The main points:
· The selection of examples is restricted to those that give interesting information and where the data are secured
· The indoor and outdoor air temperature is monitored simultaneously by the use of dry bulb thermometers
· The surface temperature is monitored in a few cases. The results are therefore sometimes less significant than expected, but nevertheless clearly illustrate the tendency.
In this chapter the thermal performance of various buildings in different climatic zones is compared, based on the indoor air temperature, which was recorded by extensive monitoring.
The building examples represent mainly built houses whose performance is monitored during their daily use, rather than abstract models or theoretical configurations. The complex situation of a house in use is therefore incorporated.
Assessment of performance
The study of these examples helps to assess the influence of construction systems on the indoor climate in quantitative terms. It provides a good idea in which range the indoor climate can be influenced. It also shows that climate control, in a purely passive way, has limits. Miracles cannot be expected: clear advantages however can be achieved.
Selection of examples
The aim was not to include as many examples as possible, but two criteria were used as a guide in the selection:
· Only examples with reliable
and validated data were used.
· Only examples giving clear information, allowing conclusions to be made, were used.
Focus on air temperature
It was not an easy task to achieve reliable recording of the indoor climate in remote locations and in different climatic zones. The study was, therefore, in general, restricted to the air temperature only.
Often the air temperature does not show a very drastic difference in the performance of the system, although the difference is felt acutely by the occupants. This is due to the fact that other factors also play a significant role. To gain a comprehensive comparison, surface temperatures, air humidity and air circulation would have to be considered as well, which would require a wider and more scientific framework to the research program, which was not the purpose of this study.
The recording of the air temperature only, however, gives a clear picture of the tendency and it has to be kept in mind that the real differences are larger than the results would suggest.
List of examples and main focus
In this chapter the following examples and construction systems are studied and compared:
1. Hot-arid zone
Experiment in Ghardaia, showing the influence of night ventilation.
2. Hot-arid zone
Computer-simulations in Ghardaia, demonstrating the influence of many variables separately.
3. Hot-arid zone
Buildings in Orissa, comparing the performance of fibre concrete tiles (FCR) in single and double layers, of clay tiles, and of buildings with differing storage mass.
4. Hot-arid zone
Experiment in Cairo, comparing a well-designed mud structure with a concrete structure of very poor design.
5. Hot-arid zone
Buildings in the Dominican Republic, comparing four different roofing alternatives: corrugated iron sheeting, palm leaves, micro-concrete tiles (MCR) and a brick vault.
6. Temperate zone
Buildings in Kathmandu: houses of good quality, making proper use of the suns radiation, compared to poorly designed concrete box type houses. Also the effect of a passive solar floor heating system is described.
7. Temperate zone
Buildings in New Delhi, India; well-designed mud structures compared to well-designed conventional concrete/brick structures; and comparing fibre concrete roofing (FCR) and asbestos roofing.
8. Temperate zone
A possible solution for a movable louvre system, which can be manufactured in local workshops without sophisticated equipment.
Mountain hut in Langtang National Park, Nepal: a rather sophisticated trial with a solar wall in a difficult and remote situation, under high-alpine conditions.
No example in warm-humid zone
In the warm humid zone the air temperature is rather even throughout the day and throughout the seasons. The indoor air temperature thus hardly fluctuates at all. The main objective of adapted construction is to improve the climate by proper air circulation and its influence is, therefore, difficult to assess. Recording the indoor temperature provides little information. This is the main reason why this zone is not represented by an example.
The main points:
· With controlled ventilation (night ventilation only) full advantage can be taken of the lower night temperatures.
· The ventilation during nighttime has only a minor effect on the daytime temperature.
· The gypsum construction keeps the temperature at a very even level.
Source: Research project by Lund University, (LCHS) and CNERIB, Algeria, carried out by Hans Rosenlund and Djamel Ouahrani. [ 101, 157 ]
4.1.1 Geographical location and climatic characteristics
Ghardaia lies in an extremely hot and arid region in the desert of Algeria, 600 km from the coast, at an altitude of 500 m above sea level and a latitude of 31.5o North.
The climate is hot and dry in the summer with temperatures variation between a maximum of around 45°C and a minimum of 20°C, thus giving a large diurnal temperature swing. Winter temperatures vary between a maximum of 24°C and a minimum of 0°C. Solar radiation is intense throughout the year with a maximum of 700 W in winter and 1000 W in summer, measured on the horizontal surface.
4.1.2 The project
In 1981, an experimental building was erected in Ghardaia. The purpose of the building was to measure the influence of different parameters on the indoor climate. The building contains two identical rooms, where one room can be manipulated while the other is kept as reference. A series of tests was conducted.
The building has walls of gypsum blocks, 40 cm thick; a roof of gypsum mini-vaults, 8 cm thick, resting on concrete beams and covered with 5 cm thick concrete plaster; and a concrete floor resting on the ground.
A characteristic feature of the building is the ventilation box consisting of a raised roof with an upper window.
Fig 4/1 Plan, section and elevation of the experimental building
4.1.3 Influence of night ventilation
One experiment was to monitor the influence of night ventilation. In the reference room the window and roof ventilator were kept closed, whereas in the experimental room they were opened during nighttime. The effect of the night ventilation is clearly seen as a remarkable drop in temperature when the window was open. During the night the indoor temperature approaches the outdoor one. This means that the number of air changes per hour is important.
Fig 4/2 Influence of increased night ventilation, measured air temperatures in the middle of the rooms
4.1.4 Performance of gypsum
During the daytime the temperatures in both rooms vary only slightly, which means that with this type of construction the cool of the night can hardly be maintained during the next day. The temperature is remarkably even throughout the day. This can be explained by the properties of the massive gypsum construction, which has medium thermal storage capacity but rather good thermal insulation value. Therefore, the exchange of heat between the air and the surface is small and, when the windows are closed, the indoor temperature is even. This structure performs in a similar way to the mud house documented in chapter 4.4.
The main points:
· Daytime overheating can be eliminated by internal storage mass
· Reflective outer surface color reduces the indoor temperature.
· The cooling effect of continous ventilation depends on the structure (heavy or light) and the outdoor temperature.
· A reduction of the ventilation rate during the day is only advantageous in the case of a heavy structure (with high thermal capacity).
· Thermal insulation decreases the indoor temperature in the hot season and increases it in the cold season. This is especially the case for surface temperature.
· The influence of the window size is higher in the case of a light structure than in the case of a heavy structure.
· The influence of double glazed window panes is negligible.
Source: Parametric study by Lund University, (LCHS) and CNERIB, Algeria, carried out by Hans Rosenlund.[ 156 ]
4.2.1 The simulation configuration
The geographical location and climatic characteristics have already been described in chapter 4.1.1
In this example a model building has been simulated by a computer program, where the influence of various parameters on the indoor temperatures were examined. The project was carried out within the framework of the research cooperation Building in Hot and Arid Climates between Lund University, Sweden (LCHS) and Center National dEtudes et de Recherches Integres du Batiment (CNERIB), Algeria. The principal researcher was Mr. Hans Rosenlund. The simulation program used was JULOTTA (Kllblad 1986).
The building model chosen for this study is a two story row house. The performance of the upper floor of the middle section of the house is calculated, with a width of 7.2 m and a depth of 10.2 m. The main facade can be varied with respect to window size and the depth of the horizontal projecting roof slab above the windows.
Fig 4/3 Section and facade of the two story house
The basic types
Two basic types of structures are examined: a heavy one and a light one.
The light structure consists of outer walls and roof of light, insulated timber and mineral wool 54 mm thick (U-value = 0.83 W/m²K), with negligible internal thermal storage capacity. The window covers an area of 5.23 m².
The heavy structure, which acts as a thermal storage with a capacity equal to 100 m² of 200 mm concrete, consists of heavy outer walls and roof of 200 mm concrete (U-value = 3.0-W/m²K). The window measures 3.34 m².
In both cases, no roof overhang above the windows, and an air change of 1.1 per hour is calculated.
The absorptivity of the outside of the walls and roof is 80% (a = 0.8) for the case in Chapter 4.2.2; for the cases in Chapter 4.2.4 - 4.2.7 the absorptivity is 20% (a = 0.2).
The internal heat load assumed is about 400 W at nighttime between 6 pm and 8 am, and 200 W during daytime.
The variable parameters
Based on the calculation of the thermal performance of the basic types, a number of variables have been introduced and their influence on the thermal performance calculated:
a) Influence of internal storage capacity
b) Influence of outer color of walls and roof (reflectivity)
c) Influence of continuous ventilation
d) Influence of reduced ventilation during daytime
e) Influence of thermal insulation on air temperature
f) Influence of thermal insulation on ceiling surface temperature
g) Influence of number of window panes
Restrictions and purpose of the study
The main results of this parametric study which are summarized hereafter, give a somewhat theoretical picture. In reality the indoor climate is always influenced by a combination of these factors as well as other factors. Simply adding the various influences of the parameters is not possible. Also, the human factor is not considered, i.e. the unreliability of controlled ventilation, which depends on the active participation of the inhabitants. Furthermore, the JULOTTA-program does not sufficiently incorporate the influence of radiation to the night sky, thus giving slightly too high indoor temperatures. The results therefore do not represent real indoor temperature figures.
It also has to be kept in mind that the building chosen represents a general model which is not adapted to the climatic conditions of Ghardaia at all.
However, the results can be used to judge the importance of the different parameters and to estimate their effects, positive or negative, strong or weak.
4.2.2 Influence of internal thermal storage capacity
Results of 4.2.2
As Fig 4/4 a) and b) show, on a hot day the maximum temperature can be significantly reduced with the help of the thermal mass of the whole structure. The internal thermal storage mass is cooled down during the night by an increased ventilation (10 air change per hour). Thus, during the day, when the ventilation rate is lower (1.1 air change per hour), the internal mass maintains a lower indoor temperature. The increased internal mass, however, means a slightly higher night temperature.
An interesting comparison between the heavy and the light structure house is that, in the former, the time lag of the heavy outer walls causes the temperature to rise to a maximum of 43.5°C as late as at 6 pm. In the light structure house, with internal mass, the maximum temperature is lower, 40.9°C, and occurs earlier, at 3 pm. The high altitude of the sun makes the difference in window size less important, while the effect of roof insulation in the light structure house is obvious.
The negative effect of the non-insulated concrete roof in the heavy structure is clearly seen in the case without internal heat storage mass, with a temperature rising up to 49°C towards evening and only dropping then, due to the increased ventilation that starts at 9 pm.
Fig 4/4 c) and d) show that on a cold day an internal mass decreases the variation in temperature while the average temperature remains the same. This phenomenon is more pronounced in the light structure house, being more affected by the solar radiation through the bigger windows.
The relatively high average indoor temperatures are a consequence of the assumed internal load, the low air change rate and the solar heat radiation gain. Moreover, the result is slightly falsified because of the radiation losses to the night sky that are not sufficiently considered in the calculation program.
As a consequence, the internal thermal storage capacity of the building, not being exposed to solar radiation, is an important means of increasing winter night temperatures and decreasing maximum temperatures during the hot season.
4.2.3 Influence of outer color of walls and roof
A lower absorptivity - or a higher reflectivity - results in generally significantly lower indoor temperature, both in the heavy and light structure houses. The heavy structure house also has clearly lower night temperatures due to decreased heat storage of solar radiation in the outer walls and roof. For the same reason the variation between day and night temperatures is smaller.
4.2.4 Influence of continuous ventilation
Conclusion for 4.2.4
Fig 4/6 a) and b) show that an increased continuous ventilation causes the indoor temperature to approach the outer one. This means - in the heavy structure house - a decreased night temperature, while the maximum temperature, being lower than the outdoor one, increases with the increased ventilation rate. The light structure house, with low thermal storage capacity, generally has lower indoor temperatures with the increased ventilation rate, due to the fact that the indoor temperature exceeds the outdoor one at all hours.
During winter, the indoor temperature can be increased by a decrease in ventilation rate.
4.2.5 Influence of reduced ventilation during the daytime
Conclusion for 4.2.5
Fig 4/7 displays the difference between a permanent ventilation of 10 air changes per hour and a ventilation reduced to 1.1 ach during the daytime. In the heavy structure house, the day temperature decreases with reduced day ventilation. In the light structure the opposite is the case.
As a consequence, reduced day ventilation is only advantageous in heavy structures. In other words, the advantage of storage mass is only fully exploited if combined with reduced ventilation in daytime.
The case of a very cold day with the same variation in ventilation rates is not relevant.
4.2.6 Influence of thermal insulation on air temperature
Conclusion for 4.2.6
Fig 4/8 a) and b) show the importance of roof insulation especially during the hot period when the solar radiation effect is at its greatest. Both structures - the heavy and the light one - perform better with increased insulation, but the light structure house has higher temperatures and a wider range. The heavy house has lower night temperatures with increased insulation due to internalization of mass which makes it more efficient in combination with night ventilation.
In the cold season, the heavy structure house has generally higher temperatures due to increased insulation, while the light one has lower maximum, but higher minimum temperatures.
4.2.7 Influence of thermal insulation on ceiling surface temperature
Conclusion for 4.2.7
During the hot season, the ceiling temperatures are equally decreased by roof insulation. The heavy roof has an almost constant temperature around 36°C. Without insulation the surface temperature of the heavy roof rises up to 42°C. This is a rather modest value, due to an assumed high reflectivity (a = 0.2). A normal grey concrete surface exposed to solar radiation would result in an inner surface temperature far above 50°C. The light structure case shows much higher maximum values due to the absence of mass.
During the cold season, the ceiling surface of the heavy structure house generally has higher and more even temperatures with increased insulation, while the light house has higher minimum, but lower maximum temperatures.
4.2.8 Influence of size of south facing windows
Comparing the cases of windows measuring 3.2 m² and 10.4 m² respectively, the indoor temperatures differ during the cold season. In the case of the heavy structure, a larger window results in an increased air temperature of 2 - 4°C. In the case of the light structure the increase is up to 6°C.
During the hot season the differences are negligible. The reason for this is that the direct radiation hardly reaches the window area and for small angles of incidence, most of the radiation is reflected. Furthermore, the portion of diffuse radiation in this climate is very low in July.
4.2.9 Influence of number of window panes
If the effect of double glazing is also calculated; a double glass sealed with 12 mm air space between the panes is studied. In both cases of the heavy as well as the light structure house, the influence of the double glazing is less than 0.4°C and can be neglected. This applies to both winter and summer. The only remarkable difference lies in the inner surface temperature of the window.
Where indoor and outdoor temperatures are similar, the main heat transfer through windows is by radiation which is only marginally affected by a second pane.
4.2.10 Concluding recommendations
· A high internal thermal storage capacity is essential to decrease temperature variations and to profit from an increased night ventilation.
· A white outer surface or a heavily ventilated double roof construction is necessary to prevent the solar radiation penetrating the building structure, especially the roof, during the summer when the angle of the sun is high.
· Southern windows of moderate size receive a great deal of the solar radiation during the cold period, while during summer they are rarely exposed to direct radiation. However, during spring and fall, when temperatures are still high and the angle of the sun is less, the quantity of solar radiation through windows can be considerably higher and needs to be considered, e.g. additional shading devices would be needed.
· The ventilation rate should be kept as low as possible during the winter period. However, due to hygienic reasons, the ventilation rate must not be too low. Another problem which could occur is condensation, especially in the case of structures with a relatively low internal surface temperature in combination with rooms with a high rate of added vapour such as kitchens.
· During summer nights the ventilation should be increased as much as possible by catching the wind or using stack effects. In the daytime, when the outdoor temperature exceeds the indoor one, the ventilation rate should be kept to a minimum. The internal mass thus retains the cool of the night until daytime.
· A good roof insulation is preferable to protect the building from the intense direct solar radiation during summer. The effect of wall insulation is, however, negligible in the hot period, as long as the house has a significant internal storage capacity. Insulation of east and west wall can be considered.
· In the winter an external insulation is very efficient in raising indoor temperatures to acceptable levels. The outer walls could even be of a lightweight and well insulated construction if the building has a considerable mass.
· However, insulation is normally scarcely available and/or expensive. Efforts should be made to develop local insulating building materials in desert regions.
The main points:
· Unprotected southern walls lead to overheating.
· FCR (Fibre Concrete Tiles) and clay tiles perform similarly.
· Double layer of tiles has no significant influence on the indoor air temperature, but certainly on the surface temperature which is not monitored.
· Buildings with a high storage mass are clearly warmer at nighttime, but not much cooler in daytime because of the high ventilation rate.
Source: AMG India International Leprosy Rehabilitation Centre,
Monitoring of performance: H.U. Lobsiger
4.3.1 Geographical location and climatic characteristics
Shanti Nagar lies in a hot and arid region in India, 220 km from the coast, at an altitude of 400-m above sea level and a latitude of 20o North.
The climate is hot and dry in the summer season (March to June) with temperature variations between a maximum of around 50°C and a minimum of 20 - 30°C, thus a large diurnal temperature swing. Winter (November - February) temperatures vary between a maximum of 20 - 30°C and a minimum of 4 - 10°C. Measurements were taken in March 1990, when the outdoor temperature varied between 21°C at night and 35°C in daytime.
4.3.2 The monitored buildings
The four houses that were compared are all residential buildings of single story structures.
Fig 4/10 House 1
· Ratio window to floor area:
· Walls: Brick, white plastered on outside, 30 cm;little sun protection on the southern side.
· Roof: Clay tiles
· Ventilation: Good
· Floor: Mud
· Ratio window to floor area:
· Walls: Brick, white plastered on outside, 40 cm.
· Roof: Double FCR sheet with 8 cm ventilation space (FCR = Fibre Concrete Roofing, 10 mm thick).
· Ventilation: Poor to moderate
· Floor: Mud
Fig 4/12 House 3
· Ratio window to floor area:
· Walls: Brick pillar structure with clay infill, 40 cm; outside color brown.
· Roof: Single FCR sheet
· Ventilation: Moderate
· Floor: Mud
Fig 4/13 House 4
· Ratio window to floor area:
· Walls: Brick pillar structure with clay infill, 40 cm; outside color brown, large storage mass.
· Roof: Single FCR sheet, alternatively clay tiles
· Ventilation: Moderate
· Floor: Mud
4.3.3 Climatic performance and conclusions
· During the daytime, house 1 is clearly hotter than all the others, up to 6°C. This is mainly due to the unprotected southern wall and window with very little roof overhang. The reduced thermal storage capacity and insulation of the outer walls (thinner walls) are also contributing factors.
· No difference could be observed between FCR roofing and clay tile roofing.
· Although no clear difference between double FCR sheeting and single sheeting could be observed, there is a clear advantage with double sheeting because of the lower inner surface temperature. This was not measured, but observation by the inhabitants supports it. Moreover, recent research works at the CECAT in Habana, Cuba, have shown, that in such a case the inner surface temperature of a ventilated double sheeting construction is lower by approximately 8°C.
· At night all houses perform similarly and have a temperature about 6°C higher than the outside temperature. This is due to the relatively high thermal storage capacity. House 1 with the least storage capacity is slightly cooler. With increased night ventilation it might be possible to decrease night temperatures.
· Houses with mud-walls are clearly superior in the daytime compared to brick structures because of the larger storage mass and also because they are less ventilated. The performance at night could be further improved by increased ventilation, but the inhabitants are not concerned because they sleep outdoors.
The main points:
· A concrete structure of extremely poor design is compared to a well-designed mud structure.
· In contrast to the mud structure, the performance of the concrete structure is drastically different, being very hot in daytime and cold at night.
· The difference is obvious both for the air temperature and for the surface temperature.
Source: Research group under the leadership of John Norton, Development Workshop, Lauzerte, France
4.4.1 The project
Cairo lies in a maritime desert region. It is only a few metres above sea level and at a latitude of 30° North.
In the 1970s, several experimental rooms were constructed at the Building Research Center in Cairo to test prototype building solutions for poor rural areas in developing countries. Among the rooms built was one of mud brick vault and dome construction and another of prefabricated concrete slab construction, illustrating the contradictory proposals for rural development. One proposed a reinstatement of traditional modes of construction and the other an importation of ideas and materials from outside.
The mud brick structure was built by Professor Hassan Fahty, who used similar design features in many of his projects.
The researchers undertook comparative measurements of the thermal performance of these buildings. The tests were done at the end of March, thus the extreme temperatures of the climate in Cairo were not recorded. However, the results illustrate clearly the different performances of the two test rooms. Since each test room was built in an open space by itself, and each is oriented in the same direction, they can be considered to be affected by the same climatic factors and thus directly comparable.
4.4.2 The experimental buildings and test configuration
The prefabricated concrete test room consists of light weight concrete block walls 15 cm thick and a roof made of reinforced concrete with a prefabricated roof panel system.
Fig 4/15 Prefabricated concrete test room
The mud brick room consists of a lime stone foundation, walls of sun dried mud bricks 50 cm thick and a roof with a dome and vault shape made of the same material.
The first step in the recorded experiment was to close the doors and windows of the two test rooms. The house stayed closed for at least 24 hours to allow the air temperature in the rooms to stabilize and not be constantly renewed by air movement and wind. In this way the influence of heat transfer through the shell could be studied in an undisturbed manner.
Fig 4/16 Sun dried mud brick vault and dome test room
4.4.3 Climatic performance
Fig 4/17 Air temperature
Fig 4/18 Inside surface temperatures at concrete room (left) and mud brick room (right),
The tests show an impressive difference in the performance of the concrete structure and the mud structure. Whereas the temperature in the mud structure fluctuates by a few degrees only, in the case of the concrete structure the temperature varies between extremely high and very low. In practice, the difference may be somewhat less because air changes would increase the fluctuation of the temperature in the mud room; however, a clear difference would still remain.
As well as the air temperature the surface temperatures of the walls and the ceiling have to be noted. The temperatures on the outer surface (not shown in the graphs) are similar in both cases, but the temperatures on the inner surface are as drastically different as the air temperatures. This is an important factor because radiant heat from inner surfaces adds considerably to the comfort level. Furthermore it demonstrates the effect of the high thermal resistance (U-value) of the mud wall.
This example illustrates that a heavy structure with thermal properties similar to the mud room tends to have indoor temperatures close to the average outdoor temperature. As a consequence, such a room would need daytime ventilation during the cold period and nighttime ventilation during the hot period. In this way, an all year round acceptable indoor climate could be provided.
The lightweight structure, on the other hand, can hardly be regulated by ventilation because its storage capacity is not sufficient to store the heat surplus of hot days until nighttime in winter, and to keep the cool of the night until daytime in the summer. Such a structure would, however, be suitable as a temporary room, to be used alternatively at nighttime during the hot period and in daytime during the cold period.
The concrete structure monitored here is, of course, of extremely poor design. It cannot be concluded that modern structures in general would perform the same way. As seen in Example 4.7, a modern structure can also perform similarly to a mud structure, if it is well designed and sufficiently insulated.
The main points:
· The corrugated iron sheet roof is extremely hot in the daytime.
· Palm leaf roofs and MCR roofs perform similarly.
· The vault roof is warm in the morning, evening and night, and similar to MCR and palm leaf roofs in the daytime.
· The measured differences are smaller than subjectively perceived, probably because the variation of the surface temperatures are higher.
Source: Grupo Sofonias, Kurt Rhyner-Pozak and Martin Melendez
4.5.1 Geographical location and climatic characteristics
The monitored houses are in the south of the Dominican Republic (Province of San Juan) where the climate is semi-arid with hot and strong winds.
The diurnal temperature range is extremely wide. In the hot season the temperature rises up to 50°C and drops at night to about 20 to 30°C, in the cool season it fluctuates between 30 to 35°C in the daytime and around 20°C at night.
4.5.2 The monitored buildings
The indoor air temperatures in four different houses were monitored
House A : Palm leaves
A simple hut which is typical for the poor segment of the population, with walls wooden of wickerwork plastered with mud and a roof of palm leaves. The wind blows rather freely through the house.
House B : CGI
A house with walls of wooden boards and roofed with corrugated galvanized iron sheeting. The wind blows rather freely through the house.
House C : Vault
The Sofonias Project House consisting of massive walls of stone or brick masonry with a 8 cm thick vault roof made of bricks
House D : MCR
A house with masonry walls roofed with micro-concrete tiles.
Fig 4/19 Plan and front elevation of house C
4.5.3 Climatic performance
Fig 4/20 Performance in the hot season
Fig 4/21 Performance in the cool season
This section illustrates clearly the influence of different roofing materials.
It is not surprising that the metal roof performs worst, being clearly the hottest in the daytime and the coldest at night.
The difference between the other three materials appears not to be very significant. Palm leaf and MCR roofs are very similar. The palm leaf roof is slightly warmer, most probably because of the generally poor quality of the building.
The brick vault roof keeps the house much warmer at night, and the time lag in the evening is clearly seen. In daytime it performs similarly to the palm leaf and MCR roof, although subjective feelings would suggest that it is cooler in daytime. The reason might be that the surface temperature of the vault is lower.
The diurnal temperature swing in the vault house is smallest, but still much larger than in the examples in Chapter 4.1 and 4.4. This can be explained by the rather thin brick structure of 8 cm .
Fig 4/22 House C, perspective view
The main points:
· In buildings with adequate storage mass, insulation and control of solar radiation, the temperature is acceptable in summer and winter, except for cold nights where an additional heating source is required. This is in sharp contrast to poorly-designed buildings.
· A well-designed building is up to 7ºC cooler in summer than the poorly-designed concrete box.
· A floor heating system with passive solar collectors - the collectors measuring 1/3rd of the floor area - increases the temperature in winter by 10°C.
Source: Paul Gut
4.6.1 Geographical location and climatic characteristics
Kathmandu lies at an altitude of 1350 m and a latitude of 28o-North. It is situated in a wide valley of about 20 km circumference, surrounded by hills reaching up to 3000 m height.
The climate is characterized by three main seasons:
· In winter-time temperatures are relatively low, ranging between 0°C at night and 15 to 20°C in the daytime. Sometimes light frost appears over clear nights. The cold air lake phenomenon, which is typical for a valley location like Kathmandu, keeps temperatures between December and February uncomfortably low. However, the frequent and strong solar radiation, which is common during this season, improves the situation and provides an excellent opportunity for passive solar room conditioning.
· The pre-monsoon season is hot and dusty, mainly in May and the first half of June. Temperatures rise up to 35°C in daytime and drop to around 20°C at night. The solar radiation is often intense, and protection is required. During this season dusty storms are frequent.
· During the monsoon season temperatures hardly reach 30°C and the diurnal differences are less. Periods of pouring rain and heavy clouds alternate with periods of clear sky and glaring sunshine. The humidity is high and proper ventilation is required.
Considering the climatic conditions which change drastically with the seasons, the design concept of a building should respond to these differences.
Cold season requirements
Passive solar heat gain is welcome during the cold season. The main rooms and the large windows should be south oriented. To provide an acceptable indoor climate in winter, buildings usually require active heating as well, unless they are very well designed and equipped with special passive solar heating devices. The heat storage capacity should be moderate, not too excessive; otherwise the space becomes non-heatable. Airtight construction is another important aspect; it is more important than the thermal insulation properties. Inner surfaces should not be highly conductive which would result in low surface temperature and uncomfortably high conductive heat losses from the human body when in contact.
Hot season requirements
During the hot season protection against solar radiation is necessary. Windows should be shaded and a proper cross-ventilation should allow accumulated heat to escape in the evening. Here again, a moderate heat storage capacity is appropriate, keeping the daytime indoor temperature at tolerable levels.
Special care is required in the design of the roof. Its inner surface should not heat up too much and it should not store much heat. The worst solution is the plain concrete roof slab, which is a common solution these days. It heats up to extreme temperatures and makes living conditions during the evening unbearable.
During the monsoon period the most important factor is cross-ventilation
4.6.2 The monitored buildings
To illustrate the effect that different design features have on the indoor climate, two different buildings have been evaluated under winter conditions (building A and B).
In the summer season the performance of two additional buildings has also been recorded. (buildings A, B, C and D).
A modern residential house, located on a southern slope with mainly south-oriented rooms. The main windows also face south and are partly protected by overhangs from the summer sun. The walls consist of 35 cm thick solid brick masonry; fair-faced outside and inside, with lime white wash on the inside. The floors are made of timber beams supporting brick vaults, covered with clay flooring tiles. The roof is pitched, covered with clay tiles and with timber panelling inside.
The windows are made of specially well seasoned timber (timber from a dismantled old building) and are built with double grooves for air tightness, equipped with imported fittings.
An interesting feature is the solar floor heating system in the living room which works entirely passively as a thermo-syphon, even without a regulatory mechanism. The system is described in more detail at the end of this chapter.
(Mana Niwas, Arch: P. Gut, built in 1980)
Fig 4/23 Building A
This is an office building, hence only the thermal performance in daytime is of relevance. Of special importance is a increased temperature during the winter mornings, when most buildings are freezing cold and non-heatable, thus it becomes extremely difficult to work in.
As a consequence, all offices are located on the main front which is oriented south-south-east. This elevation is designed in such a way that all windows receive winter sun, from sunrise to sunset. During summer an overhanging curved slab shades the windows entirely. Deciduous trees in front of the building help to control the effects of the sun.
The walls consist of 35 cm solid brickwork, the floor slabs are of concrete and the flat roof is additionally covered with a 5 to 10 cm thick screeding and clay tiles.
(National Parks Department Headquarter Building, Arch: P. Gut, built in 1981)
Fig 4/24 Building B
This old palace with small windows and massive, 70 cm thick brick walls. Floors are of timber structure with a thick layer of mud covered with clay tiles. The room monitored is south facing.
This building is a modern bungalow of international concrete box type. The walls are of 35 cm brick masonry, the windows are rather large with only minimal protection from the summer sun. The roof slab is of 12 cm plain concrete without any cover. Climatic considerations were not applied.
This type of building is the most common solution for modern development in Kathmandu, as well as in many other places in the developing world.
4.6.3 Climatic performance and conclusions
Fig 4/25 Climatic performance in early June, the hottest period of the year
The outside temperature varies between 19 and 34°C, hence the average temperature more-or-less lies within the comfort zone.
The buildings B and C show the most even temperature swing, slightly above the average temperature. This is due to the consistent shading of the windows in the case of building B and due to the excessive heat storage capacity of building C.
Building A shows somewhat higher daytime temperatures because of windows facing east and west which are less protected against solar radiation. These windows, on the other hand, allow for a better ventilation at nighttime, resulting in more comfortable conditions during the night.
Clearly worse is the performance of building D. Due to poor protection of the windows against solar radiation, and mainly due to the non-insulated flat concrete roof, temperatures constantly lie above the outside temperature and above comfort level. Characteristically, the temperature remains high during the evening, the greatest difference, compared to building A, reaches 7°C at midnight. In addition to the high air temperature the high surface temperature of the concrete ceiling has to be considered, which is not expressed in the diagram. The inner surface of such concrete roofs reaches temperatures up to 50 or 60°C, resulting in unbearable indoor climatic conditions due to radiant heat.
Fig 4/26 Climatic performance in January, the coldest period of the year
Whereas the outdoor temperature varies between -2°C and 16°C, the temperature in an unheated, west facing room in house A is rather even, at the uncomfortable low level of 6 to 10°C.
During the day the temperature of house B lies at about 5°C above this level due to the consequent utilization of direct solar heat gain through the windows. The temperature during working hours for an office building is still low but bearable, due to the direct solar radiation in the rooms.
The living room of house A, which is equipped with a solar floor heating system, performs well with temperatures about 10°C higher, thus lying within the comfort zone. The surface temperature of the floor, which varies between 20 and 28°C, is a further contribution to the comfortable climate.
4.6.4 The solar space heating system
House A is equipped with a passive floor heating system. It heats the main living room during the unpleasantly cool winter months. The system consists of a flat water heating solar collector situated in front of the room at a lower level. It works entirely passively on a thermosyphonic basis, without a pump and even without regulating instruments. As experiences over 10 years have shown, the system works extremely reliably and gives no problems with regard to maintenance.
The total collector surface measures 9 m², that is 28% of the floor area of the heated room. In January the total solar energy received by the collector amounts to about 5 kWh/m² per day with a peak of 900 W/m².
The collector is divided into 8 elements, each working independently with a separate steel pipe loop laid in the floor of the room. These 8 loops, although covering the entire floor area, are short and thus guarantee a reliable circulation of heated water. The only mechanical parts of the system are the three-way valves which are necessary to switch from winter to summer operation. Each of the 8 collector elements can be individually controlled; thus a fine regulation of the system is possible.
During the warm seasons the collected heat is diverted by these valves to a boiler which is equipped with a heat exchanger, providing pre-heated water to the electric drinking water boiler.
Except for the three-way valves, all parts of the system are produced in a local workshop. This suggests a low technological level resulting in a probably somewhat lower efficiency, compensated by the dimensioning of the collector surface. On the other hand, this has kept costs down to a reasonable level.
The adjoining structural elements are also of local manufacture, without imported insulation materials. The floor structure consists of a layer of boulders covered by a 40 cm thick layer of brick waste collected from the construction site. On top of this the heating pipes were laid in sand and carefully levelled to avoid backslope. Clay flooring tiles laid in a concrete screed form the floor finish.
This structure provides a moderate heat insulation and a large thermal mass resulting in a very inert thermal performance. Overheating of the room and also of the floor surface is avoided. The floor surface temperature never rises above 30°C.
Fig 4/27 The solar space heating system
The main points:
· A well-designed mud structure with arches, domes etc. performs similarly to a well-designed and insulated modern concrete/brick structure.
· Asbestos shhet roofing and fibre concrete roofing are hot in daytime and cool at night. In winter they are clearly too cool. Additional insulation would be appropriate.
Source: Development Alternatives, New Delhi, monitoring by Dr.-Arun Kumar, Vaidyanathan Geeta, Sanjay Prakash
4.7.1 Geographical location and climatic characteristics
New Delhi is located on the plain at an altitude of 200 m above sea level and a latitude of 28o North.
The climate is characterized by a hot and dry season in early summer determined by hot winds from the Thar desert in Rajasthan, with temperatures between a mean maximum of 32°C and 43°C and a mean minimum of 21°C to 27°C. In winter the cold, northern winds from the Himalayans dominate the climate. The temperature fluctuates between 20°C - 27°C in daytime and 4°C - 10°C at night. In between these two extremes there is a period of moderate temperatures. This includes the monsoon period during which the humidity is very high and most of the precipitation falls.
4.7.2 The monitored buildings
During the two climatically extreme seasons several building systems were monitored.
Various rooms of the headquarter building of Development Alternatives have been examined. The complex is located in the vicinity of a green belt in the Institutional Area of southern Delhi. The overall character of the building is determined by its strong roof forms which are a result of the materials used, mainly unburnt earth in the form of adobe and stabilized soil blocks. Many different systems have been applied in the building such as domes, vaults and also flat roofs. The walls are made of soil blocks laid in mud mortar, 23 to 35 cm thick. Floors are made using various options: sandstone slabs on concrete beams, prefabricated concrete jack arches or concrete slabs. Window openings are relatively small, just sufficient for natural lighting. They are arranged to allow a proper cross-ventilation. (Description of the building project see [ 160 ] )
Fig 4/28 General view
By comparing the thermal performance, two rooms give interesting results:
A room with a Nubian vault made with adobe blocks of 12-cm thickness, rendered on the inside with a lime-based plaster of a natural brown color and on the outside with a regular 15 mm cement plaster over a chicken wire mesh as a waterproofing membrane. The room is exposed to the outside on three sides, the side walls face north and south. The outer shell is painted white and contributes to the solar radiation reflectance.
Fig 4/29 The Nubian vault, room-A1
A room with a roof made of jack arches of 12 cm thick stabilized soil blocks. The arches rest on concrete beams and are covered with 10 cm lime and brick bat concrete, followed by a coat of marble dust in lime water and then a nominal layer of cement-based plaster. Further waterproofing has been achieved using a bitumen based compound. The outer shell has been painted white.
Only a small portion of the walls is exposed to the outside, on the S-W side and on the S-E side.
Fig 4/30 Jack arch, room A2
Fibre Concrete Roofing (FCR) / Corrugated Asbestos Cement roofing (ACC)
The Micro Model Unit of the Indian Institute of Technology was also selected for this study. It is located in a fairly low density area with a lot of open space. The monitored room is oriented along the east-west axis and is exposed on three sides to the weather. The structure consists of a load bearing frame made of burnt brick with soil block infill, 23 cm thick, rendered with mud plaster. The windows are fairly large, because the room is used as an architectural studio which requires good natural lighting. The roof consist of a timber structure covered with 8 mm thick Fibre Concrete Tiles. There is no ceiling. The floor slab is of concrete.
A similar structure with a corrugated asbestos cement roofing was also monitored. However, the performance was similar to that of FCR.
Fig 4/31 Building B
This is a conventional concrete and brick structure with flat roof. The building accommodates the Working Womens Hostel Prabhatara and is located in a residential area. It consists of a concrete slab and frame structure with 23 cm thick brick walls, Fare faced on the outside and cement plastered on the inside. The room selected is located on the top floor with the east and north walls exposed, while the south side opens onto a corridor. The west wall is shared by an adjoining room.
The roof is a flat concrete slab, 10 cm thick, with a waterproofing 20 cm thick, including the base concrete and brick tile finish. The window opens towards the corridor on the south side which is open at each end. The space below the test room is an open passage.
Fig 4/32 Building C
4.7.3 Climatic performance and conclusions
Fig 4/33 Performance in summer
· The indoor temperatures are generally very high compared to the performance monitored in the Dominican Republic (4.1.5). This can be attributed to the fact that while the Dominican Republic is a coastal area, New Delhi is land-locked and there is no appreciable cool night breeze flowing from the sea, as would be the case in coastal areas.
· The light roof (FCR / ACC) becomes hot in the daytime and cools down at night (damping effect 0.7) compared to heavy structures (damping effect 0.3). The daytime temperature is similar to the outdoor temperature.
· The jack arch room is generally hotter than the vault room, probably because the former is a more enclosed room. The ratio of surface area to volume being smaller for the Jack arch roofed room, the heat loss at night is less, resulting in the room being hotter.
Fig 4/34 Performance in winter
· A well constructed conventional building (Prabhatara)performs similarly to the earth construction with vault or jack arch.
· Heavy structures have almost no temperature variance between day and night.
· Light roofs become slightly warmer in the daytime, but much cooler at night.
During this study, some isolated recordings of the surface temperatures have also been carried out. These could not be included in the presentation because they are not comprehensive enough. However, in addition to its importance with regard to thermal comfort, it has been clearly shown that surface temperature readings would provide more reliable information about the qualities of a wall or roof system because the air temperature and its time lag is heavily influenced by the variables of door and window openings.
Design: P. Gut
The climatic conditions in Kathmandu (see Chapter 4.6) with warm summers and cool but sunny winters suggest itself, to improve the indoor climate by simple means of solar radiation control.
For this purpose, a simple system of movable metal louvres has ben designed in such a way, that local mechanical workshops can easily manufacture it, thus expensive, imported parts are not required.
The louvres can be operated through the open window by simply shifting a metal bar linkage. The louvres can be arrested in two positions, for summer and winter. The winter position allows to enter the solar radiation unhindered, whereas the summer position shades the window completely.
Because the climate in Kathmandu is regular, it is assumed, that the louvres have not to be moved often, but not much more than once in spring and once in fall.
So far, the performance of this system could not be monitored, because the buildings are (in 1992) still under construction.
Fig 4/35 Summer and winter position
Fig 4/36 Mounting support, isometric view
The main points:
In spite of its sophisticated design the building does not fully fulfill expectations, because:
· the system of heating air by a
passive solar collector is not efficient enough;
· the users are generally careless about heat conservation and do not close doors.
This house was built in 1979, at an altitude of 4000-m. The southern elevation is fully glazed, consisting of 1/3rd windows and of 2/3rd solar collectors as a solar wall for space heating. Because of the severe climate at this altitude (below zero) the collectors were designed as air heaters.
Other climatic design features were also applied:
· Curved south front for wind
· Buffer zones on east and west side
· built-in to the slope on the north side
Experience has shown that the concept was not fully successful:
· The human factor was not sufficiently considered; for instance the outer doors were never closed.
· Mice had blocked the air-ducts with rice which they collect and store in the inaccessible parts of the ducts.
· The efficiency of air-heating compared to water-heating systems is low.