Share thisOn the surface, vivariums housing rodents are very similar in function, use, and frankly, design. Generally, they include holding rooms, procedure rooms, cage washing facilities, necropsy, and various other support spaces.
On the surface, vivariums housing rodents are very similar in function, use, and frankly, design. Generally, they include holding rooms, procedure rooms, cage washing facilities, necropsy, and various other support spaces. Likewise, heating, ventilating and air conditioning (HVAC) systems serving these spaces can also be fairly typical. For these facilities, high ventilation air change rates are maintained by virtually constant volume systems with multiple venturi air valves maintaining supply, exhaust, and cage exhaust air flow to each space. This, in turn, maintains environmental conditions, removes odors, and maintains proper pressurization. These standard features may lead one to believe that HVAC design must be standardized or unimaginative. However, this is not the case. Many unique and innovative techniques can be employed to get the most out of a facility’s HVAC system safely and without excessive first cost.
Case Study
A recently completed project, a pediatrics research center in Atlanta, Georgia, falls within what can be considered a typical animal facility. The project was a 150,000 square foot building with a clinic, four floors of research space, and a 13,000 squarefoot vivarium. The schedule was built on a “fast-track” with design and construction completed within 18 months. The vivarium includes 15 holding rooms with a total of 44 cage racks, procedure rooms, necropsy, cage washing, feed and bedding storage, and support space. The HVAC system serving the facility is 100% outside air variable volume system that is passed through an energy recovery system. Exhaust from vivarium spaces is exhausted directly to the outside and does not pass through the energy recovery wheel. Dedicated supply and exhaust air valves that maintain minimum air change rates and space temperature serve each room. Holding rooms are provided with an additional air valve to maintain proper exhaust airflow through ventilated cage racks. The following are some techniques used on this project to reduce project costs, including capital cost, maintenance cost and long term energy costs, while meeting the owner’s criteria and expectations.
Keep Down the Air Change Rate
The amount of air required to serve an animal facility is almost always determined by the air change rate required in the spaces rather than cooling load or exhaust requirements. A minimum air change rate of 10-15 air changes per hour for rodent holding rooms is well documented in ASHRAE Applications-2003 Chapter 14 Laboratories, and Guide for the Care and Use of Laboratory Animals but are they always required? The standard air change rate of 10-15 ACH became a standard when animals were typically housed in open cages. The purpose of the high air change rate was to reduce offensive odors from the animals and their bedding. Modern housing using micro-isolator cages is now a common method. The use of ventilated cage racks, where exhaust and perhaps supply air are ducted directly to each isolator from the building HVAC system, provides clean environments for the animals and greatly reduces odors in the holding rooms. Therefore, in a space with ventilated micro-isolator racks, six to eight air changes may be a more appropriate number. The same may be true with a holding room that is not currently in use. Reducing the air change rate reduces energy usage by lowering fan horsepower. More importantly, energy usage is reduced by lowering the cooling, heating, and reheating requirements. There are many methods of modulating the air change rate through the building automation system, but how can a researcher, who may not be an HVAC expert, be confident that the correct air flow and air change rate are always provided? For this project, a relatively simple and inexpensive solution was engineered. A keyed switch was specified for each holding room, located within the secure area (Figure1). When the switch is unlocked, the user has the capability of switching the space from a high air change rate to a low air change rate, and vice versa. The space is served with two-position air valves, which upon signal from the switch, seamlessly position the air change rate from the high to low setting. Use of this simple system will save thousands of dollars in energy costs each year.