PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Sustainable Resources to Improve on Living Green Walls
Acoustics: Supply Chain Study
Ghofran SALAH1; Anna ROMANOVA2
1

University of Greenwich, United Kingdom

2

University of Greenwich, United Kingdom

ABSTRACT
Living Green Walls (LGWs) or Vertical Gardens are built and deigned using a selection of plants,
growing medium, frames, supports, and irrigation system. LGWs are considered as a natural solutionof controlling noise especially in urban environments. A better sound absorption can be achieved
through replacing the currently used growing medium by a new material with a higher porosity. A
high porosity material allows more sound to entre and dissipate in the material matrix. Coconut fiber
can be a considerable alternative for the currently used growing medium, due to its high porosity. It
has proven that natural fibers have good sound absorption coefficient at medium and high frequencies(500 – 2000 Hz). The study works on improving the LGWs acoustic using sustainable resource(coconut fiber). In order to increase the sound absorption over the current LGWs and utilize thecoconut waste obtained from grinding the coconut waste which naturally exists. Moreover discussing
the impact of introducing the coconut to the LGWs Supply Chain. The paper presents analysis basedon real data collected from LGWs companies.
Keywords: Sound absorption, Coconut fiber, Supply Chain

1. INTRODUCTION
Urban areas have been expanded rapidly in the last decades. The world population increased from
5.3 billion in 1990 to 7.7 billion in 2019 (1, 2). In 2018 the United Nation website has revealed that
55 % of the world’s population lives in urban areas (3). Based on a study done in 2000 it was provedthat more than 44 % of the population within the European Union was exposed to road traffic noiselevels over 55 dB (4). As the world continues to urbanize, many countries will face challenges in
mitigating the sound pollution levels.
Greening these cities is a key element in addressing this noise pollution levels, in order to create a
new sustainable urban lifestyle. Searching for an empty land to plant vegetation is nearly impossible
in such crowed areas. Hence, Living Green Walls (LGWs) are considered as practical solution. LGWs
concept of creating natural surfaces on the walls goes back to the hanging gardens of Babylon thatwas one of the Seven Wonders of the World at 600 BC (5). Currently LGWs design varies based on
the customer requirements. LGWs are offered by different national and international companies.
Previous acoustic studies have demonstrated the LGWs within the context of traffic noise mitigation.
The studies focused on the sound absorption and sound propagation properties of green walls andvertical greenery systems used on façades (6 – 8). It was found that green vertical systems with 4 m
width, 8 m height, and 0.3 m thickness, reduce sound propagation compared to rigid façades withmaximum road traffic noise reductions of approximately 10 - 20 dB at mid frequencies around 500 –1000 Hz. These green vertical systems were on average 1 m above the ground (7, 9).
The configurations of the systems (10), roof thickness (9, 11), and vegetation layer (12), have all
been shown to be important factors affecting the sound absorption and sound propagation propertiesof green systems. In order to absorb the sound well, materials should have high porosity (relative
volume of pore space). A porous absorbing material contains cavities, channels or interstices so that
1
2

G.M.Salah@greenwich.ac.uk
A.Romanova@greenwich.ac.uk

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sound waves are able to enter and be captured by them. When the sound waves are exposed to a porous
material, the air molecules at the surface and within the pores of the material are forced to vibrate.
This leads to loss of some incident/emitted energy. Because part of the energy is converted into heatby the air molecules due to thermal and viscous losses at the walls of the interior pores and tunnels
within the material (13, 14).
Fibrous materials consist of a series of tunnel-like openings that are formed by interstices inmaterial fibers; these fibers may be continuous filaments or discrete elongated pieces that trap emitted
sound. They are produced in rolls or in slabs with different thermal, acoustical, and mechanicalproperties. Fibers can be classified as natural or synthetic (artificial, i.e foam). Natural fibers can be
fruit or vegetable (coconut, banana, cotton, kenaf, wood, etc.), animal (wool, fur felt), or mineral(asbestos) (15). Recent measurements carried out on samples of natural fibers. The measurements
have shown that similarly to traditional porous materials natural fibers have good sound absorption
coefficients, especially at medium and high frequencies (500 – 2000 Hz) (14, 16).
Coconut fiber and coir are waste material that remains after the coconut is processed into different
products, such as: coconut meat, coconut milk, coconut water, etc. The Coconut fiber and coir are
extracted from the inner husk of the coconuts as shown in Figure 1. Coconut natural fiber ischaracterized by its thickness, coarseness and durability (17). Coconut fiber and coir are by-productwhich occur in nature,as shown in Figure 2. The coconut fruit yields 40 % coconut husks containing
30 % fiber, with coir making up the rest (18). Coir (also known as coir pith, coir meal, coir dust andcoco peat) is a waste product of the coconut fruit (19), consisting of the dust and short fibers derived
from the husk of the fruit. This amount of renewable natural resource can be utilized as an alternative
for the Black Compost Soil (BCS), to improve on LGWs sustainability.

Figure 1- Coconut component schematics (20)Figure 2- Coconut husk, fiber and coir (21)Coconut coir pith and BSC can be blended in order to obtain fluffed plant growth media. This mixed
growing medium will improve the fluffed yield characteristics and enhanced wettability as comparedwith the results obtained from using BCS individually. Coir pith is granular in nature and holds waterin a matrix equivalent to a “honeycomb” or sponge. Coir pith does not shrink as much as peat moss
and peat moss does not wet as well as coir pith (22).
To study the coconut fiber capability of noise absorption an experiment was performed. This
experiment will be illustrated in the section 2.

2. Methodology
Two methodologies were applied in this study: (a) in-situ acoustic absorption experiments oftraditional Black Compost Soil (BCS) vs. Coconut Fiber (CF), (b) case-study approach and analyticalmodelling of Supply Chain to establish benefits of the CF for LGWs companies.
2.1 Experimental Methodology
To compare the acoustic absorption of the Black Compost Soil (BCS) vs. Coconut Fiber (CF) an
in-situ experiments were carried out at the LGW nursery site. In these experiments a 3 m wide and 2
m tall LGW with only pre-filled soil in the modules was used (see Figure 3). Each compartment of
the module measures 80 mm x 100 mm. The moisture content of each of the growth medium’s was
kept at 5 %.
The acoustic method described in (23) was used, where instrumentation consisted of ‘An intensity
probe, Brüel & Kjær, type 4197 with Brüel & Kjær NEXUS conditioning amplifier type 2690 andparametric transducer (directional loudspeaker HSS-3000 Emitter) with HSS-3000 amplifier. The

6744

intensity probe was firmly attached to a telescopic tripod and placed at a height of 0.9 m and 1.7 m
away from the measured surface. The orientation of the intensity probe with respect to the wall wasperpendicular. The directional loudspeaker was also attached to a tripod and it was placed 4 m awayfrom the wall. The line connecting the center point of the directional loudspeaker and the middle ofthe intensity probe was also set perpendicular to the wall. See Figure 4 for the set-up schematics. Thismethod offers great precision and hence advantage over the traditional acoustics barrier absorption
methods, CEN/TS1793-5:2003 and ISO354-2003, as mentioned in (23).

Figure 3 - Black Compost Soil (BCS, left) and Coconut Fiber (CF, right) in plastic modules

Figure 4 - Acoustics experiment set-up, using Ans Global Ltd LGW system
2.2 Investigation Methodology
An interview was carried out with one of the well-known LGWs companies (Scotscape Ltd.) in the
United Kingdom. During the interview a set of questions were asked to Scotscape Ltd., to help in
exploring and understanding their supply chain. In large, the questions acquired the information inthese categories:a) The material / components of LGW;b) Material suppliers, supplier location and means of transportation;c) The LGW ordering process;d) Communication link between LGW company and suppliers.
The Scotscape LGW is mainly consists of five main components: modules, irrigation system, plants,
BCS, and fixtures. All of these components are sourced from different suppliers. Part of the suppliers
are local (based in the UK), except for the modules and plants.
The LGW supply chain process starts with initiating the LGW order by a client. The client contacts
the LGW company to arranges a site visit. Then company’s employ takes the site’s measurements. A
quotation is then estimated and sent to the client, to get the approval. After the client approves theoffer, the measurements are used to create the LGW design and identify the required material. After
that, they order the required material from their suppliers via e-mail. The soil and fixtures (screws,
guttering, and timber) are off the shelf from local DIY stores near the company. The orders are shipped
to LGW Company. The modules are delivered by ship to UK and then collected by the LGW company
by van. The irrigation system is delivered by van from Bristol to the LGW by van. The plants are
sourced from Holland by vans. Finally, they ship the material to client’s site and install the LGW. A
flow diagram was created to show the LGWs material supply chain Figure 5.

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Figure 5 - LGW supply chain flow diagram

3. Data Analysis
After applying both methodologies, the outcomes were analyzed in Section 3.1 & 3.2.
3.1 Experiment Analysis
The intensity probe was used to record the instantaneous intensity, where time window analysis(of 3 x 10 s repetitions) and further Fourier analysis were carried out to determine the acoustic
absorption coefficient (23) for both BSC and CF. Figure 6 below represents averaged acoustic
absorption coefficient for BSC, CF as well as 100 mm thick Melamine sample (good porous absorbent
material with known acoustical properties) and 18 mm Plywood (known for good reflection properties
as a non-porous material) to benchmark the results. It is seen that the absorption coefficient of the CF
is between 12 – 20 % higher in frequency ranges 300 – 5000 Hz.
This parameter will change with the fluctuation of the moisture content of the growth medium,
however the moisture content in the range of 0 - 20 % has been reported to be most effective atfacilitating adequate sound absorption. At higher concentration of moisture, the growth medium
becomes mostly reflective as pores are filled with water that tends to behave like a glass surface.

Figure 6 - Acoustics absorption coefficient for 100 - 10000 Hz

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3.2 Questionnaire Analysis
Carbon emission was calculated for each component based on the material weight and means oftransportation, taking into consideration the fuel type, distance travelled, material weight and vehicle
weight. Table 1, columns left to right, shows the LGW components, materials, material weight in
kg/m2 , transportation type, distance (km) from the supplier to the LGW company, emission factor(km/m2 ) and the carbon emission (CO2 /m2 ).
Based on (24), the average volume of a van = 17 m3 and the fuel type is diesel. The average capacityof ship is 58 containers, the one container is 33 m3 (25, 26) and the fuel type is diesel. The carbon
emission was calculated manually. Taking into consideration that the load utilization percentage for avan is 85 % (27), and for a ship is 70 % (28). The emission factor for the van is 0.2568 ton kg CO2(29) and 0.01592 ton kg CO 2 (29) for the ship.
The LGW components, material, weights, and the mean of transportation were deduced from thedata collected by the questionnaire. The distance was calculated using Google Maps, based on the
supplier and LGW company location as provided by questionnaire answers. The van carbon emission
was calculated using equations 1 - 5. The ship carbon emission was calculated using equations 6 - 10.
For van:𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑡𝑜𝑛) = 𝑒𝑚𝑝𝑡𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑣𝑎𝑛 + 85 % 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙
𝑡𝑜𝑛 𝑘𝑔 𝐶𝑂
𝑘𝑔 𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑡𝑜𝑛) × 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑖𝑜𝑛 () = 𝑇𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 (
)
𝑘𝑚
𝑘𝑚
𝑘𝑔 𝐶𝑂
𝑡𝑜𝑡𝑎𝑙𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑘𝑔𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑝𝑒𝑟 𝑏𝑜𝑥=
𝑘𝑚
𝑛𝑜. 𝑜𝑓 𝑏𝑜𝑥𝑒𝑠 𝑘𝑚 × 𝑏𝑜𝑥
𝑘𝑔 𝐶𝑂
𝑡𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛
𝑘𝑔𝐶𝑂𝑚
𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛=
÷ 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑝𝑒𝑟 𝑏𝑜𝑥
𝑘𝑚 × 𝑚𝑛𝑜. 𝑜𝑓 𝑏𝑜𝑥𝑒𝑠 𝑘𝑚 × 𝑏𝑜𝑥
𝑏𝑜𝑥
𝑘𝑔 𝐶𝑂
𝑘𝑔 𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛= 𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛
× 𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑘𝑚)𝑚
𝑘𝑚 × 𝑚

(1)
(2)
(3)
(4)
(5)

For ship:𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑡𝑜𝑛) = 𝑒𝑚𝑝𝑡𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑜𝑛𝑡𝑎𝑖𝑛𝑒𝑟 + 70 % 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙(6)
𝑡𝑜𝑛 𝑘𝑔 𝐶𝑂
𝑘𝑔 𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 (𝑡𝑜𝑛) × 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑖𝑜𝑛 () = 𝑇𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 (
)
(7)
𝑘𝑚
𝑘𝑚
𝑘𝑔 𝐶𝑂
𝑡𝑜𝑡𝑎𝑙𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑘𝑔𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑝𝑒𝑟 𝑏𝑜𝑥=(8)𝑘𝑚
𝑛𝑜. 𝑜𝑓 𝑏𝑜𝑥𝑒𝑠 𝑘𝑚 × 𝑏𝑜𝑥
𝑘𝑔 𝐶𝑂
𝑡𝑜𝑡𝑎𝑙 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛
𝑘𝑔𝐶𝑂𝑚
𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛=
÷ 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑝𝑒𝑟 𝑏𝑜𝑥(9)
𝑘𝑚 × 𝑚𝑛𝑜. 𝑜𝑓 𝑏𝑜𝑥𝑒𝑠 𝑘𝑚 × 𝑏𝑜𝑥
𝑏𝑜𝑥
𝑘𝑔 𝐶𝑂
𝑘𝑔 𝐶𝑂
𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛= 𝑇𝑜𝑡𝑎𝑙 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛
× 𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑘𝑚)(10)𝑚
𝑘𝑚 × 𝑚Table1 - Living Green Wall material carbon emission calculation
Living Green Wall (LGW) Materials
Components

Modules
Irrigation
SystemPlantsSoil
Fixtures

Material
Fabric +PowderCoated Steel
Strip
Pipes + Calber
Tap Timer +Drip Line
Selected
PlantsBlack
Compost SoilScrews, etc.

Weight(kg/m2 )Transportation
Mean

Distance(km)

Emission
Factor(km/m2 )CarbonEmission(kgCO 2 /m2 )2.4

Ship +Van

1952 by ship
885 by van

0.075 for ship
0.002 for van

147 for ship
1.77 for van

0.6

Van

174

0.003

0.52

8

Van

280

0.009

2.52

18

Van

8.05

0.031

0.25

5.57

Van

8.05

0.007

0.06

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The coir can reduce the weight of the LGW, hence the carbon emission. The coir density is around
0.8 g/cm3 (30), and soil is around1.6 g/cm3 (31). A bulk weight of 5 kg of coir gives 70 L of finecoconut fiber potting soil (32), this makes its transportation weight low. It will contribute in reducing
the modules and plants transportation weight and carbon emission. Because the modules were
designed to hold the BCS which is heavier than the coir. The plant transportation weight and emissions
will be reduced, by changing the soil to coir in the plant pots. The coir transportation carbon emission= 0.002 km/m2 and 0.016 kg CO2 /m2, assuming that coir is sourced from the same DIY store.
Coir pith proves a greater advantage of allowing good aeration around the roots of plants. It has theunique property of retaining water for longer duration of time. This property of the coir pith may
facilitate the continuous and prolonged availability of water for the plants grown in pots (33). Coircan minimize the water consumption in the LGW. As a result, it acts as an ideal potting medium. Bychanging the growing medium weight, the rest of LGW components weight can be changed.

4. DISCUSSION
The results of the questionnaire analysis show that CF can be a sustainable alternative to the BCF.
CF has proved to be a promising growing medium (5). The results of the analysis show that CF canbe a sustainable alternative to the BCF in LGWs. CF as a growing medium can increase the soundabsorption by 20 % compared to BCS, due to high porosity of CF. Desk study calculations proved that
CF can reduce the carbon emission of overall SCM process. The calculations considered the material
flow from the supplier to the LGW company. On average CF carbon emission of 0.016 kg CO 2/m2 andBCS carbon emission of 0.25 kg CO2 /m2 was achieved. The coconut fiber compared to black soil
compost can give the LGW company advantages, such as: (a) minimizing the overall LGW material
weight and load on the buildings due to low bulk weight (b) CF will reduce the water usage in LGW
system, because it has higher water retention than BCS (c) CF can act as a natural pesticide controller(d) CF origins are sustainable as are considered to be a waste/byproduct in the countries of growth (e)and lastly can contribute in reducing noise by 20 % in 300 - 5000 Hz frequency range.
The concept of environmentally friendly, sustainable, recycled, and green building materials iscurrently an important feature in the marketing of sound-absorbing materials. These new directions
will hopefully encourage the use of cheap renewable natural materials.
CF has proved to be a promising growing medium with higher and improved crop quality (34, 35).
It offers a high moisture to air retention capacity, which enables easy growth and well spread rootsystem. Some plants may need adding nutrients to the CF, it depends on the nutrients that is required
for each plant type.
Finally, CF average retail cost is £ 150 per ton (36) and the soil average retail cost is £82.99 per
ton (37), where 1 ton of dried compacted CF can expand to 10 tons of growth medium by exposing to
air and adding minimal water. This is due to the CF structure phenomenon, it comprises of thin hollow
shells or tubes, that allow the CF to absorb ten times of its own weight in water.

5. CONCLUSIONS
Living Green Walls is considered as a natural solution to control the sound pollution in urban areas.
The LGW sound absorption capability can be maximized by 20 % using CF that showed higher soundabsorption over the current used growing medium (BCS). CF yields higher and improved crop quality
and offers a high moisture and air retention capacity, which enables easy growth and well spread rootsystem.
Coconut fiber can reduce the carbon emission and lower the LGW cost, which in turn improves thesustainability of LGW. CF will also reduce the amount of energy (water and possibility the electricity)used to maintain LGWs. It should be noted that the study only considered the material flow from the
supplier to LGW companies. Further detailed study can be performed to include the energy
consumption at all stages: from production to installation.

ACKNOWLEDGEMENTS
The authors would like to thank the University of Greenwich for the fund towards this conference.
The authors would like to thank Scotscape Ltd. for it is collaboration especially Niall Mc Evoy thebusiness development manager for his invaluable help in getting the required information.

6748

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