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Thermal insulation system for energy efficient green buildings in tropical countries.

INTRODUCTION

Insulation system comprise of material, ancillaries and finishing substance over the building envelope. The building envelope is insulated to stop flow of heat & cold from environment. Thermal Insulation system when applied on roof and walls, creates a thermal barrier and offers resistance to the flow of heat and cold. There are specific advantages of applying insulation on the external side of roof and wall as compared to application from inside of building, typically in a tropical country like India. Since tropical countries face extremes of ambient temperatures and monsoons. The importance of proper finishing on external side over insulation is an important design aspect. There are provisions of various architectural finish options.

All these finishing items coming in contact with insulation needs to be properly selected so that they are compatible and long lasting in extreme tropical climatic conditions like India. Hence thermal insulation is defined as a total system whereby it has to be compatible with the various ancillary materials used for holding the material as well as finishing items.

Need for Thermal Insulation in Buildings

Building envelope transmit 80% of Heat & Cold into the inside of the buildings. When insulation is applied on the external side of roof and wall the heat energy coming from the environment during summer will get stopped by the insulation from heating up the Reinforced Cement Concrete roof and Brick wall. The insulation will totally keep out the heat. Similarly in the case of insulation application from inside, the Reinforced Cement Concrete roof and wall will first get heated and thereafter its transfer will be stopped by providing the insulation inside. Thus insulation either way will act towards creating a comfortable atmosphere inside the building. Usually if the roof is cool then air circulated by moving ceiling fan will also be cold, even when the building is not air conditioned. This will be an unique feature & benefit in Residential houses. The temperature inside will be maintained for a long time because heat ingress will be reduced to a great extent. The inside temperature will rise only by opening of doors and windows. In the case of an air conditioner is running, once the set temperature is achieved, the compressor running time will also get reduced. If the building is not insulated then continuously heat will be coming inside and the compressor running time will increase. Long compressor running time will mean more electricity consumption. So we are talking of electricity and energy savings.

Similarly during winter, the cold temperature which remains at the ground level will get transmitted very fast, if the walls are not insulated. During winter when heaters are used, if the walls are insulated, it will reduce the heat loss due to conduction through the walls to outer cold environment. This is the reason why in cold countries the walls are quite thick with insulation.

Presently when we talk of multi storied flats, Reinforced Cement Concrete framing is done and very thin walls are created. These thin walls allow a large amount of heat transmission during peak summer. The inside comfort level is very very low with high heat conduction inside. There is always a necessity to stop the heat conduction through the walls and create comfort inside.

Now a days most of the buildings have black body waterproofing and tiling finish on the roof. These are good conductors of heat which make the Reinforced Cement Concrete roof very hot. Summer situation in India is prevalent from April to September, hence heat conduction from roof is a major issue.

Buildings consume 40-60% of electricity produced and building envelope contributes to 70% of heat & cold transmission. So any attempt to reduce heat & cold transmission through building envelope will impose energy savings.

So we say thermal insulation is becoming a necessity to stop the heat ingress during summer for the purpose of creating human comfort and also saving energy. Both human comfort and energy conservation has become a prime importance.

Thermal Insulation System Design

Thermal insulation System Design starts with selection of Thermal Resistance 'R' value of roof and walls. Optimum 'R' value is to be considered. Optimum 'R' value is the thermal resistance that minimize total cost of electricity consumption and insulation cost while maintaining thermal comfort. R-value is related to local climatic conditions. 'R' determines the extent or thickness of insulation, which is based on mathematical calculations concerning the Thermal Conductivity 'K' of insulation material. Selection of optimum thickness is essential. Optimum thickness is the thickness that gives minimum total cost. Total cost comprises of cost of insulation material, cost of installation, plus present worth of electric energy consumption cost. Cost of insulation increases linearly (Lins) with insulation thickness. Cost of electricity consumption decreases with insulation thickness (decrease is fast at small Lins and becomes more gradual at large Lins). Thermal mass (density) of insulation is important for energy savings. So use of critical mass of insulation is important. Design also covers best location of insulation in building envelope. It is further important to draft the application specifications in a way to eliminate or minimize thermal bridges in insulated walls.

Further Energy Conservation Building Code of India (ECBC 2007) provides optimum 'R' values of roof & wall of buildings based on usage characteristics and takes into consideration local climatic conditions. The country is divided into 5 climatic zones. It also lists separately insulation density and 'K' value of different materials suitable in India.

How to determine optimum insulation thickness

It is based on detailed analysis of insulation material properties vis-a-vis the local climatic conditions and the application area viz roof or wall configuration. Due reference is taken from ECBC (Energy Conservation Building Code) to determine the thickness. ECBC provides 'R' values for building type (Roof & Wall) and climatic zone. By utilizing R = L/K (L is thickness and K is thermal conductivity of insulation product), insulation thickness can be calculated. So we have a basis and mathematical formula for calculating the insulation thickness.

Now we briefly mention about the various methods to apply insulation in a building.

Roof Insulation

The roof can be insulated by doing an underdeck insulation or overdeck insulation. In the case of underdeck insulation of Reinforced Cement Concrete buildings GI channels are installed from inside on the roof and fibrous insulation material like Bonded Mineralwool of density 48 kg/m3 or 2.99 lb/ft.3 wrapped either in Polythene sheet or with aluminium foil lamination, is placed between the GI channels and held in position with criss cross GI wire. Finally Gypsum or Cement Fibre Board is fixed to the GI channels. This way the insulation become sandwich between the finishing Board and Reinforced Cement Concrete ceiling. The heat coming from outside will get stopped. The insulation material should be non combustible as per BS:476 Part-4 (British Standard : 476--Non combustible Test for Mineralwool Insulation) because it is applied inside and also should be of Water Repellant grade so that any moisture entrapped by condensation inside do not create problems in future. In this case, the limitation is no mechanical abuse can be allowed on the Gypsum or Cement Fibre Board. Another method of underdeck insulation is using Rigid insulation materials with aluminium foil lamination in density of 32 kg/m3 or 1.99 lb/ft.3 which can be directly fastened using GI washers on to the Reinforced Cement Concrete. This system is suitable wherever false ceiling is there. Rigid foam is also fire safe and has Class O fire rating as per BS:476 Part-6 for Fire Propagation test.

Similarly for metal sheet roofing of Pre Engineered Building (PEB) or residential houses in hilly areas with metal profile sheet roofing, underdeck insulation is very common using an expanded metal mesh fixed to mild steel cleats welded to the steel structure. Fibrous insulation of density 48 64 kg/m3 or 2.99 - 3.99 lb/ft.3 with aluminium foil lamination and thickness ranging from 75mm to 100mm or 2.95 inch to 3.93 inch is placed over the metal mesh and then the metal profile sheet fixed on top. Here the insulation plays the role of stopping heat and cold and at the same time acoustical noise protection from rain water drops. An extra density allows enhanced acoustical properties fulfillment.

Overdeck Roof Insulation

Overdeck insulation is a method whereby thermal insulation material is fixed directly over the Reinforced Cement Concrete slabs followed by waterproofing and final finish. One method commonly followed in India is using Rigid Foam slabs of density 36 kg/m3 or 2.24 lb/ft.3 and thickness ranging from 50mm to 75mm or 1.96 inch to 2.95 inch fixed with cold adhesive on the Reinforced Cement Concrete slabs. The entire Reinforced Cement Concrete will be covered with Foam slabs and then plaster will be applied followed with waterproofing and finishing arrangement. This is the most common method for insulating small sized roofs. But there is another method whereby Polyurethane Foam Insulation ingredient chemicals can be sprayed over the Reinforced Cement Concrete roof surface irrespective of the area. The chemicals sprayed through special guns instantly react and foam up to form a homogenous jointless cover over the entire roof. So it is like creating a secondary Reinforced Cement Concrete layer without any joints. This foam spray is CFC-HCFC free and can be sprayed over the roof area at the coverage rate of 300 square meters / 465000.93 square inches to 400 square meters / 620001.24 square inches. per day. The spray covers the entire roof sealing all cracks and is carried on to the parapet slightly. This sprayed foam is close cell and there is negligible water absorption. The density of Foam is 42 to 45 kg/m3 or 2.62 to 2.80 lb/ft.3 which ensure foot traffic load resistance. Subsequently cement screeding arrangement is provided followed by waterproofing and finishing item. Spray foam is the latest technology for roof insulation in India where the Reinforced Cement Concrete is totally covered and not exposed to environment hazards. Large roofs can be covered very fast. Overdeck insulation does not interfere with internal activities and stops the heat right at the source. One of the critical factor to selection of good foam product is the temperature rating which in any case should be in the range of minimum 65 to 70 deg.C / 149 to 158 deg.F, so as to withstand the temperature built up of min. 65 deg.C of the typical finishing treatments on top.

Wall Insulation

Wall insulation is very important during summer when the walls get tremendously heated up in the afternoon. Similarly during cold conditions the cold waves pass through the solid walls through conduction. There are various methods to carry out wall insulation. In the case of internal application galvanized Iron channel frame work is fixed on to the walls creating cavities and non-combustible Water Repellant Grade Mineralwool insulation slabs with aluminium foil lamination are placed into the cavities and then covered with Gypsum or Cement Fibre Boards. In the case of external application depending upon the type of finish the specifications are drafted. Suppose it is of double wall specifications, after the main load bearing wall is erected, insulation covered with Polythene sheet from all sides is fixed externally with fasteners and then the second wall is constructed (cavity insulation). The density recommended is 96 kg/m3 or 5.98 lb/ft.3. There are buildings where stone cladding is used, in such case after the steel frame work for holding the stone is erected, insulation encased in polythene will be fixed with fasteners in between the holding clips. The same is also followed for aluminium cladding when insulation is placed between the holding frame work. For such cavity wall insulation, fibrous mineralwool insulation materials are used of higher grade densities eg. 48-64 kg/m3 or 2.99 - 3.99 lb/ft.3 to take advantage of extreme Rigidity and antisag properties.

Wall Insulation is also possible with fire safe Rigid slab which can be mechanically fastened to the walls. Rigid foam spray is also feasible on walls.

The most versatile method now a days recommended is applying Rigid foam slab from outside and then finishing with plaster. In this procedure Rigid close cell CFC-HCFC free Foam slabs in density of 36 kg/m3 or 2.24 lb/ft.3 and thickness ranging from 50mm to 65mm or 1.96 inch. to 2.55 inch. is fixed with a special polymerized water based adhesive directly to the plastered walls. The adhesive dries up in 2 hrs time. Thereafter, polymerized plaster in 2 layers of total thickness 6mm or 0.23 inch. with a synthetic reinforcement is applied directly on to the foam slab. In this way the entire wall is insulated and plastered from outside. Subsequently various architecture finish can be provided with POP. Another method is creating a cavity and pouring pre-mixed polyurethane chemicals, which foams & dries instantly and fills the gap creating a homogenous virtual wall of insulation.

By external insulation on wall the base wall never get exposed to the atmosphere and the heat and cold is stopped at the source.

It is very essential that the temperature range of the insulation material should be higher (more than 75 deg.C / 167 deg.F) to ensure that it remains in position for a long time and it does not get detached from the wall, neither the plaster on top gets detached. The finishing component (plaster, tile) usually touches a temperature of 15 to 20 deg.C / 59 to 68 deg.F) above the ambient temperature during summer. There are materials which are good for insulation but the temp. rating is lower (65 to 80 deg.C / 149 to 176 deg.F), shows signs of getting detached from the wall during the peak summer when ambient is around 45 deg. C/113 deg.F Materials with lower temperature rating gets detached from wall and also the finishing components over it creating water leakages during monsoon. LEED & GRIHA are standards followed locally in India to provide Green Rating to a building. There are two certifying bodies viz Indian Green Building Congress (IGBC), which provides LEED Certification and The Energy and Resources Institute (TERI) of India provides GRIHA Certification. Both these bodies provide Green Certification points for insulation under the following category viz--

For GRIHA

Under Criterion 14--Optimize Energy Performance of Building within the specified comfort limit Under Criterion 27--Minimizing Ozone Depleting Substances Under Criterion 29 for Fibrous insulation only--Acceptable Outdoor & Indoor Noise Level.

Under LEED / IGBC--Thermal insulation of building is covered under Energy Efficiency Credits improving overall Energy Performance of the building through effective / efficient building envelope.

User guide published by USAID India on Energy Conservation Building Code also advocates use of building envelope to reduce heat losses and increase thermal resistance through proper roof & wall insulation.

The concept of roof and wall insulation has become a necessity with the unpredictable environmental conditions in a tropical country whereby we find high ambient conditions during summer and very low temperatures during winters. The high summer conditions will definitely have the impact on human comfort with insulated buildings. Similarly during winter days when sun does not shine properly the comfort of warmth is experienced and retained inside the insulated building. The concept of insulation in a building is a necessity rather a luxury investment. In terms of investment the cost may go up by only 2-3% and the payback period in terms of energy conservation or by way of electricity savings, falls within 3-4 years.

PREFAB PANELS

Another versatile building construction material presently used in Steel Building construction is prefabricated insulated panels. These panels comprise of colour coated steel sheet facing on both sides with core of Rigid or Fibrous insulation materials. Now a days buildings are constructed with Steel--Pre Engineered Building Technology a latest concept in building construction. The entire steel components are fabricated at the factory and sent to site in smaller components. For such Steel framed buildings prefab panels are used for roofing & wall paneling. Such steel buildings can be multi storied and used for construction of Office buildings, Malls, Residential houses, Schools etc. The panels provide an absolutely aesthetic pleasing look. These buildings are highly energy efficient. These panels are ideal for construction of barracks used by Defence, School, Site Offices using Steel Structure. These panels are fitted with camlocks which holds to each other and become self balanced. The panels are thus self standing & light weight. Some of these panels quality have Factory Mutual (FM) laboratory approval to cater for windage & fire safety factors. These panels can be erected very fast and do not require much labour. The panels are energy efficient and comply to LEED India and GRIHA Green specifications. The thickness varies from 50mm to 80mm or 1.96 inch to 3.14 inch suitable for building construction.

Such steel buildings with panel roofing can be ideally fitted with Solar Panels on roof. Individual house modules can be built equipped with Solar Panels to generate self sufficiency energy and titled as Net Zero Building.

CONCLUSION

Thermal insulation is an important provision to stop heat / cold in leak to buildings and if judiciously selected and applied can result into lots of energy & capital savings. Thermal insulation needs to be decided during design of a building and not after installation, to derive the maximum benefits.

REFERENCES

Photographs have been taken from our Project sites in India at IREO-Gurgaon; Escorts Farmtrac-Faridabad; Prism-Gurgaon; LANCO- Korba; Parliament Annexe Building-New Delhi; Bharti Mall-Ludhiana and 3C Net Zero Building.

K.K. Mitra is a professional working with Lloyd Insulations (India) Limited, a leading Thermal Insulation Construction Company, Delhi, India President, Ashrae India

Caption: Figure 1, 2 : Underdeck Reinforced Cement Concrete Insulation

Caption: Figure 3 : Steel Roof Building Insulation

Caption: Figure 4 : Roof Overdeck Insulation with Rigid Foam Slab

Caption: Figure 5 : Roof Overdeck Insulation with Foam Spray System

Caption: Figure 6 : Double Brick Wall Cavity Insulation

Caption: Figure 7 : Cavity Wall Insulation with Aluminium / Stone Finish

Caption: Figure 8 : Double Brick Wall Insulation

Caption: Figure 9 : External Wall Insulation with Close Cell CFC-HCFC Free Rigid Foam Slab Insulation

Caption: Figure 10 (a) : External Wall Insulation with Polyurethane Chemicals--poured in situ

Caption: Figure 10 (b) : External Wall Insulation with Rigid Foam Slab Insulation

Caption: Figure 11 : Pre-fabPanel Buildings
Table 1. Typical R&U values for Fibrous Insulation also being used
for LEED & GRIHA Green points rating

Thickness                  R-Value                  U-Value

(mm)   (Inch)   (m2-Deg.C/W)   (Ft.2Hr.Deg.    W/m2-    (Btu-in/ft.
                                F/Btu-in)      deg.C    2Flr.Deg.F)

50      1.96        1.72           9.79        0.580       0.102
65      2.55        2.24          12.73        0.446       0.079
75      2.95        2.59          14.69        0.387       0.068
120     4.72        4.14          23.50        0.242       0.043

Table 2. Typical R&U values for Closed Cell CFC-HCFC free Rigid Foam
Insulation also being used for LEED & GRIHA Green points rating

Thickness                  R-Value                  U-Value

(mm)   (Inch)   (m2-Deg.C/W)   (Ft.2Flr.Deg.   W/m2-    (Btu-in/ft.
                                 F/Btu-in)     deg.C    2Flr.Deg.F)

50      1.96        1.43           8.11        0.700       0.123
65      2.55        2.38           13.52       0.420       0.074
75      2.95        3.10           17.58       0.323       0.057
120     4.72        3.57           20.28       0.280       0.049
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Author:Mitra, Krishna Kumar
Publication:ASHRAE Transactions
Date:Jan 1, 2017
Words:3231
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