Evaporator liquid preheater for reducing refrigerant charge

Abstract

A system and method for reducing the refrigerant charge in a refrigeration system by preheating the liquid refrigerant before it is introduced to the evaporator inlet. When refrigerant liquid is introduced to the evaporator inlet, a portion of the refrigerant liquid vaporizes. This refrigerant vapor displaces refrigerant liquid at the inlet of the evaporator. As more refrigerant vapor is introduced, the amount of liquid inside the evaporator is reduced. A heat exchanger is placed before the liquid refrigerant inlet of the evaporator to generate more vapor when the refrigerant enters the evaporator.

Claims

1. A method for reducing the refrigerant charge in a liquid overfeed refrigeration system comprising preheating liquid refrigerant prior to introduction of the liquid refrigerant to an evaporator of said refrigeration system to vaporize a portion of said liquid refrigerant to refrigerant vapor and introducing a mixture of said liquid refrigerant and said refrigerant vapor to said evaporator, said method further comprising measuring a property of said refrigerant at an outlet of said evaporator and adjusting an amount of said preheating based on said measured property; wherein said preheating liquid refrigerant step comprises adjusting an amount of heat that is applied to said liquid refrigerant based on data from a sensor located between an outlet of the refrigerant evaporator and an inlet of a compressor, said sensor measuring at least one of temperature, pressure and liquid vapor ratio of refrigerant leaving the refrigerant evaporator; wherein said preheating liquid refrigerant step is carried out in an indirect heat exchanger located in a refrigerant flow path between an evaporator feed pump and an evaporator inlet, in which warmed refrigerant liquid from a refrigerant condenser is used to provide heat to refrigerant leaving said evaporator feed pump.

2. The method according to claim 1, comprising heating said liquid refrigerant to convert 10% to 30% of said liquid refrigerant to said refrigerant vapor and delivering said refrigerant vapor to said evaporator with a remainder of said liquid refrigerant.

3. The method according to claim 1, said refrigeration system comprising a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser, an expansion device and a refrigerant pre-heater connected in a refrigerant flow path in the refrigerant system in the following order: (a) compressor-(b) condenser-(c) pre-heater-(d) expansion device-(e) evaporator-(a) compressor.

4. The method according to claim 3, said refrigerant flow path further comprising a separator element configured to separate liquid and vapor refrigerant leaving said evaporator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic of a refrigeration system according to an embodiment of the invention.

(2) FIG. 2 is a schematic of a refrigeration system according to a second embodiment of the invention.

(3) FIG. 3 is a schematic of a refrigeration system according to a third embodiment of the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows a piping schematic showing an evaporator heat exchanger according to an embodiment of the invention in relation to other components in a liquid overfeed system. This is a preferred piping arrangement to maximize refrigeration system efficiency. The system includes evaporators 2a and 2b, including evaporator coils 4a and 4b, respectively, and defrost/glycol coils 6a and 6b, respectively, condenser 8, compressor 10, expansion devices 11a and 11b (which may be valves, metering orifices or other expansion devices), and separator vessel 12. The foregoing elements may be connected using standard refrigerant tubing in the manner shown in FIG. 1, or according to any standard arrangement. Defrost system 18 includes glycol tank 20, glycol pump 22, glycol heat exchanger 24 and glycol coils 6a and 6b, also connected to one-another and the other element of the system using refrigerant tubing according to the arrangement shown in FIG. 1, or according to any standard arrangement. According to the invention, evaporator pre-heater heat exchanger 14 is located before (upstream of) the inlet to the evaporators 2a and 2b to preheat the liquid refrigerant prior to introduction to the evaporator inlet. The energy required to preheat the liquid refrigerant may be provided by a source internal to the system, such as heated refrigerant leaving the condenser 8, as shown in FIG. 1. An evaporator feed pump 16 may also be provided to provide the additional energy necessary to force the refrigerant through the evaporator heat exchanger. According to one embodiment, the evaporator feed pump may be selected and configured to increase the pressure of the liquid refrigerant to 100 psi or greater in order to prevent an excess amount of refrigerant from vaporizing upon pre-heating.

(5) By increasing the temperature of the liquid refrigerant at the evaporator inlet, more vapor is produced as the refrigerant enters the evaporator, thus reducing the required refrigerant charge per ton of refrigeration capacity. According to preferred embodiments, pre-heating the refrigerant prior to introduction of the refrigerant to the evaporator inlet will reduce the refrigerant charge per ton of refrigeration capacity by 10% and as much as 50%, relative to an identical system that does not include a refrigerant pre-heater. Other embodiments can reduce the refrigerant charge per ton of refrigeration capacity by 20%, by 30%, or by 40%.

(6) Sensors 26a and 26b may be located downstream of said evaporators 2a and 2b, upstream of the inlet to the separator 12, to measure the temperature, pressure, and/or vapor/liquid ratio of refrigerant leaving the evaporators. According to alternative embodiments, sensor 26c may be located in the refrigerant line between the outlet of the separator 12 and the inlet to the compressor 10. Sensors 26a, 26b and 26c may be capacitance sensors of the type disclosed in U.S. Ser. Nos. 14/221,694 and 14/705,781, the disclosures of which are incorporated herein by reference, in their entirety. According to an embodiment of the invention, the evaporator pre-heater 14 may be controlled by a control system 28 that can be used to manually or automatically control the mount of pre-heat that is provided to the refrigerant flowing through the pre-heater. According to a preferred embodiment, control system 28 may be configured to control the amount of pre-heat applied to the refrigerant passing to the evaporator based on data, including refrigerant temperature, pressure and/or liquid/vapor ratio, received from said sensors 26a, 26b, and/or 26c.