4. DESCRIPTION/BACKGROUND OF THE INVENTION
Field of invention
Demand for electrical energy is growing at the fastest rate in building sector. As per current
Indian energy scenario, close to 30% of energy is consumed by building sector (comprising
commercial and residential buildings) out of total energy generation (255 GW). In commercial
buildings, HVAC (Heating, Ventilation, and Air-Conditioning) system consumes major portion
(-56%) of energy, similarly in residential sectors the heating and cooling appliances consumes
about -58%. There are many ways to brought in energy efficiency in above mentioned systems,
namely (i) usage of energy efficient appliances, (ii) improvement in ventilation system, (iii)
better building envelope with enhanced insulation, fenestration, and roofing, (iv) make use of
available free natural energy etc. The rooms generally gets heated up by internal and external
thermal loads. Among the external thermal loads, namely; sun, earth, and atmosphere, maximum
amount of thermal loads .comes from solar heat. Further, almost 60% of the total solar heat
-penetrates only through roof surface. Thus, covering the roof to reduce heat transfers is a suitable
way to minimize solar heating, which, in turn shall increase the energy efficiency in
heating/cooling systems. In addition, the roof covering is an easier approach while working on an
existing building. It is calculated that through proper roof envelope, overall -lO%'energy can be
saved in building sector, which is equivalent to 4GW of capacity and Rs. 20,000Cr. In addition,
roof insulation process offers following benefits; reduces energy bills by decreasing airconditioning
needs, improves indoor comfort for spaces that are not air conditioned, decrease
roof temperature to extend roof life, reduces local air temperatures (urban heat island effect),
lower peak electricity demand to counter power outages, reduces toxic 'plant emission gases.
Background of invention
Insulation of roof surface from solar heat is mainly brought in through following methods; (i)
usage of insulating material as roof material, (ii) reflecting back the solar heat (UV and IR rays)
on the roof, and (iii) covering the roof with plants. Yet, above mentioned techniques have some
inherent drawbacks thus could not counter the energy consumption issues round the year. Firstly,
isolation the roof through insulating material can only be incorporated while constructing the
building and inclusion in an existing building is a cumbersome and non-economical measure.
The roof screening (also called as roof coating/layering/encrusting) techniques those work on
reflection of solar heat reflection gives rise to following issues: (i) requires additional heating
energy to maintain comfort level in winter, (ii) reflected rays from screened surface interacts
with nearby buildings and increases their temperature, energy usage by their air-conditioning
system, (iii) to a great extent depends upon location where deployed, (iv) performance greatly
reduces with settlement of dust on roof. Planting trees on the roof mainly focused towards;
absorption of rainwater, generating habitat for wildlife, bringing benevolence and aesthetic look
for people staying around the space and of course building insulation. Yet, this procedure offers
very low energy efficient benefits. Above mentioned unsolved issues were the motivations for
the invented all season energy efficient roof screening process.
Objects of the Invention:
The developed roof screening process is ripened to counter the unsolved issues discussed in
foregoing paragraphs. The developed screening process blends adequate solar reflectivity and
absorptivity property, to drop and increase the room temperature in summer and winter
respectively. Thus generates maximum energy saving potential round the year. In addition, as the
screening process is not completely dependent upon reflection phenomena, issues with nearby
buildings are overcome. Addition of well-defined glossy surface promotes potential to reduce
effects of dust settlement. The durability of the screening is quite high, thus service for money
point is justified. Expenditure in deployment of the developed process was taken care while
optimizing the screening process. Thus the developed stands out to be better roof screening
process in comparison to the existing procedures.
Statement of invention
Present investigation process makes use of hybrid heat transfer technique to offer energy
efficiency round the year without compromising the comfort. The screening process is a
perfectly blended the reflective and absorptive property of roof screening to offer above
mentioned goal. In addition, the invented screening process takes care of reflection issue on
nearby buildings, dust settlement and expense towards deployment.
Summarv of invention
Present investigation mainly aims at reduction of energy usage in buildings without
compromising the comfort of occupants through an energy efficient roof screening process. The
commercially available roof screening techniques mostly offers energy efficiency in certain
season of the year through insulating the roof, reflecting back the solar rays or simply covering
the roof with plants. However, these methods have many essential issues those are not yet
solved. Therefore, the purpose of present investigation is to develop a roof screening process that
would; (i) maintain comfortable room temperature round the year with energy efficiency, (ii)
minimize the heat reflectance effect on nearby buildings, (iii) perform against dust settlement on
roof etc. Development of envisaged roof screening process is fulfilled in multiple number of
steps. Initially, a lab-scale experimental set-up is designed and fabricated at Smart Grid lab,
POWERGRID that would mimic the real world roof situation. The experimental set-up is
comprised of lighting section to replicate the solar heating, concrete roof with typical building
roof thickness, and a virtual room. The screening on the roof is experimented with seven types of
screening processes, namely; aluminium, black, lime-stone, white portland cement, white paint,
glossy white coat, and reflective coat. Each of the mentioned screening procedures are chosen
because of their unique characteristics. Experiments are carried out to quantify the energy
efficiency potential, durability, reflection effect, effect of dust settlement, effect of screening
thickness and probable expenditure towards roof screening processes. In order to reduce the
number of experiments and shortlist the effective screening processes, a computer code is
developed with commendable assumptions. The computer code optimizes energy efficiency,
screening thickness and costing of the screening process, which gives rise to various way of
optimal screening process. Where, positioning of the screening techniques is mostly based on
roof temperature profile. For better understanding of the heat transfer model, the simulation
process is adjoined with the mathematical modelling. Results from the computer code are
validated against the experimental data. Based on overall performance two screening processes
are chosen for field testing. During field testing, to quantify the effect of developed screening
processes on the room temperature, multiple numbers of temperature sensors are deployed at the
investigation place. The field testing process is carried out for different seasons and based on the
performance the "Energy Efficient All Season Roof Screening" process is established.
In order to quantify the advantages of the invented roof screening process, its performance is
compared against the conventional roof screening processes and without roof screening case.
The temperature values are compared at the rooftop/bottom surface and inside the room at
different air temperature condition above the roof, which replicates the atmospheric situation.
The developed screening process offers comfort along with energy efficiency by
decreasinglincreasing roof-cum-room temperature at high and low atmospheric temperature
respectively. On the other hand, the widely used reflective coat always reduc-e s room tempera- ture
causing comfort issues and additional energy usage in some part of the year. Other screening
processes are useful counter to certain atmospheric condition. Further experiments are carried
out to quantify the effect of stored heat in the concrete roof on roof-cum-room temperature,
which is similar to room condition after sunset. For some screening processes it is found that due
to above mentioned stored heat the roof-bottom and room temperature either remains same or
increases for some time, while rooftop temperature reduces quickly. Decision on screening
thickness is an important aspect, thus, the screening thickness is optimized through multiple sets
of experiment and simulation method for each of the screening process.
In addition to temperature and screening thickness; other vital parameters like effect of dust
settlement, durability, expenditure (including labour charge), and energy efficiency are compared
through field testing process among developed and existing screening techniques. It is found that
concrete roof, black paint, white portland cement, glossy'white and developed screening process
performs well against dust settlement. Durability point of view the developed screening process
along with reflective coat has the highest durability factor. For screening at field, that includes
both screening material and labour charges; expenditure towards aluminium coat is highest and
the invented screening process is almost 45% cheaper than aluminium screening. The energy
efficiency potential, which is the prime objective of present investigation, is normalized against
without screening, case and it found that the developed screening process gives rise to an energy
saving potential of up to 38% round the year. In order to finalize the screening process that
would fulfil all the requirements, a performance table is constructed. Table shows that the
cumulative performance of developed screening process is much better than existing technique.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. I (a) Schematic diagram with instrumentation, and (b) pictorial view of experimental set-up
Fig. 2 Positions of thermocouple in the experimental set-up for (a) surface, and (b) air
temperature measurement
Fig. 3 Roof screening in process at POWERGRID Township for field testing
Fig. 4 lowc chart for optimization process used in present investigation
Fig. 5 Temperature distribution on the rooftop in different direction
Fig. 6 Boundary condition for present heat transfer model
Fig. 7 Application method of invented screening process in various (a), (b), and (c) shaped roof
Fig. 8 Variation in rooftop temperature w.r.t. rise in atmospheric temperature
Fig. 9 Variation in roof bottom surface temperature w.r.t. rise in atmospheric temperature
Fig. 10 Variation in room temperature w.r.t. rise in atmospheric temperature
Fig. 11 Variation in rooftop temperature after sunset w.r.t. rise in atmospheric temperature
Fig. 12 Variation in roof-bottom temperature after sunset w.r.t. rise in atmospheric temperature
Fig. 13 Variation in room temperature after sunset w.r.t. rise in atmospheric temperature
Fig. 14 Variation in rooftop temperature w.r.t. span of time (i.e. dust settlement)
Fig. 15 Formation of cracks and pores on the roof surface in case of lime stone screening
DETAILED DESCRIPTION
This section describes about the invention process; how it is made, how to use, and comparative
advantages against conventional techniques. The invention process starts with lab scale testing.
Particulars of the experimental methodology are discussed hereunder.
A. Experimental Methodology:
(i) Experimental Set-up: The lab scale prototype model is developed to carry out the
experimental work. The experimental set-up mimics the real world roof situation, and generates
provision to perform multiple experiments with varying process parameters. Figure 1 shows the
schematic diagram (a) and pictorial view (b) of the experimental set-up. The developed set-up
has three sections, namely; (i) lighting section, (ii) concrete roof, and (iii) virtual room/model
house. In order to replicate the solar heating, four (4) numbers of halogen lights were used with a
capacity level of 4kW. Power supply to the halogen lights were varied by a variable autotransformer
that would alter the temperature situation above the roof. In present experiment, Air
temperature above the roof is varied from 5" to 25OC above normal atmospheric temperature.
The concrete roof below the lighting system has a typical roof thickness, i.e. -125mm, where the
cross-section is taken as 3ft in length and 2ft in width. Adequate surface finish is brought on
either side (top and bottom) of the concrete roof. Four of the halogen lights were arranged in
such a way that the concrete surface will get uniformly heated up. The model house below the
roof is insulated from outside through OSB (Oriented Strand Board) sheets, excepting from top
side. Hence, heat transfer occurs only from the roof.
(ii) Instrumentation: The experimental set-up is incorporated with adequate measuring and
controlling devices to alter the operating parameters and note the corresponding effect. Brief
descriptions of the same are given below.
(a) Variable Auto Transformer: The variable auto transformer (Variac) varies the supply voltage
to the lighting system. Present experiments run for more than six hours to reach steady state.
Therefore, oil' cooling technique is adopted in the variac to avoid overheating. The autotransformer
can vary the output voltage in the range of 0-270V for a constant input supply and
has the current rating of 35 Amps. Calibration process is done in advance to correlate the supply
power to the lighting system and corresponding change in air temperature.
(b) Temperature Measurement: To quantify the temperature value of air and solid surface
thermocouples are used. For solid (concrete roof surface) temperature measurement, K-type
thermocouples are used. Figure 2 (a) shows the arrangement of surface thermocouple on either
side of the roof. The thermocouple bid is fabricated on a thin copper sheet having a cross-section
of 5mm x lOmm and thickness of around 0.lmm. The thermocouples are calibrated against the
standard thermometer. Accuracy of the thermocouple is better than 0.2"Cand the uncertainty
level is around *6%. The surface thermocouples were kept 2mm underneath measuring surface.
In total there are twenty six (26) thermocouples connected on either side of the concrete roof.
Similarly, for air temperature measurement, K-type temperatiire sensors are used, Three sf the
temperature sensors are kept on either side of the room and similarly above the roof area. There
are total twelve (12) numbers of temperature sensors used in present purpose, refer Fig. 2 (b).
The temperature sensors are also calibrated, and have the accuracy level of O.l°C. The
uncertainty level in the reading is around *5%.
(c) Screening Thickness gauge (Elchometer): Screening thickness gauge is used to quantify the
screening thickness on the roof. The elchometer follows non-destructive type of measurement
process. The measurable thickness range is from 50 to 1000p, with an accuracy level of*12p.
(d) Data Acquisition System: Data acquisition system is used to measure and store the output
data from the surface thermocouple and temperature sensor. The data acquisition system also
displays the temperature reading simultaneously during experiment.
(iii) Roof Screening: In present investigation seven types of screening techniques are used,
namely; aluminum paint, black paint, lime stone, white portland cement, white paint, glossy
white coat, and reflective screening. Aluminum color has high reflectivity value and glossy. The
black color coat has low reflectivity value and high heat absorptivity property. Lime stone is the
most widely used roof screening technique due its lower cost and ease of availability. Similarly,
the white portland cement is expedient as it increases the service life of the roof. White color
paint is used because of its low absorptivity and high reflectivity. Glossy white surface offers
additional polish and shine to that of white color surface. The reflective screening process has the
highest level of reflectivity, thus can counter the effects of UV and IR rays from sun. Because of
above mentioned reasons, these screening processes are chosen for initiation of the invention
process.
(iv) Experiment Process: All the measuring instruments used in the experiment process are precalibrated
with standard techniques before starting the experiment. Another set of calibration is
performed to correlate the auto-transformer supply voltage and corresponding rise in air
temperature above the rooftop in the experimental set-up. Before starting the experiment, the
rooftop surface is screened with planned screening color and thickness. It is made ensured that
the rooftop is free from any dusts or undulations. While, starting the experiment initial
temperature values are noted. The air temperature value on the roof is Tmin,aaitr t he starting of
experiment and at end of experiment, T,a,,ai, the difference is termed as Tdi~T.h e temperature
difference Tdiffis varied from 5 to 25°C in present set of experiments with three level of roof
screening thickness for each screening process. All the experiments are carried out till the entire
set-up reaches steady state, and the maximum temperature variation is less than O.l°C in a span
of one hour. Experimental readings are continuously saved to the personal computer through the
data acquisition system during the experiment for later processing and analysis.
(v) Parameter Study: In present experimental work basically three parameters are varied,
namely; screening color, screening thickness and temperature rise of air. Table 1 shows the list
of cases studied in present lab-scale experiment.
Table: 1 List of parametric study
Screening Process
Without Screening (Concrete)
Aluminum Paint
Black paint
Lime Stone
White Paint
White Portland Cement
Glossy White Surface
Reflective Screen
Temperature Rise (Tdiff)
511 011 5/20/256C
511 011 5120125°C
511 011 5120125°C
511 011 5120125°C
511 011 5120125°C
511 011 5120125°C
511 011 5120125°C
511 011 5120125°C
Screening
Thickness
--
80p, 160p, 240p
80p, 160p, 240p
80p, 160p, 240p
80p, 160p, 240p
80p, 160p;240p
80p, 160p, 240p
80p, 160p, 240p
B. Field Testing:
As mentioned earlier field testing gives the realistic data, hence the screening processes are
tested apartments of POWERGRID-Township, Gurgaon. Overall, the field testing of the roof
screening process comprises of two steps: roof cleaning and roof painting process. In roof
cleaning step, the roof is cleaned with pressurized water and then dried. Further, any cracks or
undulations are rectified. In roof painting step, the roof surface was screened keeping the
optimum screening thickness in mind. Figure 3 shows the process of roof screening. The field
testing process is carried out to quantify the effect of dust settlement, cost (including labour
charge), durability, reflective effect on nearby buildings, variation in room temperature and
energy efficiency value.
C. Optimization Process:
(i) Optimization: To achieve the desired roof screening process help of an optimization process is
taken. Above details experiment process showed that present invention consists of multiple
numbers of colors with varying screening thickness. There are seven different choices of color
and n-number of screening thickness, there will be a large or infinite number of combinations to
choose from. Further, additional quantities like cost, reflection effect, absorptivity, energy
efficiency, durability, effect of dust settlement are also needed to take in account. Consequently,
an optimization process is developed with certain assumptions for above mentioned points. Flow
chart of the basic algorithm is shown at Fig. 4.
Following are the list of assumptions with clarifying points:
a. Effect of screening is directly proportional to area deployed
b. Maximum number of screening color included in the process is three; this is to avoid
confusion at end-users
c. Screening thickness effect on energy efficiency holds good even it is applied in portion of the
surface.
d. Length considered'for programming is in steps of 5%, any variation within this is negligible
Keeping above assumptions a computer program is .generated to calculate the overall
performance value of each of the combination of screening process. The inputs to the
optimization process are given from the lab scale experiment and field testing data. As
mentioned earlier, to limit the case to finite number the color occupying length in each direction
is varied in steps of 5%. Thus one particular color can occupy 5-90% of total length in steps of
5%, in any combination of three colors.
It is further to be noted that positioning of screening color is also dependent upon the
temperature profile of the rooftop surface. From experiment, it is found that maximum
temperature of the roof is mostly at the center of the roof, and temperature reduces linearly as the
distance increases from center towards periphery, refer Fig. 5. Therefore, screening color that
offers maximum temperature drop with respect to atmosphere will be kept in the center and
screening that offers least will be kept at the corner. Effect of dust is also an important
parameter, thus screening that offers maximum resistance against dust settlement will be kept in
the center of two screening techniques.
(ii) Mathematical Modelling: Present investigation model constitutes all three modes of heat
transfer, hence a conjugate one. As stated earlier heat transfers only through roof top surface and
there in no side wall heating, refer Fig. 6. The roof surface gets heated up by the solar heat,
which is a combination of radiation and convection. Yet, major amount of heat loading from sun
is due to radiation. The heat from the top surface of the concrete surface diffuses to the bottom
surface, where conductivity of concrete is inversely proportional to the transfer of heat from top
to bottom surface of roof. With inclusion of roof screening the resistance to penetration of solar
heat into the room further increases. The resistance to heating varies with type of screening.
Now, below the roof, the room gets heated up mostly by natural convection from bottom surface.
The boundary conditions for present heat transfer case are as follows;
i) Conjugate thermal condition
aT, - ks --- k, -a Tf
ay ay
Ts = Tf
ii) Entrainment condition
Pper.@ri = P,,n
iii) Insulation condition
q = 0, at all surfaces of the room except the roof
iv) Heating condition
- 4so1ar - 4top
v) No slip boundary condition
On the solid wall : V,,,o,, = 0
Where, s = Solid f = Fluid
q = Heat Flux k = Thermal Conductivity
T = Temperature P = Pressure
atm = Atmosphere toplbottom = Roof TopIBottom
(iv) Validalion.: The optimization process gave rise to many screening methods. However, for
further steps the best ten screening processes were chosen. As the optimization results were
based on assumptions and pure calculations, for validation purpose these results are compared
against laboratory experimental data. The ten best screening processes were deployed on the
rooftop of lab model and experiments are carried out as discussed earlier. Results showed that
the simulated results are very close to that of experimental data. Further, based on the energy
efficiency value, two of the screening processes are chosen with maximum energy efficiency
potential. These, two types of roof screening processes are deployed on an apartment to obtain
field testing result and to finalize the best energy efficient screening process.
So as to finalize the screening process, the effect of roof screening on room temperature is
quantified. In this regard, four numbers of temperature sensors were deployed at the
investigation place to record the room temperature. One sensor, on the roof space to record the
atmosphere temperature; and other three in the leaving space, i.e. one in concrete roof flat, and
one in each developed screening process flat. Sufficient care has been taken about the
positioning of the temperature sensors, such that on roof top the sensor reading will not get
affected by direct sun heat, and in the room by artificial heat generating sources, e.g. air
conditioner, kitchen etc. Temperature data collected for over fourteen months and in-between
data were transferred to the computers for analysis. The year round result from the field testing
gave rise to invention of the "Energy Eficient All Season Roof Screening" process. Method to
use the same is discussed in following paragraphs.
D. Deployment Method of Invented Screening Process:
The invented roof screening process follows hybrid heat transfer process. Where, the centre
portion of the roof will be covered by reflective screen, the end portion of the roof will be
screened with black paint and in-between black and reflective screen glossy white screen will be
deployed. Initially, the centre of the roof is required to be decided. Thereafter, from centre to end
length in each direction will be quantified. Further, 45% of the total length in each direction will
be marked and corresponding area will be coated with reflective screen. Then from 45 to 85%
length of total will be marked for glossy white surface. The glossy white surface will be screened
with white paint first followed by glossy paint above the same. Further, from 85 to end of the
roof will be screened with black colour paint. This is how the screening process is distributed in
the entire rooftop area.
Following table 2 shows the distribution of screening process as per length of the roof.
Screening Thickness
-8Op
White Paint: -1 60p
Glossy: -60p
-120~
Screening process
-
Reflective Screen
Glossy White
Black Paint
Figure 7 shows the example view of several of types of roof shape (a) circular, (b) rectangular,
and (c) arbitrary, and the process to screen the same. The deployment process is tested on
multiple types of roof thus to validate the proposed process. Further, it is to be noted that to ease
the applicat~on process the screening thickness can be varied in the range of %lop, which would
not affect the performance. During the process of investigation it is found that the screening
thickness for a single round of screening varies in the range of 25 to 35p. Thus, to get a
screening thickness of Sop, three layers of screening will be adequate. Similar fashion rest of the
area can be screened.
Additionally, some of the measures that has to be kept in mind are: (i) the roof should be
properly cleaned, (ii) there should not be much undulations on the roof, (iii) it has to be ensured
that there will not be any water blockage on the roof, and (iv) any cracks or facture need to be
foiled with adequate filler material before applying the invented roof screening process. Present
roof screening process is simplified through series of investigations such that any person can use
the same for his application.
% length in each direction
0 - 45%
45 - 85%
85% - 100 (End)
E. Comparison between Invented vs. Existing Screening Processes:
A comparative discussion between the developed screening process and conventional process is
reported in this section. The results are presented by using plots, bar charts, tabular columns and
pictorial views.
(i) Data Reduction: The data from experiment are calculated in comparative form and presented
in the report.
i, TdiJimncc = ( ~ i i-, ~ Tni in )otni
ii) T i s e- top =. Tmif-top - Tnin ,otni
".' .) . Tri,ve-hottoni -- Tmoj-hottonr - T nin ,ornr
Each of the above surface temperature is the area weighted average of the concerned surface.
(ii) Roofiop temperature: The rooftop gets directly heated up by the sun ray. Figure 8 shows the
variation of rooftop average temperature for varying Tdiftfe mperature of air above the roof or the
atmospheric temperature in present context. At higher level of atmospheric temperature, i.e. TdiE
= 25"/20°C (when atmospheric temperature goes 25"/20°C above minimum/normal lab
temperature) the rooftop temperature for each of the screening process give rise to different level
of rooftop temperature. For this case, black color screened roof exhibits maximum rise in rooftop
temperature, T,is,-top= 57.5147OC above minimum temperature. This is because of high heat
absorptivity and low heat reflectivity property. Concrete rooftop surface temperature follows
black color screen and gives rise to Trise.to=p 52/40.5OC. Trailed by both, lime stone and white
portland cement reduces the rooftop temperature by 5/3"C as compared to concrete roof. White
portland cement is followed by aluminum, white paint, glossy white, invented process and
reflective coat. Aluminum although has a high reflectivity value yet it absorbs considerable
amount of heat. Similarly, white color paint although has less absorptivity does not reflect much
Ileal, Ile~~cie~ lc~easeLslle ~uuflupl er~~pe~.aluup~ ~tut :3 8132°C. The glossy surPdce offers berter
temperature level than white and aluminum paint as it has high reflectivity and low absorptivity
that does not allow the roof to get heated up. Reflective screening process, which has highest
solar reflective index rejects maximum amount of solar heat and rooftop temperature goes up to
31/26"C for TdiK = 25"/20°C. The invented screening process, which follows the hybrid heat
transfer technique, performs almost similar to reflective screening process and offers marginally
higher temperature than the reflective screen.
Temperature various because of the screening process remains almost the same for T d i=~ 1 5°C
as seen in case of Tdim= 25"/20°C. Whereas, at lower level of atmospheric temperature, Tdim=
10/5"C the performance remains the same for all screening process excepting the invented
process. The developed screening process actually absorbs heat and increases the rooftop
temperature. For, TdiF= 5OC, where it is intended to rise the room temperature black color paint
offers maximum rise in rooftop temperature followed by invented screening process and concrete
roof. Thus, the developed screening process offers favorable roof temperature in all seasons
unlike other screening techniques.
(iii) Roof bottom temperature: Figure 9 shows the variation of roof bottom surface temperature
for all considered roof screening techniques. The roof bottom temperature is mostly dependent
upon the rooftop temperature. The heat from the concrete rooftop surface basically diffuses to
the roof bottom surface through the concrete roof. The heat transfer from rooftop surface to roof
bottom surface is purely by conductive heat transfer. Thermal conductivity for concrete used as
building product is around 2 WImK, thus substantial reduction in temperature value reduces
across the concrete roof. The concrete roof offers similar resistance for all the cases studied.
Thus the temperature variation pattern observed on the rooftop surface against varying roof
screening remains same on the roof bottom surface. Hence, it is understood that the invented
screening process offers desired temperature value irrespective of any season contrasting other
screening techniques.
(iv) Room Temperature: Downstream of the roof-bottom surface, as per present model, the room
gets heated up mainly in natural convection mode by the roof bottom surface. Therefore, the
sequence in which roof bottom surface varies with respect to TdlRfo r different types of roof
screening techniques, the room temperature also varies in similar fashion. Figure 10 shows the
drop in room temperature with respect to atmosphere with varying Tdlff.I t is observed that the
reflective screened roof offers maximum reduction in room temperature at any level of TdlffS. till,
in lower level of TdlR = 10 and 5"C, the room temperature is reduced up to 10.5 and 7°C
respectively, which is below atmospheric temperature. The behavior is repeated with glossy
surface, aluminum, white paint, white Portland cement in descending temperature drop order.
Lime stone and concrete offers better comfort level at lower Tdlff = 10 and 5°C level by
increasing room temperature. However, Tdropa t higher Tdlfifs poor. Black color screened surface
offers least drop in room temperature w.r.t. atmosphere at any level of Tdlff. The developed
screening process offers comfortable room condition at any level of temperature in the
atmosphere. When the atmospheric temperature is high, i.e. Tdlff= 25, 20 and 15"C, the room
temperature is dropped by 18, 17 and 14°C. Similarly, when the atmospheric temperature is low,
i.e. Tdlff= 10 and 5"C, the drop in room temperature w.r.t. atmosphere is around 7 and 3S°C,
respectively. Thus generates energy saving potential round the year.
(v) Room Temperature after Sun Set: The stored heat in the concrete roof plays an important role
in heating the room after sunset or switching off the lighting section in the experiment. The heat
absorptivity property of the screening technique basically monitors the heat absorption and
rejection rate. From, the tested techniques, black, aluminum, glossy white and reflective screen
rejects heat at a faster rate. Meanwhile, white Portland cement and white color paint rejects heat
at a very slower rate. Therefore, a comparative study was carried out among; roof without
screening (concrete), white Portland cement, white color paint and developed screening process.
In this process, temperature is noted at the time of switching of the lighting system and one hour
after the same.
Figure 11 shows that the rooftop. temperature reduces quickly for all screening processes, as it is
exposed to atmosphere. At all Tdlu conditions, white painted roof rejects heat at least rate. This
indicates that roof screening that has low absorptivity resists heat transform from room to
atmosphere. This. is followed by white Portland cement, developed screening process and
concrete roof. On the other hand, the bottom surface of the roof behaves in an entirely different
manner as compared to rooftop surface; because this surface does not come directly in contact
with the atmosphere, refer Fig. 12. Concrete and developed screening process shows similar
level of temperature reduction, in the range of 0.5 to 1.5OC. For, white Portland cement the roof
bottom surface temperature remains almost un-altered. In case of white color paint, the roof
bottom surface either remains same or increases maximum up to I0C. This rise is may be
because of the gradient across the roof width, where rooftop temperature is much higher as
compared to the roof bottom surface. The room temperature varies in similar fashion as roof
bottom, shown in Fig. 13. Where, white color painted house temperature increases by around
0.20°C after sunset. However, all other cases room temperature reduces in the range of 0 to
0.25"C.
(vi) Durability: The performance of roof screening also reduces with increase in time span. With
the purpose of finding out the exact durability, all the screening processes are field tested. The
field testing even covers rainy season, yet without water blockage. Among all screening methods
considered, lime stone showed least durability performance, Fig. 14 shows the cracked screening
layer with porous formation on the screened surface. The screening showed cracks in less than a
time span of forty days. This is followed by, white color paint, aluminum and white Portland
cement, where cracks are formed on the surface before six months after screening. The glossy
surface and black color surface did not show any cracks till ten months, yet their performance
level slightly reduces. The reflective screen performed well up to fourteen months. Similarly, the
developed screening process is tested up to fourteen months and no issues noticed with the
screened roof. In addition, the drop in performance is also very minor.
(vii) Effect of Screening Thickness: Screening thickness is directly proportional to expenditure
and heat insulation. The optimum screening thickness is evolved by set of multiple set of
experiments. It is observed that for any kind of roof screening, the screening effect is minimal
below Sop, and above 240p there is no effect of increasing roof screening thickness. Keeping all
above facts in mind, the optimum screening thickness is decided which corresponds to the
maximum energy saving potential round the year. Table 1 shows the screening and
corresponding optimum screening thickness. It is observed that for aluminum, black and lime
stone, the effect remains same beyond Sop.
Table 1 Optimum screening thickness
Screening Lime White White Reflective Aluminium Black Glossy White
Technique Stone Portland paint Screen Surface
Cement
Optimum 80p 240p 160p 160p SOP SOP Glossy-60p,
Thickness White-1 60p
(viii) Effect of Dust Settlement: Present screening process is developed mainly for Indian
environment, where pollution is a major issue. Thus, the performances of all the screening
techniques were compared against dust settlement over a period of one month, shown in Fig. 15.
Screening performance is normalized against the maximum reduction in roof temperature. In the
beginning of the month, the rooftop temperature is reduction is highest for all the screening
techniques. With increasekin time span, dust settlement on the roof surface also increases and inturn
performance diminishes. The performance against dust settlement on rooftop temperature is
compared in every lodays interval. Figure 15 exhibits that the performance of concrete roof,
black paint white Portland cement, glossy white and developed screening process remains almost
the same with time span. On the other hand, for white color, aluminum and reflective screen the
performance against dust settlement diminishes rapidly.
(ix) ~eflectionE ffect on nearby buildings: Due to high reflectivity property'of the screen, nearby
buildings temperature increases and also the reflected UV/IR rays causes un-comfort. In this
regards, during field testing temperature variation in nearby buildings and feedback from
occupants are noted. It is observed that for black, lime stone, white Portland cement and white
paint there was no effect. Marginal glazing effect is noted for aluminum paint. For, reflective
coat the temperature and un-comfort is highest. Although, the invented screening process partly
includes reflective coat, yet it causes no problem on nearby buildings.
(x) Expenditure against Screening Deployment: Cost of the screening and associated labor
charge is obtained during field testing study. Table 3 shows the expenditure for various types of
screens at its optimum thickness condition. Tabulated value shows that aluminum is the costliest
screening method and lime stone is the cheapest process; while, invented screening process
stands at fourth level from top.
Table 3: Expenditure for various type of coat at optimum thickness
Screening
Type
Price per
ft2
Black
7.58
White
Portland
Cement
5.17
(xi) Energy Eficiency potential: The energy efficiency potential is the main objective of present
investigation. The cumulative energy efficiency value for all seasons is normalized against
without screening, i.e: concrete roof. It is seen that black color screening gives rise to higher
level of energy usage than concrete roof. Lime stone and white Portland cement consumes
almost similar energy as in case of concrete. White color and aluminum paint has similar impact
on annual energy saving, in the ordw of 85%. Progressed by, glossy white and reflective screen
those saves energy up to 21%. The developed screening process gives rise to energy saving
potential of up to 38% as compared to concrete roof, refer Table 4.
Table 4: Energy efficiency potential round the year w.r.t. concrete
Glossy
White
9.07
Lime
Stone
3.23
White
Paint
8.90
Aluminium
(All
17.43
Al
84
Screening
Type
%
variation
in annual
energy
usage
Reflective
Screen
15.96
Glossy
White
79
Reflective
Screen
79
Concrete
100
White
Portland
Cement
93
I
Invented
Process
9.58
Invented
Process
62
White
Paint
8 5
Black
107
Lime
Stone
95
(xii) Overall Performance: In order to finalize the screening process that would fulfill all the
requirements, a performance table 5 with weightage level is constructed. The required features
are as follows;
(i) Drop in room temperature during summer
(ii) Increase in room temperature during winter
(iii) Maximum durability
(iv) Low reflectivity effect on nearby buildings
(v) Low absorptivity
(vi) Less susceptible to dust settlement
(vii) Low cost' for deployment
(viii) Maximum energy saving potential round the year
Each of the screening technique's performance is shown in Table 4, color code. It is to be noted
that the color codes are quantified during optimization study, which is discussed in earlier
paragraphs. From tabulated remarks, it is finalized that the developed screening process meets
most of the above listed requirements.
Table 5: Performance table
*Weightage vs. Colour Code
Medium I I I I I Good I ( I I I Excellent 1 I

- ..-,-.. ,- - -
5. CLAIMS v
1. Nrc claim that the E~~crgEyf ficient All Season Roof Screening process is d i ~ ~ l ~ p ~ d
dedicatedly for concrete roof, which is flat in nature. In case of inclined roof the process of
deployment may alter.
2. We claim that the Energy Efficient All Season Roof Screening process requires least
maintenance and will perform against dust settlement, however in case of complete dust
coverage the performance may diminish.
3. We claim that in case of water blockage, crack formation, snow coverage and other similar
situation the Energy Efficient All Season Roof Screening process's performance will affect.
4. We claim that the Energy Efficient All Season Roof Screening process is cost effective
economical, and reduces heat island effect.
5. We claim that the Energy Efficient All Season Roof Screening process can be implemented in
any parts of Indian environment.
6. DATE AND SIGNATURE
Date: 2 -O) -mc
s ignamm ($6
Names . Indusekhar Jha
Date: %- & F%f)lC
Signature: -
Names : Dr. Subir Sen
Date: %-M -1'
Signature: &?-
Names : Mr. Hemendra Agarwal
Date: $8 -01 -31
signature: 9~ h
Names : Dr. Rajesh Kumar Panda