Advise please on Air to water heat pump and buffer tank sizing

[Andrew Schofield]

When I first designed my new well insulated 2500 sq ft house I left the heating and hot water flow and return pipework in the corner of the garage for an oil boiler, now that I am nearing completion I would like to install 6Kw solar PV to heat most of my hot water in the summer and run a heat pump with mains electricity top upin the middle of winter.

The exiting heating pipes are 35mm flow and return which go to a 28mm manifold, one for the ground floor underfloor heating and another upstairs both in solid floors, and the hot water 28mm flow and return pipes to a mainsflow hot water tank in the upstairs airing cupboard with immersions connected by a solar diverter.

It would seem the simplest way of connecting the existing pipework which would have been on either side of the oil boiler is with a large buffer tank (1650mm Ht x 500mm Dia) in between the two sets of pipes.

A small heat pump would be on the other side of the garage wall with a short connection through to a finned coil inside the buffer tank.

Does this seem reasonable?

 

 

[JohnMo]

58 minutes ago, Andrew Schofield said:

large buffer tank (1650mm Ht x 500mm Dia) in between the two sets of pipes.

A small heat pump would be on the other side of the garage wall with a short connection through to a finned coil inside the buffer tank.

Does this seem reasonable?

Think you need to step back slightly.

 

What is your expected heat demand? That will determine the heat pump size.

 

Your ideal is no buffer at all, but if you have lots of zone and some are quite small you will need a buffer, but size depends on a few factors, tied to the expected ASHP minimum output and flow rates needs. 2 or 3 port buffers are better than 4 port as there is generally less mixing going on inside the buffer.

[sharpener]

Most HPs work with priority to the HW via a 3-way valve, do your proposed arrangements take account of that?

 

From what you have said so far no obvious need for a buffer.

[JamesPa]

On 05/04/2024 at 21:51, JohnMo said:

Most HPs work with priority to the HW via a 3-way valve, do your proposed arrangements take account of that?

 

What is your expected heat demand? That will determine the heat pump size.

 

19 hours ago, sharpener said:

From what you have said so far no obvious need for a buffer.

 

Agree with both of these, subject to getting some info on heat demand and anything that falls out of that.  Best to KISS (keep it simple, stupid) in most cases.

Edited April 9 by JamesPa

[JohnMo]

14 minutes ago, JamesPa said:

Best to KISS (keep it simple, stupid) in most cases.

I have a buffer for one zone, but changing the timing and flow temp a little has allowed me prove it's actually not required, so will be removed next month, along with electronic mixer and pump for UFH. Will reinstate a small WC of 3 degrees, starting at 3 degs  OAT and stopping at -3 OAT.