ASHP with low mains water pressure

[Ommm]

Currently looking at an ASHP to replace an oil boiler and electric shower.  One thing that's arisen is we have quite low mains pressure - 2 bar and 10 litres/min flow. What would be a sensible way to address this?

 

It's a bungalow with a loft conversion, so there's not a lot of space for a header tank (~150 litre cold tank at present) nor much headroom, and access to the remaining loft is awkward. The hot cylinder is currently level with the shower so there's no head of hot water.  So we won't have a lot of head for a vented cylinder or much mains pressure for an unvented cylinder.

 

I see there's various accumulators that can be added as a reservoir, but how big an accumulator should I expect to need?  I was looking at the Stuart Turner Flomate range - they have an accumulator (for increased flow) and pump (for increased pressure).  We only have the one shower so how much runtime would you get before the accumulator is exhausted?

 

Are there any other ways to make this work?  Are all ASHP cylinders unvented?

 

[ProDave]

The ASHP is like a system boiler.  It runs on a sealed system that you charge with a filling loop and 2 bar is more than enough for that.

 

You can have a vented cylinder if you really wanted to and a header tank, but in a bungalow the pressure from the header tank would be poor.  A better solution would be an unvented cylinder with an accumulator to boos the peak flow rate.

[Ommm]

I'm not sure if anyone makes vented cylinders with ASHP-suitable coils?  So I suppose that reduces the choices down to how to boost the mains pressure...

[SteamyTea]

2 hours ago, Ommm said:

I'm not sure if anyone makes vented cylinders with ASHP-suitable coils?

I am sure you can get one made, but you can always use a plate heat exchangers and an extra pump.

[dpmiller]

I've an open-vented thermalstore with *big* coils for the ASHP and DHW.

[ProDave]

2 minutes ago, dpmiller said:

I've an open-vented thermalstore with *big* coils for the ASHP and DHW.

How do you find a thermal store works with an ASHP?

 

I thought the conventional wisdom was because you have to store the water hotter in a thermal store, they are a poor match to an ASHP that will struggle to get them hot enough?

[dpmiller]

Not living with it yet Dave but all indications so far are good. With the correct thermistor placement, the big coil should let the ASHP recover temps to sufficient levels for near continuous flow