Hi there, welcome in!
We are PerCOMFORT.
Here is the website page of our project!
Introduction
Since the industrial revolution began, more energy-related technologies emerged as key methods to speed up the world’s economic growth and improve capabilities of human that can replace human power. However, our use of energy has created unacceptable climate-change risks. A lot of important but challenging research to explore potential approaches for solving the climate issue are conducted in different fields, which leads to another industrial revolution with affordable, accessible, and sustainable sources of energy [1].
Despite the significant growth in the use of nuclear and renewable energy, petroleum, natural gas, and coal still dominate in the United States energy consumption by fuel in 2020. In this case, how efficiently and effectively we use existing energy sources is very essential to this industrial revolution. Especially for the aspect of thermal management like space heating and cooling, which counts as the majority in total United States energy consumption by end-use sectors in 2019 [2], is not negligible if our community intends to save more energy.
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- Figure 1: 2020 and 2019 US Energy Consumption
Problem Statement
Instead of heating or cooling the entire building, it is more convenient and energy-saving to regulate the surrounding space of human body. Meanwhile, the temperature preference of individuals even differs when they are in the same building. In different seasons, the perfect temperature range for individuals differs as well so that the setting of Heat, Air Ventilation, and Cooling (HAVC) system will be changed frequently. The initial point where the name of our team PerCOMFORT came up is that we prefer personalized comforts.
Here, we demonstrate an electronics system equipped with electrochemically tunable materials that can automatically adjust the potential of power supply, and then control the emissivity of materials once it monitors the temperature difference between human body and ambience. Different emissivity means that the materials can either absorb, reflect, or transmit the radiation heat from human body with materials attached to achieve personal thermal management.
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- Figure 2: emoji for Temperature Comfort
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- Figure 3: Temperature of Different Weather
Inspiration and Goals
Here, we are going to introduce the inspiration part of PerCOMFORT project.
Beside adjusting the HAVC system temperature frequently, there is another method enabling us to live more comfortably and save more energy conveniently: personalized comfort (PerCOMFORT). It focuses on heating/cooling the local environment only around the human body. Unlike traditional air-conditioner providing temperature adjusting to the whole room space, PerCOMFORT can significantly reduce the energy consumption. In addition to the energy saving, PerCOMFORT can provide a higher level of thermal comfort via its individual temperature adjusting function; instead of making all people in the sample space experiencing the same temperature, PerCOMFORT can customize different heating or cooling depending on users’ preference.
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- Figure 4: Personal thermal management [3]
Regards the implementation of PerCOMFORT, heat transfer, materials selection, and circuit designing are going to become the core of our PerCOMFORT project.
Mainly, heat transferring through bodies in three ways: convection, evaporation, and radiation. Radiation has been often overlooked in traditional personal thermal management, but it is an important factor of heat dissipation for human body. Up to 40% of heat loss comes from radiations at normal room temperature; the heat is given off in the form of infrared rays, a type of electromagnetic wave [4]. Therefore, by enhancing or suppressing the thermal radiation can help to adjust the body temperature.
Figure 5: heat loss of human body
When light or radiation hits an object, it is transmitted, absorbed, and/or reflected. Transmission means light passes through a substance; absorption means light energy hitting the surface converted to heat energy; reflection means light bounces off a surface. In thermodynamic equilibrium, the percent of emitted light is equal to the absorbed light.
If we apply these basic optics fundamentals to PerCOMFORT, our main strategy is reflecting solar light and transmitting body radiation for cooling and absorbing solar light and blocking body radiation for heating.
Figure 6: Radiation equations
Based on this main strategy, there are many new advanced materials and fabrication methods have emerged in this personal thermal management area. Here, because different materials have different emissivity, we can choose or even design the material with desired emissivity to fit the heating or cooling requirement. But if we think about a type of materials with tunable emissivity, isn’t it more convenient? After carefully consideration and chemical synthesis, a material with tunable emissivity and easy accessibility called polyaniline. It has three states. The three states correspond to different emissivity.
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- Figure 7: Three states of polyaniline
When we change the potentials that we apply to this material gradually, the emissivity will be changed gradually as well. The emissivity contrast could be up to 48.6%. This contrast means the temperature variation could be at least 10°C.
Our goal is to design a small and portable device. When it detects the difference of human body temperature and ambient temperature. it will evaluate the value of emissivity immediately and then apply the appropriate potential to the materials. During the evaluation process, we also need to consider the influence of humidity. For example, when human stays in a hot and wet room, lower temperature and colling are required to maintain comfort.
- Wearable
- Portable
- Monitor Temperature and Humidity
- Change Temperature around an individual
System Decomposition
The whole system can be divided into three sub-systems: Electronics, Simulation & Modelling, and Hardware. The Electronics module contains five sub-modules: Power Supply, Sensor, Micro-controller, Operational Amplifier Module, and Materials. Esp32 is used as the micro-controller of the entire circuit. LM324N and 4558D constitute an operational amplifier module. ELEGO and Battery pack are served as the power supply module. DHT11 and thermistor work as temperature and humidity sensors.
Because our materials need to be provided with a voltage range of -0.5V to 0.5V, we designed the entire circuit system to realize a monitoring function; the sensor detects ambient temperature and humidity, then transmits the electrical signal to a Micro-controller through a specially designed amplifier module. The function of the Microcontroller is to output the corresponding voltage which is required by the material.
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- Figure 8: System Decomposition
Narrative
- Arduino:
The use of Arduino was the very first assignment that need to be learned. First of all, the Arduino has its own software called ‘Arduino’, and the language used in the software is the same as C programing language. As a beginner, the simplest program that can be done is the lightening program. This program aimed to switch the Arduino light on and off every three seconds (an image shows on the left-hand side, please click on it to see the full video). From the image of the program code (shows on the right-hand side), the first two lines are to initiate the pin 13 which is the pin that controls the LED light specifically. The next part of the program is to demonstrate the loop runs periodically. Then, the code is finalized and ready to run.
The thermistor is a temperature sensor resistance. As the temperature increases, the resistance decreases, and as the temperature decreases, the resistance increases. When considering the choice of temperature sensor, we compared the thermistor and thermocouple, which has different principle of operation , but both of them can achieve the same function we need. However, the thermistor has much smaller size compared with the thermocouple, and is portable, which matches for our project goal.
- Temperature and Humidity Sensors (DHT 11):
DHT11 detects water vapor by measuring the resistance between two electrodes. The resistance change between the two electrodes is proportional to the relative humidity. Higher relative humidity will reduce the resistance between the electrodes, while lower relative humidity will increase the resistance between the electrodes. Please click the link and check the datasheet for DHT 11. We tested the circuit by connecting the DHT 11 with one Arduino and using the finger as the external variable to see the change on humidity and temperature. Also, we added a monitor on it to get the real-time data.
- First Law of Thermodynamics:
The first law is the most basic law in thermodynamics which stands for the sum of the heat transfer and the work transfer equals to the change in the internal energy of the system. The expression [4] is showed below.
However, the first law has different variants base on different situations. Hence, it is important for us to clarify the situation which we are located and reanalysis the first law based on it.
- First Law of Thermodynamics Variant:
Before deriving the formula, several assumptions need to be determined.
Assumptions: 1. The system (human body) is in a steady state
2. No kinetic and potential energy
From the assumptions, the first law became: 
Where T is the temperature, as for lungs, Te stands for the exhale temperature and Ta stands for ambinet temperature. So, for the heat loss in convection for lungs [5],
It is important to notice that the exhale temperature is the air temperature that goes out of the lungs.
- Psychrometric Chart:
The psychrometric chart [6] is the second part that needs to be understood as the intermediate level. As it can be seen in the figure, the x-axis is the temperature value in Celsius, and the y-axis is the relative humidity ratio at gram water per kilogram dry air. In the chart, different zones are showed in different colors. First, the zone showed in purple is the heating zone where people will feel cold at this area and need more heat. Second, the red zone showed on the top of the chart is the cooling dehumidifying zone, which means that in this area the dehumidifier needs to be used in order to decrease the humidity, at the same time the temperature needs to be decreased. Next, the yellow zone showed at the bottom is the cooling humidifying zone which the humidifier needs to be used to increase the relative humidity, also in this area the temperature needs to be decreased. Last but not least, the comfort zone showed in green and located at the center of the chart is what we are most concerned about. Thus, the chart indicates a comfort zone and leads to deep exploration about the numerical relationship between temperature and humidity.
- PerCOMFORT System 1.0:
The system 1.0 was built by Vincent Fu. Please click here to check his LinkedIn page.
First of all, the two Arduinos on the right of the picture are used to provide voltages of +5V and -5V, and the voltages are used for two operational amplifiers. The thermistor measures the human body temperature, and the human body temperature is converted into an electrical signal and transmitted to the operational amplifier. Then the current is conducted to the A0 port of Arduino. The voltage required by the material (corresponding to the temperature measured by thermistor) is calculated through the program inside the Arduino, and it is conducted to both sides of the material through D11, D10, D9, D6, and D5, thereby changing the material characteristics.
The next step was to decrease the size of the system, and that is the reason why we choose ESP32 to replace the Arduino as our micro-controller. The ESP32 has the same code as Arduino but with smaller size and a Wireless/Bluetooth function.
The ELEGO MB V2 can replace two Arduinos showed in the first version of the system. The battery is connected through the 9v Battery Clip, and then the Battery Clip is connected to the DC plug of ELEGO. Directly connect to the esp32 through the USB device connector of ELEGO, which can directly supply power to the esp32.
- PerCOMFORT System 2.0:
We have retained the battery pack, thermistor, and operational amplifier modules when we designed our 2.0 system. The ESP32 and ELEGO MB V2 are used in the 2.0 system, which save more space and make this device more portable. We also did the simulation as we heat up the thermistor and got the voltage change feedback.
- Equation build up:
From the psychrometric chart mentioned early, there must be some numerical relationships between temperature, humidity, and emissivity in order to decide the comfort level. From research, the two equations showed below can determine the comfort level [7].
TSNES stands for thermal sensation and DISC stands for thermal discomfort. Scales of TSENS and DISC indices are as follow: for the TSENS, ±5 intolerable hot/cold, ±4 very hot/cold, ±3 hot/cold, ±2 warm/cool, ±1 slightly
warm/cool, and 0 neutral. For DISC, 5 intolerable, 4 limited tolerance, 3 very uncomfortable, 2 uncomfortable and unpleasant, 1 slightly uncomfortable but acceptable, 0 comfortable.
There are still several unknows that need to be recalculated. For the three temperature terms:
The value of enthalpy of vaporization of water can be found here [8]. To obtain the exact value, the linear interpolation needs to be applied. Next, four heat loss terms are defined:
The way we use those equations is by assuming the TSNES and DISC are both equal to zero. By doing that, we find two equations which shows the relationship between material emissivity, temperature, and relative humidity.
Here are the two equations that we used for coding. The term showed in red are constants which can be found in research paper. The term showed in green is what we need to measure through our system. When coding, the temperature and humidity difference should be the input and the material emissivity is the output.
Here is the code.
This code can run successfully in esp32, but it only considers the influence of temperature. Because the above formula has several complex parameters to be determined, it is necessary to add them into the system in the future.
- Finalized System:
Here is an introduction to the circuit part of the entire device. First of all, this is a third-generation system. The new system has a very small size, like a mouse, which means it is super portable. First, esp32 is used as the micro-controller of the entire circuit. There is a small red circuit board above the esp32, which is an improved amplifier module. On the right side of esp32 is the power supply module. The part above the whole device is the combination of DHT11 and thermistor as temperature and humidity sensors. The entire system has temperature and humidity sensor modules. Therefore, temperature and humidity can jointly participate in regulating the voltage of the material.
Future Work
- Short Term:
As for the short-term plan, an enclosure can be built in order to place the system and make sure it is portable.
- Long Term:
As for the long-term plan, here are two goals that can be achieved.
- Add two more sensors (one for temperature and one for humidity) into the system to collect the temperature and humidity difference. So that the equation as well as the code can be operated without problem.
- The system can be more functional by adding Blood Pressure, Heart Rate, Oxygen Saturation sensors on it.
Reference
[1] Chu, S., & Majumdar, A. (2012). Opportunities and challenges for a sustainable energy future. nature, 488(7411), 294-303.
[2] Source: U.S. Energy Information Administration, Monthly Energy Review, Tablle 2.1, April 2020, preliminary data
[3] Li, X., Xie, W., Sui, C., & Hsu, P. C. (2020). Multispectral thermal management designs for net-zero energy buildings. ACS Materials Letters, 2(12), 1624-1643.
[4] Cengel, Y. A., & Ghajar, A. J. (2007). Heat and mass transfer. A practical approach.
[5] Handbook, A. F. (2017). American society of heating, refrigerating and air-conditioning engineers. Inc.: Atlanta, GA, USA, 59.
[6] Gh.R. Roshan, M. Farrokhzad, S. Attia (2017), Defining thermal comfort boundaries for heating and cooling demand estimation in Iran’s urban settlements, Building and Environment, Volume 121.
[7] Kaynakli, O., & Kilic, M. (2005). Investigation of indoor thermal comfort under transient conditions. Building and Environment, 40(2), 165-174.
[8] Borgnakke, C., & Sonntag, R. E. (2017). Fundamentals of thermodynamics. John Wiley & Sons.
PerCOMFORT Member
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- Yanxi (Krista) Peng
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- Zhiteng Ma
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- Wanrong Xie
