1. No category

NO Chemtrails - NO SAG (Stratospheric Aerosol Geoengineering)
Novel strategies to slow climate change
and fight global warming
New ideas (3) on how to cool Gaïa
Taking advantage of long-wave radiation
to the night sky
Read the open source paper that can be freely accessed at:
http://dx.doi.org/10.1016/j.rser.2013.12.032
The greenhouse effect is due to long wave IR radiation
Image from http://ozclimatesense.com/category/green-house-effect-on-your-health/
Image from http://www.realscience.org.uk/sciencediscussion-climate-change-clouds.html
Greenhouse gases (GHGs) are good at
absorbing long wave length heat radiation
and so the GHGs heat up.
Warm GHGs in the sky re-emit heat radiation
in all directions, so some go up to the outer
space and some go down back to the Earth's
surface. So, not all the heat (Infra-Red
radiation) leaves the planet. This is how the
Earth gets warmer by greenhouse effect.
Earth radiation management (ERM) aims to increase outgoing long wave radiation (IR release to the outer space).
Targets for ERM and SRM
Image from
http://geoengineering.weebly.com/pivotal-article.html
Outgoing EARTH LONG wave
radiation is targeted by ERM
Incoming Solar SHORT wave
radiation targeted by SRM
also called Sunlight Reflection Methods
By the atmospheric window 8-14 µm,
40 W/m2 of long wave heat radiation
energy escapes to the outer space.
In order to cool the Earth, a way to increase the outgoing long
wave radiation by the atmospheric window is to favor technologies
that make profit of the clear sky night radiative cooling
What is radiative cooling?
In the same way that thermal radiation travels from the sun to the surface of the earth, across
the vacuum of space, the heat from the earth also radiates back into space. Night sky radiant
cooling is a natural process that helps the earth maintain thermal equilibrium.
The effect of this radiant heat leaving the surface of the earth can easily be seen on some
mornings after a clear night. A layer of frost will form on rooftops and on automobiles even
though the outdoor air temperature is well above freezing. This frozen condensation is proof that
the rooftops were losing heat by radiation to the night sky faster than the surrounding warmer air
could replace that heat by natural convection. http://www.sol-ice.com/wp-content/uploads/2012/08/Potentials-of-NSRC-in-NM-1.pdf
Radiation cooling to the night sky is based on the principle of heat loss by long-wave radiation
from one surface to another body at a lower temperature. http://en.wikipedia.org/wiki/Infrared_window
Roofs of buildings radiate heat day and night at an average rate of up to 75 w/m2. During the
day, this is offset by solar radiation gains on the roof, however, at night, this heat loss has the
ability to cool air or water as roofs can experience a temperature drop of 6 to 20 °C below
ambient. http://en.wikipedia.org/wiki/Radiative_cooling
The infrared atmospheric window is a path from the
land-sea surface of the earth to space. At the scarcely
absorbed continuum of wavelengths (8 to 14 µm), the
radiation emitted, by the earth's surface into a dry
atmosphere, and by the cloud tops, mostly passes
unabsorbed through the atmosphere, and is emitted
directly to space. This is because the infrared
absorptions of the principal natural GHGs (CO2 and
H2O) are outside of this range.
A clear sky is needed
Greenhouse warming is enhanced during
nights when the sky is overcast. Heat energy
from the earth can be trapped by clouds
leading to higher temperatures as compared to
nights with clear skies. The air is not allowed to
cool as much with overcast skies. Under partly
cloudy skies, some heat is allowed to escape
and some remains trapped. Clear skies allow
for the most cooling to take place.
This map shows that a roof
facing the night sky can be
significantly colder than the
surrounding air temperature,
from 6°°C to 22°°C colder.
One limiting factor is the dew
point which explains why a dry
climate can achieve cooler night
temperatures than humid
climates such as those in Florida.
Two main strategies to cool a building
Infrared photos confirm that on clear nights a metal roof can be approximately 10°C
cooler than ambient temperature in the Great Lakes region (US) which agrees with
the ASHRAE information adapted from the 1984 Martin and Berdahl data.
Night radiation cooling has been known for decades but until now few have been
able to successfully and economically capture the cooling benefit to cool buildings or
to use it for food preservation.
The 2007 ASHRAE Handbook devotes a
separate section to cooling by nocturnal
radiation and states “Radiative building
cooling has not been fully developed.”
Although many materials emitting in the
atmospheric window have been developed
The same equipment used for
or discovered, for the moment few strategies
daytime active solar heating, can
be employed at night for
and applications have been developed for
“collecting” and storing the “coolth”
obtained by NSRC
industries to make profit of night sky cooling.
For buildings one method consists in
circulating water in existing solar thermal
panels and store hot water during the day in
1st tank and store cold water during the night
in a 2nd tank. The cold water is then used
during the day for air conditioning purposes.
輻射冷卻
輻射冷卻 / 輻射冷卻是指物件透過輻射散去熱能的過程。在氣象學上，天朗氣清、微風及乾燥的情況下，較有利輻射冷卻
輻射冷卻是指物件透過輻射散去熱能的過程。在氣象學上，天朗氣清、微風及乾燥的情況下，較有利輻射冷卻
Resfriamento radiante (português brasileiro) ou Arrefecimento radiante (português europeu) é o processo pelo qual um corpo perde o calor por radiação. No caso do sistema da atmosfera da Terra, ele se refere ao processo pelo qual radiação de grande comprimento de onda, radiação infravermelha, é emitida balanceando a absorção de energia dos
comprimentos de onda mais curtos (luz visível) oriundos do Sol.
O processo exato pelo qual a Terra perde calor é mais complexo do que muitas vezes retratado. Em particular, o transporte convectivo de calor, evaporação e transporte de calor latente são todos importantes na remoção de calor da superfície e redistribuindo-o na atmosfera. Puro transporte radiante é mais importante em altitudes superiores. A variação
diurna e geográfico complementa a complexidade do quadro
Strålingsavkjøling har man når et legeme mister mer energi ved stråling.
Tropene stråler altså mindre varme ut i verdensrommet enn de ville ha gjort om det ikke fantes sirkulasjonsstrømmer på Jorden. I tillegg ville polområdene hatt større strålingsavkjøling. De tropiske områdene har større strålingsavkjøling (mer utstråling) enn polområdene på grunn av høyere overflatetemperatur der.
I liten skala kan man kjenne et eksempel på strålingsavkjøling foran et kaldt vindu om vinteren. Den siden av ansiktet som vender mot vinduet blir kaldere enn den som vender inn mot rommet.
放射冷却（ほうしゃれいきゃく）とは、高温の物体が周囲に電磁波を放射することで気温が下がる現象のこと。
放射冷却
放射冷却
日本ではおもに秋から冬を挟み春までのよく晴れた風の弱い夜間に発生しやすい。天気予報では放射冷却が予想される場合、冬を中心に低温に注意する旨の呼びかけが行われる（「低温注意報」として発表される）。また、秋（早霜）と春（晩霜）は霜に注意する旨の呼びかけが行われる（「霜注意報」として発表される。冬は霜注意報が発表されない）。そのため単に放射
冷却と言った場合には、気象としての現象を指すことが多い。また、非電化冷蔵庫にもこの原理が利用されている。
放射冷却の条件
放射冷却の条件
絶対温度が零度ではない全ての物体は、プランクの法則により電磁波を放射している。電磁波を放射している物体は温度が下がり、他から放射を受けた物体は温度が上がる。
昼間、太陽の光が地表面に当たっている時、地表面は太陽放射を受けて温度が上昇する。逆に夜間は、地表面から宇宙空間に向けての放射があり、地表面の温度は低下する。このとき、大気中に雲が存在すると、雲からの放射を地表面が受けることにより、地表面の温度低下が妨げられる。一方、大気中の水蒸気が少ないよく晴れた夜間（日本では冬季間が代表的）には、地
表からの放射はそのまま宇宙空間に放出されるため、地表付近の温度が低下しやすい。この状態を放射冷却と呼ぶ。
風が強い場合には、放射冷却が起こっても空気が混合して上空の暖かい空気が降りてくるため、放射冷却は弱くなる。また、水は比熱容量が大きいため放射冷却が起こりにくい。海岸や湖岸などでは、風が弱くても海陸風や湖陸風によって自然と混合が起こるため、水辺に近いほど放射冷却が弱くなる。山や丘に囲まれた盆地や窪地では、低地に冷気が溜まって冷気湖となり、
混合が抑えられるので放射冷却が強い。広大な大陸の内陸部では、盆地でなくとも放射冷却した冷気層が均一に広く存在するため、混合が抑えられて放射冷却が強い。
さらに、上空に寒気が流入するなど、大気上層から中層が冷たい場合は、それに応じて下層の温度低下も大きく、より放射冷却が強い。
放射冷却によって地表付近は冷える一方で、地中は地熱が 保持されているため、地中深くなるほど放射冷却による温度低下が小さくなる。また、植物などの地面から離れたものは、地表面と違って地熱の伝導を受けない ので、地表面よりも若干温度低下が大きい。ただし、断熱効果のある覆いなどを植物の上に被せると、覆いの温度が低下してもその下は保温され、温度低下
が小 さくなる。 一般的に、比熱容量の大小差により、湿った地面は温度低下が小さく、乾燥した地面や古い積雪はやや大きく、新雪はかなり大きい。新雪に関しては、空気を多く含むので地熱が伝わりにくいことが関係している。このため、砂漠や乾燥地の1日の気温差は著しい。
放射冷却による低温を注意喚起する場合は、強い放射冷却が起こったり起こることが予想される場合である。そのため、特に晴れた夜間に限って放射冷却が発生するかのような誤解も見受けられる。正確に言えば、放射冷却はどんな場合においても常に起こっている。
放射冷却に伴う気象
放射冷却に伴う気象
放射冷却によって地面付近の空気が急速に冷却されると、上空よりも気温が低くなり接地逆転層という種類の逆転層が発生することがある。
湿度が極端に低くないとき、放射冷却によって地面付近の空気が急速に冷却されて露点温度に達し、放射霧という種類の霧が 発生することがある。また、川や海岸に近い海では、放射冷却された冷たい空気が暖かい水に接して、蒸気霧が発生することがある。地域差があるものの、少な くとも日本の多くの地域では秋から冬にかけて放射霧が多く発生する。このうえ、逆転層
ができていて湿度が比較的低いときには、人の視界の高さ以下の地面付 近にのみ薄い霧が発生する地霧が見られることもある。
霧が発生すると、雲と同じで地面放射を吸収して再放射するため、放射冷却が和らげられる。
また、霧が発生しなくても、空気中の水蒸気が飽和に近く、かつ地面付近の温度が0℃以下の場合、霜が発生する。また、地面がやわらかい土で豊富に水分が含まれていると、霜柱が発生する。森では、地面よりも木々の枝葉のほうが温度低下が大きいので、木々だけに霜が降りる樹霜が発生することもある。
Radiative cooling is the process by which a body loses heat by thermal radiation.
Radiative cooling on Earth's surface at night http://en.wikipedia.org/wiki/Radiative_cooling
Radiative cooling is commonly experienced on cloudless nights, when heat is radiated into space from the surface of the Earth, or from the skin of a human observer. The effect is well-known among amateur astronomers, and can personally be felt on the skin of an observer on a cloudless night. To feel the effect, one compares the difference between looking straight up into a
cloudless night sky for several seconds, to that of placing a sheet of paper between one's face and the sky. Since outer space radiates at about a temperature of 3 kelvins (-270 degrees Celsius or -450 degrees Fahrenheit), and the sheet of paper radiates at about 300 kelvins (room temperature), the sheet of paper radiates more heat to one's face than does the darkened cosmos. The
effect is blunted somewhat by Earth's surrounding atmosphere which also traps heat. Note that it is not correct to say that the sheet "blocks the cold" of the night sky; instead, the sheet is literally warming your face, just like a camp fire warms your face; the only difference is that a campfire is several hundred degrees warmer than a sheet of paper, just like a sheet of paper is several
hundred degrees warmer than the deep night sky.
The atmospheric and oceanic circulation redistributes some of this energy as sensible heat and latent heat partly via the mean flow and partly via eddies, known as cyclones in the atmosphere. Thus the tropics radiate less to space than they would if there were no circulation, and the poles radiate more; however in absolute terms the tropics radiate more energy to space.
Nocturnal ice making
In India before the invention of artificial refrigeration technology, ice making by nocturnal cooling was common. The apparatus consisted of a shallow ceramic tray with a thin layer of water, placed outdoors with a clear exposure to the night sky. The bottom and sides were insulated with a thick layer of hay. On a clear night the water would lose heat by radiation upwards. Provided the
air was calm and not too far above freezing, heat gain from the surrounding air by convection would be low enough to allow the water to freeze by dawn.
The same radiative cooling mechanism can sometimes cause frost or black ice to form on surfaces exposed to the clear night sky, even when the ambient temperature does not fall below freezing.
Le refroidissement radiatif ou l'effet de serre inverse : http://www.iterrae.org/techno/1.php?newsid=30 http://www.iterrae.org/techno/1.php?newsid=31
La nuit, quand l'atmosphère est pure, les corps placés à la surface de la terre rayonnent vers les espaces planétaires qui ne leur envoient en échange que de très faibles rayons. C'est ainsi qu'ils se refroidissent au-dessous de la température ambiante, malgré l'influence modératrice de l'atmosphère. Ce phénomène est appelé l'effet de serre inverse.
Vers 1963, Félix Trombe obtint par ce procédé et dans un dispositif de son invention, une différence de température de l'ordre de 40°C avec l'air ambiant.
Louis Figuier, dans Les Merveilles de l'Industrie, T.3 (1875) est le premier à vulgariser le phénomène et à en retracer son histoire. Vers la fin de 1783, Wilson observa ses effets ; il trouva, qu'un thermomètre couché sur la neige marquait -21°,7, pendant qu'un instrument semblable suspendu à 4 pieds de hauteur, marquait 13°,9. C'est à un effet semblable qu'il faut aussi attribuer le
froid dans les zones désertiques où l'air, pur et calme, prend dans ses couches inférieures la température du sol, notablement refroidi jusqu'à 10°C en dessous de la température ambiante.
D'autres phénomènes de grande ampleur illustrent l'effet de serre inverse, comme la rosée, le serein, le froid en altitude, la période des Saints de Glace...
Il fut un temps, on se servait au Bengale, pour fabriquer de la glace, du froid produit par l'effet de serre inverse. Des vases plats remplis d'eau était disposés dans une excavation isolée par de la paille de maïs. Un rebord en terre règnait tout autour et retenait l'air refroidi. Quand le ciel était serein, l'air calme et au dessous de 10°C, l'eau se congèlait, même quand un thermomètre
couché sur la paille marquait 5°C. D'après M.Williams, ces manufactures de glace occupaient plusieurs centaines d'ouvriers.
La technologie employée, appelée "refroidissement par rayonnement infrarouge sur l'espace" ou "refroidissement radiatif" est également désignée par les termes "énergie terrestre" ou "effet de serre inverse". Elle utilise le ciel, l'espace (à -270°C) et la transparence de l'atmosphère aux ondes de chaleur pour évacuer cette dernière et produire du froid.
Ce transfert de chaleur de type radiatif vers le ciel vient compléter les techniques de réfrigération « très basse consommation », aux très bons temps de retour, couramment appelées free cooling qui ne s'appuient aujourd'hui que sur l'exploitation des transferts de chaleur de type convectif : aérothermie, géothermie ou aquathermie.
Le procédé breveté par ITERRae, complète la gamme de ces techniques en exploitant également les échanges de chaleur de type radiatif sur l'espace et le ciel via des convertisseurs photothermiques du rayonnement atmosphérique.
L'évacuation radiative de la chaleur vers l'espace et le ciel se situe au niveau de la principale « fenêtre atmosphérique » (8 à 13 micromètres). Sa puissance augmente lorsque la teneur en eau de l'atmosphère diminue ou lorsqu'on monte en altitude car la couche atmosphérique devenant plus sèche ou plus fine gagne en transparence au rayonnement infrarouge (effet de serre
inverse). Réfrigération radiative. Effet de serre inverse. La transparence atmosphérique dans l’infrarouge moyen (8-13 µm), responsable du refroidissement nocturne par temps clair, a été exploitée depuis longtemps en vue d’obtenir un effet frigorifique.
Parker et al explored in deep “NightCool:
A Nocturnal Radiation Cooling Concept”
Parker, D. S., Sherwin, J. R., Hermelink, A. H., & Center, F. S. E. (2008). 2008 ACEEE Summer
Study on Energy Efficiency in Buildings, 209-222. FSEC-CR-1771-08
Radiative
building cooling
Image from http://solarwall.com/en/products/nightsolar-air-cooling.php
Tests confirmed that nocturnal
radiation cooling can cool ambient
air for use in a building by as much
as 4.7°C below ambient (2.8°C
average) when using a transpired
solar collector oriented towards a
clear night sky.
Nocturnal Radiation Cooling Tests, John Hollick, Energy Procedia,
2012, 30, 930–936. Presented at 1st International Conference on
Solar Heating and Cooling for Buildings and Industry (SHC 2012),
http://dx.doi.org/10.1016/j.egypro.2012.11.105
For buildings another method consists
in circulating the air under the roof
when it is colder than the ambient, and
hybrid methods add evaporative cooling
Night Sky Radiant Cooling also called
Radiational Cooling is still under development
Cooling buildings by long-wave radiation to the night sky has long been
identified as a potentially productive means to reduce space cooling energy
and reduce CO2 emissions.
But many other possibilities can be envisioned for radiative cooling, for
instance to increase the efficiency of thermal processes needing a cold sink,
like power plants, thus reduce cooling water needs.
Another example can be PV panels, when they are too warm the electricity
production drops, but by storing during the night a cold fluid or a phase
transition material under the panel, during day operation the temperature of
the PV cells can stay optimal and yields can increase.
Deployment of passive cooling radiators in tropical developing regions
would improve the health and comfort of humans without requiring electrical
infrastructure; and without contributing to global warming
Harrison showed experimentally in Calgary that a high content Ti02 white
paint can cool to 15°C below ambient temperature under certain conditions.
Harrison A.W., & Walton, M.R. Radiative cooling of TiO2 white paint. Solar Energy, 1978, 20(2), 185-188.
Sky cooling can help water collection from the atmosphere, and be an aid to
water condensation in distillation. There are plenty of other applications,
including cooling parked cars or cooling in equatorial regions.
Additionally, the panels have no moving parts and require no power source.
How to take advantage of sky cooling?
May be the best approach for most practical cooling devices, is to have a
convection-suppressing shield that reflects or back scatters solar radiation
while it transmits in the thermal infrared. Microparticles of ZnS can be
effective for the latter purpose. Another option is nanosized TiO2
incorporated in polyethylene.
A huge amount of research has been performed on radiative heating and
cooling with spectrally selective surfaces
Niklasson, G. A., & Granqvist, C. G. (1983). Surfaces for selective absorption of solar energy:
an annotated bibliography 1955–1981. Journal of Materials science, 18(12), 3475-3534.
Ali et al. conducted experimental
and theoretical studies of
nocturnal cooling of water flowing
through a night sky radiator unit.
Ali H.H.Taha I.M.S. & Ismail I.M. Cooling of water flowing through a night sky
radiator. Solar energy, 1995, 55(4), 235-253;
Ali H.H. Passive cooling of water at night in uninsulated open tank in hot arid areas.
Energy conversion and management, 2007, 48(1), 93-100.
Dobson, R.T. Thermal modelling of a night sky radiation cooling system. Journal of
Energy in Southern Africa, 2005, 16(2), 21.
«Green Nanotechnology: Solutions for sustainability and energy in the built environment.» by Smith, G.B., & Granqvist, C.G.S. CRC Press, 2013.
Sky Cooling reaches Sub-ambient Temperatures
A very good and complete review of sky cooling technologies and also of possible
applications to many industry sectors can be found in chapters 7 &9 of book:
«Green Nanotechnology: Solutions for sustainability and energy in the built
environment.» by Smith, G.B., & Granqvist, C.G.S. CRC Press, 2013.
Sky Cooling can be sufficiently cheap and simple, and thus be a useful adjunct for
boosting the output from renewable power systems, especially thermal systems
operating at low temperatures.
Solar thermal power generation with an input temperature in the range 80°C to 100° C could
have a boost in efficiency of 50% to 100% if the engine condensation cycle is done with
coolness collected via sky cooling.
Large-scale photovoltaic generation systems do not produce electricity at night, but they
are commonly located in near-perfect locations for night sky cooling under clear skies and in
dry air. Such generation systems would benefit from the additional cooling by use of nightcooled fluids, which may be able to decrease the temperatures of the solar cells by ~5°C or
more over what is possible with regular air cooling during daytime.
Stirling cycle engines, used in small solar thermal systems, could also have their
efficiencies raised and their environmental impact diminished by using stored coolness, but
the gains are smaller than for solar cells.
Thermoelectric power can be solar driven and would be much improved with overnightgenerated coolness.
Keeping food fresh can be done with field-based, low-cost sky cooling systems, operating
both day and night. Sky cooling can provide the temperature drop that is needed to preserve
fruit and vegetables long enough to avoid spoilage.
As written by Smith & Granqvist: it is not unreasonable to imagine a world where
clean power sources, using some combination of solar energy and sky
cooling, become the backbone of a low-carbon economy.
The prospect then is not only less pollution but, in due course, lower power cost.
Sky Cooling Devices pump heat away by
radiative cooling to the atmosphere and
cool the Earth as they dump the heat into space
Despite our ready access to it and it’s great potential, why sky cooling has not been
successfully exploited to date?
As explained by Smith & Granqvist:
First, it is not a widely understood or appreciated field, and few scientists are active in it. But
more important, there has been little effort to develop products based on sky cooling,
possibly apart from arrangements for water collection.
The diverse technological scope beyond these applications is not well understood, and this
“knowledge gap” has yet to be bridged.
Clearly, the field of sky cooling has so far fallen short of its potential by a wide margin, but it
has too much to offer to be neglected.
Thus, practical cooling at a low cost down to 15°C below the coldest ambient temperature of
the night has been demonstrated!
A new type of solar structure cools buildings in full sunlight : sky cooling can
function both night and day. Cooling during the night is most effective, but is also
effective during the day, as shown in March 2013 by Prof. Shanhui Fan and his
team at MIT, who developped panel’s with nanostructured photonic materials
(quartz and silicon carbide) that emit heat at a wavelength that causes it to pass
through the atmosphere both night and day.
http://news.stanford.edu/news/2013/april/fan-solar-cooling-041513.html and
http://phys.org/news/2013-03-solar-cools-full-sunlight.html
"Fighting global warming with nanotechnology"
http://www.gmanetwork.com/news/story/301887/scitech/technology/fighting-global-warming-with-nanotechnology
http://www.sciencedaily.com/releases/2013/03/130327132544.htm
Night Sky Cooling (Earth IR long wave management)
is complementary with the Cool Roofs strategies
(Sunlight short wave management)
Increasing the albedo of roofs is among the Solar radiation management technologies
proposed to increase sunlight reflection. See for instance the “cool roofs” programs in
California, Florida or NYC.
A Cool Roof reduces the amount of energy absorbed by the roof which helps lower a building's
temperature and cuts energy costs, as they reduce energy use, cooling costs and carbon
emissions. http://www.nyc.gov/html/coolroofs/html/how/how.shtml
A Cool Roof is more than just a roof painted white.
To be a Cool Roof, a roof must be treated with a
specialized coating material that is lightly colored
and has two unique properties: high solar
reflectivity and high infrared emissivity.
Solar reflectivity expresses the degree to which
a roof reflects the visible, infrared and ultraviolet
rays that comprise solar energy. Surfaces with
high solar reflectivity reflect more infrared and
ultraviolet rays.
Infrared emissivity refers to the roof's ability to
give off its absorbed heat. Highly emissive
surfaces are cooler than non-emissive surfaces
since they have the ability to shed more absorbed
heat at a faster rate.
White Roofs
Save Energy
White roofs and walls and have
been a common architectural
element for thousands of years in the
Mediterranean and Middle East.
http://newscenter.lbl.gov/news-releases/2010/07/19/coolroofs-offset-carbon-dioxide-emissions
Making cool roofs programs entails nothing fancy: it's extremely low tech and low cost.
Menon, S., Akbari, H., Mahanama, S., Sednev, I., & Levinson, R. (2010). Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets. Environmental Research Letters, 5(1), 014005.
What is Emissivity? The emittance of a material refers to its ability to release absorbed heat.
Scientists use a number between 0 and 1, or 0% and 100%, to express emittance. With the
exception of a metallic surface, most roofing materials can have emittance values above 0.85
(85%). One example is a metal wrench left in the sun, which is hot to the touch because it has a
low emissivity value. http://en.wikipedia.org/wiki/Reflective_surfaces_%28geoengineering%29, http://coolcolors.lbl.gov/
Link Between Energy Savings and Emissivity
Solar reflectance is the most important characteristic of a roof product in terms of yielding the
highest energy savings during warmer months. The higher the solar reflective value the more
efficient the product is in reflecting sunlight and heat away from the building and reducing roof
temperature. This is particularly important in areas of the U.S. where peak load is a concern.
Emissivity can also contribute to a cool roof. In warm and sunny climates highly emissive roof
products can help reduce the cooling load on the building by releasing the remaining heat
absorbed from the sun. However, there is also evidence that low emissivity may benefit those
buildings located in colder climates by retaining heat and reducing the heating load. Research on
the benefits of emissivity is ongoing.
Cool Roofs Benefits
Traditional roofs are dark and retain the sun's rays as heat. During the summer, heat
absorption increases roof temperatures, air conditioning costs, energy demand and
even local temperatures in a phenomenon called the Urban Heat Island Effect. Cool
Roofs can reverse these impacts!
Reduce roof temperatures
During a typical summer day, flat, black asphalt rooftops can reach temperatures up
to 190°F which is 90°hotter than the surrounding ai r temperature!
Reduce internal building temperatures
Cool rooftops can reduce internal building temperatures by up to 30%, making the
building cooler and more comfortable during the hot summer months.
Cool Roofs Offset and Reduce the
Urban Heat Island Effect
The Urban Heat Island Effect is a
phenomenon in which the high
concentration of dark material, such
as asphalt and conventional rooftops,
increases the temperature of densely
built cities by up to five degrees. Cool
Roofs mitigate this effect by reducing
the number of dark energy absorbing
surfaces. A big city can be up to five
degrees hotter than surrounding
areas due to greater amounts of dark
surfaces, such as roofs and roads,
and less shading from vegetation.
Cool Roofs
Benefits (2)
Reduce carbon emissions and Improve air quality
Every 2,500 square feet of roof that is coated can reduce the city's carbon footprint by 1 ton of
CO2 and help fight climate change. Cool roofs lower air pollution and greenhouse gas emissions
by reducing power demand.
Extend the lifespan of rooftops and HVAC equipment
A Cool Roof coating better regulates a roof's temperature as compared to typical rooftop
surfaces. By decreasing the roof temperature and cooling loads, the life of the rooftop and
cooling equipment can be extended.
Cool Roofs Lower Cooling Costs
A conventional roof can reach very high temperatures on a sunny, windless day. A Cool Roof
creates a cooler building envelope, reducing the cost to cool the building in the summer. Cool
Roofs reduce the electrical power of HVAC equipment which can run less frequently and with
lower capacity.
Buildings with Cool Roofs Last Longer
Fluctuations in roof temperatures cause rooftops to expand and contract, resulting in wear and
tear. A Cool Roof expands and contracts less which increases the longevity of the roof. The
building cooling equipment life expectancy is increased with cool roof, as HVAC doesn't need to
work as hard or as long to cool the building. Thus reduce roofing waste added to landfills.
The basis of Earth Radiation Management
and Atmospheric Convection Management
GHGs act as very good insulators that prevent heat to escape
from the planet atmosphere to the outer space
Taking the example of a house/building: to have a good
insulation, a thick insulator layer is indeed needed, but it is is
mandatory to prevent thermal bridges (conduction process).
In the case of the Earth it is the contrary: Gaïa experiences
global warming because the insulation provided by GHGs is
too good and too powerful.
A solution to cool down the planet can be to create
“IR thermal shortcuts” or “radiative thermal bridges”, and
“convection bridges or shortcuts” between the surface and
altitude in order to allow the heat to be evacuated to space.
Sky cooling devices pump heat away from the
Earth surface by radiative cooling on the atmospheric window
and cool the Earth as they dump the heat to the space.
SRM Targets
ACM Targets
ERM Targets
CDR & GHGR
Targets / CCS
Solar radiation management SRM and Carbon dioxide removal CDR are considered Geoengineering.
CDR is complementary from Carbon capture and sequestration CCS. Greenhouse gas removal GHGR targets the
other GHGs (CH4, N2O, CFCs, etc.). SRM targets short wave radiation. Earth radiation management ERM targets
long wave radiation. Atmospheric convection management targets all natural atmospheric convection
processes… The result of ACM is to increase heat release to the outer space and to cool the Earth.
SRM increases
the albedo
and sunlight
ERM and ACM
reflection
increase infrared
radiation escape to
the outer space
Image from http://www.eco-carb.com/greenhouse_gas.htm
Read the open source paper: http://dx.doi.org/10.1016/j.rser.2013.12.032
MING Tingzhen, de_RICHTER Renaud, LIU Wei, and
CAILLOL Sylvain. Fighting global warming by climate
engineering: Is the Earth radiation management and
the solar radiation management any option for fighting
climate change? Renewable and Sustainable Energy
Reviews, 2014, vol. 31, p. 792-834. Or
Listen to a 5 minute audio slide show by the authors
http://audioslides.elsevier.com//ViewerLarge.aspx?source=1&doi=10.1016/j.rser.2013.12.032