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A major problem with conditioning swimming
pool enclosures is the relatively high operating costs of maintaining
acceptable
conditions.
Some type of cost effective energy recovery devices must
be considered when the heating, ventilating and/or cooling
system is designed. One method for controlling humidity
is a ventilation system (EXHAUST FANS/FURNACE), using drier
outdoor air to replace humid air.
However:
1.
a considerable amount of heat is needed to temper
the outdoor air during cold weather
2. when temperatures are intermediate, this system may not control
humidity
3. during hot weather the system cannot control temperature or humidity |
The HVAC equipment to accomplish this is costly
both to install and to operate. It can consist
of a pool water heater, and large, noisy exhaust fans.
There are also high capacity heaters to bring the large
volume of incoming air up to comfortable temperature
in colder temperatures, and large capacity cooling equipment
to cool and dehumidify the air in the summer. When you
add the proper controls, this can be the most expensive
of all dehumidifying alternatives. Remember, recoverable
energy consists of both the sensible and latent heat
of the exhaust air. The latent component can be a very
sizable part of total recoverable energy, therefore a
heat recovery device that can extract both sensible and
latent heat should be considered.
Since a ventilation system can only provide
effective humidity control if the outdoor air is reasonably
drier than the indoor air, it will not perform well in humid
weather. Therefore, a mechanical dehumidification system
will be required to control humidity in the enclosure when
the outdoor air approaches the moisture content of the indoor
air.
B.
OPENING DOORS/WINDOWS OR RETRACTABLE WINDOWS OR SKYLIGHTS
TO CONTROL HUMIDITY
IS NOT AN EFFECTIVE MEANS TO CONTROL THE POOL ROOM ENVIRONMENT.
One traditional approach
to dealing with this humidity is to
simply open all the doors and windows
in the pool area and let nature dehumidify
with drier outdoor air. This passive
approach might work on days when the
outdoor air is at the same temperature
as that desired in the pool area and
with a lower relative humidity. These
conditions rarely exist, however. This
process can only work when the outside
air is cool and dry enough to allow
for humidity control. In the winter
time, an indoor pool without a dehumidification
system will be cool and clammy, because
the air temperature in the space will
not be heated warm enough to be comfortable.
During spring or fall, the outside
air is cool and dry enough to use this
process, but if the air is too cool
(say 20 or 30 degrees F), an enormous
amount of energy is required to heat
up the air to design space temperature.
Pre-fabricated/manufactured structures
with opening or retractable panels
still require dehumidification and
controlling the environment.
Example: If
the outside air temperature is 75 degrees and it
is raining, you bring in this 75 degree air with
100% Relative Humidity, making it impossible to control
humidity. With waste ventilation (or exhaust fan)
type systems, there will be no cooling of the space.
You will lose both temperature and humidity control
within the space. In the spring you’d want
to open doors and windows and leave them open. The
space temperature drops in the evening, increasing
evaporation from the water. At this point the windows
are shut, and fans turned on to control humidity.
But to save energy, the humidity is allowed to increase
to 80 or 90%.
This results in an uncomfortable and unhealthy environment for
the pool user, not to mention structural damage that results
in all types of buildings at such humidity levels, coupled with
the aggressive nature of chlorine.
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C. HOW DOES HUMIDITY
AFFECT YOUR POOL ENCLOSURE?
Humidity and subsequent condensation on ceilings, windows,
wall surfaces etc. in a pool enclosure without proper
dehumidification can damage the
structure by being absorbed into the walls, ceiling, & structural
members of the room. These gallons of moisture can permeate an indoor
pool enclosure creating problems where it cools to dew point and condenses.
Areas where the moisture carried in the air condenses on cooler surfaces
and becomes havens for fungus, mold, mildew and rot. Gaps or tears in
vapor barriers give this water vapor access to structural members and
insulation, where hidden condensation deposits accumulate unseen for
years. Add unavoidable decay accelerated by mold and fungus to the fact
that wet wood has a fraction of dry wood’s strength, and long term
building problems, premature structural and equipment failures are inevitable.
Even steel beams can give way after years of uncontrolled moisture.
D. HOW DEHUMIDIFICATION WORKS
TO CONTROL THE POOL ENVIRONMENT
Several factors come into play when determining evaporation rates. The
rate of evaporation is driven by your target relative humidity as well
as the evaporation rate which results from the water and air temperatures
you wish to maintain.
Typical design parameters for indoor pools are:
Relative
Humidity: 50-60%RH
Pool Water Temperature: Commercial 78-80F
Residential 82-84F
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Therapeutic: 86-90F
Whirlpools/Spas: 104F |
AIR TURNOVERS:
ASK US WHY WE NEED TO EXCEED ASHRAE REQUIREMENTS
Evaporation rate is determined by the pool surface area and the temperature
of the water and the air. Evaporation rate is typically measured in pounds/hour
of moisture added to the air per hour. Like a pot of boiling water (=pool
water), water evaporates into the air and rises toward the ceiling; this
moisture stratifies at the ceiling level, and on glass and other surfaces.
The dehumidifier senses the humidity rise and begins extracting moisture
(and latent heat) from the air. The recovered heat can be used to heat
the pool water or the room, whichever is calling for heat. The moisture
removed from the air then goes down a condensate drain. We do NOT recommend
putting this moisture back into the pool (which alleviates potential
problems with Legionnaire’s disease). Large Exhaust Fans will not
provide the ASHRAE recommended Air Turnovers for the pool room, will
not control humidity, will be expensive in heating up the colder air
being brought back in during winter months, and simply is not the most
economical or practical means of meeting dehumidification requirements.
E. COMMERCIAL PROJECTS OR EDUCATIONAL PROJECTS
Commercial projects tend to have more problems with humidity control
because, generally, owners want to install the upfront least expensive
system to control humidity. This generally consists of exhaust fans and
a furnace for room heating, and in many cases, without the proper ductwork
for equal air distribution across all surfaces. Temperatures of pool
water and air are generally not kept within recommended guidelines (air
temperature below pool water temperature), and rarely is a pool cover
used. Waste Ventilation Systems continue to be utilized today in hotels,
schools, etc., where we find structural damage, deterioration and extremely
high operating costs. Many owners do minor repairs and paint over problem
areas. The end result is still the same – deterioration of the
structure.
Environmental
Pool Systems has over 20 years experience in the
pool enclosure industry. It’s not just a
matter of selling equipment today- but includes
educating consumers so you can make an informed
decision when determining the best methods and
alternatives to control humidity in your pool enclosure,
prevent structural damage and costly repairs, and
to have an enclosure that will last for years to
come.
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