Save Energy — Dehumidifiers

Dehumidifiers can be very helpful in reducing the humidity in your home. During the summer, especially in rainy locations, the humidity can be very uncomfortable. You may have the inclination to turn down your thermostat. This may reduce the humidity but it runs your air conditioner more. While it uses energy a dehumidifier may provide a net energy savings.

Your Home Energy Living Plan

  • Operate only when necessary
  • Consider an Energy Star qualified dehumidifier when buying a new unit.
Impact of Your Energy Saving Actions

Dehumidifiers can use a significant amount of energy over time. Rampant and constant use will use much energy.

How Energy is Lost

The human body cools itself by evaporating sweat off of the skin. It takes energy to evaporate water. When the liquid sweat evaporates, the energy is taken from your skin. The amount of evaporation depends on the moisture level of the air. More specifically how close the moisture level is to the maximum. Air has a limit on how much air vapor it can hold. When air is near this limit, then little water or sweat can evaporate. The measure to show how close air is to this maximum is called relative humidity. Relative humidity is a percent, air at 100% relative humidity can not hold any more water vapor. Your sweat will not evaporate if the air is at 100% relative humidity. The relative term comes from the fact that it is dependant on temperature. Colder air holds less water vapor. Relative humidity has no meaning unless the air temperature is known.

When the air is high in relative humidity, then you feel warmer due to the reduced ability to evaporate sweat. When this happens your body will sweat more, making you feel even more uncomfortable. If the air is dryer, then you can be comfortable with a higher temperature setting on your thermostat.

A dehumidifier reduces the relative humidity. Unfortunately it uses the same process as an air conditioner to cool air. Energy use by a dehumidifier can be as high as the reduction in air conditioning.

Dehumidifier Characteristics

As your air conditioner cools the air, it can reach saturation (maximum amount of water vapor). To further cool the air, then water must condense. This is the source of water in the drain under your cooling coil. Energy is released by the condensing water. This energy is picked up by your cooling coil. This reduces the ability of the cooling coil to lower the air temperature. In essence energy is wasted as water from the coil goes down the drain.

A cooling coil (in most parts of the country) will cool and dehumidify the air. In many cases this is enough dehumidification to be comfortable. However, during high humid days the cooling coil is pulling more moisture out of the air and its temperature is higher. That is why on rainy days the air conditioner seams to work harder. A dehumidifier can reduce the moisture in your home, reducing the humidity load on the cooling coil.

The use of a dehumidifier can help with comfort, but may not save energy. This is because the dehumidifier uses a cooling coil to dry the air. It may use more energy to heat the air back up to the room temperature. A dehumidifier is a refrigeration system optimized for water vapor removal instead of cooling.

In areas like basements, that have high humidity which could result in mold or mildew is a good use of a dehumidifier. It is being used to protect your home, so the energy use can be justified.

Energy Solutions Explained

Since dehumidifiers use energy, there use should be evaluated carefully.

When buying a dehumidifier, consider an Energy Star qualified unit.

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