Model for bi-directional air flow through a large opening such as a door which can be opened or closed based on the control input signal y.

For the control input signal y=1, this model is identical to Buildings.Airflow.Multizone.DoorOpen, and for y=0, the door is assumed to be closed and the air flow rate is set to the air flow rate through the crack posed by the open door, clo.

The air flow rate for the closed door is computed as

clo = Cclo ΔpmClo,

where clo is the volume flow rate, Cclo is a flow coefficient and mClo is the flow exponent. The flow coefficient is

Cclo = Lclo CDCloRat ΔpRat(0.5-mClo) (2/ρ0)0.5,

where Lclo is the effective air leakage area, CDCloRat is the discharge coefficient at the reference condition, ΔpRat is the pressure drop at the rating condition, and ρ0 is the mass density at the medium default pressure, temperature and humidity.

The effective air leakage area Lclo can be obtained, for example, from the ASHRAE fundamentals (ASHRAE, 1997, p. 25.18). In the ASHRAE fundamentals, the effective air leakage area is based on a reference pressure difference of ΔpRat = 4 Pa and a discharge coefficient of CDCloRat = 1. A similar model is also used in the CONTAM software (Dols and Walton, 2002). Dols and Walton (2002) recommend to use for the flow exponent mClo=0.6 to mClo=0.7 if the flow exponent is not reported with the test results.

For the open door, the air flow rate ope is computed as described in Buildings.Airflow.Multizone.DoorOpen with the parameters CDOpe and mOpe.

The actual air flow rate is computed as

clo = (y-1) V̇clo + y V̇ope,

where y ∈ [0, 1] is the control signal. Note that for values of y that are different from 0 and 1, the model simply interpolates the air flow rate between a fully open and a fully closed door. In practice, the air flow rate would likely increase quickly if the door is slightly opened, and hence we do not claim that the model is accurate for values other than y = 0 and y = 1.



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