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Waste heat

(Redirected fromAnthropogenic heat)

Waste heatisheatthat is produced by amachine,or other process that usesenergy,as a byproduct of doingwork.All such processes give off some waste heat as a fundamental result of thelaws of thermodynamics.Waste heat has lower utility (or in thermodynamics lexicon a lowerexergyor higherentropy) than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example,incandescent light bulbsget hot, a refrigerator warms the room air, a building gets hot during peak hours, aninternal combustion enginegenerates high-temperature exhaust gases, and electronic components get warm when in operation.

Thermal oxidizerscanuse a regenerative processfor waste heat from industrial systems.
Air conditioningunits extractheatfrom a dwelling interior with coolant, and transfer it to the dwelling exterior as waste. They emit additional heat in their use ofelectricityto power the devices that pass heat to and from the coolant.

Instead of being "wasted" by release into the ambient environment, sometimes waste heat (or cold) can be used by another process (such as using hot engine coolant to heat a vehicle), or a portion of heat that would otherwise be wasted can be reused in the same process if make-up heat is added to the system (as withheat recovery ventilationin a building).

Thermal energy storage,which includes technologies both for short- and long-term retention of heat or cold, can create or improve the utility of waste heat (or cold). One example is waste heat from air conditioning machinery stored in a buffer tank to aid in night time heating. Another isseasonal thermal energy storage(STES) at a foundry in Sweden. The heat is stored in the bedrock surrounding a cluster of heat exchanger equipped boreholes, and is used for space heating in an adjacent factory as needed, even months later.[1]An example of using STES to use natural waste heat is theDrake Landing Solar CommunityinAlberta,Canada, which, by using a cluster of boreholes in bedrock for interseasonal heat storage, obtains 97 percent of its year-round heat fromsolar thermal collectorson the garage roofs.[2][3]Another STES application is storing winter cold underground, for summer air conditioning.[4]

On a biological scale, all organisms reject waste heat as part of theirmetabolic processes,and will die if the ambient temperature is too high to allow this.

Anthropogenic waste heat can contribute to theurban heat islandeffect.[5]The biggest point sources of waste heat originate from machines (such as electrical generators or industrial processes, such as steel or glass production) and heat loss through building envelopes. The burning of transport fuels is a major contribution to waste heat.

Conversion of energy

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See also:Second law of thermodynamics

Machinesconverting energycontained infuelstomechanical workorelectric energyproduce heat as a by-product.

Sources

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In the majority of applications, energy is required in multiple forms. These energy forms typically include some combination ofheating, ventilation, and air conditioning,mechanical energyandelectric power.Often, these additional forms of energy are produced by aheat enginerunning on a source of high-temperature heat. A heat engine can never have perfect efficiency, according to thesecond law of thermodynamics,therefore a heat engine will always produce a surplus of low-temperature heat. This is commonly referred to as waste heat or "secondary heat", or "low-grade heat". This heat is useful for the majority of heating applications, however, it is sometimes not practical to transport heat energy over long distances, unlike electricity or fuel energy. The largest proportions of total waste heat are frompower stationsand vehicle engines.[citation needed]The largest single sources are power stations and industrial plants such asoil refineriesandsteelmakingplants.[citation needed]

Air conditioning

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Conventionalair conditioningsystems are a source of waste heat by releasing waste heat into the outdoor ambient air whilst cooling indoor spaces. This expelling of waste heat from air conditioning can worsen theurban heat islandeffect.[5]Waste heat from air conditioning can be reduced through the use ofpassive coolingbuilding design and zero-energy methods likeevaporative coolingandpassive daytime radiative cooling,the latter of which sends waste heat directly to outer space through theinfrared window.[6][7]

Power generation

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Theelectrical efficiencyofthermal power plantsis defined as the ratio between the input and output energy. It is typically only 33% when disregarding usefulness of the heat output for building heat.[8]The images showcooling towers,which allow power stations to maintain the low side of the temperature difference essential for conversion of heat differences to other forms of energy. Discarded or "waste" heat that is lost to the environment may instead be used to advantage.

Acoal-fired power station.These transform chemical energy into 36–48% electricity and the remaining 52–64% to waste heat.

Industrial processes

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Industrial processes, such asoil refining,steel makingorglass makingare major sources of waste heat.[9]

Electronics

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Although small in terms of power, the disposal of waste heat frommicrochipsand other electronic components, represents a significant engineering challenge. This necessitates the use of fans,heatsinks,etc. to dispose of the heat.

For example, data centers use electronic components that consume electricity for computing, storage and networking. The FrenchCNRSexplains a data center is like a resistor and most of the energy it consumes is transformed into heat and requires cooling systems.[10]

Biological

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Humans, like all animals, produce heat as a result ofmetabolism.In warm conditions, this heat exceeds a level required forhomeostasisinwarm-bloodedanimals, and is disposed of by variousthermoregulationmethods such assweatingandpanting.[11]

Cooling towersevaporating water atRatcliffe-on-Soar Power Station,United Kingdom

Disposal

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Low temperature heat contains very little capacity to do work (Exergy), so the heat is qualified as waste heat and rejected to the environment. Economically most convenient is the rejection of such heat to water from asea,lakeorriver.If sufficient cooling water is not available, the plant can be equipped with acooling toweror air cooler to reject the waste heat into the atmosphere. In some cases it is possible to use waste heat, for instance indistrict heatingsystems.

Uses

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Conversion to electricity

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There are many different approaches to transfer thermal energy to electricity, and the technologies to do so have existed for several decades.

An established approach is by using athermoelectricdevice,[12]where a change in temperature across a semiconductor material creates a voltage through a phenomenon known as theSeebeck effect.

A related approach is the use ofthermogalvanic cells,where a temperature difference gives rise to an electric current in an electrochemical cell.[13]

Theorganic Rankine cycle,offered by companies such asOrmat,is a very known approach, whereby an organic substance is used asworking fluidinstead of water. The benefit is that this process can reject heat at lower temperatures for the production of electricity than the regular water steam cycle.[14]An example of use of the steamRankine cycleis theCyclone Waste Heat Engine.

Cogeneration and trigeneration

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Waste of the by-product heat is reduced if acogenerationsystem is used, also known as a Combined Heat and Power (CHP) system. Limitations to the use of by-product heat arise primarily from the engineering cost/efficiency challenges in effectively exploiting small temperature differences to generate other forms of energy. Applications utilizing waste heat includeswimming poolheating andpaper mills.In some cases, cooling can also be produced by the use ofabsorption refrigeratorsfor example, in this case it is calledtrigenerationor CCHP (combined cooling, heat and power).

District heating

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Waste heat can be used indistrict heating.Depending on the temperature of the waste heat and the district heating system, aheat pumpmust be used to reach sufficient temperatures. These are an easy and cheap way to use waste heat incold district heatingsystems, as these are operated at ambient temperatures and therefore even low-grade waste heat can be used without needing a heat pump at the producer side.[15]

Pre-heating

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Waste heat can be forced to heat incoming fluids and objects before being highly heated. For instance, outgoing water can give its waste heat to incoming water in aheat exchangerbefore heating in homes orpower plants.

Anthropogenic heat

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Anthropogenic heat is heat generated by humans and human activity. TheAmerican Meteorological Societydefines it as "Heat released to the atmosphere as a result of human activities, often involving combustion of fuels. Sources include industrial plants, space heating and cooling, human metabolism, and vehicle exhausts. In cities this source typically contributes 15–50 W/m2to the local heat balance, and several hundred W/m2in the center of large cities in cold climates and industrial areas. "[16]In 2020, the overall anthropogenic annual energy release was 168,000 terawatt-hours; given the 5.1×1014m2surface area of Earth, this amounts to a global average anthropogenic heat release rate of 0.04 W/m2.[17][18]

Environmental impact

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Anthropogenic heat is a small influence on rural temperatures, and becomes more significant in denseurbanareas.[19]It is one contributor tourban heat islands.Other human-caused effects (such as changes toalbedo,or loss of evaporative cooling) that might contribute to urban heat islands are not considered to beanthropogenic heatby this definition.

Anthropogenic heat is a much smaller contributor toglobal warmingthangreenhouse gasesare.[20]In 2005, anthropogenic waste heat flux globally accounted for only 1% of theenergy fluxcreated by anthropogenic greenhouse gases. The heat flux is not evenly distributed, with some regions higher than others, and significantly higher in certain urban areas. For example, global forcing from waste heat in 2005 was 0.028 W/m2,but was +0.39 and +0.68 W/m2for the continental United States and western Europe, respectively.[21]

Although waste heat has been shown to have influence on regional climates,[22]climate forcingfrom waste heat is not normally calculated in state-of-the-art global climate simulations. Equilibrium climate experiments show statistically significant continental-scale surface warming (0.4–0.9 °C) produced by one 2100 AHF scenario, but not by current or 2040 estimates.[21]Simple global-scale estimates with different growth rates of anthropogenic heat[23]that have been actualized recently[24]show noticeable contributions to global warming, in the following centuries. For example, a 2% p.a. growth rate of waste heat resulted in a 3 degree increase as a lower limit for the year 2300. Meanwhile, this has been confirmed by more refined model calculations.[25]

A 2008 scientific paper showed that if anthropogenic heat emissions continue to rise at the current rate, they will become a source of warming as strong asGHG emissionsin the 21st century.[26]

See also

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References

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  1. ^Andersson, O.; Hägg, M. (2008),"Deliverable 10 - Sweden - Preliminary design of a seasonal heat storage for IGEIA – Integration of geothermal energy into industrial applicationsArchived11 April 2020 at theWayback Machine,pp. 38–56 and 72–76, retrieved 21 April 2013
  2. ^Wong, Bill (June 28, 2011),"Drake Landing Solar Community"Archived2016-03-04 at theWayback Machine,IDEA/CDEA District Energy/CHP 2011 Conference, Toronto, pp. 1–30, retrieved 21 April 2013
  3. ^Wong B., Thornton J. (2013).Integrating Solar & Heat Pumps.Archived2013-10-15 at theWayback MachineRenewable Heat Workshop.
  4. ^Paksoy, H.; Stiles, L. (2009),"Aquifer Thermal Energy Cold Storage System at Richard Stockton College"Archived2014-01-12 at theWayback Machine,Effstock 2009 (11th International) - Thermal Energy Storage for Efficiency and Sustainability, Stockholm.
  5. ^abKovats, Sari; Brisley, Rachel (2021). Betts, R.A.; Howard, A.B.; Pearson, K.V. (eds.)."Health, Communities and the Built Environment"(PDF).The Third UK Climate Change Risk Assessment Technical Report.Prepared for the Climate Change Committee, London: 38.Although uptake may increase autonomously in the future, relying on air conditioning to deal with the risk is a potentially maladaptive solution, and it expels waste heat into the environment - thereby enhancing the urban heat island effect.
  6. ^Chen, Meijie; Pang, Dan; Yan, Hongjie (November 2022)."Colored passive daytime radiative cooling coatings based on dielectric and plasmonic spheres".Applied Thermal Engineering.216:119125.Bibcode:2022AppTE.21619125C.doi:10.1016/j.applthermaleng.2022.119125.S2CID251420566– via Elsevier Science Direct.One such promising alternative is radiative cooling, which is a ubiquitous process of losing surface heat through thermal radiation. Instead of releasing waste heat into ambient air as conventional cooling systems, radiative cooling passively discharges it into outer space.
  7. ^Aili, Ablimit; Yin, Xiaobo; Yang, Ronggui (February 2022)."Passive sub-ambient cooling: radiative cooling versus evaporative cooling".Applied Thermal Engineering.202:117909.arXiv:2107.04151.Bibcode:2022AppTE.20217909A.doi:10.1016/j.applthermaleng.2021.117909.S2CID235790365– via Elsevier Science Direct.
  8. ^"Annual Electric Generator Report".U.S. Energy Information Administration.1 January 2018.
  9. ^Fernández-Yáñez, P. (2021)."Thermal management of thermoelectric generators for waste energy recovery".Applied Thermal Engineering.196(published 1 September 2021): 117291.Bibcode:2021AppTE.19617291F.doi:10.1016/j.applthermaleng.2021.117291.
  10. ^"New Technologies' Wasted Energies".CNRS News.Retrieved6 July2018.
  11. ^Fiala D, Lomas KJ, Stohrer M (November 1999). "A computer model of human thermoregulation for a wide range of environmental conditions: the passive system".J. Appl. Physiol.87(5): 1957–72.doi:10.1152/jappl.1999.87.5.1957.PMID10562642.S2CID5751821.
  12. ^Fernández-Yáñez, P. (2021)."Thermal management of thermoelectric generators for waste energy recovery".Applied Thermal Engineering.196(published 1 September 2021): 117291.Bibcode:2021AppTE.19617291F.doi:10.1016/j.applthermaleng.2021.117291.
  13. ^Gunawan, A; Lin, CH; Buttry, DA; Mujica, V; Taylor, RA; Prasher, RS; Phelan, PE (2013). "Liquid thermoelectrics: review of recent and limited new data of thermogalvanic cell experiments".Nanoscale Microscale Thermophys Eng.17(4): 304–23.Bibcode:2013NMTE...17..304G.doi:10.1080/15567265.2013.776149.S2CID120138941.
  14. ^Quoilin, Sylvain; Broek, Martijn Van Den; Declaye, Sébastien; Dewallef, Pierre; Lemort, Vincent (1 June 2013)."Techno-economic survey of Organic Rankine Cycle (ORC) systems".Renewable and Sustainable Energy Reviews.22:168–186.doi:10.1016/j.rser.2013.01.028.Archivedfrom the original on 3 October 2016.Retrieved7 May2018.
  15. ^Simone Buffa; et al. (2019), "5th generation district heating and cooling systems: A review of existing cases in Europe",Renewable and Sustainable Energy Reviews,vol. 104, pp. 504–522,doi:10.1016/j.rser.2018.12.059
  16. ^"Glossary of Meteorology".AMS.Archived fromthe originalon 26 February 2009.
  17. ^Ritchie, Hannah;Roser, Max;Rosado, Pablo (27 October 2022)."Energy Production and Consumption".Our World in Data.Retrieved24 March2023.
  18. ^"What is the Surface Area of the Earth?".Universe Today.11 February 2017.Retrieved24 March2023.
  19. ^"Heat Island Effect: Glossary".United States Environmental Protection Agency.2009.Archivedfrom the original on 20 April 2009.Retrieved6 April2009.
  20. ^Zhang, Xiaochun (2015)."Time scales and ratios of climate forcing due to thermal versus carbon dioxide emissions from fossil fuels".Geophysical Research Letters.42(11): 4548–4555.Bibcode:2015GeoRL..42.4548Z.doi:10.1002/2015GL063514.
  21. ^abFlanner, M. G. (2009)."Integrating anthropogenic heat flux with global climate models"(PDF).Geophys. Res. Lett.36(2): L02801.Bibcode:2009GeoRL..36.2801F.CiteSeerX10.1.1.689.5935.doi:10.1029/2008GL036465.S2CID8371380.
  22. ^Block, A., K. Keuler, and E. Schaller (2004)."Impacts of anthropogenic heat on regional climate patterns".Geophysical Research Letters.31(12): L12211.Bibcode:2004GeoRL..3112211B.doi:10.1029/2004GL019852.Archivedfrom the original on 6 June 2011.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  23. ^R. Döpel,"Über die geophysikalische Schranke der industriellen Energieerzeugung." Wissenschaftl. Zeitschrift der Technischen Hochschule Ilmenau,ISSN0043-6917,Bd. 19 (1973, H.2), 37-52. (online).
  24. ^H. Arnold, "Robert Döpeland his Model of Global Warming. An Early Warning – and its Update. "(2013)online.1st ed.: "Robert Döpel und sein Modell der globalen Erwärmung. Eine frühe Warnung - und die Aktualisierung." Universitätsverlag Ilmenau 2009,ISBN978-3-939473-50-3.
  25. ^Chaisson, E. J. (2008)."Long-Term Global Heating from Energy Usage"(PDF).Eos.89(28): 253–260.Bibcode:2008EOSTr..89..253C.doi:10.1029/2008eo280001.
  26. ^Cowern, Nick E.B.; Ahn, Chihak (November 2008). "Thermal emissions and climate change: Cooler options for future energy technology".Cowern Science.arXiv:0811.0476.
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