Patent Application
20060053820
This invention relates to a heat pump system that is operable in both cooling and heating modes, with a reheat coil incorporated into the system schematic and selectively utilized in both aforementioned modes of operation to provide the benefits of precise temperature and humidity control, performance enhancement, reliability improvement and capacity modulation.
Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in the cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or an indoor heat exchanger). In the evaporator, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment. In addition, as the temperature of the indoor air is lowered, moisture usually is also taken out of the air. In this manner, the humidity level of the indoor air can also be controlled.
The above description is of a refrigerant system being utilized in a cooling mode of operation. In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger serves the purpose of the evaporator and exchangers heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle, in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way reversing valve (or an equivalent device) into the system schematic downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation respectively. Furthermore, if the expansion device cannot handle the reversed flow, then a pair of expansion devices, each along with a check valve, is to be employed instead.
In some cases, while the system is operating in the cooling mode, the temperature level, to which the air is brought to provide a comfort environment in a conditioned space, may need to be higher than the temperature that would provide the ideal humidity level. This has presented design challenges to refrigerant system designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, the reheat coils, placed on the way of indoor air stream behind the evaporator, are employed for the purpose of reheating the air supplied to the conditioned space, after it has been cooled in the evaporator, and where the moisture has been removed.
While reheat coils have been incorporated into the air conditioning systems operating in the cooling mode, they have not been utilized in the heat pump systems, that are operable in both cooling and heating modes, to achieve (in addition to precise control over temperature and humidity) performance enhancement, reliability improvement and capacity modulation in both aforementioned modes of operation. Also, the system control associated with such heat pumps has generally not been well-developed.
In a disclosed embodiment of this invention, a heat pump system is operable in either a cooling or heating mode by reversing the flow of refrigerant from the compressor through the circuit, utilizing a main flow control device such as a four-way reversing valve. A reheat coil is incorporated into the system schematic, and is selectively operated in both cooling and heating modes of operation.
In the cooling mode, the reheat coil receives a flow of a relatively hot refrigerant in a vapor, liquid or two-phase state and reheats an airflow (by means of heat transfer interaction with this refrigerant) to a higher temperature than would otherwise be provided by the conventional design schematic. In general, the reheat coil allows for the dehumidified air to be supplied to an environment to be conditioned at a desired temperature. A stream of air is passed over an indoor heat exchanger, which will maintain the air at a low temperature, assuring enough moisture to be removed from the air, but in many cases at a temperature lower than desired in the conditioned environment. At least a portion of this air is then passed over the reheat coil, where it is reheated to the target temperature.
In the heating mode, the reheat coil is employed to act as a portion of an enlarged indoor heat exchanger (a condenser in this case), in order to enhance system performance by reducing the discharge pressure. The increased size of the combined indoor heat exchanger boosts the heat pump efficiency, usually without the capacity loss. In some cases, when a designer can choose between the efficiency and capacity augmentation, selective operation of the reheat coil may offer an additional step of capacity modulation in the heating mode.
In the heating mode of operation, the reheat coil can be utilized to improve the heat pump efficiency in a number of different arrangements. The present invention provides a variety of system configurations, where separate taps and return points for the reheat coil, along with associated refrigerant flow control devices, are employed. In this way, a system designer has the option of using a reheat coil with the refrigerant having different thermo-physical properties and flow patterns. In embodiments, the reheat coil can be in either serial or parallel communication with the indoor and outdoor heat exchangers, and the refrigerant may flow through the reheat coil in the same or opposite direction, depending on the mode of operation. Again, a worker of ordinary skill in the art would recognize how this would provide beneficial control options.
The following specification and drawings are not intended to cover a wide variety of the known reheat circuit designs and system configurations and only show exemplary circuit schematics to convey the benefits obtained from the teachings of this invention.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
In the heating mode, the refrigerant passes from the discharge line 14, through the four-way valve 18, to the indoor heat exchanger 24, the expansion device 22, the outdoor heat exchanger 20, once again to the four-way valve 18, to the suction line 16, and finally back to the compressor 12. In the heating mode, the air flowing over the indoor coil 24 (a condenser in this case) is heated before entering the conditioned space.
As known in the art, in case the expansion device 22 cannot handle the reverse flow, it can be replaced by two assemblies, each containing a unidirectional expansion device and a check valve for control of refrigerant flow in the appropriate direction.
As shown in
The reheat coil 32 is positioned to be in the path of air passing over the indoor heat exchanger 24 and driven by an air-moving device 33. The reheat coil is utilized in the cooling mode of operation when a system control determines that it would be desirable to predominantly have dehumidification of the air being supplied to an environment to be conditioned, while maintaining the temperature level. The system control manages the refrigerant flow and system operation such that the indoor heat exchanger 24 conditions the airflow heading to the indoor environment to be cooled and dehumidified with at least a portion of that air then being passed over the reheat coil, which reheats the air to a desired temperature for the environment. Thus, by utilizing reheat coil 32 in the cooling mode, the present invention provides better control over the operation of a heat pump system in terms of temperature and humidity, enhancing its operational flexibility and establishing a broader coverage of the external latent and sensible load demands. Although a hot gas reheat schematic, with the reheat coil positioned upstream of the outdoor heat exchanger in the cooling mode of operation, is shown in
In the heating mode, at least a portion of refrigerant in the discharge line 14 is selectively redirected by the three-way valve 30 to flow through the reheat coil 32 to augment the heat pump efficiency, if desired. This refrigerant is then returned back to the discharge line 14 downstream of the three-way valve 30 through the refrigerant line 34 and the check valve 36. Consequently, the refrigerant continues through the heating cycle by flowing through the four-way reversing valve 18, indoor heat exchanger 24, expansion device 22, outdoor heat exchanger 20, four-way reversing valve 18 once again and finally back to the compressor 12. Thus, the combined reheat coil 32 and indoor heat exchanger 24 effectively represent an enlarged combined condenser, that allows for a discharge pressure (and consequently temperature) reduction and efficiency boost of the heat pump system 10. Although such efficiency augmentation usually is not associated with any capacity loss, in some rare cases, when a designer has to choose between the efficiency and capacity augmentation, selective operation of the reheat coil 32 may offer an additional step of capacity modulation at a higher efficiency level in the heating mode. Consequently, system efficiency and reliability can be improved through a reduction of start-stop cycles. Although this configuration is the most simplistic (since it doesn't require any additional hardware) and efficient (since, in the heating mode, refrigerant flow and air flow are arranged in a cross-counterflow manner for the heat transfer interaction) for the reheat cycle shown in
As shown in
If it is desired to have the refrigerant flow in a parallel arrangement through the reheat coil 32 and indoor heat exchanger 24, then the valve 40 is opened, the three-way valve 30 is opened, and the valves 38 and 42 are closed. At least a portion of refrigerant can now flow from the three-way valve 30, through the reheat coil 32, and be returned through the now opened valve 40 to the refrigerant line 28 downstream of the indoor heat exchanger 24. Further, if it is desirable for the refrigerant to flow through the reheat coil 32 after having flowed through the indoor heat exchanger 24, then the valves 40 and 42 are opened to pass the refrigerant through the coil 32 with the three-way valve 30 and valve 38 being closed.
In addition, by closing the three-way valve 30 and valve 40 and opening the valves 38 and 42, the inlet and outlet refrigerant lines leading to the reheat coil 32 can be switched to provide more control and flexibility. (It has to be noted that the check valve 36 should not be present in this case.) Lastly, opening the valve 42 allows for a refrigerant bypass option around the reheat coil 32 in some of aforementioned system configurations, if desired.
It has to be understood that the system arrangements shown and evaluated above are exemplary and are considered for illustrative purposes only. Obviously, each system configuration can be employed separately, as well as many other schematics are feasible by adding refrigerant flow control devices and connecting lines.
Another heat pump system schematic 50 is illustrated in
Moreover, analogously to the
Another heat pump schematic 60 is illustrated in
In addition, a bypass line 68 allows for flow of refrigerant around the outdoor heat exchanger 20. Valves 66 and 70 control the amount of refrigerant flowing thorough and around the outdoor heat exchanger 20. Such a bypass might be utilized when less sensible cooling system capacity is necessary, but dehumidification (latent capacity) would still be desirable.
As with all of these embodiments, the location of the inlet and outlet lines leading to the reheat coil can be switched in the heating mode of operation to provide greater control and operational flexibility. Also, all the shut-off valves can be substituted by regulating flow control devices, which would infinitely improve system response to varying external load demands. Furthermore, a single three-way valve can replace a pair of the conventional valves to perform identical bypass functionality around the outdoor coil to obtain a variable sensible heat ratio in the dehumidification mode of operation. A worker ordinarily skilled in the art can design an appropriate control.
Further, a worker of ordinary skill in the art would recognize what controls would be necessary to control the various valves and components of the refrigerant system, and what would be desirable conditions, at which the various controls need to be implemented.
While particular system schematics and reheat circuit concepts are disclosed, it is well understood by a person ordinarily skilled in the art that many other reheat circuit designs could be utilized and will provide the full benefits obtained from the teachings of this invention. Thus, the present invention broadly extends to the integration of a reheat circuit into a heat pump system, which is operable in both heating and cooling modes, and provides advantages of control flexibility over temperature and humidity, in order to satisfy sensible and latent load demands, as well as performance enhancement, reliability improvement and capacity modulation. Such advantages are obtained due to selective operation of the reheat coil in both heating and cooling modes of operation that characterizes the thrust of this invention.
Although preferred embodiments of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
