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Between 1975 and 1983, the newly constructed animal laboratories of the Technical University of Aachen (RWTH), the Federal Health Institution (BGA) in Berlin and of the Düsseldorf University were equipped with different air conditioning systems.The lack of experience with similar facilities necessitated extensive experimental test room investigations.It is the target of this work to compare and interpret the results of the existing three reports.It should be noted that the comparability suffers because of the different technical approaches.As a main difference, the maximum cooling loads, the cooling load simulation, the cage types, the arrangement of measuring points and the treatment of the measuring data must be mentioned.In order to make the data comparable, the following criteria were used:The maximum temperature difference between the cages, the maximum temperature in the gap between the cages, the standard temperature deviation in the cages, the difference between cage and room temperature.As far as air velocity is concerned, the maximum values in the cage as well as the average values and their standard deviation are compared.If one compares the results of the trials with maximum cooling load, it can bet noted that the use of an air distribution ceiling shows the largest differences in vertical temperature distribution with the lowest air velocity in the cages.The air conditioning system used in Aachen results in the greatest uniformity of temperature with a medium air velocity of 0.07 m/s for the 50 % respectively 0.13 m/s for 90 % total frequency point. The cooling value, however, amounts only to 62 % of the calculated maximum value. With maximum cooling load, the Berlin arrangement shows the best temperature results with an air change rate of c = 13 h-l. At the same time, maximum temperature difference between the cages was 1.6 K; the vertical temperature between cage floors was 0.9 K with average values of air velocity in the cage of 0.09 m/s (30 \% value) or 0.11 m/s (84 % value). In Düsseldorf, a linear diffuser was used for air supply. This arrangement resulted in temperatures of 2.0 K between the cages and a temperature difference of 1.9 K in the cages with an air change rate of c = 21 h-1 and an air velocity of 0.05 m/s (80 % value).Based on the available data, a positive correlation between the air change rate and the 50 % frequency point of air velocity can be determined. There is also a positive correlation between the temperature range in the cage and thecooling load per area (Q/A).For further investigations, two different air distribution system were installed in identical buildings of the Düssel-dorf University. One consisted of an air distribution ceiling with slot outlets and linear diffuser. Both rooms were supplied by the same duct. This elaboration compares both systems.As criteria of the room and cages, it"s deviation from the calculated value and the maximum air velocity were determined.The Air Distribution Performance Index (ADPI), adapted to the actual conditions, is being used for the first time for the evaluation of the air conditioning systems of an experimental small animal keeping. For a methodical approach, grid measurements in the room are considered to be most suitable. The influence of air exchange rate with the alternative use of wire and macrolon cages has to be taken into consideration.The correlation of cage and room climate can be described as follows:The grid measurements in the unoccupied laboratory result in a temperature difference of 1.7 K of the average values and air velocities of 0.00 to 0.10 m/s for the air ceiling system. The same values for the linear diffuser results in 4.8 K and 0.00 to 0.24 m/s.Due to the remarkable vertical temperature gradient for the air distribution ceiling system, the ADPI value is less than 94.4 % of the linear diffuser system. When changing the air exchange value to c = 25 h-1, the ADPI value of the air distribution ceiling system can be increased to 77.8 %.The same measurements for the occupied laboratory result in an temperature difference of 2.6 or 2.8 K. The air velocity ranges from 0.00 to .19 m/s. The ADPI was 36.4 % when using the linear diffuser system and 62.5 % when using the air distribution ceiling.The usage of wire cages results in less constant and therefore less tolerable conditions for the animals. The different manners of heat exchange between macro- and microenvironment through the open cage surface via mass transfer or through the enclosed cage surface with heat transfer are investigated with a simple method.The enclosed cage surfaces are insulated with insulation slabs.The investigation of the microenvironment demonstrated hat the linear air diffusers give a higher air flow rate causing a disadvantageous interval of 1.7 K against the temperature interval of 0.5 K of the air distribution ceiling system. The results of the above mentioned report for the air conditioning of the Düsseldorf University laboratory can therefore not be confirmed.The use of an air distribution ceiling results in more constant climatic conditions in the empty room.The air distribution ceiling is a simple and reliable system furnishing acceptable room conditions and air velocites with the advantage of a variable room usage. For the comparability and transparency of further investigations for the air conditioning system of the small animal laboratory, the use of the following parameter is recommended:In addition to the cooling load, the cooling load per area and for the reduced cooling load, the percentage of the maximum cooling load should be defined.A cooling load simulation instead of animals seems to be unsuitable.As criteria for the air conditioning, the temperature gradient in the room, in the cages, their deviation from the stipulated value and the maximum air velocity should be used.The ADPI value is more informative than the measurement of independently temperature and air velocity values.The ADPI value is being transferred to the investigated situation and is considered as a suitable value for the quality of air conditions when comparing different investigation reports.