# Patent

## Title
Apparatus and method for refrigeration cycle elevation by modification of cycle start condition

## Abstract

An apparatus includes a mechanical refrigeration cycle arrangement having a working fluid, an evaporator, a condenser, a compressor, and an expansion device, cooperatively interconnected and containing the working fluid. The apparatus also includes a drum to receive clothes, a duct and fan arrangement configured to pass air over the evaporator, condenser and through the drum, a sensor located to sense parameters, a working fluid accumulator, and a controller coupled to the sensor, accumulator and/or compressor. The controller is operative to control collection of refrigerant during a run cycle when pressure exceeds a predetermined threshold value, control retention of the collected refrigerant when the run cycle is completed, until a subsequent run cycle, control discharge of the retained refrigerant to an evaporator or condenser when the subsequent run cycle is started, and control use of discharged refrigerant to elevate the refrigeration cycle by modifying a start condition of the refrigeration cycle.

## Background
BACKGROUND OF THE INVENTION
The subject matter disclosed herein relates to appliances using a mechanical refrigeration cycle, and more particularly to heat pump dryers and the like.
Clothes dryers have typically used electric resistance heaters or gas burners to warm air to be used for drying clothes. These dryers typically work on an open cycle, wherein the air that has passed through the drum and absorbed moisture from the clothes is exhausted to ambient. More recently, there has been interest in heat pump dryers operating on a closed cycle, wherein the air that has passed through the drum and absorbed moisture from the clothes is dried, re-heated, and re-used.
Challenges exist in reducing the time constant to full capacity at start-up that is inherent in heat pump dryers. Existing approaches, attempt to use an auxiliary heater to gently add load and bring about a slow rise in the system equilibrium point during the run cycle.
BRIEF DESCRIPTION OF THE INVENTION
As described herein, the exemplary embodiments of the present invention overcome one or more disadvantages known in the art.
One aspect of the present invention relates to a method comprising the steps of: collecting refrigerant during a run cycle when pressure exceeds a predetermined threshold value, retaining the collected refrigerant when the run cycle is completed, until a subsequent run cycle, discharging the retained refrigerant to an evaporator or condenser when the subsequent run cycle is started, and using the discharged refrigerant to elevate the refrigeration cycle by modifying a start condition of the refrigeration cycle.
Another aspect relates to an apparatus comprising: a mechanical refrigeration cycle arrangement having a working fluid and an evaporator, a condenser, a compressor, and an expansion device, cooperatively interconnected and containing the working fluid; a drum to receive clothes to be dried; and a duct and fan arrangement configured to pass air over the evaporator, condenser and through the drum. The apparatus further comprises a sensor located to sense at least one parameter. The at least one parameter includes at least one of temperature of the working fluid, pressure of the working fluid, and power consumption of the compressor. The apparatus additionally includes a working fluid accumulator. The apparatus still further comprises a controller coupled to the sensor, accumulator and the compressor. The controller is operative to: control collection of refrigerant during a run cycle when pressure exceeds a predetermined threshold value, control retention of the collected refrigerant when the run cycle is completed, until a subsequent run cycle, control discharge of the retained refrigerant to an evaporator or condenser when the subsequent run cycle is started, and control use of discharged refrigerant to elevate the refrigeration cycle by modifying a start condition of the refrigeration cycle.
These and other aspects and advantages of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. Moreover, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a block diagram of an exemplary mechanical refrigeration cycle, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 2 is a semi-schematic side view of a heat pump dryer, in accordance with a non-limiting exemplary embodiment of the invention;
FIGS. 3 and 4 are pressure-enthalpy diagrams illustrating refrigerant cycle elevation, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 5 presents capacity rise curves for a refrigeration system operating at elevated state points, in accordance with a non-limiting exemplary embodiment of the invention;
FIGS. 6-8 are pressure-enthalpy diagrams illustrating capacity enhancement, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 9 presents pressure versus time for a cycle wherein an auxiliary heater is pulsed, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 10 presents operation of a charge cylinder through a run cycle, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 11 presents a shift in specific density or volume brought about by mass injection at start of a run cycle, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 12 presents resulting state points based on preheat of injected refrigerant into evaporator, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 13 presents refrigeration cycle elevation, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 14 presents start-up progressions, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 15A and FIG. 15B present accumulator function data, in accordance with a non-limiting exemplary embodiment of the invention;
FIG. 16 is a flow chart of a method for elevating a refrigeration cycle, in accordance with a non-limiting exemplary embodiment of the invention; and
FIG. 17 is a block diagram of an exemplary computer system useful in connection with one or more embodiments of the invention.



DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION
FIG. 1 shows an exemplary embodiment of a mechanical refrigeration cycle, in accordance with an embodiment of the invention. Heat (Q) flows into evaporator 102, causing refrigerant flowing through same to evaporate and become somewhat superheated. The superheated vapor is then compressed in compressor 104, and flows to condenser 106, where heat (Q) flows out. The refrigerant flowing through condenser 106 condenses and becomes somewhat sub-cooled. It then flows through restriction 108 and back to evaporator 102, competing the cycle. In a refrigerator, freezer, or air conditioner, evaporator 102 is located in a region to be cooled, and heat is generally rejected from condenser 106 to ambient. In a heat pump, heat is absorbed from the ambient in evaporator 102 and rejected in condenser 106 to a space to be heated.
In the non-limiting exemplary embodiment of FIG. 1, a temperature or pressure sensor 110 is located in the center of the condenser 106 and is coupled to a controller 112 which, as indicated at 114, in turn controls an auxiliary heater, to be discussed in connection with FIG. 2.
In review, a mechanical refrigeration system includes the compressor 104 and the restriction 108 (either a capillary or a thermostatic expansion valve or some other kind of expansion valve or orifice a mass flow device just before the evaporator 102 which limits the mass flow and produces the pressures in the low side and high side). The condenser 106 and the evaporator 102 are heat exchange devices and they regulate the pressures. The mass transfer devices 104, 108 regulate the mass flow. The pressure in the middle of the condenser 106 will be slightly less than at the compressor outlet due to flow losses.
As also illustrated in FIG. 1, one or more embodiments (as further detailed herein) can include a receiver (that can include a piston and one or more valves) with lines to and from the condenser, as well as an alternate discharge to the evaporator.
FIG. 2 shows an exemplary embodiment of a heat pump type clothes dryer 250. The evaporator 102, condenser 106, and compressor 104 are as described above with respect to FIG. 1. The refrigerant lines and the expansion valve 108 are omitted for clarity. Fan 252 circulates air through a supply duct 256 into drum 258 to dry clothes contained therein. The mechanism for rotating the drum 258 can be of a conventional kind and is omitted for clarity. Air passes through the drum 258 into a suitable return plenum 260 and then flows through a return duct 262. Condenser 106 is located in the air path to heat the air so that it can dry the clothes in the drum 258.
One or more embodiments include an auxiliary heater 254 in supply duct 256 and/or an auxiliary heater 254′ in return duct 262; in either case, the heater may be controlled by controller 112 as discussed elsewhere herein.
One or more embodiments advantageously improve transient performance during start-up of a clothes dryer, such as dryer 250, which works with a heat pump cycle rather than electric resistance or gas heating. As described with respect to 254, 254′, an auxiliary heater is placed in the supply and/or return duct and used to impact various aspects of the startup transient in the heat pump drying cycle.
With continued reference to FIG. 1, again, compressor 104 increases the pressure of the refrigerant which enters the condenser 106 where heat is liberated from the refrigerant into the air being passed over the condenser coils. The fan 252 passes that air through the drum 258 to dry the clothes. The air passes through the drum 258 to the return duct 262 and re-enters or passes through the evaporator 102 where it is cooled and dehumidified (this is a closed cycle wherein the drying air is re-used). In some instances, the heater can be located as at 254, in the supply duct to the drum (after the fan 252 or between the condenser 106 and the fan 252). In other instances, the heater can be located at point 254′, in the return duct from the drum 258, just before the evaporator 102.
Thus, one or more embodiments place a resistance heater of various wattage in the supply or return duct of a heat pump dryer to provide an artificial load through the drum 258 to the evaporator 102 by heating the supply and therefore the return air, constituting a sensible load to the evaporator 102 before the condenser 106 is able to provide a sensible load or the clothes load in drum 258 is able to provide a latent psychrometric load. This forces the system to develop higher temperatures and pressures earlier in the run cycle, accelerating the onset of drying performance.
A refrigeration system normally is run in a cycling mode. In the off cycle it is allowed to come to equilibrium with its surroundings. A system placed in an ambient or room type environment will seek room temperature and be at equilibrium with the room. When the system is subsequently restarted, the condenser and evaporator will move in opposite directions from the equilibrium pressure and temperature. Thus, the evaporator will tend towards a lower pressure and/or temperature and the condenser will seek a higher temperature and/or pressure. The normal end cycle straddles the equilibrium pressure and steady state is reached quite quickly.
In one or more embodiments, for system efficiency in a heat pump dryer, operating points that result in both the condenser and evaporator pressures and temperatures being above the equilibrium pressure of the system in the off mode are sought.
Placing a heater in the supply duct to the drum of a heat pump dryer heats the air up well above ambient temperature as it is presented to the evaporator. If the heater is on at the start of a drying cycle the heat serves to begin the water extraction process in the clothes by evaporation in combination with the airflow by diffusion. The fact that more water vapor is in the air, and the temperature is higher than would otherwise be the case, causes the evaporator to “see” higher temperature than it would otherwise “see.” The temperature of the evaporator will elevate to meet the perceived load, taking the pressure with it. Thus the temperature and pressure of the refrigerant are elevated above the ambient the refrigerant would otherwise seek as shown in FIGS. 3 and 4 and described in greater detail below.
With each subsequent recirculation of the air, a higher level is reached until leakage and losses neutralize the elevating effects. Since a suitably sealed and insulated system will not lose the accumulated heat, the cycle pressure elevation can continue until a quite high pressure and temperature are reached. Thus, the refrigeration system moves into a regime where compressor mass flow is quite high and power consumed is quite low.
With the heater on, the system moves to a higher total average pressure and achieves such a state considerably faster than in a conventional system. This is brought about by supplying the evaporator a definite and instantaneous load. This loading causes the heat exchangers (i.e., evaporator 102 and condenser 106) to react and supply better properties to accelerate mass flow through the mass flow devices (the compressor 104 and restrictor 108).
Elevation of a refrigerant cycle's pressures within the tolerance limits of the refrigerant boosts compressor capacity at approximately equal power consumption. Thus, in one or more embodiments, the efficiency of refrigeration cycles is improved as pressures are elevated.
Given the teachings herein, the skilled artisan will be able to install, control, and protect a suitable heater with minimal cost, and will also be able to interconnect the heater with the control unit for effective control.
Refer to the P-h (pressure-enthalpy) diagram of FIG. 3. The star 302 represents the equalization condition. In refrigerators and other refrigeration devices such as air conditioners, dehumidifiers, and the like, a cycle is typically started up around the equalization point. When the compressor starts, it transfers mass from the evaporator or low pressure side, to the high pressure side (condenser). The condenser rejects heat and the evaporator absorbs heat, as described above. Generally, the source temperatures for the heat exchangers are found inside the cycle curve 304. The diagram of FIG. 3 illustrates, rather than lowering (the evaporator pressure) and raising (the condenser pressure) pressures from equilibrium, elevating the cycle 304 completely (i.e., both low 397 and high 399 pressure sides) above the equalization pressure at star 302. To accomplish this, provide the aforementioned auxiliary heat source to raise the cycle to a different starting state by pre-loading the evaporator and causing the system to migrate to a higher pressure-temperature cycle.
Refer now to the P-h diagram of FIG. 4. The necessary cycle elevation is given by the bracket 411 between the two stars 302, 302′. Typically, the system will start in a cycle 413 surrounding the equalization point, which is the lower star 302. Because of the auxiliary heater (which in one or more embodiments need provide only a faction of the power actually needed to dry the clothes), the cycle elevates and spreads to the desired upper envelope 304. By way of review, if the auxiliary heater was not applied, operation would be within the lower cycle 413 wherein, shortly after startup, the upper pressure is between 80 and 90 PSI and the lower pressure is between 50 and 60 PSI. Note that these values would eventually change to an upper pressure of about 150 PSI and a lower pressure of about 15 PSI when a steady state was reached. Thus, without the extra heater, the steady state cycle obtained would have a high side pressure of about 150 PSI and a low side pressure of about 15 PSI. Upper envelope 304 shows the results obtained when the auxiliary heater is used. Eventually, the auxiliary heater is preferably shut off to prevent the compressor overheating. Thus, for some period of time during the startup transient, apply extra heat with the auxiliary heater, causing the heat pump to operate in a different regime with a higher level of pressure.
For completeness, note that upper envelope 304 represents, at 393, a compression in compressor 104; at high side 399, condensation and sub-cooling in condenser 106; at 395, an isenthalpic expansion through valve 108, and at low side 397, evaporation in evaporator 102. Enter the condenser as a superheated vapor; give up sensible heat in region 421 until saturation is reached, then remain saturated in region 423 as the quality (fraction of the total mass in a vapor-liquid system that is in the vapor phase) decreases until all the refrigerant has condensed; then enters a sub-cooled liquid region 425.
Heretofore, it has been known to place resistance heaters in the supply (but not return) ducts of heat pump dryers simply to supplement the action of the condenser in heating and drying the air. However, one or more embodiments of the invention control the heater to achieve the desired thermodynamic state of the refrigeration cycle and then shut the heater off at the appropriate time (and/or cycle the heater). With reference to FIG. 4, hf and hg are, respectively, the saturated enthalpies of the fluid and gas. When operating at full temperature and pressure, the high side 399 (line of constant pressure) is at approximately 300 PSI, which is very close to the top 317 of the vapor dome curve. At such point, effectiveness of the heat exchanger will be lost, so it is not desirable to keep raising the high side pressure.
Furthermore, at these very high pressures, the compressor is working very hard and may be generating so much heat at the power at which it is running that the compressor temperature increases sufficiently that the thermal protection device on the compressor shuts the compressor off. In one or more embodiments, employ a sensor 110, such as a pressure transducer and/or a thermal measurement device (e.g., a thermocouple or a thermistor) and monitor the high side temperature and/or the high side pressure. When they reach a certain value which it is not desired to exceed, a controller 112 (for example, an electronic control) turns the heater off.
To re-state, a pressure transducer or a temperature sensor is located in the high side, preferably in the middle of the condenser (but preferably not at the very entrance thereof, where superheated vapor is present, and not at the very outlet thereof, where sub-cooled liquid is present). The center of the condenser is typically operating in two phase flow, and other regions may change more quickly than the center of the condenser (which tends to be quite stable and repeatable). Other high side points can be used if correlations exist or are developed, but the center of the condenser is preferred because of its stability and repeatability (that is, it moves up at the rate the cycle is moving up and not at the rate of other transients associated with the fringes of the heat exchanger). Thus, one or more embodiments involve sensing at least one of a high side temperature and a high side pressure; optionally but preferably in the middle of the condenser.
Comments will now be provided on the exemplary selection of the pressure or temperature at which the auxiliary heater is turned off. There are several factors of interest. First, the compressor pressure can reach almost 360 or 370 PSI, and the compressor will still function, before generating enough heat such that the thermal protection device shuts it off, as described above. This, however, is typically not the limiting condition; rather, the limiting condition is the oil temperature. The compressor lubricating oil begins to break down above about 220 degrees F. (temperature of the shell, oil sump, or any intermediate point in the refrigerant circuit). Initially, the oil will generate corrosive chemicals which can potentially harm the mechanism; furthermore, the lubricating properties are lost, which can ultimately cause the compressor to seize up. In one or more embodiments, limit the condenser mid temperature to no more than 190 degrees F., preferably no more than 180 degrees F., and most preferably no more than 170 degrees F. In this manner, when the heater is shut off, the compressor will stabilize at a point below where any of its shell or hardware temperatures approach the oil decomposition temperature. With regard to discharge temperature, note that point 427 will typically be about 210 degrees F. when the high side pressure is at about 320 PSI. The saturation temperature at that pressure (middle of the condenser) will be about 170 degrees F. and therefore control can be based on the mid-condenser temperature. The compressor discharge 427 is typically the hottest point in the thermodynamic cycle. The discharge is a superheated gas. The discharge gas then goes through a convective temperature change (FIG. 4 reference character 421 temperature drop) until the constant “condensing temperature” is reached. This is most accurately measured in the center of the condenser. Oil is heated by contact with the refrigerant and by contact with metal surfaces in the compressor. Generally the metal parts of the inside of the compressor run 20-30 degrees F. above the hottest point measured on the outside. The actual temperature to stay below is, in one or more embodiments, 250 degrees F. Thus, there is about a 10 degree F. margin worst case. In one or more embodiments, when the cycle is run up to this point, the maximum capacity is obtained at minimum energy, without causing any destructive condition in the compressor. Heretofore, compressors have not been operated in this region because compressor companies typically will not warrant their compressors in this region.
As noted, prior techniques using a heater do so to provide auxiliary drying capacity, not for system operating point modification, and do not carry out any sensing to turn the heater off. One or more embodiments provide a sensor 110 and a controller 112 that shut off the heater 254, 254′ at a predetermined point, as well as a method including the step of shutting off the heater at a predetermined point.
Any kind of heater can be used. Currently preferred are twisted Nichrome wire (nickel-chromium high-resistance heater wire) ribbon heaters available from industrial catalogs, commonly used in hair dryers and the like.
With the desired ending cycle for a heat pump dryer at a significant elevation above the normal air conditioning state points the transient for cycle elevation is quite long. The application of an external heater 254, 254′ accelerates that transient. The observed effect is directly proportional to heater power. That is, the more power input to the auxiliary heater, the faster effective capacity and total system capacity are developed. Refer to FIG. 5, which depicts capacity rise curves of a refrigeration system operating at elevated state points with an auxiliary heater in the air circuit. The rate of capacity rise is proportional to power applied.
The faster onset of effective capacity accelerates the drying process and reduces drying time. With the heater on, the system not only moves to a higher total average pressure (and thus temperature), but also gets there significantly faster.
Thus, in one or more embodiments, application of an independent heat source to a heat pump airside circuit accelerates the progress of a refrigeration system to both effective capacity ranges and final desired state points.
Any one, some, or all of four discrete beneficial effects of the auxiliary heater can be realized in one or more embodiments. These include: (1) total amount of heat transfer attainable; (2) rate at which system can come up to full capacity; (3) cycle elevation to obtain a different state than is normally available; and (4) drying cycle acceleration.
With regard to point (2), capacity, i.e., the time it takes to get to any given capacity—it has been found that this is related to the heater and the size of the heater. In FIG. 5, time is on the lower (X) axis and capacity is on the vertical (Y) axis. Recall that with the heater elevating the system operating point, it is possible to operate at 2-3 times the rated value. The rated power of a compressor is determined by running a high back pressure compressor (air conditioning) typically at about 40 degrees F. evaporating temperature and about 131 degrees F. condensing temperature. At this rating point the rated value for an exemplary compressor is about 5000 or 7000 Btu/hr. Elevated pressures in accordance with one or more embodiments will make the compressor able to pump about 12000 or 15000 Btu/hr. This is why it is advantageous to elevate the system operating state points, to get the extra capacity. The power (wattage) of the heater also determines how fast these extra-rated values can be obtained. FIG. 5 shows the start-up curves of developed capacity versus time. With the heater in the system, it is possible to obtain more capacity faster by increasing the heater wattage.
One aspect relates to the final selection of the heater component to be installed in the drier. Thus, one or more embodiments provide a method of sizing a heater for use in a heat pump drier. The capacity (“Y”) axis reads “developed refrigeration system capacity” as it does not refer to the extra heating, properties of the heater itself, but rather how fast the use of the heater lets the refrigerant system generate heating and dehumidifying capacity. Prior art systems dry clothes with the electric heat as opposed to accelerating the refrigerating system coming up to full capacity. The size of the heater that is eventually chosen can help determine how fast the system achieves full capacity—optimization can be carried out between the additional wattage of the heater (and thus its power draw) and the capacity (and power draw) of the refrigeration system. There will be some optimum; if the heater is too large, while the system will rapidly come up to capacity, more total energy will be consumed than at the optimum point, due to the large heater size, whereas if the heater is too small, the system will only slowly come up to capacity, requiring more power in the refrigeration system, and again more energy will be consumed than at the optimum point. This effect can be quantified as follows. The operation of the heater involves adding power consumption for the purpose of accelerating system operation to minimize dry time. It has been determined that, in one or more embodiments, there does not appear to be a point at which the energy saved by shortening the dry time exceeds the energy expended in the longer cycle. Rather, in one or more embodiments, the total power to dry, over a practical range of heater wattages, monotonically increases with heater power rating while the efficiency of the unit monotonically decreases with heater wattage. That is to say that, in one or more embodiments, the unit never experiences a minima where the unit saves more energy by running a heater and shortening time rather than not. Thus, in one or more embodiments, the operation of a heater is a tradeoff based on desired product performance of dry time vs. total energy consumption.
In another aspect, upper line 502 represents a case where compressor power added to heater power is greater than the middle line 504. Lower line 506 could represent a case where compressor power plus heater power is less than middle line 504 but the time required to dry clothes is too long. Center line 504 represents an optimum of shortest time at minimum power. In other words, for curve 504; power is lowest for maximum acceptable time. Lower line 506 may also consume more energy, as described above, because the compressor would not be operating as efficiently.
As shown in FIG. 6, a basic vapor compression cycle is in thermal and mass flow balance until an external source causes the balance to be upset.
The temperature shift from auxiliary heating causes heat transfer imbalance and mass flow restriction in the capillary (or other expansion valve) resulting in capacity increase in the evaporator and pressure elevation in the condenser. Mass flow imbalance is also a result, as seen in FIG. 7, which depicts the imbalance created by additional heat input at the evaporator by raised return temperature.
Mass flow through the compressor increases due to superheating resulting in further pressure increase in the condenser. The dynamic transient is completed when the condenser reestablishes sub-cooling and heat flow balance at higher pressures. The net effect is higher average heat transfer during process migration. FIG. 8 shows thermal and mass flow equilibrium reestablished at higher state points after the heat input transient.
One or more embodiments thus enable an imbalance in heat exchange by apparently larger capacity that causes more heat transfer to take place at the evaporator. The imbalance causes an apparent rise in condenser capacity in approximately equal proportion as the condensing pressure is forced upward. The combined effect is to accelerate the capacity startup transient inherent in heat pump dryers.
Experimentation has demonstrated the effect of capacity augmentation through earlier onset of humidity reduction and moisture collection in a run cycle.
Referring again to FIGS. 6-8, via the elevated cycle, it is possible to increase the capacity, inasmuch as the temperature shift from auxiliary heating causes heat transfer imbalance and mass flow restriction in the capillary (or other expansion valve) resulting in capacity increase in the evaporator and pressure elevation in the condenser. Mass flow imbalance is also a result. Furthermore, mass flow through the compressor increases due to superheating, resulting in further pressure increase in the condenser. The dynamic transient is completed when the condenser re-establishes sub-cooling and heat flow balance at higher pressures. The net effect is higher average heat transfer during process migration.
Heat is transferred by temperature difference (delta T). The high-side temperature 871 is at the top of the cycle diagram in FIG. 8. When that temperature is elevated, there is a larger delta T between the sink temperature (air to which heat is being rejected) and the actual temperature of the heat exchanger (condenser) itself. The imbalance caused by the auxiliary heater increases delta T and thus heat transfer which creates an apparent increase in capacity above that normally expected at a given condensing pressure or temperature. The effect is analogous to a shaker on a feed bowl; in effect, the heater “shakes” the refrigeration system and makes the heat move more efficiently. Again, it is to be emphasized that this is a thermodynamic effect on the heat pump cycle, not a direct heating effect on the clothes.
One or more embodiments of the invention pulse or cycle a heater in a heat pump clothes dryer to accomplish control of the heat pump's operating point. As noted above, placing a resistance heater of various wattage in the supply and/or return ducts of a heat pump dryer provides an artificial load through the drum to the evaporator by heating the supply and therefore the return air, constituting an incremental sensible load to the evaporator. This forces the system to develop higher temperatures and pressures that can cause the cycle to elevate continuously while running. In some embodiments, this can continue well past the time when desired drying performance is achieved. When the heater is turned off during a run cycle the cycle tends to stabilize without additional pressure and/or temperature rise, or even begin to decay. If the system operating points decay the original growth pattern can be repeated by simply turning the heater back on. Cycling such a heater constitutes a form of control of the capacity of the cycle and therefore the rate of drying.
As noted above, for system efficiency in a heat pump dryer, seek operating points that result in both the condenser and evaporator well above the equilibrium pressure of the system in off mode. In one or more embodiments, this elevation of the refrigeration cycle is driven by an external forcing function (i.e., heater 254, 254′).
Further, in a normal refrigeration system, the source and sink of the system are normally well established and drive the migration to steady state end points by instantly supplying temperature differences. Such is not the case with a heat pump dryer, which typically behaves more like a refrigerator in startup mode where the system and the source and sink are in equilibrium with each other.
As noted above, with each subsequent recirculation of the air, a higher cycle level is reached until leakage and losses neutralize the elevating effects. Since a properly sealed and insulated system will not lose this accumulated heat, the cycle pressure elevation can continue until quite high pressure and temperature are reached. Thus, the refrigeration system moves into a regime where compressor mass flow is quite high and power consumed is quite low. However, a properly sealed and insulated system will proceed to high enough head pressures to shut off the compressor or lead to other undesirable consequences. In one or more embodiments, before this undesirable state is reached, the heater is turned off, and then the system states begin to decay and or stabilize. In one or more embodiments, control unit 112 controls the heater in a cycling or pulse mode, so that the system capacity can essentially be held constant at whatever state points are desired.
One or more embodiments thus provide capacity and state point control to prevent over-temperature or over-pressure conditions that can be harmful to system components or frustrate consumer satisfaction.
With reference now to FIG. 9, it is possible to accelerate the time in which the system conies up to full capacity. Once the system comes up to full capacity, then it is desired to ensure that the compressor is not overstressed. In some embodiments, simply turn off the heater when the temperature and/or pressure limits are reached (e.g., above-discussed temperature limits on compressor and its lubricant). In other cases, the heater can be cycle back on and off during the drying cycle. In the example of FIG. 9, the heater is cycled within the control band to keep the system at an elevated state.
Accordingly, some embodiments cycle the heater to keep the temperature elevated to achieve full capacity. By way of review, in one aspect, place a pressure or temperature transducer in the middle of the condenser and keep the heater on until a desired temperature or pressure is achieved. In other cases, carry this procedure out as well, but selectively turn the heater back on again if the temperature or pressure transducer indicates that the temperature or pressure has dropped off.
Determination of a control band is based on the sensitivity of the sensor, converter and activation device and the dynamic behavior of the system. These are design activities separate from the operation of the principle selection of a control point. Typically, in a control, a desired set point or comfort point is determined (e.g., 72 degrees F. for an air conditioning application). Various types of controls can be employed: electro-mechanical, electronic, hybrid electro-mechanical, and the like; all can be used to operate near the desired set or comfort point. The selection of dead bands and set points to keep the net average temperature at the desired value are within the capabilities of the skilled artisan, given the teachings herein. For example, an electromechanical control for a room may employ a 7-10 degree F. dead band whereas a 3-4 degree F. dead band might be used with an electronic control. To obtain the desired condenser mid temperature, the skilled artisan, given the teaching herein, can set a suitable control band. A thermistor, mercury contact switch, coiled bimetallic spring, or the like may be used to convert the temperature to a signal usable by a processor. The activation device may be, for example, a TRIAC, a solenoid, or the like, to activate the compressor, heater, and so on. The dynamic behavior of thermal systems may be modeled with a second order differential equation in a known manner, using inertial and damping coefficients. The goal is to cycle the auxiliary heater during operation to protect the compressor oil from overheating.
As described herein, one or more embodiments of the invention include techniques and apparatuses for refrigeration cycle elevation by modification of cycle start condition. The techniques detailed herein can include modifying the equilibrium density or specific volume of a refrigeration system in the off state by injecting additional charge into the system from a storage cylinder that is charged with excess refrigerant during the run cycle. In one or more embodiments of the invention, a bleed valve can be needed for the filling cycle, and a solenoid activated piston and bleed valve can be needed for the injection step. Additionally, one or more embodiments of the invention include a pass-through piston cylinder refrigerant accumulator that alternately collects and discharges refrigerant to elevate the start and maintain the run cycle state points of a vapor compression cycle.
As detailed herein, one or more embodiments of the invention can significantly reduce the time constant to full capacity at start inherent in heat pump dryers. By way of example and not limitation, one or more embodiments of the invention can include'time reductions from 30-40 minutes to 3-5 minutes. With capacity available so quickly, there can be a significant reduction in dry time as well. A step change in properties of the system at a discrete time can be implemented, for example, to avoid the inherent delay of trying to accomplish the task with slow incremental shifts.
As such, one or more embodiments of the invention include techniques and an apparatus to elevate a refrigeration cycle by modifying the start condition of the refrigeration cycle. The techniques and apparatus include the use of a piston cylinder accumulator that collects and discharges the refrigerant alternately to elevate the start and maintain the run cycle state points of a vapor compression cycle. In this accumulator, the piston can be activated mechanically or through a solenoid. The cylinder can also be fitted with two spring loaded normally closed flow valves. In one or more embodiments of the invention, these valves can also be controlled using solenoids. Further, both of these valves can be connected to a high or low side plumbing of the heat exchanger sections of a refrigeration system as an inlet valve to a condenser outlet and a discharge valve to the evaporator inlet.
As the system runs and builds pressure it can generate excess pressure if the system is slightly overcharged. During the nm cycle, when pressure exceeds a particular threshold value, the inlet valve of the cylinder is opened, and the refrigerant is flowed into the cylinder. This filling process continues as long as the system runs. Accordingly, an excessive amount of the refrigerant can continue to bleed into the cylinder, which prevents the overcharging of the refrigerant system. Further, when the dry cycle is over, the system shuts off and the refrigerant is retained in the cylinder until the next run cycle.
Subsequently, when a new dry run cycle is started (for example, when the control signals the start of a new run cycle), the piston is activated. The piston rams or pushes the refrigerant into the evaporator inlet through the second check valve. This injected mass raises the density of the refrigerant and the pressure of the system to a state point that includes a pressure band of the desired operating cycle. Further, when the compressor is turned on, the system expands normally from equilibrium pressure resulting in a far shorter start-up transient.
FIG. 10 presents operation of a charge cylinder through a run cycle, in accordance with a non-limiting exemplary embodiment of the invention. FIG. 10A depicts intake by passive mass transfer through a relief valve (for example, at approximately 300 pounds per square inch (psi) to maintain high system pressure at approximately 300 psi). FIG. 108 depicts off-cycle passive static pressure holding mass in cylinder. Additionally, FIG. 10C depicts before a compressor start, the mass expelled into evaporator (for example, at approximately 80 psi raising pressure to about 120-140 psi and density to a state point in the middle of the desired cycle).
As depicted by FIG. 10, when a system is up and running at pressure, the system pressure acting on the valve body can exceed the force of spring 1003, causing the valve from the condenser (1005) to open. In one or more embodiments of the invention, the inlet to the valve (for example, valve 1005) is preferably located at the exit from the condenser. When the spring 1003 is overcome by the pressure in the condenser, some mass of refrigerant 1009 is absorbed in the cylinder until the cylinder fills up. As such, extra refrigerant in the system has been accumulated in the condenser and absorbed into the cylinder. Consequently, when the system has been shut off and equalizes with the refrigerant that it has, the valves open, and there is this extra mass in the cylinder.
Similarly, attention can now be/given to FIG. 11, which presents a shift in specific density or volume brought about by mass injection at start of a run cycle, in accordance with a non-limiting exemplary embodiment of the invention. In connection with the description of FIG. 10 above, FIG. 11 depicts the equalization condition of the lower star 1102.
Typically, for example, when a refrigeration cycle is started up, as discussed herein, the evaporator pressure goes down from that point and the condenser pressure goes up from that point. If, instead, a non-trivial amount of mass is injected, the system is forced to a higher specific volume line. As such, the pressure at equalization, when you ram or push the refrigerant back into the evaporator, goes up to almost 200 PSI as seen at the higher star 1104. Now the start point 1104 is in the middle of the intended operating cycle. Consequently, when the system starts, the evaporator will go down, the condenser will go up, and the desired cycle operating point is rapidly attained.
Accordingly, one or more embodiments of the invention can include absorption of extra charge with re-introduction of that charge to move the system to a higher operating point. Then, as the system continues to run at the elevated pressure, the extra refrigerant can be absorbed back into the accumulator.
FIG. 12 presents resulting state points based on preheat of injected refrigerant into evaporator, in accordance with a non-limiting exemplary embodiment of the invention. The state point shift is horizontal if preheat=ambient (say 70° F. which is room temperature and thus equalization temperature). The state point shift is diagonal if preheat ̃desired end temp (say 120° F.). The shift is nearly vertical if you keep it warm at 170° F. or preheat ̃160° F.
As described herein, with intake by passive mass transfer (wherein, for example, the valve is spring loaded) when pressure in the system is high enough to overcome the spring (pressure times valve area equals force), the valve opens and fluid goes into the cylinder. In one or more embodiments of the invention, this continues until pressure equilibrates on both sides of valve, at which point the spring forces valve closed again, as illustrated in FIG. 10. Further illustrated in FIG. 10, in cylinder image 1006, the valve to the evaporator (1007) can be solenoid operated, and when the cycle is started up, the solenoid valve is energized, allowing the refrigerant to flow into the evaporator under action of spring and piston.
As such, one or more embodiments of the invention include an auxiliary refrigeration device that receives overpressure refrigerant from the condenser during mid to later cycle operation and holds that overcharge during intermediate intervals of dry cycles. The charge thus stored is then injected back into the evaporator as the unit is restarted for the next selected dry cycle.
FIG. 13 presents refrigeration cycle elevation, in accordance with a non-limiting exemplary embodiment of the invention. By way of illustration, FIG. 13 depicts condenser 1302, condenser inlet 1304, condenser outlet 1306, alternate refrigerant path to storage cylinder be plumbing a “T” fitting 1308, and solenoid override flow valve 1310.
FIG. 14 presents start-up progressions, in accordance with a non-limiting example embodiment of the invention. Line 1404, line 1408 and line 1406 represent the total charge active in the system: the charge in the condenser is line 1406, the charge in the evaporator is line 1408, and line 1404 is the refrigerant flow rate in pounds-mass per hour. Line 1402 represents the refrigerant flow rate at the time or cycle conditions shown on the horizontal axis. The magnitude of flow rate is shown on the right vertical axis. In one or more embodiments of the invention, when charged, a system can be charged to almost two pounds. However, this is the working charge on the left axis that is actually in the heat exchangers, and so the rest of the charge is in the oil and in various other places in the system. These are the working charges, and in one or more embodiments of the invention, if the condenser is modified through the yellow peak line at the very beginning of the system, the system start-up can be accelerated. Consequently, one or more embodiments of the invention can inject approximately a pound-and-a-half of refrigerant into a system.
The sizing of the flask of the accumulator can be made by considering the desired end state of the condenser itself. If it is desirable to immediately place the amount of charge in the condenser to bring the pressure up to the pressures at the end of the start transient, then it follows that the working charge difference between the start and end of steady state is the amount to be injected. Accordingly, when the compressor starts, it is already facing the system at elevated pressures but at a low pressure ratio.
Also, because the evaporator already has the approximately correct charge, no mass injection is needed there. Rather, the condenser is in need of charge to raise the pressure, to liquid seal the expansion device and rapidly build system mass flow at desired pressures. It should be appreciated that this embodiment detailing that extra refrigerant could be taken-in in the condenser and returned to the condenser is merely one non-limiting example embodiment of the invention.
Consequently, one or more embodiments of the invention include injecting liquid refrigerant into the latter end of the condenser tubing in the vicinity of the expansion valve. This is also the point at which excess charge in liquid form may be harvested, as the excess charge begins to over press the condenser. Additionally, one or more alternate embodiments of the invention can include taking refrigerant in at the stated point but discharging at the inlet of the evaporator, bypassing the expansion device.
In one or more embodiments of the invention, the target steady state condensing pressure in a system for efficiency and to remain within certain system limits can be approximately 300 psi. As the compressor continues its work of moving refrigerant mass from the evaporator to the condenser, liquid can begin to back up at the expansion valve. Pressure will continue to build because the system has enough refrigerant to over-press the system, for example, to 350-400 psi. If the recovery valve pressure is set at 300 psi, by way of example, the system will begin bleeding liquid refrigerant from the face of the expansion valve into the relief flask.
Refrigerant harvested under such conditions will have a density of about 62.5 lb/ft3. According to FIG. 14, for example, the charge difference in the condenser between equilibrium start and the end of the start transient is about 0.175 lb. Therefore, the volume of the flask is calculated as follows:




  
    
      
        
          V
          WORKING
        
        =
        
        ⁢
        
          
            M
            STORED
          
          /
          
            ρ
            LIQUID
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          
            0.175
            /
            62.5
          
          *
          1728
          ⁢
          
            
          
          ⁢
          
            in
            3
          
          ⁢
          
            /
          
          ⁢
          
            ft
            3
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          4.85
          ⁢
          
            
          
          ⁢
          
            in
            3
          
        
      
    
  




In one or more embodiments of the invention, this could be the size of a flask to handle refrigerant from one of two condensers when running a split or parallel system in order to reduce pressure drop in the heat exchanger. Accordingly, expressed in terms of % of total charge, the calculation for percent of working charge (PWC) would be:




  
    
      
        PWC
        =
        
        ⁢
        
          
            M
            STORED
          
          /
          
            M
            
              TOTAL
              ⁢
              
                
              
              ⁢
              CHARGE
            
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          2
          ×
          0.175
          ×
          
            100
            /
            2.0
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          17
          ⁢
          %
        
      
    
  




Expressed in terms of % of working charge, the calculation is:




  
    
      
        PWC
        =
        
        ⁢
        
          
            M
            STORED
          
          /
          
            M
            
              WORKING
              ⁢
              
                
              
              ⁢
              CHARGE
            
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          2
          ×
          0.175
          ×
          
            100
            /
            
              (
              
                0.26
                ×
                2
              
              )
            
          
        
      
    
  
  
    
      
        =
        
        ⁢
        
          60
          ⁢
          %
        
      
    
  




If the flask is charged, for example, initially to about 80-100 psi with vapor refrigerant, the flask is ideally suited to receive enough charge during the over-press to provide the required amount of liquid back to the system when the valve is opened by solenoid during the start condition when the system is equalized at low pressure. The required flask oversize for this initial charge condition should be about 3%.
FIG. 15A and FIG. 15B present accumulator function data, in accordance with a non-limiting exemplary embodiment of the invention. The data depicted in FIG. 15A (as well as the descriptive labels spells out in FIG. 15B) can indicate, in part, the volume of the accumulator to hold a particular charge. Accordingly, in one or more embodiments of the invention, when the system comes up and reaches pressure, it will start pushing the excess charge into the accumulator for the start of the next run. Then, when the system shuts down, that refrigerant is trapped in the accumulator and pushed back in at the discharge end of the condenser at the start of the next cycle. Further, in one or more embodiments of the invention, the cylinder can have a capacity of about 10% of the overall charge.
FIG. 16 is a flow chart of a method for elevating a refrigeration cycle (for example, in a heat pump clothes dryer operating on a mechanical refrigeration cycle), in accordance with a non-limiting exemplary embodiment of the invention. Step 1602 includes collecting refrigerant during a run cycle when pressure exceeds a predetermined threshold value. Collecting refrigerant can include opening an inlet valve of a working fluid accumulator and collecting the refrigerant in the working fluid accumulator. Collecting refrigerant during a run cycle can continue for the entire run cycle.
Additionally, in one or more embodiments of the invention, collecting refrigerant includes preventing overcharging of a refrigerant system. Accordingly, an excessive amount of the refrigerant continues to bleed into the cylinder.
Step 1604 includes retaining the collected refrigerant when the run cycle is completed, until a subsequent run cycle. Retaining the collected refrigerant can include retaining the collected refrigerant in the working fluid accumulator.
Additionally, as described herein, in one or more embodiments of the invention, the working fluid accumulator can include a piston cylinder accumulator.
Step 1606 includes discharging the retained refrigerant to an evaporator or condenser when the subsequent run cycle is started. Discharging the retained refrigerant to an evaporator can include, for example, activating the piston cylinder accumulator, further wherein the piston pushes the refrigerant into the evaporator through a second valve of the piston cylinder accumulator. Also, discharging the retained refrigerant to an evaporator can additionally include raising density of the refrigerant and system pressure to a state point that includes a pressure band of a desired operating cycle.
Step 1608 includes using the discharged refrigerant to elevate the refrigeration cycle by modifying a start condition of the refrigeration cycle. Using the discharged refrigerant to elevate the refrigeration cycle can include facilitating a shorter startup transient via system expansion from equilibrium pressure when a compressor is turned on.
One advantage that may be realized in the practice of some embodiments of the described systems and techniques is modifying the cycle start condition by modifying the equilibrium density or specific volume of a refrigerant. Another advantage that may be realized in the practice of some embodiments of the described systems and techniques is implementing an accumulator (which can be, for example, of piston—cylinder arrangement) for storing the excessive refrigerant in a refrigeration cycle.
Further, given the discussion thus far, it will be appreciated that, in general terms, an exemplary apparatus, according to another aspect of the invention, includes a mechanical refrigeration cycle arrangement in turn having a working fluid and an evaporator 102, condenser 106, compressor 104, and an expansion device 108, cooperatively interconnected and containing the working fluid. The apparatus also includes a drum 258 to receive clothes to be dried, a duct and fan arrangement (e.g., 252, 256, 260, 262) configured to pass air over the evaporator 102, condenser 106 and through the drum 258, and a sensor (e.g., 110) located to sense at least one parameter. The at least one parameter includes temperature of the working fluid, pressure of the working fluid, and power consumption of the compressor. As detailed herein, the apparatus can also include a working fluid accumulator (which can include, by way of example, a piston cylinder accumulator). Also included is a controller 112 coupled to the sensor, accumulator and the compressor. The controller is preferably operative to carry out or otherwise facilitate any one, some, or all of the method steps described.
Aspects of the invention (for example, controller 112 or a workstation or other computer system to carry out design methodologies) can employ hardware and/or hardware and software aspects. Software includes but is not limited to firmware, resident software, microcode, etc. FIG. 17 is a block diagram of a system 1700 that can implement part or all of one or more aspects or processes of the invention. As shown in FIG. 17, memory 1730 configures the processor 1720 to implement one or more aspects of the methods, steps, and functions disclosed herein (collectively, shown as process 1780 in FIG. 17). Different method steps could theoretically be performed by different processors. The memory 1730 could be distributed or local and the processor 1720 could be distributed or singular. The memory 1730 could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. It should be noted that if distributed processors are employed (for example, in a design process), each distributed processor that makes up processor 1720 generally contains its own addressable memory space. It should also be noted that some or all of computer system 1700 can be incorporated into an application-specific or general-use integrated circuit. For example, one or more method steps (e.g., involving controller 112) could be implemented in hardware in an ASIC rather than using firmware. Display 1740 is representative of a variety of possible input/output devices. Examples of suitable controllers have been set forth above. Additionally, examples of controllers for heater control above can also be used for cycle completion. An example can include a micro with ROM storage of constants and formulae which perform the necessary calculations and comparisons to make the appropriate decisions regarding cycle termination.
As is known in the art, part or all of one or more aspects of the methods and apparatus discussed herein may be distributed as an article of manufacture that itself comprises a tangible computer readable recordable storage medium having computer readable code means embodied thereon. The computer readable program code means is operable, in conjunction with a processor or other computer system, to carry out all or some of the steps to perform the methods or create the apparatuses discussed herein. A computer-usable medium may, in general, be a recordable medium (e.g., floppy disks, hard drives, compact disks, EEPROMs, or memory cards) or may be a transmission medium (e.g., a network comprising fiber-optics, the world-wide web, cables, or a wireless channel using time-division multiple access, code-division multiple access, or other radio-frequency channel). Any medium known or developed that can store information suitable for use with a computer system may be used. The computer-readable code means is any mechanism for allowing a computer to read instructions and data, such as magnetic variations on a magnetic medium or height variations on the surface of a compact disk. The medium can be distributed on multiple physical devices (or over multiple networks). As used herein, a tangible computer-readable recordable storage medium is intended to encompass a recordable medium, examples of which are set forth above, but is not intended to encompass a transmission medium or disembodied signal.
The computer system can contain a memory that will configure associated processors to implement the methods, steps, and functions disclosed herein. The memories could be distributed or local and the processors could be distributed or singular. The memories could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term “memory” should be construed broadly enough to encompass any information able to be read from or written to an address in the addressable space accessed by an associated processor. With this definition, information on a network is still within a memory because the associated processor can retrieve the information from the network.
Thus, elements of one or more embodiments of the invention, such as, for example, the controller 112, can make use of computer technology with appropriate instructions to implement method steps described herein.
Accordingly, it will be appreciated that one or more embodiments of the present invention can include a computer program comprising computer program code means adapted to perform one or all of the steps of any methods or claims set forth herein when such program is run on a computer, and that such program may be embodied on a computer readable medium. Further, one or more embodiments of the present invention can include a computer comprising code adapted to cause the computer to carry out one or more steps of methods or claims set forth herein, together with one or more apparatus elements or features as depicted and described herein.
It will be understood that processors or computers employed in some aspects may or may not include a display, keyboard, or other input/output components. In some cases, an interface with sensor 110 is provided.
It should also be noted that the exemplary temperature and pressure values herein have been developed for Refrigerant R-134a; however, the invention is not limited to use with any particular refrigerant. For example, in some instances Refrigerant R-410A could be used. The skilled artisan will be able to determine optimal values of various parameters for other refrigerants, given the teachings herein.
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to exemplary embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. Moreover, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Furthermore, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

## Claims

1. A method comprising:
in a heat pump clothes dryer operating on a mechanical refrigeration cycle with a mechanical refrigeration cycle arrangement comprising an evaporator, a condenser, a compressor, and an expansion device, cooperatively interconnected and containing a refrigerant,
collecting a portion of the refrigerant from the mechanical refrigeration cycle arrangement into a working fluid accumulator during a run cycle when pressure exceeds a predetermined threshold value;
retaining the collected refrigerant in the working fluid accumulator when the run cycle is completed, until a subsequent run cycle;
discharging the retained refrigerant to the evaporator or the condenser when the subsequent run cycle is started; and
using the discharged refrigerant to elevate the mechanical refrigeration cycle by modifying a start condition of the mechanical refrigeration cycle.

2. The method of claim 1, wherein collecting a portion of the refrigerant comprises opening an inlet valve of the working fluid accumulator.

3. The method of claim 2, wherein the working fluid accumulator comprises a piston cylinder accumulator.

4. The method of claim 3, wherein discharging the retained refrigerant to the evaporator comprises activating the piston cylinder accumulator, and wherein a piston of the piston cylinder accumulator pushes the retained refrigerant into the evaporator through an outlet valve of the piston cylinder accumulator.

5. The method of claim 1, wherein collecting a portion of the refrigerant during a run cycle continues for the entire run cycle.

6. The method of claim 1, wherein discharging the retained refrigerant to the evaporator further comprises raising density of the refrigerant and system pressure to a state point that includes a pressure band of a desired operating cycle.

7. The method of claim 1, wherein using the discharged refrigerant to elevate the mechanical refrigeration cycle comprises facilitating a shorter startup transient via system expansion from equilibrium pressure when the compressor is turned on.

8. An apparatus comprising:
a mechanical refrigeration cycle arrangement in turn comprising:
a refrigerant; and
an evaporator, a condenser, a compressor, and an expansion device, cooperatively interconnected and containing the refrigerant;

a drum to receive clothes to be dried;
a duct and fan arrangement configured to pass air over said evaporator, condenser and through said drum;
a sensor located to sense at least one parameter;
a working fluid accumulator; and
a controller coupled to said sensor, said working fluid accumulator and said compressor, said controller being operative to control:
collection of a portion of the refrigerant into the working fluid accumulator during a run cycle when pressure exceeds a predetermined threshold value;
retention of the collected refrigerant when the run cycle is completed, until a subsequent run cycle;
discharge of the retained refrigerant to the evaporator or the condenser when the subsequent run cycle is started; and
use of the discharged refrigerant to elevate the refrigeration cycle by modifying a start condition of the refrigeration cycle.

9. The apparatus of claim 8, wherein in controlling collection of a portion of the refrigerant, the controller is further operative to open an inlet valve of the working fluid accumulator and collect the refrigerant in the working fluid accumulator.

10. The apparatus of claim 9, wherein in controlling retention of the collected refrigerant, the controller is further operative to retain the collected refrigerant in the working fluid accumulator.

11. The apparatus of claim 10, wherein the working fluid accumulator comprises a piston cylinder accumulator.

12. The apparatus of claim 11, wherein in controlling discharge of the retained refrigerant to the evaporator, the controller is further operative to activate the piston cylinder accumulator, wherein a piston of the piston cylinder accumulator pushes the refrigerant into the evaporator through a second valve of the piston cylinder accumulator.

13. The apparatus of claim 8, wherein in controlling collection of a portion of the refrigerant, the controller is further operative to controlling collection of a portion of the refrigerant during a run cycle for the entire run cycle.

14. The apparatus of claim 8, wherein in controlling discharge of the retained refrigerant to the evaporator, the controller is further operative to raise density of the refrigerant and system pressure to a state point that includes a pressure band of a desired operating cycle.

15. The apparatus of claim 8, wherein in controlling use of the discharged refrigerant to elevate the refrigeration cycle, the controller is further operative to facilitate a shorter startup transient via system expansion from equilibrium pressure when the compressor is turned on.

16. The apparatus of claim 11, wherein the piston cylinder accumulator collects and discharges the refrigerant alternately.

17. The apparatus of claim 11, wherein the piston cylinder accumulator comprises a piston, and two or more spring-loaded flow valves, wherein the piston is activated via at least one of mechanically and through a solenoid.

18. The apparatus of claim 17, wherein the two or more spring-loaded flow valves are controlled via at least one of mechanically and through one or more solenoids.

19. The apparatus of claim 17, wherein the two or more spring-loaded flow valves are connected to at least one of a high and low side plumbing of one or more heat exchanger sections of a refrigeration system as an inlet valve to a condenser outlet and a discharge valve to an evaporator inlet.