Central Heating Ventilation Air Conditioning (HVAC) System Optimization For Reduction Of Energy Consumption

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1 Central Heating Ventilation Air Conditioning (HVAC) System Optimization For Reduction Of Energy Consumption * Sandesh Hegde, Dr. Ramachandra C G, * Department of Mechanical Engineering Srinivas Institute of Technology Mangaluru, India ramachandra_cg@yahoo.com, sandeshh.hegde92@gmail.com ABSTRACT: The world's population is growing in fast rate and, at the same time consumption of energy and resources also increasing rapidly. After the raw materials, energy got the second highest cost factor in the industry. This cost can be considered as increasing costs. Therefore energy efficiency improvement has two benefits: it benefits not only our environment, but also the profitability of the companies. Heating, ventilation and air conditioning (HVAC) systems will consume major portion of the money spent by a company on the energy. The optimization of the HVAC systems will improve the environment in the organization building and can reduce energy consumed by the particular HVAC system; Hence we can save some amount of energy which consumed by the chiller, so we can reduce the cost which is spent on the energy. Keywords: HVAC; Optimization; Thermal Storage Tank; FRP Blade; ATC Technology: 1. INTRODUCTION The world's population is growing in fast rate and, at the same time consumption of energy and resources also increasing rapidly. After the raw materials, energy got the second highest cost factor in the industry. This cost can be considered as increasing costs. Therefore energy efficiency improvement has two benefits: it benefits not only our environment, but also the profitability of the companies. The HVAC System in any organization account 4% to 5% of total energy used by the organization in the building [2]. So it is no wonder building owners, engineers are looking to improvement in the energy efficiency that can save energy so that we can reduce the costs. By implementing an optimization process, the cooling cost can be reduced by 2 to 15 percent. 1.1 HVAC SYSTEMS In Heating, ventilation and air conditioning (HVAC) systems, heating systems increase the temperature in inside the building to eliminate heat losses. Ventilation systems supply air into the building. Cooling will provide the required cooling level inside the building, where heat gains have resulted from people, equipment or the sun. Central systems, the primary conversion from energy takes place in a utility. Central systems are a combination of central supply and multiple end use subsystems. The end use subsystems are fan systems; they can be single or multiple zone type. The multiple end use zone systems use VAV boxes. 1.2 OPTIMIZATION From the optimization program [4], we can identify energy drains and system inefficiencies and can take decision and corrective actions on the system. A. Optimization Methodology 1. Evaluation of the Energy Use: It starts with a complete energy evaluation of the system. This is accomplished by metering how the each and every energy dollars are being spent now. The evaluation process covers three phase to determine what can be done to improve efficiency Mechanical Infrastructure: First we have to look at the original chillers system design, the original facility requirements and create a benchmark of operations. Take measurement for power consumption. The control system: How is the chillers system being controlled and with what type of control system? Look at the control strategies used for sequencing the equipment. Operational Evaluation: Look at the site-specification issues, such as site limitation or equipment issues forcing a workaround. 2. Identify Your Opportunities: Canara Engineering College NJCIET

2 Compile an energy checklist. Walk round your building and complete the checklist at different times of day (including after hours) to identify where energy savings can be made. Recommend an actions list for optimization. 3. Implementation: Recommended actions typically include repair and changes to mechanical system, adjustments to the control strategy. 2. OBSERVATIONS AND RECOMMENDATIONS Once the original chillers system design and the facility requirements are understood it is evaluated the condition of the equipment, how it s is all connected together and how well it has been maintained. The measurement for power consumption and process variables including temperatures, chiller loading are noted. Then the following recommendation is suggested for energy savings. 2.1 FRP BLADES FOR COOLING TOWER FAN It is observed that plant have 6 cooling tower. The cooling tower fan blades are made up of aluminium. The Fan is driven by motor having capacity of 55KW each. It is recommended to replace aluminium blade by FRP Blade for emerging saving purpose. The fan efficiency in turn is greatly dependent on the profile of the blade. Now the Metallic blades are used in the cooling tower fan. The Metallic blades are heavy; they need a high starting torque requiring a high HP motor [6]. Recommendation: It is better to use Fiber reinforced plastic (FRP) blades. Because FRP fans are light weight. They need a low starting torque and requiring a lower hp motor. The lives of the gear box, motor and bearing is increased. Non corrosive. Low noise levels. Less power consumption. Increase in airflow. Cases reported where metallic or glass fiber reinforced plastic fan blades have been replaced by efficient hollow FRP blades. As a result, the usual payback period for replacing aluminium fans is only 6-7 months.the resulting fan energy savings were in the order of 2-3% and with simple payback period of 6 to 7 months. Return on Investment for FRP Fan in cooling Tower: Sl. No Particular Table 1: Comparison of Aluminium Fan and FRP Fan. Details of existing Aluminium fan Details of FRP Fan 1 Type Axial Flow Aerodynamically Designed Energy efficient Axial Flow 2 Model - PARAG-MAP HV-P19 3 Fan Diameter 552CM 552CM 4 No. Of Blades Fan speed 193RPM 193RPM 6 Blade Material Aluminium Alloy Fiber Glass Reinforce Polymers 7 Airflow 57236ACFM 57236ACFM 8 Motor Capacity 55KW 55KW 9 Power 5.6KW 42.8KW Canara Engineering College NJCIET

3 consumption Table2:Aluminium Fan Detail Aluminium Fan Fan Diameter Air flow Power Consumed by motor for existing fan Running Hours of each motor per day Power consumption of existing fan/day Power Consumption of existing fan/month Total Energy Cost Per Month (Energy cost Rs.11.28) 552cm 57236ACFM 5.6KW/H Average 18 Hours 91KW/Day 273KW/Month Rs.3,7,944 Table3: FRP Fan Detail FRP Fan Fan Diameter 552cm Airflow 57236ACFM Power Consumption of motor for FRP fan 41.4KW/H (approximate) Running Hours of each fan per day Average18 hours Power Consumption per day 745KW/Day Power Consumption per month 2235KW/Month Total Energy cost per Month (Energy cost Rs.11.28) Rs.2, 52, 18 Total Savings from each fan per Month = Energy cost per month while using existing aluminium fan Energy cost per month considering Light weight FRP fan Energy Savings per each fan each fan per Month = 3, 7, 944 2, 52, 18 Energy Savings from each per Month = = Rs.55, 836 Table4: FRP Fan Cost Details No. Installation Sl. Specification of Cost/Unit charge per No Fan fan Total Cost Energy Efficient FRP Axial 1 Total flow fan blade Assembly 6 Rs. 2, 5, Rs. 5, Rs.18,, saving by = 6 * Energy savings per month/fan = 6 * 55, 836 Total Energy Savings = Rs. 3, 35, 16 Return on Investment =Total Cost of fan/ Total Savings per month = 18,, /3, 35, 16 =5.37 Payback Period = 5 to 6 month energy all 6 Fan 2.2 SMALL CAPACITY CHILLER Canara Engineering College NJCIET

4 At present there are six chillers of 25TR capacity of each. During the low load period the plant will operate two or more chillers in part load condition. In part load condition the efficiency of the chiller is less. It is suggested that to install a small capacity chiller of 125TR can be installed as standby unit to operate in low load condition such as 35TR/Hour, 6TR/Hour etc Below sample data shows TR demand in different days. Table5: Chiller loading Data Time\ Date Canara Engineering College NJCIET

5 2.2 SMALL CAPACITY CHILLER At present there are six chillers of 25TR capacity of each. During the low load period the plant will operate two or more chillers in part load condition. In part load condition the efficiency of the chiller is less. It is suggested that to install a small capacity chiller of 125TR can be installed as standby unit to operate in low load condition such as 35TR/Hour, 6TR/Hour etc Below sample data shows TR demand in different days. Table5: Chiller loading Data Time\ Date Canara Engineering College NJCIET

6 Graph1: Chiller loading pattern on 9 nd Oct 14 Graph2: Chiller loading pattern on 16 nd Oct 14 6 Graph3: Chiller loading pattern on 18 nd Oct 14 Graph4: Chiller loading pattern on 1 st Dec Graph5: Chiller loading pattern on 7 th Dec 14 Graph6: Chiller loading pattern on 2th Dec Graph7: Chiller loading pattern on 24th Dec 14 Graph8: Chiller loading pattern on 25 th Dec 14 Return on Investment Calculation (ROI): Existing Chiller capacity 25TR There number of chillers are installed in the utility = 6 Canara Engineering College NJCIET

7 It is observed that most of a period in a day chiller is operated at 6 to 7% load. Hence instead of running two big chillers in part load, it is recommended to install a small capacity chiller to match the demand. So energy can be saved. Now average 11 to 13 Hours/Day chiller are operated at 6 t 7% of full load Then the power consumption =.628 /Ton at 9%FLA For 25TR the total KWH would be =.63 * 25 =1, 57KWH Total power consumption at 7%FLA = 1, 99KWH Now consider a small chiller of 125TR capacity is installed. For centrifugal chiller KW/TR 9%FLA Total KWH for small chiller of 125TR capacity would be = 785KWH Then total energy Savings = 1, 99KWH-785KWH = 314KWH Savings in Energy Cost per Hour = 314 * = Rs.3, 541/Hour (Energy cost Rs /KWH) Now Consider Small chiller is operating Average 11 hours/day Then, Savings in Energy cost per month = 3, 541 * 11 * 3 =Rs. 11, 68, 833/Month The Cost of new small 25TR capacity Chiller 1.9Cr (approximate) Pump, Motor Cabling Cost +Accessories = 2 Lack (approximate) Total Cost for new 125TR chiller = 2.1Cr Pay Back Period = Cost of new chiller / Total Savings per month = 2, 1,, / 11, 68, 833 = Pay Back period will be 17 to 18 Months. I.e. nearly 1.5 years 2.3 AUTOMATIC TUBE CLEANING SYSTEM TECHNOLOGY Shell and tube condensers and heat exchangers are core to HVAC comfort cooling. Unfortunately, the accumulation of efficiencykilling deposits in these heat exchangers is also effects extremely high economic costs [7]. The effects of Accumulation of Deposits: 1. Increased power consumption. 2. Reduced production. 3. Frequent condenser cleaning costs. In HVAC applications, fouling of the chiller condenser tubes has substantial impact on the power consumption of the compressor. Reason for Fouling: 1. Because cooling water contains minerals, such as calcium and magnesium. 2. Cooling water systems are also commonly plagued by biological growth that forms slime or algae on heat transfer areas. 3. Additional foulants include mud, silt, corrosion products, petroleum products, etc. All of these foulants reduce the heat transfer efficiency. Methodologies are commonly used to mitigate or reduce fouling are: 1. Off-line mechanical or chemical cleaning. 2. On-line mechanical cleaning systems. Canara Engineering College NJCIET

8 It is observed that the condensers and heat exchangers tube are periodically cleaned using off-line method. It is recommended to install automatic tube cleaning system for improved energy efficiency and increased equipment life. Off-line Method: Off-line cleaning methods require periodic shutdown of the process for heat exchanger cleaning via hydro blasting, scrapers, nylon or metallic brushes, or chemical cleaning. Major drawbacks of an off-line cleaning approach is that process unit has to be removed from service for cleaning. That the process efficiency immediately degrades after being placed back into service On-line Method: On-line heat exchanger cleaning methods typically involve mechanical cleaning that fall into a category commonly referred to as Automatic Tube Cleaning Systems. Of these systems, the most commonly applied are sponge-ball type tube cleaning systems. Graph 9: Continuous Tube Cleaning Technology Improves Chiller Efficiency OPERATING PRINCIPLE The operation of sponge-ball type automatic tube cleaning systems is based on the passage of elastomeric balls through the heat exchanger tubes. The balls are slightly larger than the tube diameter, and prevent the deposition of scale, bio-film, silt, or other foulants. The sponge balls are periodically injected into the cooling water inlet line and are circulated through the condenser tubes by the cooling water flow. The balls are designed and injected in a method that enables a uniform distribution of balls across the tube sheet. Since the diameter of a ball is slightly larger than the inner diameter of the tube, accumulation of deposits in the condenser tube is prevented by shear forces between the ball and tube wall and the wiping action of the cleaning balls. The balls are constructed of material that is much softer than the tubes, preventing tube erosion. The balls are collected at the outlet of the condenser in a ball trap, which includes a strainer or screen that allows water flow to continue but prevents balls from escaping downstream. Advantages ATCS: Sponge-ball type ATCS technology represents a good opportunity to save energy, reduce maintenance costs, and lengthen chiller life expectancy. And energy efficiency gains up to 15% or more in HVAC applications. Canara Engineering College NJCIET

9 2.4 THERMAL ENERGY STORAGE ENERGY Thermal energy storage is particularly well adapted to air conditioning and industrial refrigeration systems. Table 6: TATA Power TODAY tariff for GVK s CSIA Mumbai Sl No Time Cost per Unit 1 6am-9am Rs am-12non Rs non-6pm Rs pm-1pm Rs pm-6am Rs.1.53 By smoothing the production of cooling energy, the thermal energy storage optimizes the use of electrical resources and protects the environment. The thermal energy storage is a flexible and reliable solution for the management of these important energy needs. It enables a significant reduction in installed chiller capacity (up to 7%), the use of low tariff electricity for significant running cost savings and effective management of cooling according to the real demand. Generally during the night, the chiller charges the STL and supplies the cooling demand. The chiller is controlled by its outlet temperature. During the peak electrical tariff periods the chiller being off and the chilled water stored in tank can be used. Table 7: Sequencing of chiller for minimum cooling cost Time 6am-9am 9am-12non 12non-6pm 6pm-1pm 1pm-6am Current Chiller loading Current average chiller loading / hour TR/H 41TR/H 44TR/H 45TR/H 42TR/H average chiller loading in period 1TR 123TR 264TR 18TR 336TR Total Energy consumed by chillers 78KWH 7995KWH 1716KWH 117KWH 2184KWH Energy cost Rs.87,984 Rs.94,181 Rs.1,93,564 Rs.1,43,676 Rs.2,29,975 Current Total Energy cost/day Rs.7,49,38 Recommended Chiller loading sequence with use of Thermal energy storage tank Time 6am-9am 9am-12non 12non-6pm 6pm-1pm 1pm-6am Recommended average chiller loading per hour 7TR/H 45TR/H 7TR/H average chiller loading in period 21TR 27TR 56TR Total Energy consumed by chillers 1365KWH 1755KWH 364KWH Energy cost Rs.1,53,972 Rs.1,97,964 Rs.3,83,292 New chiller loading sequence Total Energy cost/day Rs.7,35,228 Total Savings per Day Rs.14, 152 Total Savings per month Rs.4,24,56 Total cost of installing thermal storage tank( including tank + motor + installation charges ) Rs.7,, Pay Back period of Thermal Storage Tank 17 months CONCLUSIONS Based on the observation and the surveys of the HVAC literature, this study originally identified 4 technological options that could potentially reduce the energy consumption of HVAC systems in CSIA Mumbai. Optimization is great way to decrease the monthly energy bills. If we install one more small capacity chiller then it can be used to match the load demand and hence we can save chiller energy consumption. The replacement of aluminum blades of cooling tower by FRP blade will also reduces the energy consumption. The ATC Technology will clears the deposition killers inside the chiller coil Tube. The Thermal storage system will reduce the electricity cost Canara Engineering College NJCIET

10 of chiller by changing the operation sequence of the chiller. Hence we can some amount of energy which consumed by the chiller, so we can reduce the cost which is spent on the energy. Implementation of these techniques can result in reduction in the reduction of energy cost which benefits in profitability of the company. REFERENCES [1] Levermore G J, The development and use of building management systems (BEMSs), in Building Energy Management Systems An application to heating and control, (E&FN SPON). [2] Steven T. Taylor Optimizing the design and control of chilled water plant American Society of Heating, Refrigeration and Air- Conditioning Engineers (ASHRAE) Journal, May 29. [3] Jhon Murphy, Using Time-of-Day Scheduling To Save Energy, American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Journal, May 29. [4] Zaheer-uddin M, Zheng G R, Optimal control of time-scheduled heating, ventilating and air conditioning processes in buildings, Journal of Energy Conversion & Management, 41,. [5] Atilla Y, Building Energy Management A Case Study in METU Library, Master Thesis, Mechanical Engineering, METU, (1995), page. 1. [6] Vipin, Parag fan and cooling Impact Group of industries Journal 213. [7] Amberes Innovas Technologies WP-11 Rev. LLC 214 Canara Engineering College NJCIET