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This article seeks to present an optional cooling tool based on the integration of a Living Wall System (LWS), a fan and a dehumidification process (desiccant) to reduce the use of an HVAC system. This study showed that it is possible to use the evapotranspiration of plants for air-cooling and humidity control.
In the current world, people spend on average 80%-
90% of their time indoors; consequently, the risks
to health may be greater due to indoor air pollution
than to outdoor air pollution. Doctors around the world
face lots of complains about the fact that people feel
sick because of the misuse of air conditioning system
within their offices and they pay very expensive bills
every year, so they can work in a “comfortable place”.
In many cities across the world, the air-conditioning
system has become an essential instrument to achieve
indoor comfort within most of the buildings. Thus, it
is important that engineers, designers, manufactures
and all the professionals involved in keeping a good
the indoor environment explore new alternatives to
improve the current systems since there is an increasing
energy requirement for cooling and air-conditioning
of buildings in cities, rising indirectly, the urban heat
island (UHI) and climate change. Nowadays, Living
Wall Systems (LWS) are an emerging technology that
utilize the potentials of plants in living environments,
regarding the fact that there is an instinctive bond
between human beings and other living systems within
nature (Figure 1). Using plants as design elements in
working environments brings nature inside to create
warm and inviting spaces that reduces stress, oxygenate
the air, and increases your overall well-being, resulting
in healthier work and living areas that decrease absen-
teeism, increase productivity and overall satisfaction
and happiness in people’s lives.
Green Air Conditioning
– Using indoor living wall systems as a climate control method
This article seeks to present an optional cooling tool based on the integration of a Living
Wall System (LWS), a fan and a dehumidification process (desiccant) to reduce the use
of an HVAC system. This study showed that it is possible to use the evapotranspiration of
plants for air-cooling and humidity control.
Keywords: Indoor Environment, Climate
control, Living Wall System, Evaporative
cooler, Biofiltration.
Figure 1. Living Wall System, Quito, Ecuador.
Delft University of Technology,
Faculty of Architecture and
The Built Environment Delft,
The Netherlands
Delft University of Technology, Faculty
of Architecture and
The Built Environment Delft,
The Netherlands
Delft University of Technology,
Faculty of Civil Engineering and
Geosciences, The Netherlands
Delft University of Technology,
Faculty of Architecture and
The Built Environment Delft,
The Netherlands
REHVA Journal – June 2017 27
Some studies have shown that common indoor plants
may provide a valuable strategy to avoid rising levels
of indoor air pollution and cleaning the air inside
buildings through biofiltration and phytoremediation
(Wolverton, 1989); and it provides a natural way of
helping combat Sick Building Syndrome (SBS) (Fjeld,
2000). Besides, it has been shown that it is possible
to use the evapotranspiration of plants for air-cooling
and humidity control around the plant environment
(Davis & Hirmer, 2015). The use of vegetation as tools
to improve the overall indoor environment is a field
that needs more research to prove the real impact of
the different green systems in the indoor environment;
therefore, this project aims to conduct a multidisci-
plinary research to explore, validate and evaluate the
efficacy in terms of indoor comfort within office envi-
ronments of LWS climate control systems.
I am Tatiana Armijos Moya, I come from Quito,
Ecuador where I got my degree as an Architect at the
Pontifical Catholic University of Ecuador. I worked
at the University for two years as a researcher in
sustainable design. In 2015, I got my diploma as a
Master of Science Specialized in the field of Building
Technology in the Faculty of Architecture and the Built
Environment, TUDelft. Currently, I am PhD candi-
date within the Green Building Innovation Research
Group also at TUDelft with the guidance of my super-
visors; Andy van den Dobbelsteen, Prof. dr.
ir. Philomena Bluyssen, and Marc Ottele.
Evaporative coolers
Plants absorb water and nutrients from the environ-
ment and carry them from one zone (leaves) to another
(roots) where their roots represent a hanging system.
For instance, epiphytes, tropical plants such as English
Ivy, Peace Lily, Reed Palm, Boston ferns and Tillandsia,
are plants that get their water from the air instead of
through their roots. They are common houseplants
that filter the moist out of the air thus reducing exces-
sive humidity levels. Regarding temperature control,
the evapotranspiration from plants contributes to the
lowering of temperatures around the environment. In
this study, some strategies where reviewed and a proto-
type was built to evaluate its performance within a hot
humid environment.
Figure 2. Diagrams of the alternatives for LWS. (Armijos Moya, 2016)
Water Pump
Fan System
Water Collection
Cooling in the
back side
HVAC System Solid Dessicant
Air Exchange
through the glass
Air Exchange
through the glass
Water Pump
Fan System
Water Collection
Indoor Air Quali-
Reduce SBS
Cooling in the
back side
The system re-
quires extra
energy to get
through the
growth medium
Increase Pro-
Noise Control
HVAC System Solid Dessicant
REHVA Journal – June 201728
It was considered that a highly humid climate reduces
the effect of the living wall system substantially, acting
as an evaporative cooler; therefore, it was necessary to
integrate a dehumidification process within the system.
Several dehumidification processes and strategies were
analysed where desiccant dehumidifiers appeared to
be more suitable to apply in this system because it
can be regenerated, and it be used again. In fact, for
future applications, it may use waste heat to regen-
erate. Desiccant dehumidifiers have several benefits,
such as providing humidity control, removing bacteria
and other micro-organisms and they can use waste heat
to regenerate, as mentioned before. Regarding these
factors, it is proposed to use calcium chloride (CaCl2)
as a desiccant dehumidifier because of its properties
in control of relative humidity, its flexibility, and size
particles, residual water produced (Lewis, 2002).
As mentioned before, a prototype was built (Figure 3b)
to examine the construction system and climate
behaviour of the system. The prototype was assem-
bled as a plug-in system constituted by a wooden box
(0.60 m x 0.60 m) with mineral wool and cotton as
growth media that provides a structural system for the
plants to grow in and it must have the perfect balance
between porosity, aeration and water absorption
capacity. Furthermore, a fan (15 W, 230 V, 50 Hz) was
integrated in the bottom part of the system. This allows
cooling down the air before it enters the air gap behind
the substrate, because the air passes over the water
Figure 3. Prototype. a) Diagram of the LWS Design, b) LWS scaled Prototype and Data logger location, c) Section.
(Armijos Moya, 2016)
Water Pump
Cooling in the
back side
Indoor Air Quali-
Reduce SBS
Increase Pro-
Noise Control
HVAC System
Solid Dessicant
50 m
Dessicant with remov-
able plastic bucket
Drip Line
Air gap
Aluminum Alloy Frame
12 Module of steel
mesh with Selected
Growth Medium
(600mm x 600mm)
Fan System with
Acoustic Protection
Metal Trellis
Base Cabinet with
Removable Cover
Irrigation System
Indoor Plants
REHVA Journal – June 2017 29
There is an insncve bond
between human beings and other
living systems within the nature.
Back-to-earth, back-to-nature
Indoor plants as architectural
element define space, provide
privacy, screens unpleasant views
and provide new ones.
Indoor plants can be used as traffic
control, glare reducon or acous-
cal control.
Psychological Values
Plants can reduce stress, improve
self-image, teach long term values,
provide links between past and
Cultural and Social Values
Plants are an integral part of
people’s viasual arts. Plants provide
a topic of conversaon. They offer
the pride of possession.
Environmental Values
Plants can clean the air, water and
soil of pollutants, produce oxygen,
and may help reverse the green-
house effects.
Light Intensity
Indoor plants must be tolerant of
low light intensies
Relave Humidity
Indoor plants prefer a relave
humidity level of between 50-70%
to perform well.
Indoor plants generally are adapt-
able to interior temperature ranges.
Indoor Plants
Growth Medium
Water-holding ability
Physical Properes
Aeraon Porosity
It is the sum of the space in the
macropores and micropores
It is the percentage of total pore
space that remains filled with air
aer excess water has drained
It is the percentage of total pore
space that remains filled with water
aer gravity drainage.
Bulk DensitypH
Bulk density means weight per
Ferlity and CEC
CEC of a growing medium reflects
its nutrient storage capacity and it
provides an indicaon of how oen
ferlizaon will be required.
Chemical Properes
The main effect of pH on plant
growth is its control on nutrient
Improve Indoor Air Quality
Reduce SBS
Increase Producvity
Figure 4. Indoor Plants: Benefits and Requirements.
REHVA Journal – June 201730
storage of the system. This location of water allows a
better cooling effect within the system and it allows an
easier maintenance. The selected desiccant (CaCl2) was
placed in the top of the air cavity to dehumidify the air
before it leaves the system to the outside (Figure 3).
The evapotranspiration from this living wall, the fan and
the desiccant working together contributed to the lowering
of temperatures around the planting environment.
To build an optimum system, some requirements were
taking in account to select the type of plants to be used,
such as light conditions, climate conditions and growth
medium. Consequently, non-pollinating and, medium-
and low-light-tolerant plants, and an inorganic growth
medium were used (Figure 4).
Regarding all these aspects, spider plants and anthu-
riums were tested during this evaluation because they
are epiphytes, which are plants that absorb moisture
from the environment to get their nutrients. The plants
were pre-grown and re-pot within the LWS to allow
them to adapt to the new growth medium. Irrigation
is provided at different levels along the prototype, using
a drip irrigation method using gravity to let water flow
through the growing media.
Conclusions and recommendations
for further research
After the evaluation, the system presents several positive
results such as reducing the temperatures around the
system with a green climate control method (LWS)
which generate pleasant and healthier environment.
Some challenges were faced during the study. First,
the rise of relative air humidity (RH) in the areas
with plants is one of the major issues. In fact, a highly
humid climate reduces the effect of the LWS acting as
an evaporative cooler; thus, it was necessary to integrate
a dehumidification method within the system, in this
case a desiccant material, to control the moisture level
in the environment. Subsequently, it seems that this
green climate control system will reduce the load on the
HVAC system more significantly in a dry hot climate
due to the natural evapotranspiration of the system;
thus, not needing a dehumidification process at all.
On the other hand, the air conditioning system is like
the lungs of any building. It draws in outside air, filters
it, controls and maintains the temperature, humidity,
air movement, air cleanliness, sound level, and pressure
differential, circulates air around the building, then expels
a portion of it to the outside environment. However, it
is in constant competition between the air cooled and
air circulated. Air must be circulated to ensure a good air
quality, but the air conditioning unit relies on a closed
cycle, where if new air is brought in it needs a greater
amount of cooling. Therefore, it is expected that this
method will have important effects on the amount of
energy used by a standard HVAC system regarding that
recirculating the air through the LWS will omit the process
of cooling outdoor air because the indoor air will already
be at the required temperature and humidity level. It is
recommended that for further applications the building
where the system in going to be integrated should incorpo-
rate a solar thermal collector or a gas heater to help regen-
erating the desiccant. What is more, the desiccant-based
air conditioning systems, in general, also use a humidifier
as part of the process because the air inside sometimes is
too dry. Therefore, this system will most likely help to
decrease the loads for humidifiers as well.
There is still a lack of solid and significant figures available
to understand all the possible benefits of an active LWS
as a climate control system such as the true pollutant-
removal mechanisms, and even more the effect of these
systems within the energy performance of the building.
For forthcoming studies, this system is going to evaluate
the possibility of reducing the levels of indoor pollution
through phytoremediation and biofiltration.
Davis, M., & Hirmer, S. (2015). The Potential for Vertical
Gardens as Evaporative Coolers: An adaptatioon of
the ‘Penman Monteith Equa on’. Elsevier, Building and
Environment, 135–141.
Fjeld, T. (2000). The Effect of Interior Planting on Health
and Discomfort among Workers and School Children.
HorTechnology , 46–52.
Lewis, G. &. (2002). The Dehumidification Handbook.
Amesbury: Munters Corporation: Dehumidification Divition.
Wolverton, B. (1989). Interior Landscape Plants for indoor
Air Pollutioon Abatement. NASA.
Use of plants to remove pollutants from the air,
water and soil. Plants have been shown to uptake
air pollutants via their stomata during normal gas
Biofiltration: the process of drawing air in through
organic material (such as moss, soil and plants),
resulting in the removal of organic gases (volatile
organic compounds) and contaminants with a
mechanical system involved.
REHVA Journal – June 2017 31
... With regards to the physical measurements executed inside of the chambers, the temperature was, in general, always slightly lower in Chamber A, with the plant-based system, than in Chamber B. In contrast, the relative humidity in Chamber A was always higher than in Chamber B, which can be explained by the evaporative cooling effect created by the plant-based system placed in Chamber A [29,30]. During the sessions, the average temperature inside Chamber A was 19.7°C and the average RH was 52%, while in Chamber B, the average temperature was 20.1°C and the average RH was 43%. ...
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