Patent Application
20060048526
This invention relates to a heat pump that is operable in both a cooling and a heating mode, and wherein a discharge valve is controlled to increase and modulate the heating capacity of the heat pump.
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.
The above description is of a refrigerant system being utilized in the 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 design, with the valve located downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through the 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, than a pair of expansion devices, each along with a check valve, can be employed instead.
Heat pumps are intended to replace a furnace, such that a single unit can provide the function of both the air conditioner and the furnace. However, heat pumps have not been widely adopted in colder climates. The major reasons for this slow adoption is the concern that the heat pump cannot provide adequate heat in colder climates and/or the temperature of the heated air delivered to the conditioned environment is too cold (so called “cold blow”) and uncomfortable to the end user. An additional drawback is that to compensate for the lack of heating capacity, the system needs to rely on separate heaters. Since a heater delivers a predetermined amount of heating capacity, the system must be cycled OFF when the desired indoor temperature is reached and cycled back ON when the temperature falls below the desired value. The unit cycling is inefficient, prone to reliability problems, magnifies temperature variations in the conditioned space and causes discomfort to the end user.
In a disclosed embodiment of this invention, a four-way reversing valve selectively controls the flow of refrigerant from a compressor discharge to either an outdoor heat exchanger in a cooling mode, or to an indoor heat exchanger in a heating mode. As explained above, the refrigerant flows through a complete cycle under either mode, and returns to the compressor. The flow back to the compressor also passes through the four-way valve.
To provide greater heating capacity delivered by the heat pump, the present invention employs a restriction downstream of the compressor, such that the compressed refrigerant in the discharge line is modulated or pulsed by changing the size of the restriction. Preferably, the restriction is provided by a controllable valve that can be moved to a restricted position when greater heating capacity is desired. By restricting the flow of the refrigerant on the discharge line, the pressure, and thus the temperature, of that refrigerant is increased significantly. In this manner, the heating capacity of the refrigerant when it reaches the indoor heat exchanger is higher. Also modulating or pulsing the valve can add just the right amount of heat such that the system does need to be cycled ON and OFF. This additional amount of heat can be added, for example, to fill the gap between the heating stages of engaging an additional system heating element (often called electric strip heating). Also the extra heat added by modulating or pulsing the valve can be used as a last resort option where more heat is needed but the system has already “topped out” in terms of how much additional heat can be delivered by running the heat pump with all electric strip heaters engaged. In this manner, the conventional heat pump can be relied upon to provide adequate heating in even colder climates.
In one disclosed embodiment, the four-way valve includes a single chamber with a specially configured plunger to selectively communicate indoor and outdoor heat exchangers to either suction or discharge line of the compressor. While a separate valve may be utilized as the restriction defined above, in one preferred embodiment, it is this same four-way valve that is utilized to provide the restriction. By selectively positioning the plunger element relative to the passages, the present invention allows the flow of refrigerant from the compressor discharge line to the indoor heat exchanger to be restricted, such that this flow can be pulsed or modulated to increase the pressure and temperature of the refrigerant.
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.
This is a very simplified schematic for a heat pump system. It should be understood that much more complex systems are possible, and may incorporate a re-heat circuit, an economizer vapor injection circuit, a bypass around the outdoor heat exchanger 24, a bypass unloading from a compressor intermediate stage back to the compressor suction, etc. It should be understood that the teachings of this invention can be incorporated into any of these more complex heat pump systems.
As shown in
In the pulse mode the size of the restriction is varied on a cyclic basis. The cycling frequency and the amount of restriction opening can be varied to satisfy the required heating demand as shown in
Of course, the operation of the valve can be coupled to an information obtained from various sensors and transducers installed in the system. For example, the minimum size of the variable restriction can be limited by the pressure rating of the compressor components or the compressor maximum pressure ratio, therefore if calculations or a pressure transducer installed upstream of the valve indicate that a pressure is reaching a critical value, then the limit is placed on the size of the restriction opening. A similar logic would apply to calculations or measurements of temperature to assure, for example, that the temperature limit at the compressor discharge is not exceeded.
As shown in
As shown in
While 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.
