Comparative Study of Internal and External Thermal

Insulations Based on PET Waste Bottles

Youssef Afkir, Hassane Darhmaoui *, Khalid Loudiyi School of Science and Engineering Al Akhawayn University in Ifrane

Ifrane, Morocco h.darhmaoui@aui.ma

Abstract- We present a comparative study of internal and

external thermal insulations in two pilot rural houses in the

mountainous cold region of the middle atlas in the Dayet Aoua

region, province of Ifrane, Morocco. In both studies we used

plastic waste bottles (PET bottles) in cavity walls and roofs.

The idea is to increase insulation by reducing convection fluxes

in wall cavities using cheap insulating materials. We recorded

temperatures in different rooms of each house before and after

insulation as well as the ambient temperature outside the

houses for a long period of time. Our study shows a significant

increase in room temperatures translated in an important

reduction of wood burning and better household comfort

especially during the cold season.

Keywords: External insulation, Internal insulation, Energy

efficiency, Thermal amplitude, Decrement factor, Time lag,

Middle Atlas, Rural buildings, PET bottles.

I. INTRODUCTION

In the Middle Atlas mountainous region of Morocco, where altitudes often exceed 1000 meters, the local population endures severe cold weather conditions for several months. Each household draw down from the nearby forest its need in firewood in order to lessen the thermal discomfort within the houses. The direct effect is an increasing degradation of the local oak forests which represent the primary supply of firewood in the region. According to Berdai [1], the pressure on forest resources in Morocco, including biomass consumption for space heating and cooking in rural houses often isolated, is estimated at 3.3 megatons of oil equivalent, which causes an overexploitation of the estimated biomass at harvest the equivalent of 30,000 hectares per year. Each household in the region consumes on average 7.2 tons of firewood per year.

In this framework, we conducted a study of thermal insulation in two pilot rural houses in the Middle Atlas region in order to assess how thermal insulation can limit the misuse of forest resources. In fact, thermal insulation has been proven to provide a set of economic, environmental and comfort advantages within households. Economically speaking, it reduces the amount of energy required for heating purposes by up to 4 times [2].

Abdessadek Sesbou, Said Dahous Ecole Nationale Forestiere d'Ingenieurs

Sale, Morocco asesbou@yahoo.fr

The effectiveness of thermal insulation depends on a set of parameters involved in the process of heat flow from the outside environment to the interior of the house, and most of these parameters are related to the construction and insulating materials used in the building. In this study, the material selected for insulation purposes is plastic waste bottles. The rural nature of houses, the limited income of the region's population as well as the harsh weather conditions during winter are all factors that favored the selection of plastic waste bottles (PET bottles) as an insulating material because they are simple, freely available, and effective.

The purpose of this study is to compare the effectiveness of thermal insulation based on PET bottles in two different settings. In the first one, the insulation is applied externally to the already existing walls of a pilot house while in the second one the insulation is applied internally. Each method is applied to one or two rooms in two different pilot houses of almost the same. The methodological approach adopted to carry out the study consisted of:

• Measuring the temperature inside the insulated rooms and the non-insulated rooms over a period of four months during winter.

• Comparing the measurement records with respect to the outside temperature.

• Calculating the thermal diurnal amplitude, the decrement factor, and the time lag for both insulated and non-insulated rooms.

A. Site Selection

II. EXPERIMENT

The pilot houses selected for the experiment are located in the commune of Dayet Aoua, province of Ifrane, in the Middle Atlas region. The geographic coordinates of each house are as follows:

• Pilot house for external insulation:

o Longitude: 004°58'300,

o Latitude : 33°33'28 N,

o Altitude: 1696 m.

978-1-4673-6374-7/13/$31.00 ©2013 IEEE

• Pilot house for internal insulation:

o Longitude : 004°58'55 0,

o Latitude : 30°32' 13 N,

o Altitude: 1755 m.

The walls of the two pilot houses are built with dry stones and cement mortar, and their roofs are made of reinforced concrete slabs. The thickness of the walls in each case is 40 cm and that of the roofs is 20 cm. Fig. 1 and Fig. 2 are planar representations of the rooms in each house and their respective dimensions in meters.

11 12 m

l "------1"'""" Kitchen

3/71m

IT: Children's Room

JL (insulated)

Door

13�69 3,SSm ? 6,84

m m

�'WiDdow 13,85

[

Hall

S

,55m m

S

E+W S,90m r Living Parents'

Room Bedroom 6,15

m (insulated)

N ...---L..... -11 5 m

Figure 1. A planar representation of the pilot house for external insulation that is only applied to the children and parents' rooms.

SL Door

� 'ViDd ow

N

12.45m

10.00m

Kitchen

3.90m Bedroom

(insulated)

1.90 m S.40m

Hall

Living Room (Control room)

10.00 m

12.4Sm

Figure 2. A planar representation of the pilot house for internal insulation that is only applied to the bedroom.

The pilot house for external insulation contains one living room, two bedrooms, a kitchen and a hall. The percentage of the glazed area is 1.7% in the south fayade, 5.6% in the north fayade, and 4.6% in the east fayade. The house fayade with the highest percentage of glazed area is not well-oriented as it is facing north. If this fayade was better oriented, i.e. south-oriented, the house would make more solar gains during winter and thus reduce the amount of heating required to reach a comfort temperature [3].

The pilot house for internal insulation is basically the same as the one for external insulation. It contains a hall, a kitchen, a parents' bedroom and a living room. The percentage of the glazed area is 1.7% in the south fayade,

6.7% in the north fayade, and 2.5% in the east fayade. The fayade of this house with the highest glazed area is also not well-oriented as it is facing north.

B. Situation analysis before insulation

In order to have an idea about the typical temperature variation within the houses during winter before insulation, data was recorded for the parents' bedroom in the pilot house for external insulation over a week. Fig. 3 shows the variation of the temperature compared to the outside temperature. It shows that the variation of the temperature inside the room is following the same pattern as the temperature variation outside the house. The change of temperature in the room occurs only a few moments after the change of the outside temperature. The proximity of temperature peaks in the graph clearly shows the existence of a small time delay between the variation of the outside temperature and the room temperature, which is an indicator of the poor heat storage capacity of the house walls. These results are similar to the second house due to the similarity of the house architectures, the construction materials used, and the outside climatic conditions.

20 -Parents'Room - Ouside Temperature

GIS � �10 = ... � � 5 Q. E � 0 +-------------------------��----�------

-5

Figure 3. Variation of temperature in the parents' room before insulation compared to the outside temperature.

C. Proposed solution

The solution proposed to overcome this issue consisted on improving the thermal insulation in each house by introducing plastic waste bottles (PET bottles) as an insulating material within cavity walls and roofs. Plastic bottles trap the air inside and hence reduce heat losses due to convection [5].

In the pilot house for external insulation, a 40 cm thick wall was built outside the house casing an 8 cm layer of PET bottles that are vertically inserted between the new and old walls. The new wall is built with dry stones and cement mortar. PET bottles were also placed horizontally on the top of the concrete roof and then covered by large corrugated zinc plates 4 mm in thickness. In this house, only the children's and the parents' bedrooms were insulated (see fig. 4). The total area of the walls that were insulated after

subtracting the area of the windows is equal to 60.53 m2, and the total roof area that was insulated is 5 1.38 m2.

Kitch.ea ;8·1

11,$01

- Insulated Surface

3,7) •

Cllildrell's Room (iDs.loIled)

.... m

Pne:lI.ls· Bedroom 6�S

(ills-bled)

10,OOm

IGtdll�a Bedroom 1.OOm (in�lIl:1tprt)

7.001'1'1

S.-40m ll4!im

H:l11

1n.Mm

Figure 4. Wall areas of external insulation (right) and internal insulation (left).

In the pilot house for internal insulation, only the bedroom was insulated. PET bottles were placed vertically in an 8 cm cavity between the internal face and a new wall composed of a small brick wall that is 1.20 m high and 0.05 m thick, and wooden-gypsum plasterboards 0.02 m thick and 1.80 m high placed on top of it, between the small wall and the roof. The aim behind this arrangement is to prevent damaging the wooden-gypsum plasterboard if ever water is used for floor cleaning. The wall insulation area is shown in fig. 4 and amounts to 70.76 m2. In order to insulate the roof, a 2 cm thick wooden-gypsum plasterboard ceiling was installed and PET bottles were inserted horizontally between the new ceiling, and the original concrete roof. The total roof area that was insulated is 35.55 m2. All cavities are 8 cm thick.

Insulation was reinforced by adding single glazed glass windows and doors to the existing ones

Temperature data was measured inside each insulated room in the two houses as well as outside each house over a period of 10 weeks from the 24th of December, 20 1 1 to the 06th of March, 20 12. LogTag temperature data logger kits were used for recording the temperature data. To measure the inside temperature, they were placed in the center of the rooms hanging from the ceiling at 0.5 m. To measure the outside temperature they were placed outside the windows in the north fa.;:ade. For comparison purposes, temperature was also measured inside the non-insulated living room of the pilot house for external insulation and inside the non­insulated living room of the pilot house for internal insulation. In the next section, the results obtained are plotted for a period of one week only for clarity purposes.

III. RESULTS AND DISCUSSION

A. External insulation

Children's room Fig. 5 shows the variation of the temperature in the

externally insulated children's room with respect to the variation in the measured outside temperature for the duration of a typical winter week, from the 24th to the 3 1 st of December 20 1 1. The graph shows that the temperature inside

the room remains higher than the outside temperature most of the time, and varies only slightly during the day despite the pronounced temperature variations outside the house during the same period.

Parents' room Fig. 6 shows the variation of the temperature inside the

parents' room with respect to the change in the measured outside temperature, for the duration of one week. Similar to children's room, the temperature inside the parent's room remains higher than the outside temperature most of the time and stays almost constant during the day compared to the outside temperature.

Living Room (Control room) Fig. 7 shows the variation of the temperature inside the

living room which was not insulated (control room). As opposed to the externally- insulated rooms, the temperature in the control room does not remain constant during the day. The daily temperature in this room follows the same pattern as the diurnal variation pattern of the outside temperature, but its amplitude is smaller.

Comparison between the externally insulated rooms and the

control room Fig. 8 is a comparative representation of the temperature

variation in the externally-insulated rooms and the temperature variation in the non-insulated control room throughout the entire duration of the experiment. The figure shows that the temperature inside the children's room remains higher than the temperature inside the parents' bedroom. The difference between the temperature in the children's room and the parents' room can be explained in tenns of the orientation and the location of each room within the house. In fact, the children's room is oriented south which maximizes the solar gains during daylight, as opposed to the parents' room which is oriented north. Moreover, the children's room is adjacent to the kitchen whose temperature increases due to cooking, which increases further the heat gains in the children's room therefore the average temperature. The graph also shows that the temperature inside those two rooms remains higher than the temperature inside the control room, which proves that the insulation in this house was actually effective.

B. Internal insulation

The results obtained for the internal insulation are shown in fig. 9 for a typical winter week. The temperature inside the internally-insulated room varies between a minimum of approximately 5°C during the coldest days and approximately 15°C during relatively warmer days. It remained higher than the outside temperature most of the time during the entire duration of the experiment, which shows that the internal insulation did have an effect.

15 -Children's Room -Outside Temperature

G 10 e... ... .. 5 = '; .. ... 0 c. e ... '"' -5

-10

Figure 5. Comparison between the temperature in the externally-insulated children's room and the outside temperature.

15 -Parents Bedroom -Outside Temperature

G 10

e... ... 5 .. .E '" .. ... 0 c. e ... '"' -5

-10

Date and Time

Figure 6. Comparison between the temperature in the externally-insulated parents' room and the outside temperature.

15

0'10 o '-'

� 5 = -E � 0 Q. 8 � -5

-10

-Living Room - Outside Temperature

Figure 7. Comparison between the temperature in the non-insulated living room and the outside temperature.

14 -Children's Room -Parents' Bedroom -Control Room

2

o

Figure 8. Comparison between the temperature in the externally-insulated rooms and the control room.

C. Comparison between external and internal insulations

A comparative graph of temperature variation in the externally-insulated rooms and the internally-insulated room is shown in fig. 10. We can see that, on the average, the temperature in the internally-insulated room is higher than that in the externally-insulated rooms. But the temperature fluctuates more (by about 2 to 3 degrees) in the internally insulated room.

In order to quantitatively assess the effectiveness of each type of insulation used, we calculate the average temperatures as well as a set of thermal parameters for experimental and control rooms. The fust parameter is the diurnal thermal amplitude A, which is the difference between the maximum and minimum temperatures during one day [6].

20 -Outside Temperature

-Internally-Insulated Room

0' 15 0 '-' � 10 "" = -eo: ""

5 � Q. 8 � 0 Eo-<

-5

Figure 9. Temperature variation in the internally-insulated room and the outside temperature.

14

G 12 o ';'lO ; 8 -

f 6 � c. 4 8 � 2 Eo-<

o

-External Insulation: Children's Room

-External Insulation: Parents Bedroom

Date and Time

Figure 10. Comparison of temperature variation between extemally­insulated and internally-insulated rooms.

This parameter describes the span across which the temperature varies daily and it is expressed as

( 1)

where Tmax is the maximum temperature and Tmin is the minimum temperature. The second parameter is the decrement factor f It is the factor by which the amplitude of the outside temperature is reduced when it propagates from the outside environment to the inside of the house through the walls [6]. It is expressed as

(2)

where Am is the inside thermal amplitude and AOlil is the outside thermal amplitude.

The last thermal parameter is the time lag <1>. Also referred to as the time delay, it is the difference between the time of occurrence of the maximum outside temperature and the time of occurrence of the maximum inside temperature. It is expressed as {t(T;';:""'J - t (T;::F),

¢ = t(T;,;:a"1 - t(T��) + p, p,

if t(T;';:""'J > t(T��) if t(Ti::a.x ) < t(T�� ) if t(T;,;:a") = t(T;::F)

(3)

where t(Tir;:ax) is the time of occurrence of the maximum inside temperature, t(T7::1�X) is the time of occurrence of the maximum outside temperature, and P is the period equal to 24h [6].

Table 1 summarizes the findings related to each room in each house, including the average temperature TOl'g, the diurnal thermal amplitude A, the decrement factor J, and the time lag <1>.

The values obtained for the external insulation show that, on average, the temperature within the children's room exceeds the average temperature in the parents' room by 1.23°C and exceeds the temperature of the control room by 3.34°C. The table also shows that the children's room has the smallest diurnal thermal amplitude compared to the other rooms in the same house, therefore the smallest decrement factor. As far as the time lag is concerned, it is around 9.5 hours in the children's room which is 3 hours longer than in the parents' room and almost 6 hours longer than in the control room. This shows that the heating storage capacity of the insulated rooms had been significantly improved compared to the non-insulated control room. As previously stated, the temperature difference found in the values of the different parameters of the children's room and the parents' room is due to the difference in the orientation and the location of each room within the house. The children's room is oriented to the south which maximizes the solar gains during daylight, while the parents' room is oriented to the north which does not allow it to take advantage of solar gains. Besides, the heat gains in the children's room increase due to its proximity to the kitchen whose temperature increases due to cooking.

For the internal insulation, the values obtained show that the average temperature in the internally-insulated room is approximately 6°C greater than the average outside temperature. The average time lag between the occurrence of the outside maximum temperature and the maximum temperature inside the insulated room was found to be 5 hours and 45 minutes.

TABLE I.

External Insulation

Internal Insulation

COMPARISON OF THERMAL PARAMETERS OF EXTERNAL AND INTERNAL INSULATIONS

T.,.g (0C) A f <I> (hrs)

Children's 7.86 1.16 0.0945 9:24 Room

Parents' 6.63 1.52 0.1277 6:30 Room

Control Room 4.52 3.44 0.2663 3:42

Outside 2.11 12.70 NA NA Temperature

lnternally-insulated 8.92 2.76 0.37 5:45

Room

Outside Temperature 2.99 7.65 NA NA

Comparing the values obtained for the external insulation to the ones obtained for the internal insulation, we find that the highest average temperature was recorded in the internally-insulated room and that the lowest diurnal thermal amplitude, the lowest decrement factor, and the longest time lag (which are desired quantities), were recorded in the externally-insulated children's room. The reason why the highest average temperature was recorded in the internally-

insulated room, although it has the highest decrement factor and the shortest time lag, could be related to the difference in the outside temperature (which was found to be 0.8°C higher on average) due to the geographic difference in the position of the two houses. Moreover, the thickness of the walls in external insulation is more than 35 cm thicker than the walls in internal insulation, which explains the better results obtained for thermal amplitude, decrement factor, and time lag in the externally-insulated rooms.

IV. CONCLUSION

The use of PET waste bottles as an insulating material in rural houses in the cold region of the Middle Atlas in Morocco has stabilized the temperature inside the insulated rooms and increased the thermal comfort. Both internal and external PET insulation were successful. We registered a 25% reduction in wood burning consumption in both houses during the experimentation year [7]. This ratio would increase if all rooms in the houses were insulated. The external insulation, however, yielded better results compared to the internal insulation and thus should be favored when considering the implementation of such an insulation solution in cold rural regions.

PET waste bottles for insulation is a cheap and easy to implement solution that improves thermal comfort within rural houses, reduce forest resources abuse, and reduce plastic waste disposal.

ACKNOWLEDGEMENT

This project is funded by the International Development and Research Centre (IDRC) , CANADA. Projet#: 105568, Management Models of Forest Resources in the Atlas Mountain Chain (North Africa) 2009-20 12.

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[4] S. Nienhuys, "Plastic waste insulation for high altitude areas," Nienhuys,[Online]. Available: http://www.nienhuys. info/documents­papers.html [Accessed 09102/2012].

[5] S. Nienhuys, "Thermal insulation for houses in high altitudes," Nienhuys,[Online]. Available: http://www.nienhuys. info/documents­papers.html [Accessed 09102/2012].

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[7] S. Dahous, «Impact de l'isolation thermique et I'introduction des foyers ameliores sur la consommation en bois de feu dans la region du Moyen Atlas» Atlas (Cas de Dayet Aoua -Ifrane). Master Thesis, Ecole Nationale Forestiere d'ingenieurs, Sale, 2011.