Water source heat pump head pressure control for hot gas reheat
A heat pump system includes a compressor, usage side heat exchanger, heat source side heat exchanger, expansion mechanism, main refrigerant flow control device switchable between cooling and heating modes, gas reheat heat exchanger connected in the refrigerant circuit, a fan disposed to direct an airflow across the usage side heat exchanger and the gas reheat heat exchanger into a target space, and a secondary refrigerant flow control device switchable between first and second modes. Refrigerant flows from the discharge line to the main refrigerant flow control device in the heating mode and the cooling mode in the first mode. Refrigerant flows from the discharge line to the gas reheat heat exchanger in a gas reheat mode and then flows to the main refrigerant flow control device in the second mode. A flow of the heat transfer medium to the heat source side heat exchanger is adjustable.
1. A heat pump system comprising:
a compressor, the compressor delivering compressed refrigerant to a discharge line and receiving a refrigerant from a suction line;
a usage side heat exchanger;
a heat source side heat exchanger arranged to exchange heat between a heat transfer medium and refrigerant flowing therethrough;
an expansion valve;
a main refrigerant flow control valve switchable between
a cooling mode in which refrigerant flows from the discharge line through a refrigerant circuit, to the heat source side heat exchanger, to the expansion valve and then to the usage side heat exchanger, and
a heating mode in which refrigerant flows from the discharge line through the refrigerant circuit to the usage side heat exchanger, to the expansion valve and then to the heat source side heat exchanger;
a gas reheat heat exchanger connected in the refrigerant circuit;
a fan disposed to direct an airflow across the usage side heat exchanger and the gas reheat heat exchanger into a target space;
a secondary refrigerant flow control valve switchable between
a first mode in which refrigerant flows from the discharge line to the main refrigerant flow control valve in the heating mode and the cooling mode, and
a second mode in which refrigerant flows from the discharge line to the gas reheat heat exchanger in a gas reheat mode and then flows to the main refrigerant flow control valve; and
a heat transfer medium flow control valve disposed on an inlet side of the heat source side heat exchanger to adjust flow of the heat transfer medium into the heat source side heat exchanger;
the heat transfer medium flow control valve permitting flow of the heat transfer medium to flow to the heat source side heat exchanger when the secondary refrigerant flow control valve is in the first mode in the heating mode and the cooling mode, and
the heat transfer medium flow control valve being configured to adjust flow of the heat transfer medium to the heat source side heat exchanger when the secondary refrigerant flow control valve is in the second mode in the gas reheat mode.
2. The heat pump according to claim 1 , wherein
the heat transfer medium of the heat source side heat exchanger is a liquid.
3. The heat pump according to claim 2 , wherein
the heat transfer medium of the source side heat exchanger is water.
4. The heat pump according to claim 2 , wherein
the source side heat exchanger is a coaxial heat exchanger.
5. The heat pump according to claim 1 , further comprising
a control switch disposed between a discharge port of the compressor and an inlet of the gas reheat heat exchanger, the control switch being configured to control the heat transfer medium flow control valve.
6. The heat pump according to claim 5 , wherein
the control switch is connected in a control circuit to the heat transfer medium flow control valve.
7. The heat pump according to claim 6 , wherein
the control circuit includes a relay that receives a wired or wireless signal from a thermostat to open or close the relay.
8. The heat pump according to claim 6 , wherein
the control switch includes a pressure control switch that is normally open unless a pressure of refrigerant at the control switch falls below an actuation pressure.
9. The heat pump according to claim 8 , wherein
once the pressure at the control switch has fallen below the actuation pressure, the control switch will be closed until the pressure at the control switch rises above a release pressure that is higher than the actuation pressure.
10. The heat pump according to claim 9 , wherein
if the pressure control switch is in a normally open position, the pressure control switch will remain in the open position even when the pressure at the control switch falls below the release pressure.
11. The heat pump according to claim 1 , wherein
the secondary refrigerant flow control valve is a three-way valve that selectively communicates refrigerant from the refrigerant circuit to the reheat coil.
12. The heat pump according to claim 1 , wherein
the main refrigerant flow control valve is a four-way valve.
13. The heat pump according to claim 1 , wherein
the gas reheat heat exchanger is positioned upstream of the usage side heat exchanger in the gas reheat mode along the refrigerant circuit.
14. The heat pump according to claim 1 , wherein
the gas reheat heat exchanger is positioned upstream of the main refrigerant flow control valve in the gas reheat mode along the refrigerant circuit.