Do I need a pump for my vented system?

[std_exceptional]

Hi all, I'm installing an open vented system for my hot water (bad mains pressure rules out an unvented system) and I'm wondering if I can get away without a pump. I'm going to have 2 bathrooms run off the tank and the showers are rated for 0.1 bar. I figured if i have a 28mm pipe from the tank which then becomes 22mm to feed the hot water and showers /bath and a 15mm for the toilets and sinks, then there should be enough flow to allow 2 showers to be used (max flow of the showers is 12 litres a minute), or a shower and a sink, without the pressure dropping to a dribble.

Is my logic correct, or would I need to install a system pump to ensure consistent flow?

Thanks!

 

[steadyon]

0.1 bar is very low pressure for a shower, particularly at 12 lpm. I'd double check that they can achieve that flow rate at that pressure.

0.1 bar is the equivalent of (roughly) 1 metre in height. So:

a. If the distance from the base of your cold water storage cistern (CWSC) to the shower head is greater than 1 metre. AND
b. the shower really will run 12 lpm at 0.1 bar AND
c. the losses through the pipe runs (allowing for length and bends / fittings etc) are ZERO

Then it will work.

The most difficult part is item c. The losses can never be zero, although they can be quite close. You'll need to do the calculation allowing for the siting of your CWSC and hot water cylinder (HWC), the lengths and sizes of runs to the outlets and the fittings required. Have a look at http://yorkshirecopper.com/wp-content/uploads/Technical-Guide-full-issue-02_14_Really2.pdf to see what's involved and how to do it.

If I was asked to do it I'd turn the job down - its all too much on the limit.

Consider installing a shower pump, not forgetting it will need its own feeds from the CWSC and HWC.

 

[std_exceptional]

Thanks, the flow rate will be lower at 0.1 bar but 12 litres is the max. I guess I should reconsider having a pump!

 

[king of pipes]

Lets start again has a engineer been to your property ? and measured pressure and flow there are ways of increasing this if its poor your water supplier is duty bound to give you a certain pressure, take some good proffesional advice before committing to open vent regards kop

 

[std_exceptional]

Yes, I have had a few plumbers tell me that I should install an unvented system, but with my current combi system, but if two taps are open the flow is greatly reduced, so it is clear the 15mm mains will not support an unvented cylinder without an accumulator, and the cost of that is significantly higher than a vented system.

 

[king of pipes]

Are you sure i have installed plenty of unvented cylinders on a 15mm supply not ideal but somtimes you have to work with what you have saying that you still need a reasonable pressure and flow, no combi will supply two taps at the same time but your choice bud

 

[std_exceptional]

I'm not completely against an unvented solution, but even with an accumulator it isn't guaranteed to give me the ability to run two showers at once. It is also more expensive. Maybe a small online lump to just boost the flow slightly will be enough?