Share thisRack/Ventilation Configurations
With the widespread acceptance of ventilated rodent racks, options for integrating with HVAC systems have continued to grow. Better understanding of the variables involved, an increased installation base, and the development of new products for facilitating this integration have given us more tools with which to explore these options.
Traditionally, ventilated racks have been equipped with self-contained blowers by the rack manufacturer. This rarely presents installation issues, other than size, as this self-contained system requires only location near an adequate electrical supply. Cage air exchange rates are independent from the facility, and a typical room exchange of 15 ACH is sufficient with racks set for 30 to 80 ACH (typically 60 ACH).
In an attempt to remove heat and odor from the animal room, most ventilated racks can have the air exiting the exhaust blower captured indirectly by the facility’s exhaust HVAC system. Depending upon the type of connection, rack placement can be loosely or tightly restricted (hose, hood, or hard connection). The use of an interface device, such as an exhaust thimble or hood, allows a reasonable fluctuation in the facility exhaust system, without compromising the integrity of the ventilated rack.
More attractive in larger installations, the dedicated exhaust blowers have been removed altogether, relying solely upon the facility’s HVAC system to provide the ventilated rack’s exhaust draw. This is typically accomplished by a flexible connection from the rack to the ceiling, so rack placement is restricted, but somewhat tolerant. As there is no longer a blower providing constant exhaust flow for each rack, a more consistent HVAC exhaust is required. Ventilated caging systems with scavenging exhaust systems are more tolerant (±10%) of air flow fluctuations, but low air flow rates required by these racks of 40 to 130 CFM per drop are still difficult to design down from a significantly larger facility system (often in excess of 10,000 CFM). Control devices (introduced later) provide solutions to this air flow control problem.
Direct Supply & Exhaust
Connection of both exhaust and supply directly to the HVAC system, removing all dedicated blowers, saves on maintenance and capital investment, but places a much greater reliance upon the facility air handling. As this design is the most challenging, detailed discussion is required here.
Air delivery: The first decision to be made in a direct supply and exhaust system is the choice of air delivery to the room; there are three basic concepts to consider. The first consists of a HEPA blower module, which draws from an animal holding room, and then supplies that room with the positive pressure air for the ventilated cages. The second system would utilize an entirely separate facility-wide air handler with built in redundancy, and dedicated ducting to supply the HEPA air to the ventilated racks. The third system would utilize the existing facility-wide HEPA supply air handler and ducting, then split at the room to handle not only the general supply air but, additionally, the ventilated racks.