The present invention is directed at a hybrid refrigeration system, and specifically, a refrigeration system that cools refrigerant with both an air radiation system and with a cooling tower system to minimize water loss to evaporation, thereby achieving supercooling of the refrigerant while reducing water loss through the cooling tower system.
Refrigeration systems can accomplish heat rejection by heat transfer using either condenser-cooling tower systems or through water-cooled condensers wherein water extracts heat from the refrigerant. The water is subsequently cooled by air through a radiation system.
Cooling towers are extremely efficient in removing heat from condensers, and are used extensively in areas where water is abundant. Cooling towers and not closed systems, however, and require a substantial amount of make-up water, as cooling towers take advantage of the principles of evaporative cooling in removing heat from the system. Cooling towers also require a make-up source of water that is substantially pure, as lesser quality water or contaminated water can lead to degradation of performance of the heat exchanger components and other components that contact the water. Performance is lost as the components accumulate dirt and contaminants. Restoring the components to optimum performance conditions requires cleaning. Cleaning is expensive and can result in equipment downtime and replacement of corroded equipment. Furthermore, when less than pure water is used, components can be fabricated from expensive corrosion-resistant materials. This can reduce down-time required to replace corroded equipment, although cleaning may still be required periodically. Thus, systems using cooling towers are not practical in arid areas where water is scarce or in areas where water cannot readily be provided in a purified mode. In fact, in many regions of the world, good quality water is or is becoming a scarce and expensive commodity. Cooling towers require a continuous supply of water for make-up, thereby limiting their geographic applications.
Water-cooled condensers having water cooled by an air radiation system have higher heat rejection temperatures and require larger heat exchanger surface areas, which adds to their cost. The efficiency of such systems is reduced compared to systems utilizing cooling towers.
What is needed is a system that provides efficient cooling while minimizing the use of precious water.
A refrigeration system utilizes both an air-cooled heat exchanger and a cooling tower to cool refrigerant prior to the refrigerant being provided to the evaporator. The refrigeration system utilizes an air-cooled heat exchanger to cool and change the state of refrigerant provided by a compressor to a condenser from a gas to a liquid and cool the refrigerant in the condenser to a first temperature, T1. The air-cooled heat exchanger is a closed water loop system having a first heat exchanger in heat exchange communication with the condenser wherein water extracts heat from the refrigerant, and a second heat exchanger in heat exchange communication with air to cool the heated water. To improve the efficiency of the system, the refrigerant is then cooled to a second temperature, T2. This is accomplished by utilizing a cooling tower. Water in an open loop circulates between a subcooler and the cooling tower. Water from the cooling tower removes heat from the refrigerant in the subcooler (or a different portion of the condenser) to cool the refrigerant to the second temperature T2. The water in the open loop is then circulated to the cooling tower where its temperature is cooled by both convection and evaporative cooling. Water lost by evaporation must be replaced. Because the refrigeration system utilizes an air-cooled heat exchanger to cool the refrigerant to a first temperature T1, the thermal load on the water in the cooling tower loop, which is used to cool the refrigerant to the second temperature T2, prior to being cycled to an evaporator, is reduced. This reduced thermal load means that the cooling tower can be smaller and the amount of water lost to evaporation by evaporative cooling in the cooling tower is reduced.
An advantage of this system is that the expense required to build a cooling tower is reduced, since the cooling tower may be of a reduced size.
Another advantage of this system is that the amount of water required to replace the water lost by the cooling tower due to evaporative cooling is reduced. In arid or dry climates where water is a precious commodity and in short supply, this is a significant improvement, since no longer is the property owner faced with a choice between reduced efficiency from solely using an air-cooled heat exchanger or using a system that relies on a cooling tower requiring large amounts of water for water replacement due to evaporative cooling.
This system also has an advantage in areas in which water quality is poor. Since less water is required for water replacement due to evaporative cooling, there will be less corrosion or dirt build up as water circulates over the equipment. If the water is treated before being added to the open water loop associated with the cooling tower, there will be less water required which will lower the water treatment costs.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
In an exemplary embodiment, cooling tower supply water 38 is supplied to cooling tower 14 from condenser/subcooler 36, and cooling tower return water is returned to condenser/subcooler 36 by cooling tower return line 40. In
Refrigerant at temperature T1 is further cooled in condenser/subcooler 36 after cooling to temperature T2 by water from cooling tower 14, provided by cooling water return line, which may be supplemented by water from cooling tower return water replenishment line 61. Condenser/subcooler 36 is a hybrid unit that includes two separate heat exchange units, a condenser 60 and a subcooler 62. This hybrid condenser/subcooler may be packaged together for installation as a single unit or as part of a package, as depicted in
Heat removed from the refrigerant by the “cooling tower” water further reduces the refrigerant temperature from a temperature T1 to a temperature T2 in subcooler 62 while the water temperature is increased. This water is returned to cooling tower 14 through cooling tower supply line 38, where the heated water is cooled. In the cooling tower 14, water flows over fill, for example a plastic or a wood material used to maximize the surface area that the water contacts, to improve its heat exchange ability. Cooling tower 14 may additionally include fans to further improve heat removal from the water by providing additional air flow over the water. Some of the water evaporates, and the change in state of the water from a liquid to a gas absorbs energy from the water, further cooling the remaining liquid. The cooled liquid is then returned via cooling water return line 40 to the subcooler.
Subcooled refrigerant is then circulated from condenser/subcooler 36 to an evaporator 46 through refrigerant line 42, and optionally through an expansion valve. The cooled refrigerant in evaporator 46 absorbs heat from water circulated in evaporator 46 to provide chilled water to be circulated through chiller water supply line 48 to air handler system 22. The cooled refrigerant also undergoes a phase change as it absorbs heat in evaporator 46. As shown in
Refrigerant at a temperature T1 from condenser 60 enters subcooler 62 in the refrigerant loop where water in a water loop from cooling tower 14 or 140 enters through line 40 and is placed in heat exchange relationship with the refrigerant in subcooler 62, further lowering the refrigerant temperature to temperature T2. The water from line 40, having absorbed heat from the refrigerant, is returned to the cooling tower through cooling water return line 38. Chilled refrigerant at temperature T2 is delivered to evaporator 46 via refrigerant line 42. When condenser/subcooler 36 is supplied as a single unit as shown in
Condenser/subcooler 36 provides improved efficiency over a water-cooled condenser system using water cooled by an air radiation system. This system provides efficiency slightly reduced from that of a system solely utilizing a cooling tower, but uses less water than such a system. A smaller cooling tower can be utilized with condenser/subcooler 36 because of a smaller thermal load in the cooling tower water loop as a result of the refrigerant temperature first being lowered to temperature T1 by the closed-loop, water-cooled air-cooled heat exchanger. The smaller cooling tower requires less heat transfer surface and loses less water to evaporation, requiring less water replenishment. The condenser/subcooler 36 provides heat transfer properties that are comparable to that of a water tower system, and provides a cost advantage in that a smaller cooling tower can be utilized, and expensive replenishment water supplies are reduced. Importantly, condenser/subcooler 36 provides a lower exiting refrigerant temperature T2 than an air radiation system. The temperature of refrigerant exiting condenser/subcooler 36 approaches that of a cooling tower-only system. A smaller cooling tower also provides an advantage of not only reduced cost, but also of reduced space when space is a consideration, such as in a crowded or congested area.
While only certain features and embodiments of the invention have been shown and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US09/62913 | 11/2/2009 | WO | 00 | 4/15/2011 |
Number | Date | Country | |
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61113797 | Nov 2008 | US |