Question:

A design team sets out to create a so-called `green building', which will incorporate environmental engineering approaches such as natural ventilation, passive solar, structure assisted cooling, daylighting, etcetera.

Discuss which implications this might have in terms of occupant thermal comfort, and which aspects of thermal comfort will need particular attention.

Sample answers:

The thermal comfort of a human being is dependant on the thermal balance of the body, which is in turn dependant on parameters such as; air temperature, mean radiant temperature, relative air velocity,relative humidity.
As regards the proposed building it is clear that close attention will have to be paid to the relative air velocity within the building. As a natural ventilation system is being used the close control associated with a mechanical system may not be present and this could present a problem with thermal comfort, eg high relative air velocities could create thermal discomfort.
Also the use of daylighting implies that there may be a high glazed area within certain zones. If this is the case close attention will have to be paid to the mean radiative temperature's of all the surfaces within each zone to avoid a high degree of radiative asymetry occuring, as this would cause thermal discomfort.
If stucture assisted cooling is used there may again be poor control which could cause unacceptably high or low air temperature's which will in turn cause thermal discomfort among the occupants.
As stated above the main implication of this design in terms of occupancy thermal comfort is control. But this is not purely a question of maintaining close environmental to avoid physiological discomfort, attention has to be taken over the physcological comfort of the occupants. It has been proven that occupants feel more thermaly comfortable within an environment in which they have a high degree of control. Within this building there are a large number of passive systems which may not afford the occupants the degree of control they require.
Thomas Mullen, Environmental Engineering, University of Strathclyde, 1997.

In today's energy conscious society, it is important that every effort is made to try and reduce the energy requirements of modern buildings. However, the use of environmental engineering approaches should not be to the detriment of occupant thermal comfort. Some aspects which should be considered are discussed below.

1. Natural ventilation is a design strategy which is becoming extremely popular. It can be in the form of openable windows, the stack effect, cross-ventilation etc. It is important that these natural methods do not compromise thermal comfort by either inducing uncomfortable draughts or creating stagnant air.
2. Windows can play an important role in "green building" design. They can be used for daylighting, solar gain and (as previously mentioned) for ventilation requirements. However, it is important that the balance between the three is acceptable. Problems which could occur include glare, overheating of the building and draughts. Careful attention to window design is required to minimise potential problems.
3. The temperature within the building has the greatest influence on thermal comfort. It is important that there is neither under or over heating. As a result, heat gains from occupants, computers, lights etc. need to be calculated carefully as they can provide a considerable heat load which could affect thermal comfort. In addition, overnight cooling of a building like an office is important. Too much and it will increase the morning warm-up; too little and the occupants will suffer as the daytime temperatures climb. Indoor temperatures will also be affected by such factors as natural ventilation and window area thus illustrating the complexity of the task facing the designers.
4. Occupants are more likely to feel thermally comfortable if they consider themselves to be in control of their environment. Therefore, designers should consider this carefully as it can have a great psychological effect. For example, if windows can be opened then the occupants will feel more in control than if they are sealed shut.
5. Perhaps occupant thermal comfort can be increased if the occupants are educated on the systems operating within the building. They should be encouraged to make use of natural methods and the systems should be explained to them. A better understanding of what is occurring may prevent people from turning on fans when too hot or radiators when too cold.

It is clear that occupant thermal comfort is a complex issue but one which must be fully considered as buildings are built for people and thus their comfort is of primary importance. If occupants are comfortable, productivity will be high and everyone will be satisfied. Therefore, every effort must be made to ensure buildings are thermally comfortable.
Stuart Gadsden, Environmental Engineering, University of Strathclyde, 1997.