PREFACE
This publication provides practical, easy to follow methodologies for a range of calculations used in the design of heating ventilating and air conditioning building services systems.
The calculation sheets are presented in five sections covering:
• Heating loads and plant
• Cooling loads and plant
• Water flow distribution systems
• Air flow distribution systems
• Acoustics for building services
The calculation sheets provide practical guidance including design watchpoints, design tips and rules of thumb, and are intended to
aid the design process and reduce errors. The guidance is based primarily on data and procedures contained within the CIBSE
Guides, together with other sources such as Building Regulations, with clear cross-referencing provided to data sources.
This publication is intended primarily to help junior design engineers, working within a structured and supervised training
framework, by providing assistance in completing the basic calculations needed to define operating conditions for systems, size
distribution systems and to specify required duties for plant and equipment. It is not the purpose of this guide to identify the most
appropriate system for a particular application. Such decisions require knowledge, experience and analysis of the application.
This guidance is also not intended to be exhaustive or definitive. It will be necessary for users to exercise their own professional
judgement, or obtain further advice from senior engineers within their organisation when deciding whether to abide by or depart
from the guide. The calculation sheets are relevant to many design applications, but cannot be fully comprehensive or cover every
possible design scenario. Every design project is different and has differing needs, and it is the professional duty of the responsible
design engineer to consider fully all design requirements. Designers should exercise professional judgement to decide relevant factors and establish the most appropriate data sources and methodologies to use for a particular application.
Designers must be aware of their contractual obligations and ensure that these are met. Following this guidance - or any other
guidance - does not preclude or imply compliance with those obligations. Similarly, it is the duty of the designer to ensure
compliance with all relevant legislation and regulations.
It is hoped that design practices and individual designers will be encouraged to share knowledge and experience by extending and
adding to the design watchpoints and design tips, and disseminating this work within their organisations. BSRIA would be pleased
to receive any such contributions for incorporation into any future revisions of this publication to provide wider industry sharing of
such knowledge.
INTRODUCTION
BSRIA has been researching into the design process and design methodology in the building services industry since the mid 1990’s.
This has produced guidance on the use of engineering design margins1 , feedback to design2 and quality control systems for detailed technical design3
. The overall aim has been to develop systematic guidance for the industry that would contribute to greater consistency in design and to an overall raising of design standards.
The studies have involved considerable discussions with industrial partners on their current and future needs, and several visits to the design offices of a number of industrial contributors to the projects.
A majority of those organisations consulted said that a lack of formal design guidance and inadequate recording of calculations was a
major barrier to quality improvement in design. Many also felt that standardised formal procedures would help improve the quality of
design outputs.
BSRIA’s research also revealed that there is a lack of standardisation in design procedures, both between companies and between
individuals. Many companies have developed their own design guidance and approaches to calculation procedures, leading to
considerable diversity within the industry. This can make it difficult to cross-check work done by others, which could lead to differences in system design parameters and sizes, and even
calculation and design errors. There are many specific examples of design errors and issues that should have been considered during
design calculations and have led, (or could have led) to operational problems or subsequent litigation4 , including:
• Omission of HEPA filter resistance from fan-pressure calculations, requiring subsequent fan motor replacement which then required additional silencing
• Omission of duct sizes and flows from drawings, leading to incorrect sizes being installed
• Incorrect pipe and pump sizing for a constant temperature heating circuit, necessitating replacement of system distribution
network
• No allowance for pipework expansion on a heating mains.
Although there is considerable design guidance and data available to inform the design process much of it is intended for use by
experienced engineers, who have fulfilled a programme of education and training and have design experience. For example, while the design guides published by the Chartered Institution of Building Services Engineers (CIBSE)5 provide essential design data
for building services engineers, they are intended for use by experienced engineers, and therefore do not always show how to
design in detail by giving every necessary calculation step. They also do not show how different calculation routines link together to
build up the design process.
Research has also shown that many employers are currently finding it difficult to recruit design engineers with appropriate building
services skills and experience, which necessitates recruiting and retraining engineers from other disciplines.6 Output from building
services courses is currently falling, 7 which implies there will be no short term improvement in this situation.
These recruits, with no building services training or experience, will require close supervision and considerable training which can place a heavy burden on company resources.
While there is no substitute for an appropriate quality control framework and adequate supervision by qualified senior staff, good
training resources and technical support can provide an invaluable adjunct to company training provision.
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