This invention relates to evaporative cooling units designed to evaporatively cool air indirectly, with or without integral direct evaporative cooling of water.
Simple evaporative coolers benefit from the psychrometric process in which dry air and water can be cooled by adding moisture. This evaporation also humidifies the air being cooled. The humidification can be beneficial in very arid climates but has drawbacks in non-desert climates. In many climates, indirect evaporative cooling where two airstreams are used; a ‘wet’ airstream that evaporates water to directly cool both the water and air and a ‘dry’ airstream that is cooled through a heat exchanger (usually a thin walled plate) without moisture addition to the dry airstream. Such indirect evaporative coolers have tended to be expensive to build.
Previous attempts to provide combined water and air cooling evaporative plates have met limited success. One such system is described in U.S. Pat. No. 6,845,629 B1 issued to Bourne et al., which uses a set of plates to cool air, water, or both for building or process cooling needs. However, manufacturing the plates proved to be time consuming and problematic.
Other indirect evaporative plate-type coolers rely on labor intensive and therefore costly means to manufacture the plates. Additionally, many existing systems, such as that described in U.S. Pat. No. 6,581,402 issued to Maisotsenko et al., have high pressure drops that require significant fan energy, thus lowering the Energy Efficiency Ratio (EER) to the point that they are not significantly more efficient than traditional vapor compression systems. The heat exchanger disclosed in Maisotsenko et al. requires the heat exchanger to use at least a fraction of outdoor air, limiting layout options and actual cooling capacity during warm weather periods.
Most new low-rise non-residential buildings in the U.S. are cooled by packaged rooftop units (RTU's) that include one or more compressors, a condenser section that includes one or more air-cooled condensing coils and condenser fans, an evaporator coil, a supply blower, an intake location for outdoor ventilation air (with or without an economizer to fully cool from outdoor air when possible), optional exhaust air components, and controls. These components are packaged by manufacturers in similar configurations that, because they are air-cooled, fail to take advantage of the opportunity to improve efficiency and reduce electrical demand through evaporative cooling of both condenser coils and ventilation air streams.
A cooling unit that incorporates plate-type evaporative heat exchangers is provided to efficiently cool either water or air, or both. The cooling unit utilizes indirect evaporative pre-cooling of ventilation air, which can be used to assist in cooling various building types, for example, commercial building systems. At least 10% of supply air in many such buildings is typically outdoor air needed for building ventilation; in some cases, such as for laboratory facilities, cooling systems must deliver 100% outdoor air. In warm weather, cooling of ventilation air represents a significant fraction of the total cooling load. In very dry climates, ventilation air can be pre-cooled by a direct evaporative process, but in most applications an indirect process that adds no moisture to the ventilation air is preferred.
The plate-type evaporative heat exchanger cooling unit can also be used with “dedicated outdoor air” units that isolate the ventilation air load from other HVAC components. Such units may be incorporated into “variable-air-volume” (VAV) systems that provide required fresh air volumes at low speeds. The plate-type heat exchanger delivering 100% outdoor air, with building exhaust air used in alternating wet passages, provides an indirect evaporative ventilation air cooling unit during the cooling season, as well as a heat recovery unit in heating season by operating without water flow to wet air passages. Thus, the plate-type heat exchanger can pre-heat ventilation air from warm building exhaust air.
The plate-type evaporative heat exchanger cooling unit for evaporative pre-cooling of ventilation air can also be used with energy-efficient systems that provide cooled water for circulation through tubing to cool building structures. The plate-type heat exchanger can alternatively be used to deliver water utilized with radiant floor cooling systems.
Embodiments of a vertical counter-flow evaporative cooler (VCEC) plate-type evaporative heat exchanger are provided that can effectively cool either air or a combination of air and water. An exemplary embodiment uses a C-shaped flow path in the dry passages and an L-shaped flow path in the wet passages, instead of the conventional semi-counter flow (Z-Z or L-L) paths. The C-shaped dry passage air flow configuration provides a passage that is sealed on three sides, providing individual pockets that, when lined up in the heat exchanger stack, create alternating dry passage and wet passage assemblies that can be securely sealed together. This structure provides a robust connection to each dry passage and includes seals around the perimeter of each individual dry passage, so that the dry ventilation air stream is completely isolated from the wet zone surrounding it. This structure can be manufactured in an efficient, cost-effective manner.
An embodiment provides an evaporative section that includes a plate-type evaporative cooler that cools both water and air; a water sump, pump, and water distribution system that captures and re-circulates water within the evaporative section; automatic systems that refill and drain the water sump; a fan that draws air through the dry passages, another fan that draws air through the wet passages; electrical controls; and a cabinet that houses the unit.
In alternate preferred embodiments, the pump and sump are eliminated and replaced with a drain pan to simplify the design and to utilize a ‘once through’ water flow approach that relies on municipal water pressure to distribute water to the plates and then discards excess water through a drain.
The preferred embodiment of the VCEC uses a C-shaped flow path in the dry passages and an L-shaped flow path in the wet passages. Most plate-type heat exchangers use either straight-through cross-flow, or use semi-counter flow paths such as Z-Z or L-L flow paths to maximize counter-flow behavior. The use of C-shaped flow paths present a challenge in circulating air into the corners and avoiding short-circuiting. The C-shaped dry passages have seals on three sides, providing individual pockets that when lined up in the heat exchanger stack create alternating dry passage and wet passage assemblies that can be securely sealed together. This structure provides a robust connection to each dry passage and seals around the perimeter of each individual dry passage, so that the dry ventilation air stream is completely isolated from the wet zone surrounding it. An alternative embodiment uses a C-shaped flow path in the wet passage, which minimizes the height required for the unit by allowing the sump and drain to be located directly below the VCEC.
Many evaporative heat exchangers exhaust wet passage air out through the top of the heat exchanger, making water distribution a challenge. Spray nozzles leave space for wet air to escape, but require high pump head and a drift eliminator assembly. Gravity weir systems can restrict airflow and are susceptible to starvation from out-of-level conditions.
An embodiment of the VCEC wet passage flow path exhausts wet passage air out an upper rear surface. Without the need to accommodate exhaust airflow, this allows the top surface to be dedicated to water distribution. An embodiment of the heat exchanger provides each wet passage to have a weir thermoformed into its upper surface. The weirs are formed when the alternating first and second plates are formed together. The weirs, which can hold water such as, for example, up to ¾″ deep, eliminate out-of-level concerns. Water may be fed to the weirs by a water distribution system having, for example, a perforated sheet positioned above the VCEC, with a perforated distribution tube above the sheet.
Another embodiment provides use of the VCEC for heat recovery ventilation in heating season. In this application, no water is used but fresh air is introduced through the dry passages and building exhaust air is introduced through the “now-dry” exhaust passages. The large area and thin plates allow a significant fraction of exhaust air sensible heat to be transferred to the inlet air, reducing the amount of heat needed to bring the ventilation air up to the required temperature.
Another embodiment of the VCEC provides a total energy recovery heat exchanger. This application is similar to the sensible heat recovery application described above in that no water is applied to the wet passages. Instead, this embodiment uses a porous material that allows moisture to migrate through the plates. In this configuration, the low humidity of the building exhaust air dehumidifies the higher humidity outdoor air. Latent heat transfer can be enhanced with the use of desiccant-infused porous material. Latent heat recovery also can combine with conventional sensible heat recovery. This embodiment is particularly effective in humid climates where ventilation air latent cooling demand is greater than sensible cooling demand.
In embodiments, the VCEC plates are formed in pairs from a continuous sheet of polymer or other suitable thin material such as, but not limited, to a thin metal. Folds are created as the plates are formed to allow the entire exchanger or some subset of the exchanger to be formed by a single piece. With a polymeric material, this fan fold arrangement makes it possible to use automated sealing equipment on the top and bottom edges to completely seal the dry passages from the adjacent wet passages. The heat exchanger may be formed, folded, sealed, and stacked in one continuous operation.
These and other objects and advantages will be apparent to those skilled in the art in light of the following disclosure, claims and accompanying drawings.
The exemplary embodiments will be described in detail in reference to the following drawings in which like reference numerals refer to like elements and where:
In the following description, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements.
In an embodiment of the heat exchanger shown in
In the exemplary embodiment shown in
An alternative embodiment of a heat exchanger 10 provides a different configuration of the wet air flow passage 18, namely, the wet air passage 18 is in communication with at least one wet air flow inlet opening 26 and at least one wet air flow outlet opening 28 both of which are formed in the rear surface 10d, as shown in
In an embodiment of the heat exchanger 10, each first plate 12 has a front edge 12e and a rear edge 12f, each second plate has a front edge 14e and a rear edge 14f, and the front edge 12e of each first plate is hingedly connected to the front edge 14e of an adjacent second plate, and the rear edge 12f of each first plate is hingedly connected to the rear edge 12f of an adjacent second plate. This configuration provides first and second plates 12 and 14 that can be folded and unfolded in a fan fold arrangement.
An exemplary method of forming a heat exchanger of the fan fold configuration, shown in
The method of forming may further include step S4000, selectively sealing adjacent first and second plates along one or more of the top surface 10a, bottom surface 10b, front surface 10c and rear surface 10d, for example, by heating, ultrasonic welding, radio frequency (RF) welding, and/or induction heat welding. In the case of metal or porous plates where the base materials cannot be cost effectively joined, a clamp strip may be used. The method of forming may also include step S3000, aligning adjacent first faces 12a and 14a of the respective first plates and second plates. The aligning step may include the step of inserting at least one projection 46 extending from the surface of the first face 12a of the first plates into a receiver 48 extending from the first face 14a of an adjacent second plate that slidingly receives the projection 46. Other alignment means known in the art may be utilized to align the first face 12a of the first plates with the first face 14a of an adjacent second plate. In embodiments, the method may include step S5000, collecting and stacking folded and sealed plates.
Referring to FIGS. 1 and 6-8, the heat exchanger assembly 10 includes multiple plate pairs 12 and 14 aligned in a parallel vertical configuration. All plates 12 and 14 may be formed from a single continuous sheet 44 folded at front 12e and 14e and rear 12f and 14f edges of the plates. The top edges 12c and bottom edges 12d of the plates may be sealed to the corresponding adjacent plate to form a sealed dry passages 16 in combination with the fold on edge. A first air stream enters the top portion of the open side of the dry passage 16. This air stream is turned within the dry passage (see
Water is distributed above the VCEC into weirs 34, from which the water flows downward through water flow inlet openings 32 into the wet passages 18 of the VCEC. The design allows excess water to collect in the deep weirs 34, permitting the VCEC assembly to be slightly “off-level” and still maintain uniform water distribution. The water flows down the faces 12b and 14b of the wet passages 18 and is cooled by evaporation into the wet air stream. The dry passages 16 are in turn also cooled by conduction through the walls of the heat exchanger. Fins 42 serve as drift eliminators to minimize the possibility of water being carried out the side of the VCEC. Baffle 33 serves the dual purpose of directing water that collects and drips off the fins 42 and also prevents the wet air stream from short circuiting and exiting low on side where it would have less cooling effect. A cooling coil to cool refrigerant (serving as a condensing coil for a vapor compression cooling system,) or fluid for additional building or process cooling can be located below the VCEC to take advantage of the water that is evaporatively cooled by the VCEC.
Although the subject matter of this application has been described with reference to various exemplary embodiments, it is to be understood that the subject matter is not limited to the exemplary embodiments or constructions. To the contrary, the subject matter of this application is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, others combinations and configurations, including more, less, or only a single element, are also within the spirit and scope of the invention.
This invention was made with Government support under Contract #DE-FC26-05NT42325 awarded by the United States Department of Energy. The Government has certain rights in the invention.