Responsible Refrigeration Article 59
While I have been writing about being responsible when working on refrigeration systems and being registered as an Authorised Refrigeration Gas Practitioner we have ignored 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. When there is no new fresh outside air coming into a room there is a perception of staleness in the air.
The top five air quality problems identified and 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. A sensitivity to these pollutants listed above and the common allergies. There can also be tiredness and fatigue with headaches. The adverse effects of these symptoms result in poor work performance in the work place 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 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 has 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 not solving the 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 type of windows and door are an important consideration 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 building 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 conditioner in home and small offices, shops and work places.
The quantity of outside air introduced through a ventilation system must be based on dilution of odours, pollutants. It must be remembered that must room air conditioners especially split units do not has a fresh air feature. Therefore one has to consider a separate outdoor ventilation system with filters. Remember that the more air introduced the more 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.
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