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Figure 0.1. Ammonia generation rate measured over 10 days at high and low humidity 
• Acceptable room and cage ammonia concentrations after five days without changing cage 
bedding are produced by room supply airflow rates of about 0.85cfm (0.0004m 3 /s) per lOOg 
of body weight of mice. This is equivalent to 5 ACH for rooms with single density racks that 
were considered in this study, and 10 ACH for rooms with double density racks. This 
indicates that it could be possible to adjust the common practice of changing bedding every 
four days to changing after five days. 
The temperature of the supply air must be set appropriately for the heat load in the room. In 
this study, the change station produced 720W and the mice around 500W in the single 
density racks, which required supply discharge temperatures of 1 1 °C (52 °F) at 5 ACH to 
provide exhaust temperatures of around 22 °C (72 °F). For double density racks the supply 
discharge temperature should be 14.8 °C (59 °F) at 10 ACH. 
This study used dark period/lights off to give the highest CO2 and NH3 generation rates. If 
lighting is to be included an allowance should be made for 600W of additional heat from the 
lights leading to lower supply discharge temperatures. 
