Specifications

15
Figure 5 – Exhaust Air
INDOOR AIR QUALITY
• The outdoor air must be preheated
to 65°F – If more than 20% of the
total airflow is outdoor air or if the
winter design temperature is
below 10°F
• A certified air-balancing contractor
must balance the system airflow.
All Seresco units are equipped with
an outdoor air connection, filter and
balancing damper. Motorized dampers
and time clocks are also available.
Exhaust Air
ASHRAE recommends the room be
maintained
at 0.05-0.15” WC negative pressure
relative to surrounding spaces.
Ten percent more exhaust air than
outdoor air is a good rule of thumb.
More exhaust air than recommended
by ASHRAE will not reduce or stop
moisture migration through the
building envelope to outdoors in cold
weather. Vapor migrates based on
vapor pressure differential. There is effectively a 10”
WC pressure differential between indoors and outdoors
on cold winter days. There is no amount of negative
airside pressure you can put into a space to stop vapor
migration. The building envelope must be designed by
the architect to adequately deal with this by placing
vapor retarders in appropriate locations in the entire
building envelope.
Figure 5 illustrates how the strategic location of the
exhaust grille can also significantly improve the air
quality in the space. A spa or whirlpool should have the
exhaust air intake grille located directly above it. This
source captures and extracts the highest concentration
of pollutants before they can diffuse into the space and
negatively impact the room air quality.
Air Change Rate
ASHRAE recommendations for proper volumetric supply
air changes per hour are important, ensuring that the
entire room will see air movement. Stagnant areas must
be avoided, as they will
be prone to condensation and air quality problems.
Short circuiting between supply and return air must
also be avoided as it significantly reduces the actual air
changes within the space.
ASHRAE recommends:
• 4-6 volumetric air changes per hour in a regular
natatorium
• 6-8 volumetric air changes per hour in spectator areas
A quick calculation will determine the supply
air requirement.
• Supply air required (CFM) = room volume (ft3) x
desired air changes / 60
The room volume determines the amount of supply air a
space requires.