COLD WATER SUPPLY

Services and Utilities

Lecture Contents

• What is Water?? • How are

connections made? • Types of systems • Water Distribution • Advantages &

disadvantages

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

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)”

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!)

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

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

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

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

Secondary ‘Street’ Mains

MDPE pipes replacing all older materials such as cast iron, steel etc.

Coloured blue for ease of identification

Connection to Premises

1.Communication pipe

2.Street main

3.Water company stop tap

4.Property boundary

5.Service pipe

Typical Connection Detail

20mm MDPE pipe

Sleeve

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

Water Meters

• Record volume of water

consumed in litres

• Located in easily

accessible place

o Garage

o Outbuilding

• Recommended for

environmental and

financial reasons

Direct System

Note:

Use of high level tank to supply hot water system only.

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.

With modern combination boiler

Direct System

Indirect system

with hot storage cylinder

Indirect Systems

• All outlets except designated drinking water taps are fed from a gravity supply from a high level storage cistern

o 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

Advantages / disadvantages Direct Indirect

• 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

• 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

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.

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Commercial Rainwater Harvesting

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.

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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.

Cisterns

• Regulations stipulate that all cisterns must incorporate:

o Insulation to prevent temperature extremes

o A tight fitting lid

o A screened ventilation opening

o A screened overflow / warning pipe

Mains water supply

Insulation all around tank

Typical cold water storage cistern installation

Alternative Cold Water Service (CWS) outlet

Cold Water Service (CWS) outlet at bottom ensures better draining.

Lid

Screened vent

Screened overflow

Air gap to meet water regulations

Drain

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.

How much storage for a budget hotel with 50 rooms?

50 x 135 = 6750 Litres = 6.75m3

6750 ltrs = 6750kg (approx) = 6.75tonne

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

Pressure = ρ x g x h

ρ = densityρ for water is 1000 kg/m3

g = acceleration due to gravity9.81 m/s2

h = heightheight of water column in m

Pressure = ρ x g x h

Pressure is measured in Pascals, kiloPascals or Bar

1 kPa = 1000 Pa

1 bar = 100 000 Pa

P = ρ x g x h

It is sometimes convenient to transpose the formula so that a pressure quoted in Pascals can be converted to m head

g

Ph

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

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

7m

Insufficient Mains Pressure? Use Pressure boosters

Typical boosted system

How much pressure ?

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?

B

G

1

2

3

4

5

6

7

3.5m

8 floors at 3.5m = 28m

Pressure required = 1000kg x 28m x 9.81

Pressure required = 274680 Pa

= 2.75 bar approx