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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
The plot of concentration of CO2 is scaled to show the variation within the room air. The values 
within the cages are much higher. The concentration also rises with increasing height of the cage, 
which indicates that the lower cages are being ventilated better than the upper ones. This is 
perhaps to be expected as the flow from the supply goes down in the open center part of the room 
and passes through the racks towards the walls and then upwards towards the ceiling exhausts. 
The CFD simulations only solved directly for the concentration of CO2. Concentrations of NH 3 
are calculated in the post processing stage of the quantitative analysis using a factor derived from 
the relative generation of CO2 and NH 3 . This factor varies according to the relative humidity in 
the cages and the number of days that have elapsed since the cage bedding was changed. So 
although the values shown are incorrect, the color fill for CO2 does show the distribution of NH 3 
or indeed any airborne particulate matter that flows with the air which originates from the cages. 
This is possible, as the concentrations of both CO2 and NH 3 in the air are so low as to have no 
real effect on the density of the air, CO2, and NH 3 mixture. In effect the CO2 and NH 3 are 
intimately mixed with and flow with the air. 
Figures 2.32 and 2.33 show temperature and concentration distributions in planar slices through 
the racks. Significantly higher temperatures and concentrations within the cages are clearly 
visible. 
