The quiet revolution in air conditioning

The quiet revolution in air conditioning

More than 100 years after the founding of the American Society of Heating and Ventilating Engineers, there is a quiet revolution underway in air conditioning. Desiccant dehumidification has been the focus of product innovation and has become the foundation of one of the fastest-growing segments of our industry.

by Mike McDonald, Munters Corp.

Ten years ago, there were four manufacturers of desiccant dehumidification systems. Now there are twice that many. Dehumidifier shipments have been expanding at more than triple the 5 percent annual growth rate of the overall air conditioning industry, according to a 1997 report from research concern Frost & Sullivan (Mountain View, CA), titled “U.S. Non-Residential HVAC Equipment Market Report.” Several factors explain this startling expansion of dehumidification, beginning with strong demand from industrial and commercial building owners.

In the late 1990s, new codes mandate higher volumes of outside air to ensure the quality of indoor air. Outside air brings heating and cooling loads, but it has a far greater effect on the dehumidification load. In Boston, for example, the cooling load for every cubic foot of air brought into a cleanroom held at 72 degrees Fahrenheit, 40 percent RH is 0.5 ton-hours per year. In contrast, the dehumidification load is 5.0 ton-hours — 10 times larger than the cooling load. The numbers are far larger in Puerto Rico, and the dehumidification load remains more than 5 times larger than the cooling requirement.

Removing this moisture load is expensive, particularly for cleanrooms with their stringent requirement for fresh air and their frequent need to control humidity at 35 to 45 percent RH. Desiccant systems have become popular because they remove moisture with low-cost natural gas instead of with electrical power purchased at high, on-peak prices. For example, a large manufacturer of hard disks operating over 4,000 square feet of cleanroom space in San Jose, CA, has switched from cool-reheat systems to desiccant-assisted systems throughout the facility. The low cost of gas to reactivate the desiccant wheels saved more than $213,000 per year compared to the cost of electrical power needed to over-chill the air for dehumidification.

Cooling less, dehumidifying more

Such high loads from outside air were not present during the 1970s and 1980s. Through those decades, heating, ventilation and air conditioning (HVAC) equipment was redesigned and optimized for cooling. But the practical effect of high cooling efficiency was to reduce dehumidification capacity to nearly zero. Modern cooling units now remove heat so quickly (and are so often oversized) that they satisfy a thermostat within a few minutes. Their compressors shut off, and no dehumidification occurs.

For example, a recent study of a large retail store in Nebraska showed that although the store had a total of 398 tons of cooling installed, the actual peak load never rose above 121 tons when a desiccant system controlled humidity. Removing that excess cooling capacity allows the owner to save construction costs while improving comfort and lowering operating costs.

In retrospect, it is not surprising that equipment manufacturers had not been designing for humidity loads, because until 1997, the industry`s fundamental weather design data had been focused on temperature rather than moisture.

Better engineering design data

In 1997, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) published a new volume of its Handbook of Fundamentals. That edition contains peak weather extremes for moisture — for the first time in the 100-year history of the society. New ASHRAE research shows that moisture is highest when temperatures are moderate — during and after rainstorms. An example from Atlanta shows how significant this difference can be. When the temperature peaks at 96 degrees Fahrenheit in Atlanta, the average moisture is 100 gr/lb. But the true peak moisture is 133 gr/lb. If a cleanroom is maintained at 48 gr/lb (72 degrees, 40 percent RH), that means the ventilation moisture load is 63 percent larger at the peak moisture condition compared to the peak temperature condition. Using the 1997 ASHRAE Handbook of Fundamentals, engineers are designing better systems for controlling moisture, which has helped encourage the use of desiccant dehumidifiers.

No more overcooled buildings

The quiet revolution of the air conditioning industry is being fueled by better and cheaper dehumidifiers, from twice as many manufacturers as in the past. Adding to the momentum, better weather data now allows equal precision for humidity and temperature control, and low-cost natural gas makes desiccant operating costs attractively low.

Cleanroom managers will be able to track the progress of this revolution by their own personal experiences. When you feel cold or clammy in the summertime, you`re in a “pre-revolutionary” building — one with excess cooling capacity and poor dehumidification. When you are comfortable, it`s because cooling and dehumidification equipment is well-matched to the loads. Behind the scenes, this comfort will often be made possible by a desiccant dehumidifier controlling humidity independent of temperature. In other words… “Come the revolution — we`ll ALL be comfortable!”

Mike McDonald is president and CEO of Munters USA in Amesbury, MA, an ISO 9000-certified company that designs and produces equipment for humidification, dehumidification and cleanroom solvent emission control, and provides rapid-response drying services for temporary industrial installations and restoration after floods, fires and disasters. Prior to joining Munters, McDonald was vice president and general manager of Western Hemisphere operations for industrial pump manufacturer REDA. His earlier experience included three years as vice president of worldwide manufacturing; eight years of managing domestic and international branch plant operations; and four years at the company`s headquarters in England, managing sales, service and distribution in Europe, the Middle East and Africa. McDonald holds a BA from Drury College in Springfield, MO, and a MBA from Northwestern University in Chicago.


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