GL Plumbing Engineering Services Design Guide

8/10/2019 GL Plumbing Engineering Services Design Guide

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)9d121z.

Plumbing

Engineering

Services

Design

Guide

The Institute of

Plumbing

Compiled

and

published by

The

Institute of

Plumbing

64 Station

Lane, Hornchurch,

Essex

RM12

6NB.

Telephone:

+44

(0)1708

472791

Fax: +44

(0)1708

448987

www.plumbers.org.uk

Fl


2/249

Project

Co-ordinator

Stan

Tildsley

Secretary

&

ProjectManager

Dale Courtman

Eng

FlOP RP

loP

Technical Manager

Administration

Support

Emma

Tolley

LorraineCourtman

JaniceGrande

Jenni Cannavan

Technical Editors&

Designers

-Tarot

Milibury

Printers

-

Saunders&

Williams

PrintersLtd

ISBN

1

871956 40

4

Published 2002

The nstitute of

Plumbing

The Institute

of

Plumbing

cannot

acceptresponsibility

for

any

errors

and omissions

n this

publication

thliiiihite

The nstitute of

Plumbing

/

f

Plumbing

64Station

Lane, Hornchurch,

Essex RM12 6NB.

)

elephone:

+44

(0)1708

472791

Fax: +44

(0)1708

448987

www.pIumbers.org.uk

www.registeredplumber.com


3/249

Amendments

This

document

incorporates

the

following

amendments

Ref

Amendment

Date

1O

Corrynum

vt 10/02

2

Corrtcurii

'2

0L4/o3


4/249

DTLR

TRANSPORT

LOCAL

GOVERNMENT

REGIONS

Foreword

It is

my pleasure

to

provide

the

foreword

for this

edition

of

the

Plumbing Engineering

Services

Design

Guide. For

many

years

now,

the

Institute of

Plumbing

has

supported

the

construction

industry

on the wide

range

of

issues

that are

concerned

with

plumbing engineering

services

and

this

design guide

has

been

key

to the

success

of

that support.

As with other

sectors

of

the

construction

industry, plumbing

engineering

services

s

an

area that is

rapidly developing

with

new,

improved

and

innovative

technologies

and

the

role

of the

Institute

of

Plumbing

in this

is

an

important

one.

The Guide has

needed to

evolve

with

the

advances

in

industry

practice

and

techniques.

Since

the

guide

was first

launched

in

1977

it has

continued

to

be

an

indispensable

reference source

for

designers, engineers

and

trades-persons

and

this

is reflected

by

the

constant demand

for

it,

both

from

home and abroad.

This new

edition

will

provide

additional information and

guidance

on current

echnologies

and

practices

and

will,

no

doubt,

continue

to be a

valuable source

of

information

for those

engaged

in the

design, approval,

and installation

of


services.

I commend

it to the

plumbing industry.

Dr

Alan

Whitehead

MP

Dr

Alan

Whitehead

MP

Ministeror

Building Regulations

Department

for

Transport,

Local Government

and the

Regions

May

2002

Note:

On 29

May

2002

the

Department

of

Transport,

Local

Government

and the

Regions

(DTLR)

was disbanded and

responsibility

for

Building

Regulations

in

England

andWales

was transferred

to

he

Office

of

he

Deputy

Prime

Minister.


5/249

Acknowledgements

In

oday's

fast

moving

world,

alented volunteers

are hard to come

by.

The Institute is most fortunate

in

having

benefitted from

he

expertise

of a

number of

such

people

who

have

stepped

forward to make contributions

to

the

contents

of this

Design

Guide.

They

have been

ably

led

by

Institute

Past

President,

Stan

Tildsley,

an

engineer

of distinction in

plumbing

engineering

services,

who

has

acted

as

project

co-ordinator. He

has

been

helped

by

several loP head

office staff

members,

in

particular,

Dale Courtman and Emma

Tolley

who deserve

special

mention for their

hard

work and

commitment

to

the

project.

We

greatly appreciate

the assistance received from

contributing

organisations.

These nclude

Government

Departments

and

Agencies;

sister

professional

bodies,

research establishments and commercial

companies.

We

also

thank

printers, Saunders

and

Williams

and

echnical

editors,

Tarot

Milbury

for

their

co-operation

and

professionalism.

During

the

lifetime of

this

Guide,

it

will becomecommon

place

for

the

dissemination of

up-to-date

technical information

to take

place

hrough

fastbroadband connections to the Internet accessible

via

either

static

computers

or wireless handheld devices.As a

result,

this is

probably

the

last

time the

Guide

will be

available

as a

complete

work

n

bound,

hard-cover

printed

format.

We

pay

tribute

o

all

those

who

have contributed.

They

can be

justifiably

proud

of

their

efforts.

Andy

Watts MBE

EngTech

MIP RP

Chief Executive

and

Secretary

Onbehalf

of

he Board

ofTrustees of

The Institute

of

Plumbing

June 2002

Contributing

Organisations

ARUP

British Standards Institution

Brook

Water

Management

Building

Research Establishment Ltd

copper

Development

Association

Department

for

Environment,

Food

&

Rural Affairs

Department

for

Transport,

Local

Government

and the

Regions

Donald

Smith, Seymour

&

Rooley

Energy

Efficiency

Best Practice

Programme

Grundfos

Pumps

Ltd

Hepworth Plumbing

Products

Her

Majesty's

Fire

Service

Inspectorate (DTLR)

Marley Plumbing

and

Drainage

Spirax

Sarco

Ltd

The

Council

for

Registered

Gas

Installers

The

Institution of

Electrical

Engineers

Uponor

Ltd

Vernagene

Resource Efficient

Design: Energy

Efficiency (excluding

section

on

Plate

Heat

Exchanger):

this has

been

contributed

by

he

government's

Housing

Energy

Efficiency

Best

Practice

Programme,

and

Crown

Copyright

is eserved.

Contributing

Authors

G

F

Baker

L

C Bassett

lEng, FIDIagE,MIP, MIHEEM,

ACIBSE

M

Bates

AIR,

RP

G

Bell

MCIM, EngTech,MIP,

AR

E

Blundell

AlP,ACIBSE

I0

Boyd

lEng, FlOP,

AR

P

Cook

CEng,

FlEE, MCIBSE

A

J

Goodger

BSc, MSc,CEng, MIM,

MIC0rrST

J C

Griggs

FlOP

R

A

Hanson-Graville

MA,

FlOP

0

Harper

EngTech,

MIHEEM,

FWMSoc,MIP, MIlE,

MASEE

N

Hay

BSc

(Hons)

G

Henderson

MSc, CEng,

MIEE

N Howard

BEng Hons),CEng,

FlOP, MCIBSE,MCIWEM

D

EHuckett

S

Ingle

MSc,

lEng,

FlOP, ACIBSE,LCG,

AR

J C

Lane

AlP,

AR

P

Lang

FISPE

J

K

Love

CEng, FCIBSE,FIP, FIDHE,MInstR,

FConsE

A

J

Malkin

Eng

Tech,MIP,

AP

G

L

Puzey lEng,

FlOP,

AP, MASH,

MIHEEM

M C Shouler

BSc, MSc,

COMP P

S

Tildsley

Eng

Tech,

HON

FlOP,

MIP,

AP

C

P

Topp lEng,

FlOP, FIHEEM, MASH, MAE,

RP

M

Vint

J

S

Walley

Eng

Tech,

LCGI,

MIP,

MWMSoc,AP

S

A

Walsh

CEng,

FCIWEM, FlOP,

MCIBSE,

MIOSH, MAE,MEWI

P

JWhite

EngTech, FlOP,

RP

B

F Whorlow

lEng,

FlOP, RP

P

M Williams


6/249

Preface

This

Design

Guide

2002

replaces

the

previous

edition

published

in 1988.

The

object

of

the Guide s

to advance

knowledge

of

plumbing technology

to

those

engaged

in

plumbing

design

and

system

nstallation.

The

Guide

has

been

considerably

enhanced

utilising

an

easier

to

read

three-column

format,

bound

withina

silver cover

to

celebrate

the

25th

Anniversary

since the

original

Data Bookwas

published.

Technology

in the

plumbing

industry

has

changed considerably

in the

14

years

since

the

guide

was last

published.

Thisedition seeks

to

include

as much information as

possible,

on new

technologies.

Indeed,

the Guide

reflects as

many

of the

changes

related to

UK

plumbing technology

of

which we

are aware.

Throughout

the

publication,

several British Standards

have been

replaced

by

European

Harmonised Standards.

Many

BS/EN Standards have now

been

brought

together

within the

standards,

codes and

miscellaneous

data

section.

The

water services

section

has

been

greatly

expanded

to

include

many

additional

design

considerations

and to take

account

of

the

statutory

requirements

of the

Water

Supply

(Water Fittings) Regulations

1999 in

England

and Wales and

the

Water

Byelaws

2000 in Scotland.

The

heating

section

has

been

completely

re-written

to

concentrate on

gas,

as the most

widely

used

heating

medium. It also includes

information on

systems

and

heating appliances currently

in

use,

including condensing

boilers

and

wet under

floor

heating systems.

The

sanitary plumbing and drainage

section haschanged

significantly

to

reflect

the

requirements

of

BS

EN

12056,

which

replaced

BS

5572.

This

section has also been extended

to

include information

on

he

technologies

involved in vacuum

drainage

and

syphonic

rainwater

disposal systems.

The

piped

gases

section has

undergone

a

major

review

and

the

section

on

steam

now includes condensate

recovery

information.

Information

on the

design

and

installation

of

residential

sprinkler

systems

is

included

for the first

time,

along

with

completely

new sections on

resource

efficient

design

and

swimming

pools.

As

co-ordinator of

this

Guide,

I

acknowledge

the

unstinting

voluntary

work

of

the

many people associated

with

its production. I'm especially grateful

to the

Institute's

full time

head

office

echnical

team,

consisting

of

Dale

Courtman and

Emma

Tolley.

Finally,my

thanks

also

go

to the

authors,

manufacturers and

professional

organisations

who

have contributed

to

this

publication.

Their

essential

participation

should be

appreciated

by

all

who

adopt

the Guide as a

source

of

reference for

the

design

of


services.

Stan

Tildsley

Eng

Tech HON FlOP

MIP

RP

Design

Guide

Project

Co-ordinator

Past President

The Instituteof

Plumbing

June2002


7/249

Contents

Hot

and

cold

water

services

1

Legionnaires

disease

41

Heating

47

Resource efficient

design

67

Piped gas

services 81

Sanitary

plumbing

and

drainage

105

Pumps

and

pumping

161

fire

protection

services 169

Steam

and

condensate 179

Pipework expansion

191

Mechanical ventilation

197

Designing

for

the

disabled

205

Domestic

swimming

pools

215

Electrical

earihing

and

bonding

of

building

services 221

Standards,

codes

and

miscellaneousdata

227


8/249

Hot

and cold

water

supplies

Sources

ofwater

Waler

supply companies

Water demand

Waler

storage

Water distribution

Hot waler

production

Hot water

generators

Control of

Legionella

Safe

waler

temperatures

Water conservation

Water

regulations

Distribution

pipe

sizing

Hard

water

treatment

Water

supply

installations

Disinfection

Water

quality

Corrosion

Effectsofcorrosive environments

Prevention ofcorrosion

2

2

3

3

4

6

8

9

10

10

11

12

24

24

27

28

29

32

36

1


9/249

Hot and cold water

supplies Plumbing Engineering

Services

Design

Guide

Sources

of water

The

source

ofwater

varies

dependant

on

which areaof he British Islesa

supply

is

required.The types are:

1.

Upland

catchment

(reservoir)

2. Groundwater

(borehole/artisan)

3.

River

extraction.

These sources

provide

water or

supply

purposes,

each

withawide

range

of

physical,

and bacterial

quality

differences,

i.e.

1.

Hardness

2.

Bacteria count

3. Minerals.

The

quality

of

water

supplied

for

distribution

to,

and or

use

by persons

and

properties

is

controlled

by

an Act of

Parliament,

theWater

Supply

(Water

Quality) Regulations

1989,

and

subsequent

amendments. The

enforcement

of he Act is

undertaken

by

the

Drinking

Water

nspectorate (DWI),

who

regulate

a

wide

range

of

key

elements

to

attain

and

maintain the water

supplyquality.

See

Table

1.

The standards cover

colour,

alkalinity,

taste,

odour,

undesirable

and

toxic

substances,

and

micro-organisms

to

specified parameters.

The standards are

called

Prescribed Concentrate values'

(PCV's)

to either

maximum, minimum,

average

or

percentage

levels.

These standards

are

imposed

on

all

water

supply

companies,

with relaxation

only

considered under

emergency

situations,

i.e.

extreme

drought

or

flooding,

but under

no

circumstances

if

there is

a

riskto

public

health.

Water

supply

companies

The water

supply

companies operate

under

he

requirements

of he

Water

Industry

Act

1991,

enforced

by

he

Office

of

Water Services

(OFWAT).

Water

supply companies

are

responsible

for

the catchment

or

abstraction

of

raw

water;

it's

conditioning,

treatment

and

distribution

to

consumers

within

their

region.

Thecharacteristics of he water

supplied varies,

region

to

region and

within

regions dependant

upon

he

actual

source, single

or

multiple,

and he

level

of

reatment

provided

in order o

attain

the

prescribed quality

at the

point

of

connection

to he

customer's

supply.

2

Table

1

Drinking

water

standards

Temperature

25C

PH 5.5-9.5

Colour

20

Hazen units

Turbidity

4

Formazin units

Qualitative odour

All odour

nvest

Qualitative taste

All taste

investg

Dilution odour Dilution No

3at25

Dilution taste

Conductivity

lSOOus/cm20c

Total hardness

Applies

only

if

softened

Alkalinity

Free chlorine

Comparison

against averageotal chlorine

Faecal coliforms

0/100

ml

Clostridia 1/20 ml

Faecal

streptococci

0/100

ml

Total coliforms

0/100 ml

(95%)

Colony

count,

2day Comparison

against average

Colony

count,

3

day

Oxidisability

5

mg/I

Ammonia

0.5

mg/I

Nitrite 0.1

mg/I

Nitrate

50

mg/I

Chloride

400

mg/I

Fluoride 1500

ug/l

Phosphorus

2200

ug/l

Sulphate

250

mg/I

Magnesium

50

mg/I

Iron

200

ug/l

Manganese

50

ug/l

Aluminium

200

ug/I

Calcium

250

mg/I

Potassium 12

mg/I

Sodium 150

mg/I

Copper

3000

ug/l

Zinc

5000

ug/l

Lead

50

ug/I

Silver 10

ug/l

Antimony

10

ug/l

Arsenic

50

ug/l

Barium 1000

ug/l

Boron

2000

ug/l

Cyanide

50

ug/I

Cadmium

5

ug/g

Chromium

50

ug/l

Mercury

1

ug/l

Nickel

50

ug/l

Selenium

10

ug/l

Total

organic

carbon

Comparisons

Trihalomethanes 100

ug/l

Tetrachloromethane

3

ug/I

Trichloroethene

30

ug/l

Tetrachloroethene

10

ug/I

Benzo

3,4

pyrene

10

ng/l

Fluoranthene,

benzo

3,

4,

11,

12, fluoranthene,

benzol,

12

perylene

indeno (123cd) pyrene

Individual

testing

of hese

substances

to

provide total

Total PAH's

0.2

ug/I

Anionic

detergents

200

ug/l

Pesticides &

Comp'ds

5

ug/I

total

From

this

connection,

which

generally

incorporates

a

water

company

meter,

the

consumer

is

responsible

for all

aspects

of

the

supply

and distribution ofwater.

Consumers'

rights

Every

consumer

has the

right

to

be

supplied

with water or

domestic

purposes

from he water

supply

company's

distribution network. New or

modified

existing

connections

can ncur

a

charge

by

he water

company

for

the

following

services

1. Newor

replacement supply

2.

Meter installation

3.

Supply

network reinforcement

4.

Infrastructure charge.

All these

charges

relate to he

anticipated

daily

demand

m3),

peak

low

rate

(Its),

and numberof

draw-off

fittings

being

served

from the

supply.

Water

regulations

Consumers

water

supply

nstallations are

required

to

comply

o he

Water

Supply

(Water

Fitting) Regulations

1999,

and

The Water

Supply

(Water Fitting)

(Amendments) Regulations

1999

(2) (the

Water

Byelaws

2000

(Scotland)).

These

regulations

are

enforced

by

the

water

company

that

supplies

waterto

he

consumer.

The

regulations govern

the

wholeof

the

consumer's installation

from

the

connection

to the water

company's

communication

pipe

and meter

termination,

to

all

the

draw-off

ittings,

inclusive

of

any

alterations.

The

regulations require

that no

water

fitting

shall be

installed, connected,

arranged

or

used n such

a

manner,

or

by

reason

of

being

damaged,

worn

or

otherwise

faulty hat it

causes,

or s

ikely

to

cause:

1.

Waste

2.

Misuse

3. Undue

consumption

4.

Contamination

5.

Erroneous measurement.

The

water

supplycompanies

are

required

to

benotified ofcertain

proposed installations,

which

may

be

subject

o

inspection

and

acceptance

prior

to

receiving

the water

company's

supply

connection.

The

regulations

are

a

statutory

instrument,

which

is

supported by

an

interpretation

of he

regulations.

The

water

supply companies

have the

authority

to

apply

o

he

Regulator

for


10/249

Services

Design

Guide

Hot and cold water

supplies

of

any

part

of he

regulation

inappropriate

to a

particular

regulations guide

Water

Regulations

Advisory

Scheme

(WRAS)

publish

a

guide

which

provides

guidance

and recommendations

how the

regulations

should be

applied

he

actual

water

nstallations and

include

the

Water

Byelaws

2000

(Scotland).

demand

fora

building

is

dependant

on a numberof actors.

1.

Type

of

building

and it's

function

2.

Number

of

occupants, permanent

or

transitional

3.

Requirement

for fire

protection

systems.

4.

Landscape

and water

eatures.

In

dwellings

the

resident's water

consumption

isdividedbetween the

many

appliances.

A

ypical percentage

break down provided

by he

Environment

Agency

is:

1. WCsuite

2.

Washing

machine

3.

Kitchen sink

4. Bath

5.

Basin

6.

Shower

7. Outside

supply

8.

Miscellaneous

32%

12%

15%

15%

9%

5%

3%

no,

/0

Overall consumption increases

by

around

10%

during

warmermonthswhen

out

door

usage

increases toover25%.

In

general, consumption

per

person

decreases

with an

increase

in

dwelling

size

given

the

shared facilities.

For

guidance

on the total waterdemand

for

typical ypes

of

buildings

refer toTable

2

or

daily

water

demand.

The

igures

stated

have

been

assembled

froma

numberof

sources,

including

BS

6700,

Chartered Institute of

Building

Services

Engineers (CIBSE)

and

Environmental

Agency

studies

and

can

be

used

as

a

basis or good

practice.

Water

storage

The

storing

ofwater hasanumberof

purposes,

1.

Providing

for an

interruption

of

supply

2.

Accommodation

peak

demand

3.

Providing

a

pressure (head)

for

gravity supplies.

Design

Codes recommend

that

storage

is

provided

to cover he

interruption

ofan

incoming

mains

supply,

in order o

maintain

a water

supply

o he

building.

Water

supply companies

are

empowered

to insist on

specific

terms,

including

the

volume

or

period

of

storage,

within the

term of their

supply agreement

with

a

consumer. However

manywater

supply

companies

only

recommend

that

storage

be

provided

inaccordance with the

BS

6700, placing

the

responsibility

and

decision

firmly

on the

consumers.

Table

2

provides guidance

on

typical

water

usage

within

buildings

overa 24

hour

period.

In

designing storage capacities,

account

needs o

be

takenof the

building

and

its

location.

1.

Period and hours

of

occupation

2.

Pattern

of

water

usage

3. Potential for an

interruption

of

supply

4.

Available mains

pressure,

and

any

inadequacies during

the hours

of

building

use

5. Health &

Safety, prevention

of

bacteria, including legionella.

If

a

building

is

occupied

24 hoursa

day,

then an

interruption

of

supply

will have a

greater

mpact

than

that or

say

an

office,

which

may only

be

occupied

for

eight

o

ten

hours.

Where

a

building

is

occupied

by elderly

or

infirmed

people

then

avoiding

any

disruption

of

he

water

supply

s

an

important

consideration as

they

would

be

unable

to

easily

leave the

building

should

water

become

unavailable.

Clients,

such as the

National Health

Service, require

their

buildings

tobe

provided

with

storage

o

safeguard

against

an

interruption

of he

mains

supply.

Industrial

clients

may

well

require

storage

to ensure

theirbusiness and/or

production

is not

nterrupted.

If

water

ceases

tobe

available

withina

building

then the

occupiers

will

eventually

leave

as toilet

acilities

will

become unusable. It

is

ikely

hat when

an

interruption

of

supply

occurs

then

the water

available

would

be

conserved

as

much

as

possible, thereby extending

the

time of

occupancy beyond

that

anticipated

under

normal

usage

rates.

Table

2

Daily

water

demand

Type

of

Building

Litres

Criteria/Unit

Dwellings

-

1 bedroom 210 Bedroom

-

2

bedroom 130 Bedroom

-

3+

bedrooms 100

Bedroom

-

Student en-suite

100 Bedroom

-

Student,

communal 90

Bed

space

-

Nurses Home 120 Bed

space

-

Children's Home 135

Bed

space

-

Elderly

sheltered

120 Bedroom

-

Elderly

Care

Home

135 Bed

space

-

Prison

150 Inmate

Hotels

-

Budget

135

Bedroom

-

Travel

Inn/Lodge

l5Oav Bedroom

-

4/5 Star

Luxury

200 Bedroom

Offices

&

general

work

places

-

with

canteen

45 Person

(1)

-

without canteen

40 Person

(1)

Shops

with canteen 45 Person

-

without canteen 40

Person

Factory

-

with canteen

45 Person

-

without canteen

40 Person

Schools

-

Nursery

15

Pupil

-

Primary

15

Pupil

-

Secondary

20

Pupil

-

6th

Form

College

20

Pupil

-

Boarding

90

Pupil

Hospitals

-

District

General 600 Bed

-

Surgical

ward 250 Bed

-

Medical ward 220 Bed

-

Paediatric ward 300 Bed

-

Geriatric ward 140 Bed

Sports Changing

-

Sports

Hall 35 Person

-

Swimming

Pool 20

Person

-

Field

Sports

35

Person

-

All

weather

pitch

35 Person

Places

of

Assembly (ex

cl.staff

-

Art

Gallery

6

Person

-

Library

6

Person

-

Museum

6

Person

-

Theatre

3

Person

-

Cinema

3

Person

-

Bars

4

Person

-

Night

Club

(3)

4

Person

-

Restaurant

7

Cover

SUPPORTING INFORMATION

If

he number

of

building occupants

are not

accurately

known hen

asa

guide

the

following

criteria

can

be

used.

Offices,

one

person

per

14m2

of he

gross

building

floor

area.

Sports

hall,

four

persons

per

badminton

court

area

per

hour

open,

maximum.

Swimming

pool,

one

person

per

cubical

per

hour

open,

with a

actor

of

0.6

for

diversity.

Field

sports changing,

persons

per

eams

per

number

of

pitches,

per

day

3


11/249

Hot and cold

water


Services

Design

Guide

AllWeather

Field,

persons per

eams

per

hours used.

Museums,

Art

Galleries, Libraries,

One

person

per

30m2

of he

gross

building

floor

area.

Restaurants,

One

person

per

1.0m2

of

he

dining area.

Bars,

One

person

per

O.8m2

of he

public

bar/seating

area..

When

the water

supply companies,

regulations,

or client

requirements

do

not

specifically

dictate he

period

tocover

an

interruption

of a mains

supply

henTable

3

provides

recommendations

for

reasonable

periods

of

storage, expressed

as

a

percentage

of the

daily

water

demand.

Table3

Period

of

storage

Type

of

Building

%

of

the

daily

demand

Hospitals

50%

Nursing

Homes 50%

Dwellings

0

-

50%

Hotels,

Hostels 50%

Offices

0

-

50%

Shops

0

-

25%

Library, Museum,

Art

Galleries 0

-

25%

Cinema,

Theatre

0

-

25%

Bars,

night-club

0

-

25%

Sports

Facilities

0

-

25%

Schools, Colleges,

Universities

50%

Boarding

Schools 50%

Water distribution

The water

distribution installation

requires

tobe able o deliver

he correct

flow andvolume of hot and coldwater

when

and where

t

is

needed. The mains

pressure

can

provide

the

initial means

of

delivering

water

nto

the

building.

The

water

supply companies

are

required

to

deliver heir water

o

the

boundary

with

a

minimum

pressure

of

1.0

bar. Often their

delivery pressure

can be

higher,

however

at imesof

high

demand,

the

pressure

will be closer to theminimum

provision.

Type

of

system

The

type

and

style

ofwater

distribution

needed

fora

particular building

will

depend mainly

on the

building

height

and

its

use.

a. The

building

height

will determine

whether

pumping

will

be

required

to

deliverwater

o

the

highest

level

b. The

building

use

will determine

he

amount

of

storage

that will

be

required.

4

The

type

of water

system

will

need o

be

oneor a

combination

of he

following:

a. Directmains fed

b.

High

level

storage

with

gravity

down

feed

c.

Pumped

froma

break cistern

or

storage provision.

Potentially

aone or two

storey

building

in

a

locality

where

an

interruption

of

water

supply

is

very

nfrequent

and

causing

little

nconvenience,

there isan

option

for

the water

supply

to

be direct rom

the

mains

without

storage being provided.

If

the

provision

of

storage

is

possible

at

high

evel then he

system

could

be

enhanced to

provide

storage coupled

with it

becoming

a

gravity

down

feed

system.

See

Figure

1.

Figure

1

Supply

o

a

two

storey

building

Storage

anks

A

building requiring

a

large

water

storage

provision

may

not

be able o

accommodate

itat

high

level,

n which

casea

low level location will

be

needed,

in

conjunction

witha

pumped

distribution

system.

A

combination

of

highand

ow storage

can

be

considered

if a

gravity

distribution

is

preferred

for all or

part

of he

building.

This

has

an

advantage

of

providing

some

storage

in

the eventof an

interruption

of

the

water

supply,

or

power

supply

o

he

pumps.

A

storage

ratio of 2: 1

low/high

level

is

a

typical arrangement.

Storage

can

comprise

of wo

compartments

or

cisterns/tanks in

order

thatmaintenance can be carried out

without

nterrupting

distribution.

For small

storage quantities

one

piece

cisterns can

be

used,

which

generally

are

of a

low height construction. For

storage

of

2500 itres or

more,

sectional

panel

anks

may

be

considered more

appropriate

withacentre

divide.

Above 4000 itres

storage

twin

cisterns/tanks

may

be

considered

appropriate.

See

Figure

2.

Figure

2

Storage

cistern/tank

layout

Sectional

tanks

commonly

have

flanges,

being

nternal

or

external. External

flanges

permit tightening

without

needing

to

enter

he

tank,

and on the

base

permit

the

tank to be self

draining

through

a

single

drain

point,

without

urther

draining

of

any

entrapped

waterbetween

flanges.

Such a feature reduces maintenance and

assists

the

prevention

of

water

stagnation

which

can lead o

harmful bacteria

growth, including legionella.

In

calculating

the

storage capacity

a ree

board allowance is

necessary

to

accommodate the

float

valve,

over

low

installations

and

anyexpansion

from

the

hot

water

system. Depending

on

pipe

sizes,

commonly

a250

300 mm ree

board

depth

s

required

on

ciserns/tanks

having

a

capacitygreater

han

2500

litres. Raised

ball

(float)

valve

housings

in

conjunction

withaweir overflow

an

provide

an increased

depth

of water

stored

over he

main

area

of the

cistern/tank(s).

The

ocation

of he nlet and

outlet

connections is

important.

Across low

through

the

cistern/tank

needs

o be

achieved

to

assist

the

complete regular

turn overofwater

hroughout

the

storage

period.

Sub

divided,

twin and

multiple

cisterns/tanks

ideally

should

be

installed

in

parallel

to

each other. The inlets

require

to be

positioned

at he same evel

to

ensure

hey

supply

the

cisterns/tanks

in

unison,

andas aras

possible

the

same low

rate

toassista

balanced

throughput.

The outlet

connections

and

manifold

pipe

workneeds to be

arranged

with

symmetrical

and

equal

engths,

also

to

provide,

as aras s

possible

a

balanced

flow rom the

tanks.

The

use

of

a

delayed action

float

valve

may

also be

considered to

ensure

a

greater

urn overof

water.

Incoming supply

(balancedpipes

not

critical)

Cisterns, ectangular,

in

parallel

Outlets,

rom

opposite

corners

of

nlet,

and

strictly

balanced

n

ength

and

configuration

NOTE

Valves

to be

provided

to

enableone cistern/tank o

be isolated

whilst

other remains

open.

Option

of

gravity

tank at

high

level

Rising main,

and

drop

to

draw-off

points

Ground

evel

Utility

Co.

_____________

mains

0


12/249


Services

Design

Guide

Hot and

cold water

supplies

Access

to

storage

cisterns/tanks

Access

for

installation

and

maintenance

is

required.

Table

4

is

a

guide.

For

largebuildings,

accommodation

for

water

storage

has an

significant impact.

Table

5

provides

an

outline

guide

o

he

space

that

may

be

required.

Table

4

Access

o

storage

cisterns/tanks

Location

(mm)

Around 750

Between,

tanks 750

Above, allowing

beams to ntrude 1000

Below,

between

supports

600

For outlet

pipe work,

md.

access 1500

Tank construction thickness 100

Insulation

(may

form

part

of

ank)

25

Raised

float

valve

housing

300

Entry

o ank

800

dia

Table5

Water

storage

plant

room area

Storage

(Litres)

1.5metre

Tank

Height

2 metre 3 metre

5,000

18m2 18m2

10,000

31m2 23m2

20,000

50m2

40m2

40,000

72m2 60m2 50m3

60,000

80m2 60m2

100,000

10m2

80m2

Gravity supplies

For

gravity supplies

tobe

effective,

the

storage requires

to

be

at a

sufficient

height

o

deliver

he waterto he

draw-off

point

at

he

required

flow

rate and

pressure.

The available head

is

he

dimension between

the

bottom

of

the

storage cistern/tank(s)

and he

highest

draw-off

point,

or

draw-off

point

with

the

greatest head/pressure

oss.See

Figure

3.

The

advantages ofgravity supplies

are:

a.

Availability

of

water n the eventof

watermains or

power

ailure

Figure

3

Gravity

upplies

available

head

b.

No

pump running

costs

c.

Potentially

less

noise

due

o

lower

pipe

lowvelocities.

The

disadvantages

are:

a.

Greater

structural support

b.

Larger

pipe

sizes due

o

limited

available

head,

when

compared

to

pumps

c. Lower

delivery

pressures.

Pumped

supplies

The

delivery

ofwater

by

pumping

will

provide flexibility

in the

positioning

of

he

storage

cisterns/tanks.

The

delivery

flow

rate and

pressure

demanded

by

the

system

are

met

entirely

by

selecting

the

correctduty or the

pumps.

The

pump set

is

required

todelivera

constantly varying

flow

rate

as

draw-off

points

are

randomly

used

by

he

occupants.

The

useof

multi-

stage

variable

duty

and/or inverters

is

an

advantage.

See

Figure

4.

Generally

a

minimum

of

wo

pumps

are

used,

each

having

100%

system duty

and

controlled

to

enable

them

to

be a

stand

by

oeach

other. To

prevent high

pressure

overrun when

demand s

less

than he

design demand,

a

pressure

limiting

or

variable control

flow

device

needs

to

be fitted on the outlet rom the

pumps.

For

high buildings

a

combination of

pumped

and

gravitymay

be

appropriate.

The

advantage

of

his

is to

provide

a

proportion

of

he

daily

water

usage

n a

cisterns/tank(s)

at

roof

level,

which would

provide

a

gravity

down feed

service,

and

continue to

provide

water n the eventof

a

ailure

of

he

pump.

See

Figure

5.

Such

a

system

would

comprise

of:

a.

An

incoming

main

b. Low level

breakor

storage

cistern/tank

c.

Pump

set

d.

High

level

cistern/tank(s)

Figure

4

Pumped

upply

ayout

e.

Cold

waterand hot water cold

eed

gravity

distribution.

The low evel

pump

set can be sized to

provide

a

low

volume,

more

frequent

operation

and

high

head

to

deliver

he

water

o

he

tanks

at

roof level.

If

a

mains'water

supply

s

required

to

be

provided specifically

for

drinking

water

points

or

drink

making

equipment,

then

either

of

hese can be

supplied

from

he

incoming

main

up

to

the number

of

loors

that he

available mains

pressure

will

reach,

and from the

pumped

ising

main

above

that

level;

or

entirely

from

he

pumped

rising

main.

See

Figure

6.

Whilstall water

supplied

for

domestic

useshas to be suitable for

drinking

purposes, supplying drinking

water

points

direct rom

ncoming mains

or

pumped

mains

provides acooler,

more

oxygenated supply

for taste

purposes.

5

Cisterns/tank(s)

on

roof or

roof

plant

room

level

Low

evelbreak

or

storage

tank

Figure

5

Combined

pump

and

gravity

Figure

6

'Mains'water

or

drinking

Head

of

water

pressure

available

n

metres

Duty

of

pumps

=

static

ift

plus

distribution

loss and

delivery

pressure,

n

metres

Pumped

mains'

to

drinking

points

and

drinks machines

Utility

mains' to

drinking points

and drinks

machines

Low

level

cistern/tank

Incoming

main


13/249

Hot

and

cold

water


Services

Design

Guide

Hot water

production

Hot water

can

be

generated

by

a

differing

numberof

methods,

and the

selection

will

depend mainly

on the

quantities

of

hot

water

required

and he

types

of

energy readily

available.

The demand for hot waterwill

vary

considerably

between

types

of

buildings,

governed

by

their

occupants

and he

activities

taking place.

For

example:

Office

buildings

will

require

small

quantities frequently

and

regularly

throughout

he normal'

working

day,

and

availability

at

other

times

as

and

when

occupant's 'overtime'

working

hours

demand.

A

actory

witha

production

line

will

require

sufficient

hot water

to

meet

he

demand

at

breaks in

the

shift when the

work orce

may

all wish

o

wash

hands

etc.

A

sports

pavilion

will

need

to

be

able

o

provide

large

quantities

of hot water or

team's

showering

needsover

a

short

period

of ime

following games,

whenever

they

occur.

Selection

of

hot

water

production

In the selection

of

he

type

of

hot water

production,

the time

available

for

re-

heating

is an

important

consideration.

If

a

high

volume

or

rapid

re-heat rate

is

required

then it would be

necessary

to

ensure

that

a

sufficient

energy

capacity

is

available.

If

he

energy

capacity

needed

is

not available

thena

greater

volume

of

water

storage

wouldhave to

be

provided

to

ensure

hot water s

available

during

theslower re-heat

period.

Hot water

production

and

storage

temperatures

are

required

to

comply

to

the Health

&

Safety

equirements

for the

minimisation

of

egionella

bacteria.

This

demands

a

minimum

storage

temperature

of

6000

o

be

attained,

with

a

minimum

secondary

return

(if

provided)

temperature

of

50C.

See

Figure

7.

Therefore

in

calculating

the hot water

demand

for

a

building

it

s

necessary

to

ensure

that he

output

water

emperature

from

he

hot

water

production plant

s

never

less

than 60C,and never

less

than

50C

hroughout

he

distribution

system.

The HSC

'Controlof

Legionella'

CodeL8

states hat 50C

should

be

achieved

within

60

seconds

at

all outlets.

Type

of

building Daily

Stored Unit

(litres) (litres)

Dwellings

-

1

bedroom 115 115 Bedroom

-

2bedroom 75 115 Bedroom

-

3

+bedrooms 55 115 Bedroom

-

Student en-suite 70

20

Bedroom

-

Student,

comm 70 20

Bedspce

-

Nurses home 70

20

Bedspce

-

Children's home 70 25

Bedspce

-

Elderly

sheltered 70 25 Bedroom

-

Elderly

care

home 90 25

Bedspace

-

Prison Inmate

Hotels

-

Budget

115 35 Bedroom

-

Travel

Inn/Lodge

115 35 Bedroom

-

4/5 Star

Luxury

135

45

Bedroom

Offices

&

general

worK

places

-

with canteen 15

5

Person

-

without

canteen 10 5 Person

Shops

-

with

canteen 15

5

Person

-

without

canteen 10 5 Person

Factory

-

with

canteen 15

5

Person

-

without

canteen 10

5

Person

Schools

-

Nursery

15 5

Pupil

-

Primary

15

5

PupilI

-

Secondary

15

5

Pupil

-

6th form

college

15

5

Pupil

-

Boarding

114 25

Pupil

Hospitals

-

District

General 200 50 Bed

-

Surgical

ward 110 50 Bed

-

Medical ward 110 50 Bed

-

Paediatric ward 125 70 Bed

-

Geriatric ward 70

40

Bed

Sports changing

-

Sports

Hall 20

20

Person

-

Swimming

Pool 20

20

Person

-

Field

Sports

35

35

Person

-

All

weather

pitch

35

35

Person

Places

of

assembly

(excLsta__

-

Art

Gallery

2

1 Person

-

Library

2

1 Person

-

Museum 1 1 Person

-

Theatre

1 1

Person

-

Cinema 1 1 Person

-

Bars

2

1 Person

-

Night

Club

-

Restaurant

1

6

1

6

Person

Cover

SUPPORTING INFORMATION

The

storage figures

statedare basedona re-

heat

period

of wo

hours,

an nlet

emperature

of

10C

and

a

stored

emperature

of

65C.

If

he number

of

building occupants

are not

accurately

nown hen

asa

guide

he

following

criteria

can

beused.

Offices,

One

personper

14m2of

he

gross

building

floor

area.

Sports

hall,

Four

persons

per

badminton

court

area

per

hour

open,

maximum.

Swimming

pooi,

One

person

per

cubical

per

hour

open,

with

a

actor

of

0.6

for

diversity.

Field

sports

changing,

persons

per

eams

per

number

of

pitches,

per

day.

Allweather

field,

personsper

eams

per

hours

used.

Museums, art

galleries,

ilbraries, One

person

per

30m2

of

he

gross

building

floor

area.

Restaurants,

One

person

per

1.0m2of he

dining

area.

Bars,

One

person

per

O.8m2

of

he

public

bar/seating

area.

When

a

conventional

bulk hot water

vessel

is

used

it

is

necessary

o

ensure

that

the contents

of he whole

vessel

achieves

the correct

stored water

temperature

as

stratification canoccur.

To

overcome

this

situation

the

storage

vessel

should

ncorporate

the

following

features:

a.

Base inlet hot

watercold feed

supply

b.

Top

outlet hot water outlet

low

c.

Convex ends

to

vessel

d.

Provide

a

'shunt'

pump

to

move

he

hot water rom the

top

of

hevessel

to

he

base

to

avoid stratification.

Hot water

demand

When

assessing

the hot water

production

requirements

for

a

building

it is

necessary

o

determine the

peak

demand. The

peak

demand s the

volume

of

hot water

required during

the

building's

period

of

greatest

usage.

This

may

be

over an

hour,

or

shorter

period

dependant

on the

occupants

and

activities

taking place.

Having determined

the peak

demand the

volume

of hot water

needing

to be

stored

can

be

selected,

the

rate

of

recovery

and

theassociated

energy nput

needed can

be

established.

The

buildings

total

daily

hot water

usage

is

relevant

to

the assessment

of the

peak

Table

6

Hot water

demand

Store


14/249


Services

Design

Guide

Hot and

cold

water

supplies

demand. Once

the

daily usage

is

determined then the more critical

peak

demand can

be

assessed.

Traditionally

hot

water

peak

usage

was

based

on

a

wo hour

storage

re-heat

period

and his

has generally proved

to

be

a

satisfactory

benchmark

for

peak

demands

for that

period.

Table

6

schedules

a

compilation

of

figures currently

recommended

by

he

water

ndustry's

design

codes,

with

additional

categories

added as

considered useful.

The

recommended

storage

volumes

are

based

on a65C

storage temperature

and

a

wo hour

re-

heat

period,

i.e.a

bulk

storage

vessel.

This data should be

considered

as

representative

of

capacities,

which have

not

given

rise

to

complaints

of

inadequacy.

Two hourre-heat

The

two hour e-heat

storage

volume

figures

can

provide

a

guide

o the

peak

water

volume used

during

a

peak

wo

hour

usage period.

The same

hot water

output

could also be

achieved

by

he

use

of

ow

volume/rapid

reheat

'semi-storage'

types

of

hot water

generators,

if

the

energy

input

capacity

is available.

The

semi-storage'

type

of

hot

water

heaters can

meetshorterpeak

demand

periods

i.e.

1

hour,

or

ess, although

detailed

secure

nformation

about

peak

period

demands

during

periods

of

ess

that 1

hourare not

sufficiently available,

and

herefore

a

design

risk

margin

will

be

required.

The

established

two hour

peakusage

figures

cannot

simply

be

evenly

sub-

divided into shorter

periods

without

he

risk

of

seriously

under

estimating

the

actual

hot water

volume

that

will be

required during

thatshorter

period.

The

shorter he

period,

the

greater

he

dis-

proportion

of

he two hour

peak storage

figure

will

be

required.

For

example,

the recommended twohour

re-heat

period storage

volume

for

a

budget

hotel

is 35 litres

per

bedroom. For

a

50

bedroom hotel

the

stored volume

wouldneed

to

be 1750

itres,

which when

supplemented

by

he

re-heated water

during

the

envisaged

peak

wo hour

draw-off

period,

ess he

loss

(25%)

of

hot waterdue to the

mixing

effect

of

he

incoming

cold

water

eed,

s

capable

of

providing

a

notional

2625

itres,

should

that demand

occur.

This s

because 1750

litres

of

65Chot water s

notionally

available

at he startof he

notional

peak

draw-off

period,

and whilst he

stored hot

water s

being

drawn

off it is

also

being

re-heated

at a

rate

of

1750 itres

per

two

hours,

less

the

loss

through

the

mixing

of

incoming

cold water and he

stored hot

water

(25%).

Therefore itcan

be

seen

that

the stored

water s there

to

provide

for

a

peak

1750

litre draw-off

occurring

over

any period

from,

say

ten minutes

upwards.

For consideration

purposes

1750 litres

equates

to 35

baths, each

using50

litres

of

60C

stored

hot

water.

Dependant

on

the

bath

usage

ratio

ofeither

1200, 2400,

or

4800

seconds

frequency

of

use

(see

simultaneous demand

data)

the hot

water

stored

could be used

up

after

a

63

minute

period. Alternatively

1750 litres

could

provide

for 73

persons having

a

shower,

each

lasting

5

minutes

using

24

litres

of

60C

of

stored

hot water

(mixed

with

cold).

Dependant

on the shower

usage

rate

of

900, 1800,

or

2700

seconds

frequency

of

use,

the hot water

stored could

be

used

up

aftera

45

minute period.These

two

examples are

based

on a

peak

statistical

usage

which

would

ikely

not reoccur

during

the

remaining

timeof he two hour

re-heat

period.

A

semi-storage'

hot water

generator

requiring

to

meet he samedemand for

baths

would

need

o

be

capable

of

providing, approximately

a

3.3 litre

per

second

flow

rate

of

65C

continuous hot

water

output,

assuming

an

initial stored

volume

capacity

of500

itres.

These

potential peak

demands couldbe

considered

as

being

extreme

examples.

However

they

clearly demonstrate the

demands

capable

of

being

put

on

hot

water

generation,

when

aking

accountof

the maximum simultaneous

usage

that is

imposed

on draw-off

ittings

by

he

building occupants,

and

accordingly

has

to be

considered

for

design purposes.

Whatever

the

building,

the

likely

pattern

of

hot water

usage

should

be assessed

and

considered. The

hot water

usage

will

be

directly

related

to

he

building

function,

its

occupancy

and

the

type

of

Figure

8

Typical

demand

pattern

histogram

activity

hat

is

ikely

o

take

place.

In

determining

the

pattern

of

usage,

it s

important

to

differentiate between a

maximum

daily

demand and an

average

daily

demand,

so that

the

implications

of

the

system not meeting

the

buildings hot

water

requirements

can be

recognised,

and he maximum

requirements

designed

for where

necessary.

Measured

quantities

of hotwater

consumption

should

not standalone

as a

sizing guide.

The rate

at

which these

amounts

are

drawn

off

must

also

be

considered.To

project

thedemand

pattern

over

the

operating period

of

he

building,

an hour

by

hour

analysis

of

likely

hot

water

usage

should be

made,

taking

into account

the

numberof

occupants,

the

type

and

evel

of

activity

and

any other factors

thatmayaffect

hot

water

demand.

The

projected pattern

of

demand should

be

recorded

in

the form

of a

histogram profile.

Typical examples

of

daily

demand

n

various

types

of

buildings

are

illustrated

in

Figures

8

and

9.

By

establishing

a

hot

water

demand

histogram

a

representative

peak

demand

volume can

be

established.

Typically

the

peak

hour s between 15-20%

of

he

day's

total

usage.

When

selecting

a

semi-storage'

hot

water

production unit(s)

it

needs

to

be

recognised

that the small

stored volume

is there

o

meet he short

period peak

draw-offs

that occur

n

any

water

supply

system.

The

shortest

of these

peak

draw-

offs

is the

maximum' simultaneous

demand

litre

per

second

flow

rate

figure

calculated from he sum

of

he drawoff

'demand'

or

loading'

unitsused

or

pipe

sizing. However,

periods

of

ime that

these low rates occurare

very

short,

and

are

based

on

the

period

of

individual

draw-

off,

i.e.

length

of ime to fill a

basin,

7

3500

3000

2500

-

2000

E.

1500

1000

500

0

0 6 12 18

Period

24


15/249

Hot

and cold

water

supplies


Services

Design

Guide

w

'?

0

0.

E

C

0

t.1

U

U

sink,

or

bath,

have

a

shower,

and

he

number

of

imes he draw-off

s

used

during

the

peak

demand

period,

i.e.

every

5,

10,

or

20

minutes,

or

more. The

'maximum simultaneous

demand'

must

not

be

applied to

periods

greater

than

the

period

and

frequency

of

maximum

simultaneous

demand.

Hot water

generators

The

production

of

hot

watercan

be

achieved

by

avaried

number

of

energy

sources.

1.

Electric, generally

with

direct

immersed elements

2.

Gas,

either

direct,

or

ndirect

by

a

dedicated circulator

3.

Low

Temperature

Hot Water

LTHW)

boiler

plant,.

dedicated

or more

ikely

forming

part

of

he

space heating

plant

4.

Steam,

whenavailable from

a

central

plant facility.

Energy

forms,

which

provide

a

direct

means

of

heating

hot

water,

i.e. electric

and

gas

in

particular,

are themost

effective in

tems

of

efficiency

because

of

least oss

of

heat

during

the heat transfer

process. Sharing

hot water

generation

with

space heating

plant

candecrease

the

energy efficiency through

the

8

additional

transfer

process

and

ess

efficient

operation

when

space heating

is

not

needed.

Solar

heating,

whenavailableandviable

is

an

excellent supplementary heat

source andeffective in

reducing

annual

energy

ariffs.

Commonly

used

formsof

hot

water

heating

are:

Dwellings

and small

buildings:

Electric,

or

gas

combination

(HWS

&

Heating)

boilers.

Offices:

Electric,

local

or

'point

of

use'water

heaters.

Larger premises

and

sports

acilities:

Gas direct ired water

heaters.

Local or

central

plant

The

adoption

of

local

or

central

plant

is

generally dependant

on the

type

of

building,

where

hot

water s

needed and

the

volume

required.

For

toilet

wash

basin hand

rinse'

purposes only,

where

relatively

little hot water s

required

then

a

local

heater

positioned adjacent

to

the

draw-off

ittings

would

be

appropriate.

This

may

be

considered

particularly

suitable

for

office andschool toilets. The

advantages

of

his

type

of

nstallation can

be low

nstallation,

energy consumption,

and

maintenance

costs,

plusalleviating

the need for

secondary

circulation

pipework

and

pump

o

maintain

distribution

temperatures.

Vented

or

unvented

generators

A

vented

hot water

generator

is

supplied

bya

gravity hot

waterdown eed

and

expansion pipe

and

having

an

open

vent

pipe

over

the

feed cistern/tank

to

provide

for

pressure relief,

in

addition

to

500

School

-

Service

00

0

Catering

00

E

200

0

)

100

fl

I

18 24

5

6

Time

(hours)

12

1OC

Restaurant

-

80

'

a60

E

40

0

)

24

0

r

18

12

Time

(hours)

3000

Hotel

,

2

2000

E

81000

0

06

I

Time

(hours)

24

Figure

9

Examples

of

daily

demand

patterns

or ommercial

premises

12

Time

(hours)

Reproduced

from

CIBSE Guide G:

PublicHealth

Engineering,by

permission

of he

Chartered Institution

of

Building

Services

Engineers.

Option

of

combined

cold

eed

and

open

vent

Rot water

cold

eed

Figure

10

Vented

hot water

generator

Figure

11

Unvented

hot water

generator

HWS distribution

Check

valve

Pressure

reliefvalve


16/249


Services

Design

Guide

Hot

and cold

water

supplies

demand. Once the

daily usage

s

determined then he more critical

peak

demand can

be

assessed.

Traditionally

hot

water

peak usage

was

based

ona wo hour

storage

re-heat

period

and this

has generally proved

to

bea

satisfactory

benchmark

for

peak

demands for that

period.

Table

6

schedules

a

compilation

of

figures

currently

recommended

by

he

water

ndustry's

design

codes,

with

additional

categories

added

as

considered useful.

The

recommended

storage

volumes

are

based

ona

65C

storage temperature

anda wo hour

re-

heat

period,

i.e.

a

bulk

storage

vessel.

This data

should be considered as

representative

of

capacities,

which have

not

given

rise

to

complaints

of

inadequacy.

Two hour re-heat

The two hour

re-heat

storage

volume

figures

can

provide

a

guide

o

the

peak

water

volume

used

during

a

peak

wo

hour

usage

period.

The same hot water

output

could

also be

achieved

by

he

use

of low

volume/rapid

reheat

'semi-storage'

types

of

hot

water

generators,

if

the

energy

nput

capacity

s

available.

The

semi-storage'

type

of

hot water

heaters can

meet

shorter peak demand

periods

.e.

1

hour,

or

less, although

detailed

secure information

about

peak

period

demands

during

periods

of

ess

that 1 hourare not

sufficiently available,

and

therefore

a

design

risk

margin

will

be

required.

The

established

two hour

peak usage

figures

cannot

simply

be

evenly

sub-

divided

nto

shorter

periods

without the

risk

of

seriously

under

estimating

the

actual

hot water

volume

that

will be

required during

that shorter

period.

The

shorter he

period,

he

greater

he

dis-

proportion

of

the

two hourpeak

storage

figure

will

be

required.

For

example,

the recommended

two

hour

re-heat

period storage

volume

for

a

budget

hotel

is

35

litres

per

bedroom. For

a50

bedroom hotel the stored volume

wouldneed

to

be 1750

itres,

which when

supplemented

by

he

re-heated

water

during

the

envisaged peak

two hour

draw-off

period,

less

the

loss

(25%)

of

hot

waterdue

o

the

mixing

effect

of

he

incoming

cold

water

eed,

s

capable

of

providing

a

notional

2625

itres,

should

that

demand occur.

This is

because

1750

litres

of

65Chotwater s

notionally

available

at he start of the

notional

peak

draw-off

period,

and whilst hestored hot

water

s

being

drawn

off it is

also

being

re-heated

at a

rate

of

1750 itres

per

wo

hours,

less he loss

hrough

he

mixing

of

incoming

cold water and he

stored hot

water

(25%).

Therefore

it

can

be seen that he

stored

water s there

to

provide

for

a

peak

1750

litre draw-off

occurring

over

any period

from,

say

ten minutes

upwards.

For

consideration

purposes

1750 litres

equates

to 35

baths, each using

50

litres

of

60C

stored hot water.

Dependant

on

the bath

usage

ratio of either

1200, 2400,

or 4800

seconds

frequency

of

use

(see

simultaneous demand

data)

the hot

water

stored

could

be used

up

after

a

63

minute

period. Alternatively

1750 litres

could

provide

or 73

persons having

a

shower,

each

asting

5

minutes

using

24

litres

of

60C of

stored hot

water

(mixed

with

cold). Dependant

on the

shower

usage

rate

of

900, 1800,

or

2700

seconds

frequency

of

use,

the

hot

water

stored could

be

used

up

aftera

45

minute

period.

These

two

examples are

based

on a

peak

statistical

usage

which

would

likely

not reoccur

during

the

remaining

time of

the

two hour

re-heat

period.

A

semi-storage'

hot water

generator

requiring

to

meet he samedemand or

bathswould need o be

capable

of

providing, approximately

a

3.3

litre

per

second

flow rateof65C

continuous hot

water

output, assuming

an

initial stored

volume

capacity

of500

itres.

These

potential

peak

demands could be

considered

as

being

extreme

examples.

However

they

clearly demonstrate the

demands

capable

of

beingput

on hot

water

generation,

when

taking

accountof

the

maximum simultaneous

usage

hat is

imposed

on draw-off

ittings

by

the

building occupants,

and

accordingly

has

to

be

considered

for

designpurposes.

Whatever

the

building,

the

likely

pattern

of

hot water

usage

should be assessed

and

considered.

The

hot

water

usage

will

be

directly

elated

to the

building

function,

its

occupancy

and he

type

of

Figure

8

Typical

demand

pattern

histogram

activity

that is

likely

o

take

place.

In

determining

the

pattern

of

usage,

it is

important

to

differentiate between

a

maximum

daily

demandand an

average

daily

demand,

so

that he

implications

of

the

system

not

meeting

the

buildings hot

water

equirements

can be

recognised,

and

the

maximum

requirements

designed

for

where

necessary.

Measured

quantities

of

hot water

consumption

should

not

stand

alone

as

a

sizing guide.

The rate

at

which these

amounts

are

drawn

off

must also

be

considered. To

project

the demand

pattern

over he

operating period

of

the

building,

an

hour

by

hour

analysis

of

likely

hot water

usage

should be

made,

taking

nto account

he

numberof

occupants,

the

type

and

evel

of

activity

and

anyother

actors

thatmayaffect

hot

water

demand.

The

projected pattern

of

demand should

be

recorded

in the

form

of a

histogram profile.

Typical examples

of

daily

demand

in

various

types

of

buildings

are

illustrated

in

Figures

8

and

9.

Byestablishing

a

hot

water

demand

histogram

a

epresentative peak

demand

volume can

be

established.

Typically

the

peak

hour

s

between 15-20%

of

he

day's

otal

usage.

When

selecting

a

semi-storage'

hot

water

production unit(s)

it

needs

to

be

recognised

that

the

small

stored volume

is there

to

meet

he

short

period peak

draw-offs that occur n

any

water

supply

system.

The shortest

of

these

peak

draw-

offs is the 'maximum' simultaneous

demand

itre

per

second low

rate

figure

calculated from the sum

of

he draw off

'demand'

or

loading'

unitsused

or

pipe

sizing.

However, periods

of

ime that

these low ratesoccur are

very

short,

and are

based

on

the

period

of

ndividual

draw-

off,

i.e.

length

of time

o fill a

basin,

7

3500

3000

2500

-

2000

E.

1500

1000

500

0

0 6 12 18 24

Period


17/249

Hot

and

cold

water

supplies


Services

Design

Guide

The

Code

dentifies

specific practical

guidance

on

how

this

is to

be

achieved

in

water

supply systems.

The

key

aims

being:

1.

Maintain

cold water

below 25C

2.

Maintain stored hot waterbetween

60-65C

3.

Maintain

hot water

distribution above

50C,

and

preferably

at

55C

4.

Insulate all

cold and hot water

storage

vessels anddistribution

pipework

5.

Minimise

the

length

of

un-circulated

and none

race

heated

hot

water

pipes

6.

Avoid

supplies

to

little

or

unused

draw-off

ittings

7.

Maintain

balanced

use and

flows

through multiple

cold water

cisterns/tanks and hot watervessels.

See

Figure

13.

NOTE:

For

urtherdetails

please

see

legionella

section',

containedwithin his

guide.

Safe water

temperatures

Safe

water

emperatures

need to

be

considered

for

hot

water

supplies

to

appliances

used

by

he

elderly,

Documents

GL Plumbing Engineering Services Design Guide