Dehumidification Restores Surgery Facility’s Vision for Accuracy

A newly constructed medical facility intended to provide corneal refractive (Lasik) surgery to patients to reduce their dependency on glasses or contact lenses by reshaping the cornea with state-of-the-art equipment. The existing HVAC system serving the surgical procedure room could not deliver the required temperature and humidity necessary for optimal surgical outcomes.

Studies have shown that successful refractive surgeries demand exacting environments. That means no more than a +/- 0.5°C swing in temperature and a +/- 2% change in relative humidity over a ten-minute period. If the room doesn't hold conditions, surgery cannot be performed. As a result, the brand new surgical suite was temporarily unusable, and surgical procedures had to be performed offsite.

Obviously, the priority was to get the surgical facility up and running as soon as possible. Kroeschell Inc., a Chicago-based mechanical engineering firm, was chosen to evaluate and make recommendations to correct the problem.

According to Steve Cooper, PE of Kroeschell, an investigation determined that the existing chilled water coil temperature did not allow for the discharge air temperature to be any lower than 10°C. This would not allow the space to be much below 50% RH, which was unacceptable since the required optimal conditions are 20-21°C, 40-45% RH.

A Stand-alone Dehumidification Solution

Kroeschell, Inc. recommended a Munters desiccant dehumidifier as a stand-alone solution to the problem that incorporates Munters' desiccant wheel (rotor), which is capable of collecting and releasing water six times every hour, 24/7. In addition to the desiccant wheel, the unit includes filtration, a supply fan, and a reactivation heater and discharge fan for wheel.

Fresh outdoor air comes into the dehumidification unit, which is controlled to maintain 43% RH discharge air humidity, and then enters the air handling unit serving the room. Room temperature and humidity sensors control the chilled water coil valve, the electric duct heater and the humidifier to maintain the design parameters.

Unprecedented Accuracy

The project was a resounding success, with surgical procedures commencing immediately and continuing on schedule without interruption since the system started up. Medical personnel report that the system is maintaining humidity with a deviation of only +/- 0.6% RH most of the time – a tolerance they believe is virtually unprecedented in other Lasik surgery facilities in the country.

"We're very proud of the outcome of this high profile project," said Steve Cooper. "The Munters dehumidifier provided a straight-forward, affordable solution for a facility with extraordinary requirements. This tells us that the product has application possibilities wherever original chilled water design misses the mark in terms of latent load."