Real World Applications

Engineered Systems, Oct, 1999

Case studies prove that natural gas cooling works. The following three examples -- highlighting desiccant, absorption, and engine-driven systems in action -- are just few of hundreds that are currently available. They show why customers choose gas cooling and equipment; key equipment features, reliability factors, and installation mechanics; and, where available, the projected and accrued energy/utility savings.

Keeping patients and medical staff cool and hospital facilities germ-free is critical at Willis-Knighton Medical Center. A steam-fired desiccant system from Munters DryCool provides the hospital with the flexible temperature and humidity control it needs.

Operating rooms at Willis-Knighton Medical Center are a hub of activity. Patients, doctors, nurses and support staff are constantly moving in and out of eight operating suites. With machinery and personnel always on the go, air quality control requires constant attention. Hospital administrators solved many problems by installing a Munters DryCool MedAire System in July of 1994.

Surgical staffs nationwide are now required to wear layers of heat-retaining but protective clothing to avoid blood-borne pathogens. Operating rooms also need to be environmentally controlled to reduce the formation of germs and to keep doctors and staff comfortably cool to perform their work. To meet these demands, hospital officials pipe in only high-quality, 100% outside air.

The problem with using outside air is that it needs to be cooled and dehumidified to meet hospital standards. "We needed to better control the level of humidity in the operating rooms," says Jerry Ivey, P.E., director of hospital facilities. "Control of the humidity level required for our operating rooms was much more difficult with the previous system."

Natural gas equipment solved the hospital's problem. "We have very high moisture levels in the air down here, hut the desiccant system effectively meets staff and facility standards," says Ivey. The MedAire MD-30 supplies dry make-up air via desiccant dehumidification to the operating rooms. The 3,600-sq.ft. operating area is now maintained at 680 F and 45% relative humidity year-round.

"Another advantage to low levels of temperature and humidity can't be seen," says Ken Crooks, Munters DryCool sales engineer. "Warm, moist areas are a breeding ground for many germs floating in and out of hospitals. When temperature and humidity are kept at a constant level, germ growth is virtually eliminated."

After several weather-related power outages crippled its cooling plant, Doylestown Hospital declared zero tolerance on HVAC failures. Chief Operating Officer James Brownlow promptly approved a project design "that would prevent [power] interruptions from ever occurring again."

"The hospital wanted a redundant system," recalls Account Manager Mark King of PECO Energy, the local energy provider. An energy and cost analysis by PECO and Delaware Valley York (DVY) Inc. a Horsham, PA-based HVAC contractor, revealed that a cogeneration plant would not recover enough thermal energy to be cost-effective. Instead, PECO and DVY recommended peak-shaving equipment to prevent electric demand from rising..

In addition, "the hospital needed to comply with new building code revisions," says DVY project manager Bill Zador. "At the same time, they decided to make changes to improve efficiency and drive costs down."

Emergency generators were relocated for code compliance and the chiller plant was reconfigured in the hospital's new plant design. A natural gas-driven peak-shave generator was added to power existing chiller systems, and to eliminate PECO's peak demand service and ratchet charges. Zador explains that the generator, model G3516 Gen Set (750 kW), manufactured by Caterpillar Inc., automatically operates when the chiller systems are required. "A parallel path of power has been introduced," Zador adds.

A 600-ton York(R) natural gas absorption chiller now provides the hospital's primary cooling. It was installed by DVY two years earlier to supplement cooling after the hospital was enlarged.

As the Design/Build performance contractor, DVY monitors the DDC (direct digital control) system, analyzes the hospital's energy bills, and tracks savings. The generator has reduced peak summer demand by 700 kW. For the first six months after the peak-shave generator came online in June 1997, Doylestown Hospital reduced its electrical consumption by 360,000 kWhs, resulting in a $49,000 savings. Payback from the Caterpillar generator is expected in six years.

The hospital's natural gas consumption is up 25%. To keep energy costs low, Doylestown buys gas at competitive rates from a private provider and takes advantage of PECO's low transportation gas service rates.

Plant Manager Joe Tursi states, "The new plant has run flawlessly and was the best selection, given the scope of our initial problem." Under increasing fire to cut costs and improve patient care, Doylestown Hospital has effectively met its challenges by taking advantage of efficient, low-cost natural gas.