HVAC system with powered subcooler

An HVAC system comprising:

• a main circuit comprising a main circuit evaporator, a main circuit expansion device, a main circuit condenser and a main circuit compressor connected in a first closed refrigerant loop;
• and
• a first subcooler circuit comprising a first subcooler evaporator, a first subcooler expansion device, a first subcooler condenser and a first subcooler compressor connected in a second closed refrigerant loop, wherein the first subcooler circuit is selectably operable;
• a second subcooler circuit comprising a second subcooler evaporator, a second subcooler expansion device, a second subcooler condenser and a second subcooler compressor connected in a third closed refrigerant loop, wherein the second subcooler circuit is selectably operable;
• and
• the first subcooler evaporator and second subcooler evaporator each being arranged and disposed to exchange heat between liquid refrigerant in the main circuit and the refrigerant in the corresponding subcooler circuit to cool the liquid refrigerant in the main circuit prior to entering the main circuit evaporator,
• wherein the coils of at least one of the first subcooler circuit condenser and the second subcooler circuit condenser are positioned downstream of a cooling fluid passing over coils of the main circuit condenser;
• wherein a fluid moving device moves the cooling fluid through one or more of the subcooler condensers and the main circuit condenser;
• wherein the main circuit condenser operates independently of the first and second subcooler circuits, and
• wherein a cooling capacity of the first subcooler circuit and a cooling capacity of the second subcooler circuit is less than a cooling capacity of the main circuit.

An HVAC system comprising:

• a main circuit comprising a main circuit evaporator, a main circuit expansion device, a main circuit condenser and a main circuit compressor connected in a first closed refrigerant loop, the main circuit circulating a refrigerant with a critical temperature below about 80° C.;
• a subcooler circuit comprising a subcooler evaporator, a subcooler expansion device, a subcooler condenser and a subcooler compressor connected in a second closed refrigerant loop, wherein the subcooler circuit is selectably operable;
• the subcooler evaporator being arranged and disposed to exchange heat between liquid refrigerant in the main circuit and the refrigerant in the subcooler circuit to cool the liquid refrigerant in the main circuit prior to entering the main circuit evaporator;
• wherein coils of the subcooler circuit condenser are positioned downstream of a cooling fluid passing over coils of the main circuit condenser;
• wherein a fluid moving device moves the cooling fluid through the subcooler condenser and the main circuit condenser;
• wherein the main circuit condenser operates independently of the subcooler circuit;
• wherein a cooling capacity of the subcooler circuit is less than a cooling capacity of the main circuit;
• and
• wherein the operation of the subcooler circuit provides greater cooling capacity per unit of a mass flow of cooling fluid through the main circuit condenser and subcooler condenser for the HVAC system with a predetermined design efficiency.

A method for subcooling an HVAC system, comprising:

• providing a main circuit comprising a main circuit evaporator, a main circuit expansion device, a main circuit condenser and a main circuit compressor connected in a first closed refrigerant loop;
• providing a subcooler circuit comprising a subcooler evaporator, a subcooler expansion device, a subcooler condenser and a subcooler compressor connected in a second closed refrigerant loop, wherein the subcooler circuit is selectably operable;
• positioning coils of the subcooler circuit condenser downstream of the coils of the main circuit condenser so that cooling fluid of the main circuit condenser is configured to pass over coils of the main circuit condenser prior to passing over coils of the subcooler circuit condenser;
• subcooling refrigerant in the main circuit with the subcooler evaporator prior to the refrigerant in the main circuit entering the main circuit evaporator to provide an increased cooling capacity per unit of airflow for the HVAC system with a predetermined design efficiency, wherein the main circuit condenser operates independently of the subcooler circuit, and wherein a cooling capacity of the subcooler circuit is less than a cooling capacity of the main circuit;
• sensing one of an ambient air temperature or a refrigerant temperature;
• activating or deactivating the compressor in at least one of the main circuit and the subcooler circuit in response to the sensed condition;
• and
• activating or deactivating one or more fluid moving devices providing fluid flow to the main circuit condenser and subcooler condenser in response to the sensed condition.