Moisture Management for Energy Efficiency and Comfort
Technology Snapshot & Benefits:
You can increase comfort and save money by mindfully
managing the moisture content of the air in your home. Humans are most
comfortable at a relative humidity of 50%, plus or minus 10%. Relative humidity
is the amount of moisture that air contains relative to the maximum amount that
it could contain (at any given temperature and pressure). Two separate
strategies are required: one for summer and one for winter.
In the winter, air inside the house is cycled repeatedly past heating elements
in your heating system, where it gets drier and drier. As room air dries,
you will increasingly experience dry and itchy skin, dry eyes and mouth, chapped
hands, static electricity and a wide range of other discomforts. From an energy
efficiency perspective, the dry air increases the rate of evaporation of body
moisture from your skin and this evaporation makes you feel chilled. A normal
reaction is to turn up the heat as you attempt to keep warm. The net result is
that you will burn extra fuel to maintain a higher room temperature and the air
will become progressively drier. In the winter, your strategy is to add
moisture to the air.
In summer, the situation is generally reversed and your strategy is to reduce
relative humidity of the room air. As humidity levels increase above about 50%,
evaporation from your skin is reduced. Lower evaporation rates deprive your
body of its normal cooling mechanism and you feel warm. A typical reaction is
to turn down the thermostat of your air conditioning in an attempt to keep cool.
The net result is that you will burn extra fuel and money to maintain a lower
room temperature than necessary, compared to the amount of cooling that is
needed if relative humidity is maintained at comfortable levels.
Studies have shown that when humidity is maintained at around 50% in a living
space, air conditioner thermostats may be set as much as 5 to 7 degrees (F)
warmer while providing the same level of comfort to occupants. Since most air
conditioners are electric, and most electricity is produced in central-station
power-plants, energy and pollution savings from reduced air conditioning are
huge. This is because the electricity that arrives at your electric outlet is
produced and delivered at an overall fuel efficiency of about 30%. Turning up
the thermostat of your air conditioner has a dramatic and positive effect on your
electric bill and on summer pollution levels. To do this and maintain (or
improve) comfort, you must control relative humidity of the room air.
Estimated Cost Savings:
Economic savings achieved by moisture control are in
direct proportion to how much less you run your furnace in the winter and air
conditioner in the summer. Costs to achieve moisture control vary with the
level of sophistication of the equipment. At the inexpensive end are simple
operational changes that cost you nearly nothing. An example is the practice of
venting a clothes dryer through a lint filter to the interior of a building
rather than the exterior. This technique captures productively both the
moisture in the clothing and the heat generated by the clothes dryer. In
addition, a new generation of rechargeable desiccant technologies is emerging
that provide low-cost means of reducing moisture in buildings during the summer
months. Depending upon the level of sophistication of equipment and controls,
you may expect savings to your utility bills in the range of 10-30%.
Moisture control is not fully appreciated by the
building industry. Often, equipment is purposefully oversized as a way of
providing performance during periods of peak demand. By definition, peaks occur
infrequently and the equipment is oversized for the balance of the time,
requiring more energy than necessary to operate. A primary issue facing you in
your quest to achieve moisture control in buildings is finding an installer or
contractor that understands techniques that take into consideration the lifetime
operating costs of equipment. An
installer or builder is usually sensitive to "first cost" considerations, but
seldom appreciates the full cost of operation over the useful lifetime of the
equipment. As a homeowner, you see not only the initial cost but the full
operating cost as well.
Availability of the most energy-efficient equipment may be an issue. Sometimes
the best equipment is "in demand" and this can mean that discounts are either
unavailable or limited.
Buildings in northern
climates are more likely to benefit from humidification in winter. Buildings in
southern climates are more likely to benefit from de-humidification in summer.
Some systems can achieve both goals, but traditionally both humidification and
de-humidification functions have not been incorporated in the same piece of
equipment. Other regional issues involve supply, delivery, and installation
(Getting It Done):
Be sure to price shop and to get two or three (or more) prices. Inquire about
installation and removal of any older equipment that you may have in your
building. For any air conditioning or refrigeration unit, be sure that the
refrigerant will be removed and recycled responsibly. Refrigerants are very
potent greenhouse gases and must be captured and contained. Shopping for price
and availability will give you perspective on the true costs of equipment and
installation in your area.
Videos On This Topic:
Home Inspection for
Moisture (2:13) - Expert Real Estate Tips -
Jamie Dunsing walks viewers through different areas to look for water leakage
and how it is important to get your home inspected for moisture problems to
ensure it is functioning at its best.
What is a Vapor Retarder?
(1:19) - Johns Manville -
are installed along with insulation to help prevent moisture build up that
causes mold and mildew. In this video, find out when to use a vapor retarder and
how it can help protect your home from harmful moisture infiltration.
More Information On This Topic:
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