Water Distribution in High Rise Buildings
A better Solution for Water reticulation in High Rise Buildings.Water is often supplied to high rise buildings by pumping from the municipal supply at ground level to storage tanks on the roof. Water then flows downward under gravity with off-takes at each floor.
The problem of course is that the pressure at the bottom of the building is much higher – 1 bar for every 10m below the storage tanks. The pressure reduction needed is a factor of the incoming pressure at that level, the expected flow rate and the target pressure for taps and other appliances.
This pressure reduction can be achieved by direct action pressure reducing valves, pilot operated pressure reducing valves or ration reducing valves.
Direct acting pressure reducing valves (DAPRVs)
These valves are actuated by a spring and diaphragm. They are simple, adjustable and have a quick reaction time. However their capacity is limited, even if a full-size valve is installed (ie a 100mm valve in a 100mm pipeline).
Pilot operated pressure reducing valves (POPRV’s)
These valves have been the traditional PRV of choice in high rise buildings, as they have no problem with standard demand patterns, and are often sized one size smaller than line size.
There are, however, three issues which the design engineer has to consider carefully when using a POPRV:
- PRVs acting in series: this is often a requirement in high rise buildings, as indicated in the reticulation schematic. These valves have to be finely “tuned” when they are acting in series, in order to eliminate unstable operation caused by “hunting” between the two valves. Even then, when someone disturbs this setting, the results could be catastrophic and result in burst pipes.
- Low flow capability: in high rise buildings (or any domestic reticulation for that matter), POPRVs will become unstable when they have to operate at very low flows. This instability can also result in burst pipes. This problem can be overcome by installing a small DAPRV in parallel, which will automatically take over at low demand times, however, it makes the system more complex and vulnerable to tampering.
- Reaction time delay: because POPRVs take time to react to demand changes, it’s often advisable to install a relief valve, on the downstream side of the valves, to cater for sudden demand reductions.
Ratio reducing valves (RRVs)
A ratio reducing valve reduces pressure in a ratio between inlet and outlet pressure – so if you have a 2:1 RRV, it would reduce an inlet pressure of 10bar to 5bar. Similarly a RRV with 3:1 ratio would reduce a pressure of 12bar to 4bar etc. A RRV is non-adjustable, and has no external pilots or accessories which can be tampered with or broken.
Advantages of the ratio reducing valve:
- Extremely simple: the only working part is a piston.
- Very fast reaction times: this makes the RRV suitable to act in series without instability. It is also not totally necessary to install a relief valve downstream, although a conservative option would be to install one anyway, with the knowledge that it will seldom operate.
- Capable of handling low flow without becoming unstable. So, one valve would normally handle the whole range of flows, removing the need for a bypass valve.
The ratio reducing valve has been used successfully in buildings in Australia, where one of the first ratio reducing valves was developed.
In South Africa, this product has been used in the mining Industry, where water reticulation is similar to that in high rise buildings, with great success. The mining industry uses higher pressures than most high rise buildings, which has led to the development of a range of ratio reducing valves for higher pressures.
Ultra have a range of RRVs up to 300mm size and 100bar pressure rating.
Flow control for various appliances.
Now that we have described a better solution for getting the pressures to suitable figures on each floor level, consideration should be given to distributing the water at ideal flow rates (and pressures) for various appliances, such as:
- Taps in bathroom and kitchens.
- Water heaters etc.
The benefits of regulating the flows and pressures to the ideal levels include better distribution of water to ensure that one area or appliance does not take more than required and potentially starve other areas and vital conservation of water which has become a critical issue in water-starved countries such as South Africa.
Maric flow control valves
These valves are used to evenly distribute water throughout buildings such as high rise buildings, hospitals, and hotels, where multiple users and off-takes make effective control difficult. These relatively inexpensive and simple devices offer an excellent solution to proper flow and pressure distribution, and will result in very fast return on investment for these buildings.
Maric flow control valves have, until recently, only been manufactured in Australia, although they have been available in SA for many years. Maric is now manufactured in South Africa, under license.
Further details are available in the Maric catalogue here.
A video explaining the operation of the Maric can be viewed here.
An expanded discussion including illustrations is available here.