Air Delivery System or Ductwork for the Pool Room
EPS TECHNICAL BULLETIN #14
View this bulletin as a PDF
Diagrams are in PDF format: Examples of Proper Ducting
AHSRAE 1999 HVAC APPLICATIONS MANUAL STATES:
“As with any installation, proper duct design and installation is
necessary for proper equipment performance. Poorly installed return
duct connections, for example, can significantly reduce the
performance of a dehumidifier. The following duct construction
practices apply to natatoriums:
- -Fiberglass duct liner should not be used. Where condensation may
occur the insulation must be applied to the exterior of the duct.
- -Duct materials and hardware must be resistant to chemical corrosion
from the pool atmosphere.
- -Grilles, registers and diffusers should be constructed from aluminum.
- -Supply air should be directed against interior envelope surfaces
prone to condensation (walls, glass & doors).”
For additional information, read Pages 4.5-4.7 of this manual. These are just the basics.
1. When you build a new home, office or commercial building -- do you not heat it,
cool it when it needs cooling, humidify or de-humidify if you want to control humidity?
How do you do this? With furnaces, boiler systems, outdoor condensers, etc. and air
delivery system or DUCTWORK, right? That ductwork is attached to the unit, and one
side of the furnace supplies all the warm air to the home or building I called the
“SUPPLY”), and ductwork that comes back to the unit is called the “RETURN”.
Think in terms if in the middle of winter, you have a furnace in your basement for
heating the house, but to save expense, you don’t install ductwork throughout the
house. How does this house become warm and comfortable in the winter, and cooled
properly in the summer without the ductwork to move this air throughout your home via
the registers?
Now, let’s look at it in a different way. Every human body has a heart. This is the
“machine” that feeds the rest the body. How does it do that? With the arteries
attached to your heart and throughout your system. So if you have a dehumidifier (the
heart) and no arteries (the ductwork) then the heart is useless.
2. Clients may want to use their existing home system or believe that they
can use the home heating & cooling systems and ductwork to condition the
pool room. This is not recommended, and in many areas, not considered
CODE to use the same heating and cooling system that you do for the rest of
the house or building. Pool room environments need to be maintained
separately from other areas not related to the pool room.
A pool room is much different from your home: simply because you have a
large body of water in a room that evaporates at a certain rate at specific
temperatures:
- Humidity levels are higher (between 50-60% RH)
- Chlorine/chemical based environment
- Under negative pressure
- Glass surface areas and skylights require a flow of warm air across them to
prevent those surfaces from reaching Dew Point Temperature and
condensing.
- Potential of moisture migration into areas it should not go (i.e. the rest of
the house) where moisture damage can occur.
3. HOW TO CHOOSE BETWEEN OVERHEAD OR UNDERGROUND DUCTING
In designing your project, you may have windows/door walls, and skylights. First choice
of ducting is (continuous (peripheral) loop ductwork) is underground blowing up, second
choice being overhead. Again, this will depend upon the location of all glass within the
structure, deck area, and the where ducting will fit.
When designing the building, determine where ductwork will be installed and leave
appropriate room to do so. Ductwork is not downsized just so it can fit in between
trusses. A specific amount of air flow (cfm) and air turnovers are required for each
project. Once these parameters are set down, downsizing ductwork to fit within a
designed space can have serious consequences for the pool room and owner.
Ensure that air flow can reach the glass surface areas with a flow of warm air; if most of
your glass is at the floor level, then we would recommend underground ducting if deck
area is sufficient. If the glass is higher or closer to the ceiling area, then overhead may
be a better choice. EPS will review all aspects and make final recommendations for the
client based on their design parameters.
Note: if skylights are incorporated into the structure and ductwork
cannot be installed to address air flow into the skylights, then we
recommend that ceiling fans BLOWING UP be installed to move air
into these areas to prevent condensation.
A. Underground Ducting (continuous loop - underground PCD) (in
the deck area of the pool).
Underground ducting is generally
installed in a continuous loop before the pool plumbing is put in.
This prevents tearing out ductwork to get at a pool plumbing
problem. Generally, about 3-5 feet of deck area around the pool is
required to “trench” the underground ducting. If underground –
check your water table first!
DUCTWORK MYTH: Underground ducting should not be used because all of the
splashing in the pool will fill up the ducts with water and flood them. NONSENSE! You
would have to stand over ducts in the floor with a 5 gallon bucket and continually dump
water in them to create this type of problem. The small amount of splashing that occurs
will dry very quickly due to the air flow traveling through these ducts. Also,
underground duct is designed and installed at a slight pitch back towards drains. If your
client has a high water table, then underground ducting may need to be reviewed and
may not be feasible.
B. Overhead Ducting (Galvanized metal/can be painted,
and cable suspended or flush mounted).
Fabric ducting can be cable
suspended or flush mounted); Rectangle galvanized metal duct built
into an overhead soffit in a continuous loop.
Clients have been told that overhead ducting isn’t and shouldn’t be done,
because warm air rises and it can’t keep windows dry. NONSENSE!!! With
the ductwork designed properly by cfm required, the velocity of the duct can
move air from diffusers anywhere from 6 feet to 25 feet, depending upon the
job. Overhead ducting in commercial projects that do not use pool covers
can tend to blow air down and across an open pool, increasing evaporation
rate as it goes across that body of water. This is common to commercial and
education projects is taken into consideration when designing a system.
C. Combination of underground and overhead, depending upon the
design of the project, type of structure, glass load, etc.
4. DIFFUSERS (or registers): Located underground (in floor) or overhead (soffit
mounted or spiral ductwork) all exterior windows. Diffusers ARE NOT INSTALLED
IN WALLS ABOVE/BELOW or IN BETWEEN THE WINDOWS. All diffusers are
designed to deflect airflow across all glass or other surfaces to keep them from
reaching Dew Point Temperature.
5. WHERE DOES THE RETURN AIR GO? The return air IS NOT LOCATED AT
THE POOL DECK LEVEL. Stratification is at the ceiling level (WARM AIR
RISES) and air flow and movement in this area is critical to prevent moisture
from migrating into the ceiling and structure. The return air is always
located at the highest point in the structure. Using the return air at the floor
or deck level to eliminate chlorine or address chloramines -- and hoping
dehumidification can solve these problems is a myth. POOL BALANCING and
proper air turnovers within these structures will create a healthy
environment. Dehumidification does not cause chloramines, nor can it
effectively remove them from the air. Blowing supply across pool water is
not an effective means to controlling chloramines. This increases the
evaporation rate of the water. Again, proper pool balancing is an issue in the
natatorium industry, and needs to be addressed with the client.
6. DUCT SIZING: EPS will provide all engineering/duct sizing for the project, based on
ASHRAE and ACCA, SMACNA Requirements and Guidelines. It is imperative the
ductwork be done according to specifications provided for supply and return within this
room. Inadequate, under-sizing or over-sizing of the duct system leads to
dehumidification problems with condensation and systems not able to keep up with the
design temperatures. BIGGER IS NOT ALWAYS BETTER! ENSURE ALL DUCTWORK IS
REVIEWED BY ENVIRONMENTAL POOL SYSTEMS PRIOR TO INSTALLATION or EPS
cannot be responsible for systems that do not work properly.
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