Energy Audit

July 03, 2013
An energy audit is an inspection, survey and analysis of energy flows for energy conservation in a building, processor system to reduce the amount of energy input into the system without negatively affecting the output(s).
When the object of study is an occupied building then reducing energy consumption while maintaining or improving human comfort, health and safety are of primary concern. Beyond simply identifying the sources of energy use, an energy audit seeks to prioritize the energy uses according to the greatest to least cost effective opportunities for energy savings.
Home energy audit
A home energy audit is a service where the energy efficiency of a house is evaluated by a person using professional equipment (such as blower doors and infrared cameras), with the aim to suggest the best ways to improve energy efficiency in heating and cooling the house.
An energy audit of a home may involve recording various characteristics of the building envelope including the walls, ceilings, floors, doors, windows, and skylights. For each of these components the area and resistance to heat flow (R-value) is measured or estimated. The leakage rate or infiltration of air through the building envelope is of concern, both of which are strongly affected by window construction and quality of door seals such as weather stripping. The goal of this exercise is to quantify the building's overall thermal performance. The audit may also assess the efficiency, physical condition, and programming of mechanical systems such as the heating, ventilation, air conditioning equipment, and thermostat.
A home energy audit may include a written report estimating energy use given local climate criteria, thermostat settings, roof overhang, and solar orientation. This could show energy use for a given time period, say a year, and the impact of any suggested improvements per year. The accuracy of energy estimates are greatly improved when the homeowner's billing history is available showing the quantities of electricity, natural gas, fuel oil, or other energy sources consumed over a one or two-year period.
Some of the greatest effects on energy use are user behavior, climate, and age of the home. An energy audit may therefore include an interview of the homeowners to understand their patterns of use over time. The energy billing history from the local utility company can be calibrated using heating degree day and cooling degree day data obtained from recent, local weather data in combination with the thermal energy model of the building. Advances in computer-based thermal modeling can take into account many variables affecting energy use.
A home energy audit is often used to identify cost effective ways to improve the comfort and efficiency of buildings.
In addition, homes may qualify for energy efficiency grants from central government.
Recently, the improvement of smart phone technology has enabled homeowners to perform relatively sophisticated energy audits of their own homes. This technique has been identified as a method to accelerate energy efficiency improvements.
Industrial energy audits
Increasingly in the last several decades, industrial energy audits have exploded as the demand to lower increasingly expensive energy costs and move towards a sustainable future have made energy audits greatly important. Their importance is magnified since energy spending is a major expense to industrial companies (energy spending accounts for ~ 10% of the average manufacturer's expenses). This growing trend should only continue as energy costs continue to rise.
While the overall concept is similar to a home or residential energy audit, industrial energy audits require a different skill set. Weatherproofing and insulating a house are the main focus of residential energy audits. For industrial applications, weatherproofing and insulating often are minor concerns. In industrial energy audits, it is the HVAC, lighting, and production equipment that use the most energy.
Types of energy audit
The term energy audit is commonly used to describe a broad spectrum of energy studies ranging from a quick walk-through of a facility to identify major problem areas to a comprehensive analysis of the implications of alternative energy efficiency measures sufficient to satisfy the financial criteria of sophisticated investors. Numerous audit procedures have been developed for non-residential (tertiary) buildings (ASHRAE,IEA-ECBCS Annex Krarti,2000). Audit is required to identify the most efficient and cost-effective Energy Conservation
Opportunities (ECOs) or Measures (ECMs). Energy conservation opportunities (or measures) can consist in more efficient use or of partial or global replacement of the existing installation.
The main issues of an audit process are:
• The analysis of building and utility data, including study of the installed equipment and analysis of energy bills;
• The survey of the real operating conditions;
• The understanding of the building behavior and of the interactions with weather, occupancy and operating schedules;
• The selection and the evaluation of energy conservation measures;
• The estimation of energy saving potential;
• The identification of customer concerns and needs

Common types/levels of energy audits are distinguished below, although the actual tasks performed and level of effort may vary with the consultant providing services under these broad headings. The only way to ensure that a proposed audit will meet your specific needs is to spell out those requirements in a detailed scope of work. Taking the time to prepare a formal solicitation will also assure the building owner of receiving competitive and comparable proposals.
Generally, four levels of analysis can be outlined (ASHRAE):
Level 0 – Benchmarking: This first analysis consists in a preliminary Whole Building Energy Use (WBEU) analysis based on the analysis of the historic utility use and costs and the comparison of the performances of the buildings to those of similar buildings. This benchmarking of the studied installation allows determining if further analysis is required;
Level I – Walk-through audit: Preliminary analysis made to assess building energy efficiency to identify not only simple and low-cost improvements but also a list of energy conservation measures (ECMs, or energy conservation opportunities, ECOs) to orient the future detailed audit. This inspection is based on visual verifications, study of installed equipment and operating data and detailed analysis of recorded energy consumption collected during the benchmarking phase;
Level II – Detailed/General energy audit: Based on the results of the pre-audit, this type of energy audit consists in energy use survey in order to provide a comprehensive analysis of the studied installation, a more detailed analysis of the facility, a breakdown of the energy use and a first quantitative evaluation of the ECOs/ECMs selected to correct the defects or improve the existing installation. This level of analysis can involve advanced on-site measurements and sophisticated computer based simulation tools to evaluate precisely the selected energy retrofits;
Level III – Investment-Grade audit: Detailed Analysis of Capital-Intensive Modifications focusing on potential costly ECOs requiring rigorous engineering study.


It is necessary to find a way of describing what constitutes good, average and bad energy performance across a range of situations. The aim of benchmarking is to answer this question. Benchmarking mainly consists in comparing the measured consumption with reference consumption of other similar buildings or generated by simulation tools to identify excessive or unacceptable running costs. As mentioned before, benchmarking is also necessary to identify buildings presenting interesting energy saving potential. An important issue in benchmarking is the use of performance indexes to characterize the building.
These indexes can be:
• Comfort indexes, comparing the actual comfort conditions to the comfort requirements;
• Energy indexes, consisting in energy demands divided by heated/conditioned area, allowing comparison with reference values of the indexes coming from regulation or similar buildings;
• Energy demands, directly compared to “reference” energy demands generated by means of simulation tools.

Walk-through or preliminary audit

The preliminary audit (alternatively called a simple audit, screening audit or walk-through audit) is the simplest and quickest type of audit. It involves minimal interviews with site-operating personnel, a brief review of facility utility bills and other operating data, and a walk-through of the facility to become familiar with the building operation andto identify any glaring areas of energy waste or inefficiency.
Typically, only major problem areas will be covered during this type of audit. Corrective measures are briefly described, and quick estimates of implementation cost, potential operating cost savings, and simple payback periods are provided. A list of energy conservation measures (ECMs, or energy conservation opportunities, ECOs) requiring further consideration is also provided. This level of detail, while not sufficient for reaching a final decision on implementing proposed measure, is adequate to prioritize energy-efficiency projects and to determine the need for a more detailed audit.

General audit

The general audit (alternatively called a mini-audit, site energy audit or detailed energy audit or complete site energy audit) expands on the preliminary audit described above by collecting more detailed information about facility operation and by performing a more detailed evaluation of energy conservation measures. Utility bills are collected for a 12 to 36 month period to allow the auditor to evaluate the facility's energy demand rate structures and energy usage profiles. If interval meter data is available, the detailed energy profiles that such data makes possible will typically be analyzed for signs of energy waste.[12] Additional metering of specific energy-consuming systems is often performed to supplement utility data. In-depth interviews with facility operating personnel are conducted to provide a better understanding of major energy consuming systems and to gain insight into short and longer term energy consumption patterns. This type of audit will be able to identify all energy-conservation measures appropriate for the facility, given its operating parameters. A detailed financial analysis is performed for each measure based on detailed implementation cost estimates; site-specific operating cost savings, and the customer's investment criteria. Sufficient detail is provided to justify project implementation.

Investment-grade audit

In most corporate settings, upgrades to a facility's energy infrastructure must compete for capital funding with non-energy-related investments. Both energy and non-energy investments are rated on a single set of financial criteria that generally stress the expected return on investment (ROI). The projected operating savings from the implementation of energy projects must be developed such that they provide a high level of confidence. In fact, investors often demand guaranteed savings. The investment-grade audit expands on the detailed audit described above and relies on a complete engineering study in order to detail technical and economical issues necessary to justify the investment related to the transformations

Simulation-based energy audit procedure for non-residential buildings

A complete audit procedure, very similar to the ones proposed by ASHRAE and Krarti (2000), has been proposed in the frame of the AUDITAC and HARMONAC projects to help in the implementation of the EPB (“Energy Performance of Buildings”) directive in Europe and to fit to the current European market.
The following procedure proposes to make an intensive use of modern BES tools at each step of the audit process, from benchmarking to detailed audit and financial study:
• Benchmarking stage: While normalization is required to allow comparison between data recorded on the studied installation and reference values deduced from case studies or statistics. The use of simulation models, to perform a code-compliant simulation of the installation under study, allows to assess directly the studied installation, without any normalization needed. Indeed, applying a simulation-based benchmarking tool allows an individual normalization and allows avoiding size and climate normalization.
• Preliminary audit stage: Global monthly consumptions are generally insufficient to allow an accurate understanding of the building’s behaviour. Even if the analysis of the energy bills does not allow identifying with accuracy the different energy consumers present in the facility, the consumption records can be used to calibrate building and system simulation models. To assess the existing system and to simulate correctly the building’s thermal behaviour, the simulation model has to be calibrated on the studied installation. The iterations needed to perform the calibration of the model can also be fully integrated in the audit process and help in identifying required measurements and critical issues.[16]
• Detailed audit stage: At this stage, on-site measurements, sub-metering and monitoring data are used to refine the calibration of the BES tool. Extensive attention is given to understanding not only the operating characteristics of all energy consuming systems, but also situations that cause load profile variations on short and longer term bases(e.g. daily, weekly, monthly, annual). When the calibration criteria is satisfied, the savings related to the selected ECOs/ECMs can be quantified.
• Investment-grade audit stage: At this stage, the results provided by the calibrated BES tool can be used to assess the selected ECOs/ECMs and orient the detailed engineering study.

Energy Audit Energy Audit Reviewed by Bibi Mohanan on July 03, 2013 Rating: 5

General layout of Steam Power Station|Steam Power plant Lay out

July 03, 2013

General layout of Steam Power Station|Steam Power plant 

General layout of Steam Power Station

Units of  Steam Power plant 

The main power plant can be subdivided into several smaller units namely,

(1). Fuel handling unit.
(2). Ash handling unit.
(3). Boiler unit.
(4). Feedwater unit.
(5). Cooling water unit.
(6). Generator unit.
(7). Turbine unit.

General layout of Steam Power Station|Steam Power plant Lay out General layout of Steam Power Station|Steam Power plant Lay out Reviewed by Bibi Mohanan on July 03, 2013 Rating: 5

Rankine cycle

July 03, 2013
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   It is the idealized cycle for steam power plants. This cycle is shown on p-v,T-v, h-s, diagram  It consists of following processes: 

Process 1-2: Water from the condenser at low pressure is pumped into the boiler at
high pressure. This process is reversible adiabatic.
Process 2-3: Water is converted into steam at constant pressure by the addition of heat
in the boiler.
Process 3-4: Reversible adiabatic expansion of steam in the steam turbine.
Process 4-1: Constant pressure heat rejection in the condenser to convert condensate
in to water.
 Ideal Rankine cycle
     In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and turbine would generate no entropy and hence maximize the net work output. Processes 1-2 and 3-4 would be represented by vertical lines on the T-S diagram and more closely resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapour ending up in the superheat region after the expansion in the turbine, which reduces the energy removed by the condensers.
    The p-v diagram, h-s diagram and T-s diagram are given below.

The efficiency of ideal Rankine cycle is not achieved, which is a reference value of an ideal steam power plant.

In a real power plant cycle (the name 'Rankine' cycle used only for the ideal cycle), the compression by the pump and the expansion in the turbine are not isentropic. In other words, these processes are non-reversible and entropy is increased during the two processes. This somewhat increases the power required by the pump and decreases the power generated by the turbine. In particular the efficiency of the steam turbine will be limited by water droplet formation. As the water condenses, water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the life of turbine blades and efficiency of the turbine. The easiest way to overcome this problem is by superheating the steam. On the T-s diagram above, state 3 is above a two phase region of steam and water so after expansion the steam will be very wet. By superheating, state 3 will move to the right of the diagram and hence produce a drier steam after expansion.
      Due to the pressure drops in the passages and the irreversibilities in various components, the ideal Rankine cycle deviates from the actual Rankine cycle.

The above fig shows the actual Rankine cycle where, 1-21 is due to the irreversible process in feed pump and 3-41 is due to the turbine irreversibility.
    The actual efficiency of steam power plant, by replacing the enthalpies h2 and h4 by h21 and h41 will be,

The actual thermal efficiency, should be made as close as possible to ideal thermal efficiency.
   The thermal efficiency of a steam power plant can be increased by following ways;
a)         Increase in initial steam pressure.
b)         Increase in initial steam temperature.
c)         Increase in condenser vaccum.
d)         Regenerative feed water heating.
e)         By reheating.
f)         By use of economizer.
Reheat cycle (Rankine cycle with reheat):-
 Reheating is a process by which steam at the end of expansion in turbine stages is taken out to boiler or reheater for resuperheating. This reheated steam does more work in the next stage of turbine and increases the thermal efficiency of the plant. The fig. Given below shows a Rankine cycle with single reheat without any feed water heating.
      The purpose of a reheating cycle is to remove the moisture carried by the steam at the final stages of the expansion process. In this variation, two turbines work in series. The first accepts vapour from the boiler at high pressure. After the vapour has passed through the first
turbine, it re-enters the boiler and is reheated before passing through a second, lower-pressure, turbine. The reheat temperatures are very close or equal to the inlet temperatures, whereas the optimum reheat pressure needed is only one fourth of the original boiler pressure. Among other advantages, this prevents the vapour from condensing during its expansion and thereby damaging the turbine blades, and improves the efficiency of the cycle, given that more of the heat flow into the cycle occurs at higher temperature.[ The reheat cycle was first introduced in the 1920s,but was not operational for long due to technical difficulties. In the [1940s] it was reintroduced with the increasing manufacture of high-pressure boilers, and eventually double reheating was introduced in the 1950s. The idea behind double reheating is to increase the average temperature. It was observed that more than two stages of reheating are unnecessary, since the next stage increases the cycle efficiency only half as much as the preceding stage. Today, double reheating is commonly used in power plants that operate under supercritical pressure].

The constant pressure line 5-6 shows the reheat process. If QR is the heat supplied during the reheating, the total heat supplied will be 

Therefore, the thermal efficiency of plant with reheat will be given by,


   The efficiency of the cycle depends upon the reheat pressure. There is an optimum value of reheat pressure. At first reheat, it is 0.2 to 0.25 times the initial pressure of steam whereas for next reheat, it is 0.2 to 0.25 times the first reheat pressure of steam and so on.

Regenerative cycle:-
   The heating of feed water by steam extracted at various points while sending it to the boiler is termed as regenerative heating. Thermal efficiency can be increased by 10% and therefore it is universally used in all steam power plants. The large no. of heaters makes the system design more complicated and leads to considerable loss of pressure. The no. of heaters employed in large steam plants is 6 to 10 with a final feed water temperature of about 2850C.
  Heat rate:-
      It is a measure of the performance of the power plant in converting heat to useful output. It is defined as the no. of heat units required to develop unit power output in an hour. The heat rate decreases with the increase in thermal efficiency.

Rankine cycle Rankine cycle Reviewed by Bibi Mohanan on July 03, 2013 Rating: 5


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