ASHRAE Journal - April 2015 - 46

2015 ASHRAE TECHNOLOGY AWARD CASE STUDIES

ERV

Pre-Cooling Coil

Active Desiccant
Dehumidification

Cooling Coil

Fan

85% Efficient
Filters

Brine Cooling
Coil

HEPA Filtration

FIGURE 2 Dedicated outdoor air system.

latent energy recovery since the latent cooling load is
much higher than the sensible load.
* Pre-Cooling Coil. Chilled water from the district
chilled water plant was used to cool the outdoor air
stream and raise its relative humidity prior to entering the desiccant wheel. The higher entering relative
humidity increases the desiccant dehumidification
effectiveness.
* Active Desiccant Dehumidification. An active desiccant wheel is next used to pull a significant amount
of moisture out of the fresh airstream. The air leaving
this section of the unit has to be very dry to keep from
freezing the 15°F (-9°C) brine cooling coil. The dryer
this air is, the less defrost will be required by the low
temperature units serving the exhibit (described later
in this narrative). The air leaving this section of the
unit is warmed by the desiccant wheel which has been
heated during the regeneration process. Note, there is
a separate side stream of outdoor air that is heated to
320°F via a gas heater to regenerate the active desiccant wheel.
* Cooling Coil. Chilled water from the central plant
is next used to sensibly cool the warm, but dry, fresh
airstream. This cooling could have been done by the
brine cooling coil, but it is much more efficient to use
42°F chilled water to cool the airstream prior to the
brine coil.
* Fan.
* 85% Efficient Filters.
* Brine Cooling Coil. The last cooling portion of
the unit super cools the fresh airstream to a supply
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temperature to match the supply temperature of the
exhibit air-handling units.
* HEPA Filtration. High efficiency particulate filters
are required in the last section of this AHU for animal
health.
Fresh air supply is a vital component for keeping
the environment healthy, therefore we recommended
that two DOAS units be provided, each sized at the
specific air change rate required for the exhibit
spaces. Units are operated simultaneously to maintain the best odor control, however, if one of the units
is down for normal maintenance and/or failure, the
exhibit will still be able to function without jeopardizing animal health.
In addition to the above, specific actions to minimize
internal moisture loads had to be taken.
* Animals. Latent loads from the animals is expected
to be small.
* People Loads. Latent loads for the guests could be
large during hot, humid or rainy days. The queue areas
were designed to dry the guest prior to entering the
exhibit.
* Pools. The design required maintaining the pool
temperature at the lowest possible temperature but still
allowing optimum bird comfort and health. This helped
us to minimize water evaporation from the bodies of
water in the exhibit.
* Wash Down. The most successful approach to remove animal guano is through the use of high pressure
warmed water. This operation is the most significant
latent load in the space.

ASHRAE Journal - April 2015

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