Prior to testing & commissioning ensure that all the sections of the Air Handling Units are thoroughly cleaned. In case units are supplied with per alumna panels, polythene protective film must be peeled off and must be ensured that no traces of film is left loose within the unit. Only qualified & experienced personnel shall perform testing & commissioning.
Ensure all panels, if removed during installation, are in position. Ensure all electrical wiring carried out and all components are provided with safety protecting and isolating devices. Remove all filters including panel filters: install low efficiency filters such as gauze bags or a set of throw away type filters.
Ensure all dampers are opened. Check water/ steam/ refrigerant coil connection for any leaks. Ensure that all the air in the system and coil is vented out. Check coil face free from free from debris. Add water in condensate drain pan to prime the trap and ensure free flow of water into the drain. Ensure that minimum water levels are maintained in electrical pan humidifier/ air washers.
AHU Fan Start-up Method Statement
- Screw out security nuts if spring mounts the unit.
- Lock out the primary and secondary power sources.
- A complete inspection shall be made of all ductwork and the interior of the fan. Make certain there is no foreign material which can be drawn into or blown through the fan or ductwork. Eyes should be protected against undetected foreign material through the use of safety goggles or other appropriate means.
- Make sure the foundation or mounting arrangement are as per the approved shop drawings & duct connections are adequately designed & installed in accordance to the specification & approved drawings.
- Check & tighten all hold-down bolts.
- Check the fan assembly and bearings for proper grounding to prevent static electricity discharge.
- Spin the impeller to determine whether it rotates freely and is not grossly out of balance.
- Inspect impeller for proper rotation for the fan design.
- Check all set screws and tighten, if necessary.
- Check belt drive or coupling alignment; use recommended belt tension.
- Check the belt drive for proper sheave selection and make sure they are not reversed which may cause excessive speed.
- Properly secures all safety guards.
- Secure all access doors to the fan & ductworks.
- Momentarily, energises the fan to check the direction of rotation.
- Switch on the electrical supply and allow the fan to reach full speed.
- Check carefully for excessive vibration, unusual noise, proper belt alignment, proper lubrication & proper amperage & voltage values.
- If any problem is indicated, switch OFF Immediately. Lock out electrical supply, secure the fan impeller if there is potential for wind milling. Check carefully for the cause of trouble and correct as necessary.
- Even if fan appears to be operating satisfactory, shut down after a brief period and recheck all components as the initial start- up may have loosen some of the bolts & set screws.
- After ensuring that there is no leaks between joints of section and system is clean, stop the fan. Dispose of low efficiency filters. Install absolute filters as supplied.
- Restart the fan. In case of a stand-by fan and motor are supplied, ensure that no short circuiting of air occurs.
- In case fan is connected to a stand-by motor for automatic change-over, do not touch the terminal of standby motor, even though motor is idle. Ensure that belts are removed and the power is isolated.
- Adjust dampers position to obtain the rated air volume.
- In case fans are supplied with variable pitch pulley, adjust the same to the desired position.
- Ensure that air volume are within the specified limits.
- Check the motor current and ensure the same is within the rated data embossed on the name plate of the equipment.
- Check ON-OFF temperature across coils and adjust water/ steam flows accordingly. Check the functioning of controls.
- Check the pressure drops across the filters and ensure that the same is within the limits.
General AHU Heat Pipe Commissioning Method
Heat pipe heat exchangers are available for either heat recovery or dehumidification applications. The heat pipes are wrapped around a cooling coil and are known as horseshoe heat pipes. A heat recovery heat pipe is subject to two air streams flowing across either side and transfers heat from on air stream to the other, a horseshoe heat pipe has both of its ends in the same air stream but is located such that the air stream is at different temperature in each location.
In order to measure the performance of a heat pipe, accurate measurements must be taken of airflow velocities and mass/ volume flow rates plus accurate measurements of the temperature of the air streams.
During testing & commissioning the system, ensure that the design conditions have been achieved. Heat pipes, however, operate at a constant effectiveness which can be calculated from the measured data irrespective of the actual conditions. The effectiveness will stay constant as long as the air volume flow rate and velocity remain constant across the heat pipe.
Run Around Coil Heat Recovery
Both a supply and extract air stream flow across the sides/top/bottom of the heat pipe (RAC) and air velocities and volume flow rates may or may not be the same. Accordingly, both air flow rates/ velocities must be measured in order to quantify the performance.
The air volume on either should be measured using a pitot traverse. This can be made on either the entering or leaving air face but should be close to the coil face but a minimum of 50mm away to prevent interference form jetting between the fin surfaces.
Within the AHU, there are a number of cross sectional changes which prevent air velocities from being even. In order to obtain an effective mean value for the velocity across the face of the heat pipe (RAC) the pitot traverse should incorporate at least 9 readings evenly spread across the face of the heat pipe. The air volume flow rate through the heat pipe can be calculated from the product of the mean face velocity and the area of the section.
As the face velocity through the components of the Air Handling Unit will never be even then the temperatures of the air streams throughout the air treatment sections will not be even. Again, a minimum of 9 evenly spread temperature readings should be taken at each measuring plane and a mean value calculated. The required temperature measuring planes for a heat recovery are the entering and leaving face of the supply section and the entering and leaving face of the extract section.
Cooling Coil Test for AHU & FAHU
- All electrical, water & ductwork connections of the unit must be completed by a qualified person.
- Check that all electrical connections comply with the wiring diagram and the thermal protection is operational.
- Completely stress-free connections are essential. The pipework of the coils should be arranged to facilitate easy removal of the coil for maintenance purposes.
- Check that the coil connections and valves are not leaking. If there are leaks, rectify the problem.
- Cooling coil sections are fitted with condensate drains. Check that these are properly fitted to allow draining and avoid air suction and water carry-over.
- Check piping for any leaks. Open or close valve to check for proper operation.
- Ensure that no air bypass occurs within the AHU and that proper sealing is carried out.
- For chilled water, proprietary corrosion inhibitor should be considered in the water remembering that the coils are made of copper tubes on the fluid side.
- Never to use untreated or improperly treated water in unit coils which may cause scaling, erosion, corrosion, algae, etc.
- It is necessary to control the leaving air temperature from the cooling coil to a dry-bulb temperature of 13.5°C which corresponds to the absolute humidity level of the comfort indoor condition of 24.4°C and 50% RH.
- In the event that the coil air on temperature drops below 5°C, a thermostat is provided to switch off the supply fan on units with water coils. It is a hard- wired form of protection and can only be monitored by the controller. This prevents hot water coils from freezing and would typically operate in cold weather if the hot water coil supply has failed.
Explanation of AHU Factory Engineered Controls
Fire Signal: The AHU unit maybe interfaced to fire alarm shut down by connecting a normally closed contact to the designated terminals. If this is not required, the fire contacts are replaced by a link.
Fireman’s Override: Remote fireman’s override switches can be connected to allow operation of the extract fan after a fire alarm has been actuated. Where a mixing box is fitted, the exhaust air damper will be driven to the fully open position while the mixed air and fresh air dampers are driven closed. Override contacts can be connected to the designated terminals where this option has been ordered.
Filter Section: A common or individual filter switch is provided to indicate when the filter section differential pressure is excessive.
Frost Protection Thermostat: A thermostat is provided to switch off the supply fan on units with water coils which prevents the hot water coil from freezing and would typically operate in cold weather if the hot water coil supply has failed.
Fan Section: A pressure differential switch is provided across each fan to provide a proof airflow indication. All fan/ motor are belt and pulley driven.
Heating & cooling Valves: Each actuator is supplied with a flying lead which needs to be connected on site to a connection box fitted on the unit.
Room Temperature Sensor: The room temperature sensor should be wall mounted at a height of approximately 1.5m inside the occupied space of average zone temperature. Do not mount the sensor near a heat source, door, and direct sunlight or in the supply air stream. It requires a single pair of screened cables.
Return Air Temperature Sensor: The return air temperature sensor should be mounted in the common return air duct, ahead of the fan so as to sense the average return air temperature. It requires a single pair screened cables. When possible, the return air temperature sensor should be fitted onto the return air inlet.
Duct Static Pressure Sensor: The duct static pressure sensor should be mounted in the supply ductwork, approximately 2/3 of the distance from the fan to the end of the longest run of ductwork. The sensors require two pairs of screened cable to the control panel. One pair supplies power to the device and the other is the pressure signal from the device to the controller.
Outside Temperature Sensor: The outside temperature sensor should be mounted on north facing wall. It requires a single pair of screened cables. The sensor can be factory mounted in the fresh air inlet.