McQuay MDS030AR Applications Manual page 60

Design & installation Guide For McQuay MDS Multi System
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Select the loop with most resistance and that with minimum resistance, and then
calculate the frictional resistance and local resistance loss of each pipe segment.
Check the unbalance ratio of the loop of most resistance to that of minimum resistance
must be less than 15%. Otherwise, redesign the air pipe system, or satisfy the balance
ratio requirements by adjusting with the valve.
3.4.3 Air Pipe Design
To improve the operational efficiency of air conditioning, carefully consider and fully install
such fittings as material, adjustment valve and fire protection valve.
Material of the air pipe
The air pipe is always made from metal material, such as sheet steel, galvanized sheet
or aluminum sheet. It also can be made from non-metal material, such as hard polyvinyl
chloride, glass reinforced plastic or other composite materials. The air pipe in the construc-
tion space or duct channel also can be used according to the actual conditions. The air pipe
surface should be polished, straight and smooth. Some air pipes should even be painted.
The air duct channel should be waterproofed. The air pipe in the room with corros ive gas
may be made from glass reinforced plastic or plastics and tightly sealed.
Air pipe shape
The cross-section of the air pipe is generally rectangle or round. It also can be
designed to ellipse, semicircle or spiral.
The round air pipe has the advantages of high strength and low material loss, but it
occupies large useful space and its elbow and tee should be of long distance.
Generally, the flexible round air pipe is used for the new air pipe, small volume air
refnet joint (such as in toilet with small area).
The rectangle air pipe occupies small space, and is easy to install and neat for surface
mounting. It has been widely applied.
For the convenience of mechanical processing of the air pipe and flange and
configuring standard valves, try to improve the utilization of the air pipe cross section.
The air pipe dimension should be designed according to Calculation Form of National
Universal Air pipe. The ratio of the height of the rectangle air pipe to its width should
be less than 4, based on the outer diameter or length of external sides. The following
table shows the standard specifications of the air pipe.
Specifications of the rectangle air pipe
120
160
200
250
Specifications of the round air pipe
Basic series Auxiliary series
100 80/90
120 110
140 130
160 150
180 170
200 190
220 210
250 240
280 260
The high-speed air pipe is generally round spiral pipe with a larger thickness.
Side size of the air pipe
320 800
400 1000
500 1250
630 1600
Diameter of the air pipe
Basic series Auxiliary series
320
360
400
450
500
560
630
700
800
2000
2200
2500
2800
Basic series
300 900
340 1000
380 1120
420 1250
480 1400
530 1600
600 1800
670 2000
750
Unit: mm
3000
3500
4000
Unit: mm
Auxiliary series
850
950
1060
1180
1320
1500
1700
1900