On the Special Single Stack Drainage Systems in High-rise Buildings

Lan yan Wu ningxia Zhong guifang Huang ziqin
Guangxi Architectural Comprehensive Design & Reserch Institute
Add. NO. 39 Huadong RD., Nanning, Guangxi Zip Code:530011
Tel: 0771-2438087 Fax:077l-2435011

ABSTRACT Introducing several special single stack drainage systems in common use, this papersuggests that the special single stack drainage system with Air Admittance Valve (AAV) should bewidely used in project design.
KEYWORDS Air Admittance Valve (AAV) Special Single Stack Drainage System(SSSDS)Sovent Spiral Flow Spiral Pipe?

Along with the flourish of high-rise buildings after Chinese reform and opening, the building drainage technique develops continuely The traditional drainage system--the double or triple stacks system is composedd of drainage stack and ventilation stack, although is used in practice for long time, is limited for futher development because of the high materials cost and much space occupied. This application of SSSDS in high-rise buildings is discussed in the following.
1 The advantages of SSSDS
SSSDS, just as its name implies, is a single stack with double functions of drainage and ventilation. Therefore, SSSDS is more and more poplar for its outstanding advanages,such as less space, reducing structer load, convenient mainienance, less cost etc. Due to the functions of expansion and separation, SSSDS with special fittings is benefit for improving hydralic conditions, reducing the pressure fiuctuation and avoiding destroying the water seals. Many Chinese and foreign experts attach importance to the study of SSSDS, and have got some success and experience.? 2.Some type of SSSDS in common use
2.1 Sovent SSSDS
Frez Soma of Switzerland developed this system in 1959. He used special fittings to separate or combine the air and water. This fittings are composed of two parts, one is aerator installed in each connection of the branch and the stack-- to limit the volocity of the liquid and air in the stack, the other is draerator installed on the bottom of the stack--to prevent its pressure from being too high, thus ensure the waste water to flow fluently along the outlet pipe.?
2.2 Spiral-now SSSDS
Spiral-flow SSSDS, developed by the France Architecture Science and technolog Center, is composed of spiral fittings installed in each connection of the branchs and the stacks, and the special elbows installed in the bottom of the stacks. The wastewater flows along the stacks spiral1y, and makes a water film and an air core in the stacks. Due to the stack ventting through the roof and the special elbows in the bottom, the system has the advantages such as stable pressure and high capicity of drain and ventilation, and low noise because of sprial flow.
2.3 SpriaI stack SSSDS
This system is composed of sprial stack and eccentric inlet tee. There are six triangle spiral lines and the distance between is 50mm. While the wastewater folw along the,piral lines, an air core forms in the stack, and then the drainage capicity can be improved. Futhermore, since the connection of the eccentric inlet tee and the stack is eccentric, the water flow from the branch to the stack in tangent direct, thus the shock of the water from the branch can be reduced and the water block can be direct prevented. Due to the characteristic above, this system also has the advantages such as stable flow and low noise, and is popular.
The systems hereinbefore have been applied in China and abroad; yet, we would like to introduce a new SSSDS has not been widely used in China.?

3. SSSDS with AAV
The sewage capicity of high-rise building depends on the drainage and ventilation ability of the drainage stack. As the drainage stacks of high-rise buildings is rather long,and connect many toilets, when the flow is large, water-block would happen. If the air supplement on top of the stack is not enough and the exhaust of the bottom is not good, then the pressure before the water block is positive, and after is negative. As a result, the water .seal of the trap would be destoryed and badly effects the drainage system. If an AAV is installed at the head of the,stack and every 8~l2 floors, the flux condiction of the stack would be distinctly improved. This system has now been used in a 32-storey apartment building in Echigo Niigata Prefecture and proved to be functional and safe.
3.1 The component of SSSDS with AAV
SSSDS with AAV is a system with AAV installed at the head of the stack, and every 8~l2 floors. Its main fitting is only the AAV and the system is very simple.?
This AAV is made in Sweden with a history more than 20 years, and now is very popular in Europe, Janan and USA. In China, it is used in many building in Shenzhen Guangdong, Guangxi, Hubei and Hunan etc.
Recently, we adopt this SSSDS with AAV in the design of a 25-story building (showned in Fig. 1). There are 12 pieces of stacks in this building, and each one is 95m long. If we use double stack system, we would need 12 vent stacks, and some fittings Such as firpretection rings and H vent pipes. Therefore, it would take 41 thousand yuans ror materials while SSSDS takes only 11 thousand yuans. While consider with man cost, the double Stack system would cost more money Additionally, it occupies more space and isn‘t convenient for repair.
3.2 The work principle and the performance of AAV
The work princeple of AAV is the action of gravity and the difference of pressure.Working in Micro-negative-pressure State, it can ensure the stack not to exhaust but only get admittance. When the pressure of the stack reduces, the flap floats along the centre guide and the air is absorbed in, to prevent the low prssure from destorying the water seal (showed in Fig. 2). When the pressure increases, the flap falls off along the guide due to gravity, and then the valve is closed and prevents the effiuvium from getting into the room.
When the lower reaches of the stacks is blocked, the air in the higher would be closed in the stack, then prevents the higher reahes from charging. Therefore, in the occassion when we find the water level of the toilet drops slowly, we could cleanout immediately before the block happens.
3.3 Notices in designing and installing of AAV
3.3.1 Inorder to keep the air in the drainage system exhaust to outdoors fluently, it is important to keep the diameter of the outlet pipe must be bigger than those of the stacks in designing.
3.3.2 Because AAV can only get admittance, in the norms of USA and UK, when use AAV in high-rise buildings or residence areas, stack cowl venting through roof is needed to discharge the hardzard gases in the municipal drainage system.
3.3.3 AAV must be vertically installed, usually installed in where easy to be approched.
3.3.4 AAV must be installed in the place where the air is clear
Conclusion:
Because of its large capicity of admitance and high discharge load, AAV can be used in high-rise buildings. Therefore, the system can be simplified, and the arcthitecture cost can be lowef, and the floor structer can be optimized.
When used in multi-stroy buildings, AAV as it only get admittance and not exhaust,can be installed indoors. As a result, the stack wouldn‘t stand out of the roof and wouldn‘teffect the building‘s appearance. Futhermore, the troubles, such as rain leak of the roof and the difficulty in UPVC pipe fixing, can be avoided, thus the total cost can be lower Working in micro-negativeo-pressure and stable status, AAV can simplify the installing and reduce the cost, no matter when it is used in high-rise buildings or multi-story buildings. We can draw a conclusion, AAV should be widely used in projects.