Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. The special domestic use of hot water includes cooking, cleaning, bathing, and heating the room. In industry, hot water and heated water to steam have many uses.
In the country, water has traditionally been heated in vessels known as water heater, pot, cauldron, pots , cauldron or coppers . Metal vessels that heat up a pile of water do not produce continuous hot water supply at a predetermined temperature. Rarely, hot water occurs naturally, usually from natural hot springs. Temperature varies with consumption level, becomes cooler as flow increases.
Equipment that provides continuous hot water supply is called water heater , hot water heater , hot water tank , boiler > , heat exchanger , geyser , or calorifiers . These names depend on the region, and whether they heat up drinkable or unreachable water, are in domestic or industrial use, and their energy sources. In domestic installations, heated drinking water for use other than space heating is also called domestic hot water ( DHW ).
Fossil fuels (natural gas, liquid oil gases, oils), or solid fuels are commonly used to heat water. These can be consumed directly or can produce electricity that, in turn, heats the water. Electricity to heat water can also come from other electrical sources, such as nuclear power or renewable energy. Alternative energy such as solar energy, heat pumps, hot water recycling, and geothermal heating can also heat water, often combined with backup systems powered by fossil fuels or electricity.
Densely populated urban areas in some countries provide heating of hot water districts. This is especially true in Scandinavia, Finland, and Poland. District heating systems provide energy for heating water and space heating from combined heat and power plants (CHP), industrial waste heat, incinerators, geothermal heating, and central solar heating. The actual heating of tap water is carried out in the heat exchangers at the consumer premises. Generally consumers do not have a backup system in the building, because of the availability of high district heating system.
Video Water heating
Type of water heater
The hot water used for heating the room can be heated by fossil fuels in the boiler, while the potable water can be heated in a separate device. This is a common practice in the US, especially when warm room warming is commonly used.
Water heater storage (tank type)
In household and commercial use, most North American and South Asian water heaters are a type of tank, also called a storage water heater, consisting of a container or cylinder container that keeps the water hot and ready for use. The typical size for household use ranges from 75 to 400 liters (20 to 100 US gallons). It may be using electricity, natural gas, propane, heating oil, solar, or other energy sources. The most popular natural gas heater in the US and most European countries, because the gas is often easily channeled to all cities and towns and is currently the cheapest to use. In the United States, typical natural gas water heaters for households without unusual needs are 40 or 50 US gallons with a firing value of 34,000 to 40,000 BTU/hr. Some models offer "High Efficiency and Ultra Low NOx" emissions.
This is a popular setting where higher flow rates are required for limited periods, water is heated in pressurized vessels which can withstand hydrostatic pressures close to the incoming supply. In North America, these ships are called hot water tanks, and can incorporate electric resistance heaters, heat pumps, or gas or oil stoves that heat water directly.
Where hot water heating boilers are installed, domestic hot water cylinders are usually heated indirectly by primary water from boilers, or by electric immersion heaters (often as reserves to boilers). In the UK, these boats are called indirect cylinders, or direct cylinders, respectively. In addition, if these cylinders form part of a sealed system, providing the main pressure hot water, they are known as unventilated cylinders. In the US, when connected to their boiler it is called indirect water heater .
Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, saving heat for later use. The disadvantage is that over time, the heat exits through the tank wall and the water cools, activating the heating system to heat the water back, so investing in a tank with better insulation improves the standby efficiency. In addition, when heavy usage consumes hot water, there is a significant delay before hot water is available again. Larger tanks tend to provide hot water with lower temperature fluctuations at moderate flow rates.
Volume storage water heaters in the United States and New Zealand are usually vertical, cylindrical tanks, usually standing on the floor or on platforms lifting a short distance above the floor. The volume water heater storage in Spain is usually horizontal. In India, they are primarily vertical. In their apartment can be installed in the ceiling of the room above the laundry room. In Australia, outdoor gas and electric tank heaters have been used (with high temperatures to increase effective capacity), but the roof tank of the sun is becoming fashionable.
Tiny point-of-use (POU) electrical storage water heaters with capacities ranging from 8 to 32 liters (2 to 6 gallons) are made for installation in kitchen cabinets and bathrooms or on walls above the sink. They usually use low-power heating elements, about 1 kW to 1.5 kW, and can provide hot water long enough to wash their hands, or if thrown into existing hot water channels, until hot water arrives from high-capacity water heaters. They can be used when retrofitting buildings with hot water pipes are too expensive or impractical. Because they maintain thermostatic water temperatures, they can only supply continuous flow of hot water at very low flow rates, unlike tankers without high capacity.
In tropical countries, such as Singapore and India, storage water heaters may vary from 10 liters to 35 liters. Smaller water heaters are sufficient, because the ambient air temperature and the temperature of water entering medium.
Point-of-use (POU) vs. centralized hot water
Locational design decisions can be made between point-of-use and centralized water heater. Centralized water heaters are more traditional, and are still a good choice for small buildings. For larger buildings with intermittent or occasional hot water use, some POU water heaters may be a better choice, as they can reduce the waiting time for hot water to arrive from long-distance heaters. The decision on where to place the water heater (s) is only partially independent of the decision of tanked vs. tankless water heater, or the choice of energy source for heat.
Heater without tank
Tankless water heater - also called instantaneous , continuous flow , inline , flash , on-demand , or instant-on water heaters - are gaining in popularity. This high-powered water heater instantly heats water as it flows through the device, and does not store any water internally except for what is inside the heat exchanger coil. Copper heat exchangers are preferred in this unit due to their high thermal conductivity and ease of fabrication.
Tankless heaters can be installed throughout households at more than one point of use (POU), away from central water heaters, or larger centralized models may still be used to provide all the hot water requirements for the entire house. The main advantage of a tankless water heater is the abundant continuous flow of hot water (compared to the continuously heated hot water stream from the conventional tank water heater), and potential energy savings in some conditions. The main disadvantage is their much higher initial cost, a US study in a Minnesota study reported a 20 to 40 year return for a tankless water heater. Compared to the less efficient natural gas heat tanks, on-demand natural gas will cost 30% more during its useful life.
Stand-alone equipment for rapidly heating water for domestic use is known in North America as a water heater without tank or on demand. In some places, they are called multipoint heater , geyser or ascots . In Australia and New Zealand they are called instant hot water units . In Argentina they are called calefones . In that country calefones use non-electric gas. Similar fired wood tools are known as chip heaters.
The general arrangement in which the hot room heater is used, is for the boiler to also heat up the drinking water, providing hot water supply without any additional equipment. Equipment that can supply domestic heating and hot water is called a combination (or combi ) boiler. Although on-demand heaters provide a continuous supply of domestic hot water, the rate at which they can produce it is limited by thermodynamic water heating from the available fuel supply.
Power shower head
An electric shower head has an electric heating element that heats water as it passes through it. This self-heating shower head is a special water heater without a point (POU), and is widely used in some countries.
Invented in Brazil in the 1930s and often used since the 1940s, electric showers are home appliances that are often seen in South American countries due to higher gas distribution costs. The previous model was made of copper or chrome brass, which is expensive, but since 1970, the injection-molded plastic unit is very popular because of its low price similar to a hair dryer. The power shower has a simple electrical system, working like a coffee maker, but with a larger flow of water. The flow switch turns on the device as water flows through it. After the water stops, the device turns off automatically. Ordinary electric showers often have three heat settings: high (5.5 kW), low (2.5 kW), or cold (0 W) for use when central heating systems are available or in summer.
Energy usage
Electricity power consumption in a maximum heating setting of about 5.5 kW for 120 V and 7.5 kW for 220 V. Lower cost with electric shower compared to higher cost with boiler is due to usage time: Electricity The shower uses energy only when the water flows, while the boiler works many times a day to keep the quantity of hot water hot for use throughout the day and night. In addition, the transfer of electrical energy to water in the electric shower head is very efficient, close to 100%. The emission of electricity can save energy compared to electric heating tanks, which lose heat standby.
Security
There are various kinds of electric showers, with different types of heating controls. The heating element of an electric shower is immersed in a water stream, using electrically dislodged and electrically isolated nychrome resistance elements, such as those used in oil heaters, radiators or clothes irons, provide security. Due to electrical safety standards, modern electric showerheads are made of plastic rather than using metal casing as in the past. As electrical devices use more electric current than washing machines or dryers, electrical shower fittings require careful planning, and are generally intended to be transferred directly from power supply boxes with special circuit breakers and ground systems. Systems that are not installed properly with old aluminum cables or poor connections can be dangerous, because cables can overheat or electric current can leak through water through the user's body to the earth.
Solar water heater
More and more solar water heaters are used. Their solar collectors are installed outside the dwelling, usually on the roof or walls or nearby, and drinkable hot water storage tanks are usually existing or new conventional water heaters, or water heaters designed specifically for solar heat.
The most basic solar thermal model is a direct-gain type, in which drinking water is sent directly to the collector. Many such systems are said to use integrated collector storage (ICS), because the direct gain system usually has an integrated storage inside the collector. Inherently water heating is inherently more efficient than indirect heating through heat exchangers, but such systems offer very limited freeze protection (if any), can easily heat water at unsafe temperatures for domestic use, and the ICS system suffers severe heat loss on a cold night. and a cold and cloudy day.
In contrast, indirectly closed or closed loop systems do not allow drinking water through the panel, but instead pump heat transfer fluids (either water or water/antifreeze mixtures) through the panels. After collecting heat on the panel, the heat transfer fluid flows through the heat exchanger, transferring its heat to the potable water. When the panel is cooler than the storage tank or when the storage tank has reached its maximum temperature, the controller in a closed-loop system stops the circulation pump. In the drainback system, water flows to storage tanks contained in conditioned or semi-conditioned spaces, protected from freezing temperatures. With antifreeze system, however, the pump must be run if the panel temperature is too hot (to prevent antifreeze degradation) or too cold (to prevent water/antifreeze mixture from freezing).
Flat panel collectors are commonly used in closed-loop systems. Flat panels, which often resemble skylights, are the most durable collector type, and they also have the best performance for systems designed for temperatures in temperatures of around 56Ã, ° C (100Ã, ° F). Flat panels are regularly used both in pure water and antifreeze systems.
Another type of solar collector is an evacuated tube collector , which is intended for cold climates that do not experience severe hail and/or applications where high temperatures are required (ie, more than 94 ° C [201 ] Â ° F]). Placed on the shelf, the evacuated tube collector forms a row of glass tubes, each containing an absorption fins attached to a heat conducting rod (copper or condensing condensation). The evacuation description refers to the void created in the glass tube during the manufacturing process, which results in very low heat losses and allows the evacuated tube system to reach extreme temperatures, well beyond the boiling point of water.
Geothermal heating
In countries like Iceland and New Zealand, and other volcanic areas, water heating can be done by using geothermal heating, rather than burning.
Gravity feedback system
Where space heater heaters are used, the traditional setting in the UK is to use heated water (primary) to heat the potable water ( secondary ) contained in the cylindrical vessel (usually made of copper) - supplied from boats or cold water storage containers, usually in roof spaces. This results in a fairly stable supply of DHW (Domestic Hot Water) at low static pressure heads but usually with good flow. In most other parts of the world, water heating appliances do not use cold storage containers or containers, but hot water at pressures close to incoming power supplies.
More enhancements
Other improvements to the water heater include valve devices in inlets and outlets, cycle timers, electronic ignition in case of fuel use models, closed air intake systems in case of fuel use models, and pipe insulation. The type of sealed air intake system is sometimes called the "band-joist" intake unit. The "high efficiency" condensation unit can convert up to 98% of energy in fuel to heat water. The exhaust gas from the combustion is cooled and mechanically ventilated either through the roof or through the outer wall. At high combustion efficiency, sewer must be provided to handle the condensed water from the combustion product, which is mainly carbon dioxide and water vapor.
In traditional UK pipes, space heater heaters are set to heat a separate hot water cylinder or water heater for potable water. Such water heaters are often equipped with additional electric immersion heaters for use if the boiler does not work temporarily. The heat from the space heating boiler is transferred to a water heater vessel with a heat exchanger, and the kettle operates at a higher temperature than a potable hot water supply. Most drinking water heaters in North America are completely separated from space heating units, due to the popularity of HVAC/forced air systems in North America.
Residential burning heaters manufactured since 2003 in the United States have been redesigned to withstand flammable steam ignition and incorporate thermal disconnect switches, per ANSI Z21.10.1. The first feature tries to prevent the vapor from liquids and flammable gases around the heater from being ignited and thus causing a fire or explosion of the house. The second feature prevents the tank from overheating due to unusual combustion conditions. These security requirements are made in response to homeowners who store, or spill, gasoline or other flammable liquids near their water heater and cause a fire. Since most new designs incorporate some types of fire retaining screens, they require monitoring to ensure they are not clogged with cloth or dust, reducing the air availability for burning. If the flame retard becomes clogged, the thermal cutoff may act to turn off the heater.
A wetback stove (NZ), wetback heater (NZ), or back boiler (UK), is a simple secondary household water heater that uses incidental heat. This usually consists of piping hot water that flows behind a fireplace or stove (not hot water storage), and has no facility to limit heating. Modern Wetback can run pipes in more sophisticated designs to help heat exchange. This design is forced out by government efficiency regulations that do not calculate the energy used to heat water as 'efficiently' used.
Maps Water heating
History
Although not particularly popular in North America, other types of water heaters developed in Europe preceded the storage model. In London, England, in 1868, a painter named Benjamin Waddy Maughan discovered the first instant domestic water heater that did not use solid fuel. Named after geysers after Icelandic hot spring, Maughan invention made cold water in the upper stream through a pipeline heated by hot gas from the burner at the bottom. Hot water then flowed to the sink or tub. This discovery is somewhat dangerous because there is no smoke to remove hot gas from the bathroom. Water heaters are still sometimes called geysers in the UK.
Maughn's discovery affects the work of a Norwegian mechanical engineer named Edwin Ruud. Automatic first, a water-type gas storage tank was created around 1889 by Ruud after he immigrated to Pittsburgh, Pennsylvania (USA). The Ruud Manufacturing Company, which still exists today, made much progress in the design and operation of tank-type and tankless water heater.
Thermodynamics and economy
Water usually enters settlement in the US at about 10 ° C (50 ° F), depending on latitude and season. The hot water temperature of 50Ã, Â ° C (122Ã, Â ° F) is commonly used for washing dishes, washing clothes and bathing, which requires the heater to raise the water temperature of about 40Ã Â ° C (72Ã, Â ° F) if the hot water is mixed with cold water at the time of use. Reference Reference Shower Code Reference stream is 2.5 US gallons (9.5 L) per minute. The use of sinks and dishwashers ranges from 1-3 US gallons (4-11Ã, L) per minute.
Natural gas in the US is measured in CCF (100 cubic feet), converted into a standard energy unit called therm, which equals 100,000 British thermal units (BTU). BTU is the energy needed to raise one pound of water as much as one degree Fahrenheit. US gallon of water weighs 8.3 pounds (3.8 kg). To raise 60 gallons of water from 10 ° C (50 ° F) to 50 ° C (122 ° F) requires 60 ÃÆ'â € "8.3 ÃÆ'â €" (122 - 50) = 35,856 BTU , or about 0.359 CCF (35.856/100.000), at an efficiency of 88%. A 157,000 BTU/hour heater (as it might be in a tankless heater) will take 15.6 minutes to do this, at an 88% efficiency. At $ 1 per therm, the cost of gas will be about 41 cents.
By comparison, an electric water heater typical of a 60 gallon tank has a 4500 watt heating element (15.355 BTU), which is at 100% efficient result in a heating time of approximately 2.34 hours. At 16 cents/kWh, electricity will cost $ 1.68.
The energy efficiency of water heaters in the use of housing can vary greatly, especially depending on the manufacturer and model. However, electric heaters tend to be slightly more efficient (excluding power generation losses) with recovery efficiency (how efficient energy transfer to water) reaches about 98%. Gas-fired heaters have a maximum recovery efficiency of only about 82-94% (the remaining heat is lost with the flue gas). The overall energy factor can be as low as 80% for electricity and 50% for gas systems. Natural gas water heater and propane tank with a energy factor of 62% or greater, as well as an electric water tank heater with a 93% or greater energy factor, are considered to be high efficiency units. Natural water heaters and Solar Energy caliber water heater (as of September 2010) have energy factor of 67% or higher, which is usually accomplished by intermittent pilot along with automatic smoke absorbers, blower baffles, or power vents. The direct electric water heater resistance tank is not included in the Energy Star program, however, the Energy Star program does not include an electric heat pump unit with an energy factor of 200% or higher. Tankless gas water heaters (by 2015) should have a 90% or higher energy factor for Energy Star qualification. Since thermal power generation at the plant has an efficiency rate of 15% to just over 55% (combined gas turbine cycle), with about 40% typical for thermal power plants, direct resistance to electric water heating may be the most energy-efficient option. However, the use of heat pumps can make electric water heaters far more energy efficient and lead to a reduction in carbon dioxide emissions, even more so if low carbon sources of electricity are used.
Unfortunately, it takes a lot of energy to heat the water, as it might be experienced while waiting to boil a gallon of water on the stove. For this reason, unheated water heaters require a strong energy source. A standard 120-V, 15-ampere assessed electrical wall outlet, by comparison, is just a resource sufficient to warm a small amount of disappointing water: about 0.17 US gallons (0.64 L) per minute at 40 Ã, Â ° C (72Ã, Â ° F) temperature elevation.
US minimum requirements
On April 16, 2015, as part of the National Applicable Energy Conservation Act (NAECA), new minimum standards for the efficiency of residential water heaters established by the United States Department of Energy came into force. All new gas storage water storage tanks with capacities smaller than 55 US gallons (210Ã, Â °, 46Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã , Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã, Ã,) are sold in the United States in 2015 or later will have a minimum energy factor of 60% (for 50-US-gallon units, higher for smaller units), an increase from the minimum pre-year standard of 58% energy factor to 50-US-gallon gas units. Electric storage water storage tanks with a capacity of less than 55 US gallons sold in the United States should have an energy factor of at least 95%, up from a 90% pre-2015 minimum standard for 50-US-gallon electric units.
Below 2015 standards, for the first time, storage water heaters with a capacity of 55 US gallons or larger now face tighter efficiency requirements than 50 US gallons or less. Below the pre-2015 standard, 75-US-gallon gas storage water heater (280 Â °, 62 Â ° imp-gal) with nominal input of 75,000 British thermal units (79,000 kJ) or less capable of having energy factor as low as 53%, while below the 2015 standard, the minimum energy factor for the 75-US-gallon water storage tank is now 74%, which can only be achieved using condensation technology. Storage of water heaters with nominal inputs of 75,000 btu or greater is currently not affected by this requirement, since the energy factor is not defined for that unit. The 80-US-gallon electric storage water heater (300 Â °, 67 Â ° imp-gal) can have a minimum energy factor of 86% below the pre-2015 standard, while below the 2015 standard, the minimum energy factor for 80-pump heating water tank electric heater is now 197%, which is only possible with heat pump technology. This rating measures efficiency at the point of use. Depending on how electricity is generated, overall efficiency may be much lower. For example, in a traditional coal plant, only about 30-35% of energy in coal ends up as electricity at the end of the generator. Losses on the power grid (including line losses and voltage transformation losses) reduce further electrical efficiency. According to data from the Energy Information Administration, transmission and distribution losses in 2005 consumed 6.1% of the net generation. In contrast, 90% of the value of natural gas energy is delivered to consumers. (In this case no energy is spent to explore, develop and extract coal or natural gas resources included in the quoted efficiency figures.) Waterless water heater must have an energy factor of 82% or greater below 2015 standards, which complies with the Energy Star-2015 standard.
Water heater security
Danger of explosion
The water heater can potentially explode and cause significant damage, injury, or death if a particular safety device is not installed. Safety devices called temperature and pressure relief valves (T & amp; P or TPR) are usually installed at the top of the water heater to discharge water if the temperature or pressure becomes too high. Most plumbing codes require the exhaust pipe to be connected to the valve to direct the flow of hot water discharged into the drain, usually near the floor, or outside the living room. Some building codes allow the drain pipe to end up in the garage.
If a gas or propane gas heater is installed in a garage or basement, many plumbing codes require it to be elevated at least 18Ã, at (46 cm) above the floor to reduce the potential for fire or explosion due to spills or leakage of flammable liquids in the garage. Furthermore, certain local codes mandate that tank type heaters in new and retrofit installations should be secured to walls adjacent to ropes or anchors to prevent overturning and splitting water and gas pipes in case of earthquakes.
For older homes where the water heater is part of the heating boiler, and plumbing codes allow, some installers install automatic gas shut down (such as "Watt 210") next to the TPR valve. When the device senses that the temperature reaches 99 Ã, Â ° C (210Ã, Â ° F), it closes the gas supply and prevents further warming. In addition, an expansion tank or external pressure relief valve shall be installed to prevent pressure accumulation on pipes from broken pipes, valves, or water heater. Thermal burns (scalding)
Scalding is a serious problem with water heaters. Human skin burns quickly at high temperatures, less than 5 seconds at 60 ° C (140 ° F), but much slower at 53 ° C (127 ° F) - it takes a full minute to burn second degree. Older people and children often receive serious injuries due to defects or slow reaction times. In the United States and elsewhere it is common practice to place a tempering valve at a water heater outlet. The result of mixing hot and cold water through the tempering valve is called "tempered water".
A tempering valve mixes enough cold water with hot water from the heater to keep the water temperature at a more moderate temperature, often set to 50 ° C (122 ° F). Without the tempering valve, the reduction of the temperature of the water heater setpoint is the most direct way to reduce heat. However, for sanitation, hot water is needed at temperatures that can cause boiling. This can be done by using an additional heater in a tool that requires hot water. Most residential dishwashers, for example, include internal electric heating elements to increase the water temperature above that provided by household water heaters.
Bacterial contamination
Two conflicting security issues affect the temperature of the water heater - the risk of heat from overheating over 55 ° C, (131 ° F), and the risk of bacterial colonies incubating, in particular Legionella , in water that is not hot enough to kill them. Both of these risks are potentially life-threatening and are balanced by setting the water heater thermostat to 55Ã, ° C (131Ã,  ° F). European Guidelines for the Control and Prevention of Travels Related to Legionnaires Disease recommends that hot water should be stored at 60 ° C (140 ° F) and distributed so that the temperature is at least 50 ° C (122 ° F) and preferably 55 ° C (131Ã,  ° F) is achieved in one minute at points of use.
If there is a dishwasher without a booster heater, it may take a temperature of 57-60 ° C (135-140 ° F) for optimal cleaning, but the temperature valve is set to not more than 55 ° C (131 ° F) can be applied to the faucet to avoid heat. Temperature tanks above 60Ã, Â ° C (140Ã, Â ° F) can produce lime deposits, which can later be a source of bacteria, in water tanks. Higher temperatures can also increase glass etchings in dishwashers.
Tank thermostats are not a reliable guide to the internal temperature of the tank. A gas-fired water tank may not have the temperature calibration shown. An electrical thermostat shows the temperature at the height of the thermostat, but the lower water in the tank can be much cooler. A thermometer outlet is a better indication of the water temperature.
In the renewable energy industry (heat and solar pumps, in particular), the conflict between the Legionella thermal control every day and high temperatures, which can degrade system performance, is subject to heated debate. In a paper looking for a green exclusion from the normal Legionellosis safety standard, CEN's top European thermal solar technical committee, TC 312 confirmed that a 50% reduction in performance would occur if solar water heating systems were heated to the base on a daily basis. But some sun simulator analyzers working using Polysun 5 show that 11% energy penalty is a more probable number. Whatever the context, both energy efficiency and scalar security requirements lead to much lower water temperatures than legionella pasteurization temperatures of about 60 ° C (140 ° F).
However, legionella can be safely and easily controlled by good design protocols and techniques. For example raising the temperature of a water heater once a day or even once every few days to 55Ã, Â ° C (131Ã, Â ° F) in the coldest part of a water heater for 30 minutes effectively controls legionella. In all cases and certain energy-efficient applications, Legionnaires disease is more often than not the result of engineering design problems that do not consider the impact of stratification or low flow.
It is also possible to control Legionella's risk with water chemistry. This technique allows lower water temperatures to be maintained in the pipeline without the associated Legionella risks. The benefit of lower pipe temperatures is that the rate of heat loss is reduced and thus the energy consumption is reduced.
See also
References
External links
- How it Works - Water Heater from Popular Mechanics
Source of the article : Wikipedia
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