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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
Air Velocity Control 
Air moved horizontally through the calorimeter so the movement was from front to back along 
the animal cages. Air movement was created by recirculating air through the air recirculation 
tube described previously. The airflow rate through the recirculation fan was controlled by 
adjusting the fan speed with a voltage controller. There was a square air diffuser at the air entry 
that distributed the air around the calorimeter cross-section. To further improve the uniformity of 
airflow across the cross-section, an air settling means was placed after the diffuser and before the 
animal cages, consisting of three perforated stainless steel sheets with 60 percent, 40 percent, and 
30 percent open areas. To ensure that there was a uniform profile of air velocities approaching 
the animal cages, a 3 x 5 grid of air velocity measurements was taken between the air settling 
means and before the cages with a TSI air velocity meter (model 8738). The average air 
velocities approaching the mouse cages were set at 0.25±0.05 m/s (50±10 fpm) prior to each test 
(see appendix I: section 3.2.1 and 3.2.2 for calibration data). 
Air Humidity Control 
Relative humidity of the air within the calorimeters was controlled by three systems: 1) fresh air 
exchange, 2) desiccant drying system, and 3) humidification system. 
1) Fresh air exchange (ventilation )-was provided to each calorimeter for several reasons: a) 
maintain appropriate O2, CO2, and NH3 levels, b) remove moisture and help maintain appropriate 
relative humidity, and c) provide sample of air for gas analysis. Air was removed from the air 
entry part of the 0.20m (8”) diameter air recirculation tube and passed through a Gilmont 
Instruments model GF1300 airflow meter (accuracy = ± 2 percent of reading). These fresh air 
exchange flow meters were calibrated prior to each test against a 1 -liter bubble airflow meter 
(see appendix I: section 3.2.5 and 3.2.6 for calibration data). The air then flowed to a diaphragm 
pump that had a 500mL beaker in line to dampen the oscillation from the pump. Airflow rate was 
controlled by an air bypass system with a needle valve. Air flowed from the pump system to the 
gas analysis instruments, that were located in an adjacent environmental chamber. 
Air drawn out of the calorimeters was precisely measured and used as flow rate in the O2 
consumption and CO2 production calculations. A slight negative pressure was maintained within 
the calorimeters. This negative pressure would draw in the same amount of fresh air from the 
surrounding environmental chamber as was removed by the pump. A planned air inlet (8-mm 
diameter hole) was placed in the inlet part of the air recirculation tube, but some fresh air would 
have entered through unplanned inlets (leaks). Since the entire calorimeter was at a negative 
static pressure and a certain amount of air had to enter the calorimeter anyway, the leaks did not 
create a problem. 
The air that entered the planned inlet passed first through a container of desiccant to remove its 
moisture. This fresh air was passed through a 30x10 cm desiccant cylinder filled with 
approximately 3500g of 100 percent CaS0 4 , #8 mesh granules, to help control calorimeter 
relative humidity (see figure 4.34). 
