According to ASHRAE standards, the recommended indoor temperature ranges termed ‘comfortable’ by occupants are 22.8 to 26.1°C in the summer and 20.0 to 23.6°C in the winter. Temperatures should not fluctuate more than 1.1 °C within 15 minutes, nor change more than 2.2 °C within 1 hour. This has a direct impact on perceived comfort, concentration and productivity of the building’s occupants.
It also found that at elevated air speeds above 0.2 m/s (39 feet/min), the upper limit of the temperature range can be relaxed, as employees still find the air quality bearable.
Too high relative humidity can contribute to the growth and spread of biological contaminants, and stimulate increased perspiration, while too low a value causes increased discomfort and drying of skin and mucous membranes. As per ASHRAE standards, indoor humidity levels to be maintained between 30-65% for optimum comfort.
Moisture collects in the condensate drain pans of air handling units, filters, duct-work downstream of the cooling coil, and the drain from indoor units. This is where fungal growth is commonly found. Microorganisms causing tuberculosis and legionellosis can be transmitted by air-conditioning systems, particularly when they are poorly maintained or when the number of air exchanges per hour in a room is insufficient. In health facilities where there is a high concentration of infectious patients, evidence shows that poorly ventilated buildings have higher risks of infectious disease transmission for patients, workers, and visitors.
The most important factor influencing indoor pollution is the level of outdoor air pollution. Construction material used in Indian buildings are usually not airtight; this creates a negative pressure inside the building. In a process known as infiltration, outdoor air flows into the building through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors, bringing in moisture and pollutants.
According to India’s Central Building Research Institute, Indians are more adaptive to high temperatures during summer, have a higher tolerance for humidity, and comfortable if the air flow velocity inside a building is on the higher side. By using an adaptive temperature control method and setting the thermostat to have a floating set point rather than a fixed one, a 15% energy saving potential can be tapped.
The Indian Society of Heating, Refrigeration and Air-Conditioning Engineers (ISHRAE) recommends that rather than a rigid temperature range, operative and effective temperatures be used for controlling indoor quality, taking into account the combined effect of air temperature, humidity, and the activity and clothing of the occupants. ISHRAE recommends that both high and low humidity need to be avoided.
Facility managers need to regularly measure the levels of various IAQ parameters to ensure the health, safety and work efficiency of the building’s occupants. The IAQ monitoring must incorporate three major areas of investigation: environmental measurements, building and ventilation characterization, and an occupant questionnaire.
The monitoring protocol should also include the schedule of measurements, the specifications of the measurement equipment’, how to select the representative spaces in the building for monitoring, and how to select the sampling sites in each space. ASHRAE recommends that monitoring be done at least three location inside a building. At least 5% of rooms in offices, 10% of classrooms in educational institutions, and 15% of rooms in a healthcare facility should be selected for monitoring IQA.
IQA parameters need to be measured over a period of time. Short time sampling/monitoring (< 15 min) is chosen for investigating acute effects, while the investigation of chronic effects is done by carrying out sampling/monitoring for longer duration of several hours or even days.
For the Indian scenario, the monitoring durations proposed are:
• Schools / colleges /educational institution: two working hours)
• Offices: two working hours
• Health care units: morning and evening, one hour in each case
• Restaurants: two hours in the evening
• Museums/Historical Buildings: two hours during visiting hours)
• Industrial establishments: short time or long time monitoring during working hours
The sampling duration must represent both ‘peak’ exposure and ‘average’ exposure indoors. For chemical characterization of pollutants/microorganisms, long duration monitoring is required.
Management of Indoor Air Quality:
• Routinely cleaning office spaces and common areas by a vacuum cleaner with High-Efficiency Particulate Air (HEPA) filter
• Maintaining and regularly cleaning the building heating, ventilation, and air conditioning (HVAC) system
• Properly storing cleaning materials and chemicals that are used in the workplace
• Avoiding the use of harmful chemicals that emit volatile organic compounds
• Maintaining air purifiers and ensuring regular cleaning and replacement of filters
• Air curtains installed at main entry/exit doors of the building to prevent entry of outside air when outside doors are open
• Silicon sealing of all window gaps and installation of door dust brush underneath the doors, to prevent dust from coming into the building
• Installation of air pollution monitoring devices for improved, regular monitoring of the indoor air quality
• Wet mopping and dusting is preferable to sweeping or vacuuming, as sweeping and vacuuming can stir up additional dust and particles. However, vacuums with a High-Efficiency Particulate Air (HEPA) filter can be used.
Compiled by Mrigank Warrier