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Contents

Section 1 Introduction

Section 2 Sustainable Design

Section 3 Design of Systems

Section 4 Cold Water Supply

Section 5 Hot Water Supply


 

Description:  This unit is designed to introduce the elements needed to enable you to produce and evaluate detailed designs for cold and hot water supply systems for complex buildings.

Author:  Gates MacBain Associates


Section 1  Introduction


Before we look at the design of systems for complex buildings you will need to ensure that you understand the basic design features and requirements for water systems.  In order to do that you can consult the constructionsite unit indicated below.



Constructionsite Units

  • Services (Cold Water Supply) (Hot Water Supply)






Section 2  Sustainable Design




Aims and Objectives

At the end of this section you should be able to:
  • Suggest ways that can be implemented to conserve water through the design of the system.


The design of any system must consider that rising demand, water pollution and climate change are threats to fresh water supplies and this has resulted in the need to conserve water. The design of systems now acknowledges the need to conserve and manage water and must implement measures in the design of water supply systems.  


Water Conservation 

Water conservation can be improved through effective design, for instance a gravity hot-water system delivering low pressure water uses less water than a mains pressure hot-water system. Installing point of use water heaters ensures that cold water is not wasted while waiting for hot water to come through the taps. Well-lagged and properly positioned pipes will also help keep water hot.  The design should improve water conservation, which is achieved through the specification and installation of water-efficient appliances and fittings.  

In toilets, the use of a displacement device in the cistern will reduce the amount of water  but a more efficient solution is to fit a low-flush toilet. There are many different models including: dual flush toilets, with a lower flush option for fluids and a standard flush level for solids; gravity toilets, that depend on gravity alone; and pressure assisted toilets that combine gravity with compressed air are also options to consider. 

The selection of taps can also reduce the amount of water used as water efficient fixtures can reduce the amount used by 50%.  There are a number of fixtures available for washbasins, sinks and baths: including push taps and sensor taps (self-closing so taps aren't left running), spray taps (reduce flow volume), and other flow regulators and restrictors (restrict flow, regulate pressure and reduce the force needed to turn the flow off). 



Self-Assessment Task

  • Discuss how the specification of plumbing fittings can influence the water requirements used in a building.





Section 3 Design of Systems




Aims and Objectives

At the end of this section you should be able to:
  • State the factors which need to be considered in order to produce the design requirements for a system.


The design of the system to be incorporated into a building will depend on the: 
  • Number and type of fittings to be supplied
  • Maximum water flow
  • Spacing and location of fittings
These will depend on the type of building and their frequency of use; it will also depend on the likelihood of the number of fittings being used simultaneously and the demand required by these. 

In order to calculate this requirement a unit loading rating is used together with a recommended minimum rate of flow for each type of appliance.  Details of this can be found in the Building Services & Equipment book Volume 2 indicated below.  


Pipe Sizing and Lengths 

In order to meet the required flow rate at the appliance a number of factors need to be considered, these are: 
  • Head of water available
  • Length of the pipe
  • Diameter of the pipe
  • Smoothness of the internal bore of the pipe
An allowance is also made for any frictional resistance caused by fittings such as elbows and tees.  

The diameter of the pipe is determined for the required flow rate and the maximum length which is allowable. The determination of pipe diameters can be found in the Building Services & Equipment book Volume 2. Another good book to consult is Hall & Greeno listed below.  A guide to the number of draw offs and pipe diameter can be found at the Engineering Toolbox website linked to below. This is a useful site which provides guidance on the sizing requirements and cold water storage per occupant for different types of buildings.



Websites



Publications

  • Hall, F, (1997), Building Services & Equipment Volume 2, Harlow: Longman (Chapter 1)
  • Hall, F & Greeno R, (2001) Building Services Handbook; Oxford: Elsevier (Part 2)



Self-Assessment Task

  • State and Discuss the factors relevant in the design of a water system in a commercial building.





Section 4  Cold Water Supply




Aims and Objectives

At the end of this section you should be able to:
  • Produce a specification for the provision of cold water in medium and high rise buildings.


Prior to doing this section you should have completed the previous sections which would mean that you worked through the constructionsite unit relating to Cold Water Supply, if you havenít done this already you should do so before progressing by clicking on the link below. 

You should also consult Approved Document G of the Building Regulations to ensure you are familiar with the requirements relating to water supply. A link to this on the web is shown below. 

From this unit you will have an understanding on how water is brought into a building, distributed. You will also be aware that water can be supplied direct from the mains or stored. 

Water used direct from the main is required for each unit (dwelling, rented unit) in order to provide drinking water. In large buildings and in some areas of the country the remaining water requirements are provided by storage. In high rise buildings water will be stored at various levels which will reduce the static water pressure.  

In order to ensure the distribution of drinking water this too is stored though in order to reduce the risk of contamination sealed storage tanks are used. Details regarding requirements for potable water in low pressure systems can be found in the book Building Services Engineering listed below.  


Low Pressure System 

A low pressure system works on the basis of storing water which is used to provide the appliances. This requires a storage facility to provide sufficient water for a 24 hour period. There is a requirement that water in storage tanks is of a similar quality to that provided from the mains so they need to ensure that contamination does not occur they also need to ensure that there is stagnation within the system. 

In tall buildings the tanks may be situated at a level above the height that the pressure in the mains can lift it to, in such a case it will be necessary to install a pressure boosting system in order to lift the water.  Such a system can be seen in the Chadderton book listed below. Details of the systems which can be used in high-rise buildings can be found in Chapter 1 in the Hall book listed below.  



Websites



Publications

  • Hall, F, (1997), Building Services & Equipment Volume 1, Harlow: Longman (Chapter 1)
  • Chadderton, D (2009) Abingdon: Taylor & Francis (Chapter 6)
  • Hall, F & Greeno R, (2001) Building Services Handbook; Oxford: Elsevier (Part 2)



Constructionsite Units



Self-Assessment Task

  • With the aid of a drawing, produce a specification for the design of the cold water supply system for a 20 storey block of flats showing two flats on each floor.




Section 5  Hot Water Supply




Aims and Objectives

At the end of this section you should be able to:
  • Produce a specification for the provision of hot water in medium and high rise buildings.


A number of systems are available for the provision of hot water in a building. Chapter 2 of the Hall book provides a good introduction to the requirements which should be consulted.  You should also read through Chapter 6 of the Chadderton book, both of which are listed below.  In addition you should consult Approved Document G of the Building Regulations, a link to which can be found under websites below. 



Websites



Publications

  • Hall, F, (1997), Building Services & Equipment Volume 1, Harlow: Longman (Chapter 2)
  • Chadderton, D (2009) Abingdon: Taylor & Francis (Chapter 6)
  • Hall, F & Greeno R, (2001) Building Services Handbook; Oxford: Elsevier (Part 3)



Self-Assessment Task

  • With the aid of a drawing, produce a specification for the design of the hot water supply system for a 20 storey block of flats showing two flats on each floor.






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