Inlets
630 to 1260 ÷ 340 m³/min = 1.85 to 3.70 or 2 to 4 fans
The sizing and run times should be adjusted to suit an individual house but the basic principles remain the same. The minimum ventilation cycle run times are only guidelines and daily adjustments should be made based on air quality and maintaining humidity below 65 % where possible. If the number of fans works out to be less than 1, then cycle on time can be adjusted to less than 60 seconds to maintain correct air exchange rates and not over ventilate the house. Some newer controllers use m3/bird/hr as an input setting for their minimum ventilation rates. In order to convert to these units, first calculate the total ventilation capacity at each age based on the number of fans used and the cycle timer program and then divide by the number of birds in the house.
Important points about inlets: • Minimum ventilation
inlets should be sealed especially at the hinge, sides and along the
leading edges, to prevent the cold air being directed down to the floor. • When open, the air should only enter over the top of the inlet and not from the sides or through the bottom of the inlet • All minimum ventilation
E.g. Capacity of 2 fans = 40,800 m3/hr
inlets should direct air towards the peak of the house. The pressure drop across the inlets should be adjusted to ensure that the incoming air reaches the peak where the heat has accumulated. • The pressure drop selected will depend on the width of the house or how far the air must travel once it enters the house. • Correct air pressure is achieved by matching the inlet area and the fan capacity. • Air inlets should be pressure controlled to maintain constant air speed throughout the ventilation stages. • Table 3 can be used as a reference for the correct static pressure/inlet air speed required to ensure incoming air stays as close to the ceiling until it reaches almost half way across the house. • The pressure drop selected will depend on the house width, how far the incoming air jet must travel once it enters the house, and the outside temperature.
Cycle time at day 0 = 60s ON; 240s OFF = 20% run time
Total capacity on cycle time = 20% of 40,800 m3/hr = 8160 m3/hr House has 40, 000 birds, so = 8160 m3/hr ÷ 40 000 birds = 0.20 m3/bird/hr Static Pressure Test The number of fans to run for minimum ventilation has been calculated and a timer program for their run time has been designed. Next, it is important to achieve correct air conditioning. First, we need to ensure the house is as air tight as possible in order to effectively generate a negative pressure and ensure air enters through the inlets and not through leaks or gaps around the house. Conducting a static pressure test will let you know how tight or leaky your house is (see details of static pressure test in Andrew Bourne’s article). Once a tightly sealed house has been established it is important to ensure correct inlet management.
Table 3. The required inlet airspeed and pressure difference.
Required inlet airspeed and pressure difference
House width m ft
Pascals (Pa)
Inches of water (in wc)
Airspeed
Distance air travels m ft
m/s
fpm
10
30
20
0.08
5.7
1,112
5.0
16
12
40
25
0.10
6.5
1,280
6.0
20
15
50
31
0.12
7.2
1,417
7.5
25
18
60
37
0.15
7.8
1,535
9.0
30
21
70
43
0.17
8.4
1,654
10.5
35
24
80
49
0.20
9.0
1,772
12.0
40
3
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