New hot/cold feed

[Jimbob64]

I’m just about to re pipe my house which is undergoing refurbishment. I’ve had a new heating system installed but have decided to install new pipework to kitchen and bathrooms as the old stuff is ancient, badly corroded (V. hard water) and a mix of imperial and metric fittings. I’m going to start from fresh and use a new route before plasterers come in. I’m planning on using plastic instead of copper. The cold water is fed from a borehole at 5 bar max. The hot is fed from a pressurised cylinder (heat pump) at 3 bar. Do I need to use 22mm on the hot supply and tee off in 15mm to appliances (apart from the bath) or 15mm everywhere? I’m running the supply to kitchen, main bathroom, en-suite, downstairs cloakroom and utility room (2 showers, 1 bath, 1 kitchen sink, 3 wash hand basins and 3 WC’s).
I’m trying to avoid pressure balancing issues. None of the showers are electric.
Cheers.

 

[Deleted member 267285]

I’m slightly confused, are you saying the cylinder is heated via a heat pump? Is the central heating fed from a boiler or the heat pump too?

 

[Jimbob64]

Sorry, all hot water and heating is from the heat pump. I’m repiping the hot and cold feeds to the kitchen/bathrooms. The heating system is all brand new.

 

[Deleted member 267285]

What size is your incoming main? If it’s 15mm, I’d say 15mm is fine.

 

[Jimbob64]

Incoming is 32mm from borehole reducing to 22mm

 

[Deleted member 267285]

Incoming is 32mm from borehole reducing to 22mm

Ahh, might be one for the more experienced, sorry. It may be better in 22mm, but who knows.

 

[Madrab]

Your HW is from a pressurised cylinder, do you mean an unvented cylinder and its heat source is the heat pump?

How is your borehole cold mains delivered, do you have a pumped break tank/accumulator or is it directly pumped from the bore hole? If the latter then the pump will be regulated to allow a controlled pressure and flow with an EV attached and controlled by a flow switch?

If you have an unvented HW cylinder then I would suggest that you have a 22mm feed up to the cylinders combi valve then take the balanced feed from the valve in 22mm. Only drop to 15mm at the the branch to each outlet location where mixers are being used. Any individual taps (outside/non mixer/etc) can be fed directly from the main, but branch a separate mains supply @ 22mm and then drop to 15mm again to minimise main pressure and flow drop off and keep noise to a min. Keep the main supply's back bone for both hot and cold @ 22mm.

 

[Jimbob64]

My situation is the latter. That is pretty much what I’ve planned and what exists currently.
Very helpful and succinct.
Many thanks.
James