The selection of water supply patterns in domestic water supply system of high-rise building

Wei Fu Sheng
Faculty of Urban Construction
ChongQing JianZhu University, China

ABSTRACT: Thorough the analysis and comparison of kinds of water supply patterns in domestic water supply system of high-rise building, it demonstrated that according to specific circumstances the selection of decompression means from water storage cistern or combined pattern of several water supply means ig more economical and reasonable nowadays.
KEYWORDS: high-rise building water supply patterns decompression means of water supply

The selection of water supply patterns is the key of designing water supply system of high. rise building, it concerns directly to the usage and cost of water supply system of the project. Usually, the pressure on the water main can not ensure an adequate domestic water supply to upper part of multi-storey building, in most cases, the zoned water supply pattern is used, ie, the lower part water supplied directly from the main, the upper part water supplied from boosted system.
As far as the current situation of urban water supply system interiorly concerned, the Pressure on the water main usually can supply water inside the building up to a height of 5-6 floor, thus other methods associated with the specific circumstances should be provided for the Water services of the upper part of the building. It is stated at 2.3.4 in The Design Norm of Building Water System (GBJ15-88)( it is shortly named as The Norm below)": the vertical zone to domestic water supply system of high-rise building should be relied reasonably on the terms such as usage requirement, performance of material or equipment, manage or maintenance, height of the building etc, also the pressure on the water main should be involved.
It is necessary to limite the static pressure on the lowest draw-off points of any vertical zone. To residential building, hotel, hospital, it must be limited to 300-350Kpa,while to office building, it must be limited to 350-450Kpa." Therefore, on the basis of the static press value of the vertical) zone according to the Norm, associated with the water supply pattern of building fire system, it is reasonable that the domestic water supply system of the upper part of the multi-toreys building must be zoned vertically.
There are basically three patterns for the high Part of the building in common use:1)Water supplied directly from the high-level water cisterns; 2)water supplied directly from the frequency converter pump; 3)from the auto-pneumatic system.
There‘s another statement at 7.4.7 in the The Design Norm of Building Fire System" If the supply authority‘s main with high pressure employed, there is no need for the high-level firing water storage cistern, if the boosted system employed, then the high-level cistern is necessary......".At present, the high-level firing water storage cistern is widely employed in a multi-storey building for the reason that the authority‘s main often can not satisfy the required pressure, and the temporary boosted system often be used.
It is commercial and easy to manage if the domestic and firing water stored together in the high-level cistern while the efficient volume of the cistern won‘t increase much. The cistern can keep the pressure stable, keep the balance of the pressure for cold and hot water supply system, in order to provide comfortable washing and shower.
The use of the frequency converter pump is limited interiorly for the reason that 1)only the pump cannot store any volumn of firing water; 2) the problem that supply water with minor or zero rate of flow exsists, 3) the frequency converter costs too much.
The dominating disadvantage of the auto-pneumatic system is the regulated volumn of the pneumatic-cylinder can‘t offer enough storage of firing water. The auto-pneumatic system is
widely used as two aspects: 1) to be regularly boosted equipment in a fire control system; 2)to be boosted equipment only for the highest several floors in a domestic water supply system in multi-storey buildings. As far as all above concerned, the pattetn of supplying water directly from the high-level cistern is widely spread in most of the multi-storey buildings in despite of the shortcomings that additional strutural loading on the building and the drinking water of the cistern might be polluted.
The pattern of water supply directly from cisterns can divided into several kinds according to The Norm, that is supply water by decompression from the high-level cistern or supply in parallel from the cisterns, or supply in serial from the cisterns, even the combination of several water supply patterns being adopted based on the specific circumstance.
There are two means of decompression pattern---- by break pressure storage cistem or by pressure reducing valve. The disadvantage of break pressure cistern is 1 )the cistern will make up certain surface of the floor. 2)the chances that the drinking water being polluted will increase, 3)the noise. With a view to the pressure reducing valve, the cost may be a litter high, but the area of the floor will be occupied much less, the problems of the pollution and the noise will not exist either, on the other hand, the quality and capability of the pressure-reducing valve inland is much better than before. There for, more and more pressure-reducing valve is used in tall buildings these days.
The pattern of supply water by decompression from the high-level storage cistern can be considered in practice as below:
1 The height of the building is about 50m
The water of the upper stroeys can supply from storage tank-pump--high level cistern-draw-off points. The water of the lower stroeys can supply directly from the mains. If the reliability of water supply is necessary, a vertical pipeline directly from the high-level storage cistern can be connected to the conduit of the lower part. A electric valve and a pressure- reducing valve are necessary on the vertical pipe, the electric valve shuts up at peacetime, the valve opens when the water mains cannot supply water properly. Fig. 1 shows the water supply pattern of the building around 50m. Reliability is the outstanding characteristic of this pattern. The pattern is widely used for another reason that it can take full advantage of the water main and the energe can be saved to some degree.
2 The height of the building is between 50-80m
The water of the upper stroeys can supply from storage tank-pump--high level cistern-pressure-reducing valve--draw-off points or from the cisterns in parallel. Fig.2 shows the decompression pattern. Fig.3 shows the parallel pattern.
Every zone of parallel water supply pattern is a separate system. The advantage of parallel pattern is the reliability of the system, easy to maintenance as the pumps being gathered together and subsequent operation costs are relatively small. The disadvantage of it is two sets of pumps and cisterns being necessary, this would enlarge the area being occupied by the equipments which would increase the cost accordingly. This shortcoming is most notable to the building in big cities.
The system of the decompression water supply pattern is simple and easy to manage, the facilities cost less and the area being occupied less as well. But the reliability of decompression system is not as good as parallel pattern. the cost of power is also high. Even so, the zoned decompression water supply pattern from high-level cistern has superiority because the condition of power supply is much better than before inland, the fee of power can be acceptable now. Commonly the high stroeys be zoned into two parts which is widely spreaded in the tall buildings. The Surgery Building of NO. 1 hospital of ChongQing Medical University designed by ChongQing Jianzhu University is an example. The total floorage of the building is 37756m2, there are 2 storeys below the ground, 23 storeys above the ground, the height of the building is 89. 1m. The zoned domestic water supply system is adopted in the case. There are two zone for the building-the upper and the lower. Water of the lower (4 storey below) supplied directly from the water mains, water of the upper (5 storey above) supplied from the storage tank-pump---high level cistern-pressure-reducing valve-draw-off points.

3 The height of the building is between 80-110m
The zoned and decompression pattern from high-level cistern is the recommended means of water supply for the upper part of the tall buildings, that is the pattern from the storage tank-pump---high level cistern-pressure-reducing valve-draw-off points, as show in Fig.4.
The parallel pattern of water supply from the cisterns is another recommended means. There are three minor vertical zones in the upper zone in the case.
4 The height of the building is beyond 110m
The seriat water supply pattern must be employed to avoid excessive high of the lift of the pump for the upper zone and excessive long of the pipeline to convey water. (Intermediate relay pump is necessary if there is no intermediate cisterns).
The combination means of the serial water supply pattern front high-level cistern and the
decompression pattern is recommended in the case. That is:
storage tank-pump--intermediate cistern--pump-high-level-cistern-pressure-reducing valve
Supply water in Decompression pattern Each zone
-draw-off points
as show in Fig.5. There will be one or several intermediate cisterns, three or more zones in the upper part.

1-water meter 2-storage tank 3-pump for domestic water 4-pressure-reducing valve 5-high-level cistern 6-electric valve

The characteristic of serial water supply pattern from high-level cistern is the pumps for the water source of the upper zone. It is applicable to super high buildings. No high---lifting pump and high-pressure pipeline are the notable advantages of the system. The disadvantages are;1)not convenient for management since the equipments being separated; 2)shock and sound proof being needed because the pumps being placed on the floor; 3)reliability is not enough in respect that supplying water of the upper-storeys enslaved to the lower.
The combination of the serial and decompressure pattern of water supply is widely used in the high-rise buildings for the reason that equipments (pumps and cisterns) can be reduced which will result in the costing less, convenient to maintenance, less shock and sound.
There are exceptions of course. ChongQing Yangtze Holiday Inn is an example. The height of the building is 79.65m. There are 1 storey below the ground and 23 storeys above the ground. Water supply of the lowest three storeys is the combination of the pump-cistern system, while water between 21-23 storeys supply from auto-pneumatic system. The static pressure of the lowest draw-off point of the lower part is about 0.8Mpa, for the reason that the prssure resistance of the material and the equipment being pretty good and a series of measures to proof the shock and sound being adopted accordingly.
To sum up, some ingredients must be consided in the selection of the water supply pattern in high-rise buildings. When the height of the building is about 50m, water of the lower zone supplys directly from water mains, to the upper zone, water supplys with the combination of the pump-cistern system; when the height is between 50-80m, the water of the upper storeys "supplys with the decompression pattern from the high-level cistern; when the height of is beyond 110m, the water of the upper storeys supplys with the combination of the serial pattern of the high-level cisterns and decompression means. In brief, The selection of the water supply pattern must rely on The Norm, associated with the specific circumstance of the very region and the specific condition of the project to ensure the economical and reasonable water supply pattern being adopted.

REFERENCE

1,＜ The Design Norm of Building Water System＞ (OBJI5-88) The Project Publishing House of China, Beijing, 1997
2,＜Water engineering for high-rise buildings＞The Publishing House of ChongQing University, ChongQing, 1996.
3,Discuss in Designing the high-level cistern of high-rise buildings, Wei Fushen, Journal of ChongQing JianZhu University, V20, n5, 1998