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ENERGY AUDIT FOR BUILDINGS.
This topic provides an overview of the energy audit procedure suitable for commercial and industrial buildings. Energy audit has a vital role in the implementation of energy conservation measures. This enables them to meet the Energy Efficiency Standards.
There are several types of energy audits that are commonly performed by energy service engineers with various degrees of complexity. The key aspects of a detailed energy audit procedure and a systematic approach to identify cost efficient energy conservation measures are discussed here.
ELDHO JACOB JOY.
Register No: 45224.
The energy crisis in the present day world has led us to the design of new energy efficient buildings. However the existing buildings consume a lot of conventional energy and minimizing them will help us to conserve them for future. Moreover it would help us to meet the Energy Efficiency standards.
The capital costs for this conversion would be very high, but lower energy bills over a long period of time would offset them and helps to achieve significant profits for the industry as well as the environment. Energy audit involves the systematic collection and analysis of energy data from a particular facility for implementing energy conservation measures.
An energy audit establishes both where and how energy is being used, and the potential for energy savings. It includes a walk-through survey, a review of energy using systems, analysis of energy use and the preparation of an energy budget, and provides a baseline from which energy consumption can be compared over time. An audit can be conducted by an employee of the organization who has appropriate expertise, or by a specialist energy-auditing firm. An energy audit report also includes recommendations for actions, which will result in energy and cost savings. It should also indicate the costs and savings for each recommended action, and a priority order for implementation.
As per the Energy Conservation Act, 2001, Energy Audit is defined as the verification, monitoring and analysis of use of energy including submission of technical report containing recommendations for improving energy efficiency with cost benefit analysis and an action plan to reduce energy consumption.
2. TYPES OF ENERGY AUDITS
Energy auditing of buildings can range from a short walk-through of the facility to a detailed computer simulation of the analysis. Generally, there are four types of energy audits which are as described below.
2.1 Walk-Through Audit
This consists of a short onsite visit for the inspection of the facility. By this, simple inexpensive actions can be taken for immediate energy savings. This consists of repairing broken glass windows, lowering the preset temperatures of HVAC systems according to utility, adjusting the boiler-air fuel ratios. This is usually a maintenance procedure done periodically to improve the efficiency of energy systems.
2.2 Utility Cost Analysis
In this type of audit we carefully analyze the operating cost of the facility. The data obtained over a long period of time energy bills, peak demands, energy use patterns, weather effects are identified. This helps us to establish a relation between cost and utility. Usually this step includes,
Checking utility charges and ensuring that no mistakes are made in calculating the monthly energy bills. This is important because the energy rate structures for industrial facilities can be quite complex.
Determination of the dominant charges in the energy bills is another part of this analysis. Peak demands take-up a major share of the power consumption cost. Thus for shaving off the peak demand supplemental energy measures can be recommended.
Checking whether the facility can benefit from alternative fuels which are more cost effective than the prevailing ones. This will make significant reductions in energy bills. Moreover, the energy auditor can determine whether or not the facility is prime for energy retrofit project and implimentations by analyzing the utility data. Indeed, the energy use of the facility can be normalized and compared to indices (for instance, the energy use per unit of floor area for commercial buildings â€ or per unit of a product for industrial facilities).
2.3 Standard Energy Audit
The standard audit provides a comprehensive analysis of the energy systems of the facility. In addition to the activities described for the walk-through audit and the utility cost analysis described above, the standard energy audit includes the development of a baseline for the energy use of the facility and the evaluation of the energy savings and the cost effectiveness of appropriately selected energy conservation measures. The step by step approach of the standard energy audit is similar to that of the detailed energy audit, which is described in the following subsection.
Typically, simplified tools are used in the standard energy audit to develop baseline energy models and to predict the energy savings of energy conservation measures. Among these tools are the degree-day methods, and linear regression models. In addition, a simple payback analysis is generally performed to determine the cost-effectiveness of energy conservation measures.
2.4 Detailed Energy Audit
This is the most comprehensive but also time-consuming energy audit type. Specifically, the detailed energy audits include the use of instruments to measure energy use for the whole building and/or for some energy systems within the building (for instance, by end uses: lighting, office equipment, fans, chiller, etc.). In addition, sophisticated computer simulation programs are typically employed for detailed energy audits to evaluate and recommend energy retrofits for the facility. The techniques available to perform measurements for an energy audit are diverse. During an on-site visit, hand-held and clamp-on instruments can be used to determine the variance of some building parameters such as the indoor air temperature, the luminance level, and the electrical energy use. When long-term measurements are needed, sensors are typically used and are connected to a data acquisition system so measured data can be stored and be remotely accessible. Recently, no intrusive load monitoring (NILM) techniques have been proposed. The NILM technique can determine the real-time energy use of the significant electrical loads in a facility by using only a single set of sensors at the facility service entrance. The minimal effort associated with using the NILM technique compared to the traditional multi metering approach (which requires a separate set of sensors to monitor energy consumption for each end use) makes the NILM a very attractive and inexpensive load-monitoring technique for energy service companies and facility owners. The computer simulation programs used in the detailed energy audit typically provide the energy use distribution by load type (i.e., energy use for lighting, fans, chillers, boilers, etc.). They are often based on dynamic thermal performance of the building energy systems and usually require a high level of engineering expertise and training.
In the detailed energy audit, more rigorous economical evaluation of the energy conservation measures is generally performed. Specifically, the cost-effectiveness of energy retrofits may be determined based on the life-cycle cost (LCC) analysis rather than the simple payback period analysis. LCC analysis takes into account a number of economic parameters such interest, inflation, and tax rates.
3. GENERAL PROCEDURE FOR A DETAILED ENERGY AUDIT
To perform an energy audit, several tasks are typically carried out depending on the type of the audit and the size and function of the building. Some of the tasks may have to be repeated, reduced in scope, or even eliminated based on the findings of other tasks. Therefore, the execution of an energy audit is often not a linear process and is rather iterative. However, a general procedure can be outlined for most buildings.
3.1 Step 1: Building and Utility Data Analysis
The main purpose of this step is to evaluate the characteristics of the energy systems and the patterns of energy use for the building. The building characteristics can be collected from the architectural/ mechanical/electrical drawings and/or from discussions with building operators. The energy use patterns can be obtained from a compilation of utility bills over several years. Analysis of the historical variation of the utility bills allows the energy auditor to determine any seasonal and weather effects on the building energy usage. Some of the tasks that can be performed in this step are presented below, with the key goals expected from each task noted in italics:
Â¢ Collect at least 3 years of records of utility data [to identify a historical energy use pattern]
Â¢ Identify the fuel types used (electricity, natural gas, oil, etc.) [to determine the fuel type that accounts for the largest energy use]
Â¢ Determine the patterns of fuel use by fuel type [to identify the peak demand for energy use by fuel type]
Â¢ Understand utility rate structure (energy and demand rates) [to evaluate if the building is penalized for peak demand and if cheaper fuel can be purchased]
Â¢ Analyze the effect of weather on fuel consumption
Â¢ Perform utility energy use analysis by building type and size (building signature can be determined including energy use per unit area [to compare against typical indices]
3.2 Step 2: Walk-Through Survey
This step should identify potential energy savings measures. The results of this step are important since they determine if the building warrants any further energy auditing work. Some of the tasks involved in this step are
Â¢ Identify the customerâ„¢s concerns and needs
Â¢ Check the current operating and maintenance procedures
Â¢ Determine the existing operating conditions of major energy use equipment (lighting, HVAC systems, motors, etc.)
Â¢ Estimate the occupancy, equipment, and lighting (energy use density and hours of operation)
3.3 Step 3: Baseline for Building Energy Use
The main purpose of this step is to develop a base-case model that represents the existing energy use and operating conditions for the building. This model will be used as a reference to estimate the energy savings due to appropriately selected energy conservation measures. The major tasks to be performed during this step are
Â¢ Obtain and review architectural, mechanical, electrical, and control drawings
Â¢ Inspect, test, and evaluate building equipment for efficiency, performance, and reliability
Â¢ Obtain all occupancy and operating schedules for equipment (including lighting and HVAC systems)
Â¢ Develop a baseline model for building energy use
Â¢ Calibrate the baseline model using the utility data and/or metered data
3.4 Step 4: Evaluation of Energy-Saving Measures
In this step, a list of cost-effective energy conservation measures is determined using both energy savings and economic analysis. To achieve this goal, the following tasks are recommended:
Â¢ Prepare a comprehensive list of energy conservation measures (using the information collected in the walk-through survey)
Â¢ Determine the energy savings due to the various energy conservation measures pertinent to the building by using the baseline energy use simulation model developed in Step 3
Â¢ Estimate the initial costs required to implement the energy conservation measures
Â¢ Evaluate the cost-effectiveness of each energy conservation measure using an economical analysis method (simple payback or life-cycle cost analysis)
Tables 4.6.1 and 4.6.2 provide summaries of the energy audit procedure recommended, respectively, for commercial buildings and for industrial facilities. Energy audits for thermal and electrical systems are separated since they are typically subject to different utility rates.
4. COMMON ENERGY CONSERVATION MEASURES
In this subsection some energy conservation measures (ECMs) commonly recommended for commercial and industrial facilities are briefly discussed. It should be noted that the list of ECMs presented below does not pretend to be exhaustive nor comprehensive. It is provided merely to indicate some of the options that the energy auditor can consider when performing an energy analysis of a commercial or an industrial facility. However, it is strongly advised that the energy auditor keeps abreast of any new technologies that can improve the facility energy efficiency. Moreover, the energy auditor should recommend the ECMs only after he performs an economical analysis for each ECM.
4.1 Building Envelope
For some buildings, the envelope (i.e., walls, roofs, floors, windows, and doors) can have an important impact on the energy used to condition the facility. The energy auditor should determine the actual characteristics of the building envelope. During the survey, a sheet for the building envelope should be established to include information such as materials of construction (for instance, the level of insulation in walls, floors, and roofs) and the area and number of various assemblies of the envelope (for instance, the type and the number of panes for the windows should be noted). In addition, comments on the repair needs and recent replacement should be noted during the survey.
Some of the commonly recommended energy conservation measures to improve the thermal performance of building envelope are:
4.1.1. Addition of Thermal Insulation.
For building surfaces without any thermal insulation, this measure can be cost effective.
4.1.2. Replacement of Windows.
When windows represent a significant portion of the exposed building surfaces, using more energy-efficient windows (high R-value, low-emissivity glazing, airtight, etc.) can be beneficial in both reducing the energy use and improving the indoor comfort level.
4.1.3. Reduction of Air Leakage.
When the infiltration load is significant, leakage areas of the building envelope can be reduced by simple and inexpensive weather-stripping techniques. The energy audit of the envelope is especially important for residential buildings. Indeed, the energy use from residential buildings is dominated by weather since heat gain and/or loss from direct conduction of heat or from air infiltration/exfiltration through building surfaces accounts for a major portion (50 to 80%) of the energy consumption. For commercial buildings, improvements to the building envelope are often not cost-effective due to the fact that modifications to the building envelope (replacing windows, adding thermal insulation in walls) typically are very expensive. However, it is recommended to systematically audit the envelope components not only to determine the potential for energy savings but also to ensure the integrity of its overall condition. For instance, thermal bridges, if present, can lead to heat transfer increase and to moisture condensation. The moisture condensation is often more damaging and costly than the increase in heat transfer since it can affect the structural integrity of the building envelope.
4.2 Electrical Systems
For most commercial buildings and a large number of industrial facilities, electrical energy cost constitutes the dominant part of the utility bill. Lighting, office equipment, and motors are the electrical systems that consume the major part of energy usage in commercial and industrial buildings.
Lighting for a typical office building represents, on average, 40% of the total electrical energy use. There are a variety of simple and inexpensive measures to improve the efficiency of lighting systems. These measures include the use of energy-efficient lighting lamps and ballasts, the addition of reflective devices, de-lamping (when the luminance levels are above the recommended levels by the standards), and the use of day lighting controls. Most lighting measures are especially cost-effective for office buildings for which payback periods are less than 1 year.
4.2.2. Office Equipment.
Office equipment constitutes the fastest growing part of the electrical loads, especially in commercial buildings. Office equipment includes computers, fax machines, printers, and copiers. Today, there are several manufacturers that provide energy efficient office equipment such as those that comply with U.S. EPA Energy Star specifications). For instance, energy efficient computers automatically switch to a low-power sleep mode or off mode when not in use.
The energy cost to operate electric motors is a significant part of the operating budget of any commercial and industrial building. Measures to reduce the energy cost of using motors include reducing operating time (turning off unnecessary equipment), optimizing motor systems, using controls to match motor output with demand, using variable speed drives for air and water distribution, and installing energy-efficient motors. Table 4.6.3 provides typical efficiencies for several motor sizes.
In addition to the reduction in the total facility electrical energy use, retrofits of the electrical systems decrease the cooling loads and, therefore, further reduce the electrical energy use in the building. These cooling energy reductions, as well as possible increases in thermal energy use (for space heating), should be accounted for when evaluating the cost-effectiveness of improvements in lighting and office equipment.
4.3 HVAC Systems
The energy use due to HVAC systems can represent 40% of the total energy consumed by a typical commercial building. The energy auditor should obtain the characteristics of major HVAC equipment to determine the condition of the equipment, its operating schedule, its quality of maintenance, and its control procedures. A large number of measures can be considered to improve the energy performance of both primary and secondary HVAC systems. Some of these measures are listed below:
1. Setting up/back thermostat temperatures.
When appropriate, set-back of heating temperatures can be recommended during unoccupied periods. Similarly, set-up of cooling temperatures can be considered.
2. Retrofit of constant air volume systems.
For commercial buildings, variable air volume (VAV) systems should be considered when the existing HVAC systems rely on constant-volume fans to condition part or the entire building.
Fig 4.3.1: Variable Air Volume System (VAV)
3. Installation of heat recovery systems.
Heat can be recovered from some HVAC equipment. For instance, heat exchangers can be installed to recover heat from air handling unit (AHU) exhaust air streams and from boiler stacks.
4. Retrofit of central heating plants.
The efficiency of a boiler can be drastically improved by adjusting the fuel-air ratio for proper combustion. In addition, installation of new energy-efficient boilers can be economically justified when old boilers are to be replaced.
5. Retrofit of central cooling plants:
Currently, there are several chillers that are energy efficient and easy to control and operate and are suitable for retrofit project and implimentations.
It should be noted that there is a strong interaction between various components of a heating and cooling system. Therefore, a whole-system analysis approach should be followed when retrofitting a building HVAC system. Optimizing the energy use of a central cooling plant (which may include chillers, pumps, and cooling towers) is one example of using a whole-system approach to reduce the energy use for heating and cooling buildings.
4.4 Compressed Air Systems
Compressed air has become an indispensable tool for most manufacturing facilities. Its uses range from air-powered hand tools and actuators to sophisticated pneumatic robotics. Unfortunately, staggering amounts of compressed air are wasted in a large number of facilities. It is estimated that only about 20 to 25% of input electrical energy is delivered as useful compressed air energy. Leaks are reported to account for 10 to 50% of the waste while misapplication accounts for 5 to 40% of the loss of compressed air. To improve the efficiency of compressed air systems, the auditor can consider several issues including whether compressed air is the right tool for the job (for instance, electric motors are more energy efficient than air-driven rotary devices), how the compressed air is applied (for instance, lower pressures can be used to supply pneumatic tools), how it is delivered and controlled (for instance, the compressed air needs to be turned off when the process is not running), and how the compressed air system is managed (for each machine or process, the cost of compressed air needs to be known to identify energy and cost savings opportunities).
4.5 Energy Management Controls
Because of the steady decrease in the cost of computer technology, automated control of a wide range of energy systems within commercial and industrial buildings is becoming increasingly popular and cost effective. An energy management and control system (EMCS) can be designed to control and reduce the building energy consumption within a facility by continuously monitoring the energy use of various equipment and making appropriate adjustments. For instance, an EMCS can automatically monitor and adjust indoor ambient temperatures, set fan speeds, open and close air handling unit dampers, and control lighting systems. If an EMCS is already installed in the building, it is important to recommend a system tune-up to ensure that the controls are operating properly. For instance, the sensors should be calibrated regularly in accordance with manufacturersâ„¢ specifications. Poorly calibrated sensors may cause an increase in heating and cooling loads and may reduce occupant comfort.
4.6 Indoor Water Management
Water and energy savings can be achieved in buildings by using water-saving equipment instead of the conventional fixtures for toilets, faucets, shower heads, dishwashers, and clothes washers. Savings can also be achieved by eliminating leaks in pipes and fixtures. Table 4.6.4 provides the typical water usage of conventional and water-efficient fixtures. In addition, Table 4.6.4 indicates the hot water consumption by each fixture as a fraction of the total water usage. With water-efficient fixtures, a savings of 50% of water use can be achieved.
5. NEW TECHNOLOGIES
The energy auditor may consider the potential of implementing and integrating new technologies within the facility. It is, therefore, important that the energy auditor understands these new technologies and knows how to apply them. Among the new technologies that can be considered for commercial and industrial buildings include:
5.1 Building Envelope Technologies
Recently, several materials and systems have been proposed to improve the energy efficiency of the building envelope, especially windows, including:
Â¢ Spectrally selective glasses which can optimize solar gains and shading effects
Â¢ Chromogenic glazing which change their properties automatically depending on temperature and/or light-level conditions (similar to sunglasses that become dark in sunlight)
Â¢ Building integrated photovoltaic panels that can generate electricity while absorbing solar radiation and reducing heat gain through the building envelope (typically roofs)
Fig 5.1.1: Window Films: Fig 5.1.2: Shading Technologies.
5.2 Light Pipe Technologies
While the use of day lighting is straightforward for perimeter zones that are near windows, it is not usually feasible for interior spaces, particularly those without skylights. Recent but still emerging technologies allow one to pipe light from roof or wall-mounted collectors to interior spaces that are not close to windows or skylights.
5.3 HVAC Systems and Controls
Several strategies can be considered for energy retrofits, including:
Â¢ Heat recovery technologies such as rotary heat wheels and heat pipes can recover 50 to 80% of the energy used to heat or cool ventilation air supplied to the building
Â¢ Desiccant-based cooling systems are now available and can be used in buildings with large dehumidification loads during long periods (such as hospitals, swimming pools, and supermarket fresh produce areas)
Â¢ Geothermal heat pumps can provide an opportunity to take advantage of the heat stored underground to condition building spaces
Â¢ Thermal energy storage (TES) systems offer a mean of using less-expensive off-peak power to produce cooling or heating to condition the building during on-peak periods; several optimal control strategies have been developed in recent years to maximize the cost savings of using TES systems
This is not really a new technology. However, recent improvements in its combined thermal and electrical efficiency have made cogeneration cost effective in several applications including institutional buildings such as hospitals and universities.
6. VERIFICATION METHODS OF ENERGY SAVINGS
Energy conservation retrofits are deemed cost-effective based on predictions of the amount of energy and money a retrofit will save. However, several studies have found that large discrepancies exist between actual and predicted energy savings. Due to the significant increase in the activities of energy service companies (ESCOs), the need became evident for standardized methods for measurement and verification of energy savings. This interest has led to the development of the North American Energy Measurement and Verification Protocol published in 1996 and later expanded and revised under the International Performance Measurement and Verification Protocol.
In principle, the measurement of the retrofit energy savings can be obtained by simply comparing the energy use during pre- and post-retrofit periods. Unfortunately, the change in energy use between the pre- and post-retrofit periods is not only due to the retrofit itself but also to other factors such as changes in weather conditions, levels of occupancy, and HVAC operating procedures. It is important to account for all these changes to accurately determine the retrofit energy savings. Several methods have been proposed to measure and verify savings of implemented energy conservation measures in commercial and industrial buildings. Some of these techniques are briefly described below.
6.1 Regression Models
The early regression models used to measure savings adapted the Variable-Base Degree Day (VBDD) method. Among these early regression models, the Princeton Scorekeeping Method (PRISM) which uses measured monthly energy consumption data and daily average temperatures to calibrate a linear regression model and determine the best values for non weather-dependent consumption, the temperature at which the energy consumption began to increase due to heating or cooling (the change-point or base temperature), and the rate at which the energy consumption increased. Several studies have indicated that the simple linear regression model is suitable for estimating energy savings for residential buildings. However, subsequent work has shown that the PRISM model does not provide accurate estimates for energy savings for most commercial buildings. Single-variable (temperature) regression models require the use of at least four-parameter segmented linear or change-point regressions to be suitable for commercial buildings. , Katipamula proposed multiple linear regression models to include as independent variables internal gain, solar radiation, wind, and humidity ratio, in addition to the outdoor temperature. For the buildings considered in their analysis, Katipamula et al. found that wind and solar radiation have small effects on the energy consumption. They also found that internal gains have generally modest impact on energy consumption. Katipamula et al. (1998) discuss in more detail the advantages and the limitations of multivariate regression modeling.
6.2 Time Variant Models
Several techniques have been proposed to include the effect of time variation of several independent variables on estimating the energy savings due to retrofits of building energy systems. Among these techniques are the artificial neural networks, Fourier series, and non intrusive load monitoring. These techniques are very involved and require a high level of expertise and training.
An energy audit of commercial and industrial buildings encompasses a wide variety of tasks and requires expertise in a number of areas to determine the best energy conservation measures suitable for an existing facility. This section provided a description of a general but systematic approach to perform energy audits. If followed carefully, the approach helps facilitate the process of analyzing a seemingly endless array of alternatives and complex interrelationships between the building and its energy system components.
Fig 7.1: Typical Electrical Energy Consumption for various puposes.
8.1 Books and Journals;
Building Upgrade Manual (2007), Environmental Protection Agency (EPA),
KREITH, F. (1999). The CRC Handbook of Thermal Engineering.
8.2 Related Websites:
Bureau of Energy Efficiency. http://www.bee.com
Energy Star-Change for the better http://www.energystar.com
Environment Protection Agency. http://www.epa.gov
Advanced Energy Organization. http://www.advancedenergy.org
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13-10-2010, 12:22 PM
ENERGY CONSERVATION IN THERMAL SYSTEMS.ppt (Size: 1.84 MB / Downloads: 98)
ENERGY CONSERVATION IN THERMAL SYSTEMS
Energy can be classified into several types based on the following criteria:
Primary and Secondary energy
Commercial and Non commercial energy
Renewable and Non-Renewable energy
Indian Energy Scenario
Coal dominates the energy mix in India, contributing to 55% of the total primary energy production.
Over the years, there has been a marked increase in the share of natural gas in primary energy production from 10% in 1994 to 13% in 1999.
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Please upload Complete Report on Energy Auditing in Inidan Buildings.
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