Effectiveness of Ventilative Cooling Strategies in Hot and Dry and Temperate Climates of India

Increasing use of air-conditioning in India is applying upward pressure on energy demand and may have implications on dependability. Electrical energy can be saved if favourable outdoor conditions are effectively utilized for cooling buildings with the minimum use of energy. This could be specifically applicable to residences where night-time use is more predominant for cooling by air conditioning systems but also aligns favourably with suitable outdoor conditions to be used as ventilative cooling. The potential of cooling with natural ventilation and mechanical ventilation remains an important topic to meet the needs of the larger section of the population who cannot afford to air-conditioning system as well as to reduce the energy consumption and greenhouse gas emission due to space cooling demands. This study evaluates the benefit of ventilative cooling techniques in Indian residences of hot and dry and temperate climates. The study first identifies typical residential plans in India based on past studies of residential surveys and existing literature. These plans are then simulated in DesignBuilder for modelling natural ventilation to understand baseline comfort and cooling needs. Further, ventilative cooling design strategies (single-side opening, cross-flow, stack ventilation with natural and mechanical ventilation) are designed using sizing methods described in IEA-Annex 62 and are incorporated in the residential plans to assess the ventilative cooling benefits. The effectiveness of ventilative cooling is investigated for two representative cities (Ahmedabad in hot and dry; Bangalore in temperate) located in two different climate zones of India to draw the comparison. The ventilative cooling benefits are quantified by percentage reduction in annual uncomfortable hours and cooling needs for various natural and mechanical ventilative cooling strategies in two the climate zones. Further, a novel method to continuously measure ventilation rate is developed for affordable yet accurate measurements. Short-term field measurements are conducted in an apartment building with continuous logging of surface temperatures, air temperature and air changes rates (using tracer gas method). The measurements are made to check if the input assumptions (such as ventilation rate or air velocity estimates) are realistic. These measurements are supported by physical model that calculates instantaneous ventilative cooling. The study provides scientific basis for building designers for incorporating ventilative cooling strategies. It also provides understanding of the benefits and limitations of natural and mechanical ventilative cooling in two different climates of India for residential application.