Biomedical Engineering Reference
In-Depth Information
the hospital with urgent requests for cooling as
concern for patient safety grew. The power was
back by 6 p.m. and the conditions slowly improved.
After the event, the director of facilities was
under pressure from the hospital administrators and
doctors to explain how this could have happened.
They were amazed to find out that cooling was not
available after a power outage caused by some-
thing as common as a thunderstorm. The answer
could be traced back to a value engineering deci-
sion made during the last hospital expansion. The
chiller plant needed additional capacity to serve the
proposed expansion and a new emergency gener-
ator and electric centrifugal chiller were proposed
for the chiller plant.
One cooling tower, one condenser water pump,
one primary chilled-water pump, and one secondary
pumpweretobeaddedtothenewemergencygener-
atorinadditiontothenewchiller.Unfortunately,the
cost for this solution was value engineered and the
emergency generator was deleted after the bids for
the expansion project were over budget.
Providing air conditioning to critical areas during
a loss of normal power can require a significant
amount of electricity. A typical 300-bed hospital
will require approximately 300 tons of cooling to
offset the cooling load in the critical areas of the
facility. Even the most efficient, water-cooled, elec-
tric centrifugal chiller would require approximately
300 kW of emergency power when all ancillary
pumps and cooling towers are included.
The cost of connecting this mechanical cooling
system to an emergency generator could be as high
as $360,000. The range of these costs will obvi-
ously vary on each project, however, the magnitude
of the costs justify an analysis of alternate strate-
gies for providing mechanical cooling upon a loss
of normal power.
emergency generator plant ranging from $800 to
$1200/kW of generator capacity, the cost of adding
100 hp of motor load could be as high as $90,000.
It goes without saying that care must be taken
when determining what hvac equipment is required
to be connected to the emergency power system.
Establishing an appropriate balance between the
cost of adding equipment to the emergency gener-
ator and the risk of not having hvac service during
a loss of power is a difficult task.
Mechanical cooling is one of the most difficult
issues to resolve in establishing the criteria. There
are certain departments of a hospital that should
have provisions for providing air conditioning even
when normal power is not available. The operating
suite, post-anesthesia care units, and the inten-
sive care units are areas of the hospital where
patient safety may be compromised if the rooms are
outside certain temperature and humidity require-
ments. In certain warm and humid climates, consid-
eration should be given to providing mechanical
cooling in all patient rooms and diagnostic and
treatment areas.
18.4 What can Happen during the Loss
of Normal Power
At a recent planning meeting to discuss a major
expansion to the operating suite of a 350-bed
hospital, the director of facilities described what
happened during the loss of normal power at his
facility. It was 3 p.m. and the temperature was 95˚
with extreme humidity. A line of severe thunder-
storms had resulted in a loss of normal power at the
hospital. The emergency generators were running
hot and concern was growing that they may shut
down due to the high temperature.
As the outage continued into the second hour,
the situation was becoming much more severe
inside the hospital. The AHUs that are required to
be connected to the emergency power system for
ventilation of the critical areas were running. The
problem was that the minimum outside air dampers
were open and the system was pumping hot and
humid air into the critical areas. Fortunately, the
scheduled surgeries for the day were complete, but
doctors and nurses were calling from all areas of
18.5 Alternate Cooling Strategies
There are many strategies that will allow a facility
to achieve partial mechanical cooling during a loss
of normal power. A central chiller plant where at
least one chiller is driven by something other than
an electric motor—a natural gas-fired absorption
chiller, natural gas engine-driven chiller, or steam
