Systems and methods for defrost of heat pump systems
The present disclosure relates to a heating, ventilation, and air conditioning (“HVAC”) system include a supply damper, a return damper, and a defrost damper which are operable to control a supply airflow, a return airflow, and a defrost airflow to flow between a supply duct, a return duct, and an indoor heat exchanger without substantially flowing into and substantially cooling an indoor space. A reheat coil may also warm the supply air flow and a defrost return line may be used to bypass a bi-flow expansion device and an indoor heat exchanger.
1 . A heating, ventilation, and air conditioning (HVAC) system operable to use a refrigerant to heat or cool an indoor space and comprising:
a compressor, an outdoor heat exchanger, an indoor heat exchanger, a bi-flow expansion device, and a four-way valve operable to flow the refrigerant through the bi-flow expansion device in a first direction in a cooling mode or a defrost mode and in a second direction, opposite the first direction, in a heating mode;
a reheat
a three-way valve positioned between the compressor and the four-way valve;
a first refrigerant line extending from downstream of the three-way valve to the reheat coil and a second refrigerant line extending from the reheat coil to upstream of the four-way valve; and
a controller in communication with the compressor, the four-way valve, and the three-way valve,
wherein the controller is programmed to, when in the defrost mode:
operate the three-way valve to flow only a portion of refrigerant, which is heated and compressed, from the compressor to the reheat coil through the first refrigerant line so that a supply airflow from the indoor heat exchanger to the indoor space is heated,
flow the portion of refrigerant that flows through the reheat coil through the second refrigerant line to combine with a remainder of the refrigerant upstream of the four-way valve,
operate the four-way valve to direct the combined refrigerant flow in the first direction through the outdoor heat exchanger to defrost the outdoor heat exchanger while the indoor heat exchanger operates as an evaporator, and
operate the three-way valve to control how much of the portion of the refrigerant to flow to the reheat coil such that the supply airflow is heated so as to maintain a setpoint temperature of the heating mode.
2 . The HVAC system of claim 1 , further comprising a filter drier located between the bi-flow expansion device and the outdoor heat exchanger, wherein the filter drier is configured to filter particulate contamination in the refrigerant and capture moisture in the refrigerant.
3 . A method of defrosting a heating, ventilation, and air conditioning (“HVAC”) system operable to use a refrigerant to heat or cool an indoor space, the method comprising operating the system in a defrost mode when an outdoor heat exchanger has developed frost, comprising:
warming and compressing the refrigerant with a compressor;
flowing the compressed and heated refrigerant from the compressor through a three-way valve positioned between the compressor and a four-way valve;
flowing only a portion of the compressed and heated refrigerant from the three-way valve, through a first refrigerant line, and through a reheat coil;
flowing the portion of the refrigerant from the reheat coil through a second refrigerant line to combine with the remainder of the compressed and heated refrigerant upstream of the four-way valve;
flowing the combined portion and reminder of refrigerant through the four-way valve and an outdoor heat exchanger to defrost the outdoor heat exchanger; and
flowing a supply airflow across an indoor heat exchanger, which cools the airflow, and the reheat coil, which reheats the airflow such that an indoor space set point-setpoint temperature of a heating mode is maintained.
4 . The method of claim 3 , further comprising:
filtering the refrigerant from the outdoor heat exchanger of particulate contamination with a filter drier located between the outdoor heat exchanger and a bi-flow expansion device; and
capturing moisture from the refrigerant from the outdoor heat exchanger with the filter drier.