Volume I - Section II - Animal Room Variations 
Page II - 5 
Surrounding this block a source of CO 2 was defined at 2.12e-7 kg/s (0.76g/hr), which was based 
on the generation rate indicated for the dark period in the early tests on the effect of the 
photoperiod on the mice. This source allowed the additional concentration of CO 2 in the air to be 
calculated in the simulation. The supply air was assumed to have a zero concentration of CO 2 . It 
also allowed the concentration of other species, such as NH3, to be calculated by scaling, even 
though it has a different molecular weight than both air and CCK This was possible because the 
magnitude of the source was very small and the resulting concentrations were so low as to have a 
negligible effect on the density of the mixture of air, CO2 and NH3. In effect, the CO2 and NH3 
are intimately mixed with and flow with the air. 
Experimental data later showed the generation rate of CO 2 was actually higher than the source 
used in the CFD simulations at 0.90 g/hr/lOOg mouse body weight. This means the concentration 
of CO 2 in the room and cages was derived from the simulated concentration multiplied by a 
scaling factor (0.90/0.76). The concentrations of NH 3 in both the cages and the room were also 
derived by scaling the concentration with a factor specified in the post-processing of the data. 
This factor was assumed to vary according to two variables: the number of days that passed since 
the bedding in the cage was changed and the average relative humidity in the cages (see section 
4.2. 1.2 for the experimental determination of the factors). 
Background levels of CO2 and NH3 were assumed to be zero. This means that all values quoted 
in the CFD section of the report are relative to the background level. If an absolute value for C 0 2 
is required, an additional amount in the range of 300 ppm to 700 ppm for most locations should 
be added. 
The remaining cage boundary conditions are associated with the transfer mechanisms for air / 
gases to enter/leave the cage. The cracks at the side of the cage were modeled as 6.35e-3m 
(0.25”) high planar resistances, with the loss coefficient for these resistances having been 
determined from the cage wind tunnel CFD simulations (see section 4.2. 1.2). The top of the cage, 
which was filtered, was defined as a combination of a planar resistance and a planar source. The 
determination of the loss coefficient for the resistance and the coefficient for the source has been 
outlined (see section 4.2.1. 1). 
The spacing of the cages on the shelves was dependent on whether the racks were single density 
(seven cages per shelf), or double density (14 cages per shelf). In the single density cases, the 
cages were centrally located in the short dimension, and equally spaced in the long dimension. 
The spacing was 4.88e-2m (1.92”) from comer of cage to comer of adjacent cage. In the double 
density racks, the cages were equally spaced in both the long and short dimensions. The spacing 
was 2.20e-2m (0.87”) and 4.88e-2m (1.92”) respectively. 
