honeybee_energy.ventcool.afn module

Functions to generate an Airflow Network for a list of rooms.

honeybee_energy.ventcool.afn.generate(rooms, leakage_type='Medium', use_room_infiltration=True, atmospheric_pressure=101325, delta_pressure=4)

Mutate a list of Honeybee Room objects to represent an EnergyPlus AirflowNetwork.

This function will compute leakage component parameters for the ventilation cooling energy properties of Honeybee Room and Face objects to simulate an EnergyPlus AirflowNetwork. The leakage flow coefficient and exponent values are referenced from the DesignBuilder Cracks Template[1], which provides typical air changes rates for different envelope tightness classifications for a range of building types. Specifically this function references leakage values for an ‘Excellent’, ‘Medium’, and ‘VeryPoor’ classification of envelope tightness.

VentilationOpening objects will be added to Aperture and Door objects if not already defined, with the fraction_area_operable set to 0. If already defined, only the parameters defining leakage when the openings are closed will be overwritten. AFNCrack objects will be added to all external and internal Face objects, and any existing AFNCrack objects will be overwritten.

Note

[1] DesignBuilder (6.1.6.008). DesignBuilder Software Ltd, 2000-2020.

Parameters:

• rooms – List of Honeybee Room objects that make up the Airflow Network. The adjacencies of these rooms must be solved.

• leakage_type –

  Text identifying the leakiness of the internal walls. This will be used to determine the air mass flow rate parameters for cracks in internal floors, ceilings and walls. (Default: ‘’Medium’’). Choose from the following:

  • Excellent

  • Medium

  • VeryPoor

• use_room_infiltration – Boolean value to specify how exterior leakage parameters are computed. If True the exterior airflow leakage parameters will be derived from the room infiltration rate specified in RoomEnergyProperties. This will compute air leakage parameters for exterior cracks and opening edges that produce a total air flow rate equivalent to the room infiltration rate, at an envelope pressure difference of 4 Pa. However, the individual flow air leakage parameters are not meant to be representative of real values, since the infiltration flow rate is an average of the actual, variable surface flow dynamics. If False, the airflow leakage parameters are selected from a crack data template, corresponding to the provided leakage_type. Since these leakage parameters reflect empirically obtained values for different surface types, they will result in a more realistic simulation of air flow through orifices and cracks. In both cases, interzone airflow leakage parameters are referenced from the crack data template, corresponding to the provided leakage_type.

• atmospheric_pressure – Optional number to define the atmospheric pressure measurement in Pascals used to calculate dry air density. (Default: 101325).

• delta_pressure – Optional reference air pressure difference across the building envelope orifice in Pascals. delta_pressure is used to calculate infiltration crack flow coefficients if the use_room_infiltration argument is True. See the exterior_afn_from_infiltration method in the RoomEnergyProperties class for details on how to set this value if attempting to replicate the room infiltration rate per exterior area. Default 4 represents typical building pressures.