Home Contact Us
Contact Us


Section 1 Requirements

Section 2 Functional Requirements

Section 3 Ventilation and Air Conditioning Systems 


Description:  This unit introduces the factors relating to determining the requirements for Heating, Ventilation & Air Conditioning solutions in buildings.

Author:  Gates MacBain Associates

Section 1  Requirements

Aims and Objectives

At the end of this section you should be able to:
  • State the factors to be considered in order to determine the energy requirements.

In order to be able to determine the requirements for the heating, ventilation and air conditioning system for a building it is essential that you are aware of the factors listed below as they affect the choices available in determining the system to be employed.  
  • The analysis and interpretation of client and building operational requirements,
  • The design standards with regard to these services as they relate to the different types of buildings ie commercial, industrial etc.
  • The balance between clients needs, commercial constraints, health and safety, aesthetic and energy efficiency considerations.
  • Use and effect of natural ventilation.
  • The Inter-relationship between ventilation and air conditioning and other mechanical and electrical building services
It is also essential that you know the factors which will affect the requirements. This relates not only to the building and its’ use but also the environment in which it will be situated. The main factors which will need to be known are: 
  • Climate
  • Building envelope
  • Occupancy and Use

The climate and weather conditions will have an effect on the amount of energy that is required in a building in order to maintain a comfortable living/working environment for the occupants.   

If the weather is particularly cold there will be a greater need for energy to heat the building, conversely, if there is a heat wave more energy will be required to maintain the air conditioning. Consequently the weather is a major factor in determining the requirements in a building.  This will be affected by the location that the building is to be constructed as a building in the Middle East will need more energy to cool the building while one in Norway will require it for heating. 

Exposure is also relevant as a building situated in an unprotected location overlooking the North Sea will have a different requirement to one build in the centre of a city. 

Degree days 

A way of determining the rise in the cost as a result of the weather can be determined by using a unit of measure called the ‘degree day’ This compares the outdoor temperature to a standard of 65°F the more extreme the temperature, the higher the degree-day number and the more energy needed for heating or cooling. 

Cold days requiring energy for heating are measured in heating degree-days. Hot days requiring energy for cooling are measured in cooling degree-days. On a day with a mean temperature of 80°F, 15 cooling degree-days would be recorded. For a day with a mean temperature of 40°F, 25 heating degree-days would be recorded. Two such cold days would result in a total of 50 heating degree-days for the two-day period. 

More details on Degree days can be found at the website listed below.  

Building Envelope 

The design of the services should be integral to that of the building envelope as this has an influence on the energy requirements and also the ability to maintain or repair any system installed in it. The requirements with regard to energy efficiency of the building envelope are specified within UE directives and the Building Regulations. More details with regard to this can be found in the constructionsite unit ‘Sustainable Legislation’ a link to which is provided below. 

The building envelope will also have an influence on the amount of heat loss and the thermal properties of the materials used.  You must be familiar with the principles involved with this so you should go to the constructionsite unit Thermal Studies a link to which is provided below.  

Occupancy and Use 

The improved quality of thermal properties of buildings due to improved energy regulations is having a reduction in the overall energy use making the role of the occupant more important. Though at the design stage consideration must be given to the occupants as the temperature requirements for a hospital may be greater to maintain a comfortable environment than that for a sports centre. The processes carried out or equipment used in a building will also influence the ventilation requirements and air conditioning. 

Energy Costs 

Considering the above will enable the potential energy costs to be calculated. Further details on this can be obtained from the Building Services Engineering book indicated below.   



  • Chadderton, D, (2007), Building Services Engineering, Abingdon, Taylor & Francis, Chapter 2.

Constructionsite Units

Self-Assessment Task

  • Discuss the factors which will have an influence on the energy requirements relating to heating, ventilation and air conditioning.

Section 2  Functional Requirements

Aims and Objectives

At the end of this section you should be able to:
  • Explain the functional requirements a services system should have in order to ensure the comfort and well being of the occupants.

Any systems installed are intended to ensure that the building is able to function according to its intended purpose and it is the services which will to a certain extent, enable this to happen. It will also have a major effect on the well being and comfort of the occupants which ensures that the building is fit for the purpose that it was produced for.  From this it is easy to deduct that the main functional requirements are: 
  • Comfort and well being of those using the building, this is likely to consider the following:
    • Radiant and air temperature
    • Air movement, quality and odours
    • Humidity
    • Background noise levels of services
    • Degree of control of services
  • Health and Safety – all systems must be able to achieve their purpose in a safe manner ensuring that they do not compromise occupants either through injury by mechanical failures or by producing an environment detrimental to people’s health ie poor air quality.
  • Ease of use – the system must enable it to function simply and to ensure it is easy to control and adjust.
  • Ease of maintenance and repair – any maintenance or repairs must be able to be carried out simply, quickly and as cheap as possible with the minimum of disruption to the buildings occupants. Therefore access must be provided  to allow for this. It is quite possible that many services will need to be replaced as they tend to have a shorter working life than the building itself, this could amount to the whole service system.
  • Energy efficiency – an important consideration in its design is that it is energy efficient and functions with the minimum energy consumption. It should also have the minimum of emissions.
The requirements to ensure the above should be carried out at the design stage of the building project.  


  • Chadderton, D, (2007), Building Services Engineering, Abingdon, Taylor & Francis, Chapter 5.

Self-Assessment Task

  • Explain the factors relevant to a services system to ensure that it is functional and that it meets the requirements to ensure the comfort and well being of the occupants.

Section 3  Ventilation and Air Conditioning Systems

Aims and Objectives

At the end of this section you should be able to:
  • Differentiate between the different types of ventilation and air conditioning.

Ventilation is the intentional movement of air from outside a building to the inside. The movement of air between indoor spaces, and not the outside, is called transfer air. 

When people or animals are present in buildings, ventilation air is necessary to dilute odours and limit the concentration of carbon dioxide and airborne pollutants such as dust, smoke and volatile organic compounds (VOCs). Ventilation air is often delivered to spaces by mechanical systems which may also heat, cool, humidify and dehumidify the space. Air movement into buildings can occur due to uncontrolled infiltration of outside air through the building fabric or the use of deliberate natural ventilation strategies. Advanced air filtration and treatment processes such as scrubbing, can provide ventilation air by cleaning and re-circulating a proportion of the air inside a building. 

Air Conditioning is a system or process for controlling the temperature and sometimes the humidity and purity of the air in a building. 

A good source of information about the options and specifications available can be obtained from the manufacturers, and you should visit the company websites linked to below.   

Evaluating Ventilation and Air Conditioning Systems   

There are a number of types of ventilation system that can be selected according to the building and processes that are carried out within it and you will need to understand these and where they are used in order. These can be: 
  • Natural - occurs when the air in a space is changed with outdoor air without the use mechanical systems, such as a fan. Most often natural ventilation is assured through operable windows but it can also be achieved through temperature and pressure differences between spaces. Natural ventilation is generally impractical for larger buildings, as they tend to be large, sealed and climate controlled.
  • Mechanical – this occurs through an air handling unit or direct injection to a space by a fan. A local exhaust fan can enhance infiltration or natural ventilation, thus increasing the ventilation air flow rate.
  • Mixed flow  - Details of this and Displacement ventilation can be found by visiting the 'Displaced v Mixed Flow Ventilation' at the website below.
  • Displacement ventilation.
  • Combination of ventilation and air conditioning systems – This works on the premise that temperature humidity, air movement and solar intensity define the internal climate of a building and need to be in balance in order to ensure optimum comfort and productivity.

Classification of Systems 

Systems can be classified by:
  • Function
  • Distribution
  • Ventilation Principle
More details can be found on these by visiting the Classification of Systems web link below.  


To gain an insight into the design of a system it is worth visiting the Design of a System website below, although it should be borne in mind that this is based on standards in the USA and deals specifically with schools, the processes it considers however are relevant to all buildings.  


The selection of an air conditioning system will depend on: 
  • The relative needs.
  • Sizing and selection of plant, ductwork and pipework,
  • Design implications on space, maintenance and commissioning requirements,
  • Capital and operating costs.
  • Comparisons between centralized and packaged equipment



  • Chadderton, D, (2007), Building Services Engineering, Abingdon, Taylor & Francis, Chapter 5.
  • Hall, F & Greeno, R, (2009) Building Services Handbook, Oxford, Butterworth-Heinemann,  Chapter 6 & 7.

Self-Assessment Task

  • Using a given situation, assess the needs of the building for a ventilation and air conditioning system and determine the possible types that could be used. 
  • Select an appropriate system and justify your choice.

Site Map