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Pol. J. Environ. Stud. Vol. 33, No. X (2024), 1-13
DOI: 10.15244/pjoes/188699 ONLINE PUBLICATION DATE:
*e-mail: manhhakg@sgu.edu.vn
Original Research
Algae Windows: A Novel Approach Towards
Sustainable Building Design and Energy
Conservation
Tue Duy Nguyen1, Hieu Trung Ho Le2, Kuan Shiong Khoo3, 4, Ha Manh Bui5*
1Faculty of Mechanical - Electrical and Computer Engineering, School of Technology, Van Lang University,
Ho Chi Minh City, 700000, Vietnam, email: tue.nd@vlu.edu.vn (T.D.N.)
2Faculty of Law, Van Lang University, Ho Chi Minh City 700000, Vietnam, e-mail: hieu.lht@vlu.edu.vn (H.T.H.L.)
3Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li 32003, Taiwan,
e-mail: kuanshiong.khoo@yzu.edu.vn (K.S.K.)
4Centre for Herbal Pharmacology and Environmental Sustainability, Chettinad Hospital and Research Institute,
Chettinad Academy of Research and Education, Kelambakkam-603103, Tamil Nadu, India
5Faculty of Environment, Saigon University, 273 An Duong Vuong Street, District 5, Ho Chi Minh City 700000, Vietnam
Received: 25 February 2024
Accepted: 14 April 2024
Abstract
This study introduces an innovative approach, harnessing photobioreactors (PBRs) as algae
windows to optimize energy eciency and environmental protection in building design. The integration
of microalgae cultivation systems into windows presents a promising avenue for multifaceted benets,
encompassing energy savings, improved indoor daylight levels, hot water production, and carbon
sequestration. This research work presents a comprehensive exploration of this cutting-edge concept
by employing simulations and analyses. It delves into various facets, including energy performance,
cooling loads, daylight distribution, and hot water generation. The model room equipped with algae
windows demonstrates substantial reductions in cooling energy consumption due to the shading
eect of the algae. The daylight analysis underscores how algae windows can eectively illuminate
spaces while minimizing the need for articial lighting. Furthermore, the study reveals the potential
for these windows to harness solar energy for hot water production, oering a dual-purpose solution.
Despite the promise, this work acknowledges the existing challenges associated with technology
adoption, encompassing technical, economic, and regulatory barriers. It underscores the critical role of
governments in promoting favorable regulations, incentivizing investments, and raising public awareness
to accelerate the uptake of algae windows. Algae windows present a holistic solution by simultaneously
mitigating energy consumption, reducing carbon emissions, and improving indoor environments.
This research serves as a foundation for future studies, encouraging further investigations into
the viability and scalability of algae-integrated building systems.
Keywords: Autodesk Ecotect, cooling load, LEED standard, algae window, energy saving
Tue Duy Nguyen, et al.
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Introduction
The largest energy consumption in buildings
typically stems from HVAC systems, specically
heating, ventilation, and air conditioning. The cooling
load, crucial for maintaining comfortable indoor
conditions, consists of internal and external heat gains
[1]. Internal heat gains include factors like people,
lights, and equipment, while external heat gains
encompass solar radiation through windows, inltration,
ventilation, and heat conduction through building
envelopes. Notably, approximately 75% of the total
cooling load arises from heat loss through the building
envelope, with windows contributing the highest
proportion, potentially accounting for up to 60% of
a building’s energy consumption [2]. Architects strive to
develop envelope materials to reduce energy usage.
In recent years, buildings have increasingly
integrated renewable energy generators like solar
panels and wind turbines to cut energy costs and lessen
reliance on fossil fuels. However, these technologies
alone may not fulll a building’s energy needs.
Photobioreactors (PBRs), particularly algae windows,
emerge as a promising solution to mitigate building
energy consumption [3]. Algae cultivated within PBRs
absorb sunlight for photosynthesis and can be harvested
for valuable biomass used for bio oil, biogas, or nutrient
supply [4]. Algae windows, a specialized type of PBR
integrated into building facades, oer benets such as
reduced heat loss, natural light provision, and renewable
energy generation. Consequently, algae windows
contribute to both improved building aesthetics and
reduced greenhouse gas emissions [5].
Algae, known for their high eciency in converting
solar energy into biomass, oer several advantages over
conventional biofuels derived from edible feedstock.
Algae’s high oil content makes it an excellent source of
clean, sustainable bio-oil, suitable for powering various
transportation vehicles [6]. Moreover, algae’s ability
to absorb CO2 during growth makes them promising
candidates for biofuel production and carbon capture,
aiding in environmental preservation. Several studies
have explored the potential of algae-based technologies
for building applications. For instance, researchers have
developed algae-based air purication systems capable
of signicantly improving air quality, especially in
highly polluted urban environments. Energy simulation
studies comparing dierent window types have
consistently demonstrated the superior energy-saving
performance of algae windows. Additionally, economic
analyses suggest that algae building technologies, such
as closed tubular photobioreactors, oer favorable
returns on investment compared to traditional solar PV
systems [7]. Martin Kerner et al. [8] claimed that the
whole year’s heat production eciency is nearly 38%,
which can meet about 59% of the total heat demand of
a building. Moreover, the surplus heat can be stored in
the soil below the building and used in the winter. In
theory, algae can convert solar energy into biomass with
an eciency of up to 9%. This is at least three times
higher than the eciency of C4 plants, which are the
most ecient type of land plant. Algae can also absorb
large amounts of CO2, up to 1.8 kg of CO2 per 1 kg of
biomass. This makes algae a promising candidate for
biofuel production and carbon capture [9].
Recently, there have been several studies on PBR
for building [10]. For instance, a team of researchers
developed an algae-based air purication system in
Warsaw, one of the most polluted cities in Europe.
The algae-based air purication system consists of
52 large reactors that can hold a total of 520 liters of
Chlorella vulgaris algae culture. This amount of algae
culture can lter 200 liters of polluted air per minute.
The surrounding air quality was monitored using
sensors. The researchers reported that the system has
the potential to absorb nitrogen and ne particulate
matter (PM2.5) up to 97% and 75%, respectively. In
particular, the PM2.5 concentration dropped by 83% and
remained within the recommended zone of the World
Health Organization. M. Talaei et al. [11] conducted an
energy simulation study for buildings in Mashhad, Iran.
Researchers compared three types of windows: single
glass, double glass, and water windows. The authors
found that the algae window had the best energy savings
performance. The algae density had a small eect on
energy consumption. Nimish Biloria et al. [12] analyzed
the cost and prot of algae building technologies
and solar PV panels. A case study at a building at
the University of Technology Sydney, Australia, was
conducted. The closed tubular photobioreactors were
used for the algae system. Additionally, the use of
a closed tubular photobioreactor system increases the
return on investment and has a quicker payback time as
compared to a solar PV system. Cervera Sardá et al. [13]
examined the study of using algae windows for building
façades. The study obtained good results for energy
conservation, CO2 mitigation, and the ability to produce
biomass. Ghada Mohammad Elrayyes [4] stated that
the application of algae windows is an eective option
for green energy because of its potential to absorb CO2,
purify water, and generate oxygen. For this reason, it can
considerably reduce the electricity bill of a building and
improve air quality by absorbing CO2 and generating
oxygen in the building. Yaman et al. [14] studied the use
of building-integrated photobioreactors (PBRs) in Izmir,
Turkey. To investigate the performance of an algae
window on the south side of a building, a simulation was
carried out. The results showed that this type of façade
could signicantly reduce the number of uncomfortable
hours in the building. Additionally, the excess daylight
was cut down due to the high concentration of algae
inside the window. The study found that there was no
signicant dierence between a 100% PBR façade and
an 80% PBR façade, except for a partial improvement in
daylight illumination.
To evaluate personality traits that are attributed to
microalgae façade. Kathryn Warren et al. [15] conducted
a survey of 40 randomly selected architecture students.
Algae Windows: A Novel Approach Towards... 3
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The students were assigned to stay in a room with a
microalgae façade, and their emotions were studied
using questionnaires. The study found that people who
lived in an algae envelope were more creative and
produced better work than those who stayed in a normal
room. Martokusumo et al. [16] studied an ongoing
building in Bandung, Indonesia, which is a historic
location. The building has glass windows on the west
and east sides. The authors investigated three types of
windows: brise-soleil, horizontal xed shading device,
and algae photo-bioreactor. The experiment was carried
out for the nal type. During the investigation of each
type of façade, parameters such as indoor and outdoor
temperature dierences, daylight level, and the amount
of oxygen generation were obtained. It was reported
that algae windows are able to reduce the Solar Heat
Gain Coecient (SHGC) and indoor temperatures.
Jo et al. [17] also suggested that green algae windows
can be integrated with articial light-emitting diodes
(LED). With this integration, LED lights can change
color in response to environmental conditions, including
weather and time of day. This approach has the potential
to enhance energy savings and the aesthetic appeal
of buildings. Joud Al Dakheel et al. [18] found that
active shading systems, such as smart glazing, kinetic
shading, and algae façades, can potentially reduce
energy consumption by 10-50%. However, the algae
window is still a developing technology because it
needs further investigation to reduce factors including
investment costs, maintenance expenses, and labor
costs for specialized installation. Heru W. Poerbo et al.
[19] studied the design of the ITB Innovation Park, a
new building in Bandung, Indonesia. It was found that
the building-integrated microalgae photobioreactors
(BIMPs) have not yet been included in the Green
Building regulation in Bandung city (Indonesia) because
these are a relatively new technology. However, this
approach is able to cut down energy consumption and
boost indoor air quality. In a recent study, Chew K.W
et al. [20] stated that integrated photo-bioreactors
in buildings can play a crucial role in green energy
applications. This is attributed to their ability to
convert CO2 to oxygen and harvest biomass. However,
some challenges, such as the cost of production and
maintenance expenses, need to be tackled, and further
research is still being done.
N.A. Ardiani et al. [21] discussed the design of
a photobioreactor for building façades using Sketup
software. In this design, acrylic molding and pipes were
chosen to replace the conventional panel photobioreactor.
Algae culture ows from the top of the pipes and lls
them, then returns to a 2000-liter pond in the basement
via pipes at the bottom. At the pond, there are four types
of pipes connected to it: pipes connecting to building-
integrated photobioreactors, oxygen pipes that transfer
oxygen produced in the pond to the building, nutrient
pipes, and pipes for harvesting biomass or cleaning.
Researchers assume that their renovation has some
benets, such as a low risk of leaking and a lower
likelihood of algae death. Soowon Chang et al. [22]
developed a simulation framework using BIM (Building
Information Modeling) to evaluate the feasibility of
algae façades in dierent buildings. The framework
comprises three main components: (1) integration of
algae façades as library components in BIM; (2) use of
a system dynamics model (SDM) to model closed-loop
energy and waste streams; and (3) retrieval of data in
BIM for the SDM.
To contribute to the application of algae façades,
this research work developed a model of a conference
room in a resort in Phan Thiet with dimensions of
14 m x 6 m x 3.5 m. Three types of windows were
compared, including single glazing, double glazing,
and algae windows (microalgae photobioreactors).
The aspects of the windows that were evaluated included
energy savings, daily lighting, and energy savings for
hot water utility from the microalgae photobioreactors.
Methodology
Basic Theory
To calculate the heat conductivity Q (W) through the
envelope of the building, the Equation (1) is used:
Q = U x F x ( tex – tint ) (1)
Where U represents the total heat transfer coecient
of the envelope material (W/m2.K), F is the area of the
envelope (m2) and tex and tint are the outdoor temperature
and indoor temperature (ºC), respectively.
To reduce heat conduction through building
envelopes, such as walls and windows, the U-factor
should be low. The U-factor of window glazing can be
calculated according to Equation (2) in ASHRAE [23].
12
int 1 2
1
11
1000. 1000. 1000.
g gw g
ex g w g
Uttt
hh K K K
=
++ + +
(2)
Where:
hex and hint are convection coecients of outdoor and
indoor, respectively (W/m2.K).
Kg1, Kw, and Kg2 are the thermal conductivity of
glass layer 1, water (algae culture), and glass layer 2,
respectively (W/m.K). t is the thickness of each layer
(mm).
The thermal conductivity of glass is approximately 1
W/m.K. In a study by Negev et al. [3] there was almost
no dierence between the thermal conductivity of pure
water and algae culture. The authors recommend using
0.64 W/m 2.K for algae culture, which is about 10%
higher than pure water, because of the natural convection
of water between two glass panes. Natural convection is
caused by the temperature dierence between the water
and the glass surface.
Tue Duy Nguyen, et al.
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In addition to heat conduction through the building
envelope, radiation also contributes to the cooling load
of a building. Sunlight carries energy that penetrates
through the glass of a building, raising the temperature
inside the room. This one can be prevented and limited
by using glazing with a low SHGC (solar heat gain
coecient), which is the ratio of the amount of radiation
energy that passes through the glazing to the amount
of radiation energy that strikes the glazing surface.
Therefore, a lower SHGC means less radiation will pass
through the pane [24].
Daylight level is a crucial factor in determining
the illumination within a room. Higher daylight levels
indicate ample natural light, reducing reliance on
articial lighting and promoting energy conservation.
However, it’s important to note that this can also
elevate room temperatures [11]. Thus, when designing a
building, selecting the right Visible Transmittance (VT)
for glazing is essential to balancing lighting and thermal
considerations.
The coecient of performance (COP) is used to
estimate the energy consumption of an air conditioner.
COP is the ratio of the cooling capacity of an air
conditioner to the electricity demand of the compressor.
Therefore, the higher the COP, the lower the energy
consumption can be achieved [25]. However, the COP
of an air conditioner is aected by a number of factors,
such as the indoor and outdoor temperatures, the
eciency of the compressor, and the cleanliness of the
indoor and outdoor units. In Equation (3), COP is the
ratio of the cooling capacity of the air conditioner (Qo
in watts) to the energy input (N in watts). Normally, the
cooling capacity of the air conditioner is equal to the
cooling load of the building.
COP = Qo/N (3)
In this study, it was assumed that a hot water supply
was needed. When the algae culture absorbs sunlight,
the temperature of the culture will increase. To avoid
the death of Chlorella vulgaris algae, the temperature
of the algae culture should be lower than 38ºC [26].
Another uid was used to cool it to keep it at such a
temperature that it could be utilized for water heating.
The temperature that is also suitable for people to take
a shower is from 40ºC to 42º [27]. Therefore, in this
study, a hot water system can be used to utilize the heat
generated from cooling the algae culture, and a heater
will be used if a higher water temperature is needed.
The eciency of converting sunlight energy to heat in
a photobioreactor is about 38% [8], which is the ratio of
useful energy (Qusef in W) to incident solar radiation on
the surface of the equipment (Qrad in W), so if there is
incident solar radiation, the useful energy of a hot water
system can be determined using Equation (4).
h = Qusef / Qrad (4)
Methodology
The methodology of this study was to use Ecotect
Autodesk to develop a conference room model with
three dierent types of glazing: single glazing, double
glazing, and algae windows. This software has been
used to analyze environmental conditions such as solar
radiation, daylight level, etc. [28]. The cooling load,
energy consumption for air conditioning, and daylight
were then analyzed to evaluate the eciency of each
type of glazing. Additionally, the energy savings for hot
water production that could be achieved by using algae
windows were also analyzed. The steps of the study
were as follows:
Step 1: Design the model of the conference room.
Step 2: Determine some crucial parameters for
three kinds of glaze (single glaze, double glaze, and
algae window) which comprise the U-factor and Visible
Transmittance (VT).
Step 3: Run a simulation of Ecotect to nd out the
cooling load, daylight, and luminance of the room.
Step 4: Calculated energy savings for hot water
production when harnessing the algae window’s heat
release.
Step 5: Economic analysis.
The case study is a conference room located in Mui
Ne, Phan Thiet, Vietnam. This area is famous for its
sunny beaches and numerous resorts. Algae windows
are a good t for this type of resort because they allow
people to feel close to nature with the green of the
algae. In this study, the algae chosen for the windows
is Chlorella vulgaris, which has a spherical cell shape
[29]. This is a freshwater algae with a green color, but
it can also live in salt water. When living in salt water,
its growth rate is lower than in freshwater. However,
it can tolerate salinity up to 45 g/l. Under these salty
conditions, the total lipid content increases from 11.5% to
16.1% [30]. This type of algae is used for biodesalination
and biofuel production [31]. Therefore, when used as
building-integrated microalgae photobioreactors, it can
be used to produce biomass and oil.
The model of the room, its orientation, and the sun’s
orbit are shown in Fig. 1.
The conference room has dimensions of 14 m x
6 m x 3.5 m. The main door (2.2 m x 1.3 m) faces east
(90°), and the two long walls face south (180°) and
north (0°). There are ve windows on each side of the
room, each measuring 1.5 m x 1.3 m. The windows
make up almost 20% of the wall area. In the case of
algae windows, the solar heat gain coecient (SHGC)
decreases as the concentration increases. This means
that less solar radiation will pass through the window,
and the visible transmittance (VT) will also decline.
Therefore, Chlorella vulgaris with a concentration
of 20% was chosen (U = 5.1 W/m2.K, SHGC = 0.4,
VT = 0.45), as it has the highest VT coecient of all
the remaining concentrations. The higher the VT, the
better the daylight and illuminance will be, and the less
articial light will be needed. In terms of single glaze,
Algae Windows: A Novel Approach Towards... 5
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The total cooling load for each type of window for
months in a year is illustrated in Fig. 2.
For the single glaze and double glaze, the cooling
load peaks in May, with April as being the second
highest. However, for algae windows, the cooling load is
slightly lower in May than in April, or it peaks in April.
These months have the highest radiation and outside
temperature, which signicantly contributes to the
cooling load. The lowest cooling load is in December
due to the lowest temperature. It is clear that single glaze
has the highest cooling load, followed by double glaze,
and then algae windows. This is because single glaze
has the highest U-factor and SHGC, allowing more heat
to pass through. The cooling load is strongly dependent
on the U-factor, as shown in Equation (1). In addition
to the U-factor, single glaze also has the highest SHGC,
allowing more radiation energy to pass through.
According to Fig. 2, the room using single glazing
has the highest annual cooling load, at 30,820,088 Wh.
The next highest is double glazing, at 29,322,906 Wh.
The lowest annual cooling load is for algae windows, at
27,118,662 Wh. Although algae windows have a higher
U-factor than double glaze, their cooling load is lower
because their SHGC is two times lower than that of
double glaze. In other words, Vietnam is located near
the equator, so radiation is very high, which signicantly
contributes to the cooling load. The solar radiation
element that accounts for cooling load for each type of
glaze is shown in the tables below.
According to Table 1, solar radiation passes through
the glazing from 6:00 am to 17:00 pm, with the highest
intensity occurring from 11:00 am to 14:00 pm.
In general, the total solar cooling load is lowest in April
and May and reaches a peak in January and February.
As shown in Fig. 1a), the sun’s altitude is highest in
April and May, so solar radiation is concentrated on the
roof, not on the two sides of the room. In January and
February, the sun is positioned in the south, so sunlight
is focused on the sides, resulting in a higher solar
radiation load in these months.
it has U-factor (5.8 W/m2.K), SHGC (0.9), and VT (0.86),
and for double glaze, U-factor, SHGC, and VT are
3.12 (W/m2.K), 0.81, and 0.76, respectively [3].
In addition to the material properties of glazes,
energy simulations also require the properties of other
materials, such as walls (U = 2.62 W/m2.K), roofs
(U = 0.836 W/m2.K), and slabs (U = 0.8 W/m2.K). These
properties are available in the Ecotect library.
In this energy simulation, there are 11 people sitting
in the room. The heat emission from each person
in sedentary conditions is 70 W. The internal heat
gains (for lighting and small power loads) are 7 W/m2.
The inltration rate is 0.5 air changes per hour (ach),
which is considered to be well-sealed conditions.
The temperature setting is from 25 to 26 degrees
Celsius, and the operation hours are from 6 am to 17 am.
Results and Discussion
In this simulation, weather data from the Joint
Research Center (JRC) was used, including local
temperature, humidity, solar radiation, and other factors.
The JRC provides data and environmental knowledge
to support EU policies and combat climate change. By
using the METEOSAT satellite, weather data covering
Europe, Africa, and Asia is collected [32]. These data
are widely used by simulation experts around the world.
Cooling Load of the Room
and Energy Consumption
The cooling load in this simulation is calculated
based on the total operation time in a year. The peak load
that occurs at a specic moment in the year will be used
as the cooling capacity of the air conditioner. The peak
load for single glazing is 15,455 watts. This is also the
highest cooling load. The second highest cooling load
is for double glazing, at 14,640 watts. Algae windows
experience the lowest cooling load, at 13,838 watts.
Fig. 1. The model of simulation and sun’s orbit a) the plan view of the model and b) the perspective view of the model.
Tue Duy Nguyen, et al.
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Of the three types of glazing, single glazing has
the highest solar radiation load, followed by double
glazing and algae windows. Algae windows have
the lowest solar radiation load because they have the
lowest SHGC. This means that sunlight is less likely to
penetrate the window and raise the temperature. In other
words, if a building or room has a lot of windows, the
cooling load using algae windows will be signicantly
reduced.
In this study, the coecient of performance (COP)
of the air conditioner is chosen as 3, which is a popular
value for air conditioners. Using Equation (3), the annual
energy consumption for the air conditioner when using
three types of windows, namely single glazing, double
glazing, and algae windows, is 10,273,362.67 Wh,
9,774,302 Wh, and 9,039,554 Wh, respectively.
According to Decision No. 1062/QĐ-BCT [33],
issued on May 4, 2023, by the Ministry of Industry
and Trade, the average electricity price in Vietnam has
increased by 3% to 2,746 VND/kWh (0.11 USD/kWh).
The main reason for the increase is the rise in the price
of coal, natural gas, and crude oil on the world market.
These fuels are used to generate electricity in Vietnam.
The annual energy cost was computed based on the
air conditioner’s electricity consumption and electric
price. The results show that single-glaze windows cost
$1130, double glaze windows cost $1075, and algae
windows cost $994.35. This means that algae windows
Fig. 2. Cooling load of room during months.
Table 1. Solar radiation load for dierent walls.
Walls Hour Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
(Wh)
Single
glaze
6 0 0 0 6 18 15 5 0 0 0 0 0
7340 511 374 243 216 249 228 210 382 620 837 726
81188 1102 673 690 445 494 527 411 823 977 1121 848
91664 1627 1141 1015 1354 1253 1329 1406 1192 1514 1502 1506
10 2138 1923 1507 1171 1333 1501 1544 1150 1283 1830 1865 2068
11 2345 2105 1707 1146 1357 1655 1750 1022 1528 2058 2095 2294
12 2400 2156 1768 1218 1408 1618 1797 1253 1408 2064 2095 2218
13 2409 2093 1785 1132 1485 1630 1734 1134 1505 1891 1981 2131
14 2228 1977 1562 1117 1284 1512 1625 1183 1325 1726 1773 1873
15 1857 1712 1259 1007 1266 1270 1523 1172 1039 1350 1415 1469
16 1361 1342 936 855 1066 1033 1104 918 735 738 1002 1007
17 676 819 501 524 631 697 792 561 396 67 0 9
Algae Windows: A Novel Approach Towards... 7
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can save up to 12% (or $135.65) compared to single-
glaze windows and up to 7.5% (or $80.65) compared to
double-glaze windows. In other words, algae windows
are the most cost-eective option, followed by double-
glaze windows and single-glaze windows. Therefore, if
a room has a large number of algae windows, the cost
savings will be signicantly greater than if other types
of glazes were used. This is because algae windows have
a low solar heat gain coecient (SHGC), which means
that they allow less solar radiation to pass through them
than other types of windows. As a result, rooms with a
lot of algae windows will require less energy to cool,
which will lead to lower energy bills.
Daylight Analysis
When considering sustainable and energy-ecient
design, daylight analysis should be considered. Daylight
analysis determines how much light penetrates a room,
and designers base their decisions on this parameter
to install articial light to meet operation demand.
Therefore, natural light can be utilized eectively to
reduce energy for articial light. Cutting down on
energy leads to lowering greenhouse gas emissions
associated with electricity generation. In addition to
cost saving and lowering greenhouse gasses, exposure
to natural light can improve our mood and increase
productivity. Leadership in Energy and Environmental
Design (LEED standard), which is the world’s most
widely used green building rating system, requires
the percentage of time that a space receives enough
daylight to perform visual tasks without electric light.
LEED requires a minimum of 55%, 75%, or 90% of the
time, depending on the type of building. The required
level of daylight illuminance is 300 lux, and this is also
the minimum value that must be met when simulating
daylight levels in a building [34].
To simulate daylight levels, Ecotect utilizes the
concept of “design sky illuminance”, which is obtained
through a static analysis of outdoor illuminance levels.
The desired light levels will be met at least 85% of the
time over the period from 9 am to 5 pm during the entire
year. In this simulation, “from model latitude“ mode
was chosen for the design sky illuminance calculation.
Table 1. Continued.
Double
glaze
6 0 0 0 5 15 12 4 0 0 0 0 0
7271 406 297 193 172 198 181 167 304 493 666 577
8945 877 535 548 354 393 419 327 654 777 892 674
91323 1294 908 807 1077 997 1057 1118 948 1204 1195 1198
10 1700 1529 1198 932 1060 1194 1228 915 1021 1456 1483 1645
11 1865 1674 1358 911 1080 1316 1392 813 1215 1637 1666 1824
12 1909 1715 1406 969 1120 1287 1429 996 1120 1641 1666 1764
13 1916 1664 1420 901 1181 1296 1379 902 1197 1504 1575 1695
14 1772 1572 1242 889 1022 1203 1292 941 1054 1373 1410 1489
15 1477 1362 1002 801 1007 1010 1211 932 826 1074 1125 1169
16 1083 1067 745 680 848 821 878 730 584 587 797 801
17 538 651 399 417 502 555 630 446 315 53 0 7
Algae
window
6 0 0 0 1 4 3 1 0 0 0 0 0
779 119 87 56 50 58 53 49 89 144 195 169
8276 256 156 160 104 115 123 96 191 227 261 197
9387 378 265 236 315 291 309 327 277 352 349 350
10 497 447 350 272 310 349 359 267 298 426 434 481
11 545 490 397 266 316 385 407 238 355 479 487 533
12 558 501 411 283 327 376 418 291 328 480 487 516
13 560 487 415 263 345 379 403 264 350 440 461 496
14 518 460 363 260 299 352 378 275 308 401 412 435
15 432 398 293 234 294 295 354 273 242 314 329 342
16 317 312 218 199 248 240 257 213 171 172 233 234
17 157 190 117 122 147 162 184 131 92 15 0 2
Tue Duy Nguyen, et al.
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After calculations, the average daylight level in a
room with single glazing is the highest, at 1137.96 lux.
This is followed by double glazing at 1053.5 lux and algae
windows at 791.7 lux. This indicates that illuminance
is strongly correlated with visible transmittance (VT).
This nding is entirely in line with LEED standards.
However, the new LEED criteria (LEED v4) recommend
that windows should be temporarily closed when more
than 2% of the daylight level in space exceeds 1000
lux of direct sunlight. Moreover, the direct sunlight
illuminance of 1000 lux must not be exceeded for more
than 250 hours per year for more than 10% of the area
[35]. With the new LEED standard, in this case, single-
glaze and double glaze windows allow too much daylight
in, which leads to higher energy consumption. Algae
windows are therefore a good option in this case, as they
can reduce daylight levels while still providing adequate
light for occupants. However, it is important to note that
these results are based on simulations, and the actual
value is likely dierent from the result of the simulation.
Moreover, if a building or room has a high window-to-
wall ratio (WWR), C. vulgaris with a 30% concentration
(SHGC = 0.33, VT = 0.3) or a 40% concentration
(SHGC = 0.2, VT = 0.17) [3] can be used to reduce
energy usage. However, daylight-level simulation should
be conducted to ensure that the required daylight level
is still met. The daylight level using the algae window is
displayed in Fig. 3.
Fig. 3 shows the daylight level in dierent parts of
a room. The brighter the square, the higher the day-
light level at that location. The brightest areas are near
the windows, with approximately 1200 lux. However,
about 10% of the positions have an illuminance of 1000
to 1200 lux, which meets the LEED standard criteria.
From the two long sides to the center of the room, the
daylight level gradually decreases. Some areas near the
two long sides have a high daylight level because there
are windows there. Conversely, the daylight level is low
on the two short sides because there are no windows.
However, the illuminance is sucient for oce work
(300 to 500 lux) [36]. Generally, the higher the daylight
level, the more accurate oce workers can be, and it
should be between 500 and 800 lux [37]. Therefore, in
this design, the illumination using algae windows is
suitable for oce work and also avoids using too much
energy.
Hot Water Production
When sunlight hits an algae culture, the solar energy
is absorbed, causing the temperature to rise gradually.
To prevent the algae from dying, the temperature must
not exceed 38 degrees Celsius, so the algae must be
cooled. The energy emitted in this process can be used
to heat water for a hot water supply, saving energy. In
addition, this temperature is suitable for taking a bath.
To calculate energy savings, the solar radiation that
strikes the vertical algae window must be investigated,
as shown in Fig. 4.
It is evident in Fig. 4 that a south-facing wall
receives signicantly more solar radiation than a north-
facing wall throughout the year. This is because the
sun is in the south for most of the year in the Northern
Hemisphere (as shown in Fig. 1). In other words, the
north-facing wall only receives solar radiation during
the summer months. In the summer months, the sun’s
altitude is high, and its path tends to move north, so the
solar radiation is lower on the south-facing wall than
on the north-facing wall. However, from September to
March, the sun’s path returns to the south, leading to
higher values on the south-facing wall than on the north-
facing wall during those months.
Using Equation (4), the solar radiation in each
direction (kWh/m²) in Fig. 3, the total area of windows
Fig. 3. The daylight level at dierent parts of a room.
Algae Windows: A Novel Approach Towards... 9
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(m²), and a solar eciency of 38% [8], the energy
savings for hot water supply in south-facing windows
and north-facing windows for the entire year are
3216 kWh (USD 353.7) and 1960 kWh (USD 215.6),
respectively. Therefore, with a total of 10 windows
in both orientations, the energy saving cost is USD 569.3
per year. In other words, the cost of energy savings for
hot water is dramatically higher than the cost of energy
savings for cooling.
Table 2 compares dierent studies on the use of
photobioreactors (PRBs) as algae windows. The table
shows that the energy saving potential of algae windows
is promising, with some studies reporting that the
energy savings are up to 80%. This study is also in line
with the results evaluated in published works and further
suggests that algae windows are a viable technology
for reducing energy consumption and greenhouse gas
emissions [38, 39].
Environmental Protection
The applicability of algae windows not only provides
eco-friendly energy, but they also contribute to the
reduction of greenhouse gasses, making them a carbon-
neutral energy solution for environmental protection.
From an environmental perspective, there are apparent
advantages on account of reduced energy consumption,
improved energy eciency, on-site biomass production,
thermal generation, biofuel manufacturing, and
wastewater treatment. These structures provide
advantages of a low carbon economy via lowered
energy, operational, and tax expenditures, thereby
resulting in mitigated overall life cycle costs and rising
rental returns without compromising occupancy rates.
Moreover, these innovations hold signicance in the
realm of net zero energy, on account of which they excel
in enhancing building energy eciency, generating
renewable energy, and optimal air quality.
Specically, numerous studies indicate that the
algae window for improved temperature control can
bring signicant mitigations in energy consumption
with over 33% fuel and around 10% electricity [40].
Moreover, buildings integrated with microalgae systems
may recycle building waste into valuable resources as
well as reach self-suciency in power and water, which
simultaneously deal with air pollution and wastewater
treatment. A case in point is that buildings integrated
with microalgae in Hamburg, Germany [41]. The energy
eciency and resident satisfaction of this building
are further meliorated by aspects such as geometric
design, microalgae cell concentration, and color changes
aected by environmental conditions. The eectiveness
of the photosynthetic performance of microalgae
enclosures contributes to energy savings by mitigating
the demand for heating, cooling, and articial lighting,
leading to decreased CO2 emissions and improved
indoor air quality. This potential technology may reap
the benets of a low-carbon economy. The eective and
large scale installation results in the economic viability
of algae-integrated buildings.
Another example is a skyscraper powered by
microalgae systems called One World Trade Center in
the US. The building could potentially mitigate energy
consumption yearly (arising from heating, cooling,
lighting, and ventilation) by approximately 20%, leading
to considerable expense savings of more than one
million US dollars a year and a return on investment
of 7 years. Such signicant energy conservation also
correlates with an average mitigation of 6 thousand
tons of CO2 emissions. Together with the positive
inuence on CO2 reduction through energy savings,
these innovative buildings are able to sequester more
than 7 thousand tons of CO2 a year, consuming at a rate
of 5 g/ft2. Potential prots from the trade of biomass or
high value bioproducts, in addition to the utilization of
building waste, could help oset energy expenses. By
maximizing growth conditions and operational modes,
the potential daily productivity ranges from 1 to 5 grams
Fig. 4. Vertical solar radiation in the South and North walls.
Tue Duy Nguyen, et al.
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Reference Location Panel size
(m) PBRs function Orientation Research content Results
[38] Hamburg 2.5×0.7×0.08
129 at panel
Shading, Thermal
usage, Biomass
Southwest
Southeast Experiment on C.vulgaris
- Heat eciency for hot water production is 38%
- Converting light to biomass eciency is 10%
- Heat generation of 150 kWh/m2 per year.
[3] Tel Aviv,
Israel
15%,30%,45%,
60%,75%,90% Shading North, East,
South, West
- Determine experimentally the U-factor,
SHGC, and VT of C.vulgaris and
Chlamydomonas algae window with
dierent concentrations.
- Simulate energy consumption
At maximum concentration, the energy savings of using an algae
window can be up to 20 kWh/m2.year in the south, 8 kWh/m2.year
in the east, 14 kWh/m2.year in the west, and 18 kWh/m2.year in the
north compared to using single glass.
[16] Bandung,
Indonesia 0.7×0.6×0.05 Shading -
- Energy simulation for building.
- Experiment for algae window for
outdoor and indoor temperature
dierence, illuminance, and Oxygen
release.
- When outside temperature increases, PBR can regulate indoor
temperature.
- Algae window can reduce 90% daylight, but its illuminance is still
at an acceptable level.
- Algae windows can reduce energy consumption.
- Oxygen production can be 4.83 ml/hour/l microalgae culture
(chlorella).
[38] Iran 0.30×0.30×0.45 Shading -
Compare the performance of algae
window glazing and typical Iranian
Orosi window using simulation and
experiment.
- The light intensity in the door of an algae window glazing and an
Orosi window are approximately equal.
- Humidity increased from 25% to almost 70% with the algae
window.
- Nearly 500 ppm of CO2 can be absorbed using an algae window.
[39] Paris 10000 ft2
Shading
Biofuel production,
Waste water treatment.
-Experimentally developed microalgae Reduce water usage by up to 80% and save up to 80% energy
consumption
Current
study
Phan Thiet
province,
Vietnam
1.5x1.3x0.2
10 windows Shading
Hot water production.
South
North
-Energy, daylight simulation based on
C.Vulgaris 20%.
-Hot water production based on solar
eciency of 38%
-Save up to 12% energy consumption for cooling compared to
single glaze.
-Produce 329.84 kWh/m2.year at South facing and 201.2 kWh/
m2.year at North facing.
-Reduce daylight level from outside.
Table 2. Published studies related to algae window.
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per square foot. Applying this technology results in the
mitigation of greenhouse gas emissions. Integrating this
technology in an oce building with an average size
(100 feet in width and length and 65 feet in height) could
reach the sequestration of CO2 from 17 to just above
80 metric tons, generate dry biomass up to 50 metric
tons, and generate biofuel up to 7 thousand gallons.
In practice, the commercial expense of eliminating CO2
is likely to be between 500 and 1700 dollars per ton.
The cost savings from the applicability of this
technology could amount to as much as 145 thousand
dollars a year. Additionally, the use of algae windows
could have positive eects on wastewater treatment.
When integrated with wastewater treatment processes,
algal culture may eliminate phosphorous and nitrogen at
an ecient rate of 80% to 100% [41].
Some Current Barriers and Potential Regulations
for the Utilization of Algae Windows
While providing numerous merits, utilizing algae
integrated structures is still an emerging technology.
Several technological, economic, environmental, social,
and regulatory shortcomings should be overcome before
these technology systems can be widely applied. Many
scholars will raise questions related to sustainability
and customer satisfaction related to its guarantee
of sequestrated energy eciency and eective CO2
elimination over a long period of time, address concerns
related to thermal insulation, monitor variations in
indoor color because of changes in algae culture density,
prevent discoloration, reconsolidate the durability of
algae against climate change, and solve maintenance,
construction, and operational expenses. Furthermore,
potential adverse environmental inuences arising out of
the generation of toxins and odors by harmful algae need
to be carefully examined. Generally, all of these barriers
are exposed due to the lack of investment in research,
the governmental regulations, and the relatively high
cost of management and operation. More specically,
the number of cases of algae integrated into buildings
in reality is limited. Therefore, studies on tracking and
reporting the environmental performance and longevity
of this technology pose challenges. The Return on
Investment (RoI) remains uncertain because the lifespan
of applying this technology is at least 25 years [42].
The initial operational costs and ongoing maintenance
of algae cultivation within buildings are high and
require signicant time for management. This results in
investors and researchers being hesitant when the time
to achieve protability is too lengthy. Additionally, there
are concerns about potential pollutants from certain
algae species producing toxins or releasing harmful
volatile organic compounds [43]. Users need to pay more
expenses for the assessment of risks and adverse impacts
on human health resulting from damage or leakage and
then the development of preventive strategies. Legal
regulations to promote the utilization of this technology
in architecture and environmental protection within
some developed countries remain restricted and in some
cases, even absent in developing countries like Vietnam.
Limitations
The research reveals several limitations. Firstly,
the technology under study is novel and not widely
recognized or adopted in Vietnam. Consequently, the
study couldn’t be conducted on real buildings and relied
solely on simulations from experiments conducted in
developed nations. Secondly, variations in external
factors such as weather and infrastructure among
countries, notably Vietnam with its tropical equatorial
climate, hinder the comparability of research results
regarding temperature and building structure. Thirdly,
Vietnam’s environmental and investment policies
haven’t adequately assessed the risks and benets of this
emerging technology, thus impeding nancial support
from the government and investors.
Governments worldwide are currently emphasizing
environmental protection, particularly through the
integration of green technologies in urbanization
processes. The incorporation of algae into buildings
holds promise for achieving zero-emission structures,
environmental conservation, and improved quality of
life. Consequently, governments are urging research
funding to evaluate the long-term eectiveness of these
technologies while addressing associated societal risks,
especially concerning environmental and human health.
Moreover, governments need to establish conducive
conditions for businesses and investors to adopt these
technologies through policy incentives and regulatory
frameworks.
Enhancing regulations and enforcement within
environmental protection laws is imperative, particularly
in monitoring toxins and contaminants from algae that
may pose health risks. Public awareness campaigns
focusing on the value of algae and its application in
green urban development are essential. Algae windows,
for instance, oer energy-saving benets, carbon
sequestration, and wastewater treatment capabilities,
enhancing their appeal and potential public acceptance
[43].
Financial incentives such as carbon credits and the
development of value-added products can further drive
the advancement of this technology. Governments
should facilitate businesses in utilizing algae technology
for manufacturing biomass and bio-products, oering
tax incentives to enhance operational eciency and
protability, thus contributing to the development of
a low-carbon economy.
Conclusions
A model of a conference room using photobioreactors
(PBRs) as algae windows was created. Energy, daylight
simulation, and hot water production calculations were
Tue Duy Nguyen, et al.
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performed. Algae windows were used in a resort in
Phan Thiet province because their green color made
tourists feel closer to nature. The C. vulgaris 20%
window parameter was chosen because this type of
algae is suitable for marine water, has a green color,
and produces high yields. Algae windows have the
potential to signicantly reduce solar radiation that
passes through them. The higher the concentration
of algae, the lower the solar radiation cooling load,
which will also lead to a lower cooling load and energy
consumption. However, it is important to consider
the room’s lighting to avoid insucient daylight.
The study found that using algae windows instead of
single glazing can result in a 12% reduction in cooling
energy costs. Additionally, hot water production can be
saved by 329.84 kWh/m2.year for south-facing windows
and 201.2 kWh/m2.year for north-facing windows. These
energy savings can be signicant for businesses, as hot
water energy is essential. Biomass can also be collected
for electric generators. Overall, using a photobioreactor
as a window can eectively reduce energy consumption
and protect the environment, as algae can absorb CO2
and release oxygen. To optimize this technology and
implement it in practice, countries need to enhance
public awareness of the role of algae in environmental
protection. Simultaneously, supportive policies and
incentives for investors and businesses should be
developed and implemented properly, depending on the
capacity of every state. Legal regulations should also
establish responsibilities for users of this technology
to mitigate potential risks that could negatively impact
communities, especially human health.
Acknowledgments
We appreciate the eort of an anonymous reviewer
and the useful comments and suggestions for improving
the manuscript.
Conict of Interest
The authors declare no conict of interest.
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