Energy-Efficient Buildings

Introduction

Buildings, as they are designed and used today, contribute to serious environmental problems because of excessive consumption of energy and other natural resources. The close connection between energy use in buildings and environmental damage arises because energy-intensive solutions sought to construct a building and meet its demands for heating, cooling, ventilation, and lighting cause severe depletion of invaluable environmental resources.

However, buildings can be designed to meet the occupant’s need for thermal and visual comfort at reduced levels of energy and resources consumption. Energy resource efficiency in new constructions can be effected by adopting an integrated approach to building design. The primary steps in this approach are listed below.

• Incorporate solar passive techniques in a building design to minimize load on conventional systems (heating, cooling, ventilation, and lighting)
• Design energy-efficient lighting and HVAC (heating, ventilation, and air-conditioning) systems.
• Use renewable energy systems (solar photovoltaic systems / solar water heating systems) to meet a part of building load.
• Use low energy materials and methods of construction and reduce transportation energy

Thus, in brief, an energy-efficient building balances all aspects of energy use in a building – lighting, space-conditioning, and ventilation – by providing an optimized mix of passive solar design strategies, energyefficient equipment, and renewable sources of energy. Use of materials with low embodied energy also forms a major component in energyefficient building designs.

Climate and architecture

India is divided into six climatic zones based on different climatic conditions. Knowledge of climate at a given location can help in the design of solar passive buildings that eliminate the adverse effects of climate, yet simultaneously take advantage of effects that are beneficial. For instance, in a place like Mumbai, a building can be designed in such a way that appropriate shading prevents solar radiation and adequate ventilation reduces humidity. In a place like Shimla, where the climate is cold and cloudy, a building can be designed to make maximum use of sunlight, and thereby keep its interiors as warm as possible. The various climatic factors that affect the solar passive design are listed below.

• Wind velocity
  
• Ambient temperature
  
• Relative humidity
  
• Solar radiation

Solar passive techniques

Various concepts and techniques are used to design energy-efficient buildings. Some of these are described below.

Direct heat gain

The direct heat gain technique is generally used in cold climates. The basic principle is that sunlight is admitted into the living spaces directly through openings or glazed windows to heat walls, floors, and inside air. The glazed windows are generally located facing south to receive maximum sunlight during winter. They are usually double-glazed, with insulating curtains to reduce heat loss during the night. During the day, heat is stored in walls and floors; it is released during the night to warm the interior.

Thermal storage walls

In this approach, a thermal storage wall is placed between the living space and the glazing. The prevents solar radiation from directly entering the living space. The radiation is absorbed by the storage wall, and then transferred into the living space. Thermal storage walls include Trombe walls, water walls, transwalls, etc.

Evaporative cooling

Evaporative cooling is a passive cooling technique, generally employed in hot and dry climates. It works on the principle that when warm air is used to evaporate water, the air itself becomes cool, and in turn cools the living space of a building.

Passive desiccant cooling

Passive desiccant cooling method is effective in a warm and humid climate. Natural cooling of the human body through sweating does not occur in highly humid conditions. To decrease the humidity level of the surroundings, desiccant salts or mechanical de-humidifiers are used.

Induced ventilation

Passive cooling by induced ventilation can be most effective in hot and humid climates as well as in hot and dry climates. This method involves the heating of air in a restricted area through solar radiation, thus creating a temperature difference and causing air movements or drafts. The drafts cause hot air to rise and escape from the interior, drawing in cooler air and thereby effecting cooling.

Earth berming

Earth-berming technique is used for both passive cooling and heating of buildings. It is based on the fact that the earth acts like a massive heat sink. Thus, underground or partially sunk buildings would provide both cooling in summer and heating in winter to the living spaces within.

In addition to the above concepts, there are many other solar passive techniques such as wind towers, earth air tunnels, curved roofs, and air vents, which can be incorporated according to the requirements of the buildings. There are design features that enable maximum use of daylight inside the building.

Advantages of solar passive buildings

With the incorporation of solar passive concepts into a building, a large quantity of energy can be saved. Furthermore, these concepts help in providing comfortable living conditions to the inhabitants in an eco-friendly manner. However, they cannot totally eliminate the use of conventional energy for modern facilities such as air-conditioning.

Cost and payback period

The cost of a building may increase by about 5%-15% because of incorporation of solar passive concepts. However, the investment may be recovered within a period of five to seven years due to savings in energy.

Main Application: Energy

Contact:

Ministry of Non-Conventonal Energy Sources,
Govt. of India
Block-14, CGO Complex, Lodi Road
New Delhi – 110 003
Tel: 91 11 2436 0707/ 2436 0404
Fax: 91 11 2436 1298