Download 5.L3 Nat Vent ABBE

Energy Performance
Certificates
Natural Ventilation
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SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
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)
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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 are
particularly good in this respect.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
Single-sided ventilation
Stale warm a
air 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.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
Stack Ventilation
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
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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 reheating or thermal discomfort the following day.
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3
Ventilation Strategies
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.
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Local Mechanical Exhaust
• Follow LATEST Conventions
• Example
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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
SA AC REGIONAL 1 © STROMA CERTIFICATION LTD v1.3