get much better performance with the latter.

@batalto 

The building has radiators. Double glazed windows have been installed but other retrofits like wall and roof insulation have not been done yet.

Posted by: @mona

Hi @batalto

Good question, you are right, for London, the weather rarely is below -2 C. Just considering the worst-case scenario based on manufacturer range and comparing COPs for different brands. As some of the manufacturers have been provided a specific COP for -7 to -2 rang for example.

Hi Mona,

The actual real world achievable COP for ASHP's, is not only dependent upon the ambient air temperature, but also the heat demand, and the type and size of the heat emitters. If the heat loss, and hence heat demand, is high due to poor insulation and draft proofing, then an ASHP would have to work harder to produce warmer water, which would lower its efficiency. The lower the total heating capacity of the heat emitters, will again require warmer water to transport and distribute the required amount of heat energy. At lower ambient air temperatures, the heat demand increases as the efficiency of an ASHP reduces quite considerably.

GSHP's are more efficient than ASHP's, because their source of free energy is the ground rather than the air. At a depth of about 1 metre below ground, the temperature is a fairly constant 8C or 9C, so the efficiency of a GSHP at say -2C ambient air temperature, should be the same as an ASHP at an ambient air temperature of 8C or 9C.

@mona rads mean you will need a higher temperature and therefore get a lower COP. Have you tried a heat loss calculation yet? There is one in my signature which I suggest you do. This will tell you your heat loss and give you an idea of the size of pump you might need. However given the size of your building (I'm expecting large) you might not find a suitable one on there! 

@mona,

I think the COP numbers quoted by manufacturers should be accurate with a couple of caveats/warnings.  You need to look at them carefully and note the outside temp and radiator (flow) temp.  As others have said, both make a big difference.  Also, a lot of quoted COP numbers don't include defrost cycles; that can add a bit (up to 10%?) to the power input when it's 0-5C or so.

With a community centre you may be straying away from domestic installations into commercial sized ones.  Have you considered the alternative of air to air rather than air to water?  These might work better for a single large space rather the many smaller rooms of a house.  A2A units are still heat pumps and can have a good COP.   You may then have to consider planning issues but it might be worth a look.   

Hi @mona

The following might be of some use as an initial guide, particularly the introductory bits, though it’s probably not aimed at the general public.

MCSCERTIFIED.COM "https://mcscertified.com/wp-content/uploads/2020/07/Heat-Pump-Guide.pdf"

If I understand correctly, the MCS heat loss calculation requires a minimum outside temperature for the design. For London, it looks like -1.9C according to the spreadsheet link in @batalto signature, which corresponds to your experience and the earlier advice. The MCS guide indicates a design temperature to use that is exceeded 99.6% of the time, which I calculate at 1.5 days per year colder. I would think it reasonable to allow a few more colder days, but then I would just put another jumper on.

With radiators, to lower the flow temperature to improve efficiency, you might need to replace with bigger sizes to match the expected heat loss.

Hope this helps.

Welcome to the forums @mona. If you can cover the financial outlay, GSHPs will outperform ASHPs in winter. I don’t know where in London you are, but if the council will allow it, boreholes would be required and these days they use rigs that are slightly larger than Landrovers.

The advantage of GSHPs is that the temperature of the earth at borehole depths is a constant 11-12C so you’re removing harsh/cold winters from the equation and installing a system that will run efficiently all the time.

To find out more about borehole drilling you can listen to this interview with Geoff. We also learned from Geoff that drilling into Landon’s chalky strata is a much easier exercise than in other parts of the country.

If GSHP is not an option, there are high temperature heat pumps hitting the market that will cover most buildings. Both Hitachi and Daikin do them. Depending on the size of the space, they could be installed to run as a cascade system, but I suspect the installation costs might start to rise into GSHP territory.

If possible, upsizing rads to K3s would be a good idea as this will help the performance of  whichever heat pump system you opt for.

@mona

Just some thoughts.

It’s not clear to me what stage you are at in the process and how far along you have got. I’m just starting out looking at alternative heating systems for our house. I would say start with the heat loss calculations and consider how the building will be used, as I think that this will almost certainly affect the choices you have to make. Accurate sizing is important. A professional heat loss survey might prove better if it can be funded, though should be provided by any installer.

For a GSHP, I think, off the top of my head, you need a land area of something like three times the building floor area. So, for example, for a 200 square metre building you would need at least 600 square metres of land available for a trench mount system and a smaller footprint but similar pipe length for vertical bores, though multiple bore holes are used. Not sure of the required depths.

You could try an internet search to see if there are any case studies for decarbonisation of similar community buildings and try and contact the committee to see if they would be willing to provide some feedback.

While thinking about this, I recalled that a village hall just up the road from where we live, Woolfardisworthy aka Woosery, had refurbished using alternative energy systems. There is a youtube video:

Quite a large hall, GSHP, solar PV, wind turbine. They might be able to provide feedback on how they went about choosing, installation issues and running cost, etc. 10 years old, but may still be relevant.