Lennox FCA 60

IOM / ROOF-TOP FLEXY™ Series - Page 41
FX AIR FLOW BALANCING
1. Operation of the grids
- Balancing grids are installed on fresh air side in order to compensate for the higher pressure drop on the ducted return
air side.
- The aim is to avoid the pressure variations in the area to air conditioned (risk of doors opening in cinemas for example)
but also to avoid a current surge on the motor when running 100% fresh air.
- The objective is to maintain constant airflow/pressure operating conditions with the supply air, regardless of the
percentage of fresh air.
- Once adjusted the air treatment fans should not see the difference between the ducted return air and the fresh air.
2. Airside adjustment procedure for the FX with 4 dampers
- Adjust the machine with the 0% fresh air configuration, the grids are open to the maximum.
- Measure the Amps and Speed of the "treatment" fan motor. Determine the airflow and pressure using the Fan Curves.
- If the absorbed Amps are higher than the value on the motor plate, the supply and return ducts pressure drop is lower
than the requested value at the time of order. Reduce the rpm, change the Pulleys if necessary.
- Once the airflow and pressure have been checked and confirmed, measure the static pressure at the 5 following points :
1a : "Treatment " fan inlet (ex : -230 Pa)
2a : "Treatment" expansion box (ex : -210 Pa)
3a : Return air box (ex : -190 Pa)
4a : Extraction expansion box (ex : -70 Pa)
5a : Extraction fan inlet (ex : -120 Pa)
- Adjust the extraction grid to reach a pressure in 4 equal to the pressure in 2 (ex : reach -210 Pa when closing).
- Check the Amps absorbed by the extraction fan motor; It must be lower than the value on the plate otherwise reduce the
fan speed.
- Reverse the fresh air percentage: 100 % fresh air at the treatment.
- Measure the Static pressure at the same 5 points
1b : "Treatment " Fan Inlet (ex : -80 Pa)
2b : "Treatment" expansion box (ex : -50 Pa)
3b : Return air box (ex : -200 Pa)
4b : Extraction expansion box (ex : -220 Pa)
5b : Extraction fan inlet (ex : -250 Pa)
- Adjust the grid on the "treatment" side only to reach a pressure at point 2b identical to the pressure at 2a (reach -210 Pa
when closing)
- Check that the pressure measured in the extraction expansion box 5b has not changed too much compared with the
previous measurement 5a. Adjust the bypass grid to compensate any possible difference.
1
2 4
3
5
Figure 25