17
6. START-UP AND ADJUSTMENT
During the start-up it is possible to verify whether the AHU was made in accordance with the design and is ready
for operation.
The start-up and the adjustment of the ventilation/air-conditioning systems can be done only by the qualified and
competent personnel, equipped with necessary test devices.
After completing the activities described in point 5, you can proceed with the first start-up.
The fan should be started with lower load and lead towards parameters similar to the operational ones. The lower
load can be achieved by closing the damper to on the AHU inlet and additionally, in case of powering the motor
through the frequency converter, by lowering the rotation speed.
While increasing the load, check all the time the amount of current consumed by the motor.
Always make sure that the current intensity powering the fan's motor does not exceed the rated
value for the given air parameters.
Neglecting to comply with the recommendations concerning the first start-up can lead to the motor's overload and
its damage.
After the start-up, check if:
- there are no suspicious noises or unnatural mechanical sounds,
- there are no considerable AHU vibrations.
It is recommended to ensure a preliminary opening of damper on AHU inlet in the automatics
system before starting up the fan. It has an impact on the damper durability and operations and
eliminates the activation of pressure control.
Achieving the required performance of the AHU depends, among other factors, on the adjustment to the
recommendations and the test measurements.
6.1. Measurement of the air quantity and AHU output adjustment.
Measurement of air quantity is a primary measurement in case of:
- AHU start-up and technical acceptance,
- a situation when the system does not operate in line with the requirements and expectations,
- a periodic control of AHU operations and performance,
- a replacement of fan unit elements.
Before beginning the measurements and adjustments, make sure to:
- check if the damper has been adjusted to the recommended parameters at all air grilles.
- measure the amount of current consumed by the fan's motor. If it is necessary, minimize the air flow with the
main damper or reduce the fan rotation speed.
Quantitative determination of the air volume meters is based on the measurement of the average air-flow speed
in the ventilation duct test cross-section. One of the most common ways of determining the average speed is the
cross-section probing method with use of the Prandtl tube and the measurement of the speed-related average
dynamic pressure.
Crucial factors affecting the measurement accuracy are:
- the location of the measured cross-section in relation to the other elements,
- the quantity and location of test points in the measured cross-section,
- the stability and constancy of the air flow.
It is highly recommended NOT to locate the measurement cross-section directly after:
- network elements causing deformation of the velocity speed (knees, reductions, three-way connections,
dampers, etc.),
- the fan, because in the cross-section some reverse speed may occur.
