Reducing effective volume of inaccessible DHW pipework

[JamesPa]

probably a silly question but...

 

I will hopefully be replacing my vented cylinder with a UVC as part of a heat pump installation (if, as I sincerely hope I will, I can eventually beat my cloth-eared LPA into submission).  I have good water pressure.  Currently I have to run off 6l of water into the kitchen sink before I get hot water, which is quite a lot. 

 

I can probably replumb about half the length of the current 22mm DHW pipework with 15mm, but the rest is inaccessible - unless I rip up solid flooring which isn't going to happen).  There isn't an alternative route which can be accessed without major disruption.  I could fit a point of use heater, but that would result in COP of 1, as opposed to about 2*9/15 =1.2 (which is what I effectively get if I run say 9l of hot and 6l to waste with a HP COP of 2).

 

Is there any known way to reduce the effective volume of 22mm pipework without replacing it.  I suppose I could feed a sealed length of 10mm pipe in from places that are accessible, until I hit a stop?  I think there may be only one 90 deg bend 'in the way' but I cant see plastic pipe going round that.

 

Comments on that, and other off the wall (or well established) ideas, appreciated.  My gut tells me that the best answer is 'don't bother' but in case I have missed something its worth asking.

Edited January 23 by JamesPa

[marshian]

12 hours ago, JamesPa said:

probably a silly question but...

 

I will hopefully be replacing my vented cylinder with a UVC as part of a heat pump installation (if, as I sincerely hope I will, I can eventually beat my cloth-eared LPA into submission).  I have good water pressure.  Currently I have to run off 6l of water into the kitchen sink before I get hot water, which is quite a lot. 

 

I can probably replumb about half the length of the current 22mm DHW pipework with 15mm, but the rest is inaccessible - unless I rip up solid flooring which isn't going to happen).  There isn't an alternative route which can be accessed without major disruption.  I could fit a point of use heater, but that would result in COP of 1, as opposed to about 2*9/15 =1.2 (which is what I effectively get if I run say 9l of hot and 6l to waste with a HP COP of 2).

 

Is there any known way to reduce the effective volume of 22mm pipework without replacing it.  I suppose I could feed a sealed length of 10mm pipe in from places that are accessible, until I hit a stop?  I think there may be only one 90 deg bend 'in the way' but I cant see plastic pipe going round that.

 

Comments on that, and other off the wall (or well established) ideas, appreciated.  My gut tells me that the best answer is 'don't bother' but in case I have missed something its worth asking.

 

I have to run 4L of water from my HW tap at the Kitchen sink before I get hot - My feed is 22mm for the initial run and then 15mm for the majority of the pipework run and more annoyingly it's not insulated in the drop box in the utility (Will fix that this year) it's 3 sides of a square in terms of route from HW tank to Kitchen tap

 

From memory for every 1 metre of 22mm you replace with 15mm you half the volume in the pipework so if you have 6 litres to get to hot from 22 mm copper - if you replaced 50% with 15mm you'd reduce the volume to hot by 1.5 litres (down to 4.5 L)

 

As an aside - What is more annoying is Mrs BC will boil a kettle to wash up rather than run 4 litres of cold before she gets water that has already been heated!!!!

 

4 litres of water is less than 1p, I have told her water is cheaper than electricity.