Specifications

8
Natatorium DesigN maNual
water @ 10-30 fpm. The Vapor Pressure values can be
found in steam tables.
ER = 0.1 x A x AF (Pw – Pdp)
ER = evaporation Rate of water, lb/h
A = area of pool water surface, ft
2
AF = Activity Factor (see Table 2)
Pw = saturation vapor pressure at water
surface, in. Hg
Pdp = partial vapor pressure at room
dew point, in. Hg
It can be seen from the equation that the following
factors increase the evaporation rate:
• Increasing water temperature
• Lowering air temperature
• Lowering air relative humidity
• High activity/agitation
Once equipment has been selected and installed, any
change of the variables that increases the evaporation
rate can result in equipment no longer being suitable for
the new larger load.
Occupant Load
Swimmers are not usually considered occupants as they
are submerged in the water. Swimmers and their water
agitation are included in the Activity Factor. Spectators,
especially in facilities that host large swim meets can
total several thousand, and add a significant moisture
load, (see Table 3).
It is important to understand that when a facility is
hosting a swim meet the Activity Factor of the water
is considerably reduced. Typically there is only one
swimmer per lane and while they agitate the water
considerably, the overall agitation is much less than a
densely occupied pool during a public swim.
To evaluate the dehumidification load during swim
meets an Activity Factor of 0.65 is used to calculate the
evaporation rate. The total number of spectators and
competitors on the pool deck must also include in the
load. Codes also generally require that each spectator
be provided with 7.5 CFM of outdoor air. The load
impact of the outdoor air must also be calculated.
Seresco recommends that facilities hosting swim
meets size equipment based on the larger of the two
main operating modes, normal operation load or swim
meet load.
Outdoor Air
The introduction of outdoor air is essential to maintaining
good air quality in any facility. The impact of this outdoor
air ventilation on a natatorium changes with the weather
and the geographic location of the facility. Introducing
outdoor air during the summer generally adds moisture
to the space and in the winter removes moisture from the
space. For maximum dehumidification load calculations
the Summer Design conditions are considered.
Construction codes generally require that outdoor
air be introduced into a commercial building during
occupied hours. ASHRAE Standard 62-2004 Table
6.1 recommends the introduction of outdoor air into a
natatorium at the following rates:
• 0.48 CFM/ft2 of pool and deck area as base line
• 7.5 CFM per spectator added to the base line during
swim meets
Table 3 – Occupants Latent Load
Figure 2 – Sample of Seresco’s Load Estimating Software