Optimization of Central Air Conditioning Plant by Scheduling the Chiller Ignition for Chiller Electrical Energy Management

Article Info Abstract Article History: Received: April 5, 2021 Revision: April 15,2021 Accepted: May 28, 2021 Currently, the demand for electrical energy in homes, buildings, and industry is increasing, in line with population and economic growth. Of course, because of the massive use of electrical energy, it is necessary to increase efficiency. Large shopping malls in some countries are the biggest consume electricity, especially when it comes to cooling systems. Therefore, it is necessary to save energy in shopping centers. Because there are still few tenants and shopping centers that are relatively quiet, the mall's energy consumption is low, so it requires increasing energy-efficient consumption efficiency by optimizing power management and calculating the chiller performance coefficient (COP). This research aims to increase the chiller performance coefficient (COP) to save energy in shopping centers. The optimization method used is to make changes to the chiller ignition schedule when it's used in malls. Through the analysis from this research, it was found that the COP increased to 0.584, and the value before optimization was 6.181. With increasing COP, the chiller performance will increase. The effect of increasing the chiller's performance could optimize the electrical energy efficiency of the chiller in 138.82 kWh / day.


I. INTRODUCTION
Energy is also a vital issue needed in massive quantities [1]. Improved and economic processes with semiconductor diodes to extend energy demand. in keeping with the Energy Conservation Administration [2], the rise in energy demand from 2010 to 2021 shows that the ever-increasing process additionally causes a rise in national energy demand and makes energy use one of the most important contributors to business cost. First, it happened in Some buildings that need a great deal of energy (especially electricity) are multi-story buildings, factories, hospitals, work buildings and search centers [3].
In previous research, which researched the electrical energy management of the chiller had not tested it during holidays. so, there is a lack of test data in data collection for 1 week [4]. A store could be a multi-story building that's within the mall category and needs a great deal of electricity. Nearly 5 per hundred of the facility is employed to provide an airconditioning system (AC) [5]. To be able to save a great deal of energy, it needs strategic steps to support the authorization of electrical power the maximum amount as doable whereas still implementing the national energy policy in accordance with the provisions of the Minister of Energy and natural resources [6]. One of these sorts of work is energy expenditure for specific buildings and completely different large buildings. [7] The mall is one amongst the buildings that uses most of its energy to run the air-con system. Therefore, it's necessary to optimize the management of the power of water employed in cooling building.
The mall has three coolers, every with 500TR cooling. three coolers can work at identical times to satisfy the cooling load necessities [8]. Meanwhile, in its current condition, the Mall continues to be comparatively quiet because of its openness, therefore the energy potential ill-usage is low. Therefore, it's

B. Refrigeration and Air Conditioning
Cooling and air conditioning are interrelated processes, but each has a different scope. Cooling is the process of lowering the temperature and making the indoor temperature or indoor materials lower than the ambient temperature. In other words, the scope of refrigeration technology lies in the cooling process. AC technology can not only cool the air but also increase the comfort of the user or wearer (comfort air conditioning). According to the definition of air conditioning, the temperature, humidity, flow rate, and cleanliness of indoor air must be adjusted at the same time. Fig. 1 shows the components of the air conditioning system. In Figure 1, there are 5 main components of the air conditioning system, namely a compressor which compresses the air pressure to flow air, a condenser and fan which functions to condense hot air into water whose hot temperature will be removed by the fan. Then the dryer will dry the air that has been condensed into the water where the temperature has cooled. The expansion valve has a function as an air outlet door, from the expansion valve, the air which is still in the form of water droplets will be dried into steam by the evaporator and blower.

C. Chiller
A chiller is a device for producing cold fluid (secondary refrigerant), used in the cold-water distribution system. the chiller has a large capacity. The refrigeration cycle of the system chiller uses propylene glycol, ethylene glycol, or other secondary refrigerants. On cooler / evaporator, the liquid is cooled by the refrigerant which evaporates at a low temperature. After the liquid is cooled in the cooler, the liquid will enter the coil to cool it download. Thus, the temperature of the liquid will rise and return. to coolant and circulate. In a refrigerant system, the refrigerant vapor is sucked into the compressor and the pressure is increased, Thus, the condensation temperature rises and can be melted in the condenser. In this process, the temperature of the cooling medium of the condenser (water or air) rises. Then, the liquid refrigerant flows into the cooler. evaporator through the refrigerant control device (expansion valve). In expansion devices, refrigerants experience a pressure drop. Thus, the 78 boiling temperature drops and is lower than the refrigerant temperature secondary [4]. There are many brands of cooling equipment, one of which is Daikin as shown in Fig. 2. The chiller is used to regulate the temperature of the mall building, thus providing comfortable conditions for Mall visitors who shop at the Mall [15].

D. Vapor Compression System
The compressed steam cooling cycle is the most common type of refrigerator in use today. Cooler consists of four main components as shown in Fig. 3, namely compressor, condenser, expansion valve, and evaporator. In this cycle, the low-pressure refrigerant vapor will be compressed by the compressor into high-pressure refrigerant vapor, then highpressure refrigerant vapor will be condensed into highpressure refrigerant liquid in the condenser [16]. Then the high-pressure refrigerant liquid passes through the expansion valve to lower the pressure so that the low-pressure refrigerant liquid can evaporate back into the evaporator and become lowpressure refrigerant vapor [17].

E. Basis of Perfomance Calculation
The basic basis for calculating the performance of the refrigeration system includes the Coefficient of Performance (COP) and the electrical power consumed by the chiller [18] (1).

F. COPR (Coefficient of Performance)
= ……………….. (1) Where, COP indicates the coefficient of performance, ER is refrigeration effect, and Wk shows the electric power consumed by the chiller.

H. Chiller Electrical Energy Consumption
The total electrical energy consumed by the chiller during operation can be calculated using the following formula (3) Where, W is the electrical energy (kWh), P is the chiller electric power during operation (kW) and t is the operational time (Hours).

I. Average Electric Energy Consumption per Day
The average daily consumption of electrical energy in the chiller during operating hours can be calculated using the following formula (4): Where, kWh/Day is the average consumption of electrical energy in one day [20] (kWh), ∑P is the total chiller electrical power during operation (kW) and t is the operational time (Hours)

A. Planning for Chiller Electrical Energy Management Optimization
Optimization planning for chiller electrical energy management is carried out by changing the chiller ignition schedule from the existing schedule, which can be seen in Table I.

B. Operational Schedule During Optimization
Operational Schedule When the optimization is divided into 2, namely during active days and during holidays, for the schedule during active days it can be seen in Table II. Time Operational (hour) 10 11 12 13 14 15 16 17 18

C. Closed Operational Schedule
The operational scheduling scheme for chiller 1 and chiller 2 during holidays (weekends) is carried out alternately and sequentially as shown in Table III below:   TABLE III -Chiller 2 operates from 12:00 to 21:00.

D. Data Collection
Data taken for this study include data on currents, voltages, and parameters for calculating COP. From these data, we will look for the amount of electrical power consumed, electrical energy per kWh, the average consumption of electrical energy per day, and also the results of COP calculations as the main data that answers the problems in this study. From calculations other than COP, it will be obtained how much it costs and how much energy is needed.

E. Current Data
The current data taken is the 3-phase R / S / T chiller electric current on weekdays and holidays. Shown in Table IV below:     Fig. 5 above, it is explained that the chiller before optimization requires a current in the range of 829A to 915.67A when it is operated on holidays. In the optimized chiller, the required current is much lower at certain hours and only requires a maximum current from 12:00 to 18:00 (Table  V).

F. The Voltage Data
The voltage data taken is the 3 phase R-S / R-T / S-T voltage. operational time a day at chiller 1 and chiller 2.  Fig. 6 and Table VI shows that the chiller before being optimized requires a voltage in the range of 393V to 394V when it is operated on weekdays. For optimized chillers, the required voltage is relatively the same as those that have not been optimized, ranging from 389V to 397V. However, the difference lies at 22:00 where the optimized chiller will shut down at that hour.  As shown in Fig. 7, it is explained that the chiller before being optimized requires a voltage in the range of 394V to 396.5V when it is operated on holidays. For optimized chillers, the required voltage is relatively the same as those that have not been optimized, ranging from 394V to 400V. However, the difference lies at 22:00 where the optimized chiller will shut down at that hour.

H. COP Chiller Parameter Data
For COP, the design unit is taken from the name plate of the chiller machine or the specification of the chiller unit located on the chiller machine panel.

COP Before Optimization
The following is the current chiller specification before optimization (Table VIII).

COP During Optimization
For COP, after optimization, it is calculated from the cooling capacity data and the power input or power needed to operate the chiller. These data are as follows:

a). COP Data During Weekdays (Weekdays)
The results of data collection for chiller 1 and 2 during the optimization process take place on a working day (Table IX).

b). COP Data During Holidays (Weekend)
The results of data collection for chiller 1 and 2 during the optimization process take place on holidays ( Table X).

I. Results of Calculation of Chiller Electrical Energy Consumption Before and After Optimization
The results of the calculation of the average electrical energy consumption of the chiller before optimization with the start-up schedule at 10:00 and the blackout schedule at 22:00. While the schedule after optimization is to delay the ignition of chiller number 2 by 4 hours later on weekdays and 2 hours on holidays with the current and voltage values respectively before optimization are: 885A and 394 V and cos = 0.87. by using equation 2.2, the following results of input power is 524,81kW.
From the results, it can be obtained a comparison of the value of the electric energy consumption of the chiller before and after optimization. It can be concluded that the electric energy consumption of the chiller before optimization is higher than after optimization. Where there is a difference of 138.82 kWh / day where the average power consumption before the optimization is 522.55 kWh / day.

J. COP Average of Chiller During Weekdays and Weekends
From the results of the COP analysis on chiller 1 and chiller 2 during weekdays and weekends, it can be concluded that the COP after optimization increases by 0.584 from the COP before the optimization of 6.181 This is shown in the From the picture above, it is explained that during weekdays, COP Chiller before optimization has increased by 0.631 when compared to the optimized chiller, while during weekends, COP Chiller has increased by 0.537. The average increase in COP Chiller during weekdays and weekends is 0.584.

K. The Resulting Financial Savings
Referring to the Presidential Decree No. 10

IV. DISCUSSION
The results of calculating the COP of the chiller by optimization method is to make changes to the chiller ignition schedule when it is used in malls, it can reduce electrical energy consumption in one day as large as 138.82 kWh and operational costs in terms of chiller electrical energy consumption. Referring to the Presidential Decree No. 10 of 2011 for electricity rates above 30,000 KVA category provided by PT. PLN (Persero), the cost per kWh is Rp. 971.01, both during WBP and LWBP, the financial cost can rescue in one year is Rp. 601.727.955, -. Increasing the COP of the chiller will increase the work efficiency of the engine as well. After changing the ignition schedule according to the research method used, it was found that the average COP increase value was 0.584 which indicated an increase in efficiency by 9.45%.
Previous research on chiller power management also looked for the value of the resulting COP, but the drawback in that study, when compared with this study, is the lack of measurement data and analysis during holidays. Suggestions in this research might be tried with other approaches in order to get a more optimal value. V. CONCLUSION From the results of the optimization analysis of chiller electrical energy management carried out at the mall's Central air conditioning plan the COP was increasing by 0.584, while the value before the optimization is 6.181. So that can be concluded if the COP chiller increases the electrical energy consumption can be saved, corresponding to energy management to save electrical energy used and the performance of the machine also will improve. On the other hand, especially for the efficiency of chiller electrical energy obtained after optimization is 138.82 kWh / day, from the initial value before optimization of 522.55 kWh / day, so that it can save costs as well in future use.