Relative Humidity

Relative Humidity is the ratio of the actual moisture in the air compared to the total amount of moisture that can be held in the air at a specific temperature. This ratio is one of three aspects that impact indoor comfort in buildings. The other two are dry bulb temperature (as measure by a thermometer) and air flow. In this discussion we are going to focus on relative humidity.

In hotter temperatures, with higher humidity, the more difficulty humans have regulating normal body temperature. The added moisture in the air makes it harder for our bodies to get a cooling effect from evaporated perspiration off our skin to the surrounding air. As this relates to indoor comfort, one of the functions of a HVAC system is to remove moisture from the air as it is being cooled and distributed throughout the home. This makes sure the cooling effect as described above is felt. The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) recommends relative humidity levels between 25% and 60% for indoor comfort. Adjusting of the relative humidity by an amount as low as 5% can have significant impact on indoor comfort. For instance, lowering the relative humidity from 55% to 50% in the home can result in a higher temperature setting on the thermostat and still allow the homeowner to feel comfortable. This can lead to energy savings if thermostat settings can be left higher because relative humidity is lower in the home.

There are challenges when relative humidity gets too low such as static electricity, dry skin and in extreme cases bloody noses. For further reading on relative humidity, click on this ARTICLE from Building Science Corporation. If you have any questions regarding relative humidity or think your HVAC system might need to be checked out to make sure your indoor relative humidity is within acceptable range, please give us a call.