Various air handling units (AHUs) are implemented in the software. The developed modules that consist of specific AHUs are:
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Recuperator
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Mixing module
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Batteries and humidifiers
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Fans
The recuperator is the heat exchanger that transfers energy from the return air to the intake/fresh air entering the AHU. The mixing module is installed to enable bypassing the return air from the zonal model to the system. Air preparation is carried out in the set of batteries. Different configurations are possible to treat the conditioned air in the AHU. We use heat exchangers and humidifiers for heating and cooling. The supply fan is installed to enable airflow from the AHU to the zonal model, and the exhaust fan is used for transporting air from the zonal model back to the AHU. The parts of the AHU are shown in Figure 1.
We decided to introduce only two BCs of AHUs, based on the type of humidifier installed in the AHUs. There are:
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steam or direct humidifiers
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adiabatic or indirect humidifiers
In the steam humidifier, water vapour is injected directly into the conditioned airflow, whereas in the adiabatic humidifier, the air is humidified by passing through open water flow channels.
The set of batteries in the direct AHUs is:
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Preheating unit
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Cooling unit
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Postheating unit
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Direct humidifier
Whereas in the adiabatic AHU example, the modules are:
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Preheating unit
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Cooling unit
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Adiabatic humidifier
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Postheating unit
The purpose of the humidifier is to humidify the air when the humidity ratio of the intake/fresh air is lower than required, while the cooling battery is used to dehumidify and cool the air when the humidity ratio of the intake/fresh air is higher than required. The preheat battery is used to heat the air before the adiabatic humidifier, and the postheating battery is used to heat the air to the required temperature level before it leaves the air handling unit. Unlike the others, the postheating battery is used in both cooling and heating the conditioned air.