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air conditioning costs. Which of these options will provide the best economic return depends 
on the facility’s circumstances. 
• Increasing the room ventilation rate does not have a significant effect on cage ventilation (see 
figure 0.3). Increasing the supply flow rate from 5 ACH to 20 ACH for single density racks 
parallel to the walls reduces the CO 2 concentration from 1764 ppm to 1667 ppm, a reduction 
of only 6 percent. For the double density racks perpendicular to the walls the reduction is 
slightly more significant: about 2300 ppm to 1800 ppm, or roughly 20 percent. 
Since air exchange rates in excess of 10 ACH do not materially improve environmental 
conditions within the cages, more care should be given to proper cage arrangement and air 
distribution. 
Figure 0.3 Cage CO 2 concentrations (ppm) for single density racks with the Thoren change 
station and double density racks with both Thoren and Laboratory Products change stations. 
• Ammonia concentrations in both cages and rooms can be reduced by increasing the supply 
air temperatures. This reduces the relative humidity (RH), for a constant moisture content in 
the air. In addition, the lower RH leads to lower ammonia generation. Raising the supply 
discharge temperature from 18.8 °C (66 °F) to 22 °C (72 °F) at 15 ACH raises the room 
temperature by 3 °C (5 °F) to about 23 °C (73 °F), and the cages by 2.7 °C 
(4 °F) to around 24.8 °C (77 °F). This can reduce ammonia concentrations by up to 50 
percent. 
Using 22 °C (72 °F) as the supply discharge temperature at 5 ACH, which is the lowest flow 
rate considered, for double density racks produces a room temperature of about 26 °C (79 °F) 
with cage temperatures only slightly higher. Although this higher temperature provides a 
