Abstract: A heat pump, and in particular a heat pump for heating a hot water supply is provided with an improved defrost mode. The defrost mode is actuated to remove frost from an outdoor evaporator that may accumulate during cold weather operation. An algorithm for operation of the defrost mode is developed experimentally by seeking to maximize the heat transfer provided by the refrigerant. A heating system condition is experimentally related to the heat transfer capacity. One then maximizes the average heat transfer capacity to determine the optimum initiation point for the defrost mode. Further, protections are included into the defrost mode. When the heat pump is utilized to heat hot water, methods are provided to prevent the water that remains in the heat exchanger from becoming unduly heated. In one method, the water pump may be periodically operated to move the water.

Abstract: A method of controlling a startup operation in a heat pump water heater system prevents inadvertent shutdowns and/or low operating efficiencies via closed loop control of the system. The method includes choosing an expansion valve opening at startup near an expected steady state value to ensure high system capacity as early as possible, setting a water pump signal to a high level to maximize cycle efficiency during warm-up, and applying closed loop control over the expansion valve and the water pump to increase the pressure in the system in a controlled manner until the system reaches a steady operating state. The method provides stable startup control even if a transcritical vapor compression system is used as the heat pump.

Abstract: A refrigerant cycle is provided with a control for an expansion device to achieve a desired compressor discharge pressure. The system operates transcritically, such that greater freedom over compressor discharge pressure is provided. The system's efficiency is optimized by selecting an optimum discharge pressure. The optimum discharge pressure is selected based upon sensed environmental conditions, and the expansion device is adjusted to achieve the desired compressor discharge pressure. A feedback loop may be provided to sense the actual compressor discharge pressure and adjust the actual compressor discharge pressure by further refining the expansion device. The system is disclosed providing heated water based upon a demand for a particular hot water temperature.

Abstract: A heat pump, and in particular a heat pump for heating a hot water supply is provided with an improved defrost mode. The defrost mode is actuated to remove frost from an outdoor evaporator that may accumulate during cold weather operation. An algorithm for operation of the defrost mode is developed experimentally by seeking to maximize the heat transfer provided by the refrigerant. A heating system condition is experimentally related to the heat transfer capacity. One then maximizes the average heat transfer capacity to determine the optimum initiation point for the defrost mode. Further, protections are included into the defrost mode. When the heat pump is utilized to heat hot water, methods are provided to prevent the water that remains in the heat exchanger from becoming unduly heated. In one method, the water pump may be periodically operated to move the water.

Abstract: A heat pump, and in particular a heat pump for heating a hot water supply is provided with an improved defrost mode. The defrost mode is actuated to remove frost from an outdoor evaporator that may accumulate during cold weather operation. An algorithm for operation of the defrost mode is developed experimentally by seeking to maximize the heat transfer provided by the refrigerant. A heating system condition is experimentally related to the heat transfer capacity. One then maximizes the average heat transfer capacity to determine the optimum initiation point for the defrost mode. Further, protections are included into the defrost mode. When the heat pump is utilized to heat hot water, methods are provided to prevent the water that remains in the heat exchanger from becoming unduly heated. In one method, the water pump may be periodically operated to move the water.

Abstract: The refrigerant charge adequacy of an air conditioning system is determined by the sensing of two temperatures in the system, one being at a midpoint in a condenser coil and the other being the temperature in the liquid line of the condenser discharge, with the difference then being indicative of the degree of subcooling, which, in turn, may be indicative of refrigerant charge condition. The method is refined by measuring a third temperature at the compressor discharge, with the three temperature values then being used to calculate a pair of residual values which provide an indication of whether the two temperature approach is useful in determining charge adequacy under the existing conditions and if not, whether the system is overcharged or undercharged.

Abstract: An energy-efficient heat pump water heating system determines whether to energize a heat pump by interpreting readings from one or temperature sensors based on two thresholds. The heat pump is energized if the detected temperature falls below a first threshold and de-energized when the detected temperature rises above a second threshold. The thresholds may correspond to outputs of two or more sensors. Using multiple temperature thresholds improves the temperature sensing capabilities of the system, thereby improving energy efficiency by matching heat pump operation with hot water demand more closely than previously known systems.

Abstract: A method of controlling a startup operation in a heat pump water heater system prevents inadvertent shutdowns and/or low operating efficiencies via closed loop control of the system. The method includes choosing an expansion valve opening at startup near an expected steady state value to ensure high system capacity as early as possible, setting a water pump signal to a high level to maximize cycle efficiency during warm-up, and applying closed loop control over the expansion valve and the water pump to increase the pressure in the system in a controlled manner until the system reaches a steady operating state. The method provides stable startup control even if a transcritical vapor compression system is used as the heat pump.

Abstract: A method of controlling a startup operation in a heat pump water heater system prevents inadvertent shutdowns and/or low operating efficiencies via closed loop control of the system. The method includes choosing an expansion valve opening at startup near an expected steady state value to ensure high system capacity as early as possible, setting a water pump signal to a high level to maximize cycle efficiency during warm-up, and applying closed loop control over the expansion valve and the water pump to increase the pressure in the system in a controlled manner until the system reaches a steady operating state. The method provides stable startup control even if a transcritical vapor compression system is used as the heat pump.

Abstract: A method and apparatus for determining the sufficiency of refrigerant charge in an air conditioning system by the use of only two temperature measurements. The temperature of the liquid refrigerant leaving the condenser coil is sensed and the temperature of the condenser coil itself is sensed and the difference between these two measurements is calculated to provide an indication of the adequacy of refrigerant charge in the system. This process is refined by steps taken to eliminate measurements during transient operations and by filtering signals to eliminate undesirable noise. A permitted threshold of deviation is calculated by using probability theory.

Abstract: Refrigerant is circulated through a vapor compression system including a compressor, a gas cooler, an expansion device, and an evaporator. When a sensor detects that frozen water droplets form on the evaporator, a valve positioned between the discharge of the compression and inlet of expansion device is opened. Refrigerant from the discharge of the compressor bypasses the gas cooler and enters the inlet of the expansion device. The high temperature refrigerant melts the frost on the evaporator. As the frost melts, the passage of the evaporator is opened to allow air to flow through the evaporator.

Abstract: A method of detecting and diagnosing operating conditions for a heat pump water heating system includes the steps of monitoring system operating conditions and comparing actual operating conditions to predicted operating conditions. The predicted operating conditions are based on expected pressures and temperatures given current system inputs. A difference between the actual and expected values for refrigerant pressures and temperature outside a desired range provides indication of a fault in the system. The system controller initiates a prompt to alert of the need for maintenance and direct to potential causes.

Abstract: A control particularly useful for a hot water heating system, includes calculation of a desired leaving water temperature for water leaving a hot water heat exchanger, and a desired refrigerant condition for most efficiently achieving the desired leaving water temperature. A control looks at both desired variables and compares them to actual variables to determine an error for each. The control includes an error correction algorithm for each of the two variables that takes into account both of the errors, the integral of both of the errors, and the derivative of both of the errors. In this way, sensitivity in the error correction for one variable due to changes in the other variable is reduced, and the system functions more efficiently.

Abstract: A method of detecting and diagnosing operating conditions for a heat pump water heating system includes the steps of monitoring system operating conditions and comparing actual operating conditions to predicted operating conditions. The predicted operating conditions are based on expected pressures and temperatures given current system inputs. A difference between the actual and expected values for refrigerant pressures and temperature outside a desired range provides indication of a fault in the system. The system controller initiates a prompt to alert of the need for maintenance and direct to potential causes.

Abstract: A refrigerant cycle is provided with a control for an expansion device to achieve a desired compressor discharge pressure. The system operates transcritically, such that greater freedom over compressor discharge pressure is provided. The system's efficiency is optimized by selecting an optimum discharge pressure. The optimum discharge pressure is selected based upon sensed environmental conditions, and the expansion device is adjusted to achieve the desired compressor discharge pressure. A feedback loop may be provided to sense the actual compressor discharge pressure and adjust the actual compressor discharge pressure by further refining the expansion device. The system is disclosed providing heated water based upon a demand for a particular hot water temperature.

Abstract: A control particularly useful for a hot water heating system, includes calculation of a desired leaving water temperature for water leaving a hot water heat exchanger, and a desired refrigerant condition for most efficiently achieving the desired leaving water temperature. A control looks at both desired variables and compares them to actual variables to determine an error for each. The control includes an error correction algorithm for each of the two variables that takes into account both of the errors, the integral of both of the errors, and the derivative of both of the errors. In this way, sensitivity in the error correction for one variable due to changes in the other variable is reduced, and the system functions more efficiently.

Abstract: A heat pump, and in particular a heat pump for heating a hot water supply is provided with an improved defrost mode. The defrost mode is actuated to remove frost from an outdoor evaporator that may accumulate during cold weather operation. An algorithm for operation of the defrost mode is developed experimentally by seeking to maximize the heat transfer provided by the refrigerant. A heating system condition is experimentally related to the heat transfer capacity. One then maximizes the average heat transfer capacity to determine the optimum initiation point for the defrost mode. Further, protections are included into the defrost mode. When the heat pump is utilized to heat hot water, methods are provided to prevent the water that remains in the heat exchanger from becoming unduly heated. In one method, the water pump may be periodically operated to move the water.

Abstract: An energy-efficient heat pump water heating system determines whether to energize a heat pump by interpreting readings from one or temperature sensors based on two thresholds. The heat pump is energized if the detected temperature falls below a first threshold and de-energized when the detected temperature rises above a second threshold. The thresholds may correspond to outputs of two or more sensors. Using multiple temperature thresholds improves the temperature sensing capabilities of the system, thereby improving energy efficiency by matching heat pump operation with hot water demand more closely than previously known systems.

Abstract: A method of controlling a startup operation in a heat pump water heater system prevents inadvertent shutdowns and/or low operating efficiencies via closed loop control of the system. The method includes choosing an expansion valve opening at startup near an expected steady state value to ensure high system capacity as early as possible, setting a water pump signal to a high level to maximize cycle efficiency during warm-up, and applying closed loop control over the expansion valve and the water pump to increase the pressure in the system in a controlled manner until the system reaches a steady operating state. The method provides stable startup control even if a transcritical vapor compression system is used as the heat pump.

Abstract: Refrigerant is circulated through a vapor compression system including a compressor, a gas cooler, an expansion device, and an evaporator. When a sensor detects that frozen water droplets form on the evaporator, a valve positioned between the discharge of the compression and inlet of expansion device is opened. Refrigerant from the discharge of the compressor bypasses the gas cooler and enters the inlet of the expansion device. The high temperature refrigerant melts the frost on the evaporator. As the frost melts, the passage of the evaporator is opened to allow air to flow through the evaporator.