Cool, calm and content
June 1st 2006

The aim of HVAC is to provide good air quality and a comfortable thermal environment that will contribute positively to health and productivity.

The challenge for engineers is to achieve this objective while keeping energy costs low. Steve Kirkwood of Seeley International (Europe) outlines the problems and suggests a solution

High thermal environments affect those working in both industrial and commercial surroundings. As outside temperatures increase, buildings with inadequate ventilation become unbearably hot and stuffy. The problem is compounded in premises into which direct sunlight can penetrate, causing the building to behave like a greenhouse. Not only does this affect staff morale, but it can lead to accidents, reduced productivity and absenteeism. According to studies carried out by the National Aeronautics and Space Administration in 1968, productivity falls 3.6% for every degree above 22C and 4.7% over 30C. With moderate heat stress, cognitive performance is also adversely affected, with mental performance showing a reduction of 2%.

How the body handles heat

If air temperature is as warm or warmer than the skin, blood brought to the body surface cannot lose its heat. The heart continues to pump blood to the body surface, the sweat glands release liquids containing electrolytes onto the surface of the skin and evaporation of the sweat becomes the principal means of maintaining a constant body temperature. Sweating does not cool the body unless the moisture is removed from the skin by evaporation. Under conditions of high humidity, evaporation is decreased and the body's efforts to maintain an acceptable temperature may be impaired.

With so much blood going to the external surface of the body, relatively less goes to the active muscles, the brain and other internal organs. Strength declines, fatigue occurs and alertness and mental capacity may be affected.

Workers who perform delicate or detailed work may find their accuracy suffering; others may find their comprehension and retention of information lowered.

Studies carried out by Langkilde, 1978, found the optimum industrial work temperature to be in the range 17 to 24C with an optimum temperature for arm movements of 21C. Studies carried out by the British Industrial Fatigue Board showed a lower output in hot/heavy industries in summer than in winter and more accidents when air temperature deviated from 20C.

Office environments

Poor air quality in the office can have an enormous economic impact on costs due to poor productivity. In a study carried out by Niemela et al (2001) it was found that the productivity of call centre workers decreased by 1.8% per C when the temperature was above 25C.

While heat has a debilitating effect on workers, refrigerative air conditioning necessitates sealing a building, resulting in reduced ventilation and poor indoor air quality. Gases, vapours, dusts, fibres, pollen, insect fragments, bacteria, fungi and their spores, plus viruses, all contribute to pollution and many of these pollutants can adversely affect the health of the building's occupants.

Natural ventilation is a safe, economic and healthy way of introducing cooling into the office environment. While opening windows on days when temperatures are below 20C can produce a cooling effect, when outside temperatures exceed 23C only warm air is introduced.

The Workplace (Health, Safety and Welfare) Regulations 1992 state that workplaces should be adequately ventilated. Clean air should be drawn from an outside source and circulated around the building. The ventilation system should remove and dilute warm humid air and provide air movement; this should create a sense of freshness without causing a draught. Humidity and ventilation should be maintained at levels that prevent discomfort or problems of sore eyes.

Evaporative cooling cools the air, producing a comfortable thermal environment and it adds water vapour to the air, increasing RH and relieving symptoms such as dry skin, nasal and throat membranes. It also reduces the vapour pressure deficit, which is the force that evaporates water from the environment.

Evaporative cooling reduces the temperature of the air by natural evaporation as it passes through a water saturated cooling pad. As water is evaporated, heat energy is lost from the air reducing its temperature. Evaporative cooling systems, such as Breezair, offer an automatic drain valve that keeps the system clean. It is pre-programmed to automatically drain stale water from the reservoir and replace it with fresh. When the Breezair machine is switched off, the drain valve will automatically empty the water from the reservoir after a pre-determined time, leaving it clean, dry and healthy. A weather-seal closes the air conditioning ducts to impede dust from entering the building and to minimise heat loss and cold draughts.

Industrial environments

Providing cooling for workers in industrial environments used to be regarded as financially prohibitive. Now, many companies see evaporative air conditioning systems as a cost effective solution. A fraction of the cost of air conditioning to install and run, evaporative cooling can be used to spot cool a specific area/areas or to cool an entire building. Providing decreases in temperatures of about 8C, evaporative cooling can have a marked effect on a company's bottom line, boosting productivity and reducing accidents and absenteeism.

What's more, it's not just in summer that cooling is needed. High temperatures affect workers throughout the year. Evaporative cooling provides a cost effective solution that helps to increase production, decrease downtime and improve workers' morale.

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