The passive solar house is an ancient concept in architecture and describes a way to design a building giving due consideration to the site, climate, local building materials and the position of the Sun at the site of building construction. Now, there is a renewed interest in passive solar home design for obtaining natural heating and cooling of room air using the energy available in the immediate environment. The passive house made of mud is one of the solutions for rural habitat building constructions to conserve the energy both during construction as well as for achieving thermal comfort inside the house.

Coffman et al. [1] reported that the mud-house construction have natural air conditioning effect because the rooms are cool during daytime and warm during nighttime. The application of mud as wall material was investigated to control room air temperature for buildings by Duffin and Knowles [2]. The most common passive solar building architecture comprises of massive walls to reduce the temperature fluctuations inside a building. This is known as the thermal flywheel effect as mentioned by Duffin and Greg [3]. The popular mud-houses in Yemen city utilize this effect. The use of mud as building material is of great concerns not only for the people in hot developing countries, but also for those in cold industrialized countries in Europe and America [4]. The engineers from developed countries have realized the special features of mud as reported by Eben [4]. The wider use of mud construction has a good reputation in dry and hot places because of its distinct advantages, e.g. the mud habitat suits different weather and geographical conditions as the temperature remains temperate throughout the year inside the mud building as explained by Eben [4]. Algifri et al. [5] compared the thermal behavior of adobe house with modern concrete house in Yemen and reported the potential of mud as construction material for energy saving in passive houses. The magic of adobe houses was investigated by Miller [6].

Earth as mud bricks, has been used in the construction of shelters for thousands of years, and approximately 30% of the world’s present population still live in earthen structures as reported by Cofirman et al. [7]. Earth is a cheap, environmental friendly and abundantly available building material. It has been used extensively for wall construction around the world, particularly in developing countries reported by Ren and Kagi [8]. Binci et al. [9] investigated that home brick-makers of Turkey and the Middle East are using fibrous ingredients like straw to improve the tensile strength of mud bricks for millennia. Binici et al. [9] had investigated the thermal isolation and mechanical properties of fibre reinforced mud bricks as wall materials. Stabilized mud blocks are made in India from soil, sand, cement/lime and water. These blocks are used for making vaulted roof structure buildings as shown in Fig. 1 as reported by Reddy [10]. Roofing systems using brick masonry vaults and domes were used extensively in India till the emergence of British rule. It has several advantages as compared to reinforced slab roofing as reported by Reddy [10]. An innovation in vault was developed by Reddy [10] using a moving steel formwork (slip forming) which facilitates construction without excessive cost and time out run. Currently, catenary shaped vaults are being built due to their better performance. Both burnt bricks and stabilized mud blocks were used for building vaults and domes. More than 30 buildings were built since 1986 in and around Bangalore city in India using vaults and domes as reported by Reddy [10].

Recently, the advantage of mud-houses reported by Collet et al. [11] are reduction of energy consumption, green house gases emission, water use, waste production, etc. Thermal behavior of such low energy consuming and low carbon building having clay wall facing south was investigated by Collet et al. [11]. Hence, such mud-houses needs to be promoted especially in rural areas for the sustainable development of the environment.

Pearlmutter [12] had made the first attempt to quantitatively compare thermal behavior of vaulted and flat roofs in terms of indoor temperatures. It was shown that the vaulted roof has greater thermal stability and potentially favorable daytime temperature. Hadavand and Yaghoubi [13] had reported that the convection coefficient over vaulted roof is significantly higher on the forward side and decreases after separation on the leeward side, but its variation for flat roof is not considerable. The temperature varies along the vaulted roof during the day as a result of the auto shading of roof but for flat roof temperature distribution along the roof is nearly uniform as reported by Hadavand and Yaghoubi [13].

The numerical calculation performed by Tang et al., [14] showed that vaulted roof buildings have lower indoor air temperatures as compared to flat roof. The reason is curved roof structures dissipate more heat as compared to flat roof by convection and thermal radiation at night due to the enlarged surface area. Similarly, in this paper numerical solution of six first order linear differential heat balance equations was obtained using Runge Kutta fourth order numerical method. These numerical solutions were used to formulate the thermal model of the existing mud-house (or passive house) to predict hourly values of room air temperatures of six interconnected rooms. The predicted room air temperatures were found in good agreement with experimental data obtained on typical clear day in winter and summer months in New Delhi. Similar to the methodology of evaluation of energy saving calculations presented by Chel and Tiwari [15], the annual heating and cooling energy saving potential of mud-house was evaluated. This annual energy savings potential of passive house results in mitigation of CO₂ emission which was estimated similar to the equation presented by Chel and Tiwari [15]. The potential of earning carbon credits due to CO₂ mitigation from the energy saving potential was calculated and presented in this paper for different cities in India.

Building construction has a major role on the environment because of energy consumption for acquiring building raw materials and generation of waste during construction. Building construction indirectly emits greenhouse gases as waste. Since, environmental issues have become serious and significant; there is need for more energy efficient buildings to cut down its energy needs for operation Dimoudi and Tompa [16]. Thus, the energy required for construction and consequently for the building material production has gained greater importance nowadays. The present paper investigates the role of different construction materials and quantifies them in terms of the embodied energy and the equivalent emissions of CO₂ emissions from passive buildings as compared to cement concrete buildings. It also assesses the importance of the low embodied energy building materials such as mud for thermal comfort inside the building by estimating the energy saving potential of the mud-house in India.

The embodied energy and life cycle energy consumption were reported as key parameters for building energy assessment as reported by Casalas [17]. But these parameters are often left out of the regulation and certification proposals as reported by Casalas [17]. Hence, in this paper, the embodied energy analysis of the passive house (or mud-house) was determined and compared with results obtained by Gumaste [18] for reinforced cement concrete structure. The energy payback time for the passive house was determined and presented at the end of this paper. The input climatic data for Indian cities, e.g. solar radiation (global and diffuse) and ambient air temperature were obtain from Indian Meteorological Department (IMD), Pune which divides every month into four weather types (a–d). The thermal performance of mud-house structure was rarely reported and compared with another type of building in the literature. Hence, the present work on embodied energy analysis and thermal performance of mud-house reveals the importance of this eco-friendly and sustainable buildings in India and all over the world.