HVAC unit with hot gas reheat
The present disclosure is directed to a single compressor HVAC system with hot gas reheat. The system includes a single compressor, a pair of condensers, a reheat heat exchanger, an evaporator, and an expansion device. Within the system, the refrigerant exiting the compressor is separated into two portions. In the cooling mode, the first and second portions of the refrigerant are directed from the compressor through the two condensers in parallel. In the reheat mode, the first portion of the refrigerant is directed through the first condenser, while the second portion of the refrigerant is directed through the reheat heat exchanger. The system also may include a head pressure control device that is designed to maintain the compressor discharge pressure within a desired range by adjusting the condenser fan speed.
1. A system, comprising:
a compressor configured to circulate a refrigerant through a refrigerant circuit;
a first condenser disposed along the refrigerant circuit, wherein the first condenser is configured to receive and to condenser a first portion of the refrigerant in a first operating mode and in a second operating mode;
a second condenser disposed along the refrigerant circuit, wherein the second condenser is configured to receive and to condense a second portion of the refrigerant in the first operating mode but not in the second operating mode;
a reheat heat exchanger disposed along the refrigerant circuit, wherein the reheat heat exchanger is configured to transfer heat from the second portion of the refrigerant to a conditioned space such that the second portion of the refrigerant condenses in the second operating mode but not in the first operating mode;
a first valve configured to drain the second portion of the refrigerant from the second condenser toward a suction side of the compressor and to the reheat heat exchanger during the second operating mode, wherein the first valve is closed during the first operating mode;
a second valve configured to drain the second portion of the refrigerant from the reheat heat exchanger toward the suction side of the compressor and to the second condenser during the first operating mode, wherein the second valve is closed during the second operating mode; and
a controller configured to switch between the first operating mode and the second operating mode, wherein the controller is configured to open the first valve when switching from the first operating mode to the second operating mode, and wherein the controller is configured to open the second valve when switching from the second operating mode to the first operating mode.
2. The system of claim 1 , wherein the compressor is configured to draw the second portion of the refrigerant from the second condenser during the second operating mode and to draw the second portion of the refrigerant from the reheat heat exchanger during the first operating mode.
3. The system of claim 2 , wherein the controller is configured to regulate operation of the first valve and the second valve, such that a first amount of the second portion of the refrigerant flowing through the refrigerant circuit during the first operating mode is generally equal to a second amount of the second portion of the refrigerant flowing through the refrigerant circuit during the second operating mode.
4. The system of claim 1 , wherein the controller is configured to close the first valve when switching from the second operating mode to the first operating mode and configured to close the second valve when switching from the first operating mode to the second operating mode.
5. The system of claim 1 , wherein the controller is configured to close the first valve a first predetermined elapsed time after switching from the first operating mode to the second operating mode and configured to close the second valve a second predetermined elapsed time after switching from the first operating mode to the second operating mode.
6. The system of claim 1 , comprising a first isolation device disposed along the refrigerant circuit and a second isolation device disposed along the refrigerant circuit, wherein the first isolation device is configured to block the refrigerant from flowing toward the second condenser during the second operating mode, and wherein the second isolation device is configured to block the refrigerant from flowing toward the reheat heat exchanger during the first operating mode.
7. The system of claim 6 , wherein the refrigerant circuit is configured to direct the second portion of the refrigerant to bypass the reheat heat exchanger in the first operating mode, and wherein the refrigerant circuit is configured to direct the second portion of the refrigerant to bypass the second condenser during the second operating mode.
8. The system of claim 1 , comprising a three-way valve disposed along the refrigerant circuit and configured to switch between a first position corresponding to the first operating mode and a second position corresponding to the second operating mode, wherein the three-way valve is configured to direct the first portion of the refrigerant into the first condenser and to direct the second portion of the refrigerant into the second condenser when in the first position, and wherein the three-way valve is configured to direct the first portion of the refrigerant into the first condenser and to direct the second portion of the refrigerant into the reheat heat exchanger when in the second position.
9. The system of claim 1 , comprising an expansion device disposed along the refrigerant circuit configured to receive the first portion of the refrigerant from the first condenser and the second portion of the refrigerant from the second condenser in the first operating mode and to receive the first portion of the refrigerant from the first condenser and the second portion of the refrigerant from the reheat heat exchanger in the second operating mode.