TAB Journal Fall 2020 - 2

Desiccant Dehumidification
in Operating Rooms
Chris White, PE, TBE
Systems Analysis, Inc.

This past year, a local regional hospital our company often works for asked us to retest
an existing desiccant dehumidification unit supplying outside air to their surgery unit. The
hospital had been having problems maintaining humidity levels in the area below 60 percent
and they suspected the process air and regen air to be too high, causing these issues. The
unit was originally installed in 2010.

O

perating rooms, for years, have been designed by older
standards to a room temperature of 68-73°F and 30-60
percent relative humidity. Surgeons today are desiring
their operating rooms be maintained at 60-65°F or lower due
to longer procedures with newer technology and wearing
heavy multiple-layer gowning. The desired lower temperatures
still require room-relative humidity to remain at 50 percent.
These lower room temperatures and humidity are very difficult
to achieve with conventional HVAC chilled water and direct
expansion type systems. Desiccant dehumidification units have
been added to pre-condition the outdoor ventilation air prior
to the main surgery air handling unit (AHU). By removing
the moisture load, the main surgery AHU coil can achieve the
lower room temperatures.
A few years prior, a sister hospital was having similar issues
with their desiccant outside air unit. The sister hospital had
determined that the desiccant wheel had become saturated
with moisture after the wheel rotation motor had failed, so
the wheel had not rotated for some time. The problem was not
resolved even after replacing the rotation motor (Diagram).

2

The saturated wheel had lost its effectiveness to remove
moisture. The sister hospital replaced the desiccant wheel and
the problem was solved. Our local regional hospital decided
to replace their desiccant wheel but had no improvement to
humidity conditions.
The hospital called us onsite to meet the desiccant wheel
rep, the engineer, and hospital maintenance to investigate,
and bring the unit back to design performance. Design

TAB Journal Fall 2020



TAB Journal Fall 2020

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