McQuay MDS030AR Applications Manual page 59

The conflux of the return air inlet brings little affect on the air flow pattern in the room. So, its structure
is simple. Some only have a metal mesh in the orifice, or a shutter or grille.
The return air inlet location and shape depend on the air flow pattern. If it is installed in the lower
area of the room, the lower edge of the inlet must be at least 0.15 m away from the ground.
The return air inlet structure may be simple, but should be equipped with air volume adjustment
device.
Size of the air outlet
Determine the air volume and type of a single air outlet according to the number of air outlets to be
installed and the volume requirements in the room where the air conditioner will be installed. Make
sure there is no overlapping between the set air volume and the minimum diffusion radius, and the
maximum diffusion radius covers the whole room. In addition, check whether the vertical arrival
distance is adequate, and determine the air speed in the air outlet at the acceptable noise level.
Air flow pattern diagram
(a)side air supply bottom air return
3.4.2 Calculation of the Air Pipe Resistance
The air resistance in the air outlet and return air inlet cause pressure loss when the air pipe is being
used, and the unit can supply air only when it overcomes the resistance. It is equal to the air
pressure of the unit with pressure loss, that is, exterior static pressure (ESP).
The pipe resistance must be equal to the ESP. Otherwise, the air volume will be too large or too
small causing the unit failure.
To determine the ESP of the unit, get the whole-static pressure of the air pipe. In this case, it is
generally required to calculate the static pressure loss of the air pipe at the farthest point or
maximum static pressure.
Calculation method of the air pipe resistance
Preliminary determination of the air pipe resistance:
Air pipe resistance=R
R =0.8~1.5Pa/m
m
L: Total length of the air pipe with the loop of most resistance, m
K: Ratio of local resistance loss to frictional resistance. If there are few local components,
k=1~2; if there are many local components, k=3~5
Draw the ventilation system diagram, mark the air flow by segment and number each
pipe segment.
Assume the air speed (refer to annex 4), and calculate the cross-section dimension and
the pipe diameter.
Check the air speed according to the actual pipe diameter, and calculate the actual
speed, which should not be higher than the recommended value in the design manual.
(b)bottom air supply upper air return
(d)upper air supply upper air return
Air flow pattern diagram
L(1+K) (Pa)
m
Design & installation Guide For McQuay MDS Multi System
(c)upper air supply bottom air return
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