Cold Water Supply Systems: A Comprehensive Overview

1. 5508BESGServices and Utilities Lecture 1 COLD WATER SUPPLY

2. Lecture Contents • What is Water?? • How are connections made? • Types of systems • Water Distribution • Advantages & disadvantages

3. Learning Outcomes • To understand the various connection and distribution options open to a client • To understand the criteria that guide the decision • To understand how decisions are made and what the influencing factors are

4. Cold Water Supply Water sources & distribution Water supply systems Useful references: Randall McMullan, Environmental Science in Building, Sixth Edition Roger Greeno, Building Services Technology and Design CIBSE Guide G “Public Health Engineering” Plumbing Engineering Services Design Guide (2002) The Chartered Institute of Plumbing & Heating Health and Safety Commission, Health & Safety Series booklet HS(G)70 “The control of legionellosis including legionnaires disease” Health and Safety Commission, Approved Code of Practice “The prevention or control of legionellosis (including legionnaires disease)”

5. Nature of Water H2O exists on earth as solid, liquid and vapour Fixed amount of water in the world, same water circulates all the time Very strong solvent, will dissolve many minerals and salts, gases and even pipework materials (e.g. lead!)

6. Collection and Distribution Various sources: rivers, lakes, reservoirs, wells, boreholes, springs Stored, filtered and treated, then supplied locally – there is no “national grid” of water pipework Supply to populated areas usually runs downhill (but may have to be pumped) via large diameter (e.g. 1m or even 2m bore) trunk mains

7. Nature of water Hard water comes from mineral rich sources, tends to taste better than soft, is mildly alkaline, but can cause furring or limescale deposits Soft water usually comes from underground sources, is often slightly acidic because of dissolved CO2 and can dissolve metal from pipes

8. Supply to Buildings Trunk mains connect to smaller secondary mains run in a grid pattern under all streets Communication pipe connects water main to buildings

9. Supply to Buildings In new buildings (particularly commercial) water use is metered In existing dwellings with no meter fitted, water charges are based on “Council tax band” of property Metering is strongly encouraged for conservation purposes

10. Secondary ‘Street’ Mains MDPE pipes replacing all older materials such as cast iron, steel etc. Coloured blue for ease of identification

11. Connection to Premises • Communication pipe • Street main • Water company stop tap • Property boundary • Service pipe

12. Typical Connection Detail Sleeve 20mm MDPE pipe Note: Connection size is usually 20mm diameter to domestic premises, none-domestic, industrial or commercial buildings are usually larger than this, often considerably larger.

13. Water Meters Record volume of water consumed in litres Located in easily accessible place Garage Outbuilding Recommended for environmental and financial reasons

14. DirectSystem Note: Use of high level tank to supply hot water system only.

15. Direct Systems (Domestic) • All outlets fed directly from the rising main • Entirely dependant on mains pressure, which is likely to vary during the day. • Large premises need the availability of high water pressures. • Risk of contamination due to backflow – therefore rules apply • Simple low cost, non-storage system. • Minimum space requirements. • Drinking water quality at all outlets. • No reserves of water in the event of mains failure.

16. DirectSystem With modern combination boiler

17. Indirect system with hot storage cylinder

18. Indirect Systems • All outlets except designated drinking water taps are fed from a gravity supply from a high level storage cistern • Cistern water not considered drinking water (Potable) on older installations (Pre Bye-Law 30) • Water companies prefer this system for larger buildings and where flow and min. pressures cannot be assured. • Storage capacity is typically 24 hour reserve supply (in case of mains disruption) • Constant pressures and flow rates inside premises assured

19. Advantages / disadvantagesDirect Indirect • Constant pressures • Hot and cold pressures always roughly equal • Spaces required for storage cistern • Suitable for any size of property • More pipework • More expensive • More complicated • 24 hrs storage in case of service disruption • Variable pressures • Hot and cold pressures may be unequal • No space required to accommodate the cistern • Less pipework • Less expensive • Less complicated • No storage in case of service disruption. • Need good water pressures to be available • Mainly suited to smaller premises

20. Rainwater Harvesting • Collects rainwater from roofs and areas of hard standing (optional) • Stores the rainwater until it is required (usually in underground tanks) • Uses the rainwater for flushing toilets, outside taps and washing machines (optional). • Most suitable for new build property, but can be retrofitted. • Reduces cost of metered water consumption. • Contributes to sustainable housing.

22. Commercial Rainwater Harvesting

23. Greywater Harvesting • Collects water from showers, baths, basins. (not kitchen sinks and washing machines). • Filters and cleans (usually) the water and stores until needed. • Uses the greywater for toilet flushing and outside taps. • Most suitable for new build property, but can be retrofitted. • Reduces cost of metered water consumption. • Contributes to sustainable housing. • Can be a smaller size than rainwater harvesting. • Can be above or below ground.

25. Cisterns “An open topped vessel designed to hold a supply of cold water which will have a free surface subject only to the pressure of the atmosphere” Typically the cistern should be sized to store 24 hours cold water supply for a premises. The storage volume depends on the type and size of premises.

26. Cisterns • Regulations stipulate that all cisterns must incorporate: • Insulation to prevent temperature extremes • A tight fitting lid • A screened ventilation opening • A screened overflow / warning pipe

27. Air gap to meet water regulations Screened vent Lid Screened overflow Mains water supply Alternative Cold Water Service (CWS) outlet Insulation all around tank Drain Cold Water Service (CWS) outlet at bottom ensures better draining. Typical cold water storage cistern installation

28. How much storage ? Based on typical 24 hour water consumption rates. Ideally a full 24 hours water supply should be stored but there is a cost: Space Weight Stagnation / legionnaires disease.

30. Pressure Direct System: Mains pressure lifts water to all points. Indirect System: Mains pressure lifts water to fill cistern, pressure at any point in distribution pipework is due to gravity. Both systems have a finite amount of available pressure

34. How much pressure would be required to lift water to a height of 10 m ? P = 1000 x 9.81 x 10 P = 98,100 Pa i.e. approx. 100,000 Pa (1bar). Therefor 1 bar pressure will lift water approximately 3 floors

35. Mains Water Pressure Mains pressure is rarely constant, it often varies throughout the day, during periods of maximum demand, pressure tends to be at it’s lowest. Utility companies typically maintain a minimum mains water pressure of between 0.7 and 1 bar. Sufficient to lift water between 7 and 10 meters above the main

36. Insufficient Mains Pressure? Use Pressure boosters

37. Typical boosted system

38. How much pressure ? 7 The James Parsons building has a basement, ground floor and 7 floors above that (the break tank and “booster set” is installed in the basement. If we assume each floor is 3.5m high how much pressure does the booster pump need to produce to lift the water to the top floor? 6 5 4 3 2 1 G 3.5m B

39. 8 floors at 3.5m = 28m Pressure required = 1000kg x 28m x 9.81 Pressure required = 274680 Pa = 2.75 bar approx