Patent Publication Number: US-11378300-B2

Title: Energy recovery ventilator with reduced power consumption

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/778,305, filed Feb. 27, 2013, which claims the benefit of U.S. provisional patent application Ser. No. 61/604,559 filed Feb. 29, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein generally relates to energy recovery ventilators, and in particular to a method and system for controlling an energy recovery ventilator to reduce power consumption and provide energy savings. 
     Energy recovery ventilators (ERVs) are used to provide fresh air circulation to a location. Fresh air circulation is particularly helpful in homes that are well sealed and highly insulated. Existing residential ERV&#39;s often require the furnace or air handler blower to run during ventilation mode because the fresh air delivery is done through the main air duct system for the home. During heating and cooling cycles there is no additional cost for ventilation because the blower runs during the heating and cooling cycles. However, during heating and cooling off cycles, running the blower for ventilation results in a higher energy cost for fresh air delivery because of the need to run the blower at full speed solely for ventilation. 
     BRIEF DESCRIPTION OF THE INVENTION 
     One embodiment is an air conditioning unit including a passage having a heat exchanger; a blower for blowing air through the passage; a blower motor driving the blower in response to a drive signal; an energy recovery ventilator (ERV), the blower drawing outside air from the ERV; and a controller for adjusting the drive signal in a ventilation mode to reduce power used by the blower motor. 
     Another embodiment is a ventilation system including an energy recovery ventilator (ERV) for fluid communication with a blower, the blower drawing outside air from the ERV in response to a drive signal applied to a blower motor; and a controller for adjusting the drive signal in a ventilation mode to reduce power to the blower motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an exemplary air conditioning unit; 
         FIG. 2  depicts a motor and control circuitry in an exemplary embodiment; and 
         FIG. 3  depicts PWM on and off time along with airflow on the same time scale. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , numeral  10  generally designates an air conditioning unit having a furnace, an evaporator coil and an energy recovery ventilator (ERV). The ERV is described herein with reference to a gas furnace, but it is understood that the ERV (and control thereof) may be used with other systems, such as residential air handlers, and embodiments are not limited to a gas fired furnace as shown in  FIG. 1 . Air conditioning unit, as used herein, is intended to cover a variety of air handling equipment. 
     Air conditioning unit  10  includes a cabinet  12  housing therein furnace having a circulating air blower  26  driven by a blower motor  25 . In heating mode, a heat exchanger  16  heats air circulated by air blower  26 , which is supplied to a supply duct  30 . A burner assembly, igniter, gas source, etc. are not shown for ease of illustration. An evaporator coil  82  is located in housing  80  on top of cabinet  12  and is the evaporator of a cooling unit. The evaporator coil  82  has an inlet  84 , where subcooled refrigerant enters, and an outlet  86 , where superheated refrigerant leaves, as is conventional. In cooling mode, evaporator coil  82  cools air circulated by air blower  26 , which is supplied to a supply duct  30 . 
     Cabinet  12  also houses a controller  54 . Controller  54  may be implemented using a microprocessor-based controller executing computer program code stored on a computer readable storage medium. A thermostat  55  communicates with controller  54  to designate operational modes and temperature. Thermostat  55  may be an intelligent device that communicates requested air flow rates. 
     An energy recovery ventilator (ERV)  90  is mounted to a side of cabinet  12 , but may be mounted in other locations. ERV  90  includes a fan  92  that draws fresh air from outside the building and uses energy from return air to precondition the outside air prior to distribution to cabinet  12 . ERV  90  may be any existing type of ERV, such as a rotary heat exchanger (e.g., wheel) or plate heat exchanger with a membrane. ERV  90  may be arranged in cross-flow or counter-flow configuration. As used herein, ERV includes heat recovery ventilators (HRV), unless indicated otherwise. 
     Blower  26  is used to circulate supply air from ERV  90 , through cabinet  12  and on to supply duct  30 . Blower  26  also draws return air from location ducts back to the ERV  90  for energy recovery. ERV  90  includes an exhaust fan  94  for discharging exhaust air. 
     In embodiments of the invention, blower motor  25  is driven in a ventilation mode to reduce power consumption and still meet desired ventilation needs. In operation, thermostat  55  designates a mode such as low heat, high heat, low cool, high cool or ventilation. In ventilation mode, neither heating nor cooling is provided by air conditioning unit  10 . 
     Control of blower motor  25  in ventilation mode may be accomplished in a variety of manners, depending on the type of blower motor  25 . The goal is to reduce power to blower motor  25  while still meeting applicable ventilation requirements for the space being served. 
     In exemplary embodiments, blower motor  25  is a permanent split capacitor (PSC) motor having multiple taps. The motor speed is controlled by applying an AC voltage (e.g., 115 VAC or 220 VAC) to a particular tap to achieve a desired motor speed.  FIG. 2  illustrates an exemplary embodiment where blower motor  25  is a PSC motor having 5 taps, corresponding to fan speeds of low, medium-low, medium, medium-high and high. 
     AC voltage is applied at inputs L 1  and L 2  and relays  102 ,  104  and  106  are used to form a path from input L 1  to one of the medium-low, medium, and high taps. The medium-high tap is not terminated as a spare. Relays  102 ,  104  and  106  have contacts rated as high as 20 amps. 
     The low tap is used in ventilation only mode (i.e., no heating or cooling demand) referred to in  FIG. 2  as a stir cycle. In this ventilation mode, blower motor  25  operates at a lower speed, which results in power savings. A solid state switching device  110  is used to provide voltage to the low speed tap. Other types of switching devices (e.g., relays) may be used. Solid state switching device  110  may operate in response to commands from controller  54 . Solid state switching device  110  may be activated when the system is operating in an idle state. Relay  102  connects input voltage L 1  to solid state switching device  110 . This diverts power from the electric air cleaner (EAC) that is typically run during heating and cooling modes. 
     Solid state switching device  110  may be triggered at zero crossing points of input voltage L 1  to reduce in-rush current to blower motor  25 . Logic in solid state switching device  110  implements the stir cycle when the blower is transitioning out of a heating, or cooling state. 
       FIG. 2  represents one exemplary blower motor  25 . Embodiments of the invention may be used with other types of motors, such as discreet tap X13 motors. These motors are driven by, e.g., 24 VAC, and are supplied with 3 to 5 taps. These taps draw low current (less than 15 ma) and can also be driven with DC voltage. Existing systems switch these taps on and off with relays that have gold contacts for low current circuits. If blower motor  25  is a discreet tap X13 motor, a system of relays and solid state circuitry similar to  FIG. 2  may be used to provide voltage to a low speed tap to run the motor  25  in the ventilation or stir mode, and reduce energy consumption. 
     Another type of blower motor  25  that may be used in exemplary embodiments is a pulse width modulated (PWM) X-13 motor. These motors are driven with a PWM signal, which may be provided by controller  54 . The PWM signal is, for example, between 80 hz and 120 hz, and causes the blower motor torque to vary with the percent duty cycle of the signal. Maximum motor torque will occur at 99% duty cycle and off will occur at a duty cycle of 0.4% or less. To activate the ventilation or stir mode, controller  54  generates an on PWM signal (having 1%-99% duty cycle) for a few seconds followed by an off PWM for a few seconds.  FIG. 3  shows the on and off PWM signals, along with the airflow generated. It is understood that during the on PWM time, controller  54  is providing the PWM signal, made up of a series of pulses, to blower motor  25 . During the off PWM time, no PWM signal is provided to blower motor  25 . In exemplary embodiments, the on time may be 1 to 2 seconds and the off time may be 2 to 4 seconds OFF. The on PWM time and off PWM time may be dependent upon blower fan  26  inertia. By selectively applying the PWM signal, a lower motor RPM is achieved, meeting the airflow demands in ventilation mode and reducing energy consumption. 
     Another type of motor  25  that may be used in exemplary embodiments is a communicating electronically commutated motor (ECM). In these embodiments, controller  54  controls blower motor  25  by transmitting digital communication commands. For example, a low motor RPM (e.g., just below 200 RPM) may be achieved by controller  54  sending a very low torque command, for example, 0-200. To achieve full motor torque, controller  54  sends a torque command of, for example, 65535. If the low torque command from controller  54  still results in too high of a motor RPM for the stir mode, then the torque command may be pulsed on and off, similar to the PWM on and off discussed above with reference to  FIG. 3 . 
     Driving the blower motor  25  to a low RPM in ventilation mode results in an energy savings when compared to existing units that drive the blower motor  25  at full speed during ventilation mode. Typical controls for ERV&#39;s and HRV&#39;s include timers for run time and wall controls to call for ventilation when needed. By ventilating continuously and employing the energy saving cycle, energy is saved and makes the timers and wall controls unnecessary. Cycling power to the blower during the ventilation mode at a prescribed rate also takes advantage of rotating blower inertia in order to stir the air sufficiently to deliver fresh air through the main air duct system to accomplish ventilation for the home but save on energy cost over running the main system blower solely for ventilation, especially with electronically commutated motors (ECM). The ventilation mode is also sufficient to prevent mixing of the supply and exhaust air streams from the ERV. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.