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Cold water supply and pipe sizing
The document provides a comprehensive overview of cold water supply systems in buildings, detailing their components, functionalities, and definitions. It explains direct and indirect water supply systems, advantages and disadvantages, and considerations for preventing back siphonage. Additionally, it outlines design principles, water demand factors, and guidelines for sizing pipes to ensure adequate flow and pressure.
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Cold water supply and pipe sizing
- 1. COLD WATER SUPPLYSYSTEM Introduction Building water supply system is a system in plumbing which provides and distributes water to the different parts of the building or structure, for purposes such as drinking, cleaning, washing, culinary use, etc.; it includes the water distributing pipes, control devices, equipment, and other appurtenances.
- 2. Introduction Cold water systemprovides water for the following purposes; 1. Drinking purpose. 2. Cooking purpose. 3. Sanitary purpose. 4. Washing purpose. 5. Gardening
- 3. Definitions 1. Cistern –a container for water having a free water surface at atmospheric pressure 2. Feed cistern – any storage cistern used for supplying cold water to a hot water apparatus 3. Storage cistern – any cistern other than a flushing cistern, having a free water surface under atmospheric pressure, but not including a drinking trough or drinking bowl for animals.
- 4. Definitions cont…….. 3. Capacityof a cistern - the capacity up to the water line 4. Water line – a line marked inside the cistern to indicate the water level at which the ball valve should be adjusted to shut off. 5. Overflowing level – the lowest level at which water can flow into that pipe from a cistern.
- 5. Definitions cont…… 6. Warningpipe – an overflow pipe so fixed that its outlet end is in an exposed and conspicuous position and where the discharge of any water from the pipe may be readily seen and, where practicable, outside the building. 7. Communication pipe – any service pipe from the water main to the stop valve fitted on the pipe. 8. Service pipe – any pipe for supplying water from a main to any premises as is subject to water pressure from that main, or would be so subject but for the closing of some stop valve.
- 6. Definitions cont…. 9 Distributingpipe – any pipe for conveying water from a cistern, and under pressure from that cistern. 10 Supply pipe – so much of any service pipe which is not a communicating pipe. 11 Main – a pipe for general conveyance of water as distinct from the conveyance to individual premises.
- 7. Definitions cont……….. 12 Hotwater cylinder or tank – a closed container for hot water under more than atmospheric pressure. Note: a cylinder is deemed to include a tank. 13 Potable – water suitable for drinking. 14 Fitting – anything fitted or fixed in connection with the supply, measurement, control, distribution, utilization or disposal of water.
- 8. Fig1.1 Connection towater main water main Water authorities stop valve service pipe Installed and maintained by water authority Installed and maintained by building owner Stop valve chamber 760mm (minimum) Communication pipe
- 9. Distribution systems There aretwo types of water supply systems; 1. non storage or direct and 2. storage or indirect systems
- 10. Non storage orDirect Systems • It is a system whereby all the sanitary fittings are supplied with cold water direct from the main. In this system, a cold water feed cistern is usually required to feed the hot water supply system
- 11. Fig 1.2 Directcold water supply system
- 12. Storage or IndirectSystems • It is a system whereby all the drinking water used in the building is supplied from the main and water used for all other purposes is supplied indirectly from a cold water storage cistern. • The cistern also supplies water to the hot water cylinder therefore its capacity will almost double the capacity required for the direct system
- 13. Fig 1.3 Indirectcold water supply system
- 14. Table 1.1 Advantagesof Direct and Indirect cold water systems S/No Direct or non storage S/No Indirect or storage 1 Less pipework and smaller or no cistern, making it easier and cheaper to install. 1 Large capacity cistern provides a reserve of water during interruption of supply. 2 Drinking water is available at all draw-off points. 2 Water pressure on the taps supplied from the cistern is reduced, which minimizes wear on taps and noise. 3 Smaller cisterns which may be sited below the ceiling. 3 Fittings supplied with water from the cistern are prevented from causing pollution of the drinking water by back siphon age 4 In systems without cistern there is no risk of polluting the water from this source 4 Lower demand on the water main
- 15. Prevention of BackSiphonage • Back siphonage is the back flow of water, which may be contaminated, into the drinking water supply. • The condition for back siphonage to happen is the creation of negative pressure or partial vacuum in the pipe connected to an appliance having its outlet submersed in water, which may be contaminated.
- 16. Prevention of BackSiphonage cont… • Back pressure is the result of water pressure in the system being greater than that in the supply. Higher system pressures can be caused by the expansion of water in unvented domestic hot water supplies, or in systems where a pump is used. • Negative pressures in the supply main may be caused by a major leak in the main or the fire services drawing off vast amounts of water.
- 17. The points whichmust be observed for prevention of risk of back siphonage 1. The ball valves in the cisterns must be above the overflow pipe and if the silencer pipe is fitted must discharge water above the ball valve through a spray. 2. The outlets of taps connected to sanitary appliances must be well above the flooding level of the appliance.
- 18. The points whichmust be observed for prevention of risk of back siphonage cont….. 3. Flushing valves for WCs must be supplied from a cold water storage cistern. 4. Appliances having low-level water inlets, for example bidets and certain types of hospital appliance, must be supplied from a cold water storage cistern and never direct from the main
- 19. Water Storage Purposes ofwater storage Provide for an interruption of supply Accommodate peak demand Provide a pressure (head) for gravity supplies Design factors Type and number of fittings Frequency and pattern of use Likelihood and frequency of breakdown of supply (often design for 12- or 24-hour reserve capacity)
- 20. According to regulations,the installed cistern must be; 1. Watertight, adequate strength, and manufactured from plastic, galvanized steel, asbestos cement or copper. 2. Sited at a height that will provide sufficient head and discharge of water to the fittings supplied. 3. placed in a position where it can be readily inspected and cleansed
- 21. According to regulations,the installed cistern must be; 4. Provided with dust proof but not air tight cover and protected from damage by frost. 5. Fitted with an efficient overflow pipe which should have a fall as great as practicable not less than 1 in 10.
- 22. Fig 1.4 Methodof installing cold water storage or feed cistern 40mm 40mm 25mm 50mm 50mm Timber bearers Rising main Distributing pipe to sanitary appliances Full-way gate valve Ceiling joists Stop valve Warning or overflow pipe Vent pipe from hot-water cylinder Inlet silencer
- 23. Fig 1.6 Methodof duplicating cold water storage cisterns M anifold Cold-water Feed pipes D rain pipe O verflow and w arning pipe Isolating valves Risingmain W ater level B allvalve
- 24. Table 1.2 Provisionof cold water storage to cover 24 Hours interruption of supply Type of building Storage (L) Dwelling houses and flats per resident 90 Hostels per resident 90 Hotels per resident 140 Offices without canteens per head 40 Offices with canteens per head 45 Restaurants per head/per meal 10 Day schools per head 30 Boarding schools per head 90 Nurses homes and medical quarters per resident 115
- 25. Table 1.3 Recommendedminimum storage of cold and hot water systems (Source: Garrett, R. H., 2008. Hot and Cold Water Supply) Type of building Minimum cold water storage (litres) Minimum hot water storage (litres) Hostel 90 per bed space 32 per bed space Hotel 200 per bed space 45 per bed space Office premises: - with canteen facilities - without canteen facilities 45 per employee 40 per employee 4.5 per employee 4.0 per employee Restaurant 7 per meal 3.5 per meal Day school: - nursery or primary - secondary or technical 15 per pupil 20 per pupil 4.5 per pupil 5.0 per pupil Boarding school 90 per pupil 23 per pupil Children’s home or residential nursery 135 per bed space 25 per bed space Nurses’ home 120 per bed space 45 per bed space Nursing or convalescent home 135 per bed space 45 per bed space Note: Minimum cold water storage shown includes that used to supply hot water outlets
- 26. Table 1.4 Estimationof cold water storage per occupant Type of building Storage per occupant (litres) Hospitals, per staff on duty 45 Hostels 90 Hotels 135 Houses and flats 135 Offices with canteens 45 Offices without canteens 35 Restaurant (* per meal) 7 Schools, boarding 90 Schools, day 30
- 27. Table 1.5 Provisionof cold water storage to cover 24 Hours interruption of supply. Based on sanitary appliances Sanitary appliance Storage (L) Water closet (WC) 180 Sink 135 - 225 Water basin 90 - 250 Shower 135 - 225 Urinal 135 - 250
- 28. Table 1.6 Accessto storage cistern
- 29. Table 1.7 Waterstorage plant room area
- 30. Design principles I. Coldwater system A: Potable water • Drinking purpose. • Cooking purpose. B: Non-potable water Flushing water(fresh or salt water) Cleansing water Fire service Swimming-pool filtration Irrigation(e.g. for landscape) Fountain circulation Air-conditioning water, etc. II. Hot water system (e.g. in hotels & hospitals
- 31. Design principles cont…. Majortasks of water systems design: 1. Assessment & estimation of demands 2. Supply scheme & schematic 3. Water storage requirements 4. Piping layout 5. Pipe sizing 6. Pump system design
- 32. Water demand Water demanddepends on: Type of building & its function Number of occupants, permanent or transitional Requirement for fire protection systems Landscape & water features Typical appliances using the cold water WC cistern, wash basin, bath, shower, sink Washing machine, dishwasher Urinal flushing cistern
- 33. Water demand cont…… Simultaneousdemand Most fittings are used only at irregular intervals It is unlikely that all the appliances will be used simultaneously . Therefore there is no need to size pipe work on continuous maximum Key factors to consider: Capacity of appliance (L) Draw-off flow rate (L/s) Draw-off period, or time taken to fill appliance (sec) Frequency of use, time between each use (sec)
- 34. Water demand cont…… LoadingUnit (L.U) : A factor given to an appliance relating the flow rate at its terminal fitting to Length of time in use Frequency of use for a particular type Use of building NOTE Evaluate the ‘probable maximum’ Relates the flow rate to the probable usage Consider design & minimum flow rates
- 35. Table 1.8 Designflow rates and loading units
- 36. How about urinals? 0.004L/s/urinalcontinuous Required design flow (from graph) = 0.7 L/s + 0.008L/s = 0.71 L/s Figure1.7Conversionchart–loadingunitstoflowrate 12 wash basins × 1.5 = 18 10 WCs × 2 = 20 2 urinal bowls × — = — 2 cleaners’ sinks × 3 = 6 Total loading units = 44 Exampleofuseofloadingunits
- 37. Design flow considerations Asmall increase in demand over design level will cause a slight reduction in pressure/flow (unlikely to be noticed by users) Exceptional cases: Cleaners’ sinks (depends on one’s behavior) Urinal flushing cisterns (continuous small flow) Team changing rooms at sport clubs (high demand) Special events (ad hoc demand)
- 38. Pipe sizing-Introduction Correct pipesizes will ensure adequate flow rates at appliances and avoid problem caused by over sizing and under sizing; Over sizing will mean: – additional and unnecessary installation costs; – delays in obtaining hot water at outlets; – increased heat losses from hot water distributing pipes. Under sizing may lead to: – inadequate delivery from outlets and possibly no delivery at some outlets during simultaneous use; – some variation in temperature and pressure at outlets, especially showers and other mixers; – some increase in noise levels.
- 39. Fig 1.8 Pipesizing-Introduction
- 40. Sizing procedure forsupply pipes • The procedure below is followed by an explanation of each step with appropriate examples. (1) Assume a pipe diameter. (2) Determine the flow rate: (a) by using loading units; (b) for continuous flows; (c) obtain the design flow rate by adding (a) and (b). (3) Determine the effective pipe length: (d) work out the measured pipe length; (e) work out the equivalent pipe length for fittings; (f) work out the equivalent pipe length for draw-offs; (g) obtain the effective pipe length by adding (d), (e) and (f).
- 41. Sizing procedure forsupply pipes cont… (4) Calculate the permissible loss of head: (h) determine the available head: (i) determine the head loss per metre run through pipes; (j) determine the head loss through fittings; (k) calculate the permissible head loss. (5) Determine the pipe diameter: (l) decide whether the assumed pipe size will give
- 42. Equivalent pipe length •Equivalent pipe length Is the expression of friction resistances to flow through valves and fittings in terms of pipe lengths having the same resistance to flow as the valve or fitting. • For example, a 20 mm elbow offers the same resistance to flow as a 20 mm pipe 0.8 m long. • Effective pipe length. The effective pipe length is the sum of the measured pipe length and the equivalent pipe lengths for fittings (e) and draw-offs (f).
- 43. Fig 1.9 Equivalentpipe length cont…(seetables1.9&1.10)
- 44. Table 1.9 Equivalentpipe lengths (copper, stainless steel and plastics) (Source: Garrett, R. H., 2008. Hot and Cold Water Supply)
- 45. Equivalent pipe lengths(copper, stainless steel and plastics) cont… Notes: 1. For tees consider change of direction only. For gate valves losses are insignificant. 2. For fittings not shown, consult manufacturers if significant head losses are expected. 3. For galvanized steel pipes in a small installation, pipe sizing calculations may be based on the data in this table for equivalent nominal sizes of smooth bore pipes. For larger installations, data relating specifically to galvanized steel should be used. BS 6700 refers to suitable data in the Plumbing Engineering Services Design Guide published by the Institute of Plumbing.
- 46. Table 1.10 Typicalhead losses and equivalent pipe lengths for taps (Source: Garrett, R. H., 2008. Hot and Cold Water Supply)
- 47. Fig 1.10 Exampleof measured and effective pipe length Note: There is no need to consider both branch pipes to taps. Measured pipe length = 4.75 m Equivalent pipe lengths: elbows 2 x 0.8 = 1.6 m tee 1 x 1.0 = 1.0 m Stop valve 1 x 7.0 = 7.0 m taps 2 x 3.7 = 7.4 m check valves 2 x 4.3 = 8.6 m Effective pipe length = 30.35 m
- 48. Figure 1.11 Exampleof permissible head loss This formula is used to determine whether the frictional resistance in a pipe will permit the required flow rate without too much loss of head or pressure. Figure 1.10 illustrates the permissible head loss for the example in figure 1.9. Pressureattaps45mhead
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- 52. Table 1:11 Maximumrecommended flow velocities Water temperature (°C ) Flow velocity Pipes readily accessible (m/s) Pipes not readily accessible (m/s) 10 3.0 2.0 50 3.0 1.5 70 2.5 1.3 90 2.0 1.0
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- 56. Pipe sizing cont… Pipesizing for hot water systems is the same as cold water, except cold feed pipe must also be considered Useful formulae for pipes: 1. Thomas Box formula d = pipe diameter (mm) q = flow rate (l/s) H = head or pressure (m) L = effective length of pipe (actual length + allowance for bends, tees, etc.) Where;
- 57. Example: Determine the pipesize using Thomas Box formula. Hence, the nearest commercial size is 32 mm bore steel or 35 mm outside diameter copper. Answer: Using Thomas Box formula, = 27.83 mm
- 58. 2. Relative dischargeof pipes Example: (a) Compute the number of 32 mm short branches that can be served from 150 mm main. (b) Determine the size of water main required to supply 15 nos. 20 mm short branch pipes. Answer: Answer: Hence, the nearest commercial size is 65 mm.
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