We are having a new bathroom and en-suite re-fitted. We have gravity fed system.
For the ensuite we are thinking of having a shower and body jet column which requires 2 bar min.
For the bathroom we are thinking of having the Aqualisa Quartz pumped shower with a fixed head and a shower handset.
Our water company has said that the incoming water pressure is 1 to 1.5 bar min.
I was wondering if it would be possible to run a separate 2 or 3 bar pump, Stuart Turner Monsoon, for the shower and body jet column in our ensuite as it backs onto the airing cupboard where the HWC is and place it on the floor or site it try to have it sited in the loft using a negative head pump as it would be directly over the ensuite but below the cold water tank in the loft.
For the bathroom I was thinking of placing the Aqualisa Quartz pump under the bath as that would service the fixed 6in shower head and separate shower handset, which would a have a diverter to switch between the 2 and seems straightfoward.
The Aqualisa pump is rated at delivering 13Litres a minute or 18 Litres if boosted @ 0.1 bar.
The Stuart Turner Monsoon pump for the ensuite is rated has having a max. flow rate of 25litres.
I would just like to know if using two independant pumps to service two areas would be OK or would it pose problems.
The salesperson at my local bathstore said that it might cause backsiphonage problems and drain the water supply very quickly if both are used at the same time.
That's not really very meaningful. First of all, what actually matters is the flow of water into the house. Measure that at the kitchen cold tap by timing how long it takes to fill a container of known size. Secondly, measure the rate that the cold tank in the roof fills. This can be done by first turning off the water to it then emptying a known volume out (e.g. N bucketfuls from the bath tap.) You'll need several for this. Then turn on the supply to the tank and time how long it takes to refill.
The point of doing these tests is to check that you have enough cold water storage capacity and the ability to refill it. When you add these showers, if you run them both at the same time, you can easily be using 30 litres per minute. This doesn't mean that you have to necessarily be refilling it at that rate, but you do need to do the sums. If it's only refilling at 10 litres/min, then in my example, you are using water at a net rate of 20 lpm, so for example a 200 litre tank would empty in 10 mins. This may not please your wife if the shower stops that quickly.
The reason for measuring the kitchen flow rate from the main is that it is typical for the supply from there to the tank to be in 15mm tube. If you find that you have good flow at the kitchen, then you could upgrade the pipe to the loft and fit a larger float valve or even two float valves to improve the capacity.
Either way, you may need to consider adding tank capacity, perhaps by adding a second tank and connecting the two.
The other issue to consider is whether your hot water storage is sufficient. Again because the flow is increased, you will be going through hot water faster than before.
For this you need to use a formula to calculate the hot water required to produce a certain amount of warm water at shower temperature.
Using
Vc[Tf-Tc] = Vh[Th-Tf]
where
Vc = cold volume Vh = hot volume Tf = mixed water temperature Th = hot temperature Tc = cold temperature
If you take a worst case of wanting both showers to run simultaneously for 20 mins - that would be 600 litres of warm at 40 degrees. Consider cold temperature to be 8 degrees in the winter and hot water storage to be at 60 degrees.
First of all it ignores the fact that the boiler will be replenishing the cylinder with heat almost as soon as you start running the shower. However, if the boiler to cylinder circuit is "gravity" i.e. has large pipes to e.g. a back boiler (boiler has two pipes for HW and two for CH) then the rate of reheat may only be around 5kW. A system that is fully pumped may only be reheating at 10 perhaps 15kW if you're lucky. Modern cylinders can achieve 20kW or even more if a fast recovery type.
You can calculate the amount of heat needed to heat the water in the cylinder using the formula
Energy = mass x specific heat x temperature rise
For water measured in kg (approx litres), the specific heat is 4200 J/kg.C
Let's say that you can heat the water at a rate of 15kW and the required temperature increase is from 8 to 60 degrees (using the above numbers).
15000 = volume/sec x 4200 x 52
vol/min = (15000 x 60) / (4200 x 52)
Just over 4 litres/min, or in 20 minutes of running, 80 litres.
So.....
The implication of all of the above would mean that you would need a
290 litre cylinder !!!
However, these are worst case scenarios. You can plug in different numbers and see what you get.
However.....
- a typical existing domestic cylinder is usually only 80-120 litres
- it may well only be heating at the rate I've illustrated.
- you might not be using water at 40 lpm - especially if both showers are not used simultaneously for 20 mins and one only uses 15lpm.
The point was that it is important to look at both the hot and cold capacities before you start. If you are going to have to replace the cylinder, You might want to rethink the whole thing and go for a pressurised cylinder or a heatbank *provided that* the cold mains are up to supplying the total flow rate required. The cost of that would not be significantly different than a replacement standard cylinder plus two pumps.
Floor level is recommended by manufacturers over a loft installation.
It's a better idea to have two.
Hmm....
Well now you understand the point about total use.....
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