SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3 Energy Performance Certificates Natural Ventilation PRESENTED BY

SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3

Energy Performance Certificates

Natural Ventilation

PRESENTED BY


Ventilation Strategies

Naturally ventilated buildings typically use less than half the energy of air conditioned buildings, and reduce capital costs by some 15 percent, and associated maintenance costs. Natural ventilation is also proven to improve occupant performance and reduce incidence of Sick Building Syndrome. (The Enviromental Illness Resource)



Ventilation can be provided in a number of different ways, but each method can be categorized as either a natural ventilation system, a mechanical system or a combination of the two.

The choice of ventilation systems is largely dependent on the following factors:

• Predicted heat gains to the space.

• Occupant usage patterns.

• External noise levels and air quality.

• The need to remove contaminated air.

Natural ventilation is basically air that enters a building by natural means such as temperature difference and/or wind.



The most basic natural ventilation system is the provision of openable windows.

Windows can cause localized discomfort zones due to draughts and cold radiation in winter, or solar gain in summer.

Occupants of naturally ventilated buildings with openable windows are generally willing to accept a wider range of internal temperatures than occupants of air-conditioned buildings with sealed windows.



Windows with a large opening area provide the best summer ventilation, but large glazed areas can cause excessive overheating due to solar gain.

Large window areas can also result in excessive glare, leading to the use of blinds and artificial lighting on bright days.

A well designed and positioned window should allow adequate ventilation on warm, breezy days without causing unwanted draughts in the work area. Windows with an upper fanlight are well suited to this task.



The problem of draughts and excessive heat loss caused by opening windows during the winter months can be avoided by the provision of trickle vents in the window frame. These are small weatherproof openings which maintain a low ventilation rate.

Window mechanisms which can be finely set provide a useful addition to trickle vents during the spring and autumn when supplementary ventilation may be required.

Friction stays on side and top-hung casement windows areparticularly good in this respect.



The use of powered window actuators enables multiple windows and other ventilation openings to be controlled as part of an automatic control strategy, such as a building management system (BMS). Manual control is also possible by means of push-button switches or hand-held infrared remote controls.

Automatic control can be achieved in response to a range of parameters such as

•Internal and external temperature•Wind speed and direction•Solar gain•Rain•Air quality



Single-sided ventilation

Stale warm aair out

Fresh air in

Single-sided ventilation describes a space primarily ventilated by wind entering one or more openings within a single external wall. On days when there is little or no wind, limited ventilation is still possible if windows have top and bottom openings. This will enable convection currents in the space to expel warm air through the top opening and draw fresh air in at the bottom (known as stack ventilation). Large vertical openings are also effective, such as a horizontal sliding sash window.



Cross ventilation

Fresh air Stale, warm air

Cross ventilation is a very effective way to achieve a high rate of ventilation and can be used in relatively deep-plan offices. Wind drives air through open windows on the windward side of the building and open windows on the opposite side allow stale air to escape.



Stack ventilation describes the process of buoyant, warm air rising upwards in a building and exiting through one or more high-level openings. The air displaced from the building causes cooler fresh air to be drawn into the building through low-level openings, such as windows, and doors. The main benefit of stack ventilation is that the temperature difference between the inside and outside of a building is the driving force and can therefore provide ventilation on hot still days when there is little or no wind

Stack Ventilation



Night Cooling

Night cooling refers to the operation of natural ventilation at night to purge excess heat from occupied spaces. It also uses the lower external temperature to reduce the temperature of the building fabric. A building with sufficient thermal mass that can be exposed to night time ventilation can reduce peak internal temperatures by 2-3°C. Night cooling offers the potential to minimise reliance on air conditioning and improve the internal conditions in naturally ventilated buildings. Good control of night cooling is required in order to achieve maximum free cooling whilst avoiding overcooling and subsequent re-heating or thermal discomfort the following day.



Mixed-mode ventilation

Mixed mode is a term that describes a system which combines natural and mechanical ventilation. The mechanical element can be extract, supply or a combination of the two, however it is typically a supply system. The mechanical element ensures that an adequate air flow is maintained when natural ventilation is inadequate. This is particularly useful at night when it can be used to purge heat from the building in readiness for the next day.


Local Mechanical Exhaust

• Follow LATEST Conventions

• Example– Toilet – 2m high x 1m wide x 3m long– 6m3 x 1000 = 6000 Litres x 10 Air Changes/Hour– 60,000 Litres/Hour / 3600seconds (in an hour)– 16.666 l/s divide by 3m length– Equals 5.5 l/s/m2

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SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3 Energy Performance Certificates Natural Ventilation PRESENTED BY