Thermostats play a pivotal role in the performance of HVAC systems, acting as the central control unit that dictates when and how these systems operate. At first glance, a thermostat might seem like a simple device designed to set the desired temperature. However, its impact on system performance is profound, particularly when considering the importance of thermostat calibration.
Calibration refers to the process of ensuring that a thermostat accurately reflects and controls the ambient temperature within a space. A poorly calibrated thermostat can lead to significant inefficiencies within an HVAC system, affecting comfort levels and energy consumption. When a thermostat is out of calibration, it may misinterpret room temperatures by even just a few degrees-this slight discrepancy can cause an HVAC system to overwork or underperform.
The ramifications of such inefficiencies are manifold. For homeowners, this could mean higher energy bills due to excessive heating or cooling cycles triggered by inaccurate readings. In commercial settings, where HVAC systems often account for a substantial portion of utility costs, miscalibration can have even more pronounced financial implications. Furthermore, constant cycling due to incorrect temperature readings can lead to increased wear and tear on system components, reducing their lifespan and necessitating more frequent repairs or replacements.
Beyond economic considerations lies the issue of comfort-a paramount concern in both residential and business environments. An imprecise thermostat can create zones within a building that are either too warm or too cold, leading to discomfort among occupants and potentially affecting productivity in office settings.
Regular calibration checks ensure that thermostats maintain their accuracy over time. This practice not only helps optimize HVAC performance but also aligns with broader sustainability goals by minimizing unnecessary energy usage and reducing carbon footprints.
In conclusion, while thermostats might seem like minor components within complex HVAC systems, their role is anything but trivial. Proper calibration is essential for maintaining efficient system performance and ensuring both cost-effectiveness and occupant comfort. As we continue to advance towards smarter technology solutions in building management, understanding and prioritizing accurate thermostat calibration will remain crucial for achieving optimal results from our HVAC investments.
Thermostat calibration is a critical aspect of maintaining optimal performance in heating, ventilation, and air conditioning (HVAC) systems. When a thermostat is not properly calibrated, it can lead to a host of issues that affect both the efficiency of the system and the comfort of individuals relying on its function. Common issues arising from poor thermostat calibration include inconsistent temperatures, increased energy consumption, frequent system cycling, and even premature wear and tear on HVAC components.
One of the most noticeable effects of poor thermostat calibration is inconsistent indoor temperatures. A poorly calibrated thermostat might read the room temperature inaccurately, causing it to signal for heating or cooling at inappropriate times. This can result in areas that are too hot or too cold, creating discomfort for occupants. Such fluctuations not only impact personal comfort but can also have broader implications in environments where temperature stability is crucial, such as in healthcare facilities or data centers.
Another major issue linked to improper thermostat calibration is increased energy consumption. When a thermostat misreads the ambient temperature, it may cause the HVAC system to run longer than necessary or cycle on and off more frequently than intended. This inefficiency leads to higher utility bills as more energy is consumed without delivering any additional benefit in terms of comfort or climate control. In today's world where energy conservation is paramount, this represents both an environmental concern and a financial burden.
Frequent cycling caused by miscalibration can also put undue stress on the HVAC system itself. The constant starting and stopping associated with short cycling increases wear and tear on components such as compressors and fans. Over time, this can lead to more frequent repairs and potentially shorten the lifespan of the entire system. Regular maintenance checks that include verifying proper thermostat calibration can mitigate these risks by ensuring that all parts operate within their intended parameters.
Lastly, poor thermostat calibration can have indirect effects on indoor air quality. If an HVAC system runs inefficiently due to miscalibration, there may be insufficient airflow or inadequate humidity control within a building. These conditions create an environment conducive to mold growth or allow airborne contaminants to linger longer than they should-factors that negatively impact health.
In conclusion, ensuring that thermostats are correctly calibrated plays a vital role in maintaining efficient system performance. Proper calibration helps avoid inconsistent temperatures, reduces unnecessary energy consumption, extends equipment lifespan through reduced mechanical stressors, and supports better indoor air quality management-all contributing significantly towards achieving optimal living or working conditions while keeping operational costs in check. Regular inspections performed by qualified professionals are essential steps towards preventing these common issues associated with poorly calibrated thermostats.
Thermostats are the silent sentinels of modern comfort, discreetly governing our indoor climates with precision and reliability. However, like any sentinel, their accuracy can falter over time, leading to inefficiencies in energy use and discomfort in living spaces.
At its core, thermostat calibration involves adjusting the device to ensure that its reading matches the actual ambient temperature. A miscalibrated thermostat can lead to significant discrepancies between the set temperature and the real environment. This misalignment not only causes discomfort but also strains HVAC systems as they work harder to achieve desired temperatures based on inaccurate information.
One fundamental method for accurate thermostat calibration is regular comparison against a reliable external thermometer. This process involves placing a thermometer next to the thermostat for a few hours, comparing readings, and making necessary adjustments if there is a discrepancy. This simple yet effective practice helps ensure that thermostats reflect true ambient conditions.
Another vital practice is routine maintenance of both the thermostat and HVAC system components. Dust accumulation or mechanical wear can affect sensor accuracy over time. Regular cleaning and inspection help prevent these issues from compromising performance. Technicians often recommend cleaning around thermostats carefully without disturbing wiring or other sensitive parts.
For more advanced calibration needs, especially in complex commercial systems, digital multimeters may be employed. These devices allow technicians to measure voltage signals accurately within electronic thermostats, facilitating precise adjustments directly related to internal circuitry rather than relying solely on external temperature comparisons.
Moreover, manufacturers frequently provide detailed guidelines specific to their models regarding recalibration procedures and recommended intervals for checks or professional servicing. Adhering strictly to these guidelines ensures compatibility with warranty terms while optimizing device longevity.
Incorporating smart technology into thermostat management has further revolutionized how we approach calibration issues today. Smart thermostats often include self-calibrating features using algorithms capable of learning patterns in user behavior alongside environmental data inputs like humidity levels or occupancy rates – automatically fine-tuning settings accordingly overtime without manual intervention required from users themselves!
Ultimately though no single method guarantees perfect results across all scenarios given variability inherent among different environments; combining multiple approaches tailored specifically towards each unique situation provides best chance achieving desired outcomes consistently over long term basis reducing likelihood encountering unexpected surprises along way ensuring continued satisfaction occupants alike whilst maximizing overall efficiency entire heating cooling infrastructure involved therein itself thereby creating sustainable future generations come benefit likewise too!
The thermostat, often considered the unsung hero of a building's heating, ventilation, and air conditioning (HVAC) system, plays a pivotal role in ensuring comfort while minimizing energy consumption. A well-calibrated thermostat is not just a tool for maintaining indoor temperature; it is an integral component that significantly influences energy efficiency and cost savings. Proper calibration of thermostats can lead to optimized system performance, reduced utility bills, and a smaller carbon footprint.
At the heart of an efficient HVAC system lies the accuracy of its thermostat. Calibration ensures that the thermostat's readings are precise and reflect the actual indoor environment. Over time, thermostats can drift from their original settings due to factors such as dust accumulation, mechanical wear, or even software glitches in digital models. This drift can cause significant discrepancies in temperature readings-leading to overcooling or overheating-which consequently results in unnecessary energy usage.
When a thermostat is not calibrated correctly, it might instruct the HVAC system to run longer than necessary or not at all when needed. For instance, if a thermostat reads 70 degrees Fahrenheit but the actual room temperature is 68 degrees due to miscalibration, the system may delay activation until further cooling occurs-wasting potential energy conservation opportunities. Conversely, premature activation leads to excessive cycling of HVAC equipment which not only wastes energy but also accelerates wear and tear on components.
From a cost perspective, improper calibration translates directly into higher utility bills. Energy costs continue to rise globally due to various economic factors; thus every degree of inefficiency contributes significantly to expenses over time.
Moreover, improved calibration supports broader sustainability goals by reducing carbon emissions associated with excessive energy consumption. As society becomes increasingly conscious about environmental impacts and strives towards greener practices wherever possible-the role played by well-calibrated thermostats becomes more critical than ever before.
In conclusion , investing time into regular inspection and maintenance-including routine calibration checks-of thermostatic devices yields long-term benefits that extend beyond mere financial savings . It enhances overall comfort levels within living spaces , prolongs equipment lifespan , reduces ecological footprints , drives down operational costs-and ultimately contributes positively towards global efforts aimed at achieving greater environmental sustainability . Thus recognizing importance attached alongside calibrating correctly should no longer remain overlooked aspect amongst decisions concerning optimal management any given residential commercial infrastructure today .
In the realm of efficient energy management, the role of thermostat calibration is often undervalued. However, its impact on system performance and longevity is significant. Calibration ensures that thermostats accurately reflect the real temperature, allowing heating, ventilation, and air conditioning (HVAC) systems to operate optimally. This essay delves into various case studies demonstrating how precise thermostat calibration can extend system longevity and enhance performance.
One notable case study involved a commercial office building where the HVAC system was underperforming despite regular maintenance. The issue was traced back to improperly calibrated thermostats that misrepresented ambient temperatures by as much as 5 degrees Fahrenheit. As a result, the HVAC system was frequently overworking or underworking to meet inaccurate temperature settings. After recalibrating the thermostats, energy consumption decreased by 15%, leading to reduced wear and tear on the system components. This not only enhanced performance but also extended the lifespan of critical equipment such as compressors and fans.
In another example, a residential complex invested in smart thermostats with self-calibrating features. Over two years, data indicated a marked improvement in energy efficiency, resulting in lower utility bills for residents. More importantly, these calibrated systems required fewer service calls for repairs compared to traditional setups. The self-calibration feature ensured that even with seasonal changes and environmental shifts, the HVAC systems maintained optimal performance without manual intervention.
A third case study focused on an industrial facility where precise climate control was crucial for manufacturing processes sensitive to temperature fluctuations. Initially plagued by frequent downtime due to overheating issues, it was discovered that inaccurate thermostat readings were causing erratic system behavior. By implementing a rigorous calibration protocol every quarter, there was a significant reduction in equipment failure rates and unplanned maintenance costs dropped by nearly 30%. This proactive approach not only safeguarded production quality but also ensured consistent operational uptime.
These case studies collectively underscore the profound impact of thermostat calibration on system longevity and performance across different settings-commercial buildings, residential complexes, and industrial facilities alike. Accurate calibration minimizes unnecessary strain on HVAC systems by aligning their operation with true environmental conditions. Consequently, this enhances energy efficiency while prolonging component lifespans.
In conclusion, regular thermostat calibration emerges as an essential practice for optimizing HVAC systems' functionality and durability. The tangible benefits observed in varied contexts affirm its value as an integral part of effective energy management strategies aimed at reducing costs and enhancing sustainability over time.
In the modern era of smart homes and energy efficiency, a well-maintained thermostat is pivotal for both comfort and cost-effectiveness.
A thermostat's primary function is to regulate the temperature by communicating with your heating and cooling systems. However, over time, factors such as dirt accumulation, sensor drift, and battery degradation can lead to calibration errors. These errors may cause your system to run longer than necessary or fail to maintain desired temperatures, leading to increased energy consumption and utility bills.
To ensure optimal performance, it is essential to follow a recommended maintenance schedule. This includes regularly checking for dust and debris around the unit-especially if it is located in high-traffic or dusty areas-as these particles can interfere with the sensors. Cleaning should be done gently using a soft brush or compressed air to avoid damage.
Another key aspect of maintaining optimal functionality is ensuring proper battery health. Many thermostats rely on batteries either as their main power source or as backup during power outages. Regularly check the battery status indicator on digital models and replace them annually or when low-battery warnings appear.
Calibration checks are equally vital in this maintenance routine. At least once a year, verify that your thermostat's readings align with an independent thermometer placed nearby. If discrepancies are found, consult the manual for recalibration instructions specific to your model or consider professional servicing.
Lastly, consider software updates for smart thermostats which often include bug fixes and enhancements that improve device accuracy and efficiency. Manufacturers typically release these updates periodically; thus enabling automatic updates ensures you're not missing crucial improvements.
In conclusion, adhering to a recommended maintenance schedule significantly impacts thermostat performance by preventing calibration issues that could compromise the efficiency of your entire HVAC system. By investing time in regular cleaning, battery checks, calibration verification, and software updates, homeowners can not only extend their thermostat's lifespan but also achieve significant savings through enhanced energy management-truly embodying the harmony of technology working seamlessly within our living spaces.
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Indoor air quality (IAQ) is the air quality within buildings and structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Common pollutants of indoor air include: secondhand tobacco smoke, air pollutants from indoor combustion, radon, molds and other allergens, carbon monoxide, volatile organic compounds, legionella and other bacteria, asbestos fibers, carbon dioxide,[1] ozone and particulates.
Source control, filtration, and the use of ventilation to dilute contaminants are the primary methods for improving indoor air quality. Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone.[2] In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary.[3]
IAQ is evaluated through collection of air samples, monitoring human exposure to pollutants, analysis of building surfaces, and computer modeling of air flow inside buildings. IAQ is part of indoor environmental quality (IEQ), along with other factors that exert an influence on physical and psychological aspects of life indoors (e.g., lighting, visual quality, acoustics, and thermal comfort).[4]
Indoor air pollution is a major health hazard in developing countries and is commonly referred to as "household air pollution" in that context.[5] It is mostly relating to cooking and heating methods by burning biomass fuel, in the form of wood, charcoal, dung, and crop residue, in indoor environments that lack proper ventilation. Millions of people, primarily women and children, face serious health risks. In total, about three billion people in developing countries are affected by this problem. The World Health Organization (WHO) estimates that cooking-related indoor air pollution causes 3.8 million annual deaths.[6] The Global Burden of Disease study estimated the number of deaths in 2017 at 1.6 million.[7]
For health reasons it is crucial to breathe clean air, free from chemicals and toxicants as much as possible. It is estimated that humans spend approximately 90% of their lifetime indoors[8] and that indoor air pollution in some places can be much worse than that of the ambient air.[9][10]
Various factors contribute to high concentrations of pollutants indoors, ranging from influx of pollutants from external sources, off-gassing by furniture, furnishings including carpets, indoor activities (cooking, cleaning, painting, smoking, etc. in homes to using office equipment in offices), thermal comfort parameters such as temperature, humidity, airflow and physio-chemical properties of the indoor air.[citation needed] Air pollutants can enter a building in many ways, including through open doors or windows. Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to respiratory problems and allergies.
There have been many debates among indoor air quality specialists about the proper definition of indoor air quality and specifically what constitutes "acceptable" indoor air quality.
IAQ is significant for human health as humans spend a large proportion of their time in indoor environments. Americans and Europeans on average spend approximately 90% of their time indoors.[11][12]
The World Health Organization (WHO) estimates that 3.2 million people die prematurely every year from illnesses attributed to indoor air pollution caused by indoor cooking, with over 237 thousand of these being children under 5. These include around an eighth of all global ischaemic heart disease, stroke, and lung cancer deaths. Overall the WHO estimated that poor indoor air quality resulted in the loss of 86 million healthy life years in 2019.[13]
Studies in the UK and Europe show exposure to indoor air pollutants, chemicals and biological contamination can irritate the upper airway system, trigger or exacerbate asthma and other respiratory or cardiovascular conditions, and may even have carcinogenic effects.[14][15][16][17][18][19]
Poor indoor air quality can cause sick building syndrome. Symptoms include burning of the eyes, scratchy throat, blocked nose, and headaches.[20]
Indoor combustion, such as for cooking or heating, is a major cause of indoor air pollution and causes significant health harms and premature deaths. Hydrocarbon fires cause air pollution. Pollution is caused by both biomass and fossil fuels of various types, but some forms of fuels are more harmful than others.
Indoor fire can produce black carbon particles, nitrogen oxides, sulfur oxides, and mercury compounds, among other emissions.[21] Around 3 billion people cook over open fires or on rudimentary cook stoves. Cooking fuels are coal, wood, animal dung, and crop residues.[22] IAQ is a particular concern in low and middle-income countries where such practices are common.[23]
Cooking using natural gas (also called fossil gas, methane gas or simply gas) is associated with poorer indoor air quality. Combustion of gas produces nitrogen dioxide and carbon monixide, and can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.[24][25]
One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colourless and odourless gas that is a by-product of incomplete combustion. Carbon monoxide may be emitted from tobacco smoke and generated from malfunctioning fuel burning stoves (wood, kerosene, natural gas, propane) and fuel burning heating systems (wood, oil, natural gas) and from blocked flues connected to these appliances.[26] In developed countries the main sources of indoor CO emission come from cooking and heating devices that burn fossil fuels and are faulty, incorrectly installed or poorly maintained.[27] Appliance malfunction may be due to faulty installation or lack of maintenance and proper use.[26] In low- and middle-income countries the most common sources of CO in homes are burning biomass fuels and cigarette smoke.[27]
Health effects of CO poisoning may be acute or chronic and can occur unintentionally or intentionally (self-harm). By depriving the brain of oxygen, acute exposure to carbon monoxide may have effects on the neurological system (headache, nausea, dizziness, alteration in consciousness and subjective weakness), the cardiovascular and respiratory systems (myocardial infarction, shortness of breath, or rapid breathing, respiratory failure). Acute exposure can also lead to long-term neurological effects such as cognitive and behavioural changes. Severe CO poisoning may lead to unconsciousness, coma and death. Chronic exposure to low concentrations of carbon monoxide may lead to lethargy, headaches, nausea, flu-like symptoms and neuropsychological and cardiovascular issues.[28][26]
The WHO recommended levels of indoor CO exposure in 24 hours is 4 mg/m3.[29] Acute exposure should not exceed 10 mg/m3 in 8 hours, 35 mg/m3 in one hour and 100 mg/m3 in 15 minutes.[27]
Secondhand smoke is tobacco smoke which affects people other than the 'active' smoker. It is made up of the exhaled smoke (15%) and mostly of smoke coming from the burning end of the cigarette, known as sidestream smoke (85%).[30]
Secondhand smoke contains more than 7000 chemicals, of which hundreds are harmful to health.[30] Secondhand tobacco smoke includes both a gaseous and a particulate materials which, with particular hazards arising from levels of carbon monoxide and very small particulates (fine particulate matter, especially PM2.5 and PM10) which get into the bronchioles and alveoles in the lung.[31] Inhaling secondhand smoke on multiple occasions can cause asthma, pneumonia, lung cancer, and sudden infant death syndrome, among other conditions.[32]
Thirdhand smoke (THS) refers to chemicals that settle on objects and bodies indoors after smoking. Exposure to thirdhand smoke can happen even after the actual cigarette smoke is not present anymore and affect those entering the indoor environment much later. Toxic substances of THS can react with other chemicals in the air and produce new toxic chemicals that are otherwise not present in cigarettes.[33]
The only certain method to improve indoor air quality as regards secondhand smoke is to eliminate smoking indoors.[34] Indoor e-cigarette use also increases home particulate matter concentrations.[35]
Atmospheric particulate matter, also known as particulates, can be found indoors and can affect the health of occupants. Indoor particulate matter can come from different indoor sources or be created as secondary aerosols through indoor gas-to-particle reactions. They can also be outdoor particles that enter indoors. These indoor particles vary widely in size, ranging from nanomet (nanoparticles/ultrafine particles emitted from combustion sources) to micromet (resuspensed dust).[36] Particulate matter can also be produced through cooking activities. Frying produces higher concentrations than boiling or grilling and cooking meat produces higher concentrations than cooking vegetables.[37] Preparing a Thanksgiving dinner can produce very high concentrations of particulate matter, exceeding 300 μg/m3.[38]
Particulates can penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease, lung disease, cancer and preterm birth.[39]
Volatile organic compounds (VOCs) include a variety of chemicals, some of which may have short- and long-term adverse health effects. There are numerous sources of VOCs indoors, which means that their concentrations are consistently higher indoors (up to ten times higher) than outdoors.[40] Some VOCs are emitted directly indoors, and some are formed through the subsequent chemical reactions that can occur in the gas-phase, or on surfaces.[41][42] VOCs presenting health hazards include benzene, formaldehyde, tetrachloroethylene and trichloroethylene.[43]
VOCs are emitted by thousands of indoor products. Examples include: paints, varnishes, waxes and lacquers, paint strippers, cleaning and personal care products, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.[44] Chlorinated drinking water releases chloroform when hot water is used in the home. Benzene is emitted from fuel stored in attached garages.
Human activities such as cooking and cleaning can also emit VOCs.[45][46] Cooking can release long-chain aldehydes and alkanes when oil is heated and terpenes can be released when spices are prepared and/or cooked.[45] Leaks of natural gas from cooking appliances have been linked to elevated levels of VOCs including benzene in homes in the USA.[47] Cleaning products contain a range of VOCs, including monoterpenes, sesquiterpenes, alcohols and esters. Once released into the air, VOCs can undergo reactions with ozone and hydroxyl radicals to produce other VOCs, such as formaldehyde.[46]
Health effects include eye, nose, and throat irritation; headaches, loss of coordination, nausea; and damage to the liver, kidney, and central nervous system.[48]
Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes.[49] Indoor materials such as gypsum boards or carpet act as VOC 'sinks', by trapping VOC vapors for extended periods of time, and releasing them by outgassing. The VOCs can also undergo transformation at the surface through interaction with ozone.[42] In both cases, these delayed emissions can result in chronic and low-level exposures to VOCs.[50]
Several initiatives aim to reduce indoor air contamination by limiting VOC emissions from products. There are regulations in France and in Germany, and numerous voluntary ecolabels and rating systems containing low VOC emissions criteria such as EMICODE,[51] M1,[52] Blue Angel[53] and Indoor Air Comfort[54] in Europe, as well as California Standard CDPH Section 01350[55] and several others in the US. Due to these initiatives an increasing number of low-emitting products became available to purchase.
At least 18 microbial VOCs (MVOCs) have been characterised[56][57] including 1-octen-3-ol (mushroom alcohol), 3-Methylfuran, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone, 3-octanol, 2-octen-1-ol, 1-octene, 2-pentanone, 2-nonanone, borneol, geosmin, 1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, and thujopsene. The last four are products of Stachybotrys chartarum, which has been linked with sick building syndrome.[56]
Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, shingles, fireproofing, heating systems, pipe wrap, taping muds, mastics, and other insulation materials. Normally, significant releases of asbestos fiber do not occur unless the building materials are disturbed, such as by cutting, sanding, drilling, or building remodelling. Removal of asbestos-containing materials is not always optimal because the fibers can be spread into the air during the removal process. A management program for intact asbestos-containing materials is often recommended instead.
When asbestos-containing material is damaged or disintegrates, microscopic fibers are dispersed into the air. Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer, mesothelioma, and asbestosis. The risk of lung cancer from inhaling asbestos fibers is significantly greater for smokers. The symptoms of disease do not usually appear until about 20 to 30 years after the first exposure to asbestos.
Although all asbestos is hazardous, products that are friable, e.g. sprayed coatings and insulation, pose a significantly higher hazard as they are more likely to release fibers to the air.[58]
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Microplastic is a type of airborne particulates and is found to prevail in air.[59][60][61][62] A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics).[63] Airborne microplastic dust can be produced during renovation, building, bridge and road reconstruction projects[64] and the use of power tools.[65]
Indoors ozone (O3) is produced by certain high-voltage electric devices (such as air ionizers), and as a by-product of other types of pollution. It appears in lower concentrations indoors than outdoors, usually at 0.2-0.7 of the outdoor concentration.[66] Typically, most ozone is lost to surface reactions indoors, rather than to reactions in air, due to the large surface to volume ratios found indoors.[67]
Outdoor air used for ventilation may have sufficient ozone to react with common indoor pollutants as well as skin oils and other common indoor air chemicals or surfaces. Particular concern is warranted when using "green" cleaning products based on citrus or terpene extracts, because these chemicals react very quickly with ozone to form toxic and irritating chemicals[46] as well as fine and ultrafine particles.[68] Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts.[69]
The WHO standard for ozone concentration is 60 μg/m3 for long-term exposure and 100 μg/m3 as the maximum average over an 8-hour period.[29] The EPA standard for ozone concentration is 0.07 ppm average over an 8-hour period.[70]
Occupants in buildings can be exposed to fungal spores, cell fragments, or mycotoxins which can arise from a host of means, but there are two common classes: (a) excess moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen.[71]
While mold growth is associated with high moisture levels,[72] it is likely to grow when a combination of favorable conditions arises. As well as high moisture levels, these conditions include suitable temperatures, pH and nutrient sources.[73] Mold grows primarily on surfaces, and it reproduces by releasing spores, which can travel and settle in different locations. When these spores experience appropriate conditions, they can germinate and lead to mycelium growth.[74] Different mold species favor different environmental conditions to germinate and grow, some being more hydrophilic (growing at higher levels of relative humidity) and other more xerophilic (growing at levels of relative humidity as low as 75–80%).[74][75]
Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 and 60 %. Moisture buildup in buildings may arise from water penetrating areas of the building envelope or fabric, from plumbing leaks, rainwater or groundwater penetration, or from condensation due to improper ventilation, insufficient heating or poor thermal quality of the building envelope.[76] Even something as simple as drying clothes indoors on radiators can increase the risk of mold growth, if the humidity produced is not able to escape the building via ventilation.[77]
Mold predominantly affects the airways and lungs. Known effects of mold on health include asthma development and exacerbation,[78] with children and elderly at greater risk of more severe health impacts.[79] Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.[80][71] More than half of adult workers in moldy or humid buildings suffer from nasal or sinus symptoms due to mold exposure.[71] Some varieties of mold contain toxic compounds (mycotoxins). However, exposure to hazardous levels of mycotoxin via inhalation is not possible in most cases, as toxins are produced by the fungal body and are not at significant levels in the released spores.
Legionnaires' disease is caused by a waterborne bacterium Legionella that grows best in slow-moving or still, warm water. The primary route of exposure is through the creation of an aerosol effect, most commonly from evaporative cooling towers or showerheads. A common source of Legionella in commercial buildings is from poorly placed or maintained evaporative cooling towers, which often release water in an aerosol which may enter nearby ventilation intakes. Outbreaks in medical facilities and nursing homes, where patients are immuno-suppressed and immuno-weak, are the most commonly reported cases of Legionellosis. More than one case has involved outdoor fountains at public attractions. The presence of Legionella in commercial building water supplies is highly under-reported, as healthy people require heavy exposure to acquire infection.
Legionella testing typically involves collecting water samples and surface swabs from evaporative cooling basins, shower heads, faucets/taps, and other locations where warm water collects. The samples are then cultured and colony forming units (cfu) of Legionella are quantified as cfu/liter.
Legionella is a parasite of protozoans such as amoeba, and thus requires conditions suitable for both organisms. The bacterium forms a biofilm which is resistant to chemical and antimicrobial treatments, including chlorine. Remediation for Legionella outbreaks in commercial buildings vary, but often include very hot water flushes (160 °F (71 °C)), sterilisation of standing water in evaporative cooling basins, replacement of shower heads, and, in some cases, flushes of heavy metal salts. Preventive measures include adjusting normal hot water levels to allow for 120 °F (49 °C) at the tap, evaluating facility design layout, removing faucet aerators, and periodic testing in suspect areas.
There are many bacteria of health significance found in indoor air and on indoor surfaces. The role of microbes in the indoor environment is increasingly studied using modern gene-based analysis of environmental samples. Currently, efforts are under way to link microbial ecologists and indoor air scientists to forge new methods for analysis and to better interpret the results.[81]
A large fraction of the bacteria found in indoor air and dust are shed from humans. Among the most important bacteria known to occur in indoor air are Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae.[citation needed]
Viruses can also be a concern for indoor air quality. During the 2002–2004 SARS outbreak, virus-laden aerosols were found to have seeped into bathrooms from the bathroom floor drains, exacerbated by the draw of bathroom exhaust fans, resulting in the rapid spread of SARS in Amoy Gardens in Hong Kong.[82][83] Elsewhere in Hong Kong, SARS CoV RNA was found on the carpet and in the air intake vents of the Metropole Hotel, which showed that secondary environmental contamination could generate infectious aerosols and resulted in superspreading events.[84]
Humans are the main indoor source of carbon dioxide (CO2) in most buildings. Indoor CO2 levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.
Indoor CO2 levels above 500 ppm can lead to higher blood pressure and heart rate, and increased peripheral blood circulation.[85] With CO2 concentrations above 1000 ppm cognitive performance might be affected, especially when doing complex tasks, making decision making and problem solving slower but not less accurate.[86][87] However, evidence on the health effects of CO2 at lower concentrations is conflicting and it is difficult to link CO2 to health impacts at exposures below 5000 ppm – reported health outcomes may be due to the presence of human bioeffluents, and other indoor air pollutants related to inadequate ventilation.[88]
Indoor carbon dioxide concentrations can be used to evaluate the quality of a room or a building's ventilation.[89] To eliminate most complaints caused by CO2, the total indoor CO2 level should be reduced to a difference of no greater than 700 ppm above outdoor levels.[90] The National Institute for Occupational Safety and Health (NIOSH) considers that indoor air concentrations of carbon dioxide that exceed 1000 ppm are a marker suggesting inadequate ventilation.[91] The UK standards for schools say that carbon dioxide levels of 800 ppm or lower indicate that the room is well-ventilated.[92] Regulations and standards from around the world show that CO2 levels below 1000 ppm represent good IAQ, between 1000 and 1500 ppm represent moderate IAQ and greater than 1500 ppm represent poor IAQ.[88]
Carbon dioxide concentrations in closed or confined rooms can increase to 1,000 ppm within 45 minutes of enclosure. For example, in a 3.5-by-4-metre (11 ft × 13 ft) sized office, atmospheric carbon dioxide increased from 500 ppm to over 1,000 ppm within 45 minutes of ventilation cessation and closure of windows and doors.[93]
Radon is an invisible, radioactive atomic gas that results from the radioactive decay of radium, which may be found in rock formations beneath buildings or in certain building materials themselves.
Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe. It is a major cause of lung cancer, responsible for 3–14% of cases in countries, leading to tens of thousands of deaths.[94]
Radon gas enters buildings as a soil gas. As it is a heavy gas it will tend to accumulate at the lowest level. Radon may also be introduced into a building through drinking water particularly from bathroom showers. Building materials can be a rare source of radon, but little testing is carried out for stone, rock or tile products brought into building sites; radon accumulation is greatest for well insulated homes.[95] There are simple do-it-yourself kits for radon gas testing, but a licensed professional can also check homes.
The half-life for radon is 3.8 days, indicating that once the source is removed, the hazard will be greatly reduced within a few weeks. Radon mitigation methods include sealing concrete slab floors, basement foundations, water drainage systems, or by increasing ventilation.[96] They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks.[citation needed]
Radon is measured in picocuries per liter of air (pCi/L) or becquerel per cubic meter (Bq m-3). Both are measurements of radioactivity. The World Health Organization (WHO) sets the ideal indoor radon levels at 100 Bq/m-3.[97] In the United States, it is recommend to fix homes with radon levels at or above 4 pCi/L. At the same time it is also recommends that people think about fixing their homes for radon levels between 2 pCi/L and 4 pCi/L.[98] In the United Kingdom the ideal is presence of radon indoors is 100 Bq/m-3. Action needs to be taken in homes with 200 Bq/m−3 or more.[99]
Interactive maps of radon affected areas are available for various regions and countries of the world.[100][101][102]
Indoor air quality is linked inextricably to outdoor air quality. The Intergovernmental Panel on Climate Change (IPCC) has varying scenarios that predict how the climate will change in the future.[103] Climate change can affect indoor air quality by increasing the level of outdoor air pollutants such as ozone and particulate matter, for example through emissions from wildfires caused by extreme heat and drought.[104][105] Numerous predictions for how indoor air pollutants will change have been made,[106][107][108][109] and models have attempted to predict how the forecasted IPCC scenarios will vary indoor air quality and indoor comfort parameters such as humidity and temperature.[110]
The net-zero challenge requires significant changes in the performance of both new and retrofitted buildings. However, increased energy efficient housing will trap pollutants inside, whether produced indoors or outdoors, and lead to an increase in human exposure.[111][112]
For occupational exposure, there are standards, which cover a wide range of chemicals, and applied to healthy adults who are exposed over time at workplaces (usually industrial environments).These are published by organisations such as Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), the UK Health and Safety Executive (HSE).
There is no consensus globally about indoor air quality standards, or health-based guidelines. However, there are regulations from some individual countries and from health organisations. For example, the World Health Organization (WHO) has published health-based global air quality guidelines for the general population that are applicable both to outdoor and indoor air,[29] as well as the WHO IAQ guidelines for selected compounds,[113] whereas the UK Health Security Agency published IAQ guidelines for selected VOCs.[114] The Scientific and Technical Committee (STC34) of the International Society of Indoor Air Quality and Climate (ISIAQ) created an open database that collects indoor environmental quality guidelines worldwide.[115] The database is focused on indoor air quality (IAQ), but is currently extended to include standards, regulations, and guidelines related to ventilation, comfort, acoustics, and lighting.[116][117]
Since indoor air pollutants can adversely affect human health, it is important to have real-time indoor air quality assessment/monitoring system that can help not only in the improvement of indoor air quality but also help in detection of leaks, spills in a work environment and boost energy efficiency of buildings by providing real-time feedback to the heating, ventilation, and air conditioning (HVAC) system(s).[118] Additionally, there have been enough studies that highlight the correlation between poor indoor air quality and loss of performance and productivity of workers in an office setting.[119]
Combining the Internet of Things (IoT) technology with real-time IAQ monitoring systems has tremendously gained momentum and popularity as interventions can be done based on the real-time sensor data and thus help in the IAQ improvement.[120]
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Indoor air quality can be addressed, achieved or maintained during the design of new buildings or as mitigating measures in existing buildings. A hierarchy of measures has been proposed by the Institute of Air Quality Management. It emphasises removing pollutant sources, reducing emissions from any remaining sources, disrupting pathways between sources and the people exposed, protecting people from exposure to pollutants, and removing people from areas with poor air quality.[121]
A report assisted by the Institute for Occupational Safety and Health of the German Social Accident Insurance can support in the systematic investigation of individual health problems arising at indoor workplaces, and in the identification of practical solutions.[122]
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Environmentally sustainable design concepts include aspects of commercial and residential heating, ventilation and air-conditioning (HVAC) technologies. Among several considerations, one of the topics attended to is the issue of indoor air quality throughout the design and construction stages of a building's life.[citation needed]
One technique to reduce energy consumption while maintaining adequate air quality, is demand-controlled ventilation. Instead of setting throughput at a fixed air replacement rate, carbon dioxide sensors are used to control the rate dynamically, based on the emissions of actual building occupants.[citation needed]
One way of quantitatively ensuring the health of indoor air is by the frequency of effective turnover of interior air by replacement with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. In the US, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. Since carbon dioxide indoors comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the concentration indoors minus the concentration outdoors. The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains over 400 ppm[123] (global average as of 2023). In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. As the occupants are not the only source of pollutants, outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors.
When outdoor air is polluted, bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution. Generally, outdoor country air is better than indoor city air.[citation needed]
The use of air filters can trap some of the air pollutants. Portable room air cleaners with HEPA filters can be used if ventilation is poor or outside air has high level of PM 2.5.[122] Air filters are used to reduce the amount of dust that reaches the wet coils.[citation needed] Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils.[citation needed]
The use of trickle vents on windows is also valuable to maintain constant ventilation. They can help prevent mold and allergen build up in the home or workplace. They can also reduce the spread of some respiratory infections.[124]
Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts to conserve energy. For example, moisture management and humidity control requires systems to be set to supply make-up air at lower temperatures (design levels), instead of the higher temperatures sometimes used to conserve energy in cooling-dominated climate conditions. However, for most of the US and many parts of Europe and Japan, during the majority of hours of the year, outdoor air temperatures are cool enough that the air does not need further cooling to provide thermal comfort indoors.[citation needed] However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidity give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.[citation needed]
The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with dew points in the lower 50s °F, and some in the upper and lower 40s °F.[citation needed] Some facilities are being designed using desiccant wheels with gas-fired heaters to dry out the wheel enough to get the required dew points.[citation needed] On those systems, after the moisture is removed from the make-up air, a cooling coil is used to lower the temperature to the desired level.[citation needed]
Commercial buildings, and sometimes residential, are often kept under slightly positive air pressure relative to the outdoors to reduce infiltration. Limiting infiltration helps with moisture management and humidity control.
Dilution of indoor pollutants with outdoor air is effective to the extent that outdoor air is free of harmful pollutants. Ozone in outdoor air occurs indoors at reduced concentrations because ozone is highly reactive with many chemicals found indoors. The products of the reactions between ozone and many common indoor pollutants include organic compounds that may be more odorous, irritating, or toxic than those from which they are formed. These products of ozone chemistry include formaldehyde, higher molecular weight aldehydes, acidic aerosols, and fine and ultrafine particles, among others. The higher the outdoor ventilation rate, the higher the indoor ozone concentration and the more likely the reactions will occur, but even at low levels, the reactions will take place. This suggests that ozone should be removed from ventilation air, especially in areas where outdoor ozone levels are frequently high.
Houseplants together with the medium in which they are grown can reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. Plants remove CO2 and release oxygen and water, although the quantitative impact for house plants is small. The interest in using potted plants for removing VOCs was sparked by a 1989 NASA study conducted in sealed chambers designed to replicate the environment on space stations. However, these results suffered from poor replication[125] and are not applicable to typical buildings, where outdoor-to-indoor air exchange already removes VOCs at a rate that could only be matched by the placement of 10–1000 plants/m2 of a building's floor space.[126]
Plants also appear to reduce airborne microbes and molds, and to increase humidity.[127] However, the increased humidity can itself lead to increased levels of mold and even VOCs.[128]
Since extremely high humidity is associated with increased mold growth, allergic responses, and respiratory responses, the presence of additional moisture from houseplants may not be desirable in all indoor settings if watering is done inappropriately.[129]
The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies.
In the US, the Environmental Protection Agency (EPA) has developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions. The National Institute for Occupational Safety and Health conducts Health Hazard Evaluations (HHEs) in workplaces at the request of employees, authorized representative of employees, or employers, to determine whether any substance normally found in the place of employment has potentially toxic effects, including indoor air quality.[130]
A variety of scientists work in the field of indoor air quality, including chemists, physicists, mechanical engineers, biologists, bacteriologists, epidemiologists, and computer scientists. Some of these professionals are certified by organizations such as the American Industrial Hygiene Association, the American Indoor Air Quality Council and the Indoor Environmental Air Quality Council.
In the UK, under the Department for Environment Food and Rural Affairs, the Air Quality Expert Group considers current knowledge on indoor air quality and provides advice to government and devolved administration ministers.[131]
At the international level, the International Society of Indoor Air Quality and Climate (ISIAQ), formed in 1991, organizes two major conferences, the Indoor Air and the Healthy Buildings series.[132]
According to the Global Burden of Disease study 1.6 million people died prematurely in 2017 as a result of indoor air pollution ... But it's worth noting that the WHO publishes a substantially larger number of indoor air pollution deaths..
Burning of natural gas not only produces a variety of gases such as sulfur oxides, mercury compounds, and particulate matter but also leads to the production of nitrogen oxides, primarily nitrogen dioxide...The burning of biomass fuel or any other fossil fuel increases the concentration of black carbon in the air
MPs have been found in water and soil, and recent research is exposing the vast amount of them in ambient and indoor air.
environmental contamination with SARS CoV RNA was identified on the carpet in front of the index case-patient's room and 3 nearby rooms (and on their door frames but not inside the rooms) and in the air intake vents near the centrally located elevators ... secondary infections occurred not in guest rooms but in the common areas of the ninth floor, such as the corridor or elevator hall. These areas could have been contaminated through body fluids (e.g., vomitus, expectorated sputum), respiratory droplets, or suspended small-particle aerosols generated by the index case-patient; other guests were then infected by fomites or aerosols while passing through these same areas. Efficient spread of SARS CoV through small-particle aerosols was observed in several superspreading events in health care settings, during an airplane flight, and in an apartment complex (12–14,16–19). This process of environmental contamination that generated infectious aerosols likely best explains the pattern of disease transmission at the Hotel Metropole.
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Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.[1] Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter.
Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.[2] Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application. However, even cold ground contains heat. Below 6 metres (20 ft), the undisturbed ground temperature is consistently at the mean annual air temperature,[3] and this heat can be extracted with a ground source heat pump.
Country | Production PJ/yr |
Capacity GW |
Capacity factor |
Dominant applications |
---|---|---|---|---|
China | 45.38 | 3.69 | 39% | bathing |
Sweden | 43.2 | 4.2 | 33% | heat pumps |
USA | 31.24 | 7.82 | 13% | heat pumps |
Turkey | 24.84 | 1.5 | 53% | district heating |
Iceland | 24.5 | 1.84 | 42% | district heating |
Japan | 10.3 | 0.82 | 40% | bathing (onsens) |
Hungary | 7.94 | 0.69 | 36% | spas/greenhouses |
Italy | 7.55 | 0.61 | 39% | spas/space heating |
New Zealand | 7.09 | 0.31 | 73% | industrial uses |
63 others | 71 | 6.8 | ||
Total | 273 | 28 | 31% | space heating |
Category | GWh/year |
---|---|
Geothermal heat pumps | 90,293 |
Bathing and swimming | 33,164 |
Space heating | 24,508 |
Greenhouse heating | 7,407 |
Aquaculture pond heating | 3,322 |
Industrial uses | 2,904 |
Cooling/snow melting | 722 |
Agriculture drying | 564 |
Others | 403 |
Total | 163,287 |
There are a wide variety of applications for cheap geothermal heat including heating of houses, greenhouses, bathing and swimming or industrial uses. Most applications use geothermal in the form of hot fluids between 50 °C (122 °F) and 150 °C (302 °F). The suitable temperature varies for the different applications. For direct use of geothermal heat, the temperature range for the agricultural sector lies between 25 °C (77 °F) and 90 °C (194 °F), for space heating lies between 50 °C (122 °F) to 100 °C (212 °F).[4] Heat pipes extend the temperature range down to 5 °C (41 °F) as they extract and "amplify" the heat. Geothermal heat exceeding 150 °C (302 °F) is typically used for geothermal power generation.[6]
In 2004 more than half of direct geothermal heat was used for space heating, and a third was used for spas.[1] The remainder was used for a variety of industrial processes, desalination, domestic hot water, and agricultural applications. The cities of Reykjavík and Akureyri pipe hot water from geothermal plants under roads and pavements to melt snow. Geothermal desalination has been demonstrated.
Geothermal systems tend to benefit from economies of scale, so space heating power is often distributed to multiple buildings, sometimes whole communities. This technique, long practiced throughout the world in locations such as Reykjavík, Iceland;[7] Boise, Idaho;[8] and Klamath Falls, Oregon;[9] is known as district heating.[10]
In Europe alone 280 geothermal district heating plants were in operation in 2016 according to the European Geothermal Energy Council (EGEC) with a total capacity of approximately 4.9 GWth.[11]
Some parts of the world, including substantial portions of the western USA, are underlain by relatively shallow geothermal resources.[12] Similar conditions exist in Iceland, parts of Japan, and other geothermal hot spots around the world. In these areas, water or steam may be captured from natural hot springs and piped directly into radiators or heat exchangers. Alternatively, the heat may come from waste heat supplied by co-generation from a geothermal electrical plant or from deep wells into hot aquifers. Direct geothermal heating is far more efficient than geothermal electricity generation and has less demanding temperature requirements, so it is viable over a large geographical range. If the shallow ground is hot but dry, air or water may be circulated through earth tubes or downhole heat exchangers which act as heat exchangers with the ground.
Steam under pressure from deep geothermal resources is also used to generate electricity from geothermal power. The Iceland Deep Drilling Project struck a pocket of magma at 2,100m. A cemented steelcase was constructed in the hole with a perforation at the bottom close to the magma. The high temperatures and pressure of the magma steam were used to generate 36MW of electricity, making IDDP-1 the world's first magma-enhanced geothermal system.[13]
In areas where the shallow ground is too cold to provide comfort directly, it is still warmer than the winter air. The thermal inertia of the shallow ground retains solar energy accumulated in the summertime, and seasonal variations in ground temperature disappear completely below 10m of depth. That heat can be extracted with a geothermal heat pump more efficiently than it can be generated by conventional furnaces.[10] Geothermal heat pumps are economically viable essentially anywhere in the world.
In theory, geothermal energy (usually cooling) can also be extracted from existing infrastructure, such as municipal water pipes.[14]
In regions without any high temperature geothermal resources, a ground-source heat pump (GSHP) can provide space heating and space cooling. Like a refrigerator or air conditioner, these systems use a heat pump to force the transfer of heat from the ground to the building. Heat can be extracted from any source, no matter how cold, but a warmer source allows higher efficiency. A ground-source heat pump uses the shallow ground or ground water (typically starting at 10–12 °C or 50–54 °F) as a source of heat, thus taking advantage of its seasonally moderate temperatures.[15] In contrast, an air source heat pump draws heat from the air (colder outside air) and thus requires more energy.
GSHPs circulate a carrier fluid (usually a mixture of water and small amounts of antifreeze) through closed pipe loops buried in the ground. Single-home systems can be "vertical loop field" systems with bore holes 50–400 feet (15–120 m) deep or,[16] if adequate land is available for extensive trenches, a "horizontal loop field" is installed approximately six feet subsurface. As the fluid circulates underground it absorbs heat from the ground and, on its return, the warmed fluid passes through the heat pump which uses electricity to extract heat from the fluid. The re-chilled fluid is sent back into the ground thus continuing the cycle. The heat extracted and that generated by the heat pump appliance as a byproduct is used to heat the house. The addition of the ground heating loop in the energy equation means that significantly more heat can be transferred to a building than if electricity alone had been used directly for heating.
Switching the direction of heat flow, the same system can be used to circulate the cooled water through the house for cooling in the summer months. The heat is exhausted to the relatively cooler ground (or groundwater) rather than delivering it to the hot outside air as an air conditioner does. As a result, the heat is pumped across a larger temperature difference and this leads to higher efficiency and lower energy use.[15]
This technology makes ground source heating economically viable in any geographical location. In 2004, an estimated million ground-source heat pumps with a total capacity of 15 GW extracted 88 PJ of heat energy for space heating. Global ground-source heat pump capacity is growing by 10% annually.[1]
Hot springs have been used for bathing at least since Paleolithic times.[17] The oldest known spa is a stone pool on China's Mount Li built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. Geothermal energy supplied channeled district heating for baths and houses in Pompeii around 0 AD.[18] In the first century AD, Romans conquered Aquae Sulis in England and used the hot springs there to feed public baths and underfloor heating.[19] The admission fees for these baths probably represents the first commercial use of geothermal power. A 1,000-year-old hot tub has been located in Iceland, where it was built by one of the island's original settlers.[20] The world's oldest working geothermal district heating system in Chaudes-Aigues, France, has been operating since the 14th century.[4] The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy.
In 1892, America's first district heating system in Boise, Idaho, was powered directly by geothermal energy, and was soon copied in Klamath Falls, Oregon in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland and Tuscany at about the same time.[21] Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from the geysers began to be used to heat homes in Iceland in 1943.
By this time, Lord Kelvin had already invented the heat pump in 1852, and Heinrich Zoelly had patented the idea of using it to draw heat from the ground in 1912.[22] But it was not until the late 1940s that the geothermal heat pump was successfully implemented. The earliest one was probably Robert C. Webber's home-made 2.2 kW direct-exchange system, but sources disagree as to the exact timeline of his invention.[22] J. Donald Kroeker designed the first commercial geothermal heat pump to heat the Commonwealth Building (Portland, Oregon) and demonstrated it in 1946.[23][24] Professor Carl Nielsen of Ohio State University built the first residential open loop version in his home in 1948.[25] The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The 1979 development of polybutylene pipe greatly augmented the heat pump's economic viability.[23] Since 2000, a compelling body of research has been dedicated to numerically evidence the advantages and efficiency of using CO2, alternative to water, as heat transmission fluid for geothermal energy recovery from enhanced geothermal systems (EGS) where the permeability of the underground source is enhanced by hydrofracturing.[26][27] As of 2004, there are over one million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.[28] Each year, about 80,000 units are installed in the US and 27,000 in Sweden.[28]
Geothermal energy is a type of renewable energy that encourages conservation of natural resources. According to the US Environmental Protection Agency, geo-exchange systems save homeowners 30–70 percent in heating costs, and 20–50 percent in cooling costs, compared to conventional systems.[29] Geo-exchange systems also save money because they require much less maintenance. In addition to being highly reliable they are built to last for decades.
Some utilities, such as Kansas City Power and Light, offer special, lower winter rates for geothermal customers, offering even more savings.[15]
In geothermal heating projects the underground is penetrated by trenches or drillholes. As with all underground work, projects may cause problems if the geology of the area is poorly understood.
In the spring of 2007 an exploratory geothermal drilling operation was conducted to provide geothermal heat to the town hall of Staufen im Breisgau. After initially sinking a few millimeters, a process called subsidence,[30] the city center has started to rise gradually[31] causing considerable damage to buildings in the city center, affecting numerous historic houses including the town hall. It is hypothesized that the drilling perforated an anhydrite layer bringing high-pressure groundwater to come into contact with the anhydrite, which then began to expand. Currently no end to the rising process is in sight.[32][33][34] Data from the TerraSAR-X radar satellite before and after the changes confirmed the localised nature of the situation:
A geochemical process called anhydrite swelling has been confirmed as the cause of these uplifts. This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into gypsum (hydrous calcium sulphate). A pre-condition for this transformation is that the anhydrite is in contact with water, which is then stored in its crystalline structure.[35] There are other sources of potential risks, i.e.: cave enlargement or worsening of stability conditions, quality or quantity degradation of groundwater resources, Specific hazard worsening in the case of landslide-prone areas, worsening of rocky mechanical characteristics, soil and water pollution (i.e. due to antifreeze additives or polluting constructive and boring material).[36] The design defined on the base of site-specific geological, hydrogeological and environmental knowledge prevent all these potential risks.
During Roman times, warm water was circulated through open trenches to provide heating for buildings and baths in Pompeii.
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