Design and Sizing of Water Supply Systems Using Loading ... · PDF fileDesign and Sizing of Water Supply Systems Using Loading Units – Time for ... To design and size hot and cold

CIBW062 Symposium 2014

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Design and Sizing of Water Supply Systems Using

Loading Units – Time for a Change? S. Ingle (1), D.C. King (2), R. Southerton (3) 1. [email protected]

2. [email protected]

3. [email protected]

(1), (3) Ingle Project Design (2) Liverpool John Moores University

Abstract

To design and size hot and cold water supply systems engineers must be able to

accurately assess the demand for water at sanitary appliances. To do so in large public

buildings, which may have fluctuating or unpredictable occupancies, can be complex,

since the frequency and intensity of use of appliances must be predicted.

Since the 1940s, methods used by engineers the world over have been based largely

upon variations and refinements of the “loading units” methodology, an approach

originally advanced by Hunter in USA as long ago as 1940. Loading units are

calculated using probability theory based upon time intervals between uses of

appliances, the length of time the appliance draws water, and the average flow rate

when in use, and the approach incorporates an acceptable failure rate when design

conditions are likely to be exceeded for short periods. A great many refinements have

been carried out piecemeal over the decades, meaning that design guidance throughout

the world, despite using the same fundamental approach, may yield very different

results. Mathematical and computational models have also been developed, some of

which are applied to the loading unit approach, while others are used independently,

though again the adoption of these across international borders is inconsistent.

This paper reviews some of the most commonly used methodologies in light of a

perception that many water supply systems are routinely and substantially over-sized.

Engineers will, in general, continue to use tried and tested methodologies, despite

recognising that they are tending to over-engineer as the prospect of system failure is

commercially and professionally unthinkable. Routine over-sizing, however, shows

disregard to the principle of sustainable development and can potentially compromise

public health.


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The paper concludes that although mathematical and computational methods have been

developed and are routinely used all over the world, much more accurate and robust

models are needed for future sustainable development in buildings.

Keywords

Water supplies, pipe sizing, probability, loading units, mathematical models

1 Introduction

The basic requirement for users of cold and hot water supply systems is simple – it is

that water of appropriate quality and temperature must be supplied at acceptable flow

rates and pressures whenever required. Engineers designing and sizing such systems

must satisfy this requirement without compromising public health, whilst paying due

regard to sustainability and energy efficiency.

In order to design hot and cold water supply systems and determine the sizes of

pipework and storage vessels, engineers must be able to accurately assess the demand

for water at sanitary fittings, and pipe sizes are then derived from knowledge of water

flow rates. To predict water demand and flow rates in large public buildings, which

may have fluctuating or unpredictable occupancies, can be enormously complicated

since an accurate knowledge of factors such as the frequency and intensity of use of the

appliances is required.

A solution to the conundrum of predicting required flow rates came with the

development of the loading unit methodology advanced by Hunter in 1940 in the United

States, this being based upon probability theory, which had already been used to

determine the capacity of telephone exchanges. Hunter suggested a scale of numerical

constants, termed “fixture units”, which engineers could use to assess water flow rates

and hence determine pipe and storage vessel sizes. These units were calculated based

upon the assumed interval between uses of a sanitary appliance, the length of time that

appliance would be likely to draw water, and the average flow rate when in use (Hunter,

1940). In Sweden around 1945, Rydberg proposed a similar idea of predicting probable

flow water rates in buildings, though his mathematical method was somewhat different

to Hunter’s (Konen & Goncalves, 1993). Since the 1940s, methods used by engineers

the world over have been based for the most part upon refinements to Hunter’s and/or

Rydberg’s work, though the more modern label, “loading units” is used in preference to

fixture units. A great many modern design guides and codes of practice employ loading

unit methodology, see for example CIPHE (2002) and CIBSE (2014).

The mechanistic approach of the loading unit method lends itself to computer

simulation, and therefore software programmes exist (often designed by manufacturers)

which enable engineers to size systems with a fair degree of confidence. There is a

general perception, however, that the most commonly used methodologies lead to

systems being routinely and substantially over-sized.


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In general, engineers will continue to use tried and tested methodologies and are often

unwilling to vary from the established design guidance unless they have considerable

experience and confidence in their judgement. Designers may well recognise that they

are tending to over-engineer, but the prospect of system failure is commercially and

professionally unthinkable. Routine over-sizing is of course is wasteful of materials, it

shows disregard to the principle of sustainable development, and it can potentially

compromise public health – if water sits stationary for long periods in over-large pipes

or storage vessels for instance (Angus, Ingle, King, & Turner, 2010).

Many designers would consider a range of issues when carrying out design work and

these are presented in the “mind map” example shown below.

Figure 1 – Example of design engineers’ mind map


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2 A review of current practices

As stated previously, the basis for modern sizing methodologies owes much to work

carried out by Hunter (1940), who theorised that since the fixtures in a water system are

used intermittently, then the “loading effect” of a sanitary fitting must be dependent

upon three factors:

The time interval between uses of the fixture,

The length of time the fixture draws water,

The average flow rate of water for that fixture.

Using probability theory, Hunter developed a scale of fixture units based upon observed

usage data for sanitary fittings in use at the time in buildings in the USA. Hunter had

access to data from a number of hotels and apartment buildings, and made assumptions

based upon the time residents received morning calls and were observed to leave and

enter the buildings. From these data he was able to estimate the use of sanitary fittings

over a 24 hour period and identified the phenomenon of peak and off-peak periods.

Hunter based his development of fixture units upon probability theory, which had

already been used to determine the capacity of telephone exchanges in the USA. The

model applied to telephone exchanges allowed for a 1% failure rate, and Hunter applied

the same logic. In a telephone exchange this failure rate meant that it was expected that

for 1% of the time, the capacity of the exchange would be exceeded and any further

callers would not get a connection until another caller terminated their call. This would

appear to be a fairly minimal failure rate, probably unnoticeable for most exchange

users. When applied to water systems the result of a 1% failure rate would usually be

some reduction of pressure and flow rate for 1% of the time, and depending upon the

type of building, this may well be unnoticeable for the majority of users.

Howick (1964) adapted Hunter’s method to UK practice and his work became the basis

for British Standard Code of Practice 310 (BSI, 1965), a much respected and

internationally recognised design guide, upon which many of today’s design guides are

based.

The Hunter method has been reviewed several times since the 1940s, and Konen (1974)

studied the effect of varying the three factors used by Hunter to construct the probability

model. Konen concluded that:

The most important parameter is the time interval between uses of a sanitary

fitting,

The length of time the fitting draws water is of intermediate importance,

The flow rate of water to the fitting is of least importance.

Konen and Gonçalves (1993), in their work on mathematical models for water system

sizing, included an international survey to identify normal design procedures in a

number of countries. They made comparisons between the approaches to the design for

various types of building, including dwellings (apartments) and offices and were able to

classify three main design approaches:

Methods based on Hunter’s model (loading units), used across much of the

world, in particular USA, UK, Japan and India. Typically CIBSE or ASHRAE


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design guidance is applied, though there are several local variants. Konen and

Gonçalves (1993) identified a wide disparity between the methods used in these

countries, predicted flow rates for similar buildings differing sometimes by

factors of more than two to one.

Methods based on Rydberg’s model, this being an approach developed in

Sweden which predicts flow rates using probability theory, though in a different

way to Hunter. Not surprisingly, this approach is favoured in the Scandinavian

countries.

The other main design approach is typically found in European countries such as

France and Germany, though Konen and Gonçalves (1993) also report its use in

Brazil. This method is perhaps the simplest to use: the design flow rate (or

“flow units”) of all the appliances on a system are summated and this figure is

then multiplied by an empirically derived simultaneous demand factor. This

method almost always produces the highest design flow rates.

In addition to the different approaches listed above, each method would be refined by

reference to empirical data concerning building type and occupancy. Pinho & Abrantes

(1999) note that some countries, Russia for example, provide a more detailed selection

of buildings upon which design data may be based. However, across much of the world,

notably in Germany, UK and USA, the predominant design methods allow designers a

fairly narrow choice of building type and occupancy pattern, and there is less

opportunity for engineers to refine the design methodology they are employing.

2.1 Mathematical models

Several researchers have investigated the use of mathematical models to obtain more

precise predictions for design flow rates.

An early mathematical model was constructed by Webster (1972), who used Newton’s

Binomial Theorem alongside experimental work to construct his model. Webster used a

failure rate of 0.1% – that is, lower than Hunter’s by a factor of 10 – but still predicted

flow rates lower that those predicted by the loading units approach in BS 310. The

reason for this, it is argued, is that Webster’s method takes a less mechanistic view and

takes due account of the unpredictable nature of human behaviour. Since Webster’s

method was developed in an age where computers were not readily available, and it

required a large number of complex calculations, it was not adopted, and BS 310

remained the definitive design guide for some years.

Murakawa (1985) critically analysed the Hunter approach using “queuing theory” as the

theoretical basis for his study. Queuing theory is a technique that enables mathematical

models to be constructed to predict queue lengths and waiting times in various scientific

and engineering applications. Murakawa monitored the use of sanitary appliances in

two apartment blocks, comparing predictions made by his mathematical model and the

Hunter loading units approach with real observed data. His results showed that the

Hunter methodology predicted significantly higher design flow rates than observed data,

whereas the queuing theory method was much more consistent with the real data.

Ilha, De Oliveria, & Goncalves (2008) continued the work by Webster and others by

looking at water demand in apartments. They compared the water demand forecast by

the Brazilian Standard with that forecast by a probabilistic method which took account


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of the number of occupants in each apartment alongside the sanitary provision, and

concluded that such probabilistic model enables designers to adjust necessary

parameters in order to better reproduce the actual building systems flow rate according

to different conditions.

In furtherance of this work, Oliveira, Cheng, Gonçalves, and Massolino (2010)

constructed a water usage simulation model on apartment buildings in Brazil, which

included the techniques of fuzzy logic and the Monte Carlo method to enable

unpredictable human factors to be more properly considered. Their simulations yielded

results which predicted flow rates around 30% lower than the established Brazilian

design method, and they conclude that their model could well contribute to more

accurate sizing of water supply pipework and water meters.

These works are important and it remains to be seen whether design specifications will

embrace such methods.

2.2 Failure of a system to meet design specification

Failure in a water supply system could be caused by any number of circumstances, the

most common being:

Failure of the infrastructure of the water supplier,

Failure of the electrical supply feeding booster pumps or failure of pumps

themselves,

Failure of the distribution system to deliver the required flow to every point in

the system.

For the first two items there is normally flow design data available. Precautions can be

taken to avoid loss of supply, for example by providing a standby electrical supply for

the pumps. Alternatively the pipework system may be designed to limit the number of

points affected by any failure.

Failure of the distribution system to provide the required flow rate is not so easy to

define, however, because this depends often upon occupiers’ perception of what might

constitute a reasonable or acceptable flow rate, and what might be considered a system

“failure”.

Hunter (1940) and Howick (1964) used a failure rate of 1%, a figure which was

commonly acknowledged as practical and acceptable, and this figure is used in the

British Standard Code of Practice 310 (BSI, 1965) design guide. This failure rate

actually equates to a system not being able to deliver the design flow rate for a period of

36 seconds in a one hour period. It is, however, useful to consider what actually

happens during periods of “failure”.

In the case of an apartment block served directly from the mains, under design

conditions a suitable pressure and flow rate would be available at the highest floors,

thus ensuring that all sanitary appliances may be used normally. During periods where

design conditions are exceeded there would be a reduced pressure and flow rate at the

upper floors. Users may not, for example, be able to shower satisfactorily and may

have to wait for WC cisterns to fill, but would still enjoy a water supply, even though

pressure and flow rate are reduced. At what stage does this reduction of flow rate

become problematic such that it is considered a system failure?


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In an extreme case of failure the demand in the building would outstrip the capacity of

the distribution system (or supply connection), and upper floors would be left with no

water supply at all. It is likely, however, that users on the lower floors would

experience much less disruption to supply in conditions of high demand.

Chakrabarti & Sharma (1980) proposed a low cost solution, based upon research carried

out in apartment buildings in India. Essentially it was suggested that low pressure

fittings could be installed on upper floors and high pressure fittings could be installed

on the remaining floors, and together with flow restrictors, this would allow the system

to maintain balance during varying usage patterns, and would limit the effect of failure

periods. These techniques are often used nowadays to mitigate against periods of

reduced flow.

2.3 Pipe sizing

As has been stated, the sizing of any distribution system must be based upon the

required flow rates which have been predicted, taking account of available water

pressures and appropriate design velocities. In terms of capital cost the greatest

economy is achieved by minimising pipe sizes, though this produces a knock-on effect

of increasing flow velocities, potentially causing noise or even pipework erosion.

In recent times, life cycle costing is more likely to be considered. The operating and

running costs of any system are evaluated and added to the capital cost, to provide a life

cycle cost. Small pipe sizes would certainly minimize capital costs but, in pumped

systems, the associated greater pressure drops would increase pump power and energy

consumption over the life cycle.

As has been previously stated there is a consensus view that routine oversizing is the

norm, due to the very low acceptable failure rates applied to the loading units

methodology, although system failure often means nothing more than reduced flow

rates and pressures at peak times, and this may not even be noticeable. Angus, Ingle,

King and Turner (2010) further suggest that current sizing methods, which tend towards

over-sizing, can lead to problems of water stagnation and dirt being deposited at low

velocities during off-peak periods and this can encourage the growth of bacteria,

allowing biofilms to form, and in extreme cases even promote algae growth. There are

therefore some very convincing arguments for varying the design failure rate to allow

higher velocities depending upon the type of building, though it must be accepted that in

cases where all fittings are likely to be used simultaneously a very low failure must be

maintained.

It is also well recognised that smaller pipe sizes in the case of domestic hot water supply

systems can show a significant energy saving due to reduced heat losses from the

system as well as lower materials costs (Werden & Spielvogol, 1968), though this effect

is less pronounced on newer systems with good pipework insulation (Angus, Ingle,

King, & Turner, 2010).


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3 Factors influencing demand

Many observers have set about defining and measuring the human biological need for

water for domestic purposes such as toilets, washing, cooking, drinking, bathing and

cleaning, for example see Mendes & Lucas (1978). People living and working in

buildings are, however, notoriously unpredictable, and it is well-recognised that there is

no simple way of precisely predicting occupant behaviour and ascertaining the resultant

demands for water.

For unmetered supplies, the water industry in the UK suggests an average water

consumption of 140 litres per person per day inclusive of leakage, though there is some

conjecture about this figure (King & Brady, 2014). The level of leakage in urban areas

can vary greatly and is dependent upon any number of factors, ranging from age and

maintenance of pipework and infrastructure, to topography and geography, so is

difficult to quantify accurately in most cases. The UK figure may be considered as mid-

range: other countries (notably USA) expect water use per person to be far higher, while

others, such as Germany, use a reference figure somewhat lower.

The age, health and economic status of building occupiers (and of those in the

surrounding area) are known also to have a significant effect on water demand. Socio-

economic influences and demographics of any particular development and its type,

compared to the surrounding area, strongly influence the usage pattern and the mean

peak flow demands of buildings.

The level of occupancy for a new building is often not known by the client or architects

at the design stage, so some form of estimate is often used. In the UK this is often

assessed by reference to fire regulations or to the Health & Safety Executive’s guidance

for acceptable maximum workplace occupancy densities. This technique frequently

leads to overestimation of building occupancy and consequent over-engineering of all

building engineering services (not just water supply systems).

If the building under consideration has public or recreational areas, these will have a

higher peak demand due to seasonal variations and weather changes when compared to

buildings with a constant year-round occupancy like factories, offices and similar.

Likewise, hotels and restaurants tend to experience unique occupancy profiles leading to

peak and off-peak water demands at different times to other buildings. In addition

facilities such as spas, swimming pools have their own individual requirements and

usage profiles as does agriculture.

3.1 Factors that influence consumption

Water metering is becoming more common, and proponents would contend that it raises

awareness of the finite nature of water supplies and so reduces unnecessary

consumption. Local metering affects system design, while charging policy can

encourage users to be more aware of unnecessary water consumption. Interestingly

though, it is not a proven fact that water metering as an independent measure actually

reduces consumption: In Germany all water use is metered and consumption per person

is around 30% less than in the UK, while in the United States water usage is also


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metered, but consumption per person is almost double the UK figure (International

Bank for Reconstruction and Development, 2010).

A question that may arise as metering becomes more prevalent is whether metering has

different effects based upon socio-economic groups. Undoubtedly some people will

find metered water to be very cheap, while those with low incomes may well find the

reverse to be true.

An obvious contributor to the demand for water is the plumbing fixture itself. In the

drive to prevent water wastage, the trend in recent years has been for all sanitary

appliances to be designed and manufactured smaller and thus to consume less water.

Since Hunter’s day the habits of human beings have changed considerably. The most

obvious change is that people generally prefer to shower rather than bathe nowadays.

With reduced water demand from other fittings and appliances, the dominant demand in

dwellings is very often the demand from showers. It is, however, difficult to assess how

much water is used in a “typical” shower since habits vary so widely. Users are known

to prefer showers with high pressure jets which use large volumes of water and these

can be quite wasteful if users take long showers. One of the modern technological

developments for showers includes an air induction system which mixes air with the

water flow, thus providing what feels to the user like a high flow rate, while in reality

using low volumes of water.

While a shower unquestionably uses less water than a bath, people are tending to

shower more and more frequently, particularly in the industrialised nations. Habits as to

the length of time spent showering vary widely across the world according to many

complex economic, sociological and societal factors. In regions of the world where

water is scarce, however, local authorities may try to educate users to limit the length of

time spent showering. For example, Australians are given recommendations as to the

length of time they should shower, and are encouraged to use a timer while showering.

The use of filled washbasins for body washing has likewise declined; basins are often

used just for hand and face washing and for teeth brushing, though the practice of

leaving a tap running while brushing teeth is difficult to discourage.

There are many commonly promoted conservation practices and new technologies

designed to save water, though current design practices do not always take account of

(or permit) these. Some of these are listed:

It is known that a good general maintenance regime for sanitary equipment

throughout its working life can substantially reduce water consumption,

Low water usage taps such as spray taps, infra-red and non-concussive taps are

commonly used in public washrooms,

In several countries there are constantly updated recommendations to reduce

flow rates to taps and showers and to reduce the size of WC flushes,

Dual flush valves are now routinely fitted to WC cisterns across much of the

world,

Flow limiters are often fitted in public buildings to avoid excessive water draw-

off,

Water shut off in unoccupied parts of buildings is encouraged by BREEAM and

other environmental assessment methods, though such measure could potentially

compromise public health by allowing water to stagnate in pipework.


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Automated leak detection systems are routinely made available,

Use of infra-red sensors to effect automatic urinal flushing,

The inclusion of grey water recycling and rainwater harvesting systems to

supply non potable water, thus supplementing the water supply system,

Short, well insulated dead-legs on domestic hot water systems to prevent users

running water to drain while waiting for hot water,

Older style domestic laundry and dishwashing machines used typically 112 litres

per normal cycle, whereas the more modern models of these appliances use far

less water, and also less electricity.

Some very human problems are in evidence as people adapt to new technologies and

practices, however. Typically, many people do not understand how to use dual flush

valves on WCs properly. Familiarity will inevitably overcome these issues, though it

may well be that the ergonomics of these devices could be improved.

Whilst the general trend in industrialised countries is for people to be encouraged to

consume less water, it must also be recognised that some wealthier households tend to

feature items like hot tubs, power showers, lawn sprinklers and garden irrigation

systems.

4 Conclusions - the way forward?

Although many countries across the world use versions of the loading unit methodology,

there are, as has been reviewed, wide discrepancies in its application. International

harmonisation may be part of the answer here, though there is a considerable distance to

travel to realise this aim. The loading units methodology is now unquestionably

outdated and over-simplistic in its approach, and engineers working within its

restrictions do not have sufficient flexibility to refine results that are obtained.

As the construction industry moves into a period where routine use of Building

Information Modelling (BIM) is to become common practice in all aspects of building

design, the time must now be right for the introduction of a more accurate and robust

water supply design and sizing methodology. Information gained from BIM monitoring,

where live data are collected from real buildings, could be systematically catalogued

and analysed to give accurate data across a full range of buildings (though there will

inevitably be some caveats surrounding the veracity of such data). These data may well

enable the first steps towards a harmonised loading units model to be built.

The recent innovative work carried out in Brazil (Oliveira, Cheng, Gonçalves, &

Massolino, 2010) which yields computer simulations of water usage by applying fuzzy

logic to take account of human factors, could well be a premise upon which a more

robust methodology is based.

A newer design method must be far more flexible and allow engineers to consider more

factors than is currently possible without being over mechanistic and prescriptive. As

well as the obvious technical data, to realise a new model further research is needed in

the following areas:


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A consideration of acceptable failure rates and an appreciation of what problems

a system “failure” might actually cause,

The prospect of using higher water velocities to enable smaller pipe diameters

balanced against the risks of system noise and possible erosion,

The condition of supply infrastructure and leakage data (gathered via BIM

monitoring processes).

Caution must be exercised when collecting live data from real buildings since

data gathered from one particular building type may not always be applied

accurately to other building types. Such data should be utilised in conjunction

with data obtained from simulations.

Establishment of users’ needs – these can be further defined as people’s actual

biological needs for water (Mendes & Lucas, 1978) for washing, drinking and so

on, as compared to what might be termed psychological or aspirational needs,

the insistence of many people to shower several times per day for instance.

Hunter’s work was consistent with the state of engineering and technology available in

the 1940s, and his work has served us well. But in the 21st Century, as we aspire

towards sustainable development with a rapidly growing world population, we have far

more technological tools at our disposal than Hunter could have dreamed of. A more

modern sizing methodology is possible and necessary, and researchers today must

ensure that this aim is realised.

4 References

Angus, P., Ingle, S., King, D., & Turner, J. (2010). The effects of using water velocity

as a technique to control biofilm development in water supply systems. CIB

W062 36th International Symposium. Sydney: CIB.

BSI. (1965). British Standard Code of Practice CP 310 : 1965.Water Supply. British

Standard, London.

Chakrabarti, S. P., & Sharma, S. K. (1980). Peak hydraulic load on intermittent water

supply systems in multi-storey residential buildings. Rourkee, India: Central

Building Research Institute.

CIBSE. (2014). CIBSE Guide G: Public Health and Plumbing Engineering. London:

CIBSE.

CIPHE. (2002). Plumbing Engineering Services Design Guide. Hornchurch: CIPHE.

Howick, H. A. (1964). The pipe sizing of hot and cold water installations. Plumbing

Trade Journal.

Hunter, R. B. (1940). Methods of estimating loads in plumbing systems. Washington DC:

United States Department of Commerce.


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Ilha, M. S., De Oliveria, L. H., & Goncalves, O. M. (2008). Design flow rate simulation

of cold water supply in residential buildings by means of open probabilistic

model. CIB W062. Rotterdam: CIB.

International Bank for Reconstruction and Development. (2010). Sustaining water for

all in a changing climate. Washington: The World Bank.

King, D., & Brady, L. (2014). Part 4: Sustainable building services. In R. M, & C. A,

Construction Technology 2: Industrial & Commercial Buildings. London:

Palgrave.

Konen, T. P. (1974). A review of the Hunter model. CIB W62 Symposium 1974. CIB

W62.

Konen, T. P., & Goncalves, O. M. (1993). Summary of Mathematical Models for the

design of water distribution systems within Buildings. CIB W62.

Mendes, M., & Lucas, C. (1978). A bacteriological survey of washrooms and toilets.

Journal of Health and Hygiene.

Murakawa, S. (1985). Study on the method for calculating water consumption and water

uses in Multi-Storey Flats. CIB W062 symposium. Tokyo: CIB.

Oliveira, L. H., Cheng, L. Y., Gonçalves, O. M., & Massolino, P. M. (2010). Simulation

model of design flow rate in water submetering systems using fuzzy logic and

Monte Carlo method. CIB W062 36th International Symposium (pp. 14-29).

Sydney: CIB.

Pinho, P. J., & Abrantes, V. (1999). Pipe sizing and pressure analysis of water

distribution systems, overview and comparison of different criteria . CIB W062.

Webster, C. J. (1972). An investigation of the use of water outlets in multi-storey flats.

IHVE Journal, 215 – 233.

Werden, R. G., & Spielvogol, L. G. (1968). Sizing of service water heating equipment

in commercial and institutional buildings. New York: Edison Electric Institute.


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5 Presentation of Authors

Derek King is a Principal Lecturer in the School of the Built

Environment at Liverpool John Moores University, being

programme leader for degree programmes in Building Services

Engineering. Among his research interests are the practicalities

of applying sustainability to public health engineering systems,

and international aspects of building services engineering

education. Derek is currently Chair of his local branch of the

CIBSE

Dr Steven Ingle is an independent consultant engineer presently

working for Ingle Project Design Consulting Engineers, UK.

Steven is involved in the design of all types of Building Services

Engineering on commercial and industrial projects in the UK and

internationally. He is also an active member of the Society of

Public Health Engineers and has several research interests.

Ralph Southerton is a consultant building services engineer

currently employed by Ingle Project Design Consulting

Engineers. He has several research interests in the field of public

health engineering.

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Design and Sizing of Water Supply Systems Using Loading ... · PDF fileDesign and Sizing of Water Supply Systems Using Loading Units – Time for ... To design and size hot and cold