The Contents and Make Up of Air and Humidity
Humidity is important to our home and health and it is important to maintain the correct humidity in our homes and workplaces for our health. What is humidity? Humidity is simply little water droplets in the air. Cold air is nearly saturated with these little water droplets because the contents of cold air allow the air to hold more water droplets or humidity. As air is heated it expands and holds less humidity. When you heat the air in your home using a furnace, boiler, or heat pump this air expands and becomes drier. It is air with less humidity relatively speaking before it was heated and compared to the outside air. Air that is 30° F with 80% humidity will only be 15% humidity at 75° F. That is a big difference in humidity levels in the home after the air is heated. Granted, you are not heating air from 30° F to 75° F with your furnace. Depending on the set up of your thermostat and heating system you are most likely heating air that is 68° F to around 70° F to 75° F depending on the thermostat setting. The point is unless you have a source providing humidity to the air stream you are simply reheating dry air from inside the structure. There will be minimal infiltration humidity but the infiltration humidity will never be enough to bring the humidity levels up to healthy levels inside the structure for the inhabitants, plants, and furniture.
The Study of Psycrometrics
Yes, that is psycrometrics and it has nothing to do with psychology. It is the study of air and its properties. It is used in HVAC by HVAC technicians and HVAC engineers to determine the contents and make up of air. The HVAC industry uses Psychrometric Charts to plot the contents and make up of air. Using the Psychrometric Chart a technician or engineer can determine the relative humidity, enthalpy value, dry-bulb temperature, wet-bulb temperature, dew point and vapor pressure if they have a few of the listed values. With this data engineers and technicians can solve problems or assign values and set points. For example, an economizer system that is controlled by the building automation system can be controlled by an enthalpy value. This value associated with an And Gate will only allow the economizer to open under certain conditions that will allow the mechanical cooling systems to shut down and take in free cooling from outside the structure. The temperature, humidity, and all the contents and make up of the air will be optimum for free cooling using the economizer. By knowing the contents and make up of air one can set up HVAC systems to work better and one can also use the data provided by knowing the contents and make up of air to troubleshoot problems with HVAC and building systems.
Indoor Air Quality and Humidity
It is important to maintain correct levels of humidity in the home for many reasons. Comfort is on factor, indoor air quality is another factor, and saving energy is another factor. All three are related in one way or another but each are separate factors. If you reside in the northern climate regions where the average temperatures are less than 20° F you want the indoor humidity to be relative to outside air humidity. Temperatures about 20° F the recommended relative humidity inside the home or business is 35% to 45%. The construction of the home or business will also determine the amount of humidity. If you have vapor barriers and good tight windows and doors you need a good mechanical ventilation system. Humidity levels can rise above 60% causing excessive moisture inside the structure which will lead to mold, mildew, and possible water damage. Make sure you have a good mechanical ventilation system inside your structure to avoid moisture issues. Bathroom ventilation fans, hood fans over stoves, and other type of exhaust fans inside the structure pull out excessive moisture when cooking or showering. If you have this problem it most likely shows up in the form of mold growth inside closets, kitchens, bathrooms, and ceilings. Additionally, if you have excessive moisture problems your windows will frequently fog or have a lot of moisture on the windows.
Low humidity levels cause problems also. Static electricity, dry skin, dry sinuses, and other health problems including increased flu illness can occur. Additionally, low humidity levels cause problems with wood inside the home. To test for low humidity levels in the home make a glass of ice water and set it somewhere away from the kitchen or bathroom. If after five minutes water droplets do not form on the outside of the glass then you have a problem with low humidity levels in your house and you need to get a humidifier. If your structure is suffering from low humidity levels you will also feel cooler resulting in a desire to turn the thermostat up. Therefore adding a humidifier to the HVAC system will cause you to turn the thermostat down. The correct levels of humidity in your home can increase comfort, save you money on your utility bills, and make you healthier.
Warm Air Expands
Remember that your furnace or heat pump DOES NOT remove the moisture from the air. The furnace or heat pump simply makes the air warmer and warmer air expands making the percentage of moisture in the air less than when it was cold. Relative Humidity is the amount of water vapor percentage that is in a given amount of air at a given temperature. Air is considered to be saturated with moisture when it reaches 100% relative humidity however you can quickly change the 100% relative humidity in air by increasing its temperature. Decrease the temperature and the moisture condenses from the air or it can be considered rain. When you heat the air you increase its volume and without a humidifier adding moisture to the air you are decreasing relative humidity. Adding a whole house humidifier to your home will always help maintain higher levels of moisture in the house and that will counter all the problems associated with low humidity levels.