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Sunday, September 10, 2023

Passive daytime radiative cooling

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Passive_daytime_radiative_cooling

Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero energy consumption or pollution. Because all materials in nature absorb more heat during the day than at night, PDRC surfaces are designed to be high in solar reflectance (to minimize heat gain) and strong in longwave infrared (LWIR) thermal radiation heat transfer through the atmosphere's infrared window (8–13 µm) to cool temperatures during the daytime. It is also referred to as passive radiative cooling (PRC), daytime passive radiative cooling (DPRC), radiative sky cooling (RSC), photonic radiative cooling, and terrestrial radiative cooling. PDRC differs from solar radiation management because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation.

Some estimates propose that if 1–2% of the Earth's surface area were dedicated to PDRC that warming would cease and temperature increases would be rebalanced to survivable levels. Regional variations provide different cooling potentials with desert and temperate climates benefiting more from application than tropical climates, attributed to the effects of humidity and cloud cover on reducing the effectiveness of PDRCs. Low-cost scalable PDRC materials feasible for mass production have been developed, such as coatings, thin films, metafabrics, aerogels, and biodegradable surfaces, to reduce air conditioning, lower urban heat island effect, cool human body temperatures in extreme heat, and move toward carbon neutrality as a zero-energy cooling method.

Application of PDRCs may also increase the efficiency of solar energy systems, dew collection techniques, and thermoelectric generation. PDRCs can be modified to be self-adaptive if necessary, 'switching' from passive cooling to heating to mitigate any potential "overcooling" effects in urban environments. They have also been developed in colors other than white, although there is generally a tradeoff in cooling potential, since darker color surfaces are less reflective. Research, development, and interest in PDRCs has grown rapidly since the 2010s, which has been attributed to a scientific breakthrough in the use of photonic metamaterials to achieve daytime cooling in 2014, along with growing concerns over energy use and global warming.

Classification

Passive daytime radiative cooling is not a carbon dioxide removal (CDR) or Solar Radiation Management (SRM) method, but rather enhances longwave infrared thermal radiation heat transfer on the Earth's surface through the infrared window with the coldness of outer space to achieve daytime cooling. Solar radiation is reflected by the PDRC surface to minimize heat gain and to maximize thermal emittance. PDRC differs from SRM because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation. PDRC has been referred to as an alternative or "third approach" to geoengineering. PDRC has also been classified as a sustainable and renewable cooling technology.

Global implementation

When applied globally, PDRC can lower rising temperatures to slow and reverse global warming. Aili et al. concludes that "widescale adoption of radiative cooling could reduce air temperature near the surface, if not the whole atmosphere." To address global warming, PDRCs must be designed "to ensure that the emission is through the atmospheric transparency window and out to space, rather than just to the atmosphere, which would allow for local but not global cooling."

PDRC is not proposed as a standalone solution to global warming, but to be coupled with a global reduction in CO₂ emissions and transition off of fossil fuel energy. Otherwise, "the radiative balance will not last long, and the potential financial benefits of mitigation will not fully be realized because of continued ocean acidification, air pollution, and redistribution of biomass" from high remaining levels of atmospheric CO₂, as per Munday, who summarized the global implementation of PDRC as follows:

Currently the Earth is absorbing ~1 W/m2 more than it is emitting, which leads to an overall warming of the climate. By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth (...) If only 1%–2% of the Earth’s surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease.

The estimated total surface area coverage is 5×10¹² m² or about half the size of the Sahara Desert. Global implementation may be more predictable if distributed in a decentralized manner, rather than in a few heavily centralized locations on the Earth's surface. Mandal et al. refers to this as a "distributed geoengineering" strategy that can mitigate "weather disruptions that may arise from large-scale, centralized geoengineering." Desert climates have the highest radiative cooling potential due to low year-round humidity and cloud cover while tropical climates have a lower cooling potential due to the presence of humidity and cloud cover.

Total costs for global implementation have been estimated at $1.25 to $2.5 trillion or about 3% of global GDP, with probable reductions in price at scale. This has been described as "a small investment compared to the estimated $20 trillion global benefits predicted by limiting global warming to 1.5°C rather than 2°C," as per Munday. Low-cost scalable materials have been developed for widescale implementation, although some challenges toward commercialization remain.

Some studies have recommended efforts to focus on maximizing the solar reflectance or albedo of surfaces from very low values to high values, so long as a thermal emittance of at least 90% can be achieved. For example, while the albedo of an urban rooftop may be 0.2, increasing reflectivity to 0.9 is far more impactful than increasing an already reflective surface to be more reflective, such as from 0.9 to 0.97.

Benefits

Studies have noted the following benefits of widescale implementation of passive daytime radiative cooling:

Advancing toward a carbon neutral future and achieving net-zero emissions.
Alleviating electrical grids and renewable energy sources from devoting electric energy to cooling.
Balancing the Earth's energy budget.
Cooling human body temperatures during extreme heat.
Improving atmospheric water collection systems and dew harvesting techniques.
Improving performance of solar energy systems.
Mitigating energy crises.
Mitigating urban heat island effect.
Reducing greenhouse gas emissions by replacing fossil fuel energy use devoted to cooling.
Reducing local and global temperature increases associated with global warming.
Reducing thermal pollution of water resources.
Reducing water consumption for wet cooling processing.

Advantages to solar radiation management

Passive daytime radiative cooling is referred to as more stable, adaptable, and reversible when compared to stratospheric aerosol injection, which proposes injecting particles into the atmosphere to increase radiative forcing to reduce temperatures. Studies have warned against stratospheric aerosol injection's potential to contribute to further ozone loss and heat the Earth's lower stratosphere further, stating that the injection of sulfate particles "would reflect more of the incoming solar radiation back into space, but it would also capture more of the outgoing thermal radiation back to the Earth" and therefore accelerate warming.

Wang et al. states that stratospheric aerosol injection "might cause potentially dangerous threats to the Earth’s basic climate operations" that may not be reversible, and thus put forth a preference for passive radiative cooling. Munday noted that although "unexpected effects will likely occur" with the global implementation of PDRC, that "these structures can be removed immediately if needed, unlike methods that involve dispersing particulate matter into the atmosphere, which can last for decades."

When compared to the reflective surfaces approach of increasing the reflectivity or albedo of surfaces, such as through painting roofs white, or the space mirror proposals of "deploying giant reflective surfaces in space," Munday states that "the increased reflectivity likely falls short of what is needed and comes at a high financial cost." PDRC differs from the reflective surfaces approach by "increasing the radiative heat emission from the Earth rather than merely decreasing its solar absorption."

Function

PDRCs maximize outgoing infrared radiation (shown in orange) and minimize the absorption of Solar Radiation (shown in yellow).

The basic function of PDRCs is to be high in both solar reflectivity (in 0.4–2.5 µm) and in heat emissivity (in 8–13 µm), to maximize "net emission of longwave thermal radiation" and minimize "absorption of downward shortwave radiation." PDRCs use the infrared window (8–13 µm) for heat transfer with the coldness of outer space (~2.7 K) to radiate heat and subsequently lower ambient temperatures with zero energy input.

PDRCs mimic the natural process of radiative cooling, in which the Earth cools itself by releasing heat to outer space (Earth's energy budget), although during the daytime, lowering ambient temperatures under direct solar intensity. On a clear day, solar irradiance can reach 1000 W/m² with a diffuse component between 50 and 100 W/m². The average PDRC has an estimated cooling power of ~100–150 W/m². The cooling power of PDRCs is proportional to the exposed surface area of the installation.

Measuring effectiveness

To measure a PDRC surface's cooling power, the absorbed powers of atmospheric and solar radiations must be quantified. PDRC should not be measured when the surface is in a balanced or controlled state, but rather in a real-world setting. Standardized devices to measure PDRC effectiveness have been proposed.

Evaluating atmospheric downward longwave radiation based on "the use of ambient weather conditions such as the surface air temperature and humidity instead of the altitude-dependent atmospheric profiles," may be problematic since "downward longwave radiation comes from various altitudes of the atmosphere with different temperatures, pressures, and water vapor contents" and "does not have uniform density, composition, and temperature across its thickness."

Broadband emitters (BE) vs. selective emitters (SE)

PDRCs can be broadband in their thermal emittance capacity, meaning they possess high emittance in both the solar spectrum and atmospheric LWIR window (8 to 14 μm), or selective emitters, meaning they narrowband emit longwave infrared radiation only in the infrared window.

In theory, selective thermal emitters can achieve higher cooling power. However, selective emitters also face additional challenges in real-world applications that can weaken their performance, such as from dropwise condensation, which is common even in semi-arid environments, that can accumulate on the PDRC surface even when it has been made hydrophobic and alter the narrowband emission. Broadband emitters also outperform selective materials when "the material is warmer than the ambient air, or when its sub-ambient surface temperature is within the range of several degrees."

Both emitters can be advantageous for different types of applications. Broadband emitters may be less problematic for horizontal applications, such as on roofs, whereas selective emitters may be more useful if implemented on vertical surfaces like building facades, where dropwise condensation is inconsequential and their stronger cooling power can be actualized.

Broadband emitters can be made angle-dependent to potentially enhance their cooling performance. Polydimethylsiloxane (PDMS) is a common broadband emitter used for PDRC. Most PDRC materials are broadband primarily credited to their lower cost and higher performance at above-ambient temperatures.

Hybrid systems

Combining PDRCs with other systems may increase their cooling power. When included in a combined thermal insulation, evaporative cooling, and radiative cooling system consisting of "a solar reflector, a water-rich and IR-emitting evaporative layer, and a vapor-permeable, IR-transparent, and solar-reflecting insulation layer," 300% higher ambient cooling power was demonstrated. This could extend the shelf life of food by 40% in humid climates and 200% in dry climates without refrigeration. The system however requires water "re-charges" to maintain its cooling power, with more frequent re-charges in hot climates than cooler climates.

A dual-mode asymmetric photonic mirror (APM) consisting of silicon-based diffractive gratings could achieve all-season cooling, even under cloudy and humid conditions, as well as heating. The cooling power of APM could perform 80% more when compared to standalone radiative coolers. Under cloudy sky, it could achieve 8 °C more cooling and, for heating, 5.7 °C higher.

Climatic variations

The global cooling potential of various areas around the world varies primarily based on climate zones and the presence of weather patterns and events. Dry and hot regions generally have a higher radiative cooling power (estimated up to 120 W/m2), while colder regions or those with high humidity or cloud cover generally have lower global cooling potentials. The cooling potential of various regions can also change from winter to summer due to shifts in humidity and cloud cover. Studies mapping the daytime radiative cooling potential have been done for China and India, the United States, and on a continental scale across Europe.

Regional cooling potential

Desert climates

Dry regions such as western Asia, north Africa, Australia and the southwestern United States are ideal for PDRC application due to the relative lack of humidity and cloud cover in both winter and summer. The cooling potential for desert regions has been estimated at "in the higher range of 80–110 W/m2," as per Aili et al. and 120 W/m2 as per Yin et al. The Sahara Desert and western Asia is the largest area on Earth with a high cooling potential in both winter and summer.

The cooling potential of desert regions risks being relatively unfulfilled due to very low population densities, which may lower interest in applying PDRCs for local cooling. However, in the event of global implementation, lowly populated or unpopulated desert climates may be an important "land surface contribution to the planetary albedo" which could "reduce air temperature near the surface, if not the whole atmosphere."

Temperate climates

Temperate climates have a high radiative cooling potential and higher average population densities when compared to desert climates, which may increase willingness to apply PDRCs in these zones. This is because these climatic zones tend to be "transitional" zones between dry and humid climates. High population areas in temperate climatic zones may be susceptible to an "overcooling" effect from PDRCs (see: overcooling section below) due to temperature shifts from hot summers to mild winters, which can be overcome with the modification of PDRCs to adjust for temperature shifts.

Tropical climates

While passive radiative cooling technologies have proven successful in mid-latitude regions of Earth, to reach the same level of performance has faced more difficulties in tropical climates. This has primarily been attributed to the higher solar irradiance and atmospheric radiation of these zones, particularly humidity and cloud cover. The average cooling potential of hot and humid climates varies between 10 and 40 W/m2, which is significantly lower than hot and dry climates.

For example, the cooling potential of most of southeast Asia and the Indian subcontinent is significantly diminished in the summer due to a dramatic increase in humidity, dropping as low as 10–30 W/m2. Other similar zones, such as tropical savannah areas in Africa, see a more modest decline during summer, dropping to 20–40 W/m2. However, tropical regions generally have a higher albedo or radiative forcing due to sustained cloud cover and thus their land surface contributes less to planetary albedo.

A study by Han et al. determined criteria for a PDRC surface in tropical climates to have a solar reflectance of at least 97% and an infrared emittance of at least 80% to achieve sub-ambient temperatures in tropical climates. The researchers used a BK coating with a "solar reflectance and infrared emittance (8–13 μm) of 98.4% and 95% respectively" in the tropical climate of Singapore and achieved a "sustained daytime sub-ambient temperature of 2°C" under direct solar intensity of 1000 W/m2.

Variables

Humidity and cloud coverage

Humidity and cloud coverage significantly weaken PDRC effectiveness. A study by Huang et al. noted that "vertical variations of both vapor concentration and temperature in the atmosphere" can have a considerable impact on radiative coolers. The authors put forth that aerosol and cloud coverage can also weaken the effectiveness of radiators and thus concluded that adaptable "design strategies of radiative coolers" are needed to maximize effectiveness under these climatic conditions. Regions with high humidity and cloud cover have less global cooling potential than areas with low humidity and cloud cover.

Dropwise condensation

The formation of dropwise condensation on PDRC surfaces can alter the infrared emittance of the surface of selective PDRC emitters, which can weaken their performance. Even in semi-arid environments, dew formation on PDRC surfaces can occur. Thus, the cooling power of selective emitters "may broaden the narrowband emittances of the selective emitter and reduce their sub-ambient cooling power and their supposed cooling benefits over broadband emitters," as per Simsek et al., who discuss the implications on the performance of selective emitters:

In showing that dropwise condensation on horizontal emitters leads to broadband emittance regardless of the emitter, our work shows that the assumed benefits of selective emitters are even smaller when it comes to the largest application of radiative cooling – cooling roofs of buildings. However, recently, it has been shown that for vertical building facades experiencing broadband summertime terrestrial heat gains and wintertime losses, selective emitters can achieve seasonal thermoregulation and energy savings. Since dew formation appears less likely on vertical surfaces even in exceptionally humid environments, the thermoregulatory benefits of selective emitters will likely persist in both humid and dry operating conditions.

Rain

Rain can generally help clean PDRC surfaces that have been covered with dust, dirt, or other debris and improve their reflectivity. However, in humid areas, consistent rain can result in heavy water accumulation on PDRC surfaces which can hinder performance. In response, porous PDRCs have been developed. Another response is to make hydrophobic PDRCs which are "self-cleaning." Scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed that repel rainwater and other liquids.

Wind

Wind may have some effect on altering the efficiency of passive radiative cooling surfaces and technologies. Liu et al. proposes using a "tilt strategy and wind cover strategy" to mitigate effects of wind. The researchers found regional differences in regard to the impacts of wind cover in China, noting that "85% of China's areas can achieve radiative cooling performance with wind cover" whereas in northwestern China wind cover effects would be more substantial. Bijarniya et al. similarly proposes the use of a wind shield in areas susceptible to high winds.

Materials and production

Solar reflective and heat emissive surfaces can be of various material compositions. However, for widespread application to be feasible, PDRC materials must be low cost, available for mass production, and applicable in many contexts. Most research has focused on PDRC coatings and thin films, which tend to be more available for mass production, lower cost, and more applicable in a wider range of contexts, although other materials may provide potential for diverse applications.

Some PDRC research has also developed more eco-friendly or sustainable materials, even if not fully biodegradable. Zhong et al. state "most PDRC materials now are non-renewable polymers, artificial photonic or synthetic chemicals, which will cause excessive CO₂ emissions by consuming fossil fuels and go against the global carbon neutrality goal. Environmentally friendly bio-based renewable materials should be an ideal material to devise PDRC systems."

Multilayer and complex structures

Advanced photonic materials and structures, such as multilayer thin films, micro/nanoparticles, photonic crystals, metamaterials, metasurfaces, have been tested to significantly facilitate radiative cooling. However, while multilayer and complex nano-photonic structures have proven successful in experimental scenarios and simulations, widespread application "is severely restricted because of the complex and expensive processes of preparation," as per Cui et al. Similarly, Zhang et al. noted that "scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging." This has advanced research of simpler structures for PDRC materials that are more suited for mass production.

Coatings

PDRC coatings or paints tend to be advantageous for their direct application to surfaces, simplifying preparation processes and reducing costs, although not all PDRC coatings are inexpensive. Coatings generally offer "strong operability, convenient processing, and low cost, which have the prospect of large-scale utilization," as per Dong et al. PDRC coatings have been developed in colors other than white while still demonstrating high solar reflectance and heat emissivity.

Coatings must be durable and resistant to soiling, which can be achieved with porous PDRCs or hydrophobic topcoats that can withstand cleaning, although hydrophic coatings use polytetrafluoroethylene or other similar compounds to be water-resistant. Negative environmental impacts can be mitigated by limiting use of other toxic solvents common in paints, such as acetone. Non-toxic or water-based paints have been developed. More research and development is needed.

The cost of PDRC coatings was significantly lowered with a 2018 study by Atiganyanun et al. which demonstrated how "photonic media, when properly randomized to minimize the photon transport mean free path, can be used to coat a black substrate and reduce its temperature by radiative cooling." This coating could "outperform commercially available solar-reflective white paint for daytime cooling" without using expensive manufacturing steps or materials.

PDRC coatings that are described as scalable and low-cost include:

Li et al. (2019), aluminum phosphate coating, solar reflectance 97%, heat emittance 90%, daytime air temperature ~4.2 °C lower than ambient temperature (~4.8 °C lower than commercial heat insulation coating), predicted estimated cost by Dong et al. at $1.2/m2, tested in Guangzhou (daytime humidity 41%), selective emitter (SE).
Li et al. (2021), ultrawhite BaSO₄ paint with 60% volume concentration, solar reflectance 98.1%, heat emittance 95%, daytime air temperature ~4.5 °C lower than ambient, "providing great reliability, convenient paint form, ease of use, and compatibility with the commercial paint fabrication process."
Weng et al. (2021), porous PDMS (Polydimethylsiloxane) sponge emitter template method for coatings, solar reflectance 95%, heat emittance 96.5%, daytime air temperature ~8 °C lower than ambient, avoids hazardous etching agents (e.g., hydrofluoric acid, hydrogen peroxide, acetic acid) or VOCs (e.g., acetone, dimethylformamide, tetrahydrofuran, hexane), "compatibility with large-scale production," tested in Hangzhou (daytime humidity ~61%).
Wang et al. (2022), waterborne thermochromic coating free of ecotoxic and carcinogenic titanium dioxide, solar reflectance 96%, heat emittance 94%, daytime air temperature ~7.1 °C lower than ambient, and "can be produced at a large scale and conveniently coated on various substrates through traditional drop casting, spraying, roller painting, or spin-coating methods" and "switchable [between] solar heating and radiative cooling," tested in Shanghai (daytime humidity ~28%).
Dong et al. (2022), BaSO₄, CaCO₃, and SiO₂ particles coating, solar reflectance 97.6%, heat emittance 89%, daytime air temperature ~8.3 °C lower than ambient (~5.5 °C lower than commercial white paints), described "for large-scale commercial production" with a predicted estimated cost of $0.5/m2, tested in Weihai (daytime humidity 40%).
Zhai et al. (2022), α-Bi
₂O
₃ colored coating, solar reflectance 99%, heat emittance 97%, daytime air temperature ~2.31 °C (average cooling power 68 Wm-2), uses "low cost of raw oxide materials, and simple preparation process," tested in Nanjing (daytime humidity 54%).

Films

Many PDRC thin films have been developed which have demonstrated very high solar reflectance and heat emittance. However, films with precise patterns or structures are not scalable "due to the cost and technical difficulties inherent in large-scale precise lithography," as per Khan et al., or "due to complex nanoscale lithography/synthesis and rigidity," as per Zhou et al. Some researchers have attempted to overcome this with various methods:

Zhang et al. (2020), facile microstamping method film on low-cost polymer PDMS, solar reflectance 95%, heat emittance 96%, daytime temperature reduction up to 5.1 °C, "promising for scale-up production."
Zhang et al. (2021), low-cost film developed with a phase inversion process using cellulose acetate and calcium silicate, solar reflectance 97.3%, heat emittance 97.2%, daytime temperature reduction up to 7.3 °C below ambient (average net cooling power of 90.7 W m⁻²), "a low-cost, scalable composite film with novel dendritic cell like structures," tested in Qingdao.
Fan et al. (2022), eco-friendly preparation of superhydrophobic porous polydimethylsiloxane (PDMS) radiative cooling film, daytime temperature reduction up to 11.52 °C below ambient, "the film is promising to be widely used for long-term cooling for outdoor applications."
Nie et al. (2022), composite film made of fluorine-free reagents and SiO₂ particles, solar reflectance 85%, heat emittance 95%, daytime temperature reduction average 12.2 °C, manufactured with "a simple preparation process, which has characteristics of low-cost environmental friendliness and excellent machinal durability," tested in Hubei.
Zhong et al. (2023), hierarchical flexible fibrous cellulose (wood pulp) film, solar reflectance 93.8%, heat emittance 98.3%, daytime temperature reduction up to 11.3 °C below ambient, study is "the first time to realize high crystallinity and hierarchical microstructures in regenerated cellulose materials by the self-assembly of cellulose macromolecules at the molecular level," which "will provide new perspectives for the development of flexible cellulose materials."

Metafabrics

PDRCs can also come in the form of metafabrics, which can be worn as clothing to shield and regulate body temperatures in times of extreme heat. Most metafabrics are made of petrol-based fibers, although research and development of sustainable or regenerative materials is ongoing. For instance, Zhong et al. states that "new flexible cellulose fibrous films with wood-like hierarchical microstructures need to be developed for wearable PDRC applications."

Liu et al. (2022), eco-friendly bio-derived regenerable polymer alginate to modify cotton fiber and then in-matrix generate CaCO₃ nano- or other micro-particles, solar reflectance 90%, heat emittance 97%, lowered human skin temperature by 5.4ᵒC, "fully compatible with industrial processing facilities" and with "effective UV protection properties with a UPF value of 15, is fast-dry, and is stable against washing."
Li et al. (2022), wearable hat constructed of a radiative cooling paper with SiO₂ fibers and fumed SiO₂, solar reflectance 97%, heat emittance 91%, reduced temperatures for the hair of the wearer by 12.9ᵒC when compared with a basic white cotton hat (and 19ᵒC when compared with no hat), waterproof and air permeable, "suitable for the manufacture of radiative cooling hat to achieve the thermal management of human head."

Aerogels

Aerogels may be used as a potential low-cost PDRC material scalable for mass production. Some aerogels can also be considered a more environmentally friendly alternative to other materials, with degradable potential and the absence of toxic chemicals. Aerogels can also be useful as a thermal insulation material to reduce solar absorption and parasitic heat gain to improve the cooling performance of PDRCs.

Yue et al. (2022), superhydrophobic waste paper-based (cellulose) aerogel, solar reflectance 93%, thermal emittance 91%, reduced daytime temperatures up to 8.5 °C below ambient in outdoor test, in a building energy simulation the aerogel "showed that 43.4% of cooling energy on average could be saved compared to the building baseline consumption" in China if widely implemented.
Liu et al. (2022), degradable and superhydrophobic stereo-complex poly (lactic acid) aerogel with low thermal conductivity, solar reflectance 89%, heat emittance 93%, reduced daytime temperatures 3.5ᵒC below ambient, "opens an environmentally sustainable pathway to radiative cooling applications."
Li et al. (2022), low-cost silica-alumina nanofibrous aerogels (SAFAs) synthesized by electrospinning, solar reflectance 95%, heat emittance 93%, reduced daytime temperatures 5ᵒC below ambient, "the SAFAs exhibit high compression fatigue resistance, robust fire resistance and excellent thermal insulation" with "low cost and high performance," shows potential for further studies.

Nano bubbles

Pigments absorb light. Soap bubbles show a prism of different colors on their surfaces. These colors result from the way light interacts with differing thicknesses of the bubble’s film, a phenomenon called structural color. Part of Qingchen Shen and Silvia Vignolini’s research focuses on identifying the causes behind different types of structural colors in nature. In one case, her group found that cellulose nanocrystals (CNCs), which are derived from the cellulose found in plants, could be made into iridescent, colorful films without any added pigment. They made films with vibrant blue, green and red colors that, when placed under sunlight, were an average of nearly 7 F cooler than the surrounding air. A square meter of the film generated over 120 Watts of cooling power.

Biodegradable surfaces

With the proliferation of PDRC development, many proposed radiative cooling materials are not biodegradable. As per Park et al., "sustainable materials for radiative cooling have not been sufficiently investigated."

Park et al. (2022), eco-friendly porous polymer structure via thermally induced phase separation, solar reflectance 91%, heat emittance 92%, daytime temperature reduction up to 9 °C, sufficient durability for use on buildings and highest cooling effect reported "among all organic-based passive radiation cooling emitters."

Applications

Passive daytime radiative cooling has "the potential to simultaneously alleviate the two major problems of energy crisis and global warming" while being an "environmental protection refrigeration technology." PDRCs thereby have an array of potential applications, but are now most often applied to various aspects of the built environment, such as building envelopes, cool pavements, and other surfaces to decrease energy demand, costs, and CO₂ emissions. PDRC has been tested and applied for indoor space cooling, outdoor urban cooling, solar cell efficiency, power plant condenser cooling, among other applications. For outdoor applications, the lifetime of PDRCs should be adequately estimated, both for high humidity and heat as well as for UV stability.

Indoor space cooling

The most common application of passive daytime radiative cooling currently is on building envelopes, including PDRC cool roofs, which can significantly lower indoor space temperatures within buildings. A PDRC roof application can double the energy savings of a white roof. This makes PDRCs a sustainable and low-cost alternative or supplement to air conditioning by decreasing energy demand, alleviating energy grids in peak periods, and reducing CO₂ emissions caused by air conditioning's release of hydrofluorocarbons into the atmosphere which can be thousands of times more potent that CO₂.

Air conditioning alone accounts for 12%-15% of global energy usage, while CO₂ emissions from air conditioning account for "13.7% of energy-related CO₂ emissions, approximately 52.3 EJ yearly" or 10% of emissions total. Air conditioning applications are expected to rise, despite their negative impacts on energy sectors, costs, and global warming, which has been described as a "vicious cycle." However, this can be significantly reduced with the mass production of low-cost PDRCs for indoor space cooling. A multilayer PDRC surface covering 10% of a building's roof can replace 35% of air conditioning used during the hottest hours of daytime.

In suburban single-family residential areas, PDRCs can lower energy costs by 26% to 46% in the United States and lower temperatures on average by 5.1ᵒC. With the addition of "cold storage to utilize the excess cooling energy of water generated during off-peak hours, the cooling effects for indoor air during the peak-cooling-load times can be significantly enhanced" and air temperatures may be reduced by 6.6–12.7 °C.

In cities, PDRCs can result in significant energy and cost savings. In a study on US cities, Zhou et al. found that "cities in hot and arid regions can achieve high annual electricity consumption savings of >2200 kWh, while <400 kWh is attainable in colder and more humid cities," being ranked from highest to lowest by electricity consumption savings as follows: Phoenix (~2500 kWh), Las Vegas (~2250 kWh), Austin (~2100 kWh), Honolulu (~2050 kWh), Atlanta (~1500 kWh), Indianapolis (~1200 kWh), Chicago (~1150 kWh), New York City (~900 kWh), Minneapolis (~850 kWh), Boston (~750 kWh), Seattle (~350 kWh). In a study projecting energy savings for Indian cities in 2030, Mumbai and Kolkata had a lower energy savings potential, Jaisalmer, Varansai, and Delhi had a higher potential, although with significant variations from April to August dependent on humidity and wind cover.

The growing interest and rise in PDRC application to buildings has been attributed to cost savings related to "the sheer magnitude of the global building surface area, with a market size of ~$27 billion in 2025," as estimated in a 2020 study.

Outdoor urban space cooling

Passive daytime radiative cooling surfaces can mitigate extreme heat from the urban heat island effect which occurs in over 450 cities worldwide, where it can be as much as 10–12 °C (18–22 °F) hotter in urban areas in comparison to surrounding rural areas. On an average hot summer day, the roofs of buildings can be 27–50 °C (49–90 °F) hotter than the surrounding air, warming air temperatures further through convection. Well-insulated dark rooftops are significantly hotter than all other urban surfaces, including asphalt pavements, further expanding air conditioning demand (which further accelerates global warming and urban heat island through the release of waste heat into the ambient air) and increasing risks of heat-related disease and fatal health effects.

PDRCs can be applied to building roofs and urban shelters to significantly lower surface temperatures with zero energy consumption by reflecting heat out of the urban environment and into outer space. The primary obstacle of PDRC implementation in urban areas is the glare that may be caused through the reflectance of visible light onto surrounding buildings. Colored PDRC surfaces may mitigate glare issues, such as Zhai et al. "Super-white paints with commercial high-index (n~1.9) retroreflective spheres," as per Mandal et al., or the use of retroreflective materials (RRM) may also mitigate glare, although further research and development is needed. Surrounding buildings without PDRC application may weaken the cooling power of PDRCs.

Even when installed on roofs in highly dense urban areas, broadband radiative cooling panels have been shown to lower surface temperatures at the sidewalk level. A study by Khan et al. published in 2022 assessed the effects of PDRC surfaces in winter, including for both non-modulated and modulated PDRCs, in the Kolkata metropolitan area. A non-modulated PDRC with a reflectance of 0.95 and emissivity of 0.93 decreased ground surface temperatures by nearly 4.9 °C (8.8 °F) and with an average daytime reduction of 2.2 °C (4.0 °F).

While in summer the cooling effects of broadband non-modulated PDRCs may be desirable, they could present an uncomfortable "overcooling" effect for city populations in winter and thus increase energy use for heating. This can be mitigated by broadband modulated PDRCs, which they found could increase daily ambient urban temperatures by 0.4–1.4 °C (0.72–2.52 °F) in winter. While in the tropical metropolitan area of Kolkata, for instance, "overcooling" is unlikely, elsewhere it could impact the willingness to apply PDRCs in urban spaces. Therefore, modulated PDRCs may be preferred in cities with warm summers and cold winters for controlled cooling, while non-modulated PDRCs may be more beneficial for cities with hot summers and moderate winters. The authors expected "low-cost optically modulated passive systems" to be commercially available soon.

In a study on urban bus shelters, it was found that most shelters fail at providing thermal comfort for commuters, noting that, on average, a tree could provide 0.5 °C (0.90 °F) more cooling. Other methods to cool shelters often resort to air conditioning or other energy intensive measures that can crowd commuters in an enclosed space for cooling. Urban shelters with PDRC roofing can significantly reduce temperatures with zero added costs or energy input, while adding "a non-reciprocal mid-infrared cover" can increase benefits by reducing incoming atmospheric radiation as well as reflecting radiation from surrounding buildings, as per Mokharti et al.

For outdoor urban space cooling, it is recommended that PDRC implementation in urban areas primarily focus on increasing albedo so long as heat emissivity can be maintained at the standard of 90%, as per Anand et al. This can rapidly and significantly lower temperatures while reducing energy demand and costs for cooling in urban environments.

Solar energy efficiency

Passive daytime radiative cooling surfaces can be integrated with solar energy plants, referred to as solar energy–radiative cooling (SE–RC), to improve functionality and performance by preventing solar cells from 'overheating' and thus degrading. Since solar cells have a maximum efficiency of 33.7% (with the average commercial PV panel having a conversion rate around 20%), the majority of absorbed power produces excess heat and increases the operating temperature of the system. Solar cell efficiency declines 0.4-0.5% for every 1ᵒC increase in temperature.

Passive daytime radiative cooling can extend the life of solar cells by lowering the operating temperature of the system. Integrating PDRCs into solar energy systems is also relatively simple, given that "most solar energy harvesting systems have a sky-facing flat plate structural design, which is similar to radiative cooling systems." Integration has been shown to "produce a higher energy gain per unit area" while also increasing the "total useful working time." Integrated systems can mitigate issues of "limited working time and low energy gain" and are "a current research hotspot," as per Ahmed et al.

Methods have been proposed to potentially enhance cooling performance. Lu et al. proposes using a "full-spectrum synergetic management (FSSM) strategy to cool solar cells, which combines radiative cooling and spectral splitting to enhance radiative heat dissipation and reduce the waste heat generated by the absorption of sub-BG photons."

Outdoor tests using various PDRC materials, some more scalable than others, have demonstrated various degrees of cooling power:

Wang et al. (2021), a periodic pyramid-textured polydimethylsiloxane (PDMS) radiative film, cooled commercial silicon solar cells by over 2 °C.
Lee et al. (2021), a visibly clear PDRC designed "using a rational design to deploy an optical modulator (n-hexadecane) in SiO₂ aerogel microparticles within a silicone elastomer matrix," cooled commercial silicon solar cells by 7.7 °C on average.
Tang et al. (2022), nanoporous anodic aluminum oxide film, flatpanel solar cell relative efficiency improvement of ~2.72%, concentrated solar cell relative efficiency improvement of ~16.02%, described as "a high-performance and scalable radiative cooler."
Zhao et al. (2022), a silica micro-grating photonic cooler, cooled commercial silicon cells by 3.6 °C under solar intensity of 830 W m⁻² to 990 W m⁻².

Personal thermal management

The usage of passive daytime radiative cooling in fabrics to regulate body temperatures during extreme heat is in research and development. While other fabrics are useful for heat accumulation, they "may lead to heat stroke in hot weather." Zeng et al. states that "incorporating passive radiative cooling structures into personal thermal management technologies could effectively defend humans against intensifying global climate change."

Wearable PDRCs can come in different forms and be particularly useful for outdoor workers. Readily available wearable PDRCs are not yet available, although prototypes have been developed. This field of research is referred to as personal thermal management (PTM). Although most textiles developed are in white, colored wearable materials have also been developed, although only in select colors that are relatively successful for solar reflectance to minimize heat gain.

Power plant condenser cooling

Passive daytime radiative cooling can be used in various power plant condensers, including thermoelectric power plants and concentrated solar plants (CSP) to cool water for effective use within the heat exchanger. A generalized study of "a covered pond with radiative cooler revealed that 150 W/m2 flux could be achieved without loss of water." PDRC application for power plant condensers can reduce high water use and thermal pollution caused by water cooling.

For a thermoelectric power plant condenser, one study found that supplementing the air-cooled condenser for radiative cooling panels "get a 4096 kWhth/day cooling effect with a pump energy consumption of 11 kWh/day." For a concentrated solar plant (CSP) "on the CO₂ supercritical cycle at 550ᵒC can be improved in 5% net output over an air-cooled system by integration with 14 m2 /kWe capacity radiative cooler."

Thermal regulation of buildings

In addition to cooling, passive daytime radiative cooling surfaces can be modified to be self-adaptive for temperature-dependent 'switching' from cooling to heating or, in other words, for full-scale thermal regulation. This can be achieved through switching the thermal emittance of the surface from a high to low value. Applications are limited to testing and commercially available self-switching PDRCs are in research and development.

Thermoelectric generation

When combined with a thermoelectric generator, a passive daytime radiative cooling surface can be used to generate electricity during the daytime and nighttime, although the power generated in tests has been relatively low. Research and development is preliminary.

Automobile and greenhouse cooling

Thermally enclosed spaces, including automobiles and greenhouses, are particularly susceptible to harmful temperature increases, especially during extreme weather. This is because of the heavy presence of windows, which are act as "transparent" to incoming solar radiation yet "opaque" to outgoing long-wave thermal radiation, which causes them to heat rapidly. The temperature of an automobile in direct sunlight can rise to 60–82ᵒC when ambient temperatures is only 21ᵒC. This accumulation of heat "can cause heat stroke and hyperthermia in the occupants, especially children", which can be alleviated with passive radiative cooling.

Water harvesting

Dew harvesting yields may be improved with passive daytime radiative cooling application. Selective PDRC emitters that have a high emissivity only at the atmospheric window (8–13 μm) and broadband emitters may produce varying results. In one study using a broadband PDRC, the research condensed "~8.5 mL day of water for 800 W m2 of peak solar intensity." Whereas selective emitters may be less advantageous in other contexts, they may be more advantageous for dew harvesting applications. PDRCs could improve atmospheric water harvesting by being combined with solar vapor generation systems to improve water collection rates.

Water and ice cooling

Passive daytime radiative cooling surfaces can be installed over the surface of a body of water for cooling. In a controlled study, a body of water was cooled 10.6ᵒC below the ambient temperature with the usage of a photonic radiator.

PDRC surfaces have been developed to cool ice and prevent ice from melting under sunlight. It has been proposed as a sustainable method for ice protection. This can be applied to protect iced or refrigerated food from spoiling.

Unwanted side effects

Jeremy Munday writes that although "unexpected effects will likely occur" with global PDRC implementation, that "these structures can be removed immediately if needed, unlike methods that involve dispersing particulate matter into the atmosphere, which can last for decades." Wang et al. state that stratospheric aerosol injection "might cause potentially dangerous threats to the Earth’s basic climate operations" that may not be reversible, preferring PDRC. Zevenhoven et al. state that "instead of stratospheric aerosol injection (SAI), cloud brightening or a large number of mirrors in the sky (“sunshade geoengineering”) to block out or reflect incoming (short-wave, SW) solar irradiation, long-wavelength (LW) thermal radiation can be selectively emitted and transferred through the atmosphere into space".

"Overcooling" and PDRC modulation

"Overcooling" is cited as a side effect of PDRCs that may be problematic, especially when PDRCs are applied in high-population areas with hot summers and cool winters, characteristic of temperate zones. While PDRC application in these areas can be useful in summer, in winter it can result in an increase in energy consumption for heating and thus may reduce the benefits of PDRCs on energy savings and emissions. As per Chen et al., "to overcome this issue, dynamically switchable coatings have been developed to prevent overcooling in winter or cold environments."

The detriments of overcooling can be reduced by modulation of PDRCs, harnessing their passive cooling abilities during summer, while modifying them to passively heat during winter. Modulation can involve "switching the emissivity or reflectance to low values during the winter and high values during the warm period." In 2022, Khan et al. concluded that "low-cost optically modulated" PDRCs are "under development" and "are expected to be commercially available on the market soon with high future potential to reduce urban heat in cities without leading to an overcooling penalty during cold periods."

There are various methods of making PDRCs 'switchable' to mitigate overcooling. Most research has used vanadium dioxide (VO2), an inorganic compound, to achieve temperature-based 'switchable' cooling and heating effects. While, as per Khan et al., developing VO2 is difficult, their review found that "recent research has focused on simplifying and improving the expansion of techniques for different types of applications."^[18] Chen et al. found that "much effort has been devoted to VO2 coatings in the switching of the mid-infrared spectrum, and only a few studies have reported the switchable ability of temperature-dependent coatings in the solar spectrum." Temperature-dependent switching requires no extra energy input to achieve both cooling and heating.

Other methods of PDRC 'switching' require extra energy input to achieve desired effects. One such method involves changing the dielectric environment. This can be done through "reversible wetting" and drying of the PDRC surface with common liquids such as water and alcohol. However, for this to be implemented on a mass scale, "the recycling, and utilization of working liquids and the tightness of the circulation loop should be considered in realistic applications."

Another method involves 'switching' through mechanical force, which may be useful and has been "widely investigated in [PDRC] polymer coatings owing to their stretchability." For this method, "to achieve a switchable coating in εLWIR, mechanical stress/strain can be applied in a thin PDMS film, consisting of a PDMS grating and embedded nanoparticles." One study estimated, with the use of this method, that "19.2% of the energy used for heating and cooling can be saved in the US, which is 1.7 times higher than the only cooling mode and 2.2 times higher than the only heating mode," which may inspire additional research and development.

Glare and visual appearance

Glare caused from surfaces with high solar reflectance may present visibility concerns that can limit PDRC application, particularly within urban environments at the ground level. PDRCs that use a "scattering system" to generate reflection in a more diffused manner have been developed and are "more favorable in real applications," as per Lin et al.

Low-cost PDRC colored paint coatings, which reduce glare and increase the color diversity of PDRC surfaces, have also been developed. While some of the surface's solar reflectance is lost in the visible light spectrum, colored PDRCs can still exhibit significant cooling power, such as a coating by Zhai et al., which used a α-Bi₂O₃ coating (resembling the color of the compound) to develop a non-toxic paint that demonstrated a solar reflectance of 99% and heat emissivity of 97%.

Generally it is noted that there is a tradeoff between cooling potential and darker colored surfaces. Less reflective colored PDRCs can also be applied to walls while more reflective white PDRCs can be applied to roofs to increase visual diversity of vertical surfaces, yet still contribute to cooling.

Commercialization

The commercialization of passive daytime radiative cooling technologies is in an early stage of development.

SkyCool Systems, founded by Aaswath P. Raman, who authored the scientific breakthrough study demonstrating the use of photonic metamaterials in making PDRC possible, is a startup that is commercializing radiative cooling technologies. SkyCool panels have been applied to some buildings in California, reducing energy costs. The company has received a grant from the California Energy Commission for further application opportunities.

3M, an American multinational corporation, has developed a selectively emissive passive radiative cooling film. The film has been applied through pilot programs that are open for expansion. The film was tested on bus shelters in Tempe, Arizona. 3M's film achieved "10–20% energy savings when deployed on SkyCool Systems panels and integrated with a building's HVAC or refrigeration system."

History

Nocturnal passive radiative cooling has been recognized for thousands of years, with records showing awareness by the ancient Iranians, demonstrated through the construction of Yakhchāls, since 400 B.C.E.

Passive daytime radiative cooling was hypothesized by Félix Trombe in 1967. The first experimental setup was created in 1975, but was only successful for nighttime cooling. Further developments to achieve daytime cooling using different material compositions were not successful.

In the 1980s, Lushiku and Granqvist identified the infrared window as a potential way to access the ultracold outer space as a way to achieve passive daytime cooling.

Early attempts at developing passive radiative daytime cooling materials took inspiration from nature, particularly the Saharan silver ant and white beetles, noting how they cooled themselves in extreme heat.

Research and development in passive daytime radiative cooling evolved rapidly in the 2010s with the discovery of the ability to suppress solar heating using photonic metamaterials, which widely expanded research and development in the field. This is largely credited to the landmark study by Aaswath P. Raman, Marc Abou Anoma, Linxiao Zhu, Eden Raphaeli, and Shanhui Fan published in 2014.

Obsessive–compulsive personality disorder

From Wikipedia, the free encyclopedia

Obsessive–compulsive personality disorder
Other names	Anankastic personality disorder

A symptom of OCPD is a great attention to detail.
Specialty	Psychiatry
Symptoms	Obsession with rules and order; perfectionism; excessive devotion to productivity; inability to delegate tasks; zealotry on matters of morality; rigidity and stubbornness
Usual onset	Adolescence to early adulthood
Risk factors	Negative life experiences, genetics
Differential diagnosis	Obsessive–compulsive disorder, personality disorders, substance use disorder, personality disorder due to another medical condition
Treatment	Psychotherapy
Frequency	3%

Obsessive–compulsive personality disorder (OCPD) is a cluster C personality disorder marked by a spectrum of obsessions with rules, lists, schedules, and order, among other things. Symptoms are usually present by the time a person reaches adulthood, and are visible in a variety of situations. The cause of OCPD is thought to involve a combination of genetic and environmental factors, namely problems with attachment.

Obsessive–compulsive personality disorder is distinct from obsessive–compulsive disorder (OCD), and the relation between the two is contentious. Some studies have found high comorbidity rates between the two disorders but others have shown little comorbidity. Both disorders may share outside similarities, such as rigid and ritual-like behaviors. OCPD is highly comorbid with other personality disorders, autism spectrum, eating disorders, anxiety, mood disorders, and substance use disorders.

The disorder is the most common personality disorder in the United States, and is diagnosed twice as often in males as in females; however, there is evidence to suggest the prevalence between men and women is equal.

Signs and symptoms

Obsessive–compulsive personality disorder (OCPD) is marked by an excessive obsession with rules, lists, schedules, and order; a need for perfection that interferes with efficiency and the ability to complete tasks; a devotion to productivity that hinders interpersonal relationships and leisure time; rigidity and zealousness on matters of morality and ethics; an inability to delegate responsibilities or work to others; restricted functioning in interpersonal relationships; restricted expression of emotion and affect; and a need for control over one's environment and self.

Some of OCPD's symptoms are persistent and stable, whilst others are unstable. The obsession with perfectionism, reluctance to delegate tasks to others, and rigidity and stubbornness are stable symptoms. On the other hand, the symptoms that were most likely to change over time were the miserly spending style and the excessive devotion to productivity. This discrepancy in the stability of symptoms may lead to mixed results in terms of the course of the disorder, with some studies showing a remission rate of 58% after a 12-month period, whilst others suggesting that the symptoms are stable and may worsen with age.

Attention to order and perfection

People with OCPD tend to be obsessed with controlling their environments; to satisfy this need for control, they become preoccupied with trivial details, lists, procedures, rules, and schedules.

This preoccupation with details and rules makes the person unable to delegate tasks and responsibilities to other people unless they submit to their exact way of completing a task because they believe that there is only one correct way of doing something. They stubbornly insist that a task or job must be completed their way, and only their way, and may micromanage people when they are assigned a group task. They are frustrated when other people suggest alternative methods. A person with this disorder may reject help even when they desperately need it as they believe that only they can do something correctly.

People with OCPD are obsessed with maintaining perfection. The perfectionism and the extremely high standards that they establish are to their detriment and may cause delays and failures to complete objectives and tasks. Every mistake is thought of as a major catastrophe that will soil their reputation for life. For example, a person may write an essay and, believing that it fell short of perfection, continues rewriting it, missing the deadline or even failing to complete the task. The subject may remain unaware that others become frustrated and annoyed by repeated delay and inconvenience so caused. Work relationships may then become a source of tension.

Devotion to productivity

Individuals with OCPD devote themselves to work and productivity at the expense of interpersonal relationships and recreation. Economic necessity, such as poverty, cannot account for this behavior. They may believe that they do not have sufficient time to relax because they have to prioritize their work above all. They may refuse to spend time with friends and family because of that. They may find it difficult to go on a vacation, and even if they book a vacation, they may keep postponing it until it never happens. They may feel uncomfortable when they do go on a vacation and will take something along with them so they can work. They choose hobbies that are organized and structured, and they approach them as a serious task requiring work to perfect. The devotion to productivity in OCPD, however, is distinct from work addiction. OCPD is controlled and egosyntonic, whereas work addiction is uncontrolled and egodystonic, and the affected person may display signs of withdrawal.

Rigidity

Individuals with OCPD are overconscientious, scrupulous and rigid, and inflexible on matters of morality, ethics and other areas of life. They may force themselves and others to follow rigid moral principles and strict standards of performance. They are self-critical and harsh about their mistakes. These symptoms should not be accounted for or caused by a person's culture or religion. Their view of the world is polarised and dichotomous; there is no grey area between what is right and what is wrong. Whenever this dichotomous view of the world cannot be applied to a situation, this causes internal conflict as the person's perfectionist tendencies are challenged.

People with this disorder are so obsessed with doing everything the "right and correct" way that they have a hard time understanding and appreciating the ideas, beliefs, and values of other people, and are reluctant to change their views, especially on matters of morality and politics.

Restricted emotions and interpersonal functioning

Individuals with this disorder may display little affection and warmth; their relationships and speech tend to have a formal and professional approach, and not much affection is expressed even to loved ones, such as greeting or hugging a significant other at an airport or train station.

They are extremely careful in their interpersonal interactions. They have little spontaneity when interacting with others, and ensure that their speech follows rigid and austere standards by excessively scrutinising it. They filter their speech for embarrassing or imperfect articulation, and they have a low bar for what they consider to be such. They lower their bar even further when they are communicating with their superiors or with a person of high status. Communication becomes a time-consuming and exhausting effort, and they start avoiding it altogether. Others regard them as cold and detached as a result.

Their need for restricting affection is a defense mechanism used to control their emotions. They may expunge emotions from their memories and organize them as a library of facts and data; the memories are intellectualized and rationalized, not experiences that they can feel. This helps them avoid unexpected emotions and feelings and allows them to remain in control. They can view self-exploration as a waste of time and have a patronising attitude towards emotional people.

Interpersonal control

Individuals with OCPD are at one extreme of the conscientiousness continuum. While conscientiousness is a desirable trait generally, its extreme presentation for those with OCPD leads to interpersonal problems. OCPD individuals present as over-controlled and this extends to the relationships they have with other people. Individuals with OCPD are referential to authority and rules. OCPD individuals may therefore punish those who violate their strict standards. The inability to accept differences in belief or behaviors from others often leads to high conflict and controlling relationships with coworkers, spouses, and children.

Cause

The cause of OCPD is thought to involve a combination of genetic and environmental factors. There is clear evidence to support the theory that OCPD is genetically inherited; however, the relevance and impact of genetic factors vary with studies placing it somewhere between 27% and 78%.

A twin study of personality disorders over multiple personality disorders and the influence that genetics play on causing these disorders, found that OCPD had a .78 heritability correlation. Therefore, determining that the development of OCPD in an individual can be strongly linked to genetics.

Other studies have found links between attachment theory and the development of OCPD. According to this hypothesis, those with OCPD have never developed a secure attachment style, had overbearing parents, were shown little care, and/or were unable to develop empathetically and emotionally.

Diagnosis

DSM-5

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, a widely used manual for diagnosing mental disorders, places obsessive-compulsive personality disorder under section II, under the "personality disorders" chapter, and defines it as: "a pervasive pattern of preoccupation with orderliness, perfectionism, and mental and interpersonal control, at the expense of flexibility, openness, and efficiency, beginning by early adulthood and present in a variety of contexts". A diagnosis of OCPD is only received when four out of the eight criteria are met.

The eight criteria of OCPD described in the DSM-5 (of which four are required to be present in a patient for a diagnosis) are:

Preoccupation with details
Perfectionism interfering with task completion
Rigidity and stubbornness
Reluctance to delegate
Excessive conscientiousness and pedantry (excessive concern with minor details and rules)
Workaholic behavior
Miserliness (excessive desire to save money)
Inability to discard worn-out or worthless objects

The list of criteria for the ICD-10 is similar, but does not include the last three criteria in the above list, and additionally includes the symptoms "intrusive thoughts" and "excessive doubt and caution" as criteria for diagnosis.

Alternative model for diagnosis

The DSM-5 also includes an alternative set of diagnostic criteria as per the dimensional model of conceptualizing personality disorders. Under the proposed set of criteria, a person only receives a diagnosis when there is an impairment in two out of four areas of one's personality functioning, and when there are three out of four pathological traits, one of which must be rigid perfectionism.

The patient must also meet the general criteria C through G for a personality disorder, which state that the traits and symptoms being displayed by the patient must be stable and unchanging over time with an onset of at least adolescence or early adulthood, visible in a variety of situations, not caused by another mental disorder, not caused by a substance or medical condition, and abnormal in comparison to a person's developmental stage and culture/religion.

Differential diagnosis

There are several mental disorders in the DSM-5 that are listed as differential diagnoses for OCPD. They are as follows:

Obsessive–compulsive disorder. OCD and OCPD have a similar name which may cause confusion; however, OCD can be easily distinguished from OCPD: OCPD is not characterized by true obsessions or compulsions.
Hoarding disorder. A diagnosis of hoarding disorder is only considered when the hoarding behavior exhibited is causing severe impairment in the functioning of the person, such as an inability to access rooms in a house due to excessive hoarding.
Narcissistic personality disorder. Individuals with a narcissistic personality disorder usually believe that they have achieved perfection (especially compared to other people) and cannot get better, whereas those with OCPD do not believe that they have achieved perfection, and are self-critical. Those with NPD tend to be stingy and lack generosity; however, they are usually generous when spending on themselves, unlike those with OCPD who hoard money and are miserly on themselves and others.
Antisocial personality disorder. Similarly, individuals with antisocial personality disorder are not generous, but miserly around others, although they usually over-indulge themselves and are sometimes reckless in spending.
Schizoid personality disorder. Schizoid personality disorder and obsessive-compulsive personality disorder may both display restricted affectivity and coldness; however, in OCPD, this is usually due to a controlling attitude, whereas, in SPD, it occurs due to a lack of ability to experience emotion and display affection.
Other personality traits. Obsessive-compulsive personality traits may be particularly useful and helpful, especially in productive environments. Only when these traits become extreme, maladaptive, and cause clinically significant impairment in several aspects of one's life should a diagnosis of OCPD be considered.
Personality change due to another medical condition. Obsessive–compulsive personality disorder must be differentiated from a personality change due to a medical condition, which affects the central nervous system, and may cause changes in behavior and traits.
Substance use disorders. Substance use may cause the advent of obsessive-compulsive traits. It is necessary that this is distinguished from underlying and persistent behavior, which must occur when a person is not under influence of a substance.

ICD-10

The World Health Organization's ICD-10 uses the term anankastic personality disorder (F60.5). At least four of the following must be present:

Feelings of doubt
Perfectionism
Excessive conscientiousness
Checking and preoccupation with details
Stubbornness
Caution
Rigidity
Insistent and unwelcome thoughts or impulses that do not attain the severity of an obsessive-compulsive disorder.

Millon's subtypes

In his book, Personality Disorders in Modern Life, Theodore Millon describes 5 types of obsessive–compulsive personality disorder, which he shortened to compulsive personality disorder.


Subtype	Description
Conscientious Compulsive (including dependent features)	Those with conscientious compulsivity view themselves as helpful, co-operative, and compromising. They downplay their achievements and abilities and base their confidence on the opinions and expectations of others; this compensates for their feelings of insecurity and instability. They assume that devotion to work and striving for perfection will lead to them receiving love and reassurance. They believe that making a mistake or not achieving perfection will lead to abandonment and criticism. This mindset causes perpetual feelings of anxiety and an inability to appreciate their work.
Puritanical Compulsive (including paranoid features)	They have strong internal impulses that are countered vociferously through the use of religion. They are constantly battling their impulses and sexual drives, which they view as irrational. They attempt to purify and pacify the urges by adopting a cold and detached lifestyle. They create an enemy which they use to vent their hostility, such as "non-believers", or "lazy people". They are patronizing, bigoted, and zealous in their attitude toward others. Their beliefs are polarized into "good" and "evil".
Bureaucratic Compulsive (including narcissistic features)	The bureaucratic compulsive displays signs of narcissistic traits alongside the compulsivity. They are champions of tradition, values, and bureaucracy. They cherish organizations that follow hierarchies and feel comforted by definitive roles between subordinates and superiors, and the known expectations and responsibilities. They derive their identity from work and project an image of diligence, reliability, and commitment to their institution. They view work and productivity in a polarized manner; either done or not. They may use their power and status to inflict fear and obedience in their subordinates if they do not strictly follow their rules and procedures, and derive pleasure from the sense of control and power that they acquire by doing so.
Parsimonious Compulsive (including schizoid features)	The parsimonious compulsive is hoarding and possessive in nature; they behave in a manner congruent with schizoid traits. They are selfish, miserly, and are suspicious of others' intentions, believing that others may take away their possessions. This attitude may be caused by parents who deprived their child of wants or wishes but provided necessities, causing the child to develop an extreme protective approach to their belongings, often being self-sufficient and distant from others. They use this shielding behavior to prevent having their urges, desires, and imperfections discovered.
Bedevilled Compulsive (including negativistic features)	This form of compulsive personality is a mixture of negativistic and compulsive behavior. When faced with dilemmas, they procrastinate and attempt to stall the decision through any means. They are in a constant battle between their desires and will, and may engage in self-defeating behavior and self-torture in order to resolve the internal conflict. Their identity is unstable, and they are indecisive.

Comorbidity

Obsessive–compulsive disorder

OCPD is often confused with obsessive-compulsive disorder (OCD). Despite the similar names, they are two distinct disorders. Some OCPD individuals do have OCD, and the two can be found in the same family, sometimes along with eating disorders.

The rate of comorbidity of OCPD in patients with OCD is estimated to be around 15–28%. However, due to the addition of the hoarding disorder diagnosis in the DSM-5, and studies showing that hoarding may not be a symptom of OCPD, the true rate of comorbidity may be much lower.

There is significant similarity in the symptoms of OCD and OCPD, which can lead to complexity in distinguishing them clinically. For example, perfectionism is an OCPD criterion and a symptom of OCD if it involves the need for tidiness, symmetry, and organization. Hoarding is also considered both a compulsion found in OCD and a criterion for OCPD in the DSM-5. Even though OCD and OCPD are seemingly separate disorders there are obvious redundancies between the two concerning several symptoms.

Regardless of similarities between the OCPD criteria and the obsessions and compulsions found in OCD, there are discrete qualitative dissimilarities between these disorders, predominantly in the functional part of symptoms. Unlike OCPD, OCD is described as invasive, and stressful. Time-consuming obsessions and habits are aimed at reducing obsession-related stress. OCD symptoms are at times regarded as egodystonic because they are experienced as alien and repulsive to the person. Therefore, there is a greater mental anxiety associated with OCD.

In contrast, the symptoms seen in OCPD, although repetitive, are not linked with repulsive thoughts, images, or urges. OCPD characteristics and behaviors are known as ego-syntonic, as people with this disorder view them as suitable and correct. On the other hand, the main features of perfectionism and inflexibility can result in considerable suffering in an individual with OCPD as a result of the associated need for control.

The presence of OCPD in patients with OCD has been linked to a worse prognosis of OCD, especially when cognitive behavioral therapy was used. This may be due to the ego-syntonic nature of OCPD which may lead to the obsessions becoming aligned with one's personal values. In contrast, the trait of perfectionism may improve the outcome of treatment as patients are likely to complete homework assigned to them with determination. The findings with regards to pharmacological treatment has also been mixed, with some studies showing a lower reception to SRIs in OCD patients with comorbid OCPD, with others showing no relationship.

Comorbidity between OCD and OCPD has been linked to a more severe presentation of symptoms, a younger age of onset, more significant impairment in functioning, poorer insight, and higher comorbidity of depression and anxiety.

Autism spectrum disorder

There are considerable similarities and overlap between autism spectrum disorder (ASD) and OCPD, such as list-making, inflexible adherence to rules, and obsessive aspects of ASD, although the latter may be distinguished from OCPD especially regarding affective behaviors, worse social skills, difficulties with Theory of Mind and intense intellectual interests, e.g. an ability to recall every aspect of a hobby. A 2009 study involving adult autistic people found that 32% of those diagnosed with ASD met the diagnostic requirements for a comorbid OCPD diagnosis.

Eating disorders

Perfectionism has been linked with anorexia nervosa in research for decades. A researcher in 1949 described the behavior of the average "anorexic girl" as being "rigid" and "hyperconscious", observing a tendency to "[n]eatness, meticulosity, and a mulish stubbornness not amenable to reason [which] make her a rank perfectionist". So common are such traits as perfectionism and rigidity among anorectics, that they have been referred to in clinical literature as "classical childhood features of patients with anorexia nervosa" or classical premorbid personality descriptors of anorexia nervosa".

Regardless of the prevalence of the full-fledged OCPD among eating disordered samples, the presence of this personality disorder or its traits, such as perfectionism, has been found to be positively correlated with a range of complications in eating disorders and a negative outcome, as opposed to impulsive features—those linked with histrionic personality disorder, for example—which predict a better outcome from treatment. OCPD predicts more severe symptoms of anorexia nervosa, and worse remission rates, however, OCPD and perfectionistic traits predicted a higher acceptance of treatment, which was defined as undergoing 5 weeks of treatment.

People with anorexia nervosa who exercise excessively display a higher prevalence of several OCPD traits when compared to their counterparts who did not exercise excessively. The traits included self-imposed perfectionism, and the childhood OCPD traits of being rule-bound and cautious. It may be that people with OCPD traits are more likely to use exercise alongside restricting food intake in order to mitigate fears of increased weight, reduce anxiety, or reduce obsessions related to weight gain. Samples that had the childhood traits of rigidity, extreme cautiousness, and perfectionism endured more severe food restriction and higher levels of exercise and underwent longer periods of underweight status. It may be that OCPD traits are an indicator of a more severe manifestation of AN which is harder to treat.

Gambling Disorder

A majority of those with lifelong gambling disorder have some sort of personality disorder, and the most common personality disorder amongst them is obsessive compulsive personality disorder. OCPD has a strong comorbidity with individuals who have gambling disorder. A study of data collected in the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions looked at pathological gambling and psychiatric conditions as defined by the DSM-IV. Of the surveyed population consistent with gambling disorder, 60.8% also had a personality disorder, with OCPD appearing most frequently at 30%. About 300,000 U.S citizens have both a gambling disorder and obsessive compulsive personality disorder; and yet, there is little research on the comorbidity of the two disorders. Those with gambling disorders and OCPD do, indeed, exhibit different behavioral patterns than those with gambling disorders alone. More research on the relationship between the disorders is thought to help uncover causes and develop treatments for patients.

Mental Fatigue

Recently, in 2020, the connection between mental fatigue and OCPD was published for the first time, even though mental fatigue has been previously associated with identified characteristics of OCPD such as workaholic behavior and perfectionism.

Other disorders and conditions

A diagnosis of OCPD is common with anxiety disorders, substance use disorders, and mood disorders. OCPD is also highly comorbid with Cluster A personality disorders, especially paranoid and schizotypal personality disorders.

OCPD is also linked to hypochondriasis, with some studies estimating a rate of co-occurrence as high as 55.7%.

Moreover, OCPD has been found to be very common among some medical conditions, including Parkinson's disease and the hypermobile subtype of Ehler-Danlos syndrome. The latter may be explained by the need for control that arises from musculoskeletal problems and the associated features that arise early in life, whilst the former can be explained by dysfunctions in the fronto-basal ganglia circuitry.

Psychiatric disorder	Prevalence of OCPD in 12 month diagnosis
Substance use disorder	12–25%
Mood disorders	24%
Major depressive disorder	23–28%
Bipolar disorder	26–39%
Anxiety disorders	23–24%
Generalised anxiety disorder	34%
Panic disorder	23–38%
Social anxiety disorder	33%
Specific phobia	22%

Treatment

The best-validated treatment for OCPD is cognitive therapy (CT) or cognitive behavioral therapy (CBT), with studies showing an improvement in areas of personality impairment, and reduced levels of anxiety and depression. Group CBT is also associated with an increase in extraversion and agreeableness and reduced neuroticism. Interpersonal psychotherapy has been linked to even better results when it came to reducing depressive symptoms.

Epidemiology

Estimates for the prevalence of OCPD in the general population are 3%, making it the most common personality disorder. Current evidence is inconclusive as to whether OCPD is more common in men than women, or in equal rates among sexes. It is estimated to occur in 8.7% of psychiatric outpatient settings.

A study of data collected in the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions looked specifically for seven personality disorders as defined by the DSM-IV. The study concluded the most prevalent personality disorder of the survey's population to be OCPD, at 7.88%. This study also concluded there were no gender differences in prevalence and that OCPD was not a predicter of disability.

History

In 1908, Sigmund Freud named what is now known as obsessive–compulsive or anankastic personality disorder "anal retentive character". He identified the main strands of the personality type as a preoccupation with orderliness, parsimony (frugality), and obstinacy (rigidity and stubbornness). The concept fits his theory of psychosexual development. Freud believed that the anal retentive character faced difficulties regulating the control of defecation, leading to repercussions by the parents, and it is the latter that would cause the anal retentive character.

Aubrey Lewis, in his 1936 book Problems of Obsessional Illness, suggests that anal-erotic characteristics are found in patients without obsessive thoughts, and proposed two types of obsessional personality, one melancholy and stubborn, the other uncertain and indecisive.

In the book Contributions to the theory of the anal character, Karl Abraham noted that the core feature of the anal character is being perfectionistic, and he believed that these traits will help an individual in becoming industrious and productive, whilst hindering their social and interpersonal functioning, such as working with others.

OCPD was included in the first edition of the Diagnostic and Statistical Manual of Mental Disorders in 1952 by the American Psychiatric Association under the name "compulsive personality". It was defined as a chronic and excessive preoccupation with adherence to rules and standards of conscience. Other symptoms included rigidity, over-conscientiousness, and a reduced ability to relax.

The DSM-II (1968) changed the name to "obsessive-compulsive personality", and also suggested the term "anankastic personality" in order to reduce confusion between OCPD and OCD, but the proposed name was removed from later editions. The symptoms described in the DSM-II closely resembled those in the original DSM.

In 1980, the DSM-III was released, and it renamed the disorder back to "compulsive personality disorder", and also included new symptoms of the disorder: a restricted expression of affect, and an inability to delegate tasks. Devotion to productivity, perfectionism, and indecisiveness were the other symptoms included. The DSM-III-R (1987) renamed the disorder again to "obsessive-compulsive personality disorder" and the name has remained since then. A diagnosis of OCPD was given when 5 of the 9 symptoms were met, and the 9 symptoms included perfectionism, preoccupation with details, an insistence that others submit to one's way, indecisiveness, devotion to work, restricted expression of affect, excessive conscientiousness, lack of generosity, and hoarding.

With DSM-IV, OCPD was classified as a 'Cluster C' personality disorder. There was a dispute about the categorization of OCPD as an Axis II anxiety disorder. Although the DSM-IV attempted to distinguish between OCPD and OCD by focusing on the absence of obsessions and compulsions in OCPD, OC personality traits are easily mistaken for abnormal cognitions or values considered to underpin OCD. The disorder is a neglected and understudied area of research.

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Sunday, September 10, 2023

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Obsessive–compulsive personality disorder

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Introduction to entropy