Microprocessor control for a heat pump water heater

An electronic control system for controlling a heat pump water heater including a compressor, an evaporator, and a condenser coupled with a hot water retention tank to form a hot water circuit, the hot water retention tank including means for receiving water from a supply source and means for discharging heated water, said control system comprising:

• first means for sensing the temperature of water in the hot water circuit and generating a first output representative of such temperature;
• means for circulating water from the hot water retention tank, through the condenser and back to the hot water retention tank;
• and
• a controller for receiving said first output signal and providing periodic sampling control, said controller energizing said circulating means for a first predetermined period of time to sample said first output signal and, upon detecting a call for heat, cycling the heat pump water heater to maintain a predefined hot water setpoint, said controller maintaining the heat pump water heater in a de-energized state for a second predetermined period of time when no demand for hot water is detected.

An apparatus for heating water comprising:

• an evaporator in heat exchange relationship with a heat source;
• a condenser;
• a compressor operatively disposed between said evaporator and said condenser and having a suction line and a discharge line;
• a hot water retention tank in heat exchange relationship with said condenser, said hot water retention tank including means for receiving water from a supply and means for discharging heated water;
• means for circulating water from said hot water retention tank, through said condenser and back to said hot water retention tank;
• and an electronic control apparatus comprising:
• first means for sensing the temperature of water stored in said hot water retention tank and generating a first output signal representative of such temperature;
• second means for sensing the temperature of the domestic hot water at said discharge means of said hot water retention tank and generating a second output signal representative of such temperature;
• and
• a microprocessor-based controller for receiving said first and second signals output, whereby upon detecting a rise in the temperature of the heated water at said discharge means said controller samples said first output signal and cycles said compressor to maintain a predefined hot water setpoint.

A method of controlling a heat pump water heater having a compressor, an evaporator, and a condenser coupled with a hot water retention tank to form a hot water circuit, the hot water retention tank including means for receiving water from a supply and means for discharging heated water, said method comprising the following steps:

• sensing the temperature of the water at the receiving means of the hot water retention tank and sensing the temperature of the heated water at the discharge means of the hot water retention tank;
• utilizing a microprocessor-based controller to detect a hot water demand based upon a decrease in the temperature of the water at the receiving means of the hot water retention tank in conjunction with an increase in the temperature of the heated water at the discharge means of the hot water retention tank;
• upon detecting such hot water demand, causing water to circulate between the hot water retention tank and the condenser;
• and
• sensing the temperature of the water in the hot water circuit and cycling the heat pump water heater compressor to maintain the water in the hot water retention tank at a predetermined setpoint.

The method of controlling a heat pump water heater having a compressor, an evaporator, a condenser coupled with a hot water retention tank to form a hot water circuit, and means for circulating the water contained in the hot water circuit, the hot water retention tank including means for receiving water from a supply and means for discharging heated water, said control method comprising the following steps:

• energizing the hot water circulating device;
• sensing the temperature of the water in the hot water circuit and generating a signal representative of such temperature;
• utilizing a microprocessor-based controller to detect a call for water heating according to the hot water circuit temperature sensed and a predetermined setpoint;
• upon detecting that no call for water heating exists, said controller de-energizing the hot water circulating device and waiting a predetermined period of time before repeating the above steps;
• upon detecting a call for water heating, said controller cycling the heat pump water heater compressor to maintain the predetermined setpoint;
• and
• waiting a predetermined period of time and energizing the hot water circulating device.

A method of monitoring liming conditions for use in controlling a heat pump water heater comprising a compressor, an evaporator, a condenser coupled with a hot water retention tank to form a hot water circuit, and means for circulating the water contained in the hot water circuit, the hot water retention tank including means for receiving water from a supply and means for discharging hot water, a high pressure switch disposed in a discharge line of the compressor and generating a first output signal representative of a high pressure fault condition, and a controller for receiving said first output signal, said liming control method comprising the following steps:

• disabling heat pump water heater operation for a first predetermined period of time and reducing a hot water setpoint a first predetermined amount upon said controller receiving said first output signal;
• restarting heat pump water heater operation after said first predetermined period of time has run and maintaining the hot water temperature according to the reduced setpoint;
• disabling heat pump water heater operation a second predetermined period of time and further reducing said hot water setpoint by a second predetermined amount upon subsequent high pressure fault occurrences;
• and
• restarting heat pump water heater operation after said second predetermined period of time has run and maintaining the hot water at the further reduced setpoint.