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VTS reserves the right to implement changes without prior notice
Ventus Air Handling Units
Heater output adjustment consists in checking the heater's performance from the air's side through
temperature measurements in front and behind the heater, at designed supply and return
temperature values and amount of heating medium in the system.
Heater's output is controlled by adjustment of water supply temperature. It is achieved by mixing up
in the three- way valve supply water with high temperature and water coming back from the heater,
with lower temperature. Once mixed, water getting to the heater reaches appropriate temperature -
depending on the mixing level.
External conditions, similar to the rated ones occur within an annual cycle during relatively short
period. In most cases you have to take into consideration the fact that the adjustment must be carried
out in intermediate conditions, which must be recalculated in order to conform to the rated values.
Checking operation of the anti-frost thermostat is possible only when temperature of air supplied
onto the exchanger is lower than the thermostat setting (factory setting: +5
0
C). It is safe to carry out
this activity when the supply air temperature is 1-2 degree above 0ºC. Then, when the AHU is
running, cut for a moment the inflow of heating medium and watch if the thermostat is triggered. This
operation should be carried out before putting the AHU into service.
6.3 Adjustment of electric heater
Power adjustment of electric heater is carried out in most cases by means of turning off individual
group of heating coils. Multistage control (table.8) is carried out through connecting specific heating
coils with each other. Smooth control of heater power is carried out by applying the VTS control
module.
Perform simulation of lower power requirement by decreasing the set temperature value so as all
electric steps (contactors) were in off position. Next increase significantly the setting and check if all
electric steps turn on in the order in accordance with the operation description. Restore the previous
temperature setting.
Also check operation of overheating protection in case of lack of air-flow. To do so, reduce the air-
flow stream
flowing through the heater by pushing to the inlet damper or by reducing the fan's speed.
During AHU operation speed of air flowing through the heater should not be lower than 1.5
m/sec.
Please note that the lower air-flow is the more possible it is to overheat the system.
Bringing AHU to a standstill must involve some delay (0.5-5 minutes), so as to cool down heating
coils of the electric heater.
6.4 Adjustment of cooler performance
Adjustment of cooler performance should be carried out in conditions similar to the rated ones. As in
case of the heater, the effect from the air side is considered, including temperature and humidity in
front and behind the cooler.
Temperature of cooling agent is controlled this way as well. If cooler operation effect is not
satisfactory, appropriate adjustment is required. It can be carried out using the following methods:
- adjustment of cooling medium amount (water coolers),
- adjustment of air amount passing through the AHU (water cooler and coolers with direct medium
evaporation),
- adjustment through changing evaporation temperature (in case of systems with direct evaporation).
Coolers operate in most cases in complex air-conditioning systems equipped with automatic control.
Automatic control devices should be tested not only in extreme conditions but also in intermediate
cooler load circumstances.
