That’s because it is a key element in overall indoor environmental
quality, with high humidity closely linked to mold growth, dust mites,
and other sources of indoor allergens. High humidity can also cause
deterioration of the building itself. Excessive indoor humidity is
in residential and commercial buildings.
The incidence of allergies
and asthma is well on the rise, as people spend more time indoors.
Reaction to dust mite allergens figures prominently
in this increase, and the link between high humidity, even for a modest
period of the year, and dust mite proliferation is well documented.
However, when the relative humidity is consistently maintained below
studies show that dust mite populations virtually disappear within
a few months. Similar observations have been made about various types
another potentially potent source of allergens and toxins.
air-conditioning equipment has a fixed proportion of sensible and latent
cooling capacity, denoted as the sensible heat ratio (SHR),
the ratio of the sensible cooling capacity to the total cooling capacity.
The remaining portion is the latent or dehumidification capacity.
The trend toward more efficient buildings (e.g., the evolution of ASHRAE
90.1) has tended to reduce sensible loads and equipment size, but
loads have remained either unaffected or have even increased. When
the latent load is higher than the latent capacity of the air-conditioner,
the indoor relative humidity rises. This also occurs in the spring
fall when humidity loads are high but the need for cooling is limited,
so equipment run times are short.
The ideal range for indoor relative
humidity (RH) is 30 to 50 percent. Below 30 percent, many people experience
dry skin, irritated respiratory
passages, and other problems such as static electricity build-up
or shrinkage of building materials. Fifty-percent RH is usually
mold and dust mite growth. Thirty to 50 percent RH is also the
ideal range for thermal comfort, with the air dry enough to enable normal
control mechanisms (sweating and evaporative cooling) to function
Given these issues and the potential benefits, it is
remarkable how little is actually being done about active humidity
control. It is
not a technology
problem; a wide array of equipment options exist that can control
humidity, and they are available in a range of capacities. Solutions
air-conditioners with enhanced (and controllable) latent capacity,
enthalpy recovery ventilation
systems, refrigeration-cycle-based central dehumidifiers, and
desiccant dehumidifiers. However, none of these account for a significant
portion of either residential or commercial HVAC equipment sales.
severity of humidity-related health effects, it would seem that
a major market
opportunity is being missed by the appliance and HVAC industries.
only speculating, but several factors could account for the “disconnect” between
an apparently urgent need for effective year-round humidity control
and widespread adoption of available solutions:
Education of the potential
buyer: Most people are unaware of equipment
options to control humidity, even if they are aware of the need.
and cost of tailoring the solution to the situation: Diagnosing
the different causes of excessive humidity and specifying the best,
most cost-effective solution is a complex process.
The “chicken and egg” dilemma
of low-volume production and high cost: Sales growth is needed to bring
economies of scale into play
to lower prices. If priced moderately, a dehumidifier could easily be
added to a conventional central air-conditioning system.
Making the right
products available: A good example of limited product attractiveness
is the one mass-produced product in this category—the
room dehumidifier. They are inexpensive and reliable, but still sell
in modest numbers. They don’t yet fully address condensate-handling
These are only a few of the factors inhibiting widespread humidity
control solutions. Appliance and HVAC equipment manufacturers are in
a great position,
by virtue of their market knowledge, reputation, brand awareness, and
presence, to turn a developing need into a major future business. As
grows and consumers demand better indoor-air quality, significant opportunities
exist for those organizations that can produce products and related
services that truly serve the customer. Is this an option for your company?