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issue: November 2004 APPLIANCE Magazine

From The Top
Good Humidity Could Mean Good Business

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Dick Topping, director of Appliance Research, TIAX, LLC

While the value of interior humidity control has long been understood, it has recently been attracting more attention than ever.

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 commonplace both 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 50 percent, studies show that dust mite populations virtually disappear within a few months. Similar observations have been made about various types of mold, another potentially potent source of allergens and toxins.

Conventional 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 standard 90.1) has tended to reduce sensible loads and equipment size, but latent 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 and 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 low enough to prevent 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 body temperature control mechanisms (sweating and evaporative cooling) to function effectively.

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 include 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. Given the severity of humidity-related health effects, it would seem that a major market opportunity is being missed by the appliance and HVAC industries.

I am 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.

Complexity 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 very well.

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 public awareness 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?

Dick Topping
Dick Topping is director of Appliance Research at TIAX LLC (www.tiaxll.com). He can be reached by phone at 617/498-6058, by fax at 617/498-7206, or e-mail at Topping.R@tiaxllc.com. From the Top appears bimonthly in APPLIANCE ENGINEER®.


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