Patent Publication Number: US-8528227-B2

Title: Apparatus and method for refrigerant cycle capacity acceleration

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of, and claims priority to, U.S. patent application Ser. No. 12/843,148, filed Jul. 26, 2010 now U.S. Pat. No. 8,353,114, and entitled “Apparatus and Method for Refrigeration Cycle with Auxiliary Heating,” the disclosure of which is incorporated herein by reference. 
    
    
     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. 
     A challenge exists, however, in the inherent delay of the startup transient in heat pump dryers. 
     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 of operating a heat pump clothes dryer operating on a mechanical refrigeration cycle and comprising an auxiliary heater. The method includes enabling the auxiliary heater to provide an artificial load to an evaporator in the heat pump clothes dryer, wherein enabling the auxiliary heater to provide an artificial load to an evaporator comprises heating a supply of the evaporator, and using the artificial load provided to the evaporator to accelerate system capacity development of the heat pump clothes dryer. 
     Another aspect of the present invention relates to a method of operating a heat pump clothes dryer operating on a mechanical refrigeration cycle. The method includes partitioning all energy available in the heat pump clothes dryer into a first amount of energy and a second amount of energy, using the first amount of energy to attain a standard parameter performance for the heat pump clothes dryer, and using the second amount of energy to accelerate a dry cycle of the heat pump clothes dryer, wherein using the second amount of energy to accelerate a dry cycle of the heat pump clothes dryer comprises using the second amount of energy to energize or increase wattage of an auxiliary heater during a start transient phase of the dry cycle to decrease the start transient phase. 
     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; an auxiliary heater, and a duct and fan arrangement configured to pass air over the condenser and through the drum. The apparatus further comprises a sensor located to sense at least one parameter. The apparatus still further comprises a controller coupled to the sensor, the auxiliary heater and the compressor. The controller is operative to: enable the auxiliary heater to provide an artificial load to the evaporator, wherein enabling the auxiliary heater to provide an artificial load to the evaporator comprises heating a supply of the evaporator. 
     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; 
         FIG. 6  is a pressure-enthalpy diagram illustrating a basic vapor compression cycle is in thermal and mass flow balance until an external source causes the balance to be upset, in accordance with a non-limiting exemplary embodiment of the invention; 
         FIG. 7  is a pressure-enthalpy diagram illustrating temperature shift from auxiliary heating causes heat transfer imbalance and mass flow restriction in capillary resulting in capacity increase in evaporator, pressure elevation in condenser and mass flow imbalance, in accordance with a non-limiting exemplary embodiment of the invention; 
         FIG. 8  is a pressure-enthalpy diagram illustrating mass flow through compressor increases due to superheating resulting in further pressure increase in condenser, the dynamic transient is completed when condenser reestablished subcooling and heat flow balance at higher pressures and the net effect is higher average heat transfer during process migration, 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  is a flow chart of a method for accelerating refrigerant cycle capacity, in accordance with a non-limiting exemplary embodiment of the invention; 
         FIG. 11  is a flow chart of a method for accelerating a dry cycle, in accordance with a non-limiting exemplary embodiment of the invention; and 
         FIG. 12  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 
     Principles of the present invention include refrigerant cycle capacity acceleration by auxiliary heater.  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. 
       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&#39;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 , h f  and h g  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&#39;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 comes 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 cycled 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 refrigerant cycle capacity acceleration by auxiliary heater and/or or artificial load cycling. 
     One or more embodiments of the invention includes using an auxiliary heater (for example, a resistance heater) in a heat pump dryer to pre-load the evaporator and cause the system to more quickly accelerate to full capacity. One or more embodiments of the invention include providing a resistance heater of variable watts in the supply or return duct of the heat pump dryer. The resistance heater provides an artificial load to the evaporator by heating the supply of the evaporator. Accordingly, the return air constitutes a sensible load to the evaporator before the ability of the condenser to provide a sensible load or the clothes load to provide a latent psychrometric load. This causes the system to develop higher temperatures and pressures earlier in the run cycle, accelerating the onset of drying performance. 
     For a desired ending cycle of the heat pump dryer at an elevation that is above the normal air conditioning state points, a transient of cycle elevation can be quite long. However, in one or more embodiments of the invention, application of an auxiliary heater accelerates this transient. Additionally, if more watt inputs are supplied to the auxiliary heater, a relatively faster effective capacity and total system capacity can be developed. As a result, drying process is accelerated and drying time is reduced. 
     Accordingly, 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, thereby ameliorating the inherent delay of the startup transient. 
     A refrigeration system often runs in a cycling mode. In the off cycle, the system is allowed to come to equilibrium with its surroundings. Accordingly, a system placed in an ambient or room type environment will seek room temperature to be at equilibrium with the room. When the system is subsequently restarted, the condenser and evaporator will go in opposite directions from the equilibrium pressures and temperatures. Thus, the evaporator will go to a lower pressure/temperature and the condenser will seek a higher temperature/pressure. The normal end cycle straddles the equilibrium pressure and the steady state is reached quite quickly. 
     With the desired ending cycle for a heat pump dryer at a significant elevation above the normal air conditioning state points, the transient of cycle elevation can be quite long. The application of an external heater, as detailed herein (see, for example,  FIG. 2 ), accelerates that transient. As depicted in  FIGS. 2 ,  254  and  254 ′ are locations at which an auxiliary heater can be placed. In one or more additional embodiments of the invention, an auxiliary heater can also be placed between  106  and  252 . The observed effect is directly proportional to heater watts. That is, the more Watts input to the auxiliary heater, the faster the effective capacity and total system capacity is developed (see, for example,  FIG. 5 ). As such, the faster onset of effective capacity accelerates the drying process and reduces drying time. With the heater on, the system moves to a higher total average pressure and gets there faster. 
     In one or more embodiments of the invention, capacity, that is, the time it takes to get to any given capacity, is related to the (auxiliary) heater and the size of the heater. Refer to  FIG. 5 . Time is on the lower (X) axis and developed refrigeration system capacity is on the vertical (Y) axis, detailing how fast the use of the heater lets the refrigerant system generate heating and dehumidifying capacity. Recall that with the heater elevating the system operating point, it is possible to operate, for example, at 2-3 times the rated value. The wattage of the heater also determines how fast these extra-rated values can be obtained.  FIG. 5  illustrates the start-up curves versus time of developed capacity. With the heater in the system, it is possible to obtain more capacity faster by increasing the wattage. 
     By way of example, refer again to  FIG. 5 . Upper line  502  represents heater wattage plus compressor power added to heater power that is includes power than middle line  504 . Lower line  506  represents compressor power plus heater power that is less than middle line  504 , but also includes a time required to dry clothes that is too long. Center line  504 , in this example, represents an optimum: the shortest time at minimum power. In other words, for line  504 , power is lowest for a maximum acceptable time. Additionally, in one or more embodiments of the invention, use of different compressors and/or refrigerants will lead to different optimal lines. 
     As described herein, the drying cycle can be visualized in three segments or phases. The first segment is the startup transient; the second segment is the constant rate drying; the third segment is declining rate drying. Constant rate drying, the second segment, is typified by the compressor providing maximum flow rate and therefore maximum drying rate without heat assist within the performance limits of the compressor. To apply additional heat here could cause the compressor, for example, to over-temp and shut off with the overloads. Thus, this segment would likely not be improved with heat addition. 
     Declining rate drying is the phase where the clothes no longer have enough water to fully load the system. When thought of in terms of heat access to the water, it can be said, for example, that dry surface cloth “insulates” the water from receiving heat to vaporize. System symptoms of this behavior can include the latent load being reduced because of the availability of water vapor while the sensible load starting to drop with diminishing mass flow through the compressor. Accordingly, it may be possible to prop up the supply temperature with additional heat, maintaining higher heat input into the drum and maintaining water evaporation rate. 
     The first segment of the cycle, the start transient, can be, for example, approximately 30 minutes in duration and is characterized by slowly building temperatures and mass flow rates. As such, the capacity is building at the same slow rate as increases in mass flow and temperatures. Adding heat in this phase, as detailed herein, stimulates both temperature rise (and therefore system capacity) and water evaporation rate so that drying in this phase is accelerated. 
     One subsequent question becomes determining how much heat to add, as well as the heater size allowable within the energy standard. The follow depicts arithmetic used by taking the energy factor, subtracting it from the energy factor the standard requires, and dividing the remainder into the clothes (cloth) load, as detailed below.
 
 EF =CLOTH DRY WEIGHT /ENERGY TO DRY TO 4%  
 
Let
 
     F=EF 
     C=CLOTH WEIGHT    
     E=ENERGY TODRY    
     So
 
 F=C/E  
 
And
 
 E=C/F  
 
And:
 
                                                E A  = C/F A     ACTUAL           E S  = C/F S     STANDARD                        
Therefore
 
                           E   R     =       ⁢       E   S     -     E   A                   =       ⁢     C   ⁡     (       1   ⁢     /     ⁢     F   S       -     1   ⁢     /     ⁢     F   A         )                     =       ⁢       C   ⁡     (       F   S     -     F   A       )       /     (       F   S     ⁢     F   A       )         ,               RESIDUAL             
where E R  is the residual or additional energy that can be used for drying and remain within the standard allowance. As used and detailed herein, the “standard” is that parameter established by law or rule from a regulating entity. The “actual” is the level attained in the manufactured or prototype unit.
 
     If, for example, all of the residual energy is used to accelerate drying, the start transient can be decreased, allowing the system to build capacity faster. By way of example, increasing the wattage from an original 700 watts to 1200 watts until the protection limit of the compressor was reached would reduce the time until the limit was reached, accelerating the drying time by a proportional amount. A numerical example, by way simply of illustration and not limitation, can include the following. 
     Assume that the standard called for a minimum energy factor (EF) of 4.3 and that the actual system were shown to be capable of EF=5.5. This means that the dryer uses: 
     
       
         
           
             
               E 
               R 
             
             = 
             
               
                 
                   7 
                   ⁢ 
                   
                     ( 
                     
                       5.5 
                       - 
                       4.3 
                     
                     ) 
                   
                   ⁢ 
                   lb 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   lb 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       ( 
                       kWhr 
                       ) 
                     
                     2 
                   
                 
                 
                   
                     ( 
                     
                       5.5 
                       * 
                       4.3 
                     
                     ) 
                   
                   ⁢ 
                   
                     lb 
                     2 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   kWhr 
                 
               
               = 
               
                 .355 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 kWhr 
               
             
           
         
       
     
     With this power, the following analysis can be performed with respect to the heater: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Additional 
                   
                 Total heating 
                 Approximate 
               
               
                   
                 heating 
                 Duration 
                 watts 
                 time reduction 
               
               
                   
                   
               
             
            
               
                   
                  355 W 
                 60 min 
                 — 
                 — 
               
               
                   
                  800 W 
                 26 min 
                 693 Whr 
                  5 min 
               
               
                   
                 1000 W 
                 21 min 
                 630 Whr 
                 10 min 
               
               
                   
                 1200 W 
                 17 min 
                 567 Whr 
                 12 min 
               
               
                   
                   
               
            
           
         
       
     
     One advantage that may be realized in the practice of some embodiments of the described systems and techniques is placing an auxiliary heater in the supply air duct or return air duct of a heat pump clothes dryer to reducing the drying time of the heat pump clothes dryer. 
     Reference should now be had to the flow chart of  FIG. 10 .  FIG. 10  is a flow chart of a method for accelerating refrigerant cycle capacity, in accordance with a non-limiting exemplary embodiment of the invention. Step  1002  includes providing an auxiliary heater in the heat pump clothes dryer. The auxiliary heater can be located, for example, in a supply duct and/or in a return duct of the heat pump clothes dryer. 
     Step  1004  includes enabling the auxiliary heater to provide an artificial load to an evaporator in the heat pump clothes dryer, wherein enabling the auxiliary heater to provide an artificial load to an evaporator comprises heating a supply of the evaporator. Enabling the auxiliary heater to provide an artificial load to an evaporator can additionally include providing a sensible load, via return air, to the evaporator before a condenser in the heat pump clothes dryer provides at least one of a sensible load and a clothes load to provide a latent psychrometric load. 
     Step  1006  includes using the artificial load provided to the evaporator to accelerate system capacity development of the heat pump clothes dryer. Using the artificial load to accelerate system capacity development can additionally include causing the heat pump clothes dryer to develop higher temperatures and pressures earlier in a run cycle, accelerating onset of drying performance. Further, using the artificial load provided to accelerate system capacity development can also include accelerating the drying process of the heat pump clothes dryer as well as reducing drying time. 
     The techniques depicted in  FIG. 10  can additionally include determining an amount of heat to provide to the evaporator via the artificial load. In one or more embodiments of the invention, determining the amount of heat to provide can include subtracting an actual energy factor from a standard-required energy factor, and dividing the difference into a clothes load weight amount. 
       FIG. 11  is a flow chart of a method for accelerating a dry cycle, in accordance with a non-limiting exemplary embodiment of the invention. Step  1102  includes partitioning all energy available in the heat pump clothes dryer into a first amount of energy and a second amount of energy. Step  1104  includes using the first amount of energy to attain a standard parameter performance for the heat pump clothes dryer. In one or more embodiments of the invention, the second amount of energy can include all remaining energy not needed for the first amount of energy. 
     Step  1106  using the second amount of energy to accelerate a dry cycle of the heat pump clothes dryer, wherein using the second amount of energy to accelerate a dry cycle of the heat pump clothes dryer comprises using the second amount of energy to increase wattage of an auxiliary heater during a start transient phase of the dry cycle to decrease the start transient phase. Using the second amount of energy to increase wattage of an auxiliary heater during a start transient phase of the dry cycle to decrease the start transient phase can further include enabling capacity to build more quickly in the heat pump clothes dryer. Further, as detailed herein, the auxiliary heater can be located, for example, in the supply duct or return duct of the heat pump clothes dryer. 
     Additionally, in one or more embodiments of the invention, using the second amount of energy to increase wattage of an auxiliary heater during a start transient phase of the dry cycle to decrease the start transient phase can include enabling the auxiliary heater to provide an artificial load to an evaporator in the heat pump clothes dryer. 
     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, an auxiliary heater (e.g.,  254  or  254 ′), a duct and fan arrangement (e.g.,  252 ,  256 ,  260 ,  262 ) configured to pass air over the 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. Also included is a controller  112  coupled to the sensor, the auxiliary heater and the compressor. The controller is preferably operative to carry out or otherwise facilitate any one, some, or all of the method steps described. For example, the controller is operative to enable the auxiliary heater to provide an artificial load to the evaporator, wherein enabling the auxiliary heater to provide an artificial load to the evaporator comprises heating a supply of the evaporator. 
     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. 12  is a block diagram of a system  1200  that can implement part or all of one or more aspects or processes of the invention. As shown in  FIG. 12 , memory  1230  configures the processor  1220  to implement one or more aspects of the methods, steps, and functions disclosed herein (collectively, shown as process  1280  in  FIG. 12 ). Different method steps could theoretically be performed by different processors. The memory  1230  could be distributed or local and the processor  1220  could be distributed or singular. The memory  1230  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  1220  generally contains its own addressable memory space. 
     It should also be noted that some or all of computer system  1200  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 application-specific integrated circuit (ASIC) rather than using firmware. Display  1240  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.