E10: Natural Ventilation – Above Green

Requirement Summary

This measure can be claimed when two conditions are met.

Room geometry conditions must be met. These include the ‘room depth to ceiling height ratio’ and the ‘minimum area of opening.’
If the rooms are air-conditioned, the air-conditioning system in the rooms must be provided with an auto-shut off control that switches the air-conditioning off while the room is being naturally ventilated.

The methodology for the calculation is explained in the Potential Technologies and Strategies section, which also shows the minimum required ventilation conditions and an example of auto-shut off controls.

Table 26 shows the spaces that must be naturally ventilated for each building type to claim the natural ventilation measure. Each row in the table represents a separate measure in the software.

Table 26: Areas to be Naturally Ventilated, by Building Type

Building Type	Spaces that must have Natural Ventilation
Homes	Bedrooms, Living Room, Kitchen
Hospitality	Corridors
	Guest Rooms (with auto controls)
Retail	Corridors, Atrium, and Common Areas
Offices	Offices, Corridors, and Lobby
Hospitals	Corridors
	Lobby, Waiting, and Consultation Areas
	Patient Rooms
Education	Corridors
	Classrooms

For multiple rooms of one type, the condition must be met by 90% of the rooms of that type in the building e.g. rooms of a hotel.

Intention

A well-designed natural ventilation strategy can improve occupant comfort by providing both access to fresh air as well as reducing the temperature. This results in a reduction of the cooling load, which lowers initial capital and maintenance costs.

Approach/Methodologies

The key factors in deciding the ventilation strategy are room size (depth, width and height), and the number and location of openings.

Both the ‘room depth to ceiling height ratio’ and the ‘minimum area of opening’ must be calculated using the built-in calculator in EDGE. Each relevant space type for a project must be entered on a separate row in the calculator, to ensure adequate natural ventilation for all the required spaces in the building. All space types required for a building type must pass in the calculator in order to claim the measure.

To evaluate whether the openings on a wall qualify for natural ventilation, take the window-to-wall ratio for that particular wall. The window area must be at least 10% of the wall area to be counted as an opening for natural ventilation. Openings less than 10% of the wall must not be considered for natural ventilation (although it will still count towards the WWR calculation).

Potential Technologies/Strategies

Figure 9. Auto shut-off control for air-conditioning based on natural ventilation

EDGE uses cross-flow ventilation, where fresh air is drawn from outside into the occupied space and the exhaust air is delivered at a different location, as explained in Table 27. This type of ventilation is used for the improved case as it is most effective if the external air temperature is neither too hot nor too cold (temperate climates). As EDGE takes into account the external temperature, the software can test the ventilation’s potential effectiveness. If EDGE predicts significant savings, then a suitable strategy should be considered.

Two basic approaches are most often implemented in the design of cross ventilation: single-sided and two-sided. Two-sided ventilation is used to ventilate single spaces (which have openings on both windward and leeward sides) and double-banked rooms that rely on openings in corridors between rooms. Single-sided ventilation is used where two-sided ventilation is not possible, but the room depth that can be ventilated in this way is much lower.

Table 27: Types of natural ventilation

To achieve acceptable natural ventilation flow, the following methodology must be considered: i) maximum ratio of floor depth to ceiling height, and ii) the heat gains to be dissipated, which determine the total area of the opening. The latter is simplified by only providing the % of floor area as the openable area.

The depth of space that can be ventilated using a cross-flow ventilation strategy is dependent on the floor to ceiling height and the number and location of the openings. The rules of thumb below can be used to assess compliance.

Room Depth to Ceiling Height Ratio

EDGE’s methodology for natural ventilation requires that the maximum ratio of the room depth versus ceiling height must be calculated first. See Table 28 for the maximum ratios for different room configurations.

Table 28: Depth of floor to ceiling height ratios for different room configurations

Minimum Area of Opening

The minimum area of opening required depends on the expected heat gains in a space. Table 29 indicates the percentage of the opening area required in each space type in order to dissipate those heat gains from the space. The built-in calculator in the EDGE App incorporates these percentages automatically. The minimum required area of the opening is calculated by multiplying the total area of the room by the required percentage.

Table 29: Minimum area of opening as a proportion of floor area for different heat gain ranges.

Example:

Q: A corridor with 20sqm floor area and ceiling height of 3m has 2 windows for cross ventilation. What are the design criteria to ensure compliance with natural ventilation requirements?

A: The ratio of the depth of the floor to the ceiling height should be less than 5. The ceiling height is 3m, therefore, the maximum depth of the corridor can be 15m. For example, the corridor plan can be 2m x 10m where 10m is the depth.

10% of the floor area should be openable which is 2m2 , making each window opening area at least 1m.

Q: A classroom with 16sqm floor area and a ceiling height of 3m has a single window for ventilation. What are the design criteria to ensure compliance with natural ventilation requirements?

A: The ratio of the depth of the floor to the ceiling height should be less than 1.5. The ceiling height is 3m, therefore, the maximum depth of the room can be 4.5. For example, the room plan can be 4mx4m where the depth is 4m.

20% of floor area should be openable, which is 3.2m2 . This can be provided by a French door that is 2m high and 1.6m wide.

Relationship to Other Measures

Since employing natural ventilation can significantly reduce the cooling load, the impact of more efficient cooling systems is sometimes reduced to an insignificant level. As with all passive design solutions, natural ventilation should therefore be considered before the detailed design of any HVAC equipment.

Assumptions

The base case assumes that ventilation is delivered using mechanical means, while the improved case assumes that natural ventilation provides cooling during the hours when the temperature outside is suitable. If the building has mechanical cooling, the savings are reflected in the main Energy chart in the Cooling and associated energy uses. If the building does not have mechanical cooling, the cooling load is still calculated and is shown as “virtual” energy on the charts.

Cooling load is reduced through natural ventilation and other passive measures including improved insulation, reduced window-to-wall ratio, reduced SHGC, improved solar shading, and specifying ceiling fans. Reducing the cooling load will result in improved performance even when no mechanical cooling is specified and the savings are only reflected in “virtual energy”.

Compliance Guidance

If this measure is claimed, then the design team will need to demonstrate compliance with the depth of floor-to-ceiling height ratio and minimum area of opening for all corridors as explained in the Potential Technologies/Strategies section above.

Design Stage

Post-Construction Stage

At the design stage, the following must be used to demonstrate compliance:

Typical floor plans for every floor showing the layouts of the naturally ventilated spaces and the location of openings; and
Typical sections showing the floor-to-ceiling height for every floor; and
Calculations showing the depth-to-ceiling height ratio and the minimum area of opening for each typical space

At the post-construction stage, the following must be used to demonstrate compliance:

Confirmation from the project team that no changes have been made to the layout or the floor to ceiling height during the design/construction process; or
As-built drawings including floor plans and sections; and
Photographic evidence to demonstrate that the plan layouts and location of openings as specified at the design stage have been constructed.