How do High-Rise Water Distribution Systems Work?
As a building manager or property owner, it is important to learn about high-rise water distribution systems.
High-rise buildings have more complicated methods of water distribution than residential systems, since pressure needs to be consistent across all floors. There must be sufficient surplus pressure to cover resistance in riser pipes, single components such as shower heads, toilets, and cooling towers. Furthermore, the peak load flow might be greater than what is possible to supply from the mains.
First, let us look at the components of high-rise water distribution systems. The basic booster system consists of several basic hydraulic elements that can be combined
-Break tanks, or underground tanks, provide backup supply in case the mains cannot keep up with the demand or in case the main supply is unstable. However, contamination is a potential issue when the break tank is connected directly to the incoming main supply.
-Booster Pumps ensure water pressure and supply are reliable and consistent.
-Risers and branches are the main method of distribution within a building, where the risers distribute to different floors and the branches to individual tap points.
-Pressure reduction valves equalize the pressure on all floors. However, if a PRV fails, it can let higher pressure water into a lower grade pipe, potentially causing a flood.
Booster systems may be designed in several different ways using the elements described above.
There are four basic methods of distribution of water to multi-story buildings: direct pumping systems, hydro-pneumatic systems, overhead tank distribution, and direct supply from mains to ablutionary taps and kitchen with bathrooms and urinals supplied by overhead tanks.
Below we will explain in more depth the four distribution systems.
With a direct pumping system, water is pumped directly into the distribution system without the aid of any overhead tank, except for flushing purposes. Water can be pumped from a ground level or basement gravity tank to a gravity roof tank, through a set of booster pumps that can have multiple stages and speeds that draw water directly from a gravity storage tank or the public water main, or through a gravity storage tank or public water main into a hydropneumatic pressure tank that uses captive air pressure to provide adequate drinking-water supply pressure (see the hydro-pneumatic system below). The direct pumping systems available are single booster system, zone-divided system, roof tanks, or series-connected systems.
The pumps are controlled by a pressure switch installed on the line. Normally a jockey pump of smaller capacity is installed which meets the demand of water during low consumption and the main pump starts when the demand is greater. The start and stop operations are accomplished by a set of pressure switches installed directly on the line. In some installations, a timer switch is installed to restrict the operating cycle of the pump.
The most basic type of system, this system is adopted when adequate pressure can be available round the clock at the topmost floor through the city main power supply. With limited pressure available in most city mains, water from direct supply is normally not available above two or three floors.
Hydro-pneumatic systems are a variation of direct pumping systems consisting of a pressure pump and a pressure tank.
With a hydro-pneumatic system, an air-tight pressure vessel is installed on the line to regulate the operation of the pumps. The vessel capacity is based on the cut-in and cut-out pressure of the pumping system, depending on allowable start/stops of the pumping system. As pumps operate, the incoming water compresses the air on top. When a predetermined pressure is reached in the vessel, a pressure switch installed on the vessel switches off the pumps. As water is drawn into the system, pressure falls into the vessel starting the pump at preset pressure. The air in the pressure tank slowly reduces the volume due to dissolution in water and leakages from pipe lines. An air compressor is also necessary to feed air into the vessel so as to maintain the required air-water ratio. The system is automatic, but requires reliable power supply to avoid breakdown in the water supply.
Overhead Tank Distribution
This is the most common of the distribution systems adopted by various types of buildings. Overhead tanks have been used for over a century since reliable pumps and pressurized systems were not available at the time. The overhead tank setup allows gravity to do the work of bringing the water down and ensuring sufficient pressure. The system comprises pumping water to one or more overhead tanks placed at the top most location of the hydraulic zone. Water collected in the overhead tank is distributed to the various parts of the building by a set of pipes located generally on the terrace. Water is then distributed down to various fixtures. The simple construction basically entails a tank, inlet and discharge piping, a float switch, and a pump. When the water level in the tank drops below a certain level, the float switch engages the pump, refilling the tank.
However, the downsides of overhead tanks are higher capital costs during set-up, greater structural requirements, and a lack of pressure control. There are also potential sanitation issues with overhead tanks.