Humidity – what is it, what are the benefits for living, and what solutions are there for improving indoor humidity?

Humidity is a fundamental element of our atmosphere, and can be defined simply as the amount of moisture in the air around us, and an atmospheric element detected by human skin as much as atmospheric temperature is. Humidity is represented as a percentage ‘relative’ to the temperature of the external air; this is because cooler air can hold less moisture than warmer air. Humidity in the home is highly impactful to health and wellbeing of occupants.

There are a number of reasons for regulating humidity in the home. A regulated, constant humidity contributes significantly to the comfort residents feel inside the home, and can significantly aid people living with certain medical conditions. Also, extensive private collections kept in a domestic environment need a regulated climate to protect their integral value and longevity of existence.

Humidity for residential comfort

Increasingly air-tight buildings (often through misguided efforts to maximise energy efficiency) with inadequate ventilation are being constructed, and have resulted in residential environments that are stale, humid, and much more susceptible to becoming contaminated. A healthy, maintained humidity level in a home would be between 40% and 60% RH (relative humidity), as the human body relies on lower humidity air to allow evaporation of sweat from the skin into the air. If the air is too dry then moisture from human skin is evaporated much quicker, leaving skin that is too dry. If the home is warm as well as dry then the skin is unable to cool itself adequately becoming less comfortable for occupants.Drier homes can also be caused by ongoing or excessive use of heating or air-conditioning systems, which allows pathogens in aerosol form to survive for longer, and aggravates and increases allergies, eczema and respiratory infections – as well as the symptoms of dry sinuses, nosebleeds and lip-cracking. Low humidity is especially a concern during winter, when cold outdoor air with a low moisture level is heated indoors, which can cause the relative humidity indoors to drop to as low as 20%. Homes can also become more humid often as a result of poor heating and ventilation, which creates a perfect environment for moulds, bacteria, dust mites and other adverse elements to grow and develop, resulting in respiratory problems and infections.

Dr Stephanie Taylor, MD, Infection Control Consultant at Harvard Medical School - "In light of the COVID-19 crisis, it is now more important than ever to listen to the evidence that shows optimum humidity can improve our indoor air quality and respiratory health"

Solutions to improve indoor humidity

Care is needed in designing air conditioning and mechanical ventilation systems to ensure that humidity control is considered. In cooling mode, air conditioning will decrease humidity because moisture from warm air condenses on the coils of the fan-coil units and is drained to outside. A correctly sized condenser and indoor fan-coil units with a correctly calculated temperature differential, coupled with inverter-controlled fan speed for even airflow over the coils is the best way to prevent humidity control issues.Some simple solutions to provide an environment that is both healthy and pleasant to live in include humidity sensors and hygrometers – this is a digital device that detects the relative humidity of indoor air. Humidifiers and dehumidifiers can also be utilised, either as standalone portable units, or permanent components of a wider ventilation system.A ventilation system such as mechanical heat recovery ventilation (MVHR) that serves an entire property can have additional humidifying or dehumidifying units installed ‘in-line’ to the ductwork system that delivers fresh air to the property. In-line humidifier units are most commonly controlled by humidity sensors mounted in the room or rooms they serve, or probes installed into the ventilation supply ductwork. Rooms then receive fresh air supply with a constant, accurate humidity level, providing a regulated, and most importantly comfortable, environment for living in.