Pulse width modulation control for heat pump fan to eliminate cold blow

Abstract

A heat pump refrigerant system is provided with a pulse width modulation control for a fan moving air over the indoor heat exchanger. When it is determined that there is insufficient heat rejected by the indoor heat exchanger to heat the volume of air being delivered by the fan into the conditioned environment, the volume of air supplied to the conditioned environment is reduced by utilizing one of pulse width modulation techniques to cycle the indoor fan motor to reduce the average volume of supplied air. Therefore, a precise control over the temperature of air delivered to the conditioned space is achieved, temperature of the delivered air is increased to the target value, and so-called “cold blow” conditions are avoided.

1 . A heat pump comprising:
 a compressor for compressing refrigerant and delivering the refrigerant to a downstream indoor heat exchanger, said indoor heat exchanger being provided with an air-moving device for moving air over said indoor heat exchanger and into an environment to be conditioned, refrigerant passing from said indoor heat exchanger through an expansion device and then through an outdoor heat exchanger, refrigerant from the outdoor heat exchanger returning to the compressor; and   a control for said air-moving device for said indoor heat exchanger, said control providing a pulse width modulation signal to adjust the time-average volume of air moved by said air-moving device over said indoor heat exchanger when it has been determined that there is insufficient heat rejected by said indoor heat exchanger to heat a nominal volume of air to a desired temperature.   
   
   
       2 . The heat pump as set forth in  claim 1 , wherein a four-way valve selectively routes refrigerant from said compressor to said indoor heat exchanger when the heat pump is operating in a heating mode, and to said outdoor heat exchanger when the heat pump is operating in a cooling mode. 
   
   
       3 . The heat pump as set forth in  claim 1 , wherein said air-moving device is a fan. 
   
   
       4 . The heat pump as set forth in  claim 1 , wherein a motor for said air-moving device is a single-speed motor, and said pulse width modulation control rapidly cycles the motor. 
   
   
       5 . The heat pump as set forth in  claim 4 , wherein said pulse width modulation control rapidly cycles the motor between an “on” position and an “off” position. 
   
   
       6 . The heat pump as set forth in  claim 5 , wherein a time interval for said “on” position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       7 . The heat pump as set forth in  claim 1 , wherein a motor for said air-moving device is a two-speed motor, and said pulse width modulation control rapidly cycles the two-speed motor between at least one of a higher speed and a lower speed, the lower speed and the “off” position and the higher speed and the “off” position. 
   
   
       8 . The heat pump as set forth in  claim 7 , wherein the time interval at each speed position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       9 . The heat pump as set forth in  claim 1 , wherein a motor for said air-moving device is a multi-speed motor, and said pulse width modulation control rapidly cycles the multi-speed motor between multiple speeds, including the motor “off” position. 
   
   
       10 . The heat pump as set forth in  claim 9 , wherein the time interval at each speed position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       11 . The heat pump as set forth in  claim 1 , wherein the environment to be conditioned is provided with a temperature sensor for sensing the temperature of air being delivered into the environment, and said sensed temperature being provided to said control, such that said control can adjust the time-average volume of air moved into the environment by utilizing said pulse width modulation technique to match the sensed temperature to a desired temperature. 
   
   
       12 . The heat pump as set forth in  claim 1 , wherein said indoor heat exchanger is a condenser, while said heat pump operates in a subcritical region at least for a portion of the time. 
   
   
       13 . The heat pump as set forth in  claim 1 , wherein said indoor heat exchanger is a gas cooler, while said heat pump operates in a transcritical region at least for a portion of the time. 
   
   
       14 . The heat pump as set forth in  claim 1 , wherein the pulse width modulation cycling rate is determined by at least one of the air-moving device reliability requirements, the temperature variation tolerance band requirements and efficiency considerations. 
   
   
       15 . The heat pump as set forth in  claim 1 , wherein the pulse width modulation control cycles said air-moving device between at or near zero speed and a non-zero speed, and the consequent cycle starts while the air-moving device is still in motion. 
   
   
       16 . A method of operating a heat pump comprising the steps of:
 (1) compressing refrigerant and delivering the refrigerant to a downstream indoor heat exchanger, indoor heat exchanger being provided with an air-moving device moving air over said indoor heat exchanger and into an environment to be conditioned, refrigerant passing from said indoor heat exchanger through an expansion device and then through an outdoor heat exchanger, refrigerant from the outdoor heat exchanger returning to the compressor; and   (2) controlling said air-moving device for said indoor heat exchanger, by providing a pulse width modulation signal to adjust the time-average volume of air moved by said air-moving device over said indoor heat exchanger when it has been determined that there is insufficient heat rejected by said indoor heat exchanger to heat a nominal volume of air to a desired temperature.   
   
   
       17 . The method as set forth in  claim 16 , wherein a four-way valve selectively routes refrigerant from said compressor to said indoor heat exchanger when the heat pump is operating in a heating mode, and to said outdoor heat exchanger when the heat pump is operating in a cooling mode. 
   
   
       18 . The method as set forth in  claim 16 , wherein said air-moving device is a fan. 
   
   
       19 . The method as set forth in  claim 16 , wherein a motor for said air-moving device is a single-speed motor, and said pulse width modulation control rapidly cycles the motor. 
   
   
       20 . The method as set forth in  claim 19 , wherein said pulse width modulation control rapidly cycles the motor between an “on” and an “off” position. 
   
   
       21 . The method as set forth in  claim 20 , wherein a time interval for said “on” position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       22 . The method as set forth in  claim 16 , wherein a motor for said air-moving device is a two-speed motor, and said pulse width modulation control rapidly cycles the two-speed motor between at least one of a higher speed and a lower speed, the lower speed and the “off” position and the higher speed and the “off” position. 
   
   
       23 . The method as set forth in  claim 22 , wherein the time interval at each speed position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       24 . The method as set forth in  claim 16 , wherein a motor for said air-moving device is a multi-speed motor, and said pulse width modulation control rapidly cycles the multi-speed motor between multiple speeds, including the motor “off” position. 
   
   
       25 . The method as set forth in  claim 24 , wherein the time interval at each speed position is determined by at least one of temperature requirements and efficiency considerations. 
   
   
       26 . The method as set forth in  claim 16 , wherein the environment to be conditioned is provided with a temperature sensor for sensing the temperature of air being delivered into the environment, and said sensed temperature being provided to said control, such that said control can adjust the time-average volume of air moved into the environment by utilizing said pulse width modulation technique to match the sensed temperature to a desired temperature. 
   
   
       27 . The method as set forth in  claim 16 , wherein said indoor heat exchanger is a condenser, while said heat pump operates in a subcritical region at least for a portion of the time. 
   
   
       28 . The method as set forth in  claim 16 , wherein said indoor heat exchanger is a gas cooler, while said heat pump operates in a transcritical region at least for a portion of the time. 
   
   
       29 . The method as set forth in  claim 16 , wherein the pulse width modulation cycling rate is determined by at least one of the air-moving device reliability requirements, the temperature variation tolerance band requirements and efficiency considerations. 
   
   
       30 . The method as set forth in  claim 16 , wherein the pulse width modulation control cycles said air-moving device between at or near zero speed and non-zero speed, and the consequent cycle starts while the air-moving device is still in motion.