J1V5 Natural Ventilation Requirements

What are the requirements for modeling natural ventilation in both the proposed building and reference building under J1V5?

Natural ventilation in both buildings must be modeled with:

• Frequency of data output at least hourly.

• Opening flow properties as specified in Table S45C3m.

• Wind pressure coefficients according to Tables S45C3n and S45C3o.

• Infiltration values, unless building sealing is verified using J1V4, in which case infiltration values equivalent to the intended building air change rate at 50 Pa divided by 20 may be used for the proposed building only.

Wind pressure according to Tables S45C3n and S45C3o are general in nature, provided to maintain consistency in the J1V5 method. They are unlikely to represent accurate wind pressure for your site and can also be generated from your climate file within the Airflow Network Simulation settings.

Table S45C3m: Window Opening Area Percentage

Table S45C3m specifies the window opening area percentages based on window type. These must be nominated to complete an Airflow Network for your model.

Window Type	Opening Area Percentage
Any window with restricted opening due to safety requirements	10%
Sliding and double hung	45%
Casement, awning, louvre, bi-fold, pivot, tilt and turn, French	90%

Table S45C3n: Wind Pressure Coefficients

Table S45C3n outlines wind pressure coefficients for natural ventilation in low-rise buildings (under 12 m) based on exposure type, façade component, and wind direction.

Exposure Type	Façade Component	Wind Direction (0°)	Wind Direction (45°)	Wind Direction (90°)	Wind Direction (135°)	Wind Direction (180°)
Exposed	Wall	0.70	0.35	-0.50	-0.40	-0.20
	Roof pitch < 10 degrees	-0.80	-0.70	-0.60	-0.50	-0.40
	Roof pitch 10 to 30 degrees	-0.40	-0.50	-0.60	-0.50	-0.40
	Roof pitch > 30 degrees	0.30	-0.40	-0.60	-0.40	-0.50
Semi-exposed	Wall	0.40	0.10	-0.30	-0.35	-0.20
	Roof pitch < 10 degrees	-0.60	-0.50	-0.40	-0.50	-0.60
	Roof pitch 10 to 30 degrees	-0.35	-0.45	-0.55	-0.45	-0.35
	Roof pitch > 30 degrees	0.30	-0.50	-0.60	-0.50	-0.50
Sheltered	Wall	0.20	0.05	-0.25	-0.30	-0.25
	Roof pitch < 10 degrees	-0.50	-0.50	-0.40	-0.50	-0.50
	Roof pitch 10 to 30 degrees	-0.30	-0.40	-0.50	-0.40	-0.30
	Roof pitch > 30 degrees	0.25	-0.30	-0.50	-0.30	-0.40

Table S45C3o: Wind Pressure Coefficients for High-Rise Buildings

Table S45C3o details wind pressure coefficients for natural ventilation in high-rise buildings (height > 12 m) based on exposure type, façade component, and wind direction. The table provides coefficients for different wall heights (h/H) and flat roof scenarios.

Exposure Type	Façade Component	Wind Direction (0°)	Wind Direction (45°)	Wind Direction (90°)	Wind Direction (135°)	Wind Direction (180°)
Exposed	Wall h/H = 0.0	0.30	0.22	-0.23	-0.43	-0.24
	Wall h/H = 0.2	0.32	0.22	-0.43	-0.44	-0.25
	Wall h/H = 0.4	0.39	0.16	-0.56	-0.43	-0.27
	Wall h/H = 0.6	0.55	0.24	-0.62	-0.41	-0.29
	Wall h/H = 0.8	0.65	0.32	-0.65	-0.39	-0.28
	Wall h/H = 1.0	0.40	0.15	-0.65	-0.38	-0.26
	Flat roof h/H = 0.0	-0.23	-0.23	-0.23	-0.23	-0.23
	Flat roof h/H = 0.2	-0.43	-0.43	-0.43	-0.43	-0.43
	Flat roof h/H = 0.4	-0.56	-0.56	-0.56	-0.56	-0.56
	Flat roof h/H = 0.6	-0.62	-0.62	-0.62	-0.62	-0.62
	Flat roof h/H = 0.8	-0.65	-0.65	-0.65	-0.65	-0.65
	Flat roof h/H = 1.0	-0.65	-0.65	-0.65	-0.65	-0.65
Semi-exposed	Wall h/H = 0.0	0.19	0.08	-0.15	-0.28	-0.15
	Wall h/H = 0.2	0.20	0.08	-0.28	-0.29	-0.16
	Wall h/H = 0.4	0.25	0.10	-0.36	-0.28	-0.18
	Wall h/H = 0.6	0.36	0.16	-0.40	-0.27	-0.19
	Wall h/H = 0.8	0.42	0.20	-0.42	-0.25	-0.18
	Wall h/H = 1.0	0.26	0.10	-0.42	-0.25	-0.17
	Flat roof h/H = 0.0	-0.15	-0.15	-0.15	-0.15	-0.15
	Flat roof h/H = 0.2	-0.28	-0.28	-0.28	-0.28	-0.28
	Flat roof h/H = 0.4	-0.36	-0.36	-0.36	-0.36	-0.36
	Flat roof h/H = 0.6	-0.40	-0.40	-0.40	-0.40	-0.40
	Flat roof h/H = 0.8	-0.42	-0.42	-0.42	-0.42	-0.42
	Flat roof h/H = 1.0	-0.42	-0.42	-0.42	-0.42	-0.42
Sheltered	Wall h/H = 0.0	0.10	0.04	-0.08	-0.15	-0.08
	Wall h/H = 0.2	0.11	0.04	-0.15	-0.15	-0.08
	Wall h/H = 0.4	0.13	0.05	-0.19	-0.15	-0.09
	Wall h/H = 0.6	0.19	0.08	-0.21	-0.14	-0.10
	Wall h/H = 0.8	0.22	0.11	-0.22	-0.13	-0.09
	Wall h/H = 1.0	0.32	0.05	-0.22	-0.13	-0.09
	Flat roof h/H = 0.0	-0.08	-0.08	-0.08	-0.08	-0.08
	Flat roof h/H = 0.2	-0.15	-0.15	-0.15	-0.15	-0.15
	Flat roof h/H = 0.4	-0.19	-0.19	-0.19	-0.19	-0.19
	Flat roof h/H = 0.6	-0.21	-0.21	-0.21	-0.21	-0.21
	Flat roof h/H = 0.8	-0.22	-0.22	-0.22	-0.22	-0.22
	Flat roof h/H = 1.0	-0.22	-0.22	-0.22	-0.22	-0.22

How are operation settings for natural ventilation defined under J1V5 for both the proposed and reference buildings?

Operation settings for natural ventilation S45C3(3)(e) mandate that:

• Openings must close when the external dry bulb temperature is ≤ 1°C higher than the air-conditioning service cooling set point.

• Openings must close when the external dry bulb temperature is ≥ 1°C lower than the air-conditioning service heating set point.

• Openings must remain open during all hours of the year that do not meet the above closing conditions.

As per Table S45C3l, If windows are open in accordance with S45C3(3)(e), the Heating, ventilation and air-conditioning schedule must be Off.

Why is it important to model natural ventilation with consistent parameters between the proposed building and the reference building under J1V5?

Consistent modeling of natural ventilation parameters ensures fair and accurate comparisons between the proposed building and the reference building in terms of energy efficiency and compliance with J1V5 standards. This consistency helps evaluate the effectiveness of natural ventilation strategies in both buildings.

Where can I find detailed information about Tables S45C3m, S45C3n, and S45C3o referenced in J1V5 for modeling natural ventilation properties?

Detailed information about Tables S45C3m (opening flow properties), S45C3n (wind pressure coefficients), and S45C3o (wind pressure coefficients) can be found in the National Construction Code (NCC) documentation or through guidelines provided by the Australian Building Codes Board (ABCB). These tables specify the parameters necessary for accurately modeling natural ventilation as part of compliance assessments under J1V5.