Shower Pump Buffer Tank - Mad Idea?

[RobG]

Hi there, this is my first post, so I'll try to make it an interesting one...

I'm looking to install a 2 bar shower pump in a 4-storey terraced house to improve the flow to a shower, bath and en-suite shower, which are on the same floor - the 3rd floor. The hot water cylinder (an economy 7 job with about 250L capacity) is on the same floor too.

The cold water tank is in the loft (5th storey).

However, there is a 4th storey between the loft and the bathroom, which will make it very difficult to run a dedicated cold feed from the loft tank to the new pump 2 floors below.

There is some space (maybe 2ft cubed) in the tank cupboard directly above the hot water cylinder.

I had the idea that rather than run a new cold feed from the loft (very difficult given the layout) I could buffer the existing cold water feed by installing a small (maybe 50L) cold water cistern tank in this space above the hot cylinder, and using that as the cold feed for the shower pump. This small tank would be filled by a ballvalve and tee'd-into the existing, shared cold water feed. Of course this small tank would be gravity fed from the main tank 3m above, and not filled by mains pressure.

A slightly complicated setup maybe, but easier to install than running a pipe from the loft through the room above, through the floor partition and into the tank cupboard.

Has anyone tried anything like this before - are there any potential cotchas with something like this?

Thanks!

 

[pcollins]

I think that the problems I can see with this is that your shower pump will probably empty a tank like this pretty quickly as the feed to it wouldn't be able to keep up (unless you have very short shower).

The above happening means that you will have a risk of getting badly scalded as a result, with the cylinder being much higher volume and fed from the main tank, the cold water will run out before the hot water.

Some shower mixers stop when this happens but not all...

 

[stevetheplumber]

unequal preasure might be a big problem as lower tahk could back fill

 

[RobG]

Thanks for your thoughts.

After measurement, I calculated that I can fit an 80 Litre tank in the cupboard space, so assuming a 50/50 mix with hot and cold for the shower, that would give say, 150 Litres total for a shower before the tank emptied. Should be plenty for a shower?

Shower and bath mixers will be thermostatic, so there should hopefully be little chance of getting scalded.

As a backstop, I was thinking that perhaps I could install a float switch in the lower tank and use it as a cutoff for the shower pump in the event that the level dropped too low. Should be easy enough to rig-up with a simple relay circuit.

 

[WHPES]

You will have unequal pressures if the tanks are on different levels.

 

[RobG]

Thanks - that makes sense.

 

[Plumbstar Tom]

Find out what litres per minute the pump will produce and this will give you a good idea of how long the pump can run for with your tanked supplies

 

[RobG]

I appears that if the incoming hot and cold feeds are at unequal pressures to the pump (hot will be 0.4 bar, cold will be 0.2 bar) that will cause problems...?

I had kind of assumed that the pump would eliminate the differences in the inbound pressures, since it would effectively be 'sucking' from the sources rather than being actively gravity fed by them.

 

[Plumbstar Tom]

Afraid not

I have read your post again to check and cannt think of a way round it to be honest

Whats the big problem with running the pipework from the loft?

 

[RobG]

The loft room has a sloping wall, and there's a stairwell right in the way, so the pipe run would be tortuous and need boxing in and floorboards and carpet all taken up. A major PITA.

In the end, it may just be easier to go for thermostatic shower and bath fittings with a < 0.4 bar pressure requirement, but that cuts down the choice quite a bit. They almost all state > 1.0 bar minimum.

Thanks for your suggestions though!

 

[Coldwell]

I would like to gate-crash this thread with a similiar problem.

I have just moved into a one-bed all-electric flat. There is no bath or cylinder or cold water tank. Hot water to the kitchen and bathroom taps is via a 9KW instant water heater. The shower is a 9KW unit. There is a dish washer and washing machine. All units operate from the in-coming mains which is via a 15 mm pipe direct from the supply in the street (stopcock about 15 m from entrance to flat).

Normal pressure is 3 bar and all units work well. However during the morning peak demand period the pressure drops so low that the electric shower "low-pressure" light comes on (I think this is less than 1 bar) and the shower stops working.

Can I fit a small tank and 1.5 bar pump to the shower unit to overcome this problem? What minimum size of tank should I fit? Is there a combo unit I could use?

Thank you
John