The Consideration on Revision of "Code for Design of Building Water Supply and Drainage"

ZENG XUEHUA WU JUNQI

Beijing Institute of Civil Engineering and Architecture, China
Add:No.1 Zhan lanGuan Rd, Beijing China, Post code:100044
Tel:010-68322425

Abstract: This paper centres on water saving in building and proposes some amendment opinions on installation of water meter, control of outflow with excess pressure, selection of circulating style in hot water system and so on for "Code for design of building water supply and drainage".

Key words: water saving in building, water meter, outflow with excess pressure, circulation of hot water

Water is important resource for all the lives in the world, and it is becoming a retarding factor for the economy development in our country because of water shortage and pollution. According to the statistic data of Water Conservancy Department, the situation of water shortage is worsening. There are more than 400 cities with different degree of water shortage, 110 cities with serious water shortage among the established 670 cities. Water shortage is 6000000000m3 in normal year in the cities of China . Because of spring and summer drought in the north of China, there is serious water shortage for urban water supply. More than 100 counties and cities have to limit the water supply in this summer. Saving water is the basic law in our nation. Therefore, how to reflect the water shortage situation of our nation in the revision of the designing code is worth considering.
Although water saving in buildings such as water saving sanitary facilities and so on has aroused the recognition of related departments, the improvement in the design and promoting scientific water usage are limited. The change of sanitary facilities form normal type to water saving type is feasible and will not influence the running of the system, but the system alteration will cost a lot. Therefore water saving should be reflected in the designing code. The following are some suggestions:
1. Quality requirements of water meters and valves and regulations of water meters placement should be definite.
Water meter is the legal measure equipment and basis of charging, therefore water meter quality is very important for water saving. With the long term usage, the precision of water meter decreases. According to the calibration of used 1432 water meters in 10cities, The meters with a tolerance of less than ±4% account for 60.9%, the fast 33.4%, the slow 5.7%, According to the norm of state, water meter in living area should be examined before using and used within limited years. The research team for water saving in buildings investigated water using condition in living areas and colleges of Beijing form 1998 to 1999. and found that more than 80% of users‘ valves before the meters are damaged or eroded. Although practical measures haven‘t been taken by the meters are damaged or eroded. Although practical measures haven‘t been taken by the water supply department to fulfil the norm of state, water users‘ requirements for water measurement accuracy will increase with the adjustment of water price. Therefore, specific quality requirement of valve before the water meter should be reflected in the code to facilitate water meter reparation in order to protect the interests of the users.
According to above reasons, It is suggested that"3.4.1 pipes and its accessories in water supply system should comply with product standard"."3.4.4 pipe materials should be corrosion-resistant and pressure-resistant. According to the diameter of pipe and degree of pressure, copper core with iron-clad, full stainless steal and full plastic valves can be adopted usually." should be changed to "3.4.4 pipe materials should be corrosion-resistant and pressure-resistant. According to the diameter of pipe and degree of pressure, copper core with iron-clad, full stainless steal and full plastic valves should be adopted."
On the other hand, water meter is an indispensable instrument for reasonable water usage analysis and water balance test that analyze the relationship on balance between water input and output. By now, many cities have had regulation on water usage analysis and water balance test, for example, users whose monthly water consumption is more than 2000t should have water usage analysis. It is benefit for making reasonable water plan and saving water to do the above work periodically. For example, many hidden faults of water waste were found after water balance test in Shanghai Jiaotong University, after renovation of water supply system, 30000t water is saved per month, accordingly ￥1000000 water cost is saved per year. Because that the requirements of water meter setting in the original code is less concrete than that of accessories such as valves and check valves etc, and that some designers are not familiar with the requirements for reasonable water usage analysis and water balance test. Thus, water meter setting is only based on water rate. In order to fulfil the requirements of water waving, many users have to break the pipes to mount water meter, which causes much trouble.
Therefore, It is suggested that two factors should be added to term 3.4.18 in the code, one is water meter setting requirements, the other is a requirement of water meter‘s function for water balance test and reasonable water usage analysis.
2. In order to promote scientific water usage, the control of excess pressure outflow should be reflected in the code.
The rate of flow of a sanitary facility is the flow volume in unit time and it satisfies the normal function of the facility. Outlet water pressure is to warrant rate of flow .Excess Pressure at the outlet makes excess volume of water outflow, which is an invisible water waste. The phenomenon is called as excess pressure outflow and the excess water volume is called as excess outflow rate. When excess pressure outflow happens, not only normal water distribution is disturbed, but also negative effect on water usage is made. At the same time, excess water outflow is wasted. Different degree of this kind of water waste exists in different buildings and the volume is very large.
According to the statistic data of the research team on residential districts, dormitories, comprehensive buildings in Beijing from 1998 to 1999. it is found that excess pressure outflow exists very commonly. Two kinds of 15mm diameter water taps were tested, one is traditional tap, the other is ceramic core tap. If it is hypothesized that the rate of flow is 0.2 I/s with tap half open, the rate of excess pressure outflow for the former is 54%,the latter is 24%, Because that there is screen plate at the outlet of ceramic core tap, the cross dimension of the outlet is relatively smaller than that of traditional tap. In order to get comfortable hand feeling, relatively small water outflow rate is favorable, So it is hypothesized that the rate of flow is 0.16l/s happens with ceramic core tap half open, accordingly the excess pressure outflow rate is 52% Thus, the conclusion is that even though the ceramic core tap has the function of water saving and water pressure control, the problem of excess pressure outflow can not be solved if the water supply system is not designed properly. On the other hand, the volume of the invisible water waste can not be ignored, sometimes it is more than the visible water waste. For example ,the waste dribbling volume of 15mm diameter water tap is 3.6l/h, the total dribbling volume of 20 taps is 1728l/d. The research team tested outlet rate of two kinds taps at half open in a toilet at the first floor of a 12 floor building in an university of Beijing. They are 0.42l/s and 0.21l/s respectively. The theoretical waste outlet rates are 0.22l/s and 0.05l/s respectively. If the average using time of taps is 15min daily, total theoretical waste volume of 20 traditional taps is 3960 l/d and it is larger than the volume of dribbling waste. That of ceramic core tap is 900l/s and it almost equals the dribbling volume of 10 taps in a day. It vill be an astonishing volume in our country for the large quantities of buildings. Therefore, the requirement of controlling excess pressure outflow should be reflected in the code.
The effective measure to control excess pressure outlet is to control the pressure at the outlet, which has been commonly recognized by the designer of water system. Measures such as mounting porous plate or water saving plug before the outlet have been put forward in the late 1970s and the problem has been solved in many buildings in 1980s and 1990s. For example, in an 18-floor dormitory of an institute in Beijing, relief valve unit is mounted at the inlet pipe of 5-13 floor in the high area(5-18 floor)of water supply. The outflow rate of half open tap at 5-floor is 0.16l/s. In another 18-floor dormitory of another university in Beijing, the outlet rate of a half open tap at 7-follr is 0.23l/s without relief valve in inlet pipe of 7-18 floor. Based on engineering experience, feasibility of design and construction, statistic data(Fig.1) of the research team. It is suggested that" if the static pressure at water distribution point is above 0.15MPa, measures of decreasing pressure should be adopted" be added to the code on the basis of original standard:(1) Water pressure should not exceed the regulated product testing pressure. (2)The static pressure of lowest sanitary facility should be below 0.45MPa at better and should not be above 0.55MPa.
3. Hot water circulation in trunk pipes and riser pipes in central hot water supply system should be guaranteed to decrease water waste
According the investigation of the research team, water waste in hot water supply system is serious. The waste mainly comes from cold water discharging before hot water‘s arrival. The fault of construction and administration as well as designing led to the result. According to designing, the choice of hot water circulation pattern is one of the main factors that determined the quantity of water waste. At present, there are three patterns of hot water circulation specified in the code: trunk pipes circulation; riser pipes and trunk pipes circulation; branch pipes, riser pipes and trunk pipes circulation. Apparently, the water waste in trunk pipes circulation is the most. For example, in a department which has periodical hot water supply (once a day) with trunk pipes circulation, 16 riser pipes, diameter 32mm ,length 18m, average yearly water waste reaches 105m³. The total water waste of same kind buildings in our country will not be a small amount. At the same time, eliminating this kind of waste is the urgent requirements of users‘ at present. By now, planed water usage has been operated in many cities of China, therefore users have to renovate water supply system to control water use. Mary effective water saving measures have been taken. For example, after renovation by addition of return pipers in the hot water system of bathhouse in an university of Beijing, the saving on water is 50t per month. Although circulation in branch pipes, riser pipes and trunk pipes is the best way to save water ,it can not come true at present for economical limitation. To adopt riser pipes and trunk pipes circulation in periodical hot water supply system of multi-storied building is necessary and feasible. Therefore, it is suggested that item 1,2,3 in term 5.2.10 should be combined as: hot water circulation in trunk pipes and riser pipes should be guaranteed in central hot water supply system.
The industry of construction is an important industry of our nation and now it is developing rapidly. With the promotion of people‘s living condition, the requirements for water quantity and quality are increasing at an amazing speed. Protection of water resources and maintaining the sustained development of water resources have been becoming the focus of governments and people, which has promoted new requirements for the design of water system in building. Therefore, it is suggested that the authorities of code revision strive for funds supply to study the key problems for the development of water supply and drainage in building. In order to keep the code up with the development of new situation and make it scientific and advanced.

　

fig.1 Outflow rate comparison between two kinds of half open tap