Energy Audit for Buildings

8/19/2019 Energy Audit for Buildings

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ENERGY AUDIT FOR BUILDINGS.

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ABSTRACT

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 efficientenergy conservation measures are discussed here.

1. INTRODUCTION

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


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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,


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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 projects 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 — 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


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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.


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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


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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:

• Collect at least 3 years of records of utility data [ to identify a historical energy use

pattern]

• Identify the fuel types used (electricity, natural gas, oil, etc.) [ to determine the fuel

type that accounts for the largest energy use]

• Determine the patterns of fuel use by fuel type [ to identify the peak demand for

energy use by fuel type]

• 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 ]

• Analyze the effect of weather on fuel consumption

• 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

• Identify the customer’s concerns and needs

• Check the current operating and maintenance procedures

• Determine the existing operating conditions of major energy use equipment

(lighting, HVAC systems, motors, etc.)

• 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


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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

• Obtain and review architectural, mechanical, electrical, and control drawings

• Inspect, test, and evaluate building equipment for efficiency, performance, and

reliability

• Obtain all occupancy and operating schedules for equipment (including lighting and

HVAC systems)

• Develop a baseline model for building energy use

• 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:

• Prepare a comprehensive list of energy conservation measures (using the

information collected in the walk-through survey)

• 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

• Estimate the initial costs required to implement the energy conservation measures

• 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.


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Energy audits for thermal and electrical systems are separated since they are typically

subject to different utility rates.


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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.


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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.


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4.2.1. Lighting.

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.

4.2.3. Motors.

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.


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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:


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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.


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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 projects.

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


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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 manufacturers’ 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.


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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:

• Spectrally selective glasses which can optimize solar gains and shading effects

• Chromogenic glazing which change their properties automatically depending on

temperature and/or light-level conditions (similar to sunglasses that become dark in

sunlight)

• 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.


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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:

• 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

• 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)

• Geothermal heat pumps can provide an opportunity to take advantage of the heat

stored underground to condition building spaces

• 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

5.4 Cogeneration

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.


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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


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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.


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7. CONCLUSION:

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.


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8. REFERENCES

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. www.bee.com

Energy Star-“Change for the better” www.energystar.com

Environment Protection Agency. www.epa.gov

Advanced Energy Organization. www.advancedenergy.org

Energy Audit for Buildings

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