Compact HVAC

Compact HVAC systems are used when the HVAC model option is set to Compact and can be a useful entry route into EnergyPlus HVAC modelling allowing you to model HVAC systems in quite some detail without the need to draw an air flow network and deal with the complexities of control systems and node connections. You can model many common HVAC systems including VAV with terminal reheat, VAV with PIU, Constant volume, Fan coil units, Packaged DX units and Mechanical ventilation.

 

Compact HVAC is intermediate in detail between the Simple and Detailed HVAC model options. The heating/cooling systems defined in DesignBuilder using Compact HVAC descriptions are automatically expanded into detailed HVAC definitions behind the scenes and modelled in EnergyPlus including components such as boiler, chiller, coils, pump, cooling tower and fan part-load characteristics.

 

EnergyPlus simulations are carried out on the detailed HVAC component models generated by DesignBuilder from the compact descriptions.

 

When the HVAC model option is set to Compact, there are 5 HVAC system types:

 

 

Note: Now that Detailed HVAC is available in v3 and later we generally recommend this in preference to Compact HVAC as it provides much more control over the HVAC simulation without a lot of extra work being required to set up the data.

System type

When using Compact HVAC data, the HVAC Type is displayed beneath the Template. This cannot be edited directly - if you want to choose a different HVAC system type you should do this by selecting an appropriate template.

System availability

When using Compact HVAC data, the system availability schedule can be defined to control the overall operation of the HVAC system, including heating, cooling and ventilation. This schedule is used at the building level for 2-Unitary multizone, 3-VAV and 5-CAV systems and at the zone level for 1-Unitary single zone and 5-Fan coil.

System availability schedule

The System availability schedule defines the operation of the air system fans. For Compact Unitary systems the Fan operation mode can be set to 2-Cycling in which case air distribution only occurs when there is heating or cooling demand.

Rules

  1. Only one CAV, VAV or Unitary multizone system can be defined per building.
  2. If you select Unitary multizone, CAV or VAV at zone level, then the same selection must be made at building level.
  3. You can enter Fan coil and Unitary single zone systems in any zone without concern for the selection at building level.
  4. Pumps are modelled using typical default data.
  5. Unitary multizone and Fan coil units cannot be used in same building.
  6. Fan coil units are incompatible with Calculated natural ventilation.

HVAC Components

While most Compact HVAC data is entered directly on the HVAC model data tab, the following HVAC components are used in Compact HVAC: