waste heat

intrigue from a convo on most of energy going toward heat.. that then needs to be cooled off.. is this a broken cycle..? a manufactured waste.. we could potentially disengage from..?

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Waste heat is by necessity produced both by machines that do work and in other processes that use energy, for example in a refrigerator warming the room air or a combustion engine releasing heat into the environment. The need for many systems to reject heat as a by-product of their operation is fundamental to the laws of thermodynamics. Waste heat has lower utility (or in thermodynamics lexicon a lower exergy or higher entropy) than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms. Rejection of unneeded cold (as from a heat pump) is also a form of waste heat (i.e. the medium has heat, but at a lower temperature than is considered warm).

Instead of being “wasted” by release into the ambient environment, sometimes waste heat (or cold) can be utilized by another process, 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 with heat recovery ventilation in 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 is seasonal 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. An example of using STES to utilize natural waste heat is the Drake Landing Solar Community in Alberta, Canada, which, by using a cluster of boreholes in bedrock for interseasonal heat storage, obtains 97 percent of its year-round heat from solar thermal collectors on the garage roofs. Another STES application is storing winter cold underground, for summer air conditioning.

so what about storage issues.. taking more energy..?

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

*Anthropogenic waste heat is thought by some to contribute to the **urban heat island effect. 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.

*anthropogenic – chiefly of environmental pollution and pollutants) originating in human activity : anthropogenic emissions of sulfur dioxide.

**urban heat island – An urban heat island (UHI) is a city or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. The temperature difference usually is larger at night than during the day, and is most apparent when winds are weak. UHI is most noticeable during the summer and winter. The main cause of the urban heat island effect is from the modification of land surfaces. Waste heat generated by energy usage is a secondary contributor. As a population center grows, it tends to expand its area and increase its average temperature. The less-used term heat island refers to any area, populated or not, which is consistently hotter than the surrounding area.

Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of growing seasons, and decreases the occurrence of weak tornadoes. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems.

Not all cities have a distinct urban heat island. Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-colored surfaces in urban areas, which reflect more sunlight and absorb less heat.

There are concerns raised about possible contribution from urban heat islands to global warming. Research on China and India indicates that urban heat island effect contributes to climate warming by about 30%. On the other hand, one 1999 comparison between urban and rural areas proposed that the urban heat island effects have little influence on global mean temperature trends. Many studies reveal increases in the severity of the effect with the progress of climate change

There are several causes of an urban heat island (UHI); for example, dark surfaces absorb significantly more solar radiation, which causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day; materials commonly used in urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than the surrounding rural areas. This causes a change in the energy budget of the urban area, often leading to higher temperatures than surrounding rural areas. Another major reason is the lack of evapotranspiration (for example, through lack of vegetation) in urban areas. With a decreased amount of vegetation, cities also lose the shade and cooling effect of trees, and the removal of carbon dioxide.

Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the “urban canyon effect“. Another effect of buildings is the blocking of wind, which also inhibits cooling by convection and prevents pollution from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI. High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the radiative properties of the atmosphere. As UHI raises the temperature of cities, it also increases the concentration of ozone, a greenhouse gas whose production accelerates with an increase in temperature.

Some cities exhibit a heat island effect, largest at night. Seasonally, UHI shows up both in summer and winter. The typical temperature difference is several degrees between the center of the city and surrounding fields. The difference in temperature between an inner city and its surrounding suburbs is frequently mentioned in weather reports, as in “68 °F (20 °C) downtown, 64 °F (18 °C) in the suburbs”. “The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4 °F (1.0–3.0 °C) warmer than its surroundings. In the evening, the difference can be as high as 22 °F (12 °C)

Conversion of energy

Machines converting energy contained in fuels to mechanical work or electric energy produce heat as a by-product



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 a sea, lake or river. If sufficient cooling water is not available, the plant has to be equipped with a cooling tower to reject the waste heat into the atmosphere. In some cases it is possible to use waste heat, for instance in heating homes by cogeneration. However, by slowing the release of the waste heat, these systems always entail a reduction of efficiency for the primary user of the heat energy.

curiouser and curiouser

Energy in the form of power dissipation or ‘losses’ occur as a byproduct of the efficiency of the device while in use. The less efficient the device or circuit, the more losses/power dissipation that must be removed as heat. – bg

must be removed as heat.. why ..? why is it heat.. because work/friction happened.?

if so.. then do you work on reducing that (work/friction or whatever that turns into heat) … when you’re working on efficiency.. or do you just assume that much heat and work on cooling it.. toward efficiency.


For the present situation, one might consider moving to a surface mount regulator that offers better power handling capability (by using the circuit board as a heat sink) or it may be worth looking into adding a power resistor (or zener diode) before the regulator to drop most of the voltage outside the regulator package, easing the load on it. Or better yet, seeing if there’s a way to build your circuit without the lossy linear regulator stage.


There are real limitations, however, and one could spend a lifetime learning the nuances of power consumption, particularly at lower currents or high frequencies where small losses that we have neglected become important.


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Power Dissipation

We say a component is dissipating or absorbing power when it is causing a loss in electrical poten- tial of the charge carriers going through it. An ideal example is where current traveling through a resistor causes a voltage “drop” to occur across its terminals. The voltage drop is indicative of a loss in energy, as voltage is the change in potential energy as charge is moved between two points. Where did this energy go? For passive elements, the electrical energy was converted to heat. The same mechanism occurs in a electrical space heater, just to a greater degree.

We say a component is generating or delivering power when it is converting some type of energy into electrical energy. An example would be a battery whose operation converts stored chemical energy into electrical energy.


waste heat to power

waste heat used to generate electricity.. source is heat not natural gas… capture energy in waste heat..

no longer just a by product.. a valuable resource…

so rather than cool down… use it.. ?


googled.. does work always produce heat and got..


Light does not produce heat. It is the absorption of light that produces heat. Light is energy. Heat is energy. When a physical body absorbs light, it converts the energy of the abs


Thermal radiation is emitted by any surface having a temperature higher than absolute zero. So the short answer to your question is yes. Light (electromagnetic radiation) of any frequency will heat surfaces that absorb it. In case of Fluorescence, the emitted light has a longer wavelength (lower frequency), and therefore lower energy, so that’s why you feel the heat is absent.


Computers generate heat when they work. Is it a result of information processing or friction (resistance)? Are these just different ways to describe the same thing? Or does some definite part of the heat “come from each explanation”?

I often read that it’s a necessary byproduct of information processing. There are irreversible operations such as AND gates and the remaining information goes to heat.

But so many other things generate heat as well! A light bulb, electric hotplates, gears, etc. (These probably don’t process information the way the computer does, but I may be wrong from a physical perspective.) Earlier I had always assumed the computer is like this as well. It basically has small wires in the processor and the resistance could explain the heat.

Maybe these are parallel explanations. The information processing aspect may say that there has to be some heat as byproduct in some way in any realization of an abstract computer, and the friction aspect could then describe how this actually happens in this concrete wires-and-transistors-type physical implementation of the abstract computer.

But maybe the two explanations account for separate amounts of the heat. Or maybe one accounts for a subset of the other, again in a partially parallel explanation way. can someone explain.


Most of the heat in modern digital (CMOS) chips are generated by charging and discharging stray and intentional capacitors, the faster the chip is the more dissipative cycles it goes through per unit time. The heat dissipation is of course is in the unavoidable resistances




upcycling ness