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NEW DELHI: The government has issued guidelines addressing concerns associated with air conditioning (AC) and ventilation to control the spread of coronavirus in residences, work spaces and healthcare facilities.According to the guidelines compiled by the Indian Society of Heating Refrigerating and Air Conditioner Engineers (ISHRAE), a temperature between 24-30 degree centigrade should be maintained while operating ACs at home. While, a relative humidity level of 40 per cent to 70 per cent is considered to be the most suitable as it decreases problems from pathogens.Here are a few air conditioning and ventilation guidelines that must be followed.Set room temperature between 24°C and 30°C and maintain relative humidity between 40 per cent and 70 per cent: In humid climates set temperature closer to 24°C for de humidification and in dry climates closer to or at 30°C and use fans to increase air movement.In dry climates, do not allow relative humidity to fall below 40%. Water evaporating from a pan kept in the room will increase humidity if it falls below 40%.Recirculation of cool air by room air conditioners, must be accompanied by outdoor air intake through slightly open windows and exhaust by natural exfiltration.Fresh air intake through a fan filter unit will prevent outdoor dust entry and exhaust through kitchen and toilet exhaust fans kept operational.Evaporative coolers must draw air from outside to ensure good ventilation.Evaporative cooler tanks must be kept clean and disinfected and the water drained and refilled frequently.Windows must be kept open to release humid air. Portable evaporative coolers that do not draw outdoor air are not recommended, since their cooling reduces with humidity rising inside the space.Fans should be operated with windows kept partly open.If an exhaust fan is located at a nearby location then it must be kept running to exhaust air for better ventilation.The study of the transmission of Covid-19 virus in 100 cities of China indicates that high temperature and high humidity significantly reduce the transmission of influenza.Low temperatures (7–8 °C) have been observed to be optimal for the survival of airborne influenza. However, the virus survival decreases progressively at moderate temperatures (20.5–24 °C) and further decreases at higher temperatures of greater than 30 °C . The SARS-CoV-2 has been found highly stable on surfaces for 14 days at 4 °C; one day at 37 °C and 30 minutes at 56 °C were needed to inactivate the virus.The guidelines further state that the best action to limit risk of Covid-19 infection by air is to ventilate indoor environments with outdoor air as much as possible.Mechanical ventilation systems and air conditioning systems, which provide ventilation, can perform this function more effectively than simply opening the windows, because they improve the quality of the outdoor air with filtration.