Share thisPlanning, designing, and implementing a facility with ventilated rodent racks directly connected to facility supply and exhaust air systems isn’t rocket science.
Planning, designing, and implementing a facility with ventilated rodent racks directly connected to facility supply and exhaust air systems isn’t rocket science. Yet the subtle nuances of a well performing system elude many. The following pages will lay out some basic guidelines for those who seek to take advantage of ventilated racks on a centralized air handling system.
Introduction for the Novice
Ventilated rodent housing is nothing new. Widely accepted for their ability to extend cage changing frequency, ventilated racks (IVCs) have also proven to provide healthier conditions for both occupants and caretakers alike. They have enabled institutions to dramatically increase the size of their colonies, and subsequently serve a greater range of investigators.
The “heart” of the ventilated rack is the blower system, pumping its lifeblood of fresh, pure (HEPA filtration removes 99.97% of all particles down to 0.3 microns in size) air to each and every cage. Typically, a companion blower system captures exhaust air from each and every cage, which is in turn refiltered before being returned to the macro environment. This mechanically forced exchange of air at the cage is what separates a ventilated cage from a static cage. However, the blower system that makes this all possible now introduces several factors into the facility: noise, heat, and a point of maintenance.
Facilities with large installations (possibly hundreds) of ventilated racks would experience these drawbacks in spades. Forward thinking designers have sought to proactively address the issues of noise, heat, and maintenance. By eliminating the individual dedicated blowers, and replacing with centralized blower systems, noise and heat from the individual blowers are effectively removed from the animal holding room. Individual ventilated racks are all directly connected to the central blower systems through multiple ports located in the animal holding room. Maintenance can now be more tightly focused on a few large blower systems, rather than spread across multiple individual HEPA filtered supply and exhaust blowers. And, maintenance personnel do not need to enter the animal room, removing an unwanted risk to the animals.
Sounds simple, so why doesn’t every one use centralized blower systems? First and foremost, this type of system needs a network of ducting to deliver and remove the air to the individual rack systems. Existing facilities would have to bear the burden of significant remodeling, or do not have physical space; centralized blowers are typically only an option for those contemplating new construction. The second hurdle to centralized air systems is the balanced delivery of air. Anyone who has ever been scalded in the shower when someone flushes the toilet can understand the difficulties in providing a consistent, stable supply in a changing system. Well meaning engineers and contractors confidently assure us of their experience with air handling systems. However, a one cubic foot cage that needs to be constantly positively pressurized (but only a little bit) is quite different than thousands of cubic feet of laboratory or office space. Additionally, there is a scarcity of air control products (valves, dampers) that are effective at the low airflow rates required by ventilated racks. The final major resistance to centralized blower systems is the confidence that the central system is providing the proper airflow at each cage. Rack mounted blowers provide localized confirmation of their operating status; a centralized system offers nothing in the room to indicate airflow at the rack or cage level. Investigators have an inherent distrust of anything they cannot see and confirm for themselves.
Planning & Implementing
So, despite the obstacles to setting up a proper centralized air handling system, you have decided that the cost and convenience advantages are worth the effort. How do you proceed? For the purposes of this discussion, we are referring to direct connected supply and exhaust air, connected to ventilated rodent racks.