Level control in an evaporator

A heating, ventilation and air-conditioning (HVAC) a falling film evaporator in flow communication with a condenser. The falling film evaporator includes a separator to separate vapor from liquid refrigerant and a plurality of evaporator tubes through which a volume of thermal energy transfer medium is flowed. A distribution system is operably connected to the separator to distribute a flow of liquid refrigerant over the plurality of evaporator tubes. A primary feed conduit delivers a flow of refrigerant to the separator, and at least one secondary feed conduit is in flow communication with the primary feed conduit. At least one auxiliary valve is located at the secondary feed conduit to regulate flow into the separator from the primary feed conduit. At least one sensor senses a level of a refrigerant pool in the evaporator. The sensor is operably connected to the at least one auxiliary valve to control operation thereof.

BACKGROUND

The subject matter disclosed herein relates to heating, ventilation and air conditioning (HVAC) systems. More specifically, the subject matter disclosed herein relates to evaporators for HVAC systems.

HVAC systems, such as chillers, use an evaporator to facilitate a thermal energy exchange between a refrigerant in the evaporator and a medium flowing in a number of evaporator tubes positioned in the evaporator. In a flooded evaporator, the tubes are submerged in a pool of refrigerant. In the flooded evaporator system, compressor guide vanes and system metering tools control a total rate of refrigerant circulation through the system. The specific requirement of maintaining an adequate refrigerant level in the pool is achieved by merely maintaining a level of charge, or total volume of refrigerant in the system.

Another type of evaporator used in chiller systems is a falling film evaporator. In a falling film evaporator, the evaporator tubes are positioned typically below a distribution manifold from which refrigerant is urged, forming a “falling film” on the evaporator tubes. The falling film terminates in a refrigerant pool at a bottom of the falling film evaporator. On advantage of a falling film evaporator is typically the use of a lower amount of refrigerant charge compared to a flooded evaporator system. One challenge with falling film evaporators, however, is maintaining an adequate refrigerant level in the refrigerant pool, while still achieving the savings in refrigerant utilized.

BRIEF SUMMARY

In one embodiment, a heating, ventilation and air conditioning (HVAC) system includes a condenser flowing a flow of refrigerant therethrough and a falling film evaporator in flow communication with the condenser. The falling film evaporator includes a plurality of evaporator tubes through which a volume of thermal energy transfer medium is flowed. A distribution system distributes a flow of liquid refrigerant over the plurality of evaporator tubes. A primary feed conduit delivers a flow of refrigerant to the evaporator, and at least one secondary feed conduit is in flow communication with the primary feed conduit. At least one auxiliary valve is located at the secondary feed conduit to regulate flow into the evaporator from the primary feed conduit. At least one sensor senses a level of a refrigerant pool in the evaporator. The sensor is operably connected to the at least one auxiliary valve to control operation thereof.

In another embodiment, an evaporator system for a heating ventilation and air conditioning (HVAC) system includes a plurality of evaporator tubes through which a volume of thermal energy transfer medium is flowed. A distribution system distributes a flow of liquid refrigerant over the plurality of evaporator tubes. A primary feed conduit delivers a flow of refrigerant to the evaporator and at least one secondary feed conduit is in flow communication with the primary feed conduit. At least one auxiliary valve is located at the secondary feed conduit to regulate flow into the separator from the primary feed conduit and at least one sensor senses a level of a refrigerant pool in the evaporator. The sensor is operably connected to the at least one auxiliary valve to control operation thereof.

In yet another embodiment, a method of regulating flow of refrigerant to an evaporator system for a heating ventilation and air conditioning (HVAC) system includes flowing the refrigerant through a primary feed conduit toward the evaporator system. At least a portion of the refrigerant is flowed into a secondary feed conduit arranged in parallel to the primary feed conduit. A refrigerant level in a refrigerant pool of the evaporator is sensed and the flow of refrigerant through the secondary feed conduit and into the evaporator via the primary feed conduit is regulated based on the sensed refrigerant level.

DETAILED DESCRIPTION

Shown inFIG. 1is a schematic view an embodiment of a heating, ventilation and air conditioning (HVAC) unit, for example, a chiller10utilizing a falling film evaporator12. A flow of vapor refrigerant14is directed into a compressor16and then to a condenser18that outputs a flow of liquid refrigerant20to an expansion valve22. The expansion valve22outputs a vapor and liquid refrigerant mixture24to the evaporator12. A thermal energy exchange occurs between a flow of heat transfer medium28flowing through a plurality of evaporator tubes26into and out of the evaporator12and the vapor and liquid refrigerant mixture24. As the vapor and liquid refrigerant mixture24is boiled off in the evaporator12, the vapor refrigerant14is directed to the compressor16.

Referring now toFIG. 2, as stated above, the evaporator12is a falling film evaporator. The evaporator12includes housing100with the evaporator12components disposed at least partially therein, including a separator30to separate liquid refrigerant20and vapor refrigerant14from the vapor and liquid refrigerant mixture24. Vapor refrigerant14is routed from the separator30through a suction port32and toward the compressor16, while the liquid refrigerant20is routed toward a distribution system34of the evaporator12. The distribution system34includes a distribution box36having a plurality of drip openings38arrayed along a bottom surface of the distribution box36. Though in the embodiment ofFIG. 2the distribution box36is substantially rectangular in cross-section, it is to be appreciated that the distribution box36may have another cross-sectional shape, for example, T-shaped or oval shaped. The distribution box36and drip openings38are configured to drip liquid refrigerant20onto evaporator tubes26and resulting in the falling film terminating in a refrigerant pool40at a bottom of the evaporator12. A feed pipe42extends from the separator30into the distribution box36and terminates in the distribution box36.

Referring toFIG. 3, flow from the expansion valve22into the separator30is via a primary feed conduit44with a feed outlet46that is, in some embodiments, below a separator refrigerant level48. The expansion valve22is a self metering device that self adjusts based on pressure in the primary feed conduit44upstream and downstream of the expansion valve22. It is to be appreciated that the expansion valve22may include electronic expansion valve, thermostatic expansion valve, capillary tube, or other types of self-metering device. A secondary feed conduit52branches from the primary feed conduit44upstream of the expansion valve22and reconnects to the primary feed conduit44downstream of the expansion valve22. The secondary feed conduit52includes an auxiliary valve54to meter flow through the secondary feed conduit52. The auxiliary valve54is not, however, self-adjusting, but is connected to a level meter56in the evaporator12that senses the level of refrigerant in the refrigerant pool40. In some embodiments, the level meter56is a float, but other types of level meters56, for example, mechanical, electronic, or optical devices, such as capacitive sensors, may be used. An increased level of refrigerant in the refrigerant pool40detected by the level meter56, in some instances exceeding an upper threshold, results in the auxiliary valve54moving towards a closed position reducing a flow through the secondary feed conduit52. A decreased level of refrigerant in the refrigerant pool40detected by the level meter56, in some instances below a lower threshold, results in the auxiliary valve54moving towards a open position increasing a flow through the secondary feed conduit52.

During normal, nominal operation of the evaporator12, both the expansion valve22and the auxiliary valve54are at least partially open, so flow proceeds through both the primary feed conduit44and the secondary feed conduit52. The primary feed conduit44and the expansion valve22are sized to handle a majority of the flow while, depending on the refrigerant level in the refrigerant pool40, the auxiliary valve54can be opened to increase flow into the separator30, and thus increase flow rate into the refrigerant pool40to raise its level. Similarly, the auxiliary valve54can be closed to decrease flow into the separator30and likewise flow into the refrigerant pool40thus lowering its level.