Download ventilation and lighting design for green and odourless public toilets

VENTILATION AND LIGHTING DESIGN FOR
GREEN AND ODOURLESS PUBLIC TOILETS
Ir. K.F. LAU
Chief Building Services Engineer
Ir. M.T. SUEN
Senior Building Services Engineer
Building Services Branch, Architectural Services Department
Government of the Hong Kong Special Administrative Region
ABSTRACT
Public toilets are generally small building structures but they could have big impact on the
image of a city. Visitors and business people from overseas as well as local residents will all have
the chance to use pub lic toilets. As such, the design for public toilet needs to be considered very
carefully. Artificial lighting and mechanical ventilation systems are two of the main building
services installations that would need to be considered. However, in order to achieve a green and
odourless public toilet one cannot rely solely on the artificial lighting and mechanical ventilation
systems. The overall integration of the architectural design with the lighting and ventilation
systems of the toilet is indeed necessary. The Building Services Branch of the Architectural
Services Department of the HKSAR Government has been involved in the design and construction
of hundreds of public toilets in Hong Kong. This paper shares the experiences of the department in
designing for green and odourless public toilets. Various types of environmentally friendly
lighting and ventilation systems employed in public toilets will be discussed. The basic principle
we employed in our designs is to utilize artificial lighting and mechanical ventilation systems only
when they are absolutely necessary so as to minimize the use of energy.
INTRODUCTION
Public toilets are generally small building structures but however, their importance should
not be overlooked. A poorly designed and/or maintained public toilet may have very serious
impact on the image of a country or a city.
In an international city like Hong Kong, the users of public toilets include both local
residents as well as visitors from all over the world. Every year there are more than a million
visitors coming from all over the world to Hong Kong for business, sightseeing or some other
purposes. These visitors have very great chance to use public toilets that are located at scenic spots,
shopping areas, public transport terminus, parks and playgrounds, etc. To foreigners, the toilet
culture of a place could well represent the civilization and living standards of the people of that
city. Their images about a city could well be influenced by their experiences in using the public
toilets in that place.
In Hong Kong, there are more than 290 public toilets and 590 aqua privies located all over
the territory. Due to high population density, the usage rates of public toilets in Hong Kong are
often very high especially in urban areas. These public toilets are either standalone or integrated
with building structures such as public transportation terminus, market complex, parks and
playgrounds, etc. Most of these public toilets were designed and constructed under the supervision
of the Architectural Services Department (ArchSD) of the Government of the Hong Kong Special
Administrative Region (HKSAR). Besides building new toilets, the HKSAR Government has also
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launched a programme to renovate and improve all existing public toilets in the territory and the
project is still ongoing.
To make a public toilet successful, good design on the architectural features and layout is
certainly very important. But one must not forget that ventilation and lighting are also two vital
elements that contribute to the success of a public toilet. In fact, these two elements have direct
and instant influences on people ’s feeling when they enter and use the toilet. On the one hand,
sufficient artificial lighting and mechanical ventilation should be provided to achieve a good
service environment inside a toilet but on the other hand it is also necessary to minimize energy
usage for environmentally friendly considerations. These two different aspects seem to be
contradictory to each other. However, if they are properly coordinated and balanced off, a green
and odourless public toilet is by all means achievable.
VENTILATION
Whilst public toilet itself is actually the source of malodour, it is practically impossible to
eliminate malodour completely unless the toilet is kept away from being used which does not
seem sensible at all. Having said that, however, by careful consideration on the design of both
natural and mechanical ventilation system for a public toilet, it is possible to minimize the
nuisance of malodour both to the users as well as to the general public in the vicinity.
Ventilation requirement
According to international design guidelines and standards 1,2 &3 , the recommended
mechanical ventilation rate for toilet is around 6 to 10 air changes per hour. However, in Hong
Kong, due to its high population density, the usage rate of public toilet is generally high. It is
therefore necessary to design the ventilation rate at 15 air changes per hour. With a higher air
change rate, the removal of malodour is mo re effective. Furthermore, it will also create a higher
air movement inside the toilet that would help drying up wet floor more quickly as well as provide
some cooling effect to the users especially during hot and humid summer days.
Remove malodour at source
To minimize the spread of malodour inside a toilet, controlled and effective exhaust
ventilation system is vital. The most effective approach would be to remove the malodour at its
source as soon as possible before there is any chance for it to spread out. In general, the two major
sources of malodour in a toilet are the WC cubicles and the urinals area. Conventional toilet
ventilation system normally has exhaust ventilation outlets at ceiling level. However, this
arrangement is considered not appropriate as malodour is generated at low to mid level when
people use the toilet. The generated malodour will have to pass around the user’s nose before it
can be removed by the exhaust air grilles at ceiling level. Besides, when the malodour substances
move along, they might also be trapped inside the slits of the building materials and become very
difficult to be removed. To avoid this, therefore, exhaust ventilation outlets should be located at
low to mid level and close to the source so that malodour generated could be removed instantly
before causing any nuisance to the users or diffusing to other parts of the toilet.
Control malodour flow path
To further enhance the ventilation effectiveness and also avoid malodour being spread
through the whole toilet, the push and pull design approach should be adopted. Ducted fresh air
should be supplied at high level of the clean areas in the toilet (e.g. wash hand basins area,
circulation areas, etc.) so that a positive pressure is created at these areas. On the other hand, the
malodour generation area is maintained at negative pressure by the exhaust ventilation system.
The airflow path inside the toilet will thus be under control and fresh air will flow from the clean
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areas towards the malodour generation areas and then removed by the mechanical exhaust system.
Alternatively, when the supply air is discharged above the WC cubicles, laminar flow diffusers
should be employed and the supply air should be kept at very low velocity. This would avoid
agitating the malodour at the source due to turbulent air current. Annex I shows a typical
arrangement of the mechanical ventilation system for controlling odour flow path inside a toilet.
Besides, the high level fresh air supply will also enhance internal air movement, which results in
better human comfort as well as help drying up wet floors more quickly.
Enhanced floor drying
From experience, it is found that the floor under and near to the wash hand basins area is
often in wet condition. The problem is more obvious when the hand dryers are located at some
distances from the basins area. It is because many toilet users do not use the hand dryers and they
just shake off the water droplets from their hands onto the floor after washing. To tackle this
problem, blower fans are installed under the basins and blow air directly onto the floor to help
drying up the wet floor more quickly (refer Annex I). Moreover, this would also induce some
evaporative cooling effect to the toilet during hot summer days. If the basins area is attaching to an
external wall, air can be drawn from the outside atmosphere and this would further increase the
overall ventilation air change rate for the toilet.
Natural ventilation
Special consideration on the design of the toilet enclosure and layout could also enhance
its natural cross ventilation and thus minimize the use of mechanical ventilation. Features like
lifted-up roof, roof ventilation openings, external wall undercut, high and low level external
louvres, entrance gate in lieu of solid door, unobstructed air flow path with respect to entrance
opening position, openings on opposite walls, etc. are measures that could increase natural cross
ventilation inside a toilet and help to remove malodour more quickly and effectively. However, the
outdoor wind situation changes all the time and no one can really predict precisely how the wind
would blow. As such, careful investigations on the wind statistics and site surveys must be carried
out if a public toilet is to rely solely on natural ventilation. Moreover, in places like Hong Kong,
the city development changes day to day. The designer must also consider whether the wind
situation will be affected in future due to the erection of surrounding new building structures.
LIGHTING
Lighting for public toilets basically includes three main aspects namely internal lighting,
external lighting and signage lighting. Internal lighting is basically required for providing a safe
and effective operating environment for the toilet users and the cleaners. The external lighting
could enhance the architectural features of a toilet and also to make it perceptible at night time to
the people who need it. The signage lighting enables the users to identify the appropriate toilet to
go to.
Illumination level
In general, the recommended illumination level inside a toilet is designed at 100 to 150
lux 4&5 . This illumination level is basically sufficient for general applications. However, from
experiences in Hong Kong, with this illumination level users often complain that the toilet looks a
bit gloomy. This might probably due to improved living standards nowadays and people get used
to brighter environments. As such, a higher illumination level of say 250 to 300 lux inside the
toilet is recommended. With a brighter internal environment, the toilet would look to be cleaner
and people who use the toilet would tend to give more care to avoid messing up the place. Besides,
a higher illumination level could also deter crimes to happen inside the toilet.
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Artificial lighting
The selection of proper light fittings for use in public toilets is very important. To
minimize future maintenance requirements, the fittings chosen should preferably be of waterproof
and vandal-resistant type. They should also be mounted at a height that is out of reach by the
general public so as to minimize vandalism. Since the operating hours of these light fittings are
rather long (some of them might need to operate 24-hours round the clock), high efficacy and/or
energy efficient lamp elements should be selected. As for exterior lighting, it should be so
designed that the public toilet would blend with the local environment and/or surrounding
buildings but could still effectively review its functional purpose.
Natural lighting
The use of artificial lighting inside a public toilet could be greatly reduced especially
during bright sunny days if the toilet enclosures were designed to be more transparent. This could
be achieved by providing more windows, use of skylights, glass blocks, etc. that would allow
more daylight to penetrate into the toilet. However, care must also be taken to avoid causing green
house effect inside a toilet due to excessive glass enclosures. Provisions for escape of hot air at
high level of the toilet should therefore be allowed if there were considerable glazing areas.
Careful consideration on a suitable balance between artificial and natural lighting for a public
toilet is therefore required at the design stage.
ENVIRONMENTAL CONSIDERATION
In general, the major electricity consuming installations in public toilets are ventilation
and lighting systems. To reduce the energy consumption of the lighting system the designer has to
make good use of the available daylight. Whilst for ventilation system, maximize natural
ventilation can reduce the energy requirement for mechanical ventilation fans. However, when
minimizing the use of artificial lighting and mechanical ventilation, we must not desert the proper
performance of the toilet and a careful balance should be made. Hence, a basic principle to be
applied would be to shut down the unnecessary lighting and/or ventilation fans whenever they are
not required in order to minimize energy consumption.
Wind sensor control
If the design of a toilet enclosure has maximized its natural ve ntilation capability, the
operation of mechanical ventilation fans could be minimized. Wind sensor could therefore be
employed for on/off control of the toilet mechanical ventilation fans. The wind sensor should be
composed of a wind speed sensor and a wind direction sensor. By careful site adjustment during
testing and commissioning, the toilet ventilation fans can be switched off when outdoor prevailing
wind is strong enough to effect sufficient air replacement inside the toilet.
Photocell sensor control
The lighting system for a public toilet often operates 24 hours a day and 365 days
throughout a year. It is therefore an area of concern in terms of energy conservation aspect. At
areas near window openings, skylights, external door openings, etc., photocell sensor should be
used to switch off or dim down the lightings with due reference to the outdoor daylight intensity
so as to save energy. There are some light fittings now available in the market that incorporate
individual built- in photocell sensor and the installation of these fittings are no more difficult than
an ordinary light fitting.
Occupancy sensor control
There are certain periods of a day, e.g. mid-night to dawn, that a public toilet may not be
occupied and some of the artificial lightings can then be switched off to save energy. This can be
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achieved by the use of occupancy sensors located at strategic locations inside a toilet to control the
on/off of some of the lightings. To avoid frequent switching of the lightings which would shorten
the life of the lamp element as well as the fitting, time delay device should also be incorporated.
The locations of the occupancy sensors should be carefully planned such that no light fitting
would be switched off when there is still someone using the toilet. The designer should also bear
in mind not to switch off the lightings at the toilet entrance area otherwise it may give a wrong
impression to people that the toilet is out of service.
Photovoltaic panel
Photovoltaic (PV) panel is environmentally friendly equipment for generation of clean
and renewable electrical power. In Hong Kong, the duration of sunny and bright days throughout a
year is comparatively long. It is therefore worthy to consider the use of PV panels especially the
Building Integrated PV panels (BIPV) to obtain green power from the sky. BIPV panels can be
used as the roof or external cladding of a toilet building. The generated DC power can be used to
operate DC light fittings and/or DC ventilation fans inside the toilet. This is particularly useful for
toilets at remote sites where utility supply is not readily available. In future, when the PV
technology advances to achieve even higher energy output density, free air-conditioning to public
toilets might also be realized.
Other design considerations
Besides electrical energy, one other natural resource that needs preserving is water. To
avoid unnecessary wastage of water, infrared sensor water tap could be used. This would avoid
running water tap being left unattended due to absent- minded toilet users forgot to close or not
closing the water taps properly. Furthermore, subject to the approval from the local water authority,
rainwater collected from the roof of a toilet could be stored up and used for flushing purpose.
Besides, the use of auto-flushing device with infrared sensor for urinals and WCs is also a good
means to deter the spread of malodour. Foul stuff generated by the users could be automatically
flushed away as soon as the user leaves the urinal or WC. By doing this, it wo uld minimize the
retention time of the foul stuff inside the toilet and enhance the ventilation effectiveness.
INTEGRATED GREEN DESIGN CONCEPT
To achieve an ultimate green and odourless public toilet, neither building services
installation nor architectural arrangement alone can achieve the best design solution. Careful and
comprehensive design co-ordination among the building services engineers and the architects is
vital. An integrated green design concept must be adopted by the design team.
When artificial lighting and mechanical ventilation systems are required, the building
services engineer should design an effective but yet energy saving lighting and ventilation
installation to be used. The energy consuming equipment should be designed to operate only when
they are absolutely necessary to enable the proper functioning of the toilet.
As for the architectural side, the building enclosure and layout should be designed so as to
maximize the use of natural resources, i.e. natural ventilation, daylight, rainwater, etc. But at the
same time the designer should also consider the necessity of incorporating artificial lighting and
mechanical ventilation systems to ensure that the toilet would still function properly when there
were shortfalls in the na tural resources. Besides, the choice of proper building materials is also
essential. Malodour substances and/or bacteria could be trapped in building materials easily and
start to grow. As time goes by, these smelly substances would become very difficult to get ride of.
Building materials with smooth surfaces and minimum gaps should therefore be used.
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Above all, whichever type of lighting and ventilation system or architectural arrangement
is adopted, it should not be at the expense of the effective functioning of the public toilet.
HOUSE KEEPING AND PUBLIC EDUCATION
Finally, good house keeping and maintenance are also the vital elements for achieving a
successful green and odourless public toilet. Frequent and proper cleaning using suitable cleaning
agent is necessary. A clean and dry toilet will definitely have less malodour problem and it will
also render the users a more comfortable feeling both physically and psychologically. As for
public education, campaigns should be organized to advocate the general public to behave more
considerately when using public toilets, i.e. to flush away the foul stuff after using the toilet, avoid
wetting the toilet floor carelessly, shut off water taps properly after use, etc. With the combined
effort of both the ma nagement personnel and the users, the spread and growth of malodour inside
public toilets would certainly become less disturbing.
CONCLUSION
Mechanical ventilation and artificial lighting are the two major building services
installations that need to be considered carefully in designing for a green and odourless public
toilet. From energy conservation point of view, it is necessary to minimize the use of energy
consuming equipment whenever possible. But however, this should not be at the expense of the
proper functioning of the public toilet.
Mechanical ventilation system should be so designed that malodour generated is removed
at the source as quickly as possible and will not be diffused away. The toilet enclosure and layout
should be designed to maximize its breathing ability. With the aid of energy conservation devices
such as wind sensors, the ventilation fans can be shut down whenever the outdoor prevailing wind
condition can achieve sufficient air replacement inside the toilet.
In terms of lighting design, long life and high efficacy lamp source should be used. The
building enclosure should be designed for maximum utilization of natural daylight but yet to avoid
causing green house effect. With the aid of energy conservation devices such as photocell sensors
and occupancy sensors, unnecessary artificial lightings could be switched off when situation
permits.
Finally, to achieve a green and odourless public toilet, integrated green design concept
must be adopted. Both the building services design engineers and the architects must work hand in
hand and coordinated among themselves carefully to come up with a design that could achieve the
best toilet environment with minimum electricity consumption. Last but not least, frequent
cleaning, maintenance and proper usage are also the indispensable factors that contribute to a
successful green and odourless public toilet.
End of Paper
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REFERENCES
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2.
3.
4.
5.
The CIBSE Design Guide Book B
BSRIA Rules of Thumb
ASHARE Handbooks
The CIBSE Code for Interior Lighting
The IES Lighting Handbook
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