The System Design Process of Net Zero Carbon Buildings
EXECUTIVE SUMMARY
Reduction in total energy consumption can be achieved by developing integrated designs for net zero carbon buildings to reduce the energy requirements with the use of green energy (renewable). The present study focuses on evaluating a system design process for net zero carbon buildings using core principles to critically evaluate preliminary and detailed design of construction site, photovoltaics, cooling system, hydroponic wall system, power grid, heat exchange etc. The paper also illustrates long terms future benefits of selected system evaluation, validation, optimization and challenges faced during strategic development of sensitive management systems. The design process is a collaborative approach of the building’s life cycle to meet the needs of sustainable development in minimal cost.
Table of Contents:
Executive Summary……………………………………………………………………………. 2
Introduction………………………………………………………………………………………4
Strategic Integrated Design……………………………………………………………………….4
Feedback Loops…………………………………………………………………………………..5
Benefits of Integrated Process…………………………………………………………………….5
Sustainable Building Design………………………………………………………………………6
Methods……………………………………………………………………………………………7
Preliminary Design………………………………………………………………………………..7
Detailed Design and Development………………………………………………………………8
System test evaluation, validation and optimization…………………………………………….11
Conclusion……………………………………………………………………………………………………………………14
Recommendations……………………………………………………………………………….15
References………………………………………………………………………………………. 16
INTRODUCTION
Construction of net zero carbon buildings to give high performance in terms of sustainability, cost efficiency and low energy usage is the key reconstructing strategy to meet energy needs these days. The building that consumes net zero or negative energy is known to be a net zero carbon building (Wang et al., 2009). The system design process focuses on designing a sustainable building with integrated solutions of architecture, energy and environment. Net zero carbon building works on the principle to reduce energy use and to make use of renewable techniques such as solar, thermal, wind etc., to balance energy needs. Energy supply is managed through optimisation technologies which use a system to track photovoltaics, wind and thermal turbines (Koutroulis and Kalaitzakis, 2006). It also manages stored energy and to provide that energy to the grid when required. Parameters like total energy consumption, net costing, total carbon emission are measured and to calculate the total performance of the net zero carbon building (Torcellini and Crawley, 2006; Tsoutsos et al., 2010).
Fig. 1: Designing Strategy (Source: Bejder, A. K., Knudstrup, M-A., Jensen, R. L., & Katic, I., 2014)
Strategic Integrated Design –
Integrated design concept is a combination of holistic and modern design simultaneously to design net zero carbon buildings. Holistic approach helps to achieve sustainable building designing goals with better success rates. This process works on element support which is facilitated and structured through inclusiveness and collaborative decision with expertise.
Fig. 2: Integrated design process parameters (Knudstrup 2004)
Feedback loops –
Integrated design process works on feedback mechanisms to evolve and improve regularly while in conventional design process a linear system of decisions is followed without any upgradation. Feedback loops and human factors are essential for an effective small scale success of the team involved. In an integrated design process feedback loops helps to refine conventional views i.e., provide iterations commissioned occupancy after design implementation.
Benefits of Integrated Process-
The integrated process is based on conceptually proven approaches rather than new ones. The benefits of this process includes low cost with high quality design that helps to reduce the re designing cost with increasing productivity. Based on net cost and energy efficiency, a curve known as the Macleamy Curve (Figure 2) represents the benefits of integrated design process. Integrated design process proved to be the most effective process to design buildings with high performance outcomes at a low cost (Attia and et. al., 2013).
Fig.3: the Macleamy Curve (Attia and et. al., 2013)
Sustainable Building Design-
Sustainable design concept consists of all the components other than energy consumption, required in a building lifecycle. Integrated design process is an important tool which helps to design new energy efficient buildings sustainably. It involves the critical evaluation of net energy cost, quality, productive approach, impacts on environment and energy efficiency. A successful sustainable design can be achieved using integrated design process through a collaborative method involving variable design professionals such as users, managers etc.
METHODS
Preliminary Design-
In the preliminary design, challenges faced in microclimate are used as a tool to design an integrated building to identify proper use of wind and solar energy. Net zero carbon buildings should be designed in a way to regulate proper daylight quality and amount while avoiding solar heat passively which results in overheating which can be known through shade, daylight hours sun’s position in various seasons. Daylight position of sun and shade helps to construct and design building according to the need by referring parameters like light and solar heat conditions.
Wind flow and its speed in the preferred location is also considered while designing building with proper ventilation and shelter facilities. Other parameters taken into account while designing is the location or site of the building where it will be made i.e., already developed area or a new setup which is influenced by wind (Brunsgaard et. al 2012). Therefore, any change in the site microclimate such as solar heat, shade or wind conditions are evaluated while designing a net zero building.
Fig. 4: Horizontal and vertical movement of sun during different solstice (Source:(Source: Bejder, A. K., Knudstrup, M-A., Jensen, R. L., & Katic, I., 2014)
Indoor Environment-
The main characteristic feature of a net zero carbon building is its indoor environment. So, while designing such buildings improvised indoor environment is taken into account with low energy usage such as ventilation is considered to be an important factor during summers for natural aeration of the building which helps to reduce energy costs through rooms opening, vaulted windows and ceilings. While designing buildings factors such as rate of ventilation and measures to control rise in temperature in an indoor environment are considered to meet the demands of ventilation in a net zero building.
- Detailed Design and Development-
A detailed design of net zero carbon building is a framework of various conditions that works under low or negligible energy requirements while providing inhabitants well being. It provides a detailed layout of architecture and positioning, daylight conditions and materials of the building. However, technical details such as energy required of the building, need for natural ventilation etc, and building overall performance through parameter based calculation can be estimated using detailed design.
Space: Insulation and compactly packed net zero carbon buildings help to reduce complexity which in turn results in heat and solar heat reduction passively. According to the need, a holistic strategy based on daylight condition is used to design a detailed structure based on complexity, net gain of heat, sheltered spaces, windows and open spaces. On the basis of space net zero buildings are divided into three design principles:
Rectangular- Narrow space with partition provides high daylight conditions with even distribution of light in all the rooms from both sides and ventilation. Reduction in ducts helps to reduce energy use. Based on temperature requirements zoning helps to improve heat loss.
L-Shape- Both side of the room is lit due to transparent partitioned wings. This shape provides an outdoor shelter space. Rooms have double height to increase ventilation through buoyancy of thermal heat.
Compact: Small surface area is provided by the compact shape. This shape also provides double height to increase ventilation, outdoor shelter.
Daylight: Daylight consists of direct solar heat and reflected skylight. Proper daylight conditions through direct solar heat gain are required while designing. Daylight is an important factor that depicts changes in microclimate, patterns of light, and space. Direct solar heat results in sharp directional shades while reflected skylight is preferred for cooling surfaces of floors, walls etc.
Fig.5.1: Direct Sunlight Fig.5.2: Reflected Skylight
Shading- Overheating is prevented through exterior shading as it blocks direct sunlight and helps to reduce solar heat passively while in interior shading direct sunlight is already inside the building so it does not prevent complete overheating. Combination of both the shading helps to minimize energy requirement and provides an effective indoor environment.
Ventilation: Natural and mechanical are two ventilation strategies taken into account while designing a net zero carbon building. The mechanical ventilation system works on recovery of the heat to reduce heat loss during heat requirements. However, when natural ventilation is required buildings are designed with an openings based on pressure differences caused by wind and buoyancy. Many factors determine the efficiency of natural ventilation such as microclimate, building environment, design and operation.
- System test, evaluation, validation and optimization-
The net zero carbon building design is validated using simulation tool to predict performance and energy consumption. The calculated annual performance of the building is entered into a programmed system module i.e., simulation module. The evaluation and validation is done for indoor environments, net energy consumption, and efficiency of the system.
Evaluation tools integrate algorithms into optimal calculations of energy requirement and needs. A net zero carbon building is designed with the help of a database, knowledge and information about the building’s life cycle, its systems and materials and calculated performance. Balanced energy analysis is the total energy consumption evaluation of a net zero carbon building.
Fig. 6: Energy system of net zero carbon building (Source: S. Deng et al.,2014)
System evaluation of liquid based systems and air based water pumps depicts that water based systems provides an even supply annually while air based systems are meant to work in summers. EED and TRNSYS software tools analyse complexity, design and operation of the building while sustaining system and energy needs (Pavlov 2014). HVAC conventional systems are cost effective compared to combined systems. Solar heat supplies energy to the building. Solar heating system produce more energy compared to photovoltaic system.
A Photovoltaic system generates electricity both in case of sunlight and cloudy weather but with diffused light and energy yield reduction. This system relies on inclination of panel and its orientation which defines the system yield. Photovoltaics (PV) systems are used to generate electricity for a building on its own at high cost. Photovoltaic systems provide a benefit over other system that price fluctuation of energy can be avoided.
Fig.7: Photovoltaic System
Simulation tool works to evaluate energy requirements of a building to reduce energy needs, and to improve indoor environment. Net zero building performance can be increased through simulation method. In simulation method as variable is used to analyse their effect on design while keeping all the other variables constant. Simulation based optimization is a combined process of simulation method with optimisation strategies and algorithms. Requirements of net zero carbon buildings are meet up using optimisation measures.
Fig.8: Building Optimisation program
CONCLUSION
Simulation analysis is the tool to evaluate the net zero carbon building performance. Several tools and programs analyse buildings and prepare a feedback based on energy consumption, quality indoor environment, and comfort. However, simulation tools evaluate conventional and modern systems along with materials their high cost and minimal outcomes is what make them challenging. Compared to a conventional HVAC system, hybrid system of water based and air based system with heat pump meet the demand of net zero carbon buildings. Several simulation models based on thermal heat are efficient enough to calculate the response of the system which helps to integrate strategies related to control and assess efficient energy needs. These systems are a necessity for operational net zero buildings and for improvising their performance. However, optimization and validation of building systems and applying them in practical design is still a challenge. This area still requires a lot of development at later stages. Several systems are proposed along with simulation tools but with limitations in energy usage, performance efficiency and optimization in net zero carbon buildings.
RECOMMENDATIONS
Presently available thermal systems can be improved by installing equipment’s to monitor buildings such as sensors. Sensors will help to monitor wind speed and flow, sunlight, temperature and other parameters as variation in these conditions affect the availability of resources and simulation. Therefore, predetermined control methods based on studied systems is an important criteria to calculate and evaluate net energy consumption, passive solar heat gain or loss. Life cycle assessment of net-zero carbon buildings is necessary to interpret the use of materials with embodied energy. A more sustainable and validates system for buildings is required that proves to be beneficial in terms of energy cost reduction, reduce environmental impact and sustainable design.
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