Whole house dehumidifier – How it works
Probably the phrase I hate to hear the most in the daily weather forecast is “hot and humid.” The reason is that hot air can hold a lot of water and moisture in the air on a humid day is partly what makes you feel uncomfortable. I could get real technical here but what is important to know is that hot air can hold more moisture than cold air. When hot, humid air cools, water is released. This is why you see dew on the grass in the morning and water on your car’s windshield at night even when it has not rained.
On those days, one of my favorite things to do is to sit outside in the shade and enjoy a nice cold beverage. What you have surely noticed on these days is that water collects on the glass holding your cold drink. What is happening is that the coldness of the drink is cooling the air around the glass reducing the amount of water the air can hold. The water leaves the air, because the cool air cannot hold as much water, and condensates on the glass.
Now think about how good it feels on that same hot day when a breeze blows on your skin and you feel cooler. Now your body heat is heating the air increasing its ability to hold water. The air can hold more water and some of the sweat on your skin goes into the air. You feel cooler because the breeze is evaporating your sweat and cools you down in the process. Evaporation is the opposite of condensation.
A whole house dehumidifier uses these same principles to remove moisture from your home. A typical whole house dehumidifier looks like a box with a bucket attached to the back. A fan inside the dehumidifier draws air into the box where it passes over cold metal tubes. As the air cools the moisture in the air condenses on the cold pipes and drips into the bucket attached to the dehumidifier. The air passing out the back of the unit now contains less water.
If a whole house dehumidifier sounds like an air conditioner to you, your thinking is not far off. The basic process is the same except that the goal of the air conditioner is to cool the air whereas the goal of a dehumidifier is to dry the air. You may have noticed that the air in an air conditioned room is often dry and you often see water dripping from the air conditioner, which you now know is the result of condensation.
What is interesting is that the process of removing the water from the air heats the air a little bit (remember condensation is the opposite of evaporation and evaporation involves cooling). This is important because if the air were to stay cool after it left the dehumidifier it would not be able to collect more water from your home Some dehumidifiers have heating coils that warm the air as it leaves the unit for this exact purpose. The heating elements also prevent ice from building up on the cooling coils.
While whole house dehumidifiers that rely on cooling may be the most common, desiccant dehumidifiers also do a great job of keeping a space nice and dry. These dehumidifiers draw air in and pass it over a desiccant material such as silica gel. Desiccants absorb moisture in the same way as the little packets that you often find little in medicine bottles or electronic goods.
Whole house dehumidifiers vary in size and strength. Portable dehumidifiers are the kind that you usually see in home improvement stores. They are designed to be most effective in smaller spaces like a bedroom or kitchen. Restoration humidifiers are heavy-duty machines that can withstand harsh conditions they are usually used to repair heavy water damage. The largest models on the market, whole-house whole house dehumidifiers, usually are part of a home’s existing heating, ventilating and air conditioning (HVAC) system. Some manufacturers offer specially sized crawlspace dehumidifiers to address the humidity in storage areas and powerful dehumidifiers that are targeted toward the high humidity created by some indoor pools and spas.
Probably for most situations, a portable dehumidifier will do the job. Portable dehumidifiers are good for smaller sized rooms and larger ones will cover a larger room area. Just as too much humidity can be a problem, too little humidity can be a problem as well. Most dehumidifiers have a humidistat that is a sensor that detects the level of moisture in the air. A digital readout on the dehumidifier will tell you how much moisture is in the air and the dehumidifier will let you specify how dry you want the air to be. When the dehumidifier detects that the desired moisture level has been reached the dehumidifier will automatically turn itself off. This way you do not risk possible damage from drying out materials too much and you get a much more energy efficient dehumidification process.
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