Feasibility Study of Central Regulators in. Hong Kong s Residential Projects

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1 Young erson s aper Competition 2012 Feasibility Study of Central Regulators in Hong Kong s Residential rojects Name: (IGEM Far East District Section) Company: The Hong Kong and China Gas Co. Ltd., Hong Kon

2 Feasibility Study of Central Regulators in Hong Kong s Residential rojects Feasibility Study of Central Regulators in Hong Kong s Residential rojects ABSTRACT Any fluctuation in gas supply pressure would affect the performance of gas appliances significantly. For most of the residential flats in Hong Kong, a gas regulator is usually installed before the gas in order to regulate the downstream pressure within the internal pipes. However, gas regulator installed in a residential household usually occupies significant space inside a kitchen cabinet. As the housing price in Hong Kong is getting more and more expensive nowadays, the usable area in each residential flat has become more valuable than before. It is suggested to study whether the gas regulators in individual flats can be combined into a central regulator in each buildin In this paper, the feasibility of implementing a central gas regulator design in Hong Kong s residential developments is studied. Besides certain design criteria, the benefits and limitations of such design are also discussed. age 2 of 16

3 Feasibility Study of Central Regulators in Hong Kong s Residential rojects 1. INTRODUCTION In Hong Kong, over 70% of the residential households adopt town gas as heating fuel where town gas is a manufactured gas produced from mainly naphtha and natural gas. Due to its relatively low calorific value (17.27MJ/m 3 ) and the high concentration usage of households, the regulators used in Hong Kong are usually bigger than those in other countries. Over the years, it has been a usual practice for design engineers in Hong Kong to arrange a gas regulator before the in each residential flat (See Figure 1.1). Its major applications include: 1. To regulate the maximum gas supply pressure before entering the gas and internal pipes. 2. To avoid fluctuation in pressure across the internal pipes and ensure the best performance of the gas appliances. Town Gas Regulator with dia approx. 200mm Figure 1.1 Standard installation drawing for an Elster BK-U25 gas with regulator Under the influence of rising property prices, the usable space in the residential flats of Hong Kong are getting more valuable than before, it is suggested to study whether the gas regulator in individual flats can be combined into one central regulator for each buildin age 3 of 16

4 Feasibility Study of Central Regulators in Hong Kong s Residential rojects 2. DESIGN CRITERIA In order to determine the feasibility of such design, the current situation in Hong Kong has to be studied thoroughly. Most of the gas water heaters available in Hong Kong are equipped with built-in gas regulator. This ensures the water heaters to work under stable gas supply pressure. However, most of the hotplates (cooking appliances) in the market do not have such facility. Any fluctuation in gas supply pressure will affect the appliance s performance significantly. In order to remove the gas regulator from individual flats, the maximum allowable pressure fluctuation has to be determined. Based on extensive research and feedback from major manufacturers of hotplates in Hong Kong, the optimum operating pressure of a hotplate without built-in regulator is between 4 w. and 6 w.g (pressure unit: w. = inch water gauge, where 1 w. is approximately equivalent to 0.25ka). This range is established according to the minimum pressure requirement of the appliances and the maximum operating pressure with safety concern. Based on this pressure range, the allowable pressure fluctuation before the gas point can be calculated as follow: before_ internal_ pipe cooking (1) where _ : Gas supply pressure just before the point (see Figure 2.1) before : ressure drop across the gas internal_ pipe (assume 0.5 w. for typical gas ) : ressure drop across the internal pipe between the gas and the hotplate (assume 0.5 w. for typical design) cooking : Gas pressure just before the cooking point (see Figure 2.1) age 4 of 16

5 Feasibility Study of Central Regulators in Hong Kong s Residential rojects before_ cooking Figure 2.1 Schematic drawing for residential gas installation (not in scale) From Equation (1), for cooking to be maximum (i.e. 6 w.) before_ internal_ pipe cooking before_ 0.5" w. 0" w. 6" w. before_ 6.5" w. From Equation (1), for cooking to be minimum (i.e. 4 w.) before_ internal_ pipe cooking before_ 0.5" w. 0.5" w. 4" w. before_ 5" w. Therefore, if the gas regulator is removed, the pressure fluctuation before the point should be within 1.5 w. age 5 of 16

6 Feasibility Study of Central Regulators in Hong Kong s Residential rojects 3. RESSURE VARIATIONALONG A GAS RISER Assume a central regulator is installed at the bottom of a vertical gas riser as shown in Figure 3.1. Vertical Town Gas Riser Location of Central Town Gas Regulator Figure Schematic diagram showing a central regulator at the bottom of a residential building Change in gas supply pressure within the vertical gas riser Figure 3.1 can be caused by two major factors: Factor One - ressure gain, which can be calculated as follow: gain gain gh / air (1 S. G.) g (1 0.52)(9.81) 5.67a " w. (2) where S.G. : Specific gravity of town gas in Hong Kong (= 0.52) : Density of air at S.T.. (= kg/m 3 ) air age 6 of 16

7 Height (m) Feasibility Study of Central Regulators in Hong Kong s Residential rojects The above result is plotted in Figure 3.2 for easy reference. 30 ressure Gain by Attitute Effect ressure Gain (inch w.) Figure 3.2 Building height against pressure gain along a vertical riser Factor Two - ressure lost due to friction between town gas and the internal surface of the riser, which can be calculated as follow: With reference to CIBSE Guide C4, pressure loss along a gas riser can be calculated by: loss f ( Q, d, pipelength ) (3) k s N 4d Q 4( N3 pl d ) log d ( N 3 pld ) (4) where Q : Volumetric flow rate (m 3 /hr) p l : ressure change per length (a/m) d : Dia of pipe (m) k s : Absolute roughness (m), for galvanized iron pipe k s = 0.15mm : Density (kg/m 3 ), for town gas in Hong Kong = 0.54kg/m 3 : Dynamic viscosity (a s), for town gas in Hong Kong = 11a s N 3 : N 4 : age 7 of 16

8 Feasibility Study of Central Regulators in Hong Kong s Residential rojects And the cumulative pressure loss along a gas riser can be calculated by: N th ) loss@ r floor r 1 loss b N r q UF b( N r 1 1 (5) where loss : ressure loss as a function of gas flow (a) b : No. of flats per floor N : Total no. of floors q : Consumption of each flat (m 3 /hr) UF : Utilization factor, x x UF for 1 x 156 where x is the no. of flats This empirical formula is based on a field survey for seven residential buildings in Hong Kong in 1995 and the result is summarized in Figure 3.3 Figure 3.3 Utilization Factor (%) against no. of flats (based on field survey in Hong Kong) By applying equation (3), (4) and (5), it is observed that the following variables can affect the pressure loss along a vertical gas riser: age 8 of 16

9 Feasibility Study of Central Regulators in Hong Kong s Residential rojects Variable 1 Size (i.e. dia) of a gas riser. For example: Figure 3.4 Difference in pressure loss between a 80mm-dia riser and a 50mm-dia riser (assume all other variables are identical for both cases) Variable 2 No. of flats per floor supplied by a gas riser. For example: Figure 3.5 Difference in pressure loss between a riser supplying 1 flat per floor and 2 flats per floor (assume all other variables are identical for both cases) age 9 of 16

10 No. of Floor Feasibility Study of Central Regulators in Hong Kong s Residential rojects Variable 3 No. of floors supplied by a gas riser. For example: Figure 3.6 Difference in pressure loss between risers of different building heights (assume each floor s height is 3m and the gas consumption per flat are identical for all cases) Variable 4 Gas consumption per flat. For example: 30 ressure Loss by Friction (Gas Load er Flat) ressure Loss (inch w.) 1 x 28kW per flat 2 x 28kW per flat 1 x 37kW per flat 2 x 37kW per flat 1 x 40kW per flat 2 x 40kW per flat 1 x 48kW per flat 2 x 48kW per flat Figure 3.7 Difference in pressure loss along a riser with different consumption load (water heater quantity and power rating) per flat, assume other variables are identical for all cases age 10 of 16

11 Height (m) Feasibility Study of Central Regulators in Hong Kong s Residential rojects 4. IMLEMENTATION OF CENTRAL GAS REGULATOR DESIGN Recall the result from session 2, a central gas regulator design requires the pressure fluctuation before the point of each flat to be within 1.5 w. Two extreme cases should be considered: Extreme Case 1 Maximum gas supply pressure before point (i.e. minimum pressure loss) Assume there is no gas demand from a residential building at an instant (i.e. idle system). If the hotplate on the top floor is suddenly switched on, it will receive the highest gas supply pressure owing to the maximum pressure gain along the vertical riser. 30 ressure Gain by Attitute Effect Maximum gas supply pressure ressure Gain (inch w.) Figure 4.1 Location of maximum pressure when the town gas inside a riser is idle age 11 of 16

12 No. of Floor Feasibility Study of Central Regulators in Hong Kong s Residential rojects Extreme Case 2 Minimum gas supply pressure before point (i.e. Maximum pressure loss) During peak demand hours, the gas utilization pattern follows Figure 3.3. ressure loss will be the highest at certain floor below the top floor because part of the pressure loss is compensated by the pressure gain. (See Figure 4.2) ressure loss by Friction (Combine With Altitute Gain Effect) Minimum gas supply pressure ressure loss (inch w.) Figure 4.2 Location of minimum town gas supply pressure during peak demand hours If the pressure difference between the two extreme cases can be kept within the design range of 1.5 w., a central gas regulator design can be implemented. age 12 of 16

13 Feasibility Study of Central Regulators in Hong Kong s Residential rojects Example One Assume a residential building with 3.3m floor-to-floor height and a 50mm-dia vertical riser supplying one flat per floor. Each flat has a combination of a two-burner hotplate (10kW) and an instantaneous gas water heater (39kW). The pressure variation can be kept within the range of 1.5 w. only if this building is 13-storey-high or below. In other words, a central regulator design can be implemented only if this building is 13-storey-high or below. Allowable ressure Fluctuation Range (1.5 w.) Figure 4.3 Difference in pressure loss along 50mm riser for different building heights (1 riser supplying 1 flat per floor) age 13 of 16

Feasibility Study of Central Regulators in Hong Kong s Residential rojects Example Two This example has the same configurations as Example One.

14 Feasibility Study of Central Regulators in Hong Kong s Residential rojects Example Two This example has the same configurations as Example One. However, the riser this time is supplying two flats per floor. ressure fluctuation in this case can be kept within the range of 1.5 w. only if this building is 11-storey-high or below. In other words, a central regulator design can be implemented only if this building is 11-storey-high or below. Allowable ressure Fluctuation Range (1.5 w.) Figure 4.4 Difference in pressure loss along 50mm riser for different building heights (1 riser supplying 2 flats per floor) age 14 of 16

15 Feasibility Study of Central Regulators in Hong Kong s Residential rojects 5. DEVELOMENT OF USER-FRIENDLY TOOL FOR DESIGN ENGINEERS A user-friendly Excel program is developed to identify whether a particular development is suitable for installing a central gas regulator. Design engineers can simply input certain paras and the program will determine the feasibility of such design for particular project automatically. Besides, it can also help the engineers to generate a gas design proposal efficiently. ara Inputs: 1) Estimated average consumption per flat 2) Floor-to-floor height of the building 3) Total no. of floors of the building 4) No. of flat per floor served by each gas riser 5) roposed riser size on each floor aras input for particular projects Turns Green if central regulator is feasible Turns Red if central regulator is not feasible Figure 5.1 A user-friendly Excel program for a Central Regulator Design age 15 of 16

16 Feasibility Study of Central Regulators in Hong Kong s Residential rojects 6. BENEFITS TO BOTH THE CUSTOMER AND THE GAS COMANY With the aid of this design program, engineers can determine the feasibility of a central regulator design and tailor-make gas design proposals for customers effectively. The idea of central regulator has been welcomed by residential developers in Hong Kong while several projects have already adopted such design. A central regulator not only allows the customers to acquire more usable space in their kitchens, it also helps the gas company to achieve material cost savings by reducing the total quantity of regulators. Besides, since the central regulator is usually located in public area, it is easier for the gas company to carry inspection and maintenance duties. 7. CONCLUSION A central regulator design can be implemented in a residential building if the fluctuation of gas supply pressure for each flat can be kept within a design range. For the best appliance operation in Hong Kong, this range should be kept within 1.5 w. The gas supply pressure at each flat fluctuates with the utilization pattern from all users in the buildin If certain paras are known, the feasibility of a central regulator design for particular building can be determined. A user-friendly Excel program based on this concept is developed. By inputting certain design paras, the program will determine the feasibility of such design for particular project automatically. It can also help design engineers to generate a gas design proposal efficiently. Under the influence of rising property prices, the usable spaces in the residential flats in Hong Kong have become more valuable nowadays. The idea of central regulator can increase the effectiveness of space usage. It is welcomed by the developers in Hong Kong while some buildings have already adopted such design. On the other hand, it also helps the gas company to achieve material cost savings by reducing the total quantity of regulators. Since the central regulator is usually located in public area, it is also easy for the gas company to carry out inspection and maintenance duties. 8. REFERENCE CIBSE Guide C: Reference data, section C4: Flow of fluids in pipes and ducts (1977). Utilization survey by HKCG Domestic Sales Department (1995), Hong Kon The Guidebook of Housepiping Work Design (Abstract) by Osaka Gas Company Ltd. (1981), Japan. age 16 of 16

SIZING AND CAPACITIES OF GAS PIPING

APPENDIX A (IFGS) SIZING AND CAPACITIES OF GAS PIPING (This appendix is informative and is not part of the code. This appendix is an excerpt from the 2003 International Fuel Gas Code, coordinated with