APPLICATION OF SMART SENSORS IN REDUCING ENERGY USAGE IN AIR CONDITIONING
In this elaborated study, the amount of energy used for air conditioning and ventilation is reduced using cell phones, wearable gadgets, detectors that detect temperature and human motion by integrating them as smart sensors. Cell phones, smart wearable gadgets and portable devices placed on human body or integrated with the building structure provide feedbacks to the advanced newly built smart sensors. The data or information given by these can be used to adjust (increase or decrease) air conditioners and ventilation systems in advanced to the tenant’s intentions or activities. Results using this technology show that the indoor temperature can be controlled faultlessly with errors of less than ±0.1 °C. After occupants enter a room, fast chill off or cooling down can be obtained within 2 to 3 minutes to the indoor capacity. Also the total compressor yield or output of the smart air conditioner can be reduced by than that of the particular case using On-Off control. The advanced smart air conditioner could determine the sleeping state and human temperature during sleep using wearable or portable gadgets and adjust the sleeping function flexibly. The sleeping or rest function optimized by the smart aeration and cooling system with wearable units could reduce the energy usage up to 46.9% and keep the human health intact. This new way of smart air conditioner could accomplish a comfortable environment and achieve the goals of energy conservation and environmental protection.
1. DEVELOPMENT OF HEATING, VENTILATION AND AIR CONDITIONING TECHNOLOGY TO REDUCE ENERGY CONSUMPTION.
For a higher quality and comfortable modern lifestyle, individuals depend on air conditioners (ACs) much more than the past. In both developing and developed countries, ACs expands the inhabitance proportion of building zones. This additionally prompts a fast and rapid development in the energy consumption by Air conditioning systems. Concurring to static information, HVAC very nearly expended half of the energy in buildings and 20% of the total national energy utilization. Therefore, it is essential to diminish the energy consumption of Air Conditioning systems in private residential as well as commercial buildings. The techniques of creating new energy-efficient equipment, applying complex and unpredictable control strategies, using sun’s energy as a new vital energy source, etc., are all being considered for saving energy in ACs. Among them, applying control methodologies may be the more economical and proficient technique. The outcomes demonstrate that the energy consumption of pumps can be brought down by using these control procedures. A feedback controller for ACs is designed and improves the energy efficiency of aeration and cooling systems. Experimental outcomes demonstrate that the technique can come with a better coefficient of performance of the Air Conditioner and a comfortable indoor environment even in very hot and humid uncomfortable weather. For multi-unit Air Conditioners, a fuzzy rational control method is used to control the operational number of compressors and fans to enhance energy proficiency. The past researches of applying control methodologies on ACs are mainly based on the difference of parameters and cause the response. This is one kind of passive responses and may not be suitable for human comfort and health. The developing history of Air Conditioners is connected to the efficiency, technology, human comfort, and energy utilization. Air Conditions’ progress includes window type, split type, fixed frequency, convertible frequency, and the recently presented smart type. In the 1990s, to reduce the noise and satisfy the users, window type air conditioners were modified to the split type by moving the compressor outside the occupancy area. Since 2000, the high oil price and the requirement for energy conservation have forced the control of compressors to be changed and improved from fixed frequency to convertible. The fixed frequency control of compressors adopts full power as the On-Off output, and causes temperature varieties and misuse of energy. However, the compressor output and the flow rate of refrigerant can be adjusted using the modified convertible frequency control by utilizing an electronic expansion valve according to the indoor thermal mass for energy conservation. Since 2010, smart cell phones, tablets, personal computers, and cloud computing and 4th generation (4G) communication in 2014 were generally used and have resulted in an information revolution. By utilizing communication technologies, the adjustment of air conditioners is not only a single feedback of setting information. A smart air conditioning system can be combined with an infrared sensor for human position sensing, meteorological webs for outdoor weather information, wearable devices for human activity and intention awareness. Henceforth, air conditioners are expected to alter the indoor temperature efficiently considering human comfort and energy conservation.
2. MATHEMATICAL MODELLING OF AIR CONDITIONING CONTROL AND ENRGY USAGE
This study focused on controlling or managing Air conditioning systems smartly by making use of cell phones, wearable gadgets and smart sensors. It’s the most up to date trend in air conditioner development. Before the design is presented, a mathematical model of aeration and cooling control is derived from fundamental theorems. This will help in the clear cut understanding of the concepts. The basic operating principle of the air conditioner (aeration and cooling system) is the vapor cycle understood using thermodynamics. The steps of vapor cycle are:
(1) The saturated refrigerating liquid is compressed to a higher pressure vapor, also known as superheated vapor;
(2) Eliminating heat energy from the system by either circulating water or air and is condensed into saturated liquid;
(3) Undergoing an unexpected decrease in pressure through the throttle and expansion process, and becoming a liquid and vapor refrigerant mixture with lesser temperature and pressure;
(4) Absorbing or taking in the heat of an enclosed space or space by a circulating fan in the evaporator and expands into the saturated vapor;
(5) Vapor is send back to the compressor in order to complete cooling cycle by cycle. The vapor cycle incorporates compression, heat extraction, expansion, and heat absorption.
This process is completed using the compressor, condenser, expansion valve and evaporator. The more explained operating principles of the vapor cycle include the change in temperature, pressure, enthalpy and entropy. These 4 devices were installed in an air conditioner to carry out the vapor cycle and chill down the closed area in case of a traditional window type air conditioner. Almost 90% of the traditional window type air conditioners are replaced by the split type now. The compressor and condenser of the split type air conditioner are integrated in the outdoor unit to avoid the compressor making noise and disturbing the occupants. In the indoor unit the expansion valve and evaporator are included. One of the many advantages of split AC is the fact that it produces less noise, and this feature has made it the main trend of air conditioners for home and business purposes.
3. SMART CONTROLLER DESIGN BASED ON SMART SENSORS
Before the introduction of the smart control, the On-Off and Inverter control are perfectly described in the following two sub-sections. Both of them, compared with smart control, represent the difference causing control. Then the smart sensors, including portable phones, wearable gadget units and other sensors, are introduced. These will be the key components to decide human intentions. Finally, the outline of a smart controller based on smart sensors and gadgets is illustrated to show the intention causing control.
3.1. On-Off Control of the Fixed Frequency Air Conditioner
The meaning of fixed frequency is the compressor of the AC works in the fixed rotation velocity. The association between the rotation speed of motor and electrical frequency can be explained as:
Speed (rpm) = (120*f) (1-d) p
f = the electrical frequency
p = is the magnetic poles of motor
d = is the rotary slip difference (d = 0 under zero loading).
The temperature inside is kept stable by operating the compressor to on and off positions, when the motor works in the fixed rotation speed and the indoor air conditioning load is less. This method of operating the Air Condition is also mentioned as On-Off control.
In the method of On-Off control, the fixed frequency air conditioner turns on the compressor when the return air temperature is higher than the set one, and turns it off when it’s the opposite. By doing this, the refrigerant would flow through the condenser and evaporator for heat exchanging with the indoor and outdoor air to keep the indoor temperature stable.
3.2. Inverter Control of the Convertible Frequency Air Conditioner
The main air conditioning product for energy conservation is the convertible frequency Air conditioner. It may be characterized as the situation where the rotation speed of the motor could be adjusted or changed according to our wish for regulating the refrigerant energy output by changing the input electric power frequency
Comparing the convertible frequency type with the fixed frequency could first rectify the 60 Hz electricity into the direct current type, and then by using pulse width modulation, modulate the frequency of output electricity. As stated by the feedback temperature difference, the AC could provide the air flow of stable temperature to control the temperature of indoor space by adjusting the refrigerator flow.
4. SMART SENSORS
Smart sensors, including smart versatile phones, wearable units and other sensors, are introduced in the market now. They are the key components of smart control for detecting the human’s intention and passing it on to the system. Mobile phones would provide occupants’ information by incorporating to the GPS and personal schedule for collecting the position and intentions of the person. The air conditioner could cool down the indoor temperature fast before the occupants enter.
The wearable gadgets and their provisions are predicted to have a sudden increase in the coming future. Gadgets that are wearable, such as watches or bracelets, may be adopted for detecting the human sleeping state as the feedback signals of the sleeping function. The accelerator could detect the acceleration between 10 and 10?6 g, the velocity between 10 and 1.67 ×10?9 m/s, and the displacement between 10 and 2.78 ×10?13 m. It can collect human motion information and feedback to the smart air conditioner for further control.
4.1. Smart Control Based on Smart Sensors
Counting the examination of the fixed and convertible frequency control schemes, the quantitative investigation of the smart control based on the smart sensors is the fundamental focus in this paper. Smart control, in view of the information collected by the use of mobile phones and wearable gadgets, strengthens the connection with occupants and carries out the intention causing control. It might incorporate the following aspects: (1) Mobile telephones with GPS and individual timetables, for recognizing the tenants’ position and intentions, could anticipate the occupants’ intention of entering the enclosed area. At this minute, the compressor, which is off in the usual situation, could turn on in the full power. Before entering, the circling fan turns on at the highest speed, and the air deflector swings for 10 min to enhance the air circulation. Consequently, smart control may enable the enclosed space could be chilled off quickly after the tenants enters. (2) The arm ornament with the accelerator could detect the development of tenant while sleeping. After the occupant falls into a deep sleep, the air conditioner would increase the inside temperature lightly to avoid energy consumption. The smart air conditioner could adjust the compressor output actively according to the occupants’ active intention (going home) and passive one (falling into a deep sleep) for the goals of human comfort and energy conservation. The smart air conditioner includes the following devices:
(1) Air conditioner with changeable refrigeration power;
(2) Novel sensors capable of collaborating with inhabitants;
(3) Communicating units for cell phone and network.
Figure demonstrates the controlling structure of smart air conditioner, including ventilation system, temperature sensor, IR indicator, mobile phone and wearable gadgets. The control structure of the smart aeration and cooling system in Figure utilizes a multi-sensor framework to achieve smart control. The indoor infrared sensor can distinguish peoples’ position and carry out the air flow direction control. Cell phones with GPS and personal timetable can be utilised to detect the inhabitants’ position and intention. Wearable units can be the bracelet with the accelerator. It understands the movement of occupants while sleeping. After the occupant fallings into a deep sleep, the smart air conditioner would uplift the indoor temperature lightly to avoid energy utilization.
Figure- The control plan of a smart ventilation system with Inverter control: different from the fixed and convertible frequency air conditioner with difference causing control, it’s an intention causing control that adjusts the compressor output effectively based the occupants’ active intention (going home) and passive one (falling in a deep sleep) for the goals of human comfort and energy conservation.
4.2. Types of smart sensors integrated with the buildings automation system
Like other types of shrewd building innovation, smart HVAC uses sensors that incorporate with your building’s automation system. These sensors gather information about the conditions throughout your building. Other specialized HVAC equipment gives the ability to adjust temperature, dampness, and air flow in various zones (based on data from the sensors) to optimize comfort while decreasing energy consumption.
Strategically-placed thermal sensors can recognizes the differences in conditions in each zone of a room or building. For instance, a crowded conference room can get warm in a hurry, while an open office room with high ceilings can get chilly (since warm air rises and people are closer to the floor). A smart HVAC framework utilises that data to adjust to changing conditions throughout the day or week.
As indicated in a current research by Harvard School of Public Health, high CO2 levels in a building can have a direct negative impact on thinking and decision making. CO2 sensors detects the levels of CO2 gas in an area, which can increase to undesirable levels as occupancy increases. When the threshold is reached, a smart HVAC system can increase levels of fresh air supplied to the space. This technology can have a significant impact on workforce wellbeing.
Occupancy sensors are useful for office conditions (like most) that don’t have uniform utilization constantly. The high increasing in moving workers are leaving desks and conference rooms empty as much as 50 to 60 percent of the time. It means the place is getting heated and cooled for people who are not there. Occupancy sensors detect the presence of people (typically by detecting motion) currently using singular spaces within an office. This information can be used to alter the temperatures based on real-time utilization, saving you money on energy consumption.
The present day modern office spaces and buildings are constructed in such a way that it allows more passage of natural light. But the daylight varies from morning until evening, and from one side of the building to another, and this can create problems on the operation of your Heating, ventilation and air-conditioning system. As a result, spaces exposed to more sunlight turn up too hot while areas with less sun light can become too cold.
5. EXPECTED GOALS AND RESULTS
The expected goals of smart control for air conditioner include human comfort and energy conservation. They could be evaluated by:
(1) Human comfort represented by temperature response: the time to reach the indoor temperature of the setting value, oscillating amplitude of temperature after the steady state and the level of temperature shift.
(2) Energy conservation calculated by compressor energy: a smart socket is used for measuring compressor output during two experiment cases. For On-Off control of the fixed frequency air conditioner, the results of indoor temperature response and compressor output from the beginning to the steady state of 28 °C are shown in Figure 1.
Figure 1- The results of indoor temperature response and compressor output for the fixed frequency air conditioner with On-Off control.In Figure 1, the solid line is the indoor temperature response, and the dotted line is the compressor output. When reaching the setting value of 28 °C, the compressor will be turned off/on to adjust the refrigerant. This will result in the compressor output ratio oscillating between 0 and 100%, and the indoor temperature also oscillating between ±0.6 °C. It is also noted that the indoor temperature increases from 27.4 °C to 29 °C gradually, due to the error of the temperature sensor feedback being within ±0.2 °C. In Figure 15, the accumulated errors of temperature feedback make the switching timing of the compressor occur later, and the indoor temperature also becomes higher subsequently. Therefore, the On-Off control obviously has problems resulting from feedback errors, especially the accumulated error.
For Inverter control of convertible frequency air conditioner, the results of the indoor temperature response and the compressor output from the beginning to the steady state of 28 °C are shown in Figure-2.
Figure 2- The results of indoor temperature response and compressor output for the convertible frequency air conditioner with Inverter control.
In Figure-2, the solid line is the indoor temperature response, and the dotted line is the compressor output. The compressor output decreases from 100% to a stable value of 12%. The indoor temperature keeps at 28 °C, with the error less than ±0.1 °C. Inverter control presents a more stable response of indoor temperature and compressor output than the On-Off one. However, the control output still depends on the error of temperature feedback. For the Inverter control, the PID algorithm in Equation (17) times the errors with a constant, differentiates the errors by time and accumulates the errors. All the complicated calculations take a longer time for the air conditioner to adjust the refrigerant, and the indoor temperature may reach the set value later, after 8 min.
From the theoretical analysis and experimental results, the design of a smart air conditioner with mobile phones and wearable devices could be carried out the intention causing control as the a significant improvement of air conditioner technology. There are some conclusions and recommendations for the smart air conditioners as follows:
(1) The total compressor output of a smart air conditioner is 48.4% less than the fixed frequency one. Indoor temperature can be controlled accurately with errors less than 0.1 °C. Rapid cool down can be achieved in 2 min to the optimized indoor capacity after occupants enter.
(2) The intention causing control of smart air conditioner could be practiced by combing with the GPS, personal schedule and setting information of the mobile phone for the optimized setting of compressor output.
(3) The smart air conditioner with wearable devices could detect the human temperature and action during sleep for determining the sleeping state and adjusting the sleeping function flexibly. The sleeping function optimized by the smart air conditioner with wearable devices could reduce the energy consumption up to 46.9% and maintain the human health. Based on these results, the smart air conditioner with mobile phones and wearable devices could carried out the intention causing control as a significant improvement of air conditioner technology, and be improved for human comfort and energy conservation in the coming future.
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