As I approached the club's main entrance, the automatic doors
opened and a rush of air filled the lobby. I noticed the receptionist's hair
rustle as she placed her hand on the papers on the desk to keep them from blowing
on the floor. As I waited for the club
manager, I could smell a slight mustiness in the air, furnishings felt sticky,
and the air conditioning diffusers were sweating. Discussions with the club
manager revealed that members complained frequently of being warm. The card rooms
were stuffy and the humidity was so high in the locker rooms that mold was growing
on some of the golf shoes. Further investigation revealed that the building was
operating under a severely negative pressure condition.
Few
things damage a clubhouse more profoundly than a negatively balanced HVAC
system. It is most acute in humid, Southern climates.Operating a clubhouse with
severely negative pressure can set off an avalanche of bad things that can
result in serious indoor air quality problems over time. Correcting these
problems after the microbial growth has started can be a very expensive
process.The good news is that these problems can be averted with proper HVAC
equipment selection and a good maintenance program.
How it Happens
A
negatively pressurized building draws unconditioned outside air through every available
opening. The lobby area is usually the first to feel the impact. Automatic
doors opening and closing allow a huge amount of humid air to enter with each
cycle, making the receptionist sweat in the summer and freeze in the winter.The
lobby diffusers begin to sweat and soak into the surrounding hard ceiling where
mold starts to grow.The humidity level everywhere inside the building rises.
Members
feel warm because the evaporative cooling they get naturally from their skin
under lower humidity conditions is reduced, so they call the facilities manager
to lower the temperature in the space. Under elevated humidity conditions, the temperature
usually needs to be maintained at 68-69 degrees for the majority of people to feel
comfortable. When this happens, the building is in its most dangerous state for
microbial growth. When the interior temperature of the building maintained is
lower than the outdoor dew point temperature for a significant amount of time,
water vapor will be drawn through the exterior walls. It usually condenses on
the first impervious membrane it encounters. This can be the back of the wall board
or some vinyl wallpaper. Once condensation occurs, mold, and the inevitable remediation
costs, will not be far behind.
Negative
pressure is a condition found in clubhouses with alarming frequency. Clubhouse buildings,
by their nature, employ significant numbers of constant volume exhaust fans. Usually
the largest component of exhaust is located in the food service facility. It is
not unusual for a major cooking facility to be exhausting 10,000-20,000 cubic feet
per minute (CFM) of air from the cooking hoods. A properly balanced cooking
hood system should be replacing approximately 80 percent of the exhausted air
with fresh make-up air. This is usually supplied through a make-up air plenum
located near the front of the hood. This leaves a net exhaust of 3,000-4,000
CFM from the kitchen area.
Add
to this another 600-1,200 CFM from the dishwasher hood and another 500-1,000
from a display kitchen hood, and the aggregate exhaust can be in excess of
6,000 CFM from the food preparation area alone. Another 2,000-3,000 CFM likely will
be added from the locker rooms and restrooms throughout the building. The net result
is that a large clubhouse building can have a constant volume exhaust rate of 8,000-10,000
CFM. This is particularly problematic for clubhouse buildings because the
exhaust rate is large compared with the square footage of the building, and
units are run continuously.
To
counteract the exhaust and maintain a neutral or preferably positive pressure
in the building, an offsetting amount of outside air must be introduced.
Because exhaust fans are at
Operating a clubhouse building with severely negative pressure can set off an avalanche of bad things that can result in serious indoor air quality problems over time.
constant volume
(which means they run continuously
with no variation in the flow rate), the make-up air also must be introduced in
a similar manner.This is done through the air conditioning system- and therein
lies the challenge.In humid Southern climates the humidity in the outside air is
normally very high and goes through dramatic seasonal swings.The HVAC engineer
is faced with the daunting task of providing a stable temperature and humidity condition
inside the building with wildly varying outdoor temperature and humidity
conditions.
Air
conditioning systems maintain inside conditions normally by increasing or decreasing
the air flow and/or the supply air temperature.There are a number of techniques
engineers use to accomplish this task and some are more successful than
others. Chilled water systems can use variable frequency drives on the air handlers
to vary the air flow. Direct expansion systems, such as package roof top units,
simply turn on and off based on the sensible demand. The challenge for
clubhouse engineers is that neither of these methods are effective in
maintaining neutral or positive pressure in the building when exhaust fans are running
continuously.
What
to Do?
Clubhouse
buildings must be equipped with a dedicated 100 percent outside air pre-conditioner.
This unit runs continuously and supplies a constant and equal volume of
dehumidified outside air to the building. It should be interlocked to run when the
cooking hood exhaust system runs. There are a number of manufacturers that
produce this type of equipment. It can be done with chilled water or direct expansion
equipment. The units are designed to remove large amounts of moisture from the
air stream.
The units also include a method of reheating the
supply air to prevent overcooling the space. It can be done with a non-energy
absorbing hot gas reheat coil or with electric heat. Sizing the unit is a subject
of design as long as it can deliver an amount of outside air at least equal to the
exhaust.
A very
useful system to include is a cooking hood variable air volume system. This system
uses variable frequency drives on the exhaust and make-up air fans to slow the
exhaust rate down when there is no significant cooking being done on the line.
The reality is that a fairly small amount of the hood's total daily operating time
involves heavy grease and smoke-laden cooking. There is no need for the hood to
be running full speed when there is no smoke being generated.
To
provide comfort at the cooking line, it is advisable to provide temperature
control for the hood make-up air. In the summer, the ambient air temperature can
easily be 95 degrees plus. Dumping this air down on the chef at the cooking line
can raise the temperature in this area to 110 degrees. This alone frequently drives
the chef to turn the make-up air fan breaker off. Cooling half of the makeup
air stream to 55 degrees and re-mixing with the remaining air will drop
the temperature from 95 degrees in the summer to 75 degrees and
70-80 percent humidity.
With
the basic equipment in place, the unit needs to be maintained regularly. All of
the above discussed equipment can fail due to lack of maintenance and put the building
into a negative air balance. The problem is that the equipment can fail and not
be immediately noticed until serious problems start to develop. An aggressive maintenance
program will keep the building properly balanced and healthy for many years.
About the Author
Robert Davenport is president and principal Engineer of RGD & Associates Inc., a South Florida firm specializing in
clubhouse construction and renovation projects.
For more information about our services, visit RGD Consulting Engineers corporate website.
