WINDOWS AND THERMAL INSULATION

HUYS ADVIES

WINDOWS AND THERMAL INSULATION Technical Working Paper ~ Number 8 Himalayas, Pakistan, Afghanistan and Tajikistan GBAO

Report by: Sjoerd Nienhuys Renewable Energy Advisor www.nienhuys.info Date: April 2012

TABLE OF CONTENTS INTRODUCTION ............................................................................................................................................ 1 1. EXISTING WINDOWS ......................................................................................................................... 2 1.1 1.2 1.3 1.4 1.5

The Glass Window is the Coldest Area ................................................................................................3 Inside Condensation...................................................................................................................................4 Outside Drainage .........................................................................................................................................5 Paint Maintenance .......................................................................................................................................6 Dimensions of Glass Windows ................................................................................................................7

2. SOLAR WINDOWS................................................................................................................................. 8 3. INSULATION VALUES OF WINDOWS....................................................................................... 11 3.1 3.2 3.3

General Observations...............................................................................................................................12 Conclusions..................................................................................................................................................14 Environmental Considerations ..............................................................................................................14

4. DOUBLE GLASS..................................................................................................................................... 16 4.1 4.2 4.3 4.4 4.5 4.6

Eye-Screw Fitting of Beads....................................................................................................................17 Practical Example ......................................................................................................................................17 Inside and Outside Turning Windows ................................................................................................19 Double Joints in Window Frame...........................................................................................................20 Ventilation ....................................................................................................................................................20 Shutters ........................................................................................................................................................21

5. ADD-ON GLASS FRAME .................................................................................................................... 22 6. TRANSPARENT WINDOW INSULATOR (TWI)..................................................................... 25 7. ROLL CURTAINS................................................................................................................................... 27 7.1 7.2

Manufacturing, Installation and Delivery..........................................................................................27 Assembly and Fitting a Roll Curtain ...................................................................................................30

Abstract Thermal insulation options for windows, using double glass windows, add-on glass frames, roll curtains and add-on transparent winter insulation. Solar windows for intake of solar heat during the winter in combination with better insulation. Illustrated with sketches and photos.

Photo on Cover Page Clean double glass window in a village house allows solar heat intake. Although the technology of double glass and solar heat gain are well known, in practice it is not widely applied. In reality, many low-income house owners spend a large percentage of their income on space heating because the windows are poorly insulated.

HA Technical Working Paper #8 – Windows and Thermal Insulation (April 2012)

INTRODUCTION The Technical Working Papers incorporate knowledge gained from more than 30 years experience in project development and implementation in several development countries. Much time has been dedicated to providing practical information on how to realise beneficial, low-cost solutions for the inhabitants of the mountain regions of the Himalayas. Introducing technologies without adapting these to local circumstances in not always possible because of socio-economic circumstances. Existing, proven technical solutions have been modified taking into consideration local customs, skills and building materials; ease of transport; availability of materials in the local markets of the mountain regions and possibility of introducing new items; and the affordability by the village people. Making the buildings more comfortable and reducing Internal Air Pollution (IAP) in traditional and new high altitude buildings are important aspects linked to thermal insulation. The document incorporates the best experiences in window design to improve the light level as well as the thermal insulation for traditional and new houses in remote mountain regions. For low-income people, it is important to find appropriate solutions taking into consideration the local economy of the people and local entrepreneurs, as well as the available skills, tools, materials and other resources, to create affordable products for an improved living condition and livelihood. This Technical Working Paper #8 gives a resume of the possible window designs for both traditional houses and new house constructions, and includes the following topics: • • • • • •

Overview of different insulation options for glass, curtains and shutters. Examples of window designs and possible improvements. Solar window and energy/heat gain. Double glass frames with cleaning possibility. Add-on glass frame as a low-cost thermal insulation solution. Roll-curtains as a very low-cost thermal insulation solution.

Capacity building of technical project staff or local engineers and architects is realised by formal education and study of additional information on existing and new technologies. It is hoped that this paper can contribute to this capacity building. The professional staff in turn will need to educate local entrepreneurs and village craftsmen, as well as community leaders, traders, salespersons and contractors, who in turn will be responsible for providing information to the clients (villagers). In the case of the roll-curtains, women groups can be capacitated to manufacture and install these in village housing. Sustainable marketing will be achieved only when the villagers buy the house improvements without the need for intensive promotion by external agents. Once a good understanding of the product is reached, local entrepreneurs and craftsmen can further improve upon it. The aim of the present document is to provide a better understanding of the insulation of windows. The document can be used as a basis for awareness development, training and as part or basis of curriculum development and vocational training.


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1.

EXISTING WINDOWS

When analyzing a problem and trying to improve upon it, the existing situation or the starting point of the process must be known. This differs per country, but for windows, there exist many similarities. The problem is that the window is usually the least insulated section in the walls of a house. The solution is to improve the insulation of the window and thereby reducing the heat loss with the following immediate effects: (a) (b) (c) (d) (e) (f) (g) (h) (i)

Less space heating required to keep the house warm. Less fuel needed, such as firewood, coal or dung. Improved comfort due to less draft or dust/smoke from the fire. Less time spent on firewood collection, chopping and keeping the fire going. Time saved can be use for other activities, such as education or income generation. Less environmental degradation in deforestation, soil erosion or watershed areas. Less climate change due to lower CO2 emissions and reduced deforestation. Improved health due to a higher in-house temperature and less smoke. Increased family budget due to lower expenses for fuel.

When addressing a specific issue, it must be known who the audience is. This audience needs to be addressed in a manner whereby the information provided can be absorbed and understood. The audience for insulating windows consists of: (1) Technical people, manufacturers and builders working in the construction sector. (2) Managers and finance organisations making investment decisions. (3) House owners living in the cold and non-insulated houses. These three main categories require different communication methods. While the construction workers want to know the practical manufacturing details, the managers want to see the financial implications, and the house owners want to know the cheapest solution for better comfort. Some can draw information from reports, others from posters and drawings, and again others from seeing it in reality. All categories need to be addressed adequately to obtain massive replication of the best solutions. The problem needs to be known before the product is promoted. This has to do with awareness raising. When only a new product is shown without providing the knowledge of what it does and how it works, people may buy it for status, but not use it properly; thus defeating its purpose. Awareness raising is an essential and preliminary component in product marketing. Only when people understand what the product is for and how it works, can they be convinced to buy the product to solve their problem. If it does solve their problem, they will communicate that to their neighbours and the product may become self-sustainable in production and marketing. For example: When a rich house owner has too much firewood available and he does not see the problem of space heating, he is not inclined to insulate, especially not when he himself is not chopping the firewood and keeping the stoves burning. When that same house owner does see that all the trees in the country being scavenged for firewood causing erosion and landslides, that person not easily start insulating.

not are soil will

For each of the three target groups mentioned above (managers, construction people and house owners), a specific media plan needs to be developed to bring the message across and get them motivated to undertake action. Depending on the group, this action can be organisation, teaching, production, demonstration, purchase and/or installation.


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1.1

The Glass Window is the Coldest Area

A window with single glass would be, during the winter, the coldest wall surface in the house. This means that per m2 surface of window, far more heat will be lost than per m2 wall construction. A single glass window has a thermal insulation value of RC = 0.17 m2.K/W, while a traditional stone wall has a thermal insulation value of RC = 0.6 m2.K/W, or three times as good. For an altitude of 1500 m above sea level, the recommended insulation value of walls is RC = 2.0 m2.K/W, or at least ten times the insulation value of single glass windows. The above means that a 1 m2 window loses as much heat as 10 m2 of a well-insulated wall. The effects are various: ¾

¾

¾

The glass surface is by far the coldest area and humidity in the house will condensate on the glass and drip down along the inside. Without proper drainage, pools of water will enter into the wall under the window and cause fungus, mould and other damage. Because of the cold window surface, the air along the window will be cooled, becomes heavy and flows downwards. This causes a cold draft next to the window, making it very uncomfortable for people sitting or sleeping in that area of the room. Because of the large heat loss through the single glass, the space-heating stove needs to provide more heat, requiring additional fuel, which in turn needs extra air for the burning process. The new air from outside is extra cold and fuel is consumed to heat that cold air.

Cold air is heavier than warm air. Having a cold window surface in a room will cause the air to circulate. The person on the chair therefore will get cold feet because of the draft. Circulating air increases the speed of heat transfer or heat loss.

In the photo on the right, one window is closed with an outside shutter during the winter. Sitting or sleeping in this area under the window would be uncomfortable because of the cold draft that will flow down from the window. Recommendation Above 1500 m altitude, all windows should have at least double glass. When special insulation glass is unavailable, above 2000 m altitude, all windows should have triple glass and above 2500 m two times double glass. In addition, the windows can have outside insulating shutters and inside insulation curtains, both should be easy to open and close.


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1.2

Inside Condensation

Glass windows, even if insulated, remain the coldest areas in the wall and condensation will form when the humidity inside the house is high. Exhaled air and cooking activities increase the humidity level in a room. Plastered walls will absorb some of the humidity. However, with the use of reflective or impermeable foils as insulation on the warm side of the wall, the humidity will condense on the window, especially during the early morning hours when the air temperature in the room is at its lowest.

A large amount of vapour is produced when cooking, especially when boiling water. The vapour will condense on the coldest area of the room, being the inside of the window. The horizontal timbers of the glass frames are all badly affected by the moisture of the condensation. The amount of condensation will be less with double glass.

Condensation has dripped down on the inside of the double glass PVC window frame and penetrated the windowsill. If the inside wall gets wet, the moisture will reduce the thermal insulation and may cause more damage when it freezes. Recommendation Window and windowsill designs should ensure that condense water is easily evacuated to the outside and does not infiltrate into the wall construction below.

Although double windows have been installed, it is visible that the entire floor near the outside wall has deteriorated. Increased humidity in the wall and under the floor planks is caused by heat loss and subsequent condensation of the inside air on the cold surfaces. The increased humidity will cause fungus and eventually wood rot. Recommendations • Condensation must be minimised by good thermal insulation. • Condensation must be captured in a gutter and drained outside. • All rooms should be ventilated regularly to reduce air humidity. • Ventilation is necessary under cold timber floors to remove built-up moisture.


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1.3

Outside Drainage

Rainwater running down the walls and windows should drain off the outside windowsill. Water penetrating the wall under the window will negatively affect the structure, causing rotting of the beams anchored in the wall and flooring and reducing the thermal insulation.

Outside windowsills and damaged timber from the window due to inadequate drainage of rainwater.

Photo above: View from above – the water infiltrates in between the window frame and the cement plaster. Photo right: A galvanised sheet on the windowsill will drain away most of the rainwater. However, it should start under the timber, slope downwards and overhang the wall.

Good quality inside and outside windowsills can be made from inclined ceramic (floor) tiles fitted under the timber window frame. Prefabricated concrete elements can be made to fit under the wooden window frame and hang out over the wall.

Recommendation Outside windowsills need to slope downwards starting from under the timber or PVC window frame and overhang the wall.


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1.4

Paint Maintenance

Many windows are never maintained after installation. Lack of maintenance results in deterioration of the timber, especially when fully exposed to the strong UV light from the sun. Weak timber causes torsion of the glass frame when opened and will break the glass. Painting of timber is a very important means to conserve the wood, but it should be applied after assuring the window operates smoothly (opening and closing). After painting, the glass frame needs to be left open for a minimum of three days to ensure the paint has fully dried; otherwise, the window might stick together when closed. Once the paint is completely dried, the window needs to be controlled again for smooth operation and adjustments made if necessary. When the paint has not completely dried before closing the window, or when the paint has been applied too thick, the glass frame will stick to the window frame. When forcing the window open, the pulling effect on the free corner will cause torsion of the thin glass frame, which may break the glass. Larger glass sheets will break more easily.

Left photo: The original double window construction was painted, but not adjusted for smooth opening and closing before the paint job. When forced open, the inside glass panes broke and only a single glass remains. Middle photo: The original single glass window was broken when the glass frame got stuck in the window frame because the paint was applied without first adjusting the frame and hinges. Right photo: Here an old window frame is being re-utilised. The (new) timber window frame has no protective paint; moisture from the adobe wall will negatively affect the frame, whereas rainwater from the glass will negatively affect the lower windowsill and wall construction. The durability of the window constructions and their thermal insulation aspects are greatly related to the maintenance level of the windows. Without UV protective painting, the timber will deteriorate, while lack of professional window adjustment before painting may cause it to get stuck and breakage of glass; thus losing half the insulation value in the case of double glass. Recommendations • Carpenters and construction workers should learn how to manufacture, install and maintain windows so the timber of the window frames and glass frames remains well protected from UV light, rain and condensation. • Carpenters, construction workers and house owners should be made aware of how to paint a window properly (perhaps via DIY pamphlets).


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1.5

Dimensions of Glass Windows

The desire to have better-illuminated houses (both day and night) results in new houses having larger glass windows and house owners placing large windows in new additions and blind walls. Because of the difficulty of getting large glass sections in one piece to remote areas, windows are often composed of rather small glass frames.

New hand-made windows with rounded corners.

Glass carried into mountain area.

The above window is very decorative and is most likely the choice of the wealthy house owner. With better knowledge, a better-insulated window with double glass could have been made for the same cost. Problems with the above window design are: • • • • •

Because of the non-square shapes, glass cut-off has been wasted. The large timber surface limits the amount of (sun) light into the interior. The large knots in the timber will cause irregular drying and deformation, which in the long term will affect the durability of the timber and painting. The lower side of the glass frames do not drain rainwater to the outside, causing leakage of rainwater on the inside. The lower windowsill is horizontal, allowing standing rainwater to affect the window frame and soak into the top of the wall.

A better solution would have been to make each glass frame with only three glass panes above each other instead of seven glass panes. The house owner could have also set a status precedence by making a larger double glass window, rather than a fancy timber design in small single glass. Carpenters and building material shops often sell premanufactured window frames and glass frames of standardised sizes. In such a case, the window manufacturers should present different glass sizes, larger size double glass options and window and glass frames draining the rainwater outside. Recommendation Carpenters and building material merchants need to be made aware of the lower insulation effects of larger windows. Different types of pre-manufactured double windows and double glass frames should be available in their shops.


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2.

SOLAR WINDOWS

Windows facing the morning, midday and evening sun gain large amounts of heat from the sun if the glass is kept clean and the windows are not fitted with fly screens. When these windows are double glazed, the gained heat will be retained. Woman and child sitting in the sunroom at midday. When the sunlight touches the floor or wall, it is converted into heat, which warms the air inside the room. The building materials store this heat and the heat is released during the night.

The amount of solar radiation at 2000 m altitude and higher in the Himalayas is above the 1500 Wh/m2 for clear skies during the winter, measured perpendicular to the line of the sun’s radiation. For the purpose of calculation, the value of 500 Wh/m2 average is used for vertical glass surfaces, considering some dust. When the sun is at an azimuth (inclination from horizon) of 45°, the section of the solar light A projects against the vertical surface of the window with a surface of 1.41 x A. In addition, each clean single 4 mm thick glass sheet absorbs 4% of the light (1% per mm). Crossbars in the glass frame will also block the sunlight. When the sky is not very clear or blue, the amount of light is less. While in the middle of the day the sun may be facing the building, it projects at an angle in the morning and afternoon, increasing the surface and thus reducing the intensity. Combining all these reducing factors, the following estimate can be made: For the azimuth or inclination of the sun: 1500 Wh/m2 : 1.4 (azimuth) = 1071 Wh/m2 For the daily horizontal average deviation: 1071 Wh/m2 : 1.4 = 765 Wh/m2 For the glass support bars: 765 x 80% = 612 Wh/m2 For double glass: 612 - (2 x 4%) = 563 Wh/m2 (not yet counting dust on the glass = 10-20%) For vertical glass windows, the solar heat intake is averaged at 500 Wh/m2.


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With 6 hours of sun from 9:00 hrs to 15:00 hrs on a vertical window of 1 m2, that amounts to 3 kWh, being equivalent to the same amount of electricity if an electric heater would have been used in the room. The window frame, fly screens, burglar bars, trees and dirt on the glass will block the sun and thereby block the heat intake. Installation of solar windows must ensure easy and regular cleaning of all the glass surfaces: outside, inside and in-between. How does solar energy compare with firewood? 1 kg air-dry (22% humidity) firewood produces about 13.6 Mega Joule. With 1 kWh = 3.6 Mj, then → 1 kg dry firewood = 3.7 kW. 1 When a common firewood space-heating stove has a burning efficiency of 27% (because the rest of the heat goes out of the chimney along with the smoke), one obtains from 1 kg firewood about 1 kW only. The amount of 3 kWh from a solar window is therefore the same amount of energy produced from 3 kg firewood. A 2 m x 1.5 m = 3 m2 vertical south-facing window receives that same amount of energy in two hours when the sun shines and the glass is clean. The above information about the power of the sunshine can be used for houses and public buildings. In the school right, most of the classes are held outside because the classrooms inside are too cold. To heat the classrooms, each child needs to bring a 3 cm stick of firewood every day to school for the wood stoves. The morning sun is warm, making it more comfortable for the schoolchildren to sit outside than inside. The three windows in the classroom are together 4 m2 vertical surface facing the eastern morning sun. From 09:00 hrs to 13:00 hrs = 4 hours of full sun, these can generate 4 m2 x 4 hrs x 500 Wh/m2 = 8 kW heating energy or equivalent to 8 kg of firewood, the same amount the children bring each day. To make this possible, the green painted metallic fly screen should be removable for the winter season and replaced for the summer to keep the flies out. Thermal insulation in the walls and double glass will retain the heat in the building, requiring less energy to warm up the following day. If the glass windows need to be protected, shutters can be added and closed after school hours. The shutters will also help to conserve the heat inside the room. Recommendations • Fly screens in front of windows on the sunny side of the buildings should be removed and stored away during the winter. • Classrooms should be designed with solar windows facing the winter morning sun for heating up the room quickly.

1

Energy (Joule) = mass (kg) x specific heat x temperature (°C). The specific heat of air is 1 J/g.°C. To make 1.2 kg air (= 1 m3) 1°C warmer, requires 1200 Joule = 0.33 Watt = 0.285 kiloCalorie. To make 1000 kg stone masonry 20°C warmer: 1000 kg x 0.85 kJ/kg.°C x 20°C = 17000 kJ = 4.7 kW.


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For the building on the right, the amount of glass is considerable and contributes greatly to warming the house during sun hours. To retain that heat inside, three measurements are required: (1) Double glass, doubling the insulation value of the windows. (2) A vestibule to avoid large amounts of cold outside air from entering the room. (3) Curtains, to be drawn closed as soon as the sun disappears. With such measurements and when the ceiling and walls are well insulated, the house will hardly require additional heating. The window pictured does not work as a solar window for three reasons: (1) The timber window frame and glass frames are very wide, blocking the sun. (2) The burglar bars block part of the sunlight. (3) The glass is very dirty, shown by the shadow of the burglar bars on the glass. If burglar bars are needed, they should be placed inside for a solar window. The burglar bars should not hinder cleaning the glass on the inside or outside.


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3.

INSULATION VALUES OF WINDOWS

Single glass has a low thermal insulation value. Double glass and coated glass are substantial improvements, but seldom reach the thermal insulation value of the wall. Condensation will first occur on these glass surfaces and the cooled air will flow down along the cold surfaces and cause an uncomfortable draft. Thermal insulation should be related to the cost. The cost can include the modification of the existing window frame, an entirely new window frame for thicker type of double or triple glass, or adding a new window frame. In most cases, when a new window frame is installed, structural and decorative repair of the wall and interior finishing will be required as well. These costs need to be added. The following table provides an overview of existing options in Europe with cost and insulation values. The grey areas are options that are not yet available in many countries.

#

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Type of Glass

Glass in lead strips Single glass Double glass Add-on window Add-on glass frame Hinged window Aluminium frame + 2 rubber profiles HR glass + coating HR+ HR+ HR++ HR++ HR++ Plexi glass only Plexi glass add-on Transparent PVC Transparent PVC roll curtain inside Polycarbonate Polycarbonate Add-on window Foil + single glass Foil + double glass Foil + HR++ glass Laminated glass Vacuum glass HR+++ (triple) HR+++ (triple) HR+++ (triple) HR+++ (triple) HR & HR++ HR+ & HR++ HR++ & HR++ Add-on frame only Add-on frame only Timber shutter Insulating shutter

Trader Cost+Tax* or DIY Custom made only 2 10/m 20/m2 15/m2 5/m2 10/m2 15/m2 2

20/m 35/m2 40/m2 55/m2 60/m2 75/m2 35/m2 35/m2 3/m2 5/m

2

15/m

2 2

15/m

Luxasolar® Luxasolar® Luxasolar® 180/m2 500/m2 130/m2 140/m2 180/m2 160/m2 75/m2 75/m2 75/m2 100/m2 150/m2 25/m2 35/m2

Placed at House**

Construction mm With H profile lead strips soldered

2

20/m 30/m2 20/m2 10/m2 20/m2 30/m2 Belned® 40/m2 60/m2 65/m2 70/m2 80/m2 90/m2 50/m2 50/m2 10/ m2 25/m

2

25/m

2

2

75/m " 75/m2 " 75/m2 " 220/m2 600/m2 170/m2 180/m2 240/m2 210/m2 + frame + frame + frame 150/m2 200/m2 40/m2 50/m2

4-12-4 dry air only 4, 20 air, single glass 40 - 60 wide 60 - 80 wide 20 wide, painted screwed or hinged 0 4-12-4, argon 4-15-4, argon 5-15-5, argon 5-20-5, argon 5-16-5, krypton 4 4 + > 2 cm air 0.2 TW-I or TW-II 0.2 free hanging 8 hollow profile 8 hollow profile + > 2 cm air layer 0.5 plastic 0.5 plastic 0.5 plastic 4 - 0.5 plastic - 4 3 - 2 vacuum - 3mm 4-12-4-12-4, argon 4-16-4-16-4, argon 4-12-4-12-4, krypton 4-16-4-16-4, argon HR >2 cm air HR++ HR+ >2 cm air HR++ HR++ >2 cm air HR++ 60 - 100 wide 80 - 120 wide


Thick mm 4 4 20 3-4 20-30 40-45 10 0 20 23 25 30 36 4 4 0.2 0.2 8 8 0.5 0.5 0.5 8.5 6.2 36 44 36 44 +36 +36 +36 40-50 50-60 30-40 50-60

New RC Value Glass only in m2.K/W 0.12 - 0.11 0.17 0.33 +0.20 incl. 2 cm air +0.20 incl. 2 cm air +0.20 incl. 2 cm air +0.20 incl. 2 cm air before existing glass 0.6- 0.5 0.7 0.8 0.9 1.0 1.2 0.25 + 0.42 incl. 2 cm air + 0.15 incl. 2 cm air + 0.10 incl. >2 cm air before existing glass 0.33 + 0.50 incl. 2 cm air before existing glass 0.33 (= glass + 0.17) 0.28 (= glass + 0.34) 0.13 (= glass + 0.9) 0.31 1.2 1.4 1.7 2.0 2.0 0.6+0.17+1.2 = 1.97 0.8+0.17+1.2 = 2.17 1.2+0.17+1.2 = 2.57 Double joint design Depending on core 0.35 incl >2 cm air 1.0 incl >2 cm air

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Notes: (a) For vertical air layer > 1.7 cm, RC = 0.17 m2.K/W; air layers wider than 2 cm do not add thermal insulation. (b) For numbers 20, 21 and 22, the cost indication is for small quantities. The added value for HR+ and HR++ is less. (c) For the numbers 29, 30 and 31, the first HR or HR+ or HR++ is the existing window. (d) For number 32, the add-on timber HR+ window requires a double joint construction. The following aspects are relevant for the costing: The cost indications in the table are per m2 and in Euros, including sales tax. The solutions in the table are for the European market. Placement cost at the house is related to urban situations in the proximity of the manufacturers/dealers. * Minimum 30 m2 orders per house; >0.5 m2/glass sheet; 2 cm air 1.13 m2.K/W

As a more durable solution, two double glass windows with a shutter (above 2500 m): 3 3 34

Double glass Double glass Timber shutter Total Construction

20/m2 20/m2 25/m2 65/m2

30/m2 30/m2 40/m2 100/m2

4-12-4 dry air only 4-12-4 dry air only

20 20 30-40 100 mm

3.0 3.0 timber

0.33 0.33 0.35 incl. >2 cm air 1.01 m2.K/W

In addition to the above table, insulating curtains can be fitted.


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3.2

Conclusions

(a) The Do-It-Yourself (DIY) solutions are by far more cost-effective than when a professional supplies and fits the window on site. Finishing is not yet included in these costs. DIY can also be realised with the final painting. This is not included in the above list. (b) A good sealing transparent PVC roll curtain fitted inside an existing single glass window has the same insulation value as a double window, but a much lower cost. This is the most costeffective solution with an economic return period of only two years (or 1 year with DIY). (c) An add-on glass frame with an existing single glass window has the same insulation value as a double window, but a much lower cost. This is the second most cost-effective solution with an economic return period of four years (or 2 years with DIY). This is the same as annual interest of 20% (40%). (d) An additional window frame on the inside is easier to clean and operate than a screwed-on add-on glass frame. The timber dimensions are larger and therefore the additional window is more expensive. This is the third most cost-effective solution with an economic return period of six years (or 3 years with DIY). This is the same as an annual interest of 15% (30%). (e) Combinations of the above insulation methods are feasible, with every standing air layer added providing an additional insulation value of RC = 0.17 m2.K/W. (f) The lowest cost options for window thermal insulation are the transparent PVC roll curtains and add-on glass frame when these are properly closing all around. A double glass window with a fully transparent roll curtain and a second decorated roll curtain. By keeping the transparent curtain down during the winter and rolling the second blinding curtain down for the night, good additional insulation is obtained. (g) The economic return period will become shorter when energy prices increase. In addition, there is the added comfort gained by the insulated windows. (h) The window design needs to consider the following aspects: • Current state of maintenance of the window and eventual upgrading costs. • Desire to have more daylight in the room. • Size of the window and the heat loss or solar heat gain during the winter. • Availability of local craftsmen to modify or improve the current construction • Cost of making double glass, insulation curtains and shutters. • Possibility of DIY making of the thermal insulating windows or curtains. • Comfort desired as compared with the situation of the past winter. • Amount of space-heating fuel needing to be saved in the future. • Amount of ventilation still required after the window is insulated. • Structural integrity of the wall construction for placing larger window sizes.

3.3

Environmental Considerations

Depending on the material use for the double glass or window frame, a number of environmental considerations apply. A. Thermal insulation of the house will reduce fuel consumption for space heating for the lifetime of the insulating construction. Reduced fuel consumption leads directly to reduced CO2 emissions, almost directly comparable with the percentage fuel saved. The type of material used for the double or triple windows, roll curtains and shutters is not very relevant in this


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respect, since the resources to produce these windows are much smaller than the spaceheating energy resources saved by the thermal insulation for the lifetime of the window. To determine the best window insulation method, the cost of the measurement needs to be divided by the new RC value. The solution with the lowest result is the most cost-efficient construction for installation. However, the solution with the highest RC value is the best option in the longer term as energy is saved each year. B. When the materials of the window frames are compared, locally produced materials has preference. However, timber harvest from non-sustainable sources and not replanted by a properly managed reforestation programme has a very poor environmental rating. Unfortunately, this is the case in nearly all Himalayan countries, except Bhutan. C. When the timber is imported from Siberia, it can be collected from environmentally wellmanaged forests, but road transport over 6000 km consumes vast amounts of fuel and transport equipment; therefore, it is not environmentally friendly. D. Timber needs to be preserved and adequately treated for conservation. This requires painting, labour and periodic maintenance. Horizontal surfaces exposed directly to the sun in high mountain areas are subject to extra erosion by the sun’s UV radiation and need more frequent maintenance than vertical surfaces. When the timber is not maintained with light coloured protective paints, it will quickly deteriorate and replacement may be required within 15 years. E.

Painting timber will increase the lifetime of the product and can be done with a variety of materials. In solvent-based paints, the solvent, pigment, binding agent and manufacturing process are responsible for equal proportions of environmental loading. Without going into much detail, water-based paints with 100% acrylic binders are durable and flexible, as well as least environmentally damaging. Painting below 15°C, in the sun or in windy conditions must be avoided.

F.

Accoya timber is named after the process of acetylisation of fast-growing softwood, such as pine, resulting in Class 1 quality timber in durability and hardness, making it virtually rot proof. The result is at least a 60-75 year serviceable life, equivalent to PVC windows, but totally nontoxic. Usually Accoya timber is made from FCS certified forests and thus an environmentally friendly produced. It is fully UV resistant. The timber can be worked like any other timber and therefore is highly versatile and the best choice.

G. Aluminium requires an enormous amount of energy (CO2 emissions) to produce, at least 100fold to PVC and 1000-fold for timber. With an increasing amount of aluminium used and recycled, the energy consumption will reduce. It will last for 100 years and the special advantage of aluminium is the very low maintenance factor. H. Polyvinyl chloride (PVC) can be made from recycled plastic (better than all new). By adding calcium and zinc, the durability against deterioration by UV radiation is reduced. Burning PVC at the end of its lifecycle will emit CO2 and highly toxic dioxin. Because PVC windows are reasonably well insulating and will last between 50-75 years without maintenance, it is a costefficient solution. PVC windows should be recycled, not burned.

Although PVC is not environmentally recommended, the good insulating and durable construction saves large amounts of energy and is better than poor quality timber that needs regular paint maintenance. Windows should allow permanent trickle ventilation; the left window is therefore not a good design.


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4.

DOUBLE GLASS

If double glass frames or windows are made by a carpenter, they should be made to allow easy cleaning in between the double glass sheets. This should be done at least once a year to remove dust that has settled on the inside glass surfaces. The glass in the window becomes warm in the sun and cools down at night. So does the air in between the two glass sheets. In carpenter-made double glass windows, even with good quality rubber seals, the air will suck in and out from between the double glass on a daily basis, meaning that it “breathes” 365 times per year. Air contains dust particles (especially in rooms with a space-heating stove) and those dust particles settle against the inside faces of the double glass sheets. Depending on the quality of the seal, the dust will become visible within a year. Although glass beads are in theory removable, a house owner seldom removes these to clean the glass.

To clean just the bottom glass sheets of the above double glass window – removing the wooden glass beads, cleaning the glass and replacing the beads – required almost one hour. The comment of the engineer who was assigned this task: “People who make these double glass windows should try to clean these themselves; then they would understand how wrong the design is.” Recommendation Non-hermetically factory-sealed double glass frames should be made in such a way that they can be easily cleaned by a single person annually. In this respect, double windows or hinged add-on frames are easy to operate.


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4.1

Eye-Screw Fitting of Beads

Non-hermetically factory-sealed/welded double glass should not be fixed with nails in the window (photo right). The glass beads should be made larger/thicker to be adequately stiff and placed on the inside. The larger timber size of the glass bead allows for fewer fixing points than the many nails currently being used. Depending on the height and width of the glass frame, the glass beads can be fixed onto the main window frame with 4-5 cm long eye-screws. A 1” eye-screw can easily be unscrewed by hand, simplifying the yearly (springtime) cleaning of the inside glass sheets and avoiding damage to the beads. Cleaning the glass is especially important for windows receiving sunlight during the day; only clean glass will provide maximum solar heat intake. Open and closed eyescrews on the hinged add-on glass frame for easy opening once a year.

The add-on glass and fixed on the window. In this resulting in triple RC = 0.5 m2/K/W.

4.2

frame (left) is hinged on the right external side of the inner double case, there was sufficient space glazing and an insulation value of

Practical Example

In a secondary school office, two large windows were located on the sunny side of the building, catching the full morning sun. The room, however, required additional kerosene heating. With no ventilation, the burning gasses from the kerosene burner quickly filled the office. After only one hour, the amount of fumes from the kerosene burner was so high and the oxygen level so low that our eyes began to burn and clear thinking of the occupant(s) was affected. The difference in heat intake can easily be experienced by placing one’s hand behind the glass or fly screen. Burglar bars reduce some heat intake as well. The additional heating in the winter would be unnecessary with the following measurements: ¾ Cleaning the glass windows on the outside (difference +5% solar heat intake). ¾ Cleaning the glass windows on the inside (difference +5% solar heat intake). ¾ Removing the fly screens to allow more sunlight into the room (+15% solar heat intake). ¾ Keeping the upper ventilation window closed when the kerosene burner is not in use (-5% heat loss through unnecessary ventilation). ¾ Adding a roll curtain in the evening to minimize heat loss during the night (-10% heat loss). ¾ Adding an add-on glass frame on the inside of the existing glass frame (-10% heat loss), for both sunny side and shaded side of the building. The sketch below illustrates the above situation.


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A. A large amount of the sun is reflected because of the dirty glass (1/3rd) and fly screen (1/3rd); only part of the solar heat is entering the room (1/3rd). B. With clear glass and the fly screen open, almost all solar sunlight is entering the room where it is converted into heat when meeting a surface in that room. C. Applying a single roll curtain in the evening will create an insulating layer and avoid heat loss. This roll curtain should close precisely to the day sides of the wall. While in the winter the objective is to allow more solar light intake to warm a room and then contain the warmth, in the summer months the opposite affect is desired, reduce direct sunlight to keep the room cool. The sun’s position in the summer will be higher in the sky, resulting in less heat intake. A small outside overhang can further reduce the summer sun intake. When the fly screen is fitted on the outside and painted white (causing 30% sun reflection), more sunlight is blocked. The following sketch shows the option of changing the position of the glass frame with the position of the fly screen and the option of a hinged add-on glass frame for additional insulation. This addon glass frame is also recommended for the north side of the building having no sun intake. With the glass frame opening inwards, it is less vulnerable to damage due to wind gusts.

D. The glass frame has changed position with the glass frame; the glass frame inside. If the fly screen is fitted outside and is painted white, it will reflect the summer heat. E. Opening the fly screen in the winter allows maximum sun intake. This implies that opening and closing the fly screen needs to be managed and the glass kept clean. If pin hinges are used to attach the fly screen, it can easily be removed and stored away in the winter period. F. A hinged lightweight glass frame is screwed onto the inside glass frame. The optimum space between the two glass sheets is 2 cm. A roll curtain can be applied for additional insulation at night.


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G. The light add-on glass frame is reinforced in the corners with a screwed-on iron strip. One side is fitted with two sections of a piano hinge, while on the other side an eye-screw closes the glass frame (right side of sketch; l ). H. A thin sash is cut out from the glass frame, equal in thickness to the glass. Duck tape (width of the glass frame) can be used to hold the glass firmly in its place so it does not fall out of the sash when the window is opened for annual cleaning. Recommendation Carpenters manufacturing double glass window frames should make their designs to allow the inside glass frame to be easily removed for cleaning in between the glass sheets. These inside glass frames can be fixed with eye-screws or a combination of eye-screws and hinges. Sample of a pin hinge.

4.3

Inside and Outside Turning Windows

Glass frames opening inwards require an overhang to avoid rainwater from entering the lower joint. Rainwater should be drained away from the horizontal window frame and the windowsill. Making the outside windowsill from ceramic floor tiles and having some overhang will keep the wall under the window dry. A rubber seal can be applied inside the lower part of the glass frame and along the three other sides. A second seal can be made from a metal strip or metal-rubber combination and screwed onto the glass frame. Glass frames opening outwards should have a sloping surface for the horizontal sections of the window frame. For good quality paintwork, the corners of all the timber profiles need to be chamfered and sanded round. In addition, the paint should go 2 mm onto the glass to avoid that water enters the putty holding the glass sheet. The sketch shows an inside gutter for the capture of condensation water. From the gutter, one on each side, a small opening should allow drainage of the condensation water to the outside on the lower window frame. It is also possible to manufacture a tube leading to the outside ceramic tile. For saving timber, the lower window frame can be composed of two pieces glued together with waterproof glue. The application depends on the level of mechanisation, cost and timber quality.


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4.4

Double Joints in Window Frame

To improve the insulation and reduce possible draft through the joints of the windows (and doors), a double joint can be made. Further improvement can be achieved by applying soft rubber profiles inside the window frame joints. Making the windows (and doors) airtight is only useful when a fuel burning space-heating stove is not used. In order to burn, a stove requires a large amount of fresh air (containing 20% oxygen) to maintain its burning process. Making the room airtight will prohibit the burning process. Small ventilation window in larger window frame. The glass is fitted in a soft rubber profile and the double joint has been improved with a single rubber profile. In this design, the glass cannot be easily cleaned and will become dirty inside after a few years. Double window composed of two thin timber glass frames screwed together. The larger glass frame has a rubber profile that fits the joint of the window frame. If the glass beads in this glass frame are large and screwed on with eyescrews, the inner glass surfaces can be regularly cleaned.

The following two sketches provide a cross section of possible double window designs with double rubber seals. Because both the glass frames are hinged, the round-head screw can be loosened and the glass sheets regularly cleaned by the house owner.

4.5

Ventilation

When rooms are better insulated, it is important to have a little (trickle) ventilation for fresh air, especially in rooms insulated with reflective foils. In PVC windows, special profiles can be made to fit above the double glass inside the frame. These openings can be regulated with a lever from the inside. The pictures below give a handle-based option for trickle ventilation.


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Closed with Double Seal Trickle Ventilation Full Ventilation

4.6

Shutters

Timber or insulated metal shutters will provide additional thermal insulation. These shutters need to be operated on a daily basis to obtain maximum gain from the solar heat intake; opening them in the morning to allow the sun inside and closing them when the sun is gone from that façade. Using the winter sun properly in house designs and for other buildings will substantially reduce the space heating needs. With adequate thermal insulation of the building and solar windows, the need for space heating can be drastically reduced.

Shutters can close from the inside (left photo) or from the outside (centre / right photos). Shutters closing from the inside can contribute to the security of the building, especially when the building is unoccupied. Timber frame shutters covered with GI sheet are durable and little affected by the strong UV sunlight or rain. They can be made to close from the inside. If the shutters open outwards, they need to open flat against the outside wall of the house and strongly fixed so they do not loosen and get damaged by the wind. Expanded polystyrene (EPS) or PE foam in between the GI sheets will provide insulation. Manufacturing these requires cooperation between sheet metal workers and carpenters. Recommendation Shutters provide additional thermal insulation for windows because of the added air layer, as well as added security. Shutters should close well and be insulated, preferably with plastic foam-type insulation material. The shutters should be made from weather-resistant, durable material.


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5.

ADD-ON GLASS FRAME

Double glass windows are a 100% thermal insulation improvement over single glass windows and an essential element to better house insulation in all mountain areas. However, replacing a single glass window with a double glass window (in wood or PVC) is often too expensive for most households. Double glass windows are usually only considered when building a new house or an extension. The add-on glass frame has the same insulation benefit as double glass, but with a much lower cost and easy to install. The add-on glass frame is a forerunner of double glass windows and is still being widely used in Europe and elsewhere. The glass frame can be fitted onto the existing moveable single glass window frame either outside or inside. If the window opens outwards, it can also be fitted inside onto the window frame (middle photo). It can be made from timber or aluminium profiles.

Aluminium Profile Outside on Moveable Frame

Aluminium Profile (+ Rubber) Inside Fixed on Window Frame

Timber Profile Inside on Moveable Frames

The add-on glass frame has a simple construction and can be easily made by village craftsmen and handy DIY house owners. Only the 3 mm glass needs to be ordered. The following materials and construction techniques are required: •

Timber Profiles – 20 mm x 40 mm, shaved, with central groove on one side measuring 4 mm wide and 8 mm deep, all four sides chamfered (2 mm). It is advised to purchase these profiles ready-made from a carpenter having machines and producing the profiles in large quantities. A bundle of 30 m (100 ft.) is sufficient to make 5-6 add-on glass frames for common windows. In most cases, the timber will have irregularities, such as knots or cracks. These sections cannot be used because knots will cause torsion in the timber. Cutting the required lengths in between the knots is important. Making the 4 mm groove in the centre of the shaved strips is realised by passing the timber twice over the saw blade, the second time after turning the timber length horizontally 180°. The arrows in the photo indicate the location of knots in the timber. These need to be avoided in the glass frame because the thin lengths of timber will bend around these knots, in particular when it is still freshly sawn, planed and cut into the smaller required sections. When the timber bends, the glass may break. This is a quality control point that should be highlighted in the construction manual.


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The glass frame profiles (shaved) should be manufactured in quantity in at least two different sizes for internal add-on glass frame panels (e.g. 2 cm x 4 cm for large frames and 16 mm x 32 mm for smaller frames), including a perfectly central groove for 3 mm glass (3.5-4 mm wide and 7 mm deep). The four sides of the profiles should be chamfered (bevelled). •

Sawing Jig with Hacksaw – precisely manufactured from hardwood or good quality multi-ply board with 45° and 90° cutting guides. The hacksaw should be thin with fine teeth (8-10 teeth/inch). Good quality sawing jigs (mitres) should be available from local hardware shops. alternative, the sawing jig can be made from good quality thick, waterproof plywood.

As an

Good quality hardwood diagonal sawing jig (mitre) and hacksaws are essential for precise work, but difficult to come by for village carpenters or DIY. •

GI Metal Corner Connection Pieces (with screws) – 30 mm wide, 100 mm long, 1 mm thick galvanised iron with screw holes for ¾” flat-head screws (18 mm). For six windows, 24 corner pieces and 144 screws (one gross) are needed. The corner pieces are fixed after the glass sheet has been inserted into the grooves.

The corner pieces simplify and strengthen the construction of the add-on glass frames. Easy work is important for fast product delivery. Manufacture in quantity two types of L-shaped galvanized iron sheet (1 mm thick) hook reinforcements for the above wood profiles (being 10 mm smaller), including accurately drilled holes for precisely matching the ball-headed screws. The flat, 90° corner connection pieces must be precisely made, preferably by a factory. For 30 villages, more than 1000 households may possibly want on average four add-on frames. These 4,000 units would require 16,000 corner pieces, along with screws and hinges.


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•

Hinges – folded closed having a width of ¾” or open 1½” along with 18 mm screws. The hinges should not be wider than the thickness of the timber profiles (20 mm).

•

Eye-Screws – two 2” (5 cm) eye-screws to fix the add-on glass frame onto the existing glass or window frame. The holes for the screws are predrilled through the timber of the add-on profiles and fitted on the opposite side from the hinges. For large windows, additional eye-screws can be fitted in the bottom and upper profile if needed (see arrows in photo).

•

Paint – to treat the timber against the elements of weather. This is especially necessary when the add-on frames are placed on the outside. With outside fitting, the glass should also be placed in very soft mastic in order to avoid water entering the lower groove in which the glass stands. When the add-on frames are placed on the inside, paint in the colour of the existing windows can be used.

The house owner needs to decide whether the add-on glass frames are to be placed on the outside or on the inside. When placing the add-on glass frames on the inside, the fittings of the existing window sometimes need to be repositioned. The availability of glass sheets needs to be assessed before defining the dimensions of the add-on glass frames. When the add-on glass frame needs to be painted, it is far easier to do the painting first, before inserting the glass sheets and fixing the corner hooks. The hook iron is 1 cm smaller than the glass frame to avoid that the screws touch the glass groove and placed 2 mm from the outside against the bevelled side. The groove is 1 mm wider than the glass and the glass dimensions are 4 mm smaller than measured inside the groove. Resuming the choices that need to be made before manufacturing: ¾ Add-on glass frame to be on the inside or outside of the existing windows or glass frames? ¾ Add-on glass frame on the window frame (large) or on the glass frame (smaller)? ¾ Are the corner connections to be visible or not? The right-hand glass frame of the “Timber Profile” photo on page 22 has the four corner hook pieces in sight, while they are behind the timber profile in left-hand window (same photo). ¾ Is the add-on glass frame to be painted or varnished? ¾ Can the glass sizes (3 mm) be obtained locally? ¾ Are extra eye-screws necessary when the add-on glass frame is large? Recommendations • Include add-on insulation glass frame manufacturing as a short technical training course on window insulation. • Make a DIY manual. • Ensure that the source materials (hinges, hooks, eye-screws, bundles of pre-grooved profiles and mitre boxes with hacksaws) are readily available in the principle markets and with local carpenters. Recommendations for Minimum Window Insulation Altitude 1500 m – double glass + curtains Altitude 2000 m – triple glass + curtains Altitude 2500 m – 2 x double glass + curtains


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6.

TRANSPARENT WINDOW INSULATOR (TWI)

The transparent window insulator (TWI) is actually an adaptation of a common practice – covering the windows on the inside or outside with thin (0.02 mm), cheap, translucent plastic during the winter. Due to the strong UV radiation, the plastic deteriorates after only one season and has to be replaced. In addition, being only translucent, it blocks some sunlight. Good quality, transparent foil in two thicknesses (0.1 mm and 0.135 mm, the latter being slightly more stiff 2 ) is available in most local markets. The thicker foil is recommended for inside application. Although the foil will become stiff when cold, this should not be a problem because, when it is cold outside, there is no reason to remove the foil as the standing air layer created by it provides thermal insulation. Being transparent, it allows daylight into the room. Because the TWI is fixed to the inside of the window, the effect of UV radiation on the plastic will be reduced and the foil will last several years when rolled up and stored away during the summer. For this reason, the TWI should be well marked for each window. Type I – Over the Whole Window Frame The fully transparent PVC foil (sold as tablecloth) is cut about 1 cm wider than the day and 1 cm longer than the height to ensure it sits against the four sides of the wall opening. Two wooden strips (7 mm x 20 mm) are cut 2 cm shorter than the width of the window day. The eye-screws are 1” (the eye is 1” diameter and the screw section is 1”). The foil is stapled onto the wooden strips, one at the top and one at the bottom. The strips are centrally placed along the border of the foil, leaving 1.5 cm on each side, and positioned 4 cm from the top and bottom edges. The 4 cm is necessary; otherwise, it will be difficult to insert the eye-screws into the window frame. Two eye-screws are inserted in each strip from the other side. Type II – Over the Glass Frame Only The transparent foil is cut about 5 cm shorter and narrower than the timber of the glass frame to ensure it is well inside the size of the frame. The two wooden strips (7 mm x 20 mm) are 2 cm shorter than the width of the foil. The eye-screws are 1”. The wooden strips are stapled to the foil – one at each end, centrally placed leaving 0.5 cm on each side, and aligned with the top and bottom edges of the foil. Two eye-screws are inserted in each strip on the other side.

Photo left: Type I – over the whole window. Photo right: Type II – only over each glass frame.

2

The thickness can be measured by cutting a 2 cm wide strip off the side of the roll and folding it five times double. This creates 32 layers. The measured thickness is divided by 32. If no precise measuring instrument is available, try three of these 32 layer packs (total 96) plus four pieces and divide by 100.


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An ordinary office staple machine can be used to attach the foil to the wooden strips (left photo above). Ensure the foil is a perfect rectangle and the wooden strips are placed 4 cm from the edges (centre photo). To assist in turning the screw into the window for the first time, another eye-screw can be used (right photo above). Placement of the eye hooks (right). Installing the TWI The foil should be cleaned before fixing the TWI to the window. After marking the rear side of the wooden strip with the window name or location, start with fixing the top strip. Ensure the wooden strip(s) are positioned horizontally. With Type I, ensure the overlapping foil is flush against all sides of the window frame. Because the eyescrew is small, it may be difficult to drive the screw into the timber of the glass frame. When fixing the bottom wooden strip, the foil should be slightly stretched. The fully transparent PVC plastic foil (0.135 mm) window insulation, which is fitted on the inside of a glass window, is one of the lowest cost and durable insulators for windows. Advantages:

Very low cost and added thermal insulation; transparent instead of translucent (occupants of room can still see outside); low-cost investment; can be used for several years because it is less affected by UV radiation than outside plastic; with fixing method (II), the window can be opened for ventilation; it is not seen from the outside. Disadvantages: Eye-screws need to be taken out at the end of the winter, the plastic foil rolled up and stored until the next winter.

Recommendation Materials for making a TWI should be readily available in the market, together with a picture DIY manual. The salesperson or woman’s group can also provide the service for in-house installation.


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7.

ROLL CURTAINS

The roll curtain is the second lowest cost option after the TWI for window insulation. The fully transparent or decorative (blinding) roll curtain, if properly placed, can increase the insulation value of the window by RC = 0.08 to 0.1 m2.K/W, being >50% of a well-sealed, closed single glass window. If the decorative roll curtain is used on a single glass window in combination with the transparent window insulation (TWI), the new insulation value is more than a double glass window, but costs only 1/4 to 1/5 of a double glass window when self-manufactured. The decorative roll curtain can be made in many different types of materials, such as smooth plastic, transparent with lace pattern, plasticized cloth or thick cloth. There are two types of plastic foil used for tablecloths; one is PVC only and rather stiff to roll and the other is plasticized cloth, being more supple, flexible and durable. This second type is preferred because it rolls better and requires only a light stick at the bottom. 3 This type of roll curtain has three main benefits: (1) added thermal insulation; (2) provides privacy when closed and (3) creates a decorative element in the room To give the curtain an additional finished look and hide the operating strings, a valance (strip of material) can be placed across the top (see photo below). The design is a permanent fixture and can be rolled up and lowered by means of strings. 4 Because the decorative cloth blocks out the sunlight, if placed on a south-facing window, the curtain should be rolled up during the day to allow for sun intake and solar warming of the room. When there is no more sunlight, it then needs to be rolled down to conserve the gained solar warmth. Advantages:

Low material and installation cost; added insulation; decorative; gives privacy; durable. Disadvantages: Needs to be fully rolled up before opening the glass window for ventilation to avoid damage from window fittings; if the window is not fitted with a transparent window insulator (TWI), then it needs to be raised during the day to allow solar intake and lowered at night.

7.1

Manufacturing, Installation and Delivery

Marketing of the roll curtain can be either through the supplier of the curtain material or a villager (male or female) who has interest in setting up such a business. Each house can have as many as ten roll curtains. A large marketing book (60 cm x 60 cm) should be made containing samples of the different curtain materials available in the market from which the house owner can make a selection. The entrepreneur should have the timber material in stock so it can be rapidly cut to the required lengths.

3

The thick plastic roll curtain material requires a heavier bottom stick. Making a 3 cm x 3 cm wooden stick heavier is achieved by making a groove in one side and inserting a 6 mm metal bar (from reinforced concrete). 4 The quality of a cotton string is not very durable; woven 4 mm nylon cord is recommended.


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The translucent “lace” roll curtain is fixed against the ceiling, but now the window cannot be opened. In such a case, the roll curtain should be placed on the inside of the wall above the window opening creating an air layer with the thickness of the entire wall (see “B” in sketch below).

Precision work is required in cutting the material rectangular and hanging the curtain horizontal. A carpenter’s square with legs of 60 cm x 80 cm (24” x 32”), a spirit level and straight rulers are necessary tools. 5 Using a 2-ft. long spirit level, a horizontal line is drawn on the upper window frame to ensure the wooden strip holding up the roll curtain is placed precisely horizontal; otherwise, the curtain will not roll up and down properly. With straight and rectangular day openings, and precise measurements per window day, the entrepreneur can manufacture the roll curtains at his/her workshop. This should only be done when sufficient on-site experience has been obtained. A roll curtain flush with the inside wall requires less precise measurements. Steel bar inserted into the lower timber to allow straight rolling and hanging. When the roll curtain is hanging before the wall, sitting it on a windowsill will improve the sealing and reduce air circulation. A. In this option, the roll curtain is fixed inside the “day” of the window. B. In this option, the roll curtain is fixed on the wall in front of the window. C. To improve the performance of the roll curtain, a wooden plank can be added to extend the existing windowsill or, D. An additional lower plank can be added. This depends on the other uses of the windowsill, such as for displaying articles. E. A cornice or a strip of the same curtain material can be fixed on the upper side. This depends on the preference of the house owner.

5

A large carpenter’s square can be made with the mathematic 3:4:5 ratio sides.


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Photo below: The nylon string is guided through several eyehooks and attached to a wall anchor below when the curtain is rolled up.

Photo right: Example of a transparent roll curtain being down for the entire winter in front of a double glass window. The string and lower weight (roll-up stick) are visible, but the very transparent PVC is hardly visible and allows good view of details outside. The second blinding roll curtain is raised during the daytime to allow daylight to come into the room. It can also be fully raised. Recommendation Roll curtains and transparent add-on PVC foils (WTI) are simple to make locally and install. They can be made and installed by village women groups; thus creating low level barriers for communication. Simple step-by-step manuals with pictures and in local language should be available. Projects involved with this subject should facilitate the supply of source materials and tools through local hardware shops.


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7.2

Assembly and Fitting a Roll Curtain


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