System and method for heating and cooling

Abstract

An HVAC system is provided. Embodiments of the present disclosure generally relate to an HVAC system in which multiple indoor units are coupled to central outdoor unit, where at least one of the indoor units is configured to provide conditioned air through ductwork and at least one indoor unit is configured to provide conditioned air without ductwork. Moreover, a gas furnace can be provided in the system, for harsher environments that benefit from more robust heating. Additional systems, devices, and methods are also disclosed.

What is claimed is: 
     
         1 . A method for utilizing a dew-prevention system, the method comprising preventing or reducing dew condensation on a liquid line positioned between an indoor heat exchanger and an outdoor heat exchanger of a heating, ventilation, and air-conditioning (HVAC) system by:
 increasing a level of a liquid refrigerant in the liquid line; and   increasing a temperature of the liquid refrigerant in the liquid line,   wherein increasing the level and the temperature of the liquid refrigerant in the liquid line are achieved by decreasing a flow rate of the liquid refrigerant into the outdoor heat exchanger of the HVAC system operating as an evaporator in a heating mode.   
     
     
         2 . The method of  claim 1 , wherein preventing or reducing dew condensation on the liquid line further comprises operating at least one controller to control the temperature of the liquid refrigerant in the liquid line based at least in part on data received from at least one sensor of the HVAC system. 
     
     
         3 . The method of  claim 2 , further comprising:
 determining a risk for dew condensation, wherein the risk is determined by the formula:
   Risk for dew condensation=((Determined Dew Point Temperature (“ DDPT ”))−(Refrigerant Temperature (“ RT ”)))*(Length of Time that  RT<DDPT ),
 
    wherein DDPT is a calculated dew point temperature based on at least one of the at least one sensor or an external source in communication with the HVAC system,    wherein RT is a measured temperature of the liquid refrigerant in the liquid line, and    wherein Length of Time that RT<DDPT is a length of time that the measured temperature of the liquid refrigerant has been less than the calculated dew point temperature; and    controlling, via the at least one controller, the temperature of the liquid refrigerant in the liquid line of the HVAC system based at least in part on the determined risk for dew condensation.   
     
     
         4 . The method of  claim 3 , further comprising changing a target temperature of the liquid refrigerant exiting the indoor heat exchanger by operating the controller to control at least one of a first expansion valve, a second expansion valve, or a compressor to reduce subcooling and to increase the temperature of the liquid refrigerant in the liquid line following the indoor heat exchanger. 
     
     
         5 . The method of  claim 3 , wherein increasing the level and the temperature of the liquid refrigerant in the liquid line further comprises the at least one controller controlling the indoor heat exchanger to reduce an amount of heating provided to an indoor space than previously provided. 
     
     
         6 . The method of  claim 3 , further comprising operating the at least one controller to deactivate the HVAC system entirely to cease operations due to a formation of dew condensation on the liquid line. 
     
     
         7 . The method of  claim 1 , wherein preventing or reducing dew condensation on a liquid line further comprises:
 opening an expansion valve when the indoor heat exchanger is not actively heating an indoor space to increase circulation of a heat-absorbed refrigerant through the indoor heat exchanger; and   concurrently reducing a speed of a fan blowing air over the indoor heat exchanger such that an increased amount of heat remains in the heat-absorbed refrigerant compared to not opening the expansion valve and not reducing the speed of the fan.   
     
     
         8 . The method of  claim 1 , further comprising opening an expansion valve further to allow more refrigerant to flow through the indoor heat exchanger when a gas furnace is operating such that at least some heat from the gas furnace is transferred to the indoor heat exchanger and thus to the refrigerant in the indoor heat exchanger, thus increasing the temperature of the liquid refrigerant in the liquid line. 
     
     
         9 . A method of operating a heating, ventilation, and air-conditioning (HVAC) system comprising:
 operating the HVAC system in a heating mode whereby liquid refrigerant undergoes evaporation in an outdoor heat exchanger; and   preventing or reducing dew condensation, while in the heating mode, on a liquid line positioned between an indoor heat exchanger and the outdoor heat exchanger of the HVAC system by:
 restricting a flow of the liquid refrigerant into the outdoor heat exchanger by reducing an orifice size of a first expansion valve, thereby causing the liquid refrigerant to transition to a gaseous refrigerant at an earlier point in the outdoor heat exchanger and become superheated; and 
 flowing the superheated gaseous refrigerant to an accumulator, the superheat of which transitions residual liquid refrigerant within the accumulator to a gaseous refrigerant, causing more refrigerant to be in circulation than if the first expansion valve were less restricted, 
 wherein more refrigerant in circulation and restricting the flow of the liquid refrigerant into the outdoor heat exchanger causes an increased level of the liquid refrigerant in the liquid line, and 
 wherein the increased level of the liquid refrigerant in the liquid line and the inability of the increased level of the liquid refrigerant in the liquid line to be compressed causes an increased temperature of the liquid refrigerant in the liquid line than if the expansion valve were less restricted, thereby preventing or reducing dew condensation on the liquid line. 
   
     
     
         10 . The method of  claim 9 , wherein preventing dew condensation on the liquid line further comprises operating at least one controller to control the temperature of the liquid refrigerant in the liquid line based at least in part on data received from at least one sensor of the HVAC system. 
     
     
         11 . The method of  claim 10 , further comprising changing a target temperature of the liquid refrigerant exiting the indoor heat exchanger by operating the controller to control at least one of a first expansion valve, a second expansion valve, or a compressor to reduce subcooling and to increase the temperature of the liquid refrigerant in the liquid line following the indoor heat exchanger. 
     
     
         12 . The method of  claim 10 , wherein increasing the level and the temperature of the liquid refrigerant in the liquid line further comprises the at least one controller controlling the indoor heat exchanger to reduce an amount of heating provided to an indoor space than previously provided. 
     
     
         13 . The method of  claim 10 , further comprising operating the at least one controller to deactivate the HVAC system entirely to cease operations due to a formation of dew condensation on the liquid line. 
     
     
         14 . The method of  claim 9 , wherein preventing or reducing dew condensation on the liquid line further comprises:
 opening an expansion valve when the indoor heat exchanger is not actively heating an indoor space to increase circulation of a heat-absorbed refrigerant through the indoor heat exchanger; and   concurrently reducing a speed of a fan blowing air over the indoor heat exchanger such that an increased amount of heat remains in the heat-absorbed refrigerant compared to not opening the expansion valve and not reducing the speed of the fan.   
     
     
         15 . The method of  claim 9 , further comprising opening an expansion valve further to allow more refrigerant to flow through the indoor heat exchanger when a gas furnace is operating such that at least some heat from the gas furnace is transferred to the indoor heat exchanger and thus to the refrigerant in the indoor heat exchanger, thus increasing the temperature of the liquid refrigerant in the liquid line. 
     
     
         16 . An HVAC system for providing conditioned air to a structure:
 an outdoor unit configured to operate a compressor at variable speeds;   a plurality of indoor units configurable to provide conditioned air to the structure, wherein the plurality of indoor units comprises:
 a ducted indoor unit comprising a first expansion valve for controlling refrigerant flow; and 
 a ductless indoor unit comprising a second expansion valve for controlling refrigerant flow. 
   
     
     
         17 . The HVAC system of  claim 16 , wherein the outdoor unit is configured to couple to refrigerant piping that was previously coupled to a different outdoor unit. 
     
     
         18 . The HVAC system of  claim 17 , wherein the outer diameter of the refrigerant piping in the structure that conveys refrigerant in predominately in gas phase between the indoor units and the outdoor unit is larger than the outer diameter of the outdoor unit's corresponding piping for routing refrigerant in predominately in gas phase. 
     
     
         19 . The HVAC system of  claim 16 , wherein the refrigerant comprises at least 50%, in terms of weight, R32 refrigerant. 
     
     
         20 . The HVAC system of  claim 16 , wherein the refrigerant at least partially comprises a hydrofluoro-olefin (HFO) refrigerant. 
     
     
         21 . The HVAC system of  claim 16 , wherein the plurality of indoor units comprises a plurality of ductless indoor units. 
     
     
         22 . The HVAC system of  claim 16 , comprising an oil-recovery system configured to estimate an amount of stray oil in the HVAC system based the flow rate of refrigerant in a refrigerant line coupling at least one of the indoor units to the outdoor unit.