Abstract:
In a transport temperature control system having a cooling and heating mode of operation an apparatus and method are provided for enhancing the heating capacity during the heating mode of operation. A second expansion valve is provided to connect the higher pressure liquid line to the refrigerant circuit downstream of the evaporator. When additional refrigerant is needed in the heating circuit to increase heating capacity, especially during low ambient temperature operating conditions, the second expansion valve is caused to open to admit more refrigerant to the system. After passing through the second expansion valve low pressure gas is passed to the compressor, optimizing compressor efficiency such that an increased amount of hot refrigerant gas is delivered to the evaporator for enhanced heating capacity.
Abstract:
A method and apparatus for making a pretrip diagnosis and identification of generator set problems which could cause shutdown or undesired operation of the generator set.
Abstract:
A method of monitoring and protecting a transport refrigeration unit and a load in a load space to be conditioned by circulating air between the load space and the transport refrigeration unit. The transport refrigeration unit maintains a selected set point temperature SP in the load space by electrical control which selects cooling and hot gas heating conditioning modes initiated by switching a three-way valve between first and second positions. The method includes the step of detecting a reverse operating mode, wherein the actual conditioning mode is the opposite of the conditioning mode requested by the control means, and the step of pulsing the three-way valve in an attempt to cause the three-way valve, when stuck, to switch to the required position.
Abstract:
Methods and apparatus for extending engine operating time, with a given amount of fuel, of an internal combustion engine connected to drive a compressor of a transport refrigeration unit. A fuel level signal is provided in response to the amount of fuel in a fuel tank associated with the internal combustion engine. The operation of the transport refrigeration unit is modified in different predetermined ways at predetermined different values of the fuel level signal, as fuel is consumed, to reduce the rate at which engine fuel is used after each modification. The time that a space being conditioned by the transport refrigeration unit for a given fuel supply is thus extended, maintaining temperature control of the conditioned space over this extended time while sacrificing non-load threatening, incremental degrees of control precision.
Abstract:
A transport refrigeration system having electrical control which controls the temperature in a served space via heating and cooling cycles using hot refrigerant gas from a refrigerant compressor. The refrigeration system has high and low pressure sides. The high pressure side includes a discharge manifold of the compressor, a condenser coil, a refrigerant receiver tank, and an evaporator coil associated with the served space. The low pressure side extends from the evaporator coil to a suction manifold of the compressor. A first controllable refrigerant flow path means is controlled by the electrical control to purge the condenser coil in response to predetermined system parameters, causing refrigerant trapped in the condenser coil to flow to the low pressure side of the system. A second controllable refrigerant flow path is controlled by the electrical control to pressurize the receiver tank in response to predetermined system parameters, forcing refrigerant to flow from the receiver tank to the evaporator coil.
Abstract:
A method of monitoring a refrigeration unit including detecting premature return of air discharged into a conditioned space, and distinguishing this "short cycling" problem from a refrigeration capacity problem. The method includes determining the rates of change of the temperatures DA and RA of the discharge air and return air, respectively, during temperature pull down of the conditioned space, and comparing the rates of change with predetermined constants selected to detect a short cycling of the discharge air. When the rates of change do not fit a normal temperature pull down, the differential .DELTA.D between the temperatures DA and RA of the discharge air and return air is determined and compared with a third constant. Predetermined results of the comparisons of the rates of changes of DA and RA, and the temperature difference .DELTA.D with the first, second and third constants, respectively, are utilized to identify proper air flow in conditioned space, to indicate a problem with air flow in conditioned space, and to indicate that refrigeration capacity should be checked.
Abstract:
A method of operating a transport refrigeration system having a compressor driven by a prime mover at a selected one of high and low speeds, an evaporator, and an evaporator blower driven by the prime mover. Refrigeration control provides an error value which controls the temperature of a load space to a predetermined set point via heating and cooling modes. The method includes the steps of driving the compressor at high speed during pull down, and injecting hot gas into the evaporator when the error is reduced to a predetermined value. The prime mover is maintained at high speed, to keep evaporator air flow at a high rate, continuing a relatively rapid temperature pull-down across the entire load space. The speed of the prime mover is reduced to low speed when the error is further reduced to a second value, which also initiates suction line modulation while maintaining hot gas injection.
Abstract:
A transport refrigeration system having a compressor, condenser, receiver, and evaporator, for controlling the temperature of a served space via hot gas heating and cooling cycles. The receiver is selectively pressurized during a hot gas heating cycle, pressurizing the receiver at low ambient temperatures as sensed by compressor head pressure, and terminating or preventing receiver pressurization above a predetermined head pressure. This is useful for transport refrigeration systems which have a single compartment to condition, and it is even more useful in compartmentalized transport refrigeration systems having two or more compartments to condition.
Abstract:
A method for controlling a transport refrigeration system is provided that advantageously avoids the top-freezing of items stored in a conditioned space without the need for modulating the flow of refrigerant through the heater-evaporator coil that heats and cools the space. The method includes the steps of operating the refrigeration system in a cooling mode at high speed for no more than 300.degree. minutes below the temperature set point of the conditioned space to rapidly cool the space. Next, the system is operated in a low speed heating mode in order to raise the temperature of the conditioned space to no more than about 5.degree. F. above set point in order to avoid top-freezing items in the conditioned space. Thirdly, the refrigeration system is operated in a low speed cooling mode to reattain a temperature set point assigned to the conditioned space. If necessary, these three basic steps of the method may be reiterated in order to stabilize the temperature of the space at set point. The method is particularly applicable to refrigeration systems capable of cooling or heating multiple conditioned spaces.
Abstract:
A method of adding asynchronous logging of data relative to events into a time based data logger which stores operator initiated headers in a data array, as well as synchronously storing data relative to variables of a transport refrigeration unit at predetermined constant time intervals. The operator associated headers include a preamble having a predetermined number of data bytes which include a header designator and a digital code which identifies the specific type of header being entered. An event header is provided having a preamble which includes the same number of data bytes as the preamble of the operator associated headers, for each type of event to be asynchronously stored in the data array. The header designator associated with the operator associated headers is inserted into the preamble of each of the event headers. A digital code is provided which identifies each event header, and the digital code is inserted into the preamble of each of the event headers. A data field follows the preamble of each event header, with predetermined data being inserted into the data field when an event occurs. An event header is stored in the data array asynchronously, at the time the associated event occurs. Each event header is time stamped when stored in the data array, and data stored in the data array is downloaded to a predetermined device, including asynchronously stored event headers and synchronous data stored at predetermined time intervals.