Active cooling

Last updated August 13, 2023

Active cooling is a heat-reducing mechanism that is typically implemented in electronic devices and indoor buildings to ensure proper heat transfer and circulation from within.

Unlike its counterpart passive cooling, active cooling is entirely dependent on energy consumption in order to operate. It uses various mechanical systems that consume energy to dissipate heat. It is commonly implemented in systems that are unable to maintain their temperature through passive means. Active cooling systems are usually powered through the use of electricity or thermal energy but it's possible for some systems to be powered by solar energy or even hydroelectric energy. They need to be well-maintained and sustainable in order for them to perform its necessary tasks or the possibility of damages within objects could occur. Various applications of commercial active cooling systems include indoor air conditioners, computer fans, and heat pumps.^[1]^[2]^[3]

Building usage

Many buildings require high demands in cooling and as much as 27 out of 50 largest metropolitan areas around the world are located in areas of hot or tropical weather. With this, engineers have to establish the heat balance in order to ensure proper ventilation throughout the structure.

The heat balance equation is given as:

$p\cdot c_{p}\cdot V\cdot dT/dt=E_{int}+E_{Conv}+E_{Vent}+E_{AC}$

where $p$ is the air density, $c_{p}$ is the specific heat capacity of air at constant pressure, $dT/dt$ is the rate of heat transfer, $E_{int}$ is the internal heat gains, $E_{Conv}$ is the heat transfer through the envelope, $E_{Vent}$ is the heat gain/loss between indoor and outdoor air, and $E_{AC}$ is the mechanical heat transfer.^[2]

Using this, it can be determined how much cooling is required within the infrastructure.

There are three active cooling systems commonly used in the residential sectors:

Fans

A fan is three to four blades rotated by an electrical motor at a constant speed. Throughout the rotation, airflow is produced and having the surrounding being cooled through the process of forced convection heat transfer. Because of its relatively low price, it is the most frequently used out of the three active cooling systems in the residential sector.

Heat pumps

A heat pump utilizes electricity in order to extract heat from a cool area into a warm area, causing the cool area to lower in temperature and the warm area to increase in temperature.^[4]^[5]

There are two types of heat pumps:^[6]

Compression heat pumps

Being the more popular variant of the two, compression heat pumps operates through the use of the refrigerant cycle. The vapor refrigerant in the air gets compressed while increasing in temperature, creating a superheated vapor. The vapor then goes through a condenser and converts into a liquid form, dispelling more heat in the process. Traveling through the expansion valve, the liquid refrigerant forms a mixture of liquid and vapor. As it passes through the evaporator, vapor refrigerant forms and expels into the air, repeating the refrigerant cycle.

Absorption heat pumps

The process for the absorption heat pump works similarly to the compression variant with the main contrast being the usage of an absorber instead of a compressor. The absorber takes in the vapor refrigerant and creates a liquid form which then travels into the liquid pump to be turned into superheated vapor. The absorption heat pump utilizes both electric and heat for its functionality compared to compression heat pumps which only uses electricity.^[2]

Evaporative coolers

An evaporative cooler absorbs the outside air and passes it through water-saturated pads, lowering the temperature of the air through water evaporation.^[7]

It can be divided by:

Direct

This method evaporates the water which would then travel directly into the air stream, producing a small form of humidity. It usually requires a decent amount of water consumption in order to properly lower the temperature of the surrounding area.

Indirect

This method evaporates the water into a second air stream and then putting it through a heat exchanger, lowering the temperature of the main air stream without adding any humidity. Compared to direct evaporative coolers, it requires much less water consumption to operate and lowering temperature.^[2]

Electronic device cooling

Other applications

Besides normal commercial usage of active cooling, researchers are also looking for ways to improve the implementation of active cooling into various technologies.

Thermoelectric Generator(TEG)

The thermoelectric generator, or TEG, is a power source that has been recently experimented with to test its viability in maintaining active cooling. It is a device that makes use of the Seebeck effect to convert heat energy into electrical energy. Applications of the power source are more commonly found in technologies requiring high power. Examples include space probes, aircraft, and automobiles.

In a 2019 research, the viability of TEG active cooling was tested.^{[ citation needed ]} The test was applied on a Raspberry PI3, a small single-board computer, equipped with a fan powered by TEG and was compared alongside another powered by a commercial passive cooler. Throughout the research, the voltage, the power, and the temperature in both of the Raspberry PIs were observed and recorded. The data showed that throughout the benchmark test, the TEG- powered Raspberry PI3 stabilized to a temperature a few Celsius lower than the passive cooling Raspberry PI3. The power produced by the TEG was also analyzed to measure the possibility of the fan having self-sustainable capabilities. Currently, using only TEG to power the fan isn't enough to be completely self-sustainable because it lacks enough energy for the initial startup of the fan. But, with the implementation of an energy accumulator, it would be possible.^{[ citation needed ]}

The power generation of TEG is given as:

$P_{TEG}\rightarrow {fanairflow \over fanpower}\rightarrow \sum R_{thermal}\rightarrow \bigtriangleup T_{TEG}\rightarrow P_{TEG}$

where $P_{TEG}$ is the power generated by TEG, $R_{thermal}$ is the thermal resistance, and $T_{TEG}$ is the temperature from TEG.

Based on the result, the thermoelectric generator active cooling has been shown to effectively decrease and maintain temperatures that is comparable to commercial usage of passive coolers.^[8]^[9]^[10]

Near Immersion Active Cooling (NIAC)

Near Immersion Active Cooling, or NIAC, is a thermal management technique that has been recently researched in an effort to reduce the amount of heat accumulation generated by Wire + Arc Additive Manufacturing, or WAAM (a metal 3-D printing technology). NIAC utilizes a cooling liquid that surrounds the WAAM within a work tank and increases the water level when metal is being deposited. The direct contact with the liquid allows for quick withdrawal of heat from the WAAM, decreasing temperature by a significant amount.^[11]

In a 2020 experiment, researchers wanted to discover the feasibility of using the NIAC and to test its cooling capabilities. The experiment compared the effectiveness of mitigating temperature generated by the WAAM between natural cooling, passive cooling, and near immersion active cooling. Natural cooling used air, passive cooling used a cooling liquid that stays on a fixed level, and NIAC used a cooling liquid that rises based on the actions of the WAAM.^[11]

The following tests were used to measure the feasibility of using NIAC:^[11]

Thermal analysis: In the thermal analysis, there was a significant disparity of heat between NIAC and the other cooling types, with NIAC cooling the technology at a much faster rate.
Geometric quality: For the geometric quality of the walls, NIAC had the slimmest and tallest wall which shows tough durability of the WAAM when using active cooling.
Porosity assessment: The porosity assessment showed that active cooling contained the lowest porosity level. A high porosity level has adverse effects on mechanical properties, such as limited ductility.^[12]
Mechanical properties: NIAC tends to equalize the mechanical properties, especially ductility, in contrast to both natural and passive cooling.

They concluded NIAC is viable and comparable to conventional cooling methods such as passive and natural cooling.^[11]

Comparison with passive cooling

Active cooling is usually compared alongside passive cooling in various situations to determine which provides a better and more efficient way of cooling. Both of these are viable in many situations but depending on several factors, one could be more advantageous than the other.

Advantages

Active cooling systems are usually better in terms of decreasing temperature than passive cooling systems. Passive cooling doesn't utilize much energy for its operation but instead takes advantage of natural cooling, which takes longer to cool over a long period of time. Most people prefer the use of active cooling systems in hot or tropical climates than passive cooling because of its effectiveness in lowering temperature in a short time interval. In technologies, it helps maintain proper thermal conditions, preventing the risk of damages or overheating of the core operation systems. It is able to better balance out the heat generation from the technology, maintaining it in a consistent manner. Some active cooling systems also contain the possibility of being self-sustainable as shown in the application of the thermoelectric generator compared to passive cooling where it is highly dependent on natural means to operate.^[9]^[11]

Disadvantages

The issues with active cooling compared to passive cooling are mainly the financial costs and energy consumption. Because of active cooling's high energy requirement, it makes it much less energy efficient as well as less cost efficient. In a residential setting, active cooling usually consumes a large amount of energy in order to provide enough cooling throughout the entire building which increases the financial costs. Engineers of the building would need to take in account that an increase in energy consumption would also play a factor in negatively affecting the global climate.^[2] Compared to active cooling, passive cooling are more seen being used in places with average or low temperatures.

Related Research Articles

A heat pump is a device that uses work to transfer heat from a cool space to a warm space by transferring thermal energy using a refrigeration cycle, cooling the cool space and warming the warm space. In cold weather a heat pump can move heat from the cool outdoors to warm a house; the pump may also be designed to move heat from the house to the warmer outdoors in warm weather. As they transfer heat rather than generating heat, they are more energy-efficient than other ways of heating a home.

<span class="mw-page-title-main">Heat transfer</span> Transport of thermal energy in physical systems

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.

Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC) and occasionally a thermoelectric battery. It can be used either for heating or for cooling, although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.

A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.

An evaporative cooler is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning systems, which use vapor-compression or absorption refrigeration cycles. Evaporative cooling exploits the fact that water will absorb a relatively large amount of heat in order to evaporate. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation). This can cool air using much less energy than refrigeration. In extremely dry climates, evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.

For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, and hydraulic motors that are assembled into hydraulic machinery, hydraulic drive systems, etc. In pneumatics, the working fluid is air or another gas which transfers force between pneumatic components such as compressors, vacuum pumps, pneumatic cylinders, and pneumatic motors. In pneumatic systems, the working gas also stores energy because it is compressible.

<span class="mw-page-title-main">Chiller</span> Machine that removes heat from a liquid coolant via vapor compression

A chiller is a machine that removes heat from a liquid coolant via a vapor-compression, adsorption refrigeration, or absorption refrigeration cycles. This liquid can then be circulated through a heat exchanger to cool equipment, or another process stream. As a necessary by-product, refrigeration creates waste heat that must be exhausted to ambience, or for greater efficiency, recovered for heating purposes. Vapor compression chillers may use any of a number of different types of compressors. Most common today are the hermetic scroll, semi-hermetic screw, or centrifugal compressors. The condensing side of the chiller can be either air or water cooled. Even when liquid cooled, the chiller is often cooled by an induced or forced draft cooling tower. Absorption and adsorption chillers require a heat source to function.

Computer cooling is required to remove the waste heat produced by computer components, to keep components within permissible operating temperature limits. Components that are susceptible to temporary malfunction or permanent failure if overheated include integrated circuits such as central processing units (CPUs), chipsets, graphics cards, and hard disk drives.

An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. The system uses two coolants, the first of which performs evaporative cooling and is then absorbed into the second coolant; heat is needed to reset the two coolants to their initial states. The principle can also be used to air-condition buildings using the waste heat from a gas turbine or water heater. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration. Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater or by a mains-powered electric heater. Unlike more common vapor-compression refrigeration systems, an absorption refrigerator has no moving parts.

Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.

<span class="mw-page-title-main">Turboexpander</span>

A turboexpander, also referred to as a turbo-expander or an expansion turbine, is a centrifugal or axial-flow turbine, through which a high-pressure gas is expanded to produce work that is often used to drive a compressor or generator.

Solar air conditioning, or "solar-powered air conditioning", refers to any air conditioning (cooling) system that uses solar power.

An air source heat pump (ASHP) is a type of heat pump that can absorb heat from outside a structure and release it inside using the same vapor-compression refrigeration process and much the same equipment as air conditioners but used in the opposite direction. Unlike an air conditioning unit, most ASHPs are reversible and are able to either warm or cool buildings and in some cases also provide domestic hot water.

A thermal expansion valve or thermostatic expansion valve is a component in vapor-compression refrigeration and air conditioning systems that controls the amount of refrigerant released into the evaporator and is intended to regulate the superheat of the refrigerant that flows out of the evaporator to a steady value. Although often described as a "thermostatic" valve, an expansion valve is not able to regulate the evaporator's temperature to a precise value. The evaporator's temperature will vary only with the evaporating pressure, which will have to be regulated through other means.

A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux directly into electrical energy through a phenomenon called the Seebeck effect. Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient.

Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. A heat pump is a mechanical system that allows for the transmission of heat from one location at a lower temperature to another location at a higher temperature. Thus a heat pump may be thought of as a "heater" if the objective is to warm the heat sink, or a "refrigerator" or “cooler” if the objective is to cool the heat source. In either case, the operating principles are similar. Heat is moved from a cold place to a warm place.

In systems involving heat transfer, a condenser is a heat exchanger used to condense a gaseous substance into a liquid state through cooling. In so doing, the latent heat is released by the substance and transferred to the surrounding environment. Condensers are used for efficient heat rejection in many industrial systems. Condensers can be made according to numerous designs, and come in many sizes ranging from rather small (hand-held) to very large. For example, a refrigerator uses a condenser to get rid of heat extracted from the interior of the unit to the outside air.

HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

Thermoelectric acclimatization depends on the possibility of a Peltier cell of absorbing heat on one side and rejecting heat on the other side. Consequently, it is possible to use them for heating on one side and cooling on the other and as a temperature control system.

References

↑ "Thermal Management of Electronics: Active vs Passive Cooling". arrow.com. 2020-01-31. Archived from the original on 2020-12-18.
1 2 3 4 5 Oropeza-Perez, Ivan; Østergaard, Poul Alberg (2018-02-01). "Active and passive cooling methods for dwellings: A review". Renewable and Sustainable Energy Reviews. 82: 531–544. doi:10.1016/j.rser.2017.09.059. ISSN 1364-0321.
↑ "Cooling systems for buildings". www.designingbuildings.co.uk. Retrieved 2020-11-15.
↑ "Heat Pump Systems". Energy.gov. Retrieved 2020-11-11.
↑ "What are the advantages & disadvantages of a heat pump?". www.heatpumpchooser.com. Retrieved 2022-09-02.
↑ Lechner, Norbert (2014-10-13). Heating, Cooling, Lighting: Sustainable Design Methods for Architects. John Wiley & Sons. ISBN 978-1-118-58242-8.
↑ "Evaporative Coolers". Energy.gov. Retrieved 2020-11-11.
↑ Champier, Daniel (2017-05-15). "Thermoelectric generators: A review of applications". Energy Conversion and Management. 140: 167–181. doi:10.1016/j.enconman.2017.02.070. ISSN 0196-8904.
1 2 Tosato, Pietro; Rossi, Maurizio; Brunelli, Davide (2019). Saponara, Sergio; De Gloria, Alessandro (eds.). "Investigating an Active Cooling System Powered by a Thermoelectric Generator". Applications in Electronics Pervading Industry, Environment and Society. Lecture Notes in Electrical Engineering. Cham: Springer International Publishing. 573: 205–211. doi:10.1007/978-3-030-11973-7_24. hdl: 11572/279975 . ISBN 978-3-030-11973-7. S2CID 164862741.
↑ Zhou, Y.; Paul, S.; Bhunia, S. (March 2008). "Harvesting Wasted Heat in a Microprocessor Using Thermoelectric Generators: Modeling, Analysis and Measurement". 2008 Design, Automation and Test in Europe. pp. 98–103. doi:10.1109/DATE.2008.4484669. ISBN 978-3-9810801-3-1.
1 2 3 4 5 da Silva, Leandro João; Souza, Danielle Monteiro; de Araújo, Douglas Bezerra; Reis, Ruham Pablo; Scotti, Américo (2020-03-01). "Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM". The International Journal of Advanced Manufacturing Technology. 107 (5): 2513–2523. doi:10.1007/s00170-020-05201-4. ISSN 1433-3015. S2CID 216315774.
↑ DebRoy, T.; Wei, H. L.; Zuback, J. S.; Mukherjee, T.; Elmer, J. W.; Milewski, J. O.; Beese, A. M.; Wilson-Heid, A.; De, A.; Zhang, W. (2018-03-01). "Additive manufacturing of metallic components – Process, structure and properties". Progress in Materials Science. 92: 112–224. doi: 10.1016/j.pmatsci.2017.10.001 . ISSN 0079-6425.

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[1] "Thermal Management of Electronics: Active vs Passive Cooling". arrow.com. 2020-01-31. Archived from the original on 2020-12-18.

[:0-2] 1 2 3 4 5 Oropeza-Perez, Ivan; Østergaard, Poul Alberg (2018-02-01). "Active and passive cooling methods for dwellings: A review". Renewable and Sustainable Energy Reviews. 82: 531–544. doi:10.1016/j.rser.2017.09.059. ISSN 1364-0321.

[3] "Cooling systems for buildings". www.designingbuildings.co.uk. Retrieved 2020-11-15.

[4] "Heat Pump Systems". Energy.gov. Retrieved 2020-11-11.

[5] "What are the advantages & disadvantages of a heat pump?". www.heatpumpchooser.com. Retrieved 2022-09-02.

[6] Lechner, Norbert (2014-10-13). Heating, Cooling, Lighting: Sustainable Design Methods for Architects. John Wiley & Sons. ISBN 978-1-118-58242-8.

[7] "Evaporative Coolers". Energy.gov. Retrieved 2020-11-11.

[8] Champier, Daniel (2017-05-15). "Thermoelectric generators: A review of applications". Energy Conversion and Management. 140: 167–181. doi:10.1016/j.enconman.2017.02.070. ISSN 0196-8904.

[:1-9] 1 2 Tosato, Pietro; Rossi, Maurizio; Brunelli, Davide (2019). Saponara, Sergio; De Gloria, Alessandro (eds.). "Investigating an Active Cooling System Powered by a Thermoelectric Generator". Applications in Electronics Pervading Industry, Environment and Society. Lecture Notes in Electrical Engineering. Cham: Springer International Publishing. 573: 205–211. doi:10.1007/978-3-030-11973-7_24. hdl: 11572/279975 . ISBN 978-3-030-11973-7. S2CID 164862741.

[10] Zhou, Y.; Paul, S.; Bhunia, S. (March 2008). "Harvesting Wasted Heat in a Microprocessor Using Thermoelectric Generators: Modeling, Analysis and Measurement". 2008 Design, Automation and Test in Europe. pp. 98–103. doi:10.1109/DATE.2008.4484669. ISBN 978-3-9810801-3-1.

[:2-11] 1 2 3 4 5 da Silva, Leandro João; Souza, Danielle Monteiro; de Araújo, Douglas Bezerra; Reis, Ruham Pablo; Scotti, Américo (2020-03-01). "Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM". The International Journal of Advanced Manufacturing Technology. 107 (5): 2513–2523. doi:10.1007/s00170-020-05201-4. ISSN 1433-3015. S2CID 216315774.

[12] DebRoy, T.; Wei, H. L.; Zuback, J. S.; Mukherjee, T.; Elmer, J. W.; Milewski, J. O.; Beese, A. M.; Wilson-Heid, A.; De, A.; Zhang, W. (2018-03-01). "Additive manufacturing of metallic components – Process, structure and properties". Progress in Materials Science. 92: 112–224. doi: 10.1016/j.pmatsci.2017.10.001 . ISSN 0079-6425.

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