Ingenieur Vol 77 Jan-Mar 2019 ingenieur 2019 Jan-March | Page 35

Consider The Following Case Study: In a survey of 100 office buildings, 23% of office workers experienced frequent symptoms of SBS such as respiratory ailments, allergies and asthma. The impact was usually hidden in sick days, medical costs and lower productivity, but the economic impact is enormous, with an estimated decrease in productivity around 2% nationwide, resulting in an annual cost of approximately USD60 billion. Source: Emerging Energy-Efficient Technology in Promoting Workplace Productivity and Health, a report by Lawrence Berkeley National Laboratory Figure 1: Outside air load - Mumbai Outdoor Air Requirements For Ventilation Of Air Conditioned Spaces The LEED standard states to “Increase breathing zone outdoor air ventilation rates to all occupied spaces by at least 30% above the minimum rates required by ASHRAE Standard 62.1-2007 as determined by EQ Prerequisite 1.” This increased amount of ventilation has definitely solved IAQ related problems, but the inability to maintain the right humidity using our HVAC systems has led to other problems. Mould and mildew, which are caused by lack of humidity control are a serious dilemma in themselves. The question is: have we traded one problem for another? IAQ & Relative Humidity (RH) Control The benefits of increased ventilation have been clearly established and absorbed by the HVAC industry at large. The health of occupants is of great concern and more and more systems are being designed with the right amount of outside air. The outside air however, while solving this problem, poses a great challenge for the HVAC system. The saviour of IAQ brings along with it a quandary of high latent load, cornering the HVAC equipment and resulting in high levels of RH inside. Let us examine the load profile of outside air in a tropical country like ours. Figure 1 shows the outside air for the city of Mumbai, which is similar to Kuala Lumpur. The curve defines the load of outside air in terms of the sensible and latent load in tonnes for the entire year. Clearly one can see that latent load of the city is quite high and is around 78% of the cumulative fresh air load. Similarly, if one studies the profile of the cumulative loads (i.e. cooling and dehumidification only) for major cities in Asia, one can see that the latent load component of fresh air is quite high (ranges between 60% and 85%). With outside air bringing in high amounts of latent energy, RH management becomes difficult. The HVAC fraternity received a wakeup call for IAQ and RH control when the bacteria spread by a hotel air conditioning system killed 34 people and afflicted more than 200 people at an American Regional Convention in Philadelphia around 20 years ago. Lack of RH control leads to growth of mould and mildew which leads to various health related issues. Mould releases tiny spores to reproduce. These spores then waft through the indoor air and start developing in damp areas. They can cause several problems like rashes, asthma, runny noses and respiratory problems including serious diseases like hypersensitivity pneumonitis. 33