The Hvac System To Water Cooled Chiller Construction Essay
Many studies, empirical analysis, and energy consultants repeatedly claim that there is a large unexploited economic potential for saving energy. Usually, this potential is estimated to be in the range of 10 – 20 %.This dissertation explores the determinants which influence the management of energy efficiency in commercial building, and discuss possibilities how to support the exploitation of energy saving measures.
The theoretical concept is based on the ideas of behavioral decision theory and recent research in the field of organization development. In this view, energy related behavior and decision making in commercial building are formed by ability and the readiness to act of the person involved, and by the internal organizational structure, corporate routine and values.
Conducting the initial energy audit is a critical hurdle for energy efficiency, regardless whether the audit is integrated in an energy management process or a stand alone activity. The initial energy audit requires readiness to act, considerable effort and an extensive amount of practical and methodical knowledge and know how, which commercial building do not possess.
We do the modeling by using the simulate a commercial building. As an example, we identify and thoroughly describe energy saving measures within building heating, ventilation and air conditioning (HVAC) system. Taking into account the conditions of initial energy audit, we modal the measurement in such a way that, apart from basic data no further measurement are required to come to conclusion. The information necessary is acquired using formula, data tables, rule of thumb, estimate and cover in a simplified calculating costs of labor, material, equipment of HVAC equipment and system and how to calculate the resultant energy saving.
Abbreviations, Units and Conversion Factor
List of symbols
Table of Contents
The use of air conditioning in Hong Kong attributes a large proportion of our total electricity consumption, due primarily to its geographic location and economic activities. In 2004, air conditioning accounted for 30% of the total electricity consumption. Our electricity consumption by air conditioning had a growth of about 17% from 1994 to 2004. The use of air conditioning is expected to grow further in view of our increasing population and economic activities. We therefore need to take measures to improve our energy efficiency, in particular, on air conditioning.
Currently, a large amount of energy is being consumed by HVAC systems in buildings. According to the statistics from the Hong Kong SAR government, about 17% of the total energy, which is about 30% of the electric energy (Chow 2006) is being consumed by HVAC systems in buildings. Therefore, energy conservation of HVAC systems in buildings will clearly have a sizeable impact on total energy consumption.
Up to date, a lot of efforts have been made in various buildings to minimize the energy consumption in HVAC systems. For example,
Marriott (2006) proposed three approaches that can be easily applied in buildings to improve the energy efficiencies of HVAC systems. The approaches are optimizing the supply air temperature, recovering energy from condenser water and making use of the geothermal heat pump system.
According to a study conducted by the EMSD, the energy saving from various types of the water-cooled air conditioning system ranges from 14% to 35%. The capital cost of evaporative water-cooled air conditioning system is about 15% lower than air-cooled air conditioning system on new system basis. Hence, if the conversion of existing air-cooled air conditioning system to evaporative water-cooled air conditioning system can be planned at the end of economic life of existing air-cooled air conditioning system, it is likely to have a reduction in replacement cost for choosing evaporative water-cooled air conditioning system in lieu of air-cooled air conditioning system. The operating life of air-cooled packaged chiller condensers is around 15 years while for fresh water cooling towers is around 20 years.
Chan (2006) proposed optimum control logic for the HVAC system of a building in Hong Kong, which minimized the mismatch of cooling load demand and chilled water flow demand. Around 435,000 kWh was saved by the developed control logic from June 2003 to May 2004.
Mathews et al. (2002) developed a simulation tool, QUICK control. It estimates the effect of different control strategies on the energy saving performance in various buildings. Effects of control strategies such as fan scheduling, set point setback, economizer cycle, new set point, fan control, heat plant control, etc. can be investigated in detail this simulation tool. Mathews et al. used this simulation tool to study the energy saving potential in a conference center in South African. A new control strategy was developed with the aid of this simulation tool. It was predicted that about 58% of the HVAC system energy could be saved.
Chan (2006) and Mathews et al. (2002) showed that besides the energy efficiency of the machines (chillers, pumps, fans, etc.), control strategy also plays a very important role on HVAC energy consumption.
Kim et al. (2001) conducted a computational fluid dynamic simulation for analyzing the indoor cooling/heating load. It was coupled with a radioactive heat transfer simulation program and a simulated HVAC control system. The output of the simulated HVAC control system can be fed back to the boundary condition of the CFD simulation program and the indoor environment was simulated. New control signal can then be determined based on the indoor environment. Energy saving performance of the control strategy can be investigated accurately. With the same simulation program, thermal comfort can also be estimated by the calculated indoor status using PMV based approach.
In this paper, a practical study on energy saving in a commercial building was carried out. Chillers, pumps and the control system were retrofitted based on the analysis of the characteristics of commercial building cooling load. Energy conservation performance of the retrofit was investigated.
1.2 Research questions
The aim of this dissertation has been to be answered and prices calculated regardless of what the retrofit involves.
What various options are available to rectify this waste, what is the retrofit cost of each and how much will each save in energy cost?
What is realistic purchase prices of any equipment needed?
How much labor is needed to remove the old one and install the new one
What piping, valve and ductwork change will be needed?
Hoe much labor will be involved in draining original system, flushing, pressuring, testing and refilling new system and start up?
How much will be needed for balancing and adjusting the system and monitoring energy costs?
And lastly, the big question, what will the energy saving be with this approach and what is the payback and return on investment?
It is absolutely necessary to obtain this information and compare the various avenues available and make a wise decision based on accurate and thorough cost projections and energy saving.
1.3 Research objectives
1.3.1 Main objective
The main of the objective is to consideration of perform various retrofit change, calculate the energy saving and the renovation costs. It provides procedure and formulas for energy program, audits, engineering and estimating.
1.3.2 Specific objective
The focus of this dissertation is placed on the specific objective is thinking about energy conservation in HVAC system in the following manner.
Generalities: Start off energy conservation program thinking in terms of principles or generalities and then follow up with particulars. Think about reducing HVAC loads, O & M saving, improving efficiency of equipment and system, reducing flow, etc.
Specific: After a general concept is formed then think in terms of specific heating and cooling equipment, particular HVAC system, piping system, ductwork system, insulation, control, etc.
Load Variation: Think about hoe the building cooling load may vary due to occupancy, the shifting sun, operations, etc. and about which cooling loads are constant on a daily basis without variation.
Low Cost, No Cost Item: Think in terms of no cost, low cost energy saving measures which can be done easily and quickly and which may have phenomenal payback.
Capital Investment Item: Then think in term of capital investment energy improvement searching for those with the greatest energy savings and the highest rate return or fastest payback.
Electrical: Distinguish electrical consumption cost of fans, pumps, chillers, condenser, cooling tower, lighting etc.
1.4 Research methodology
This dissertation using the regression analysis method for establishing the commercial baseline. Regression analysis involves finding the relationship that shows how energy use alters with changes to an independent variable or variables. This relationship can be used to quantify energy use for different values of the independent variables.
Data is collected over the same time period and interval for the proposed independent variables and the dependent variable, in this case energy consumption. The data is then analyzed to develop an equation, generally linear, that describes the relationship or ‘regression line’. This line is an estimate of the dependant variable for values of the independent variable or variables.
Independent variables that affect energy consumption can include factors such as production rate, product mix, raw material, occupancy and ambient temperature.
1.5 Structure of the dissertation
Chapter 2 provide review of existing literature for actual research process of energy saving technique, thereby providing the basis technical information for the energy saving. The chapter begins by estimate the energy auditing for the commercial building and then provides the energy consumption of the commercial building and a methodology for retrofit cost and analysis, financial evaluation.
Chapter 3 addresses research methodology used to generate the energy conversion model for the process used in this study. In additional to this, data collection for Secondary data and Primary data are defined.
Chapter 4 deals empirical simulation using case studies of actual commercial building. This lead to discuss on the procedure and applicability of the models for auditing, retrofit Cost and Analysis, financial Evaluation, as well as an explanation of the energy cost saving that can be obtained as a result.
Chapter 5 concludes the theoretical and the empirical findings and closes the research report by summing up the results and providing ideas for further research.
2. Literature Review
2.1 Energy Audit
The purposed of an energy audit is to determine the energy consumption and cost of overall building and of its specific components, the structure, system and equipment. It is to generate energy improvement options, to project energy saving, to estimate the cost of energy improvement, calculate payback, and on this basis evaluate the various options.
The code of practice mentions the energy audit in Hong Kong. As state by EMSD, (2010) the technical guidance and details in respect of the energy audit requirements under the Ordinance. Energy audits conducted in accordance with this Energy Audit Code are deemed to have satisfied the relevant requirements of the Ordinance in the technical aspects. Energy Audit Code is developed by the EMSD in conjunction with various professional institutions, trade associations, academia and government departments.
(EMSD 2007) In fact, the guideline of energy audit indications that an effective energy management tool. By identifying and implementing the means to achieve energy efficiency and conservation, not only can energy savings be achieved, but also equipment/system services life can be extended. All these mean savings in money.
Based on the principle of “The less energy is consumed, the less fossil fuels will be burnt”, the power supply companies will generate relatively less pollutants and by-products. Therefore, all parties concerned contribute to conserve the environment and to enhance sustainable development.
(International Congress ISPE/PDA Pharmintech 2010) Given that case study at
Sanofi Midy Research Center covers a renovation of a research centre included the data collection review of the documentation it is possible to identify the facility weak points. The example of site survey for verify the consistency of the documentation and the identify the major problems to identify areas more easily upgradeable
According to recent research by (Robert Greenwald 2004), are presentations the overview of the energy audit and conducting the energy audit process included data gathering, utility analysis, inventory and review of equipment performance, measurements and monitoring, identify potential energy conservation measures, analysis of saving potential, financial analysis and reporting.
The (Minnesota Legislature and the Governor commissioned the Minnesota Department 2007) of Commerce to work with the University of Minnesota, Minnesota State Colleges and Universities (MnSCU), and state agencies to identify barriers, describe the costs and benefits of actions that would lead to an annual 1.5 percent energy savings energy used in buildings, and develop policy recommendations that could lead to those actions. The report provides background on energy savings in government buildings and addresses the questions asked by the state law. It also found that state government-owned buildings are a significant potential source of energy savings. The government is in a unique position to think about the long-term implications of present day decisions. Through leading by example, the government can serve as a platform for the development and implementation of energy savings programs, policies and technologies. That said, there are information, organization, and resource barriers to achieving energy savings in Minnesota government buildings.
2.2 Energy Saving Technical
As a corollary (ASHRAE 2011) provide recommendations to design a low-energy-use building and is not a minimum code or standard. The Guide provides both multidisciplinary design strategies and prescriptive design packages to significantly reduce energy consumptions in small to medium office buildings. Even though several design packages are provided in the document, this Guide represents a way, but not the only way, to build energy-efficient small to medium office buildings with 50% energy savings. Energy Standard for Buildings Except Low-Rise Residential Buildings. Use of this Guide can help in the design of major renovations that consume substantially less energy compared to the minimum code-compliant design, resulting in lower operating costs. This Guide presents a broad range of subject matter, including broad concepts such as the integrated design process, multidisciplinary design strategies, and design tips and good practices on specific energy systems, while the focus of this Guide, especially the later chapters, is on building and system details that can help achieve the desired results.
(Dr. James Brodrick, 2002) disturb on surveys of the HVAC literature, identified 170 technology options that could potentially reduce the energy consumption of HVAC systems in commercial buildings. After developing first-cut energy savings potential estimates for each option, 55 options were selected for further study in consultation with a range of HVAC experts Each of the 55 options received further study, including more detailed investigation of their technical energy savings potential, current and future economics (cost), barriers to achieving their full market potential. Many of the 40 technologies have significant technical energy savings potentials. Many of the 15 technologies selected for refined study have significant technical energy savings potential, combined with attractive or reasonable simple payback periods. Three of the options, Novel Cool Storage, Variable Refrigerant Volume/Flow, and Adaptive/Fuzzy Control, had highly variable simple payback periods that did not readily translate into an average simple payback period, while the simple payback period for Microenvironments exceeded 100 years.
Except the above energy saving potential of Literature Review, some valuable Specific topics are shown as below.
2.2.1 Automatic Tube Cleaning System
As the condenser is an important component in the chilled water system, the operating condition of the condenser is the key factor that affects the efficiency of the unit. However, the condenser will be seriously deteriorated by the debris and foul ants accumulated in the tubes of the condensers. When fouling and scaling in the condenser increase, the heat transfer efficiency will be decrease, resulting in more power consumption of the chiller.
The Engineering Department of The Park Lane hotel identified the above problem and started to install an automatic tube cleaning system called “CQM” for chiller in October 2003. The system has been running for 12 months. Feedback from operators and engineers are good, In the COP comparison approach, the percentage of energy saving was 11.9% and the average COP was improved from 3.7 to 4.2. ( Richmond Consulting Engineers, 2005 ).
Further more, (Wallace Wu & Dave Chan, 2003) proves that estimate the improvement on COP is around 11.8% and CQM Automatic Tube Cleaning System can greatly improve the heat transfer efficiency of the condenser tube and save significant amount of energy in water cooled chiller. Besides, from the economic analysis, it shows that the payback is less than 2 years.
2.2.2 Retrofit of the HVAC system to Water Cooled Chiller
The (EMSD 2000) of HKSAR completed a Preliminary Phase Consultancy Study (PPCS) regarding “Wider Use of Water-cooled air conditioning system in Hong Kong” was completed in April 1999. The PPCS established the technical viability of the wider application of WACS and its economic/environmental benefits. The implementation study for WACS in Hong Kong was commissioned in 2000 to examine in greater details on technical viability, financial viability, infrastructure works, land use, traffic impact, environmental/health issues, and regulatory control; especially for nondomestic buildings.
A study guide done by HKUST Research, (2005), describe energy saving in a hotel HVAC system was carried out. It included replacement of the chillers and pumps.
In review the retrofit of the hotel HVAC system, the improved energy efficiency resulted from three aspects, i.e., improved energy efficiency of the chillers, improved energy efficiency of the pumps and the intelligent control system. Comparing the COPs of the original and the new chillers, it is seen that the new chillers has an energy efficiency about 18% to 36% higher than the original chillers which may contribute to about 14.4% to 28.8% of the total energy saving. The efficiency of the new pumps is estimated to be 30% higher than the original pumps. As the pumps generally consume about 20% of the total chiller/pump system energy, the replacement of the pumps contributes to about 6% of the total energy saving. Then, the remaining 27% to 45% of the energy saving should result from the intelligent control system. With the new system, 63% to 74% of the chiller/pump energy was saved. The result shows that a considerable amount of energy can be saved in hotels with a good control system and high efficiencies of the chillers and pumps.
(Kenny Chan 2009) research claims the investigate for sustainable design and life cycle costing considerations in adopting relevant air-conditioning system to cater for long range planning in facility/maintenance management. Form the research and analysis, conversion from ACAS to WCAS would save around 35% running costs.
2.2.3 Variable speed drives
A case study done by ( G Jones 2009) to compares the energy consumption of the centrifugal fan when driven by a star/delta starter and using variable speed drives to control motor speed. During the initial monitoring of the energy consumption, the centrifugal fan was controlled by the original star/delta starter. This had been the method of controlling the fan since the machine was initially installed/ commissioned. After the fan had been running for over 390 hours the exact run-time and energy consumption was recorded. The Motor Control Warehouse then replaced the star/delta starter for a 22kW open loop Inverter. After optimizing the Inverter settings, the fan was used in normal production and after approximately 300 hours, as with the star/delta starter the exact run-time and energy consumption was recorded. Changing the 22kW centrifugal fan control from a star/delta starter to an Inverter introduced an energy saving of 41.3%.
( Lappeenranta x.x.2008 ) analyses the calculation of Fan and Pump energy saving tools calculation. With these programs energy consumption of variable speed drive control for fans and pumps can be compared to other control methods. With Fan centrifugal and axial fans can be examined and Pump deals with centrifugal pumps. By means of these programs also suitable frequency converter can be chosen from the ABB collection.
2.3 Conclusion on the literature review
The chapters above have discussed the related information for the dissertation to assist estimate, measure, evaluate and track energy savings, quantifiable costs and benefits created as a result of implementing energy efficiency opportunities.
Specific improve the understanding of how to forecast and measure energy savings, realize energy savings by accurately quantifying the whole of business costs, benefits and payback of energy efficiency opportunities, determine the economic value of an energy efficiency opportunity so that investment quality information is provided to company decision makers and quantify the accuracy range for each stage of the energy savings analysis.
3.1 Research Methodology
This dissertation is descriptive in nature: it aims to describe the energy saving of the commercial building. Time wise, it focuses on the year 2009, when the research was carried out. Changes in commercial building’s energy consumption between earlier studies and the present one are also observed. To construct a comprehensive picture of the studied phenomenon, the present research utilized both quantitative and qualitative data and means of analysis.
This study is divided into two parts. The theoretical part of the study is a literature review. This existing theory was used as a conceptual tool to gain a more structured understanding of the energy consumption and saving potential of commercial building. Based on the theoretical part, an initial understanding of the commercial building of energy use was built.
The empirical part of the study consisted of one case studies that provided energy consumption of commercial building and the building description of Category, Heating and cooling system, etc. should be present. The research focused on describing the situation of the problem with the existing HVAC system and building and proposed energy saving method of renovation.
The data collected in the theoretical part was also utilized in the empirical part in estimating the current energy consumption of commercial building.
3.2 Data Collection
3.2.1 Secondary data collection
Secondary data sources were utilized both in the theoretical part and the empirical part of this study. Most of the sources used in the literature review were either article published in journals and in industry magazines or conference papers that were accessible through the databases of the Public library. In addition, publicly available resources such as reports from EMSD were used. The secondary data collected for the empirical part consisted of technical details from device manufacturers’ websites.
3.2.2 Primary data collection
The primary data for this research was collected used Hong Kong energy efficiency and conservation competition awards were organized by EMSD. These were used in the empirical part of the study. To estimate the energy consumption of the commercial building in Hong Kong. The dissertation consult the competition awards of the energy saving method to adopted for estimate the energy saving.
3.2.3 Problems related to data collection
The energy analysis was the most problematic part of the data collection phase. This was due to involve much formulation of the questions and lack of open source. It turned out that did not have such information.
In the device convergence case, the purpose was to compare devices in terms of
their life cycle energy consumption. However, life cycle energy data was available for
only a few products. Information on the weight of the products was readily available on the manufacturers’ web sites. In turn, data from which energy consumption could be estimated had to be collected from various sources, including Manufacturer technical report, product descriptions at Internet retailers’ websites and external party sites. Even so, the data sometimes had to be completed with educated guesses.
3.3 Data analysis
The collected data help to develop a strategic plan for energy decisions, just as they would for other key business decisions. A major focus of an energy management plan is performing a self-assessment to identify energy savings opportunities.
4. Results, discussion and evaluation
The typical 34 storey Commercial Building situated at Causeway Bay of Hong Kong Island. used as an caste study in this dissertation was built in 1992. Overall the HVAC, electrical and plumbing system in the building consumed total $ 8 million for the year.
Generate and develop potential energy saving improvement, operation and maintenance correction, reducing flows and resistance of HVAC system, considering more energy efficient equipment and system, lighting, electrical, control, heat recovery possibilities, solar, etc. Then, calculate the potential energy saving of the various improvements and estimate the retrofit costs involved. Lastly, evaluate payback and return on investments.
4.1 Energy Auditing
An energy audit involves the systematic review of the energy consuming equipment/systems in a building to identify energy management opportunities, which provides useful information for the building owner to decide and implement energy saving measures for environmental consideration and economic benefits.
The purpose of an energy audit is to determine the energy consumption and costs of the overall building and its specific components, the structure, system and equipment, it is to generate energy improvement options, to project energy saving, to estimate the cost of energy improvement, calculate payback, and on this basis evaluate the various options.
A good audit is diagnostic in nature, develops a valid prognosis of the cause of energy wastes, and leads to scientific establish remedies. There are two basic phases phase or type of audit, short walk through audits and in depth detail audits, either of the entire building or of only select parts of building.
4.1.1 Collecting Building Information
The audit team should then proceed to collect information on the building. The information should include:-
General building characteristics such as floor areas, numbers of end-users, construction details, building orientation, building facade, etc.;
Technical characteristics of energy consuming equipment/ systems, design conditions and parameters; Building services design report with system schematic diagrams and layout drawings showing system characteristics;
Equipment/system operation records, including data logs of metered parameters on temperature, pressure, current, operational hours, etc.;
Record of EMOs already implemented or to be implemented;
Record of maximum demand readings;
O&M manuals and testing and commissioning (T&C) reports
Energy consumption bills in previous three years.
In general, it should be assumed that the building manager would have information on general building characteristics and the O&M personnel would keep the equipment/system technical and operation records. The audit team should determine the appropriate parties to be approached for information collection, the need to discuss with these parties for familiarization of the building, the equipment/ systems to be investigated and data verification and the need to discuss with selected end-users.
The audit team should consider issuing questionnaires to end-users to collect information on thermal comfort, lighting comfort, operational hours of individual floors/offices, electrical equipment and appliances, etc.
4.1.2 Conducting Site Survey and Measurement
More activities should include the following actions:-
Proceed to plan the site survey for the areas and the equipment/systems to be investigated.
Develop energy audit forms to record the findings.
Plan ahead on the site measurement to supplement or verify the information collected. The measurements should focus on equipment/systems that inadequate information is available to determine their efficiency and equipment/systems that appear to be less efficient.
4.1.3 Analyzing Data Collected
At this stage of the audit, the audit team has collected a lot of information on:-
Equipment/system characteristics obtained from site surveys;
Equipment/system performance data obtained from O&M log sheets;
Equipment/system performance data obtained from site measurements; and
Equipment/system operating conditions of equipment/systems based on design and/or general engineering practices.
Based on the above, the audit team should screen and spot the parameters with values and trends that deviate from what would be anticipated or required respectively. These are the potential EMOs. However, they should take into account the analysis of the irregularities caused by changes in occupancy or other activities.
To identify the improvement works for the potential EMOs, calculations should be performed to substantiate the improvement works by quantifying energy savings. In evaluating the effectiveness of an EMO, the auditor has to calculate the payback period, net present worth or rate of return.
Most calculations can be done using simple payback approach by dividing the EMO’s capital cost by the cost of anticipated annual energy saving to obtain the payback period in years.
However, if there are appreciable deviations between the trends of energy cost and the interest rate or if the capital costs of EMOs are to be injected at different stages with different energy savings achievable at different times, the audit team may have to perform a life cycle cost assessment that can better reflect the cost effectiveness of EMOs.
4.1.5 Annual Monthly Energy Consumption Profile
Based on the energy consumption bills over past years (preferably 3 or more), the auditor should estimate the annual energy use of the building. Graphs of energy consumption against different months of the year can be plotted, from which a pattern or general trend over a number of years can be seen.
These graphs can show normal seasonal fluctuations in energy consumption. More importantly, any deviations from the trend are indication that some equipment/systems had not been operating efficiently as usual, which warrant more detailed studies to identify if further EMO has existed.
4.1.6 The sophistication of an audit
The sophistication of an audit refers to the scope and the extent to which investigations should be conducted and which findings should be analyzed. Based on available resources, the size and type of building, and the energy audit objective, the auditor should adopt the energy audit of different levels of sophistication.
Under such terms, there are two types of audits:-
a.) Walk-through Audit
b.) Detailed Audit
Walk-Through Energy Audit Procedure
Make an initial walk through inspection to become familiar with the building, system, equipment, maintenance, operation, status.
Examine the overall building energy consumption history.
List maintenance, cleaning, adjustment, repair and balancing needed to this point. Determine what maintenance and repair must be done before the detail audit can be performed.
Fill out a “Building and System Description” report
Write out a list of existing energy problem
List obvious and potential energy saving improvement. Develop the most promising energy improvement further.
In-Depth Energy Audit Procedure
Make a through inspection of building system and equipment and become thoroughly familiar with them. Check out operation, performance, maintenance, malfunction, comfort, problem, etc.
Conduct in depth interview with building personnel. Review maintenance, schedule, performance, comfort and problem of building, equipment and system.
Become familiar with actual hours of operation of system and equipment, and the hours of occupancy of the personnel.
Study and analyze at 3 year history of the building electrical and fuel energy consumption. Compare with building consumption indexes of similar building.
Take test reading of actual flow, temperature, pressure, rpm, amps, volts, etc. at HVAC equipment.
Check pressure drop across filter, coil, strainers, etc. Check outside air flow at minimum and maximum.
Seasonal and peak energy calculation
Determine the actual existing seasonal and peak energy consumption and efficiencies of specific system and equipment, etc. based on test and other data.
Calculate the peak and seasonal heating, cooling loads actually required for to meet current conditions for the overall building and various areas of the building. Compare with the design and existing capacities.
Evaluation of energy improvement
List all problems with building, system and equipment.
Generate energy improvement and develop those with most potential. Write out list of improvement.
Calculate the potential energy saving in term of electrical consumption and in cost.
Estimate cost of retrofit work
Calculate payback and return on investment.
4.1.7 Analysis and Identification of Energy Management Opportunities
This part focuses on the detailed analysis and identification of EMOs and should include:-
Comparison on actual performances of equipment/systems against original design (if information available) and/or actual site measurements for any discrepancies and identify the causes thereof;
Possible EMOs and corresponding substantiations;
Implementation costs for EMOs (making reference to corresponding reference numbers assigned to the findings, detailed calculations, schematics and drawings included as appendix); Comparison on the different solutions to the same EMOs, as appropriate;
Initial investment and payback of each EMO in the summary
4.2 Energy Audit Report
To illustrate the energy audit report, a case study is presented in this section. The activities performed for each step of the energy audit are briefly description.
4.2.1 Building and Utility Data Analysis
The first step in the building energy audit process is to collect available information about the energy system and the energy use pattern of the building. This information was collected before the field survey. In particular, from the architectural/ mechanical/ electrical drawing and utility bill, the following information and engineering data were gathering:
Category of Structure
Total Gross Floor Area (m2) : Total 32,607 (office – 26,408 ; retail – 6,199)
Number of Storey - Total 34 storey (B2/F, B1/F, G/F, UG/F and 1/F to 33/F)
Description of floors:-
i) Car park – B2/F and B1/F
ii) Shop – G/F, UG/F and 1/F
iii) Office – 3/F to 33/F
iv) Facilities rooms – 2/F, roofs
Building Construction Detail
Hours of Occupancy and operation
Monday – Sunday (08:00 – 24:00)
Central air-conditioning system
Central air-conditioning supply capacity - Total 1,640 TR (air-cooled type chiller plant)
Central chiller plant system configuration-
The existing system configuration: 4 x 410 TR air-cooled reciprocating type chiller units (using R22)
Central air-conditioning supply (air-side equipment)- 20 nos. of PAUs supply pre-treated air to each tenant units
Electricity supply - 4 nos. of 1,500 kVA electricity supply
Emergency generator 1 no. of 550 kVA generator
Connected electrical loads
For Water Side equipment of central chiller plant – 41.9%
PAU for tenant unit from 3/F to 33/F – 4.1%
Fresh and Flush Water Pump inside 2/F Pump Room – 1.9%
PAU for atrium over the escalator install inside 2/F pump room – 0.5%
Lift No.1 – (Fireman Lift) – 1.8%
Lift No.5,6 and 7 – (Passage Lift for low zone) – 4.9%
Lift No.2,3 and 4 – (Passage Lift for high zone) – 3.5%
Other Include PAU, Ventilation Fan for carpark, public lighting, general power, FS Equipment, control room, fresh/ Flush Pump..etc. – 41.4%
4.2.2 Interview with building personnel.
4.2.3 Walk-Through Energy Audit
After a one day field survey was conducted with the assistant of the building operator. Much useful and revealing information and engineering data were collected.
Problem with the existing HVAC system
It was found that the maintenance is poor. Filter, coil, condenser tube and strainers are generally dirty.
It was discover that the energy consumption paying higher demand rate than need be
Air cooled chiller is old and operate in high COP
4.2.3 In-Depth Energy Audit
Equipment Schedule (HVAC, Fan, Pump)
Overall listing of all HVAC equipment, air handling units, fans, pumps, chillers are required for a concrete comprehensive view of the system of the system in the building and easy review of the their performance.
It is necessary to know the key design figure of the major HVAC equipment as indicated on the plans and specification of flow, pressure, temperature, electrical, etc. and then to take actual reading to know what the current figures factually are.
Electrical Consumption Graphs
The electrical consumption figure can be punched into a spread sheet and graphed automatically as shown.
This help greatly to visualize and analyze the electrical energy situation in term of overall costs, demand charges and KWH per month. Peaks and valleys are more easily recognized and dealt with.
Electrical Cost per month
Electrical consumption history per month
Electrical Demand per month
Electrical KWH per month
Equipment test report
Detailed test report for each major piece of equipment in the building involved with the energy audit and retrofit are very important for accuracy, auditing, redesigning and monitoring later.
Test report is required on major equipment such as fans, chiller, and condensers.
Electrical load per system
This valuable form lists the electrical loads and costs separately for each system in the building and allows to summarize the total for all of the figures and provides an easy review of the system in recap form.
Recap of all electrical loads
This form summarizes all the electrical loads in the building or in the complex, from all sources, not just major HVAC equipment.
It include the total loads from lighting, air handling equipment, air conditioning equipment, computer, office equipment, machinery. The total from this sheet get transferred to the building and system description form.
Cooling Load calculation form
The original cooling load calculations and capacity HVAC equipment chosen at the time, may have greatly changed over the year and new cooling load calculations are required based in the actual current conditions, to end up with reliable energy retrofit program.
Peak Cooling CFM per Area
This is very valuable form shows the peak cooling loads for the main areas in the building and the amount of CFM in each area. The form can be used to examine the original design or what the current loads actually are, in order to analyze and find areas waste and then to do calculations based in energy saving proposals.
4.3 Evaluation of energy conservation Opportunities
Base on the evaluation of energy use pattern of the building, several energy conservation opportunities for the building were analyzed. Among the energy conservation opportunities consideration in the study, some of them successfully reduced energy consumption.
4.3.1 Install automatic tube cleaning system for central chiller.
As the condenser is the important component in chiller, the operating condition of the condenser is the key factor that affects the efficiency of the unit. However, the condenser will be seriously deteriorated by the debris and foul ants accumulated in the tubes of the condensers immediately after the unit comes into operating. When fouling and scaling in the condenser increase, the power consumption of chiller will increase too, as result the efficiency of chiller will decrease.
4.3.2 Energy Recovery Heat Exchangers for Ventilation
Air to air energy recovery heat exchangers can significantly reduce the energy needed to cool and heat ventilation make-up air. The technology is cost effective, with payback periods ranging from less than 1 year to 3 years in most applications. The technology can be used effectively in any building that is reasonably tightly constructed, with the return/exhaust air duct(s) located close to the fresh make-up air intake(s). Currently, ERVs are specified in only about 1% of the potential applications, so a large untapped potential for energy saving exists with this current technology.
4.3.3 Improved Duct Sealing
Duct leakage is a significant source of wasted energy in HVAC systems and both poor workmanship and failure of seals contribute to leaky ductwork. Aerosol duct sealing systems effectively seal existing leaks but do not guarantee that the seals will not fail in the future – especially if the ductwork was poorly supported – and the joints pull apart over time due to thermal and pressure cycling. To reduce energy losses from duct leakage, future efforts should focus on improving the quality of duct installation.
4.3.4 Radiant Ceiling Cooling / Chilled Beam
Buildings with radiant ceiling cooling systems, also known as “chilled beam” systems, cool the room via natural convection and radioactive heat transfer. As noted by Mumma (2001b), current systems almost always require dedicated outdoor air systems (DOAS) and tight building envelopes to manage humidity. Energy saving are realized by significant reductions in air moving power (only the outdoor make-up air is distributed to the building) and the higher evaporator temperature of the chiller supplying cool water to the chilled ceiling panels.
4.3.5 Variable Refrigerant Volume/Flow
Variable Refrigerant Volume, or VRVTM, systems are ductless commercial HVAC systems that can be configured in a highly flexible manner by matching numerous (e.g., up to 16) indoor evaporator units of varying capacity and design with a single condensing unit. Currently widely applied in large buildings such as offices and hospitals outside the U.S., especially in Japan and Europe, these systems are just starting to be introduced in the U.S. The systems use multiple compressors, including inverter-driven variable speed units, and deliver excellent part-load performance and zoned temperature control, resulting in excellent occupant comfort. Both installed costs and energy operating costs are highly application dependent, and current simulation tools are probably inadequate to accurately capture the true energy savings potential of VRVTM systems. The most effective way to address these cost and performance issues would be to perform rigorous field tests comparing them to the best available conventional systems in various real-world buildings and operating conditions.
4.3.6 Water-cooled Air- Conditioning System (“WACS”) to replace the existing air-cooled chiller plant
There has long been shortage of energy resources. Before new sources of energy could be developed, saving would be the only means to safeguard human beings on earth. To improve the air-conditioning plant efficiency is one achievable way to go ahead. Form the above research and analysis, conversion from ACAS to WCAS would save around 35% running costs.
4.3.7 Install Variable Air Volume System
The primary benefit of VAV over constant volume systems (CV) is its ability to simultaneously provide the required level of cooling to any number of zones within a building. VAV systems can be particularly energy efficient as a result of their ability to operate the main supply/extract fan(s) at reduced speeds for much of the year, when the overall volume of air required by the various zones is low (fans are generally the most significant user of energy in a centralized air system).
4.3.8 Install Variable speed drive
At a time of ever increasing energy cost, using variable speed drives to control motor speed instead of the traditional fixed speed direct on line, star/delta starters or soft starters can save energy and money.
4.3.9 Summary of energy conservation Opportunities
To think about the factor of energy conservation opportunities, it should be included the analysis of HVAC retrofit energy consumption and the financial evaluation. The detail is listed as below.
Analysis of HVAC Retrofit energy consumption
Estimate is calculated labor, material and overhead cost on a project and coming up with a reasonably accurate total price which properly reflects the final actual costs of material and labor of the particular project.
Calculate the potential energy saving in electrical and in cost
Estimate cost of retrofit work
The purpose of the following financial evaluation is to determine payback periods, return on investment and rates of return. The involves first costs, operation and maintenance cost, depreciation, taxes, energy saving, present values, future values, interest rates, time period and salvage values.
Return on investment
Rate of return, life cycle discount
According to the above analysis of the energy conservation opportunities, the select three system to be adopt in the first stage base on the energy saving and the payback period. The details of the system are listed below.
4.4.1 Install automatic tube cleaning system for central chiller.
After conversion the chiller system from air cooled chiller to water cooled chiller, it produced another energy saving opportunity.
As the condenser is an important component in the chilled water system, the operating condition of the condenser is the key factor that affects the efficiency of the unit. However, the condenser will be seriously deteriorated by the debris and foul ants accumulated in the tubes of the condensers. When fouling and scaling in the condenser increase, the heat transfer efficiency will be decrease, resulting in more power consumption of the chiller.
To solve the above problem, install an automatic tube cleaning system can be a solution to solving this problem, the advantage of this system is the refrigerant temperature is closer to the condenser water leaving temperature than before and Less frequent for manual cleaning. From the above facts, operation cost of the condenser will be lower. In fact, the condenser is maintaining its cleanliness, therefore the heat transfer is more efficient which result is energy saving.
Automatic tube cleaning system vs. Manual Off-line Cleaning
MANUAL OFF-LINE CLEANING
at maximum efficiency.
decreases between treatments.
No shutdown normally.
Requires shutdown for cleaning.
Cleaning chemicals & residues
harmful to environment.
High due to performance
monitoring & manual cleaning.
In this project, it used water injection system. The Water Injection and Drain System uses to its advantage the fact that the pressure in the heat exchanger main outlet is higher than that of the inlet, (circulation pump is installed after the heat exchanger). It is suitable for low and high-pressure systems.
The sponge balls are injected by water pressure through the check valve into the main inlet of the heat exchanger. The balls return to the collector through the check valve. The cycle is fully automatic and controlled by the PLC commander. The system consists of two automatic valves, the first, a 40mm ball valve that controls water injection, the second 25mm ball valve that controls the drain. The detail scheme is shown as below.
Automatics Cleaning System Scheme
The improvement of energy efficiency in energy management for chiller is concerned with the Coefficient of Performance (COP). The approach used in this report to study the improvement of COP after the installation of automatics tube cleaning system. The supplier provide the data on chiller operation were collected before and after
the automatics cleaning system installation which enable the study of effectiveness of the system in improving the working condition and in reducing energy used.
Assume Chiller No.1 is the one installed with automatics tube cleaning system and Chiller No.2 is the one that without automatics tube cleaning system. In this approach, we shall compare the COP of Chiller No.1 and Chiller No.2. Both chillers’ capacity is
450 TR, and put into operation almost at same time. We assume that both Chiller No.1 and Chiller No.2 are running at the same efficiency when without automatics cleaning system.
The average percentage of energy saving can be calculated using the following formula:
By the definition of coefficient of performance (COP) – cooling, it is the ratio of the rate of heat removal to the rate of energy input. The following equations shall be used to calculate the COP:-
M = Mass flow rate of chilled water (kg/s)
C = Specific heat capacity of water (kJ/kg)
T e = Entering chilled water temperature ( o C)
T l = Leaving chilled water temperature ( o C)
WD = Power Consumption of Chiller (kW)
V = Voltage (V)
I = Current (A)
PF = Power Factor
We assume that the PF = 0.9 and constant M = 70 for the above.
Logged data received by manufacturer’s data from October 2003 to September 2004 of the above parameters for Chiller No.2 and Chiller No.1 were collected for the analysis.
Result and Analysis
COP can be compared when the both Chiller No.1 and Chiller No.2 are running at the same conditions. Chiller No.1 is installed with automatic tube cleaning system, and Chiller No.2 is without automatic tube cleaning system.
According to Figure 1, the COP of Chiller No.1 with automatic tube cleaning system, is generally above that of Chiller No.2 without automatic tube cleaning system,
By using equations (2) & (3), the calculated average COP for Chiller #3 is 3.7 and the average
COP for Chiller #1 is 4.2.
Thus, by equation (1), the average percentage of energy saving = 11.9%
On the other hand, the effectiveness of automatics tube cleaning system can be easily understood by comparing the Condenser Refrigerant Temperature (CRT) and Leaving Condensing Water Temperature (LCWT) Differences. The table below summarizes the above findings.
The average temperature difference dropped to 3.8 0 C after automatic tube cleaning system installation. It drops about 36.7% when comparing to the chiller No.2 that without automatic tube cleaning system installation. The narrowing in temperature difference implies the heat transfer efficiency between condensing water and refrigerant was greatly improved.
In general, automatic tube cleaning system helps in maintaining the cleanliness of the
Condenser Units, thus keeping the peak efficiency of the chiller and hence save energy.
From the above analysis, we can see that automatics tube cleaning system provide a significant improvement on COP. The projected energy saving can be estimated by the following formula
Annual Energy Saving = Rated Power Input x working hour per day x working days per year x diversity factor x Electricity charge x % saving on COP
Working hour per day = 12 hours
Working days per year = 5 1/2 days * 52 weeks = 286
Diversity Factor = 0.5
Electricity charge = HK$ 0.94 per kwh
Simple Payback Period = Cost of automatics tube cleaning system / (Annual energy saving – annual maintenance)
From the above analysis, it proves that Automatic Tube Cleaning System can greatly improve the heat transfer efficiency of the condenser tube and save significant amount of energy in water-cooled chiller. Besides, from the economic analysis, it shows that the payback is less than 2 years.
4.4.2 Water-cooled Air- Conditioning System (“WACS”) to replace the existing air-cooled chiller plant
As describe, over 40% of total electrical energy is estimated to be consumed by water side equipment in central chiller plant. Refer to EMSD information, water cooled air-conditioning systems (WACS) are more energy efficient than their conventional air-cooled counterparts.
In large scale commercial building, the central A/C system can mainly be divided into two parts, i.e. air-side and water side. The components in the air-side include AHU, PAU and FCU. The heat and moisture of conditioned space will be absorbed and taken away to obtain the designed temperature by the air-side equipment. The heat absorbed through the air-side components will be transferred to the water-side; and rejected to atmospheric air or water. The heat rejection component of the water-side (condenser unit) is classified as water type and air type. Higher condensing temperature would lead the compressor doing more work to produce the same cooling effect, giving a lower performance and a higher running cost.
Water cooled chillers use less energy used than their air cooled counterparts. Yet, the circulation of chilled water to room equipment, including the fan coil units, or air handling units is the same for both types of chiller. The main difference between an air cooled chiller and a water cooled chiller is the method of heat rejection - as the name suggests instead of air being used for cooling water is used.
Water cooled chillers do not have large V coils, and fans found in air cooled chillers, so they are physically much smaller, and don't have heat rejection fans like air cooled chillers to discharge the waste heat, instead they are connected to a device called a cooling tower that provides a wet evaporative process to handle the heat rejection from the chiller to the outside air.
Water cooled chiller performance vs Air cooled chiller performance
Water Cooled Chiller Operation and Maintenance
Whilst the running cost is lower, with water cooled chillers, their necessary cooling towers require active management, and should not be operated without regular maintenance. To reject heat, water is passed through a cooling tower where a portion of it evaporates, thus cooling the remaining water. A particular cooling tower’s effectiveness at transferring heat depends on water flow rate, water temperature, and ambient wet bulb. The temperature difference between the water entering and leaving the cooling tower is the range. The temperature difference between the leaving water temperature and the entering wet-bulb temperature is the approach.
The operation and maintenance of the cooling tower is vital the chiller performance since in addition to their primary purpose cooling the condenser water, they are efficient air cleaners.
A large quantity of outdoor air is circulated through the cooling tower and the air is scrubbed cleaning the air, that means the dust and dirt in the air is now deposited into the cooling tower water, this forms muds and sludge which collect in the cooling tower fill and the basin, these must be property treated and cleaned.
Because it is an evaporative process the concentration of chemical elements and solids will increase over time, therefore water treatment protocols are needed to monitor and control the water quality.
The air-conditioning for the shop and office was supplied through a total of
1640 RT air-cooled air-conditioning system (4nos. 340RT; 2nos. 100RT & 1nos. 80RT) installed on podium.
Substantial noise/hot emission/nuisance was created. Silencer was later on installed to reduce the noise, but it also deterred the hot air emission from the system and subsequently reduces the A/C’s overall efficiency. Due to space constrain, it was required to demolish the existing chiller to provide space for the new WCAS.
From the above analysis, it proves that water cooled chiller can save around 35% running costs. Besides, from the economic analysis, it shows that the payback is less than 5 years.
4.4.3 Install Variable speed drive on chiller compressor
Induction motors that typically used for compressors and fans in air conditioning systems are sized to handle maximum load under worst case conditions and then leaving them to run at full power. They are basically fixed-speed motors. Their speed is determined by the constant frequency of the power supply (typically 50 or 60 Hz).
Variable speed drives (VSD) or frequency inverters are solid-state devices and save energy whenever electric motors run at less than full power. VSD is actually a frequency converter in which 50Hz or 60Hz ac input voltage is first rectified into dc which is then converted back into variable-frequency ac voltage. It must be noted that the power demand of motor varies with the cube of the motor speed, i.e. power is proportional to (speed) 3.
This means that a reduction of speed by 20% will result in reduction of power consumption by nearly a half, i.e. 50% saving. Since most HVAC equipment seldom runs at full power, significant energy savings can be made with these variable speed drives.
Motor Energy Saving with VSD
The motors on chillers, pumps, cooling towers and fans account for a significant portion of the energy consumption in HVAC system. The use of retrofit variable speed drives (VSD) is one of the most effective technologies applied in recent years. The VSD can be added on to conventional equipment or can be part of the factory-supplied equipment. The detail of characteristic are shown as below.
Primary Air-handling Unit (PAU)
PAU fan motor without VSD runs at constant speed, disregarding the actual demand.
PAU fan motor is regulated by the actual fresh air demand, ensuring to save energy in part load condition.
Variable Air Volume (VAV) Air-handling Unit (AHU)
AHU fan motor runs at constant speed, airflow regulated by Inlet Guide Vane (IGV) or Outlet Damper (OD), hence increases the resistance in the air path.
AHU fan motor with VSD eliminates the IGV and OD, saving energy through matching airflow to actual demand.
Secondary Chilled Water Circuit
Secondary chilled water pump motor without VSD runs at a constant speed, excess chilled water flow at part load condition will be flown through the bypass pipe.
The speed is regulated according to the differential pressure across the supply and return chilled water pipes, saving energy as the flow of excess chilled water is minimized.
VSD for PAU (Primary Air-handing Unit)
Conventional Primary Air Handling Units (PAUs) usually pre-treat outdoor air at a constant air volume (i.e. CAV). The PAUs supply air to different areas in the building at a constant air flow rate of full load condition, disregard the actual demand. This will waste energy because the PAUs operate at part load instead of full load in most of the time.
Demand control on PAUs using carbon dioxide (CO2) provides unique opportunity to resolve the problem of how to reduce energy costs while optimizing indoor air quality.
CO2 control is best applied to spaces with variable or intermittent occupancy.
Typical Arrangement of variable flow PAU using VSD & CO2 sensors
VSD for Chilled Water Circuit
In chilled water system, the primary loop consists of primary pump sized to circulate the chilled water through the chiller and the rest of the primary piping loop. The secondary chiller water loop, which consists of secondary pump, is a variable flow system. Chilled water is circulated by the secondary pump through the control valves and cooling loads connected to the circuit. However, most of the control valves in the circuit are not fully open because of part load in most of the time. Therefore, the chilled water flow in the secondary water loop can be regulated by VSD to handle the chilled water required by the cooling load, thus to save energy.
Variable Chilled Water Flow System using VSD
Result and Analysis
With damper control, the input power reduces as the flow rate decreases, however under VSD control the power reduction is far more dramatic. The variable torque characteristic of the fan means that the relationship between flow and the speed of the fan is such that the input power reduces in a cube law relationship with the speed reduction, as shown in the graph. Variable speed fan control can be applied in a wide variety of applications including most kinds of ventilation systems, air extract systems, industrial cooling, and combustion-air control systems for boilers. One of the limitations of VSDs is that it is not normally possible to reduce the flow all the way to zero due to a reduction of cooling capacity in the motor; a minimum speed of around 30% is permissible, however this is dependent on the specification of the VSD and motor.
In addition to reducing the power absorbed, VSDs in fan applications may also result in reduced noise in heating and ventilation ductwork due to the elimination of dampers. When regulating flow rates dampers can induce unwanted vortexes in the airflow which create noise and vibration. In a VSD system, making flow-rate changes generally only results in slight changes to the noise levels, which are normally undetectable to the ear.
Fan power when flow regulated by damper vs. flow (speed)
VSD for Chilled Water Circuit
Like fans, using a VSD to control the flow rate from a pump rather than using simple throttle control can result in large power – and therefore cost – savings. This is illustrated in Figure 6, where the broken line indicates the power input to a fixed-speed motor and the solid line indicates the power input to a VSD. The shaded area represents the power saved by using a VSD for a given flow.
In a similar way to using damper control in fan applications, using throttle control for pumping applications results in a drop in pump efficiency, whereas the efficiency remains higher when the output is regulated by speed control. This is illustrated in Figure 7 on page 13.The original fixed speed operating point (1480rpm) of the pump is at (Point 1) where the system curve intersects the head-flow profile at a flow rate of 700m3 /hr, the efficiency is circa.85.1%. If the output is regulated by a throttle the system curve effectively moves to the left (Point2) where the pump efficiency has declined to78%. Conversely if the output is regulated by speed control the operating point moves down the system curve (Point 3) whilst the pump efficiency declines marginally.
Pump power saving when flow regulated by throttle valve vs. speed reduction
A fixed speed pump operates 6000 hours per annum at 1450rpm delivering 125m
3 /hr against a pressure head of 32m, and absorb 15.1kW (Point 1). It is possible to reduce the flow demand by 25% for 60% of the operating time (Point 2). Calculate the associated energy savingpotential, and the electrical cost savings given anelectrical price of £0.08/kWh:First apply the Affinity Laws to calculate thepotential power reduction based on the changein flow from 125m
3 /hr to 93.75m
3 /hr as follows:Calculate the speed (flow) reduction ratio:
3 /hr = 0.75
To calculate new operating head:
2x 32m = 18m
To calculate power absorbed:
3x 15.1 = 6.37kW
Now calculate the current consumption:
6,000 hours x 15.1kW = 90,600kWh
Then calculate the consumption at thedifferent duties:
6,000 x 40% x 15.1kW = 36,240kWh6,000 x 60% x 6.37kW = 22,932kWh
Calculate the annual savings potential:
90,600kWh – (36,240kWh + 22,932kWh)=31,428kWh
Calculate the electrical cost savings:
31,428kWh x £0.08 = £2,514 per annum.
Adjusting pump duty by VSD control
5.1 Conducting This Study
5.2 Energy Efficiency
5.3 HVAC Energy Saving Method
5.4 Model Verification
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