THERMAL INSULATION OF ENERGY EFFICIENT BUILDINGS

Abstract:
Thermal insulation is the easiest and most effective energy efficient technologies available today. Thermal
insulating materials commonly used are flexible (mineral wool, glass fibre), loose fill, and spray. Using these
materials insulation techniques like stud walls with standard sheathing and cladding, stud walls with exterior
thermal sheathing and foundations like concrete foundation with exterior insulation, permanent wood foundation
renders good amount of efficient thermal insulation. But with the use of GRP, ACC and some insulating paints
thermal insulation can be increased to an optimum level. This paper includes the case study of residential
complex at Thatipur, Gwalior in which composite technique has been introduced.
1. Introduction
Over the past 30 years, rising power costs and energy conservation concerns have prompted the building industry
to improve the efficiency of newly built constructions. Since each site has its own unique climatic and
topographic characteristics, a considerate response to the site limitations which utilize the natural resources and
integrate them into the design will bring about an energy efficient building. The main goal of energy conscious
designer is to condition the interior environment to support a level of climate comfort acceptable to the users.
Efficient use of energy is important since global energy resources are finite and power generation using fossil
fuels (such as coal and oil) has adverse environmental effects.
Thermal insulation is a technique that minimizes the transfer of heat energy from inside to outside and viceversa,
of the building by reducing the conduction, convection and radiation effects. Insulation is the building
component which controls temperature directly, and indirectly affects the movement of moisture to and from
building spaces. Insulation in the building is maintained by thermal insulating material like flexible material,
loose fill and spray. Most common of these is Flexible. Insulating material used along with insulation technique
brings optimum insulation inside a building.
1.1 Review of Thermal Insulating Materials
The selection of thermal insulating materials depends up on their R & RSI values. Thermal resistance index
(RSI) is the resistance of an assembly to the transfer of heat and is given in units of m2•°C/W. The imperial
equivalent is R value expressed in units of ft2•h•°F/BTU. Insulation for the home has R-values usually in the
range of R-10 up to R-30. The following table shows R & RSI values of a few thermal insulating materials:
Table 1: RSI & R values of different insulating materials
Thickness Thermal Resistance
Sl. No.
Insulation Materials
mm inch
RSI
m2*°C/W
R
ft2*h*°F/BTU
low density 140 5-1/2 2.83 16
medium density 140 5-1/2 3.30 19
1.
Flexible
(mineral wool, glass
fibre) high density 140 5-1/2 3.93 22.5
glass fibre 100 4 2.00 11
mineral fibre 100 4 2.30 13
2.
Loose fill
cellulose fibre 100 4 2.50 12.5
polyurethane 100 4 4.1 23
isocyanurate 100 4 3.4 19
3.
Spray
cellulose fibre 100 4 2.4 13.5
Thermal Insulation of Energy Efficient Buildings 411
1.2 Review of Insulation Techniques
1.2.1 Stud Walls with Exterior Thermal Sheathing
The insulation of stud wall can be achieved by providing rigid or semi-rigid insulation panels that are nailed to
these walls using special nails with large plastic washers. In these types of wall, diagonal bracing is provided
which adds the rigidity to it (fig. 1).
1.2.2 Concrete Foundation with Exterior Insulation
Foundations wall enclosing heated space are insulated with rigid insulation boards made from polystyrene or
glass fiber installed vertically on the exterior of the wall. The above grade portion of the rigid insulation is
fastened to the sill plate or to the foundation wall with an adhesive. If the above grade portion is not covered by
the exterior cladding the exposed insulation is protected from mechanical damage with flashing and cement
parging on wire lath. Damp proofing is done before applying insulation.
Figure 1: Stud walls with exterior thermal sheathing Figure 2: Concrete foundation with exterior insulation
1.3 Insulation by Planning
In order to implement thermal insulation in the building, planning with proper orientation is essential. The
orientation should be such that it allows optimum amount of air and light to enter into the building. India
being a tropical country, efforts are directed to prevent entrance of excessive heat.
Following factors should be considered while planning a building:
• Total area covered by doors and windows should be as less as possible. Also they should be placed
according to seasonal wind direction.
• Use of sunshading devices (natural or artificial). The artificial sunshading devices like Louvers,
Overhangs, Screens proves to be effective.
• Longer outside walls should run in EW direction and shorter walls in NS direction.
• Provision of deep verandah in SW direction.
• Plantation of grass and shady trees around the building help in reducing the temperature of the building.
412 Advances in Energy Research (AER – 2006)
1.4 Review of Innovative Techniques
1.4.1 Autoclaved Aerated Concrete
AAC building blocks are manufactured conforming to IS 2185 having density
range of 551-600 kg/m³ and minimum compressive strength of 3N/mm². The
thermal insulating properties of these blocks is due to the closed air cell
structure and there increased level of thermal performance (K=0.16W/m deg.
K) leads to more comfortable living and efficient energy saving of air
conditioning.
1.4.2. Insulating Coatings
Thermal insulating coatings is a ceramic , insulating roof and exterior coating
which comprise of best in acrylic binder and ceramic/silica coating materials
which provide unequal resistance to adverse weather conditions and also
provide thermal insulation to the building. It attacks heat or cold penetration
before it enters the substrate. It has exceptional property of producing cross
linking structure which grows stronger over time thereby adhering and
bonding better to the substrate and also within itself providing it better
strength, longevity and flexibility.
1.4.3. Glass Reinforced Plastics (GRP)
GRP is a composite material or fiber reinforced plastic made of a plastic reinforced by the fine fibers made of
glass like graphite reinforced plastic. The applications of GRP in doors and windows are explained as follows:
1.4.3.1. GRP Windows
These are the new types of windows with narrower frames which give the
building a more elegant appearance and allow more light to enter the room.
The GRP material prevents thermal bridges and insulates so well that the Uvalue
of the total window structure is reduced to as low as 1.3 W/m2K which
is about 1.8 W/m2K in case of traditional windows. Moreover, windows can
not rot and require practically no maintenance and windows weigh 25% less
than traditional windows.
1.4.3.2. GRP Door Steps
Profiles of GRP prevent thermal bridges, reducing hest loss and condensation
problems. This simple solution can diminish heat loss by 20% or more, while
ensuring that residents are not exposed to the inconvenience of cold,
condensation and rot. The low, thin door step combines superior stiffness with
excellent thermal insulation properties. They are strong and durable solution.
2. Case Study
The site selected for the case study is located at Darpan Colony, Thatipur, Gwalior (M.P.) with Latitude-26°12'
N, Longitude- 76°18' E and Altitude-212 m above MSL. Following data shows the variation in various
environmental factors of the site:

2.1. Environmental Data
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Mean max.temp. 22 24 32.4 37.4 46 41.4 37.6 23.2 34.4 36.2 27 24
Mean min.temp. 3.2 10.9 15.8 18 25 29 28 26.4 22 16.3 14.2 8.5
Rainfall 20.8 23.6 12.9 9.7 67.6 186 169 14.2 2.0 8.6 2.0 8.6
Wind direction NW NW NW NW N N N NW NW NW NW NW
Thermal Insulation of Energy Efficient Buildings 413
2.2. Thermal Discomfort Index*
SEASON MONTH DISCOMFORT DURATION INDEX %
APRIL 21.5 1 21.5
HOT DRY MAY 23.5 1 23.5
JUNE 23.5 1 23.5
SEASONAL TOTAL 68.5 38
JULY 22.6 1 22.6
AUGUST 22.6 1 22.6
WARM HUMID SEPTEMBER 16.5 1 16.5
OCTOBER 18.1 1 18.1
SEASONAL TOTAL 73.0 34
DECEMBER -15.6 1 15.6
COLD DRY JANUARY -14.1 1 14.1
FEBRUARY -14.6 1 14.6
SEASONAL TOTAL 49.3 28
ANNUAL TOTAL 100
* Data used here are collected from M.P. Housing board (Gwalior)
• This table for thermal discomfort explains that hot season is much more important for thermal design than
cold season. Thus for thermal comfort techniques of insulation should be adopted.
• In the last twenty years there is an increase of 2°C in Gwalior and the summer duration is expanding. Thus
this increasing thermal discomfort should be cured so that occupants can enjoy the next coming years.
• Following figure shows the plan of the residential complex, which was built in yr 1992 by M.P. Housing
Board. In this case study we are estimating the approximate cost for thermal insulation of a single house of
this complex.
Figure 4: Plan of M.P. Housing Board residential complex
414 Advances in Energy Research (AER – 2006)
Figure 5.1: Ground floor plan Figure 5.2: First floor plan
Figure 5: Plan of single house
Table 2: Dimensions of different components of the house
GROUND FLOOR FIRST FLOOR
Verandah 2.8 x 1.5 Verandah 2.8 x 1.5
Drawing Room 3.1 x 3.9 Bed Room-I 3.1 x 3.9
Dining Room 3.7 x 2.5 Bedroom -Ii 3.7 x 2.5
Kitchen 3.0 x 2.4 Kitchen 3.0 x 2.4
Garage 3.1 x 4.5 Balcony 3.1 x 4.5
Toilet 2.0 x 1.5 Toilet 2.0 x 1.5
Wind Opening 1.2 x 1.0 Duct 1.2 x 1.0
(All dimensions in meter)
2.3. Observations: After studying all these, we suggest the following economic techniques for our site:
2.3.1. Insulation for Roof
• Average hours of solar radiations – 8.2 hours (9.7 hours/day in May, 6.4 hours/day in August).
• About 50-65% heat is transferred inside through roof, hence insulation of roof is essential.
• Figure 6 shows our suggestion, where we are using thermocol (1.5”), plywood (6mm), J-hooks, washers and
bolts. The bottom of the bolts should be covered with caps to give aesthetic view. This is a durable solution as
compared to the thermocol placed over the roof.
• Height of the topmost slab should be at least 3.10m
2.3.2. Insulation for Walls
• The walls directly exposed to sun radiations should be insulated by maintaining air gap.
• Cavity wall free from load should be constructed in front of the pre-existing wall. This technique is useful in
case of ground floor, because it may increase the load of the structures above the ground floor.
• ACC can be used (In case if they are economic).
• Honey comb the wall structure.
Figure 6: Iinsulation for roof Figure 7: Insulation for walls Figure 8: Insulation for windows
Thermal Insulation of Energy Efficient Buildings 415
2.3.3. Insulation for Windows & Door Steps
• GRP should be used (In case if they are economic).
• Provision of buffer zone at entry.
• Plantation on south and west sides.
• Provision of double glass window
• Proper overhang length of sunshade should be provided.
• Proper projection on south, east and west side.
• Construction of air tight door windows and ventilators by using rubber gaskets.
2.4. Estimation
S. No. Building component Area (m²) Material Details
Material Price/m² Cost
(Rs.)
Roof ( 1st Floor only)
Bed Room I 12.09
Bed Room II 9.25
Thermocol (1.5”
thick)
5
Kitchen 7.2
Verandah -
plywood
(6mmthick)
18
Balcony -
Staircase -
1.
Toilet 3
J-hooks
Washers,
bolts & caps
6 x 20
4510
Exterior walls Length in
running
meter
Ht.
Rear wall 11.1 3.1 34.41 x 2
Front wall
(verandah)
3 3.1 9.3 x 2
2.
*Deduction For Doors& windows 6.84 x 2
Cavity wall with
reinforcement in
cement mortar (1:4)
250
18435
3. Fully glazed Z- section window 10 x 1.8 - 950 17100
4. Flush doors 35 mm thick with all
necessary fittings
4 x(2 x
2.14)
- 900 15408
5. Synthetic enameled paint with putty
and priming
4 x 8.56 - 70 2400
Total 57853
Work Charge expenses (2%) 1157
GRAND TOTAL 59010
3. Conclusion
Thermal insulation is one of the important aspects which should be considered for the energy efficient building.
From the past 20 years data it is found that the temperature is increasing and thus thermal insulation is an
immediate need to be considered for occupant comfort. These days many techniques are being adopted for the
same. In this paper we have tried to emphasize on one of such technique by using the thermal insulating material
thermocol at the lower end of the roof along with plywood, bolts that are covered with caps to give your ceiling
an aesthetic look. The technique mentioned hereby is very economic, reliable and durable.
Reference
1. D B Mundra, Paper on AAC Building for Thermal Blocks for Reducing Air Conditioning Load in Buildings.
2. S. C. Rangwala, Building Construction, P-573 to 579
3. S. P. Bindra & Arora, Building Construction, P-801 to 814
4. Office: M.P. Housing Board, Sanjay Complex, Gwalior
5. www.mascotsingapore.com
6. www.cwc.com
7. www.fibreline.com