Vapor compression circuit controller

Abstract

 A method of starting a vapor compression system includes receiving an indication of a start-up of the vapor compression system, loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up, and running the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

Description

Background

[0001] Vapor compression circuits are generally used in devices transporting heat from low temperature reservoirs (e.g. outdoor air) to high temperature reservoirs (e.g. hydronic heating water) by using mechanical and/or electrical energy input. Typical examples are heat pumps, refrigerators and air-conditioners ranging from household units to sophisticated industrial sized devices. The objective of the vapor compression circuits design and control is to transport the heat with the highest efficiency. This efficiency can be characterized by a ratio of transported heat to overall mechanical and/or electrical energy consumption (e.g. compressor electric power consumption). This ratio is for example denoted as the Coefficient Of Performance (COP) for heat pumps.

[0002] During start-up of a typical vapor compression device, the system manipulated variables are maintained at fixed, conservative values for a fixed time period. The objective of start-up procedure is to introduce a degree of superheat to the refrigerant circuit, crucial for safe operation, as quickly as possible. A significant limitation of existing start-up procedures is that, due to the conservative values of manipulated variables and time period, large overshoot/undershoot in the controlled variables can be observed after the start-up phase. This leads to reduced system efficiency and indeed reduced system stability.

Summary

[0003] A method of starting a vapor compression system includes receiving an indication of a start-up of the vapor compression system, loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up, and running the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

[0004] A machine readable storage device having instructions for execution by a processor of the machine to perform a method of starting a vapor compression system, the method including receiving an indication of a start-up of the vapor compression system, loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up, and running the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

[0005] A controller for a vapor compression system, the controller including a processor and a memory device coupled to the processor and having a program stored thereon for execution by the processor. The program causes the processor to receive an indication of a start-up of the vapor compression system, load a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up, and run the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

Brief Description of the Drawings

[0006] 

FIG. 1 is a graph illustrating a typical trajectory of a vapor compression circuit manipulated variable during start-up of a vapor compression circuit according to an example embodiment.

FIGs. 2A and 2B are graphs illustrating undershoot/overshoot observable in controlled variables after a start-up phase has finished according to an example embodiment.

FIG. 3A illustrates an interface for setting manipulated variables according to an example embodiment.

FIGs. 3B, 3C, and 3D graphically illustrate the effect of manipulated variable settings on controlled variables according to an example embodiment.

FIGs. 4A and 4B illustrate an example of an optimized vapor compression circuit start-up according to an example embodiment.

FIG. 5 is a block flow diagram illustrating a vapor compression circuit according to an example embodiment.

FIG. 6 is a flowchart illustrating a method of starting a system including vapor compression circuit according to an example embodiment.

FIG. 7 is a flowchart illustrating a method of providing an interface to an operator for modifying manipulated variables and providing graphical representations of the response of the vapor compression system calculated from the calibrated models according to an example embodiment.

FIG. 8 is a schematic block diagram of an advanced architecture for controlling a vapor compression circuit according to an example embodiment.

FIG. 9 is a schematic block diagram of a model predictive controller according to an example embodiment.

FIG. 10 is a schematic block diagram of an inferential sensor according to an example embodiment.

FIG. 11 is a schematic block diagram of open loop operation of a heat pump having a vapor compression circuit according to an example embodiment.

FIG. 12 is a block diagram illustrating processing circuitry to perform methods according to example embodiments.

Detailed Description

[0007] In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.

[0008] The functions or algorithms described herein may be implemented in software or a combination of software and human implemented procedures in one embodiment. The software may consist of computer executable instructions stored on computer readable media such as memory or other type of hardware based storage devices, either local or networked. Further, such functions correspond to modules, which are software, hardware, firmware or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, ASIC, microprocessor, or other type of processor.

[0009] Vapor compression circuits are generally used in devices transporting heat from low temperature reservoirs (e.g. outdoor air) to high temperature reservoirs (e.g. hydronic heating water) by using mechanical and/or electrical energy input. Typical examples are heat pumps, refrigerators and air-conditioners ranging from household units to sophisticated industrial sized devices. The objective of the vapor compression circuits design and control is to transport the heat with the highest efficiency. This efficiency can be characterized by a ratio of transported heat to overall mechanical and/or electrical energy consumption (e.g. compressor electric power consumption). This ratio is for example denoted as the Coefficient Of Performance (COP) for heat pumps.

[0010] During start-up of a typical vapor compression device, the system manipulated variables are maintained at fixed, conservative values for a fixed time period in a controller. The objective of the start-up procedure is to introduce a degree of superheat to the refrigerant circuit, crucial for safe operation, as quickly as possible. A significant limitation of existing start-up procedures is that, due to the conservative values of manipulated variables and time period, large overshoot/undershoot in the controlled variables can be observed after the start-up phase. This leads to reduced system efficiency and indeed reduced system stability. One problem recognized by the inventors is how to effectively initialize the start-up manipulated variables, such that a vapor compression device obtains a sufficient degree of superheat as quickly as possible, while at the same time maintaining control variables within acceptable tolerances after the start-up phase has finished.

[0011] In various embodiments, additional logic in a compression cycle controller uses pre-computed optimized values for each manipulated variable during a start-up phase. The use of such pre-computed optimized values during the start-up phase results in the controlled variable being brought close to their references, while at the same time, ensuring that a sufficient degree of superheat is present as quickly as possible. In one embodiment, the pre-computed optimized values for each manipulated variable may be obtained by a multivariable model based control and optimization algorithm.

[0012] An example of a typical trajectory 100 of a vapor compression circuit manipulated variable (in this case Electronic Expansion Valve position (EEV)) is given in graph form in FIG. 1. The EEV valve position is shown as a percent open position versus time.

[0013] A consequence of this conservative manipulated variable setting is that large undershoot/overshoot can be observed in the controlled variables after the start-up phase has finished. This leads to a reduction in overall system efficiency and indeed stability. A typical example of this effect is shown FIGs. 2A and 2B. FIG. 2A illustrates at 200 the percentage of EEV valve position versus time, while 2B shows at 210, a controlled variable (CV) superheat (SH) in degrees versus time. In an effort to quickly provide superheat, the percentage of the valve position is initially set high at 215 (greater than 60%) for a very short period of time, then lowered at 220 to 30%, then jumped back at 225 to above 50%, and then stepped down at 230, and gradually increased at 235 to a steady state of about 45%, indicated at 240. The superheat controlled variable is indicated by line 245, and overshoots a reference temperature setting 250 and does not settle to the reference for over 500 seconds in this example.

[0014] In order to start-up a VCC device in a fast, efficient and reliable way, a set of calibrated models of the VCC device under consideration may be utilized. In one embodiment, a graphical user interface (GUI), such as seen in FIGs. 3A, 3B, 3C, and 3D may be used to obtain values for the manipulated variables corresponding to the desired operating point (Heat Rate and Degree of Superheat) considering the given ambient conditions (Inlet Water Temperature, Outdoor Air Temperature).

[0015] In FIG. 3A at 300, user settable slide bars are shown for compressor speed, fan speed, pump speed, expansion valve percentage open, refrigerant charge in kg, air temperature in °C, water temperature and °C, and a receiver on/off. These re example manipulated variables that may be used by a user in conjunction with one or more models of the VCC to determine optimized values for start-up. Effects of different settings of the manipulated variables are shown in FIGs. 3B, 3C, and 3D. At 310 in FIG. 3B a graph of pressure versus specific enthalpy in a VCC cycle is illustrated. Saturation curves 315, isotherms, 320, inlet air isotherm 325, and inlet water isotherm 330 are illustrated. Different portions of the vapor compression cycle are illustrated by the four dots with lines extending between them. Line 335 corresponds to condensation, line 340 corresponds to a throttling valve, line 345 corresponds to evaporation, and line 350 corresponds to the refrigerant moving through the compressor.

[0016] FIG. 3C at 355 illustrates effects of the changes to manipulated variables on the evaporator in a temperature versus relative position of the evaporator. Refrigerant is illustrated at 357, air/water at 360, saturation at 362, inlets are shown at 365, and outlets at 367.

[0017] FIG. 3D at 370 illustrates condenser temperature versus relative position. Refrigerant is illustrated at 372, air/water at 375, saturation at 377, inlets are shown at 380, and outlets at 382.

[0018] An example of an optimized VCC startup is shown 400 in FIG. 4A and at 410 in FIG. 4B. EEV is constant as show by line 415. The superheat is illustrated by line 420 which reaches a reference value 425 within 100 seconds. A simple comparison with the existing method, shown in FIG. 2A and 2B demonstrates the improved efficiency of the optimized VCC startup method. The speed of start-up is improved four-fold in this example. Other examples may have different results. Similarly, an overshoot of approximately 10K is observed in the example of typical start-up behavior, whereas the optimized start-up behavior displays little-to-no overshoot.

[0019] A vapor compression circuit 500 is illustrated in block flow form in FIG. 5. Vapor compression circuit 500 in one embodiment is constructed of multiple components, and may operate as an advanced heat pump. A refrigerant is used in the circuit 500 and may be stored in a refrigerant receiver tank 510. The refrigerant is sent through an electronically controlled expansion valve 515 that expands the refrigerant into gas form, and in the process, lowering the temperature of the refrigerant. Expansion valves each have a controllable position which is used to control the amount of expansion of a fluid passing through the valves. The cooled refrigerant than progresses through an evaporator 520 having a fan 525 controlled via a fan speed normally expressed in rotations per minute to cool air moving past evaporator heat exchanger surface.

[0020] The process of flowing air past the heat exchanger surface also raises the temperature of the refrigerant, which is then compressed via a modulating compressor 530 having a controllable speed, which may have enhanced vapor injection. The compressed refrigerant is then sent to a condenser 535. The condenser 535 may be coupled to transfer heat between the condenser 535 and water from a hydronic heating system 537 via a water pump 540 having a controllable pump speed, and return line 541. The refrigerant at this point may be mostly in liquid form, and is collected in receiver tank 510.

[0021] A second electronically controlled thermal expansion valve 545 may also be coupled to the refrigerant receiver tank, and be used to cool the compressor 530 in some embodiments. A filter dryer may also be included as indicated at 550 between the receiver tank 510 and expansion valves 515 and 545. An internal heat exchanger indicated at 555 may also be placed following each of the expansion valves 515, 545 in some embodiments. Check valves indicated at 560 and 565 may also be used to control the flow of refrigerant.

[0022] In further embodiments, a suction line accumulator 570 may be placed between the evaporator 520 and compressor 530. A four way valve 575 may also be used to route refrigerant between the evaporator, compressor, and condenser.

[0023] A controller 580 may be coupled to multiple of the above components to control the components and overall operation of the circuit 500 to optimized efficiency. Circuit 500 provides for efficient operation on multiple load levels and under changing conditions. A higher seasonal (overall) efficiency may be obtained for heat pumps such as circuit 500 by using modulating components (modulating compressor, digital compressor, evaporator with modulating fan, electronic expansion valves, modulating hydronic pump, and sophisticated components such as modulating compressors with an Enhanced Vapor Injection (EVI compressor).

[0024] The heat transport efficiency is mainly determined by the quality of the components (mechanical, electrical and heat losses), but also by the performance of control and optimization strategy with respect to the actual load level (e.g. heat demand) and operation conditions. A typical vapor compression circuit control configuration has an independent Single Input and Single Output (SISO) control loop for each modulating component.

[0025] Current SISO control strategies utilized for individual components are not able to fully utilize the additional degrees of freedom for energy efficiency optimization provided by the modulating components. Such individual component based control cannot achieve and keep maximum energy efficiency under variable load and disturbances such as outdoor air temperature and humidity change, evaporator icing, and return hydronic water temperature change when the circuit 500 is operating as a heat pump.

[0026] The individual control loops in one embodiment are replaced by a multivariable controller 580 that covers the interactions between individual manipulated variables. Model-based predictive control (MPC) technology with embedded steady-state values optimization can be used to cover the required functionality.

[0027] The controller 580 in one embodiment collects sensor data from all available sensors, which may typically be very limited. Typical sensors may include temperature sensors and pressure sensors. Example sensors include pressure and temperature sensor 581 coupled between tank 510 and check valves 565, temperature sensor 582 coupled to sense air temperature entering evaporator 520, temperature sensor 583 coupled to return line 541, pressure and temperature sensor 584 coupled between heat exchanger 555 and compressor 530, and pressure and temperature sensor 585 coupled between four way valve 585 and suction line accumulator 570. The sensors are coupled in a wired or wireless manner to provide data representative of sensed parameters to controller 580. Additional or fewer sensors may be used in further embodiments.

[0028] The sensor data can be processed by Kalman filters to estimate the current state of the vapor compression circuit and unmeasurable disturbances. The state and the disturbances are used by the controller acting as an optimizer to determine modulating component set-points with the highest overall efficiency under current load and conditions. The set-points are supplied to the multivariable controller 580 (e.g. model predictive controller), which keeps the set-points while eliminating the influence of disturbances and model uncertainty by feedback control action.

[0029] Controller 580 may utilize many different model types and control theories in various embodiments. The creation of a simplified mathematical model of a controlled technology is generally the first step in control system monitoring, diagnostics, or real time optimization system design. Most reliable models are obtained from the first principles: mechanical, thermodynamic, chemical, and other laws. Such models naturally obey the mass or energy conservation laws, etc. Any such law imposes additional constraint on the identification problem thus eliminating uncertainty of the problem (often equivalent to the number of unknowns). Consequently, first principle models can be calibrated using smaller data sets compared to the data sets required for purely empirical black box models (i.e. a model of a system for which there is no a priori information available).

[0030] Typically, the first principle models exhibit greater prediction error towards the data set used for the calibration when compared to the black box models. But the opposite is usually true when comparing the model prediction accuracy on a data set not used for the calibration (i.e. extrapolating the model behavior further from the calibration data). Models derived from the first principles can still have a number of unknown parameters. To identify their values is called the "grey box identification problem" (to distinguish it from the black box identification, where the model structure is arbitrary and not derived from the physical laws).

[0031] There are two approaches to the grey box model identification of complex large scale nonlinear problems (where the problem size quickly grows with a number of blocks and a number of operating points), a local method and a global method. Utilizing the local method, individual components, blocks or subsystems in the block diagrammatic representation of circuit 500 are fitted separately using their local input and output data, whereas in the global method all components are fitted simultaneously while always evaluating the predictions of the whole system. The global method can begin with local identification and then use the results as the initial condition for the global method.

[0032] There are advantages to both approaches. For example, the local method may have better convergence properties while the global method may be statistically more efficient. In one embodiment, a method combines advantages of both in addition to providing additional benefits.

[0033] In creating a block diagram to describe a control system, the component or subsystem parameters are usually fitted individually to their input and output data. Such component level calibration is not optimal and does not utilize all the information content in the measurements. To illustrate this assertion, model calibration can be represented as a general constrained optimization problem wherein a signal link connecting diagram blocks represents an equality constraint and the value produced by a block equals value accepted by other block. These constraints can be referred to as "structural constraints". In the Cartesian product of parameters and signals, the probability is zero at points which violate the structural constraints.

[0034] Controller 580 in one embodiment includes an optimized model-based start-up algorithm. The controller 580, when an ON request is received, initializes each available manipulated variable to values calculated using a calibrated model of the vapor compression device. This ensures that the desired operating conditions are achieved in a safe, fast and reliable manner. It some embodiments, the optimized start-up procedure may be integrated into a multivariable heat pump controller. Note that the start-up algorithm bypasses closed loop feedback control in one embodiment, and then transitions to normal control algorithms once start-up is achieved.

[0035] FIG. 6 is a flowchart illustrating a method 600 of starting a system including vapor compression circuit according to an example embodiment. At 610, an indication of a start-up of the vapor compression circuit is received. This may occur when a work shift first starts, following maintenance of vapor compression circuit, or any other time that the vapor compression circuit needs to be started. At 620, a set of start-up manipulated variables is loaded into a controller. The start-up manipulated variables may be derived using calibrated models of the vapor compression system during start-up along with a user interface to test various manipulated variable effects on the start-up given different environmental conditions.

[0036] At 630, the vapor compression circuit is run in open loop control using the start-up manipulated variables for a fixed period of time. The fixed period of time may be determined for each vapor compression circuit based on the models used and operator experience, but basically corresponds to when the vapor compression circuit has started to run and reached a steady state such that normal closed loop control of the circuit may occur without significant instability. Once the fixed period expires, the vapor compression circuit is run at 640 in closed loop feedback control.

[0037] In one embodiment, start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up. The controlled variables may be kept within acceptable tolerances after the fixed period of time.

[0038] In further embodiments, a method 700 provides an interface to an operator, wherein the interface provides a mechanism to manipulate the manipulated variables and provide graphical representations of the response of the vapor compression system calculated from the calibrated models. At 710, a graphical user interface having user modifiable settings for manipulated variables such as compressor speed, fan speed, pump speed, expansion valve percent open, and refrigerant charge is provided to the user. The graphical user interface may also have settings for environmental parameters.

[0039] User changes to the manipulated variables may be accepted at 720 and processed via calibrated models to determine their effect on controlled variables. At 730, the interface illustrates pressure versus specific enthalpy for a vapor compression circuit cycle, including a saturation curve and multiple isotherms relative to manipulated variable settings. At 740, the interface illustrates temperature and relative position of an evaporator relative to manipulated variable settings. At 750, the interface illustrates temperature and relative position of a condenser relative to manipulated variable settings. An operator may continue to adjust settings at 720, resulting in the illustrations of 730-750 changing to reflect the new settings.

[0040] An alternative to the GUI interface for optimizing manipulated variables for use in start-up is described with references to FIGs. 8, 9, 10, and 11.

[0041] A schematic of an advanced control architecture for optimal year round performance of a heat pump utilizing a vapor compression circuit is illustrated in block form at 800 in FIG. 8. The architecture 800 may include a set-point optimizer 810, model predictive controller 820, inferetial sensor 830 and regulatory control PID (proportional-integral-derivative) 840. A heat pump is indicated at 850 coupled to the inferential sensor 830 and control 840.

[0042] A block schematic diagram of the model predictive controller 820 is shown further detail at 900 in FIG. 9. Set-point optimizer 810 computes an optimal operating point for heat demand (or supply water temperature) which minimizes total power consumption, satisfies component constraints 910 (compressor envelope, temperature limits etc), and which can be reached by manipulated variables (MVs) such as compressor speed, evaporator fan speed, condenser pump speed and electronic expansion valve. External conditions such as ambient air temperature and humidity and return water temperature may be given as inputs, as well as observable disturbances 920 such as evaporator fouling due to frost formation. The setpoint optimizer 810 uses a set of precomputed tables (based on computationally intensive offline optimization using high fidelity calibrated component models) in combination with on-line adaption.

[0043] The model predictive controller 820 performs the task of operating point realization (as delivered by the set-point optimizer 810) and disturbance rejection (such as model discrepancy, oscillation attenuation). The model predictive controller 820 also performs transient control 930 due to step changes in e.g. supply water temperature. Due to the highly non linear behaviour of a vapour compression cycle, this is designed as a switched linear MPC utilizing a feedforward mechanism indicated at 940.

[0044] The inferential sensor 830 is shown in a high level schematic form at 1000 in FIG. 10, and provides online estimation of the evaporator fouling due to frost formation 1005. Frost formation significantly degrades overal system performance through increase of thermal resistance on evaporator coil and decrease of heat transfer due through blockage of the air free flow area. Frost formation, while not directly measurable, is observable from measurements 1010 of evaporator efficiency (evaporating temperature) and evaporator fan power consumption. A Kalman filter, based on statistical inference, may be used to provide on-line estimates of the current state of evaporator fouling. This is in turn used by the Set-Point Optimizer 810 and the Model Predictive Controller 820.

[0045] Ubiquitous in industrial control, the task of the regulatory control is to variables with fast dynamics (e.g. evaporator superheat). The fast control loop is integrated in the overall control architecture.

[0046] During startup, the heat pump 850 is operated in an open-loop condition as indicated in FIG. 11. The set-point optimizer 810 sends, directly to the heat pump 850 via line 1110, a set of MVs as calculated based on the desired operating conditions. The quality of the calculated MVs with respect to the desired operating condition is completely dependent on the fidelity of the component models used in the set-point optimizer 810. The start-up phase is deemed completed when either a fixed timer expires, or a target threshold of controlled variable to reference is reached. This is configurable by the user. Once the conditions are fulfilled for completion of start-up, the system reverts to the structure in FIG. 8, and closed loop control is activated.

[0047] FIG. 12 is a block schematic diagram of a computer system 1200 to implement a controller according to an example embodiment. The controller 580 may be implemented using fewer components than shown in FIG. 12 as may be typically found in process control facilities. One example computing device in the form of a computer 1200, may include a processing unit 1202, memory 1203, removable storage 1210, and non-removable storage 1212. Memory 1203 may include volatile memory 1214 and non-volatile memory 1208. Computer 1200 may include - or have access to a computing environment that includes - a variety of computer-readable media, such as volatile memory 1214 and non-volatile memory 1208, removable storage 1210 and non-removable storage 1212. Computer storage includes random access memory (RAM), read only memory (ROM), erasable programmable read-only memory (EPROM) & electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD ROM), Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing computer-readable instructions. Computer 1200 may include or have access to a computing environment that includes input 1206, output 1204, and a communication connection 1216. The computer may operate in a networked environment using a communication connection to connect to one or more remote computers, such as database servers. The remote computer may include a personal computer (PC), server, router, network PC, a peer device or other common network node, or the like. The communication connection may include a Local Area Network (LAN), a Wide Area Network (WAN) or other networks.

[0048] Computer-readable instructions stored on a computer-readable medium are executable by the processing unit 1202 of the computer 1200. A hard drive, CD-ROM, and RAM are some examples of articles including a non-transitory computer-readable medium. For example, a computer program 1218 capable of providing a generic technique to perform access control check for data access and/or for doing an operation on one of the servers in a component object model (COM) based system may be included on a CD-ROM and loaded from the CD-ROM to a hard drive. The computer-readable instructions allow computer 1200 to provide generic access controls in a COM based computer network system having multiple users and servers.

Examples:

[0049] 

1. A method of starting a vapor compression system, the method comprising:

receiving an indication of a start-up of the vapor compression system;

loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

running the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

2. The method of claim 1 and further comprising following the start-up period of time, running the vapor compression system in closed loop feedback control.

3. The method of any of claims 1-2 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up.

4. The method of claim 3 wherein controlled variables are kept within acceptable tolerances after the fixed period of time.

5. The method of any of claims 1-4 and further comprising ending the start-up period of time after a fixed period of time.

6. The method of any of claims 1-3 and further comprising:

measuring a controlled variable; and

ending the start-up period of time when the measured controlled variable reaches a reference value.

7. The method of any of claims 1-6 wherein the manipulated variables include compressor speed, evaporate fan speed, condenser pump speed, and electronic expansion valve setting.

8. The method of claim 7 and further comprising sensing external conditions and wherein the start-up manipulated variables are further derived from the sensed external conditions.

9. The method of claim 8 wherein the sensed external conditions include ambient air temperature and humidity.

10. The method of any of claims 7-9 and further comprising sensing an observable disturbance including frost formation.

11. A machine readable storage device having instructions for execution by a processor of the machine to perform a method of starting a vapor compression system, the method comprising:

receiving an indication of a start-up of the vapor compression system;

loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

running the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

12. The machine readable storage device of claim 11 wherein the method further comprises following the start-up period of time, running the vapor compression system in closed loop feedback control.

13. The machine readable storage device of any of claims 11-12 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up.

14. The machine readable storage device of claim 13 wherein the start-up period of time is a fixed period of time.

15. The machine readable storage device of claim 13 wherein the start-up period of time ends when a controlled variable reaches a reference value.

16. The machine readable storage device of claim 15 wherein the manipulated variables include compressor speed, evaporate fan speed, condenser pump speed, and electronic expansion valve setting.

17. The machine readable storage device of claim 16 wherein the start-up manipulated variables are further derived from the sensed external conditions including air temperature and humidity.

18. A controller for a vapor compression system, the controller comprising:

a processor; and

a memory device coupled to the processor and having a program stored thereon for execution by the processor to:

receive an indication of a start-up of the vapor compression system;

load a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

run the vapor compression system in open loop control using the start-up manipulated variables for a start-up period of time.

19. The controller of claim 18 wherein the program further causes the processor to, following the start-up period of time, run the vapor compression system in closed loop feedback control.

20. The controller of any of claims 18-19 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up, and wherein controlled variables are kept within acceptable tolerances after the start-up period of time.

[0050] Although a few embodiments have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Other embodiments may be within the scope of the following claims.

Claims

1. A method of starting a vapor compression system, the method comprising:

receiving an indication of a start-up of the vapor compression system;

loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

running the vapor compression system in open loop control using the start-up manipulated variables for a fixed period of time.

2. The method of claim 1 and further comprising following the fixed period of time, running the vapor compression system in closed loop feedback control.

3. The method of claim 1 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up.

4. The method of claim 3 wherein controlled variables are kept within acceptable tolerances after the fixed period of time.

5. The method of any one of claims 1-4 and further comprising providing an interface to an operator, wherein the interface provides a mechanism to manipulate the manipulated variables and provide graphical representations of the response of the vapor compression system calculated from the calibrated models.

6. The method of claim 5 wherein the interface comprises a graphical user interface having user manipuable settings for compressor speed, fan speed, pump speed, expansion valve percent open, and refrigerant charge and wherein the interface further comprises settings for environmental parameters.

7. The method of claim 5 wherein the interface illustrates pressure versus specific enthalpy for a vapor compression circuit cycle, including a saturation curve and multiple isotherms relative to manipulated variable settings, illustrates temperature and relative position of an evaporator relative to manipulated variable settings, and illustrates temperature and relative position of a condenser relative to manipulated variable settings.

8. A machine readable storage device having instructions for execution by a processor of the machine to perform a method of starting a vapor compression system, the method comprising:

receiving an indication of a start-up of the vapor compression system;

loading a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

running the vapor compression system in open loop control using the start-up manipulated variables for a fixed period of time.

9. The machine readable storage device of claim 8 wherein the method further comprises following the fixed period of time, running the vapor compression system in closed loop feedback control.

10. The machine readable storage device of claim 8 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up and wherein controlled variables are kept within acceptable tolerances after the fixed period of time.

11. The machine readable storage device of claim 8 wherein the method further comprises providing an interface to an operator, wherein the interface provides a mechanism to manipulate the manipulated variables and provide graphical representations of the response of the vapor compression system calculated from the calibrated models.

12. The machine readable storage device of claim 11 wherein the interface comprises a graphical user interface having user manipuable settings for compressor speed, fan speed, pump speed, expansion valve percent open, refrigerant charge and settings for environmental parameters, and illustrates pressure versus specific enthalpy for a vapor compression circuit cycle, including a saturation curve and multiple isotherms relative to manipulated variable settings, illustrates temperature and relative position of an evaporator relative to manipulated variable settings, and illustrates temperature and relative position of a condenser relative to manipulated variable settings.

13. A controller for a vapor compression system, the controller comprising:

a processor; and

a memory device coupled to the processor and having a program stored thereon for execution by the processor to:

receive an indication of a start-up of the vapor compression system;

load a set of start-up manipulated variables, wherein the start-up manipulated variables are derived from calibrated models of the vapor compression system during start-up; and

run the vapor compression system in open loop control using the start-up manipulated variables for a fixed period of time.

14. The controller of claim 13 wherein the program further causes the processor to, following the fixed period of time, run the vapor compression system in closed loop feedback control.

15. The controller of claim 13 wherein the start-up manipulated variables are effective to introduce superheat to a refrigerant circuit of the vapor compression system during start-up, wherein controlled variables are kept within acceptable tolerances after the fixed period of time, and wherein the controller provides an interface to an operator, wherein the interface provides a mechanism to manipulate the manipulated variables and provide graphical representations of the response of the vapor compression system calculated from the calibrated models.

Drawing