Design and control of mixed-mode cooling and ventilation in low-energy residential buildings in India

Abstract

Energy security, climate change and economic growth are matters of critical international importance in an effort to achieve a sustainable future. Energy consumption in buildings contributes to higher greenhouse gas emissions than the industrial or transportation sectors combined. In India, the energy in the residential sector accounts for almost 50% of the total energy consumption. The need for comfortable internal environments, healthy indoor air quality and the consequences of global warming are all contributing factors to the high reliance on mechanical cooling and ventilation systems. In recent years, financial growth and increase in disposable income in India, have accelerated purchases of such mechanical systems. In metropolitan cities of India with extreme climates (hot and dry, warm and humid), the use of these systems increases by 30% every year. This upward trend is likely to continue in response to occupants’ higher comfort expectations and the continuous increase of the outside temperature during the summer months due to climate change. This could further impact the climate and the electricity grid. Innovative solutions should establish reliable strategies for cooling purposes by utilizing the use of natural ventilation. Mixed-mode buildings rely on both mechanical and natural systems to maintain comfortable conditions. Although the performance of mixed-mode buildings has already been studied and there is evidence for its positive impact on the reduction of energy demand, there is still a lack of knowledge on the best methods for controlling mixed-mode buildings. Today, the majority of the available algorithms for the control of mixed-mode systems are very simplistic and at a primitive stage of development. Typically, the control algorithms “make the decision” based on a predefined static set-point temperature, disregarding other important parameters, such as relative humidity, the position of windows and activity of occupants. Control algorithms that would account for a variety of parameters are of paramount importance to achieve energy savings whilst maintaining thermal comfort conditions. The aim of this research was to investigate the impact on thermal comfort and energy savings of novel and sophisticated control algorithms in mixed-mode residential buildings in India.Initially, it was important to identify all the control parameters that were important to be included in the control algorithms. Then the control algorithms were designed and presented in flow charts. To analyse the performance of the proposed control algorithms, computer simulations were performed, whilst a validation analysis was conducted to provide evidence of the validity of the control algorithms. Computer modelling comprised of co-simulations, using Dynamic Thermal Modelling (DTM) (EnergyPlus) and equation-based tools (Dymola using the Modelica language). The coupling of these was achieved using the Functional Mock-up Interface (FMI) for model exchange. The co-simulations enabled to examine the energy saving potential that can be achieved by the proposed control algorithms. In order to evaluate the ventilation performance of the proposed control algorithms, the ventilation rates and ventilation effectiveness of the systems were analysed using Computational Fluid Dynamics (CFD). This allowed the final analysis which included the evaluation of the ventilation performance of the control algorithms by calculating the ventilation effectiveness. To provide evidence of the proposed control algorithms and simulation approach, a validation study was done using data from an experimental chamber in India. This research has contributed to the existing body of knowledge by providing four main conclusions concerning the design and control of mixed-mode ventilation and cooling systems: i) to deliver comprehensive guidelines on the design and control of mixed-mode buildings, and the ways in which the co-simulations can be implemented to improve the existing control algorithms that can be found in the literature; ii) the use of the co-simulations showed that the developed control algorithms, when dampers/windows and ceiling fans are used, can improve the predicted hours of thermal comfort by up to 1900h compared to the scenarios when the ceiling fans were turned off, while achieving up to 55% energy reduction depending on the city; iii) the CFD simulations predicted that cross ventilation with the maximum opening areas for windows and dampers in combination with the operation of the ceiling fans can dillute the contaminants and/or heat in the building resulting in comfortable internal environments resulting in heat removal effectiveness of 1.65; and iv) the accurate and validated control algorithms that were developed in this research can be used for any study that requires control of mixed-mode buildings regardless of the geometry of the building. The use of co-simulations provides great flexibility since the same control algorithms can be used in any geometry or building location without the need for any modification of the code.