Energy retrofit analysis for an educational building in Mumbai

Some previous research:

Several authors have emphasized the energy and material efficiency of the building envelope for ensuring building sustainability. Research suggests that efforts for enhancing energy efficiency through the envelopes should take into consideration the assessment of building energy performance corresponding to different envelope designs. The different elements of a building envelope- external walls, floors, roof, ceiling, and windows determine the energy required for heating and cooling a building, thermal comfort, ventilation, and lighting. There are several strategies for improving building energy efficiency through these envelope components. In the following sections, the study explores the approaches that are new, sustainable, and can be easily used in retrofit constructions. These energy-efficiency measures which can be applied to an existing building include improvement in thermal insulation and performance of windows, using green roofs, increasing the façade shading, and applying reflective materials.

Thermal properties of opaque and transparent surfaces such as heat transmittance, thermal conductivity, capacity, and reflectance considerably influence heat gains and can reduce yearly cooling loads by up to 38% in the tropics. Many researchers have represented cool roofs as an innovative and inexpensive technique to reduce demand for space cooling and improve indoor thermal comfort. It includes flat roofs covered with high-solar reflectance and high-emissivity coatings. The use of cool clay tile can reduce summer peak indoor air temperature in residential buildings in Italy by up to 4.7 °C and peak external roof surface temperature by approximately 15 −18 °C during summers. Placing a radiant barrier on an exterior surface of a conventional RCC roof can result in a reduction in the temperature of the insulation layer by up to 5 K . Coating surfaces with paint can offer up to 50% savings in cooling energy and up to 66% reduction in heat flux. Combining cool roofs with shading and insulation is found to offer 78% savings in energy consumption. In tropical climates, using a cool roof can result in the most savings concerning Phase Change Material (PCM), and green roofs. A light-colored roof causes 30% lesser total heat gain, compared to a dark-colored roof. Their use can also reduce discomfort hours by up to 53%.

The loads in a building and the temperature of the exterior surfaces also depend on factors like the ambient outdoor temperature, incident solar radiation, and the thermal conductance of the surface. Improving the insulation or U-value of the building envelope is one of the most common ways of enhancing building thermal performance. Literature suggests that the effects of insulation in reducing cooling loads in the tropics can be complicated. Several authors suggest that an increase in insulation can result in higher energy demand for cooling in hot climates due to higher indoor temperatures and poor nighttime cooling. Other authors conversely suggest that more insulation corresponds to lesser heat exchange via conduction and thus better energy efficiency. An increase in envelope insulation has been found to reduce the annual space cooling load by up to 38% in the hot humid climate of Hong Kong. It has been that the cooling loads increase or reduce depending on the thermal mass of the walls, and the number and position of the insulation layer. Higher insulation though minimizes heat gain through conduction during the daytime, it prevents the solar gains to radiate outside during the night.

Window treatments and the use of appropriate shading elements are also of critical importance in hot climates. Heat ingress through windows is determined by factors like the window's thermal insulation, SHGC,  and WWR. SHGC along with shading control forms the most influential factor to affect cooling energy demand, with an average of 39% more impact than other parameters in warm climates. Research suggests that improving solar control properties of windows, particularly for large WWR is a better solution for reducing energy demand and that effectiveness of changing U-values of windows depends on the WWR and insulation of the roof and wall. Solar controls like reflective coatings, tinted glass, or low- e glazing can lower the radiative heat transfer and reduce the cooling demand. A well-insulated envelope with double-glazed windows for a WWR of 20% can produce maximum annual energy savings in different cities in India. The savings reduce by around 70% with a lower U-value and high SHGC. A lower SHGC may increase energy savings by up to 30%. Lowering the SHGC is thus more effective than reducing thermal transmittance. Lower U-values can be effective when the building façade is poorly insulated.

Thermal insulation along with shading can offer temperature reductions up to 10 °C. Shading serves to be the most effective measure for reducing energy demands in the tropics. Adding shading in the hot climate of Egypt reduced the demand for cooling by 25- 33%. Coleridge and Huh observed energy savings ranging between 30% to 50% for different device typologies for an office building in Cape Town, South Africa. Increasing the depth of horizontal shading devices for east and west-orientated windows in Singapore has been shown to result in up to 10% savings in cooling energy load. Shading in the west and the southwest orientations produces the highest savings. Heat transfer in the tropics can also be minimized by installing greenery on the external walls and roofs of buildings. Shading provided by green façades offers the potential to minimize external surface temperature and subsequently reduce the incoming heat flux. An annual air-conditioning load reduction of 76% can be obtained through the application of a Double-Skin Green Façade (DSGF). These green facades can reduce annual energy consumption for cooling by up to 20%. Vertical greenery can cause a reduction in indoor air temperature in the hot and humid summer of Hong Kong by 8.4 °C. Depending on the type of plant used, a 4 °C decrease in internal air temperature, and an estimated reduction of 64% in electricity consumed by air conditioning can be achieved. The green roof can produce energy savings ranging between 31.61% and 39.74% and reductions in indoor air temperature by around 4 °C.

In the context of global climate change and a growing reliance on air-conditioning, several studies have lately started investigating the effect of different green building materials on the energy efficiency of buildings in the tropics. One such material is bamboo which is not only economically viable but low-cost, light in weight, biodegradable, effective CO2 absorber, rapidly renewable, has low capital and maintenance costs, is easy to process and transport, and has low embodied energy along with superior thermal and mechanical properties. It is found in abundance in tropical climates and can withstand wind speeds of up to 150 km/ hour. Being the fastest-growing plant, it can well suffice the needs of rapid urbanization.

Bamboo in recent times has seen a growing research interest due to its several practical applications and benefits in the areas of composite materials and the building sector. Research reveals structural use of bamboo has a less negative impact on the environment compared to common building materials like steel or concrete. Findings show that bamboo-based structures exhibit better thermal performance in terms of envelope insulation compared to conventional brick-concrete buildings. A recent study by Kandya and Mohan shows that the use of bamboo concrete composite- Bamcrete walls can produce cooling energy savings of around 7.5% concerning a traditional brick wall. Bamboo can also be used as an external shading screen in tropical climates like China and effectively reduces transmitted solar radiation in summer while ensuring sufficient daylight ingress. India, being a tropical country and the second major global producer of bamboo thus offers huge potential to realize these benefits.

All these measures can improve thermal comfort by moderating indoor temperatures. Optimizing the building envelope can directly affect the installed capacity of HVAC systems reduce heating and cooling loads, and energy costs. Improvements in the building envelope can thus significantly reduce the need for operational energy and enhance sustainable use. Recognizing the crucial role that building envelope plays in enhancing thermal comfort and building energy performance in the tropics, transformations for creating high-performing building envelopes are crucial for reducing total energy requirements and thus fulfilling multiple Sustainable Development Goals (especially SDGs 7, 11, and 13) and becoming net-zero. Transformation is particularly important in developing nations, especially in the tropics, where the demand for buildings and cooling energy is the fastest-growing demand.

Despite several studies that have evaluated the impacts of one or more design variables on cooling energy efficiency, limited studies have attempted to perform and visualize the energy performance of additions made to existing buildings through Rhino/ Grasshopper, particularly in India. The general trend is biased toward using e- quest, and Design Builder. Many studies have demonstrated the effect of energy efficiency retrofits on building energy use. Deep retrofits can help in reducing building energy use by up to 50%. Given that buildings in India account for approximately 37% of the nation's annual primary energy consumption, employing even a fraction of these actions can make a substantial contribution to the nation's reduction targets.

                               (Academic blocks surrounding CUSE at IIT Bombay.)