HW cylinder recovery rate

[pmx_super]

I'm planning to pump my HW to the bath / shower with a 2.25bar salamander pump that I expect to deliver about 15l/min (mixed) at the shower head. I'm also having a high recovery cylinder put in, currently spec'ed at 90l capacity. I'm a bit worried that the pump will use HW too fast for this tank size, so was wondering how high "high recovery" really is.

I'm having an 18kW Cat A boiler installed in my 3-bed semi as part of the same job. I've been told that 20 minutes to replenish the full 90l tank could be expected (i.e. approx 4l/min), but I'm rather cynical. Does that sound realistic? I'm used to waiting hours for a full tank!

If that's accurate does this logic hold:

15l/min mixed will use approx 10l/min of hot water
10l/min hot from a 90l cylinder = 9 minutes
"New" hot at 4l/min for those 9 mins = 36 extra litres of HW
10l/min hot using further 36 litres = 3.5 minutes

So roughly speaking my new set up would give me 12.5 mins of continuous showering at 15l/min.

 

[mehran]

90L sounds a bit small but never mind...

right what make and modal of tanks is it? what's the surface area of the coil. water stored at 60 degrees then mixed down with cold to 45 will give you a 3 to 1 ratio.(if I remember right)

so 90L of 60 will give you 270L of 45 degree hot water and 45 degree water is more then enough to shower in.

I have a similar sounding job coming up. we are fitting a 210L vented twin coil fast recovery cylinder which is rated to re-heat in 19 minutes with a 30kw input. so a 20 minutes recovery time with 18kw input does sound about right.

 

[Agile]

I think 120 litres would be nearer to the mark ignoring the reheat.

The minimum for a two person property should be 210 litres of stored hot water.

It seems you have a nupty plumbing advisor so be very careful or you will end up with a non performing system.

That reheat time would need hot water priority which is not the usual way to configure it.

Tony

 

[mehran]

to the op I am not sure about that 3 to 1 ratio. I will need to look it up... having a bit of a brain fog ATM

 

[Agile]

Yes, three of hot water and one of cold water!

 

[pmx_super]

I think 120 litres would be nearer to the mark ignoring the reheat.

The minimum for a two person property should be 210 litres of stored hot water.

It seems you have a nupty plumbing advisor so be very careful or you will end up with a non performing system.

That reheat time would need hot water priority which is not the usual way to configure it.

Tony

Thanks Tony. Is 210 a typo? Did you mean 120? If not I don't understand the consistency between your first and second statements.

That aside, I'll try to ensure we get the biggest cylinder we can fit in the airing cupboard. Since we're constrained to 35cm diameter a 1200x350 - 103l - looks like the biggest. Should I consider downgrading the pump to 1.5bar to limit the flow to what our supplies can actually support? Would 1.5 vs 2.25 make a material difference?

 

[Agile]

My posting was totally correct.

The first line referred to Mehran's statement.

From then onwards it was my advice based on best solutions to your needs.

But we still dont know haw many people you have living there!

The consumption rate of the shower depends on the setting of the head if its variable.

A 1.5 Bar pump would usually be adequate for anyone normal.

Tony

 

[pmx_super]

My posting was totally correct.

The first line referred to Mehran's statement.

From then onwards it was my advice based on best solutions to your needs.

But we still dont know haw many people you have living there!

The consumption rate of the shower depends on the setting of the head if its variable.

A 1.5 Bar pump would usually be adequate for anyone normal.

Tony

Understood. There are 2 people. Cupboard is only 43cm deep so 210 won't fit. I'll enquire with plumber as to the biggest tank he can fit in. I'll definitely downgrade the pump to 1.5bar.

 

[Agile]

Dont you have a loft or another location?

It would be a pity to fit something totally unsuitable.

Tony