Economizers (US and
Oxford spelling
Oxford spelling (also ''Oxford English Dictionary'' spelling, Oxford style, or Oxford English spelling) is a spelling standard, named after its use by the University of Oxford, that prescribes the use of British spelling in combination with th ...
), or economisers (UK), are mechanical devices intended to reduce
energy consumption
Energy consumption is the amount of energy used.
Biology
In the body, energy consumption is part of energy homeostasis. It derived from food energy. Energy consumption in the body is a product of the basal metabolic rate and the physical activity ...
, or to perform useful function such as preheating a
fluid
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
. The term economizer is used for other purposes as well.
Boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
, power plant, heating,
refrigeration
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
, ventilating, and air conditioning (
HVAC
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
) uses are discussed in this article. In simple terms, an economizer is a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
.
Stirling engine
Robert Stirling
Robert Stirling (25 October 1790 – 6 June 1878) was a Scottish clergyman and engineer. He invented the Stirling engine and was inducted into the Scottish Engineering Hall of Fame in 2014.
Early life
Robert Stirling was born at Fatal Fiel ...
's innovative contribution to the design of
hot air engine
A hot air engine (historically called an air engine or caloric engine) is any heat engine that uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work. These engines m ...
s of 1816 was what he called the 'Economiser'. Now known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of
Stirling engine
A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work.
More specif ...
enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine.
Boilers
In
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
s, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the
boiling
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Th ...
point of that fluid. Economizers are so named because they can make use of the
enthalpy
Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the
exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
es from the boiler to preheat the cold water used to fill it (the ''
feed water
Boiler feedwater is an essential part of boiler operations. The feed water is put into the steam drum from a feed pump. In the steam drum the feed water is then turned into steam from the heat. After the steam is used it is then dumped to the mai ...
'').
Steam boilers use large amounts of energy raising feed water to the boiling temperature, converting the water to steam and sometimes superheating that steam above saturation temperature. Heat transfer efficiency is improved when the highest temperatures near the combustion sources are used for boiling and superheating, while using the residual heat of the cooled combustion gases exhausting from the boiler through an economizer to raise the temperature of feed water entering the steam drum.
An indirect contact or direct contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from the boiling temperature of the fluid to little more than the incoming feed water temperature while preheating that feed water to the boiling temperature. High pressure boilers typically have larger economizer surfaces than low pressure boilers. Economizer tubes often have projections like fins to increase the heat transfer surface on the combustion gas side. On average over the years, boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency.
The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam, and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38 °C and there is 15% excess air, then the efficiency will be 94%. The condensing economizer can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process.
The economizer is made of an aluminium and stainless steel alloy. The gases pass through the cylinder, and the water passes through the finned tubes. It condenses about 11% of the water contained in the gases.
History
The first successful economizer design was used to increase the steam-raising
efficiency
Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...
of the boilers of
stationary steam engine
Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars ...
s. It was patented by Edward Green in 1845, and since then has been known as ''Green's economiser''. It consisted of an array of vertical
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
tubes connected to a tank of water above and below, between which the boiler's exhaust gases passed. This is the reverse arrangement to that usually but not always seen in the fire tubes of a boiler; there the hot gases usually pass through tubes immersed in water, whereas in an economizer the water passes through tubes surrounded by hot gases. While both are heat exchange devices, in a ''boiler'' the burning gases heat the water to produce steam to drive an engine, whether piston or turbine, whereas in an ''economizer'', some of the heat energy that would otherwise all be lost to the atmosphere is instead used to heat the water and/or air that will go into the boiler, thus saving fuel. The most successful feature of Green's design of economizer was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of
soot
Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
.
Economizers were eventually fitted to virtually all stationary steam engines in the decades following Green's invention. Some preserved stationary steam engine sites still have their Green's economisers although usually they are not used. One such preserved site is the
Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring one set of economisers and the associated steam engine which drove them. Another such example is the
British Engineerium
The British Engineerium (formerly Brighton and Hove Engineerium) is an engineering and steam power museum in Hove, East Sussex. It is housed in the Goldstone Pumping Station, a set of High Victorian Gothic buildings started in 1866. The Goldst ...
in Brighton & Hove, where the economiser associated with the boilers for Number 2 Engine is in use, complete with its associated small stationary engine. A third site is
Coldharbour Mill Working Wool Museum
Coldharbour Mill, near the village of Uffculme in Devon, England, is one of the oldest woollen textile mills in the world, having been in continuous production since 1797. The mill was one of a number owned by Fox Brothers, and is designated by ...
, where the Green's economiser is in working order, complete with the drive shafts from the Pollit and Wigzell steam engine.
Power plants
Modern-day boilers, such as those in
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
-fired
power station
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many p ...
s, are still fitted with economizers which are descendants of Green's original design. In this context they are often referred to as
feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of ...
s and heat the condensate from
turbines
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful Work (physics), work. The work produced by a turbine can be used ...
before it is pumped to the boilers.
Economizers are commonly used as part of a
heat recovery steam generator
A heat recovery steam generator (''HRSG'') is an energy recovery heat exchanger that recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. It produces steam that can be used in a process (cogeneration) or u ...
(HRSG) in a
combined cycle
A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turb ...
power plant. In an HRSG, water passes through an economizer, then a
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
and then a
superheater
A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming. There ar ...
. The economizer also prevents flooding of the boiler with liquid water that is too cold to be boiled given the flow rates and design of the boiler.
A common application of economizers in steam power plants is to capture the
waste heat
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
from
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
stack gases (
flue gas
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced a ...
) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater, lowering the needed energy input, in turn reducing the firing rates needed for the rated boiler output. Economizers lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection.
HVAC
A building's HVAC (heating, ventilating, and air conditioning) system can make use of an air-side economizer to save energy in buildings by using cool outside air as a means of cooling the indoor space. When the temperature of the outside air is less than the temperature of the recirculated air, conditioning with the outside air is more energy efficient than conditioning with recirculated air. When the outside air is both sufficiently cool and sufficiently dry (depending on the climate) the amount of enthalpy in the air is acceptable and no additional conditioning of it is needed; this portion of the air-side economizer control scheme is called ''free cooling''.
Air-side economizers can reduce
HVAC
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
energy costs in cold and temperate climates while also potentially improving
indoor air quality
Indoor air quality (IAQ) is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort, and well-being of building occupants. Poor indoor air quality has been linked to sick building syndrome, reduced ...
, but are most often not appropriate in hot and humid climates. With the appropriate controls, economizers can be used in climates which experience various weather systems.
When the outside air's dry- and wet-bulb temperatures are low enough, a water-side economizer can use water cooled by a wet
cooling tower
A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and ...
or a dry cooler (also called a fluid cooler) to cool buildings without operating a
chiller
A chiller is a machine that removes heat from a liquid coolant via a vapor-compression refrigeration, vapor-compression, adsorption refrigeration, or absorption refrigerator, absorption refrigeration cycles. This liquid can then be circulated th ...
. They are historically known as the ''strainer cycle'', but the water-side economizer is not a true
thermodynamic
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ther ...
cycle. Also, instead of passing the cooling tower water through a strainer and then to the cooling coils, which causes fouling, more often a plate-and-frame heat exchanger is inserted between the cooling tower and chilled water loops.
Good controls, and valves or dampers, as well as maintenance, are needed to ensure proper operation of the air- and water-side economizers.
Refrigeration
Cooler Economizer
A common form of refrigeration economizer is a "walk-in cooler economizer" or "outside air refrigeration system". In such a system outside air that is cooler than the air inside a refrigerated space is brought into that space and the same amount of warmer inside air is ducted outside. The resulting cooling supplements or replaces the operation of a compressor-based refrigeration system. If the air inside a cooled space is only about 5 °F warmer than the outside air that replaces it (that is, the ∆T>5 °F) this cooling effect is accomplished more efficiently than the same amount of cooling resulting from a compressor based system. If the outside air is not cold enough to overcome the refrigeration load of the space the compressor system will need to also operate, or the temperature inside the space will rise.
Vapor-Compression Refrigeration
Another use of the term occurs in industrial refrigeration, specifically
vapor-compression refrigeration
Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and ...
. Normally, the economizer concept is applied when a particular design or feature on the
refrigeration cycle
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. A heat pump is a mechanical system that allows for the transmission of heat from one locat ...
, allows a reduction either in the amount of
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
used from the power grid, in the size of the components (basically the
gas compressor's nominal capacity) used to produce refrigeration, or both.
For example, for a walk-in freezer that is kept at , the main refrigeration components would include: an
evaporator
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, ...
coil (a dense arrangement of pipes containing refrigerant and thin metal fins used to remove heat from inside the freezer), fans to blow air over the coil and around the box, an air-cooled
condensing unit sited outdoors, and
valves
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
and piping. The condensing unit would include a
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
and a coil and fans to exchange heat with the ambient air.
An economizer display takes advantage of the fact that
refrigeration systems have increasing efficiencies at increasing pressures and temperatures. The
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
the
gas compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
needs is strongly correlated to both the ratio and the difference, between the discharge and the suction pressures (as well as to other features like the
refrigerant's heat capacity and the type of compressor). Low temperature systems such as freezers move less fluid in same volumes. That means the compressor's pumping is less efficient on low temperature systems. This phenomenon is notorious when taking in account that the evaporation temperature for a walk-in freezer at may be around .
Systems with economizers aim to produce part of the refrigeration work on high pressures, condition in which
gas compressors
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
are normally more efficient. Depending on the application, this technology either allows smaller compression capacities to be able to supply enough
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
and flow for a system that normally would require bigger compressors, increases the capacity of a system that without economizer would produce less refrigeration, or allows the system to produce the same amount of refrigeration using less power.
The economizer concept is linked to
subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
as the
condensed liquid line temperature is usually higher than that on the
evaporator
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, ...
, making it a good place to apply the notion of increasing efficiencies.
[Danfos, The Influence of Subcooling on Refrigeration Control Quality. Page 2]
/ref> Recalling the walk-in freezer example, the normal temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
of the liquid line in that system is around or even higher (it varies depending on the condensing temperature). That condition is by far less hostile to produce refrigeration, than the evaporator at .
Economizer setups in refrigeration
Several displays permit the refrigeration cycle
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. A heat pump is a mechanical system that allows for the transmission of heat from one locat ...
to work as economizers, and benefit from this idea. The design of this kind of systems demands certain expertise on the matter, and the manufacture of some of the gear, particular finesse and durability. Pressure drop, electric valve controlling and oil drag, must all be attended with special caution.
Two staged systems and boosters
A system is said to be in a two staged set up if two separate gas compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
s in serial display work together to produce the compression. A normal booster installation is a two staged system that receives fluid that cools down the discharge of the first compressor, before arriving to the second compressor's input. The fluid that arrives to the interstage of both compressors comes from the liquid line and is normally controlled by expansion
Expansion may refer to:
Arts, entertainment and media
* ''L'Expansion'', a French monthly business magazine
* ''Expansion'' (album), by American jazz pianist Dave Burrell, released in 2004
* ''Expansions'' (McCoy Tyner album), 1970
* ''Expansio ...
, pressure and solenoid valves.
A standard two staged cycle of this kind will possess an expansion valve that expands and modulates the amount of refrigerant
A refrigerant is a working fluid used in the heat pump and refrigeration cycle, refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Ref ...
incoming at the interstage. As the fluid arriving to the interstage expands, it will tend to evaporate
Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
, producing an overall temperature drop and cooling the second compressor's suction when mixing with the fluid discharged by the first compressor. This kind of set up may have a heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
between the expansion and the interstage, situation in which that second evaporator may serve to produce refrigeration as well, though not as cool as the main evaporator (for example to produce air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
or for keeping fresh products). A two staged system is said to be set up in a booster display with subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
, if the refrigerant arriving to the interstage passes through a subcooling heat exchanger that subcools the main liquid line arriving to the main evaporator of the same system.[Danfos, The Influence of Subcooling on Refrigeration Control Quality. Page 6]
/ref>
Economizer gas compressors
The need to use two gas compressor, compressors when considering a booster set-up tends to increase the cost of a refrigeration system. Besides the gear's price, two staged systems need special attention over synchronization, pressure control and lubrication. To reduce these costs, special gear has been elaborated.
Economizer screw compressors are being built by several manufacturers like Refcomp, Mycom, Bitzer and York. These machines merge both gas compressor, compressors of a two staged system into one screw compressor
A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors w ...
and have two inputs: the main suction and an interstage side entrance for higher pressure gas. This means there is no need to install two compressors and still benefit from the booster concept.
There are two types of economizer setups for these compressors, flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid ...
and subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
. The latter works under the same principle as the two staged booster displays with subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
. The flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid ...
economizer is different because it doesn't use a heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
to produce the subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
. Instead, it has a flash chamber or tank, in which flash gas is produced to lower the temperature of the liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
before the expansion. The flash gas that is produced in this tank leaves the liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
line and goes to the economizer entrance of the screw compressor
A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors w ...
.[SWEP, Refrigeration Systems: Two Staged Systems](_blank)
/ref>
Subcooling and refrigeration cycle optimizers
All previous systems produce an economizer effect by using compressors, meters, valves and heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
s within the refrigeration cycle. Depending on the system, in some refrigeration cycles it may be convenient to produce the economizer using an independent refrigeration mechanism. Such is the case of subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
the liquid line by any other means that draw the heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
out of the main system. For example, a heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
that preheats cold water needed for another process or human use, may withdraw the heat from the liquid line, effectively subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
the line and increasing the system's capacity.[APS Bussinss Service, Refrigeration Efficiency Measures](_blank)
Recently, machines exclusively designated for this purpose have been developed. In Chile, the manufacturer EcoPac Systems developed a cycle optimizer able to stabilize the temperature of the liquid line and allowing either an increase in the refrigeration capacity of the system, or a reduction of the power consumption
Electric energy consumption is the form of energy consumption that uses electrical energy. Electric energy consumption is the actual energy demand made on existing electricity supply for transportation, residential, industrial, commercial, and o ...
.[Pesca y Medioambiente Nº45, New Challenges on Refrigeration, Cycle Optimizer]
/ref> Such systems have the advantage of not interfering with the original design of the vapor-compression refrigeration, refrigeration system being an interesting alternative for expanding single staged systems that do not possess an economizer compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
.[AQUA News, Efficiency and Saving in Refrigeration](_blank)
Internal heat exchangers
Subcooling may also be produced by superheating
In thermodynamics, superheating (sometimes referred to as boiling retardation, or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling. This is a so-called ''metastable state ...
the gas leaving the evaporator
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, ...
and heading to the gas compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
.[Refrigerant Subcooling and System Efficiency, The influence of refrigerant subcooling on system efficiency.] These systems withdraw heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
from the liquid line but heat up the gas compressors suction. This is a very common solution to insure that gas reaches the compressor and liquid reaches the valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
. It also allows maximum heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
use as minimizes the portion of the heat exchangers used to change the temperature of the fluid, and maximizes the volume in which the refrigerant changes its phase (phenomena involving much more heat flow, the base principle of vapor-compression refrigeration).
An internal heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
is simply a type of heat exchanger that uses the cold gas leaving the evaporator
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, ...
coil to cool the high-pressure liquid that is headed into the beginning of the evaporator coil via an expansion device. The gas is used to chill a chamber that normally has a series of pipes for the liquid running through it. The superheated gas then proceeds on to the compressor. The subcooling
The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed "subcooled". A subcooled liqui ...
term refers to cooling the liquid below its boiling point. of subcooling means it is 10 °F colder than boiling at a given pressure. As it represents a difference of temperatures, the subcooling value won't change if it is measured on the absolute scale, or the relative scale (10 °F of subcooling equals of subcooling).
See also
*Countercurrent exchange
Countercurrent exchange is a mechanism occurring in nature and mimicked in industry and engineering, in which there is a crossover of some property, usually heat or some chemical, between two flowing bodies flowing in opposite directions to each ...
*Regenerative heat exchanger
A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where heat from the hot fluid is intermittently stored in a thermal storage medium before it is transferred to the cold fluid. To accomplish this the hot fl ...
*Feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of ...
*Thermal efficiency
In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc.
For a he ...
References
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{{HVAC
Energy recovery
Thermodynamics
Energy conversion
Heating, ventilation, and air conditioning