By Barney Richardson
While I have been writing about being responsible when working on refrigeration systems and being registered as an Authorised Refrigeration Gas Practitioner, I have not commented on the quality of the air in a home, shop or office.
Far too often when a room air conditioner is installed the user assumes that the windows can be closed to keep the cool air in and the hot air out. However, when there is no new fresh outside air coming into a room there is a perception of staleness in the air.
Air quality problems caused by pollutants are all contributors to indoor problems. These pollutants are:
- Moisture in the form of high humidity and moulds in damp walls;
- Bacteria and viruses;
- Organic compounds that are volatile and come from furnishings;
- Building materials and paint;
- Smoke;
- Pesticide sprays like doom and the common mosquito repellent sprays; and
- Dust particles.
- The common symptoms of poor air quality indoors are dryness of the nose, throat, and irritation of the eyes. There can be coughing and sneezing from a sinus congestion as well as sensitivity to the pollutants listed above and common allergies. There can also be tiredness and fatigue with headaches. The adverse effects of these symptoms result in poor work performance in the workplace and absenteeism.
Ventilation of a space is the process of bringing in fresh filtered air and displacing used air in a space to ensure the quality of indoor air. Filtered ventilation is used to remove the pollutants and odours, dust, bacteria and excess carbon dioxide. To avoid indoor air stagnation requires the continuous circulation of fresh air through a correctly sized ventilation system. Complaints about the freshness of indoor air have increased as buildings are built with greater tightness and low infiltration. Air quality has become a major discussion point with architects and HVAC design engineers. The trend to reduce energy usage has prompted designers to reduce the fresh air flow through the air conditioning system but this is not solving the air quality problem. A large proportion of the heat load can be the fresh air component of the system which has to be considered.
The factors that affect air quality are the tightness of the building mentioned above and what air infiltration can be expected. The types of windows and doors are important considerations when trying to determine infiltration. Wind pressure is a force on a building that further complicates any assessment because of the variable nature of wind. In tall buildings the ‘stack effect’ can be a serious factor. For our consideration here we can ignore the ‘stack effect’ if we are to concentrate on the application of room air conditioners in homes, small offices, shops and workplaces.
The quantity of outside air introduced through a ventilation system must be based on dilution of odours and pollutants. It must be remembered that most room air conditioners especially split units do not have a fresh air feature. Therefore, one has to consider a separate outdoor ventilation system with filters. Remember that the more air introduced, the more air is added to the heat load.
For minimum fresh air requirements, a good rule of thumb is 6 ℓ/s to 12 ℓ/s per person dependent on the activities in the in the space or alternatively 1.2 ℓ/s/m². Greater fresh air volumes per person have been promoted for smoking designated areas.
