Ventilation for Indoor Pools

http://www.ee-solutions.com/resources/Shared%20Documents/Ventilation%20for%20Indoor%20Pools.pdf

Ventilation Air for Indoor Pools
Technical Bulletin 5
I NTRODUCTION
This technical bulletin reviews the outdoor air ventilation
requirements for indoor swimming pool enclosures. It provides
in-depth analysis of what the existing standard means
and how ventilation air should be introduced to the air
handler/dehumidification system. A review of energy
recovery and conservation is also included.
As with all rules and regulations, interpretations vary.
DESERT AIRE has provided the following summary in order
to address the issue of ventilation air. This bulletin is for
discussion only and is not intended to overrule the opinion of
the consulting engineer.
D EHUMIDIFIER SYSTEM AIR VOLUME
ASHRAE Standard 62, the industry accepted ventilation
code for indoor air quality, defines the minimum volume
of outdoor air which must be introduced into the indoor pool
enclosure. This volume is generally only a small percentage
of the total air volume required by a dehumidification system
to maintain the space humidity. Air velocities across the pool
surface must be minimized to avoid excessive evaporation.
The design of the dehumidifier should target approximately
four to eight air changes per hour.
Ventilation Air Standard
Pool Area: 0.5 cfm / ft2
2.5 liters/s per m2
Spectator Area: 15 cfm / person
8.0 liters/s per person
ASHRAE 62 requires a ventilation air volume of 0.5 cfm per
square foot of pool and deck area. In addition to this volume,
an additional amount is required if the facility has a spectator
area (bleachers). For these facilities, 15 cfm per person needs
to be introduced during times that spectators are present.
D EFINITION OF POOL AND DECK AREA
The standard refers to pool and deck areas, but does not offer a
detailed definition of the area. It is generally accepted that the
deck area is a six to eight foot wide tile or concrete area
surrounding the pool. Locker rooms, vestibules and hallways
are not included in this measurement. (See Figure 1.)
Figure 1 – Pool, Deck, and Spectator Area Calculations
A
B
C
POOL
BLEACHERS
Pool and Deck Area = A x B
Spectator Area = A x C
W ATER CHEMISTRY AND ODOR
When planning natatoriums, designers are concerned about
preventing any unpleasant odors. Typically, they design a
ventilation system which brings in an excess amount of
outdoor air in order to control any potential odor problems.
While a complete analysis of pool water chemistry is beyond
the scope of this bulletin, a quick review is required to eliminate
some myths with respect to ventilation air requirements.
Many people often complain about a strong, objectionable
“chlorine” odor found in pool rooms. Actually, this odor is
not chlorine (which cannot be smelled by humans until it is
above toxic levels), but an intermediate compound formed
during the disinfection process. The odor is produced by the
combination of chlorine and organics (sweat, oils and urine)
in water. What we smell are chloramines, which are volatile.
They are readily released to the air and are detectable by
humans at low concentrations.
The formation of chloramines happens only when there is not
enough free chlorine in the pool. To rid a pool of chloramines,
it must be “shocked” by adding seven times the amount of
combined chlorine present. A pool water treatment company
can analyze the pool water and recommend appropriate
solutions. When people smell “chlorine,” the pool water
chemistry is out of control and more, not less, chlorine must
be added. Properly installed and maintained chemical feed
systems will eliminate this odor.
Proper ventilation can assist with maintaining water quality by
removing the airborne chloramines. This process will cause
more waterborne chloramines to release into the air, allowing
the free chlorine in the water to better do its job. Please refer
to DESERT AIRE Technical Bulletin #9 for a more complete
description of this interaction.
Alternative disinfection systems, such as ozonization, UV
treatments and ionization, are increasingly being used. Since
these methods do not produce volatile intermediates,
complaints about odor will decrease.
I NTERPRETATION OF THE VENTILATION CODE
The standard exists to protect the health of pool users. Proper
interpretation, however, can also enhance energy conservation
by reducing the volume of outdoor air required to the minimum
allowed by code.
The interpretation is based on the following assumptions:
1) that normal pool user load is small and spectator
crowds will be handled as an exception;
2) that automatic chemical feed systems are installed
and operational; and
3) that a dehumidifier is installed and operational.
Ventilation may be regulated based upon occupancy. When
the facility is unoccupied, outdoor air flow may be closed.
During normal operation, outdoor air flow may be set to a
minimum code-approved level. For higher-than-normal
occupancy (such as a swim meet), an increased outdoor
air flow rate is engaged. (See Figure 2.) Optimizing outdoor
air will have a dramatic effect on operational heating and
cooling costs.
EVAP
COIL
RETURN
AIR
REHEAT
COIL
MOTORIZED
DAMPER
DRIVEN BY
OCCUPANCY
TIMER OR
SWITCH
OUTSIDE AIR
F
I
L
T
E
R
F
I
L
T
E
R
F
I
L
T
E
R
Figure 2 – Damper Assembly
TECHNICAL BULLETIN 5
Ventilation Air for Indoor Pools
The control of outdoor air dampers can be accomplished in
two ways: a manual switch or a timer.
For either of these two actuation methods, the system will
establish three control points to automate the outdoor air
damper: closed for unoccupied conditions; minimum code
ventilation for normal activity; and an event mode to handle
spectator load requirements.
Spectator occupancy is not constant in most facilities except
during swim meets or shows. Spectator ventilation air can be
introduced by a dedicated outdoor air system (DOAS) that
has its duct work flush spectators with clean, fresh air. The
DOAS can also produce temperatures that are a couple of
degrees lower than the pool space temperature to help keep
fully clothed spectators cooler. To further reduce energy
costs, the code ventilation for this area can be controlled via
a manually activated switch or a building management system
with a scheduling program. In this way the facility can reduce
its energy costs by conditioning the air only when spectators
are present.
I NTRODUCTION OF OUTDOOR AIR
The dynamics of a pool enclosure are unique because of the
need for humidity control. Most other applications can accept
outdoor air upstream of the air handler without affecting the
system’s performance. This is not true in the case of a
dehumidifier. If outdoor air is introduced into the return air
duct, two problems can occur in cold weather (winter). The
first problem is condensation in the duct when cold air meets
the moist return air from the pool room. The second problem
is that the mixed air temperature will be lower than the pool
return air and will decrease the moisture removal capacity of
the dehumidifier.
To eliminate these problems, the outdoor air should be
introduced downstream of the evaporator (see Figure 3.)
Then the dehumidifier has maximum moisture removal
capacity and the reheat and auxiliary heating coils can raise
the temperature of the outdoor air, avoiding cold drafts
to the swimmers.
Figure 3 – Outdoor Air Introduction to Dehumidification System
EVAP
COIL
RETURN
AIR
REHEAT
COIL
OUTSIDE AIR
AUXILIARY
HEAT
COIL
F
I
L
T
E
R
F
I
L
T
E
R
SUPPLY
AIR
105 6/03
8300 West Sleske Court
Milwaukee, WI 53223
(414) 357-7400
FAX: (414) 357-8501
http://www.desert-aire.com
E CONOMICS OF HEATING AND COOLING
WINTER
An indoor pool enclosure has several sources of energy loss:
1) convection through the ceiling, windows, and walls
2) exhaust air
3) evaporation of the pool water
The convection heat loss and the exhaust air heat loss in a
pool enclosure is a function of the coolness of the outdoor air
temperature. The greater the temperature differential between
indoor and outdoor, the greater the loss of energy.
Uncontrolled heat loss causes swimmer discomfort and also
increases the pool water evaporation rate. Heat loss through
ceilings, walls, and windows can be minimized by using
adequate insulation and multipane windows. Heat loss
through exhaust air can be minimized by eliminating exhaust
during unoccupied times and by bringing in the minimum
amount of outdoor air that code permits.
The water’s heat loss can be minimized by maintaining the air
temperature at several degrees above the water temperature.
A key factor is maintaining the room relative humidity at
50-60 percent. Should the relative humidity drop below 50
percent, the evaporation rate will increase significantly.
Relative humidity below 50 percent can occur when extra
amounts of outdoor air are introduced in the wintertime.
The simplest method to calculate the effects of ventilation is
the total enthalpy method. This method compares the difference
in enthalpy (BTU/lb) of indoor versus outdoor air at different
ventilation rates. A direct energy cost can then be calculated.
SUMMER
During the summer months, heat gain – not loss – is a problem.
A higher volume of outdoor air increases the cooling demand
and introduces extra moisture. The increased load requires a
larger sensible cooling capacity, and the increased moisture
requires a larger dehumidifier that must run longer. This
effect must be included in the dehumidifier sizing calculation.
C ONCLUSION
A dehumidification system in an indoor pool facility not only
protects the structure and recovers energy, but it also
allows a reduction of outdoor air, thereby increasing energy
savings. If your state has adopted ASHRAE 62 ventilation
codes, then the following design specifications should be
incorporated into your plans:
◆ Dehumidification system – designed to provide four to
eight air changes per hour while maintaining a relative
humidity of 50 percent for unoccupied space and not
greater than 60 percent for occupied (active) space.
◆ Automatic chemical feed system – designed to eliminate
the need to introduce extra outdoor air to control the odor
of treatment chemicals.
◆ Provide 0.5 CFM/square foot of pool and deck area
during normal usage, and 0.5 CFM plus 15 CFM per
spectator during swim meets or shows.
◆ Outdoor air introduced after the evaporator coil in the
pool dehumidifier -maximizes the capacity of the unit.
A DOAS can be used for the spectator outdoor air volume

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