Energy savings potentials in buildings through energy audit - A case study in an Indian building

Rajesh Tilwani Electronics & Instrumentation Engineering

Dept. of EEE/ENI Birla Institute of Technology and Science, Pilani

K.K. Birla Goa Campus, India Email: rajesh.tilwani3@gmail.com

C. Sethuraman Senior Scientist

CSIR-Central Scientific Instruments Organisation CSIR Madras Complex, Chennai, India,

Email: csramcsio@gmail.com, Ph.: +91 44 22541061

Abstract— International reports show about 25 to 35% energy saving potential in commercial buildings. Many buildings in India, situated in different climatic zones are energy inefficient since they were not constructed following energy conservation building codes and techniques of solar passive architecture. It is impractical to redesign and reconstruct such buildings. In such cases retrofitting of utilities provides a cost effective solution than going for altering the existing building structures. The aim of this paper is to present the results generated from a detailed energy audit study conducted in an office buildings to propagate the awareness of energy saving potentials in Indian buildings. Based on data collection and measurement undertaken, the present case study envisages many energy-saving measures to be considered for implementation towards achieving the energy saving potential in the identified areas. The identified areas were Air conditioning, Lighting, UPSs, Power factor improvement and installation of Energy Management System (EMS). The analysis revealed that the public office building in which the detailed energy audit was carried out has the annual energy saving potential of 231656 kWh, in terms of cost saving; it would be Rs. 16.2 Lakhs. In order to achieve this benefit, it requires one time investment of Rs. 27.5 Lakhs, resulting the payback period of 1.7 years.

I. INTRODUCTION The growing energy demand and supply gap is one of the reasons for hike in price of fossil fuels. The increasing use of fossil fuels has caused air pollution leading to global warming. These sources of energy are not replenishable and thus the focus is shifting towards energy conservation and use of renewable energy. It is estimated that around 50% of global energy consumption is due to buildings [1]. Energy consumption in buildings varies according to climate, geography, building type and location. The difference between developed and developing countries is also important in this context [2]. India ranks fifth as a global energy consumer [3]. By 2035, India will become import-dependent. India’s energy production would increase by 112%, while consumption would rise by 132% [4]. Indian government has initiated many policies and regulatory measures to ensure energy security but a large number of issues still remain and they require

significant attention. Incorporation of energy efficiency measures in existing and new buildings will help India to achieve a reliable energy future [5]. Energy Audit can be classified into i) Preliminary Audit ii) Detailed Audit. Preliminary energy audit is relatively quick exercise, it estimates the scope for saving using the existing or easily obtained data and helps identify the areas for more detailed study. The detailed energy audit is carried out in three phases: Phase I - Pre Audit Phase, Phase II - Audit Phase, Phase III - Post Audit Phase. This is a comprehensive audit which offers the most accurate estimate of energy savings and cost [6]. In this present study, the methodology used for detailed energy audit was adopted. This paper highlights energy saving potentials and feasibility of achieving the same in the existing public office building in India.

II. METHODOLOGY A public office building located in Chennai, India was

selected to conduct a detailed energy audit study. This building is like many other buildings in India, constructed earlier and expanded its utilities to meet the requirement of functional demand. Such buildings provide a large scope for energy savings through energy efficient retrofit solutions. The building is operational for 5 days in a week. The following steps were taken in order to conduct the study:

• A team of engineers consisting of different disciplines (i.e. electrical, electronics, energy and air conditioning systems) was formed to address the various tasks of detailed energy audit involved in an office buildings.

• Inventory on list of connected loads, month wise energy consumption and bill details collected for last 5 years (2009-2014).

• Electrical single line diagram was prepared mentioning the type of loads connected with transformers and generators to understand the electrical flow and load distribution pattern.

• Performance of energy consuming utilities and various loads were carried out using electrical and thermal energy measuring instruments without disturbing the officials day to day functioning.

• Areas with energy wastage and potential for energy conservation opportunities were found as a results of various rigorous energy analysis.

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Energy saving proposals (ESPs) were prepared with the

details of expected energy savings in kWh, cost saving and approximate investment required for proposals implementation. ESP periods for ESPs were worked out. Instruments used for this study were calibrated, accuracy of the instruments checked in full scale range at lab and then taken to the field for energy study. Transformers loading patterns were recorded continuously with one minute time interval during working and nonworking days. Some realistic assumptions were also made to work out the energy saving proposals.

III. ENERGY USE The building is getting power supply from Tamilnadu

Generation and Distribution Corporation Ltd (TANGEDCO) through 11-kV HT feeder. The incoming high voltage is stepped down to 440 volts through two nos. of 250 kVA transformers. Contract demand of this office building is 350 kVA. The total connected load was 550kVA. The annual energy consumption for the year 2013-14 was 702900kWh. The annual electricity bill was Rs. 61.0Lakhs. The charges for maximum demand (kVA) and energy use are as per Table 1.

Line chart prepared for month wise energy consumption for the past 5 years is shown in Fig.1. It was observed that the energy consumed in the month of December during the last five years was less compared to other months. The reason behind this may be less or no requirement of air conditioning systems due to the low atmospheric temperature in December month. The energy consumption is gradually increasing from December to April and then decreasing in the month of May which may be due to holidays and very less functional activities during that month.

Table-1 Electricity charges

Sr. No

Particulars Value

1 Contract Demand, CD 350 kVA

2 Billing Demand, BD 315 kVA

3 Demand Charge Rs. 300/kVA

4 Energy Charge Rs. 7.0/kWh

The actual demand (kVA) was always less than the contract demand (350kVA) except for one month i.e. Aug. 2009. It might be due to simultaneous operation of more number of connected centralized AC units. There is a possibility of maintaining the actual demand to 300kVA (Fig. 2) but since the billing demand is 90% of 350kVA, there won’t be any benefit of maintaining the demand to 300kVA until and unless there is a proposal from the management to surrender the excess demand to TANGEDCO. Based on the present trend of loading pattern and expansion in activities, it has been suggested to the management that there is no need of surrendering the demand.

Fig.1 Month wise energy consumption for the year 2009-14

Fig. 2 Actual demand in KVA for the year 2009 to 2014

Based on information of major equipment installed the approximate percentage of connected load in kVA is given in Table-2 and Fig. 3

Table-2 Connected load details in kVA

Sr.

No

Name of Energy

Consuming Utilities

Connected load

in kVA

1 Centralized AC 66

2 Stand Alone AC Units (167Nos of 1.5kVA) 250

3 Lighting 80

4 UPS 65

5 Solar Water Heating System 21

6 Others (Pump, Reverse Osmosis, Lift etc.) 68

Total 550

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Fig.3 Percentage of connected load in the building It was observed that the connected load of standalone air conditioning unit was 45% of total electrical load; centralized ac unit was 12%. It can be stated that the office buildings located in India especially in the southern region may consume about 55 to 60% of total energy for air conditioning systems alone followed by lighting, 14%; UPS, 12%; Solar water heating system, 4% and others which includes pumps, RO plant, lift etc, 13%.

IV. ENERGY SAVING PROPOSAL ESP – 1: Replacement of energy inefficient old centralized AC plant with energy efficient inverter variable refrigerant flow (IVRF) system.

The tropical climate of Chennai makes air conditioning one of the major energy consumers during summer months. Presently the building is using a centralized air conditioning plant, vapour compression type. The centralized ac unit consisting of 3 separate units is shown in Fig. 4 and has the capacity of running with 3 nos. of 22TR refrigerant compressors in each unit. The present conventional system installed runs with full speed at all the times. Manual intervention is required to change the operating condition of compressor system.

Fig.4 Photo image of centralized AC plant installed in the building.

The main advantage of IVRF system is that the speed of the compressor motor can be varied from 3% to 100% and maintains constant room temperature throughout the period of operation. The work of heat transfer fluid and working fluid refrigerant is done by refrigerant itself thus increasing efficiency [7]. IVRF reduces duct losses [7]. An experiment conducted by the team revealed that IVRF air conditioning systems consume 40-50% less power than centralized air conditioning system currently installed. The study revealed that the air conditioning systems are not being used properly. The employees sometimes leave their rooms without closing the doors and windows which causes the cool air to escape. Thus general awareness is to be created which will lead to energy saving without any investment. Poor maintenance of the old air conditioning units is causing less overall efficiency. Thus proper maintenance will ensure a long life of system and increased efficiency as well.

ESP – 2: Use of Energy Monitoring and Targeting System (EMTS)

Once the energy flows are transparent there would be a scope for energy saving. Energy flow transparency is the basis for creating energy bench mark i.e. specific energy consumption. Continuous comparison of target values against actual values paves the way for reduction in energy consumption. The benefits of EMTS include energy cost savings up to 15%, better preventive maintenance and waste avoidance [8]. At present there is no energy recording system installed in this office buildings. Payment for the energy use is done as per the bill received from TANGEDCO.

The energy performance index (EPI) of Indian buildings ranges from 200 to 400 kWh/m2/yr. Leaders in Energy and Environmental Design (LEED) and Green Rating for Integrated Habitat Assessment (GRIHA) have adopted Energy Conservation Building Code (ECBC) as a minimum compliance requirement. Bureau of Energy Efficiency (BEE) has developed a star rating for buildings based on actual performance of buildings in terms of its specific power consumption kWh/m2/yr. Hence, it is suggested to install online energy monitoring and targeting system. In the 1st phase of EMTS, it is proposed to monitor energy consumption status at 16 points mainly at the outgoing feeders of MV Panels.

ESP – 3: Energy Saving on Standalone AC Units by improving the overall performance

The unit used for describing the heat extraction capacity of an air conditioner is ton of refrigeration (TR). It was observed from the results of measurement that the overall specific power consumption (SPC), kW/TR of connected standalone ac units was varying from 0.60 to 1.47kW/TR. The average specific power consumption was found to be 0.935kW/TR. It is possible to maintain the specific power consumption as 0.8kW/TR or even below upto 0.6kW/TR if the stand alone AC units are maintained well, by effectively using the thermostat control, removal of dust accumulated in the filter, maintaining the refrigerant gas pressure, slightly increasing the room temperature setting by 2 to 3°C during favourable

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ambient condition and switching off the individual ac units when not required etc.

ESP-4: Energy Savings on UPS by optimum loading

Most manufacturers test their UPSs at full load to show high efficiency of their product. But in real world most UPSs are generally operated at 25 percent to 60 percent of full load. Hardly any system runs at full load. This results in less efficiency of UPS system than expected [9]. In this building 5 Nos of 10kVA and 3 Nos of 5kVA, total 65kVA UPS was installed in this building at various places. The loading patterns of these UPSs installed were studied during the energy audit. Sum of measured load at UPS input and output point was 22.5kVA and 12.86kVA, Table 3. It was observed that except one all other UPSs were lightly loaded i.e. less than 25% of full load.

Table-3 Details of UPS installed and its loading patterns UPS Installed Location Connected

load in kVA

Load at UPS output in kVA

% Loading w.r.t output

kVA

Admin Office 10 2.19 22 Near Projector Room 5 0.63 13 Near Projector Room-New 10 1.48 14.8 Near Projector Room-Old 10 5.76 57.6 UPS room MF1 5 0.44 9.0 UPS room MF2 10 1.08 10.8 UPS room MF3 10 0.68 6.8 UPS in hostel internet 5 0.60 12

Total 65 12.86 18.25 avg

It is known that the efficiency of UPS at 100% loading would be 93%, there would be meager 3% reduction in efficiency up to 30% loading and if the UPS is loaded less than 30% there would be drastic reduction in efficiency. It was proposed to operate the installed UPSs at atleast 50% load always by shifting loads from very lightly loaded UPS to another lightly loaded UPS, which is proposed to be operated at 50% or more loading .Thus it saves the no load losses of lightly loaded UPSs. The no load losses due to heat dissipation would be 750W to 1kW for 10kVA UPS.

ESP-5: Installation of Capacitor Banks at User End to Improve the Power Factor

Real power is the power that performs the actual work. Reactive power (kVAr) is not the useful work but is required to sustain mainly inductive loads like motors. The power actually consumed includes both real power and reactive power and is called as apparent power. Power factor is the ratio of real power to apparent power [10]. During the energy audit the power factor at most of the places was found to be less than 0.8. The total reactive power needed to increase the power factor to 0.98 was calculated and equivalent capacity of capacitor banks was proposed to be installed. This exercise will cause reduction in I2R energy loss where I is the expected reduced current due to improved power factor and R is corresponding cable resistance.

ESP-6: Energy saving by having Separate Lighting Feeder with Servo Voltage Stabilizer

The voltage of the power supply varies between high and low throughout the day and is not constant. There are many disadvantages of variable voltage. Most frequent of which is breakdown of the electrical equipment. Servo voltage stabilizer gives a constant output voltage even when the input supply voltage varies. It reduces breakdown of machinery and equipment. It has high efficiency so will lead to energy saving [11]. During the audit, the potential to reduce the voltage variation in lighting loads was discovered. The voltage measured continuously on 250kVA transformer LT side varies from 370 to 470V. It was suggested to installing a separate 3 phase lighting feeder with a servo voltage stabilizer to control the voltage variations. At higher voltage, for every 1% voltage reduction there would be a saving of 1 to 1.2% energy consumed by the lighting loads at higher voltage. The servo voltage stabilizer would provide stabilized voltage for the lighting equipment. The performance of chokes and ballasts would also improve due to the stabilized voltage supply to the lighting loads.

V. RESULTS AND DISCUSSIONS The ESPs in Section IV were proposed after the analysis of

data obtained from energy audit. Payback period for each proposal was calculated to assess the feasibility of the ESPs. The payback period was calculated by dividing the investment on an ESP by the annual cost saving through the implementation of ESP.

The annual electricity consumption of present conventional air conditioning plant is 168780 kWh. With IVRF system installed this will reduce to 101250 kWh. This means saving of 67530 kWh and Rs. 4.73 Lakhs per year. The total investment required to install IVRF system proposed is Rs. 15 Lakhs. Thus the payback period for this ESP would be 3.17 years.

The annual energy consumption is 702900 kWh. The projected annual energy saving after the installation of EMTS is 35145 kWh. This means an annual saving of Rs. 2.46 Lakhs. The total investment required for purchase and installation of EMTS is 6 Lakhs. Thus the payback period for EMTS would be 2.5 years.

The total installed capacity of all standalone AC units is 282.5 TR. The annual energy consumption @ 0.935 kW/TR considering minimum 5hrs/day and 22days/month operation is 348662 kWh. Annual energy saving achieved by maintaining SPC at 0.8 kW/TR would be 50342 kWh. This corresponds to Rs. 3.52 Lakhs. The approximate investment required for general maintenance to keep SPC at 0.8 kW/TR is 2.5 Lakhs. The payback period for this ESP would be only 9 months.

The total installed capacity of UPSs is 65 kVA. Whereas the actual loading at input of UPSs was only 22.5 kVA and corresponding loading at output point was 12.86kVA. It was proposed to keep UPS capacity as only 30 kVA and to make the remaining 35 kVA as standby. The annual energy saving by keeping 35kVA standby and thus saving 3.5kW power per hour is 30660kWh. The annual cost saving by keeping 35

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kVA UPSs as standby would be Rs. 2.14 Lakhs. The investment required for load setting and control would be around 1.5 Lakhs. The payback period was calculated as 8.5 months for this ESP.

The annual energy and cost savings after power factor improvement from existing to 0.98 would be 37755kWh and Rs. 2.64 Lakhs respectively. The capacitor bank at different sizes needed to be installed for power factor correction at different end user places was 115kVAr and their installation would cost Rs. 1.15 Lakhs. The payback period for this ESP would be 5.22 months.

Presently connected lighting load is 80 kVA. The annual energy consumption on lighting is 102240 kWh. The average voltage recorded was 444V. By maintaining the lighting voltage at 400V, the approximate energy saving would be 10224 kWh. This corresponds to annual saving of Rs. 0.715 Lakhs. Approximate investment required for separate 3 phase feeder with servo voltage stabilizer is Rs. 1.4 Lakhs. The calculated payback period was 2 years.

VI. CONCLUSION The data for energy consumption of the building for 5

years i.e. 2009-2014 were collected and analyzed. A detailed energy audit was carried out which was followed by in-depth analysis of the data obtained. This was done to find out the energy consumption by various equipment installed in the building. This led to identification of opportunities for energy saving. Energy saving proposals that were cost effective were proposed. The energy consumption by centralized air conditioning unit is expected to be reduced by 40% with a payback period of 3.17 years. Atleast 5% of total energy consumption would reduce with a payback period of 2.5 years because of installation of EMTS. The energy consumption by standalone air conditioners would reduce by 15% with a payback period of 9 months. By optimum loading of the UPSs, 5% of total energy consumption would be saved with a payback period of 8.5 months. The total energy consumption would reduce by 5.6% after installation of capacitor banks with a payback period of 5.22 months. The breakdown of lighting loads would reduce along with energy savings after the installation of servo voltage stabilizer with a payback period of 2 years. Many other low cost measures such as use of energy efficient pump and effective use of solar water heating system were proposed along with general recommendations to further help in reducing energy consumption in this building.

ACKNOWLEDGEMENT The authors thank Prof. Amod Kumar, Director, CSIO

Chandigarh and Prof. K. Srinivas, Chief Scientist and Scientist in Charge of CSIO Chennai Unit for their support given during the time of this energy study. The authors also thank the temporarily formed energy audit team members Mr. N. Balakrishna, Mr. Y. Vijayakrishna, Mr. Vamshi Gole, Ms. Chandini Chandrasekaran and Mr. R. Gopinath for their full-fledged support given in the field to take measurements and in the office to prepare the detailed energy audit report.

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