Cold-heat Recovery For Air Conditioning

Abstract

A cold air replenishment unit for an enclosed building space comprising a purge air system, a replenish air system, a heat pipe assembly spanning the two systems to simultaneously provide cold-heat potential transfer from the purge air to the replenish air, a mechanical refrigeration system comprising the commonly known cycle components, having an air-over fin tube evaporator located downstream of the replenish air heat pipe section, and having an air-over fin tube condenser located upstream of the purge air heat pipe section, all systems jointly forming a cold-heat recovery apparatus.

Description

FIELD OF THE INVENTION

The field of the invention is concerned primarily with large volume cold storage warehouses, wherein itinerant stored produce or produces are material-handled by means of manually operated forklift trucks. Such material handling equipment during constant operation produce carbon monoxide exhaust byproducts which contaminate the warehouse air, thereby posing a danger to both operators working within the enclosures and to certain aspirating produce, say apples.

Also within the field of the invention are large produce ripening rooms such as tomato repack storage vaults. These require an atmosphere of ethylene gas for ripening prior to market preparation, and which require air purging.

BACKGROUND OF INVENTION

The invention is particularly applicable as a makeup air unit for use, but not necessarily limited as such, within the prior-explained intended field of use. The cold-heat recovery mechanism of the present invention provides for the contaminated enclosure cold air heat potential recovery, plus the added utilization of the contaminated purge air and replenish air electromechanically induced airstreams for further supplementary refrigeration effect, this effect being required to return replenishing air to the enclosure at the same approximate temperature as the outgoing purge air temperature.

THE DRAWINGS

FIG. 1 is a top plan view of a cold air replenishment unit embodying the invention.

FIG. 2 is a side elevational view of the FIG. 1 unit.

FIG. 3 illustrates a charging apparatus for heat pipes unit in the FIG. 1 embodiment.

FIG. 4 is a chart depicting the performance of a refrigeration machine used in the FIG. 1 unit.

FIGS. 1 and 2 show a cold air replenishment unit comprising a rectangular casing 10 having a top wall 12, sidewalls 14 and 16, bottom wall 18, and end walls 20 and 22. The unit as shown in FIG. 2 is mounted on the rooftop 24 of a building which may be a cold storage warehouse, but not necessarily limited to such structures, or other structure requiring both a periodic (or continuous) replacement and purge of its room air with fresh air replenishment, at a temperature below the prevailing outdoor ambient temperature and near equivalent to the purged air temperature.

Unit 10 is subdivided by a longitudinal partition 26 into a purge exhaust air passage 28 and a replenish air supply passage 13. A fan (propeller or otherwise) 32, driven by an electric motor 34, draws air out of the building through a duct elbow 36 that connects with a duct opening in the building roof. When the building is a cold storage warehouse the temperature of the air to be purged may be as high as + 30.degree. F. or as low as - 20.degree. F., depending on the product storage requirement of the warehouse. The purge air of the warehouse, at an illustrative temperature of say 30.degree. F. is drawn by fan 32 rightwardly through section 40a of the transversely extending heat pipe or sealed container assembly 40. As this cold purge air flows across the heat pipe assembly it causes condensation of a volatile saturated gas element contained internally in each parallel bank pipe of assembly 40, thus abstracting coolness from the purge air and raising the heat pipe assembly leaving-air temperature to a high value such as 60.degree. F. The 60.degree. air is impelled by fan 32 through a conventional finned condenser coil 42 which forms part of a mechanical refrigeration system. The 60.degree. air flows across the condenser coil finned surface and out of the unit through an outlet opening 44 in the unit top wall 12 (or thereabouts), thereby condensing refrigerant flowing through condenser coil 42; the outlet air temperature may be on the order of 97.degree. F. when the refrigerating system is operating, all in the same manner as commonly known air cooled condensing units operate.

Replenish air passage 30 comprises an inlet opening 46 in end wall 22. Flow through the passage or duct is established by a conventional fan (centrifugal or otherwise) 48 which is belt-driven or direct-driven by an electric motor (not shown). The fan discharges into a flaring transition duct 50 leading to section 40b of the heat pipe assembly 40. It will be seen from FIG. 1 that pipes 40 are of sufficient length to span both ducts 28 and 30, i.e., the entire space between sidewalls 14 and 16. Thus, the heat pipes enjoy complete thermal contact with both necessary system airstreams, thus allowing for its performance of cold-heat transfer plus preconditioning its resultant oppositely flowing airstreams.

The incoming replenish air in duct 30 will in many cases be at a comparatively high temperature, for example averaging 85.degree. F. This high temperature air flows across the heat pipes and causes evaporation of the volatile cold potential liquid in the heat pipes, thereby conductively cooling this air to a lower temperature, for example 60.degree. F. The 60.degree. F. air flows through a conventional refrigerant evaporator coil 50 which is refrigerant cycle-connected with condenser 42 and an interconnecting refrigeration compressor, not shown. The compressor may be located upstream of coil 42, below outlet 44 or in a compartment 43 on the unit top wall 12, or in any event, in close proximity to this cold-heat recovery apparatus. In operation, the compressor conduit transmits hot-compressed refrigerant gas (containing both the heat of compression and low side 50 extracted heat) to condenser coil 42 which is cooled by the duct 28 airstream to effect change of state condensation of the refrigerant. Condensed refrigerant is transmitted through a liquid line and then directly fed to a restriction (e.g., capillary tube) to the evaporator 50 where it is vaporized by the duct 30 airstream. Vaporized refrigerant is returned to the compressor for recycle. The aforegiven description of the refrigerant cycle operation is brief and intended so for such U.S. Pat. No. 2,445,527 to Hirsch and U.S. Pat. No. 2,511,127 to Phillip show the art detail of such commonly known refrigeration systems. The resultant cooled replenish air flowing off of the fins on evaporator 50 is directed through an outlet 52 into an elbow passage 54 that communicates with an opening in the building roof. Suitable duct work within the building (not shown) is acceptable to distribute the cold replenish air to different areas of the building as required.

At the same time suitable purge air is drawn from the building at near to equal volumetric flow rate as the replenish makeup air, thus providing needed enclosure (building) air change rate and satisfactory air pressure balance in the building. The replenish makeup airflow may be greater than or equal to the purge airflow, since some enclosure air leakage may be expected to occur through various normal openings, etc. In a typical installation the airflow through each duct 28 or 30 might be about 1,000 c.f.m. Each duct might have a cross-sectional area of about 2 square feet to provide a linear flow rate of about 500 ft./min., but understanding that these air values and duct sizes will vary as to the applications and requirement, they are not limited therein but only typical in nature.

HEAT PIPE 40 (SEALED CONTAINERS)

FIG. 2 shows three rows of heat pipes, each row containing seven pipes. In practice a greater number of pipes would probably be required, depending on the heat load, airflow, and refrigerating or heating effect to be produced by the heat pipes. In most cases it is preferred to provide extended heat transfer surface in each airstream, as by means of the illustrated plate-type fins 38 extending parallel to the duct axes. Such fins would be provided for the full length of the heat pipe assembly.

Each heat pipe may be formed as shown and described in U.S. Pat. No. 2,350,348 issued to R. S. Gaugler. As shown in FIG. 1, an individual heat pipe comprises a sealed container in the form of an elongated cylindrical tube 56. The plate-type fins 38 are secured on the tube outer surface by the usual flangelike collars 39. Each heat pipe is preferably lined with capillary wick material 58 for its full length. As described in aforementioned U.S. Pat. No. 2,350,348, the wick material may be porous sintered metal bonded to the interior surface of the tube, for example as a part of the sintering operation. Various other methods of retaining the capillary lining in the tube may be employed, as described for example in U.S. Pat. No. 3,095,255 to J. F. D. Smith or U.S. Pat. No. 3,460,612 to E. I. Valyi. As before mentioned, each pipe or tube is charged with a volatile liquid which undergoes condensation in pipe area 40a and vaporization in pipe area 40b.

FIG. 3 illustrates an apparatus for charging each tube 56 prior to installation of the heat pipe assembly into casing 10. As shown in FIG. 3, the tube may be closed at its left end by means of a conventional cap 60. The right end of the tube may have inserted therein a cap 62 having a capillary filler tube 64 projecting therethrough. The apparatus designated by numeral 66 is used initially to evacuate pipe 56, and to then introduce volatile liquid from fluid source 68 into pipe 56.

The apparatus comprises a stationary cylinder 70 having a movable piston 72 slidable therein to alternately compress and relax an O-ring seal element 74. In operation, compressed air from a source, not shown, may be introduced through a fitting 78 to chamber 76, thereby moving cylinder 72 leftwardly to compress the O-ring 74 and produce an inward radial motion of the seal element against the outer surface of tube 64. With the passage structure thus sealed, the vacuum pump 80 may be operated to evacuate the interior of pipe 56 through passage 82 and selector valve 84. Upon establishment of a suitable low pressure in tube 56 the selector valve 84 may be rotated to the dotted line position wherein pipe 56 communicates with fluid source 68. The vacuum in pipe 56 then draws fluid from source 68 into the pipe 56 interior. Valve 84 is maintained in the fluid-charging mode for a sufficient time period calculated in accordance with the thickness and length of porous lining 58. Normally the charging time will be chosen so that sufficient liquid is charged into pipe 56 to completely saturate lining 58 without substantially supersaturating the lining. A slight liquid excess is not fatal to performance. After tube 56 is charged a suitable pinch clamp (not shown) may be closed on tube 64 to seal the unit, after which valve 84 may be turned to its full line position, and the air pressure vented from space 76 by valve means, not shown; this allows spring 86 to move piston 72 rightwardly for relaxing O-ring 74 to permit insertion of the next heat pipe unit into the apparatus.

The various heat pipes 40 may be evacuated and charged together in a single fixture which includes duplicates of apparatus 66; alternately the various heat pipes may be evacuated and charged in successive operations, using a single apparatus 66 or a single row of such apparatus.

HEAT PIPE OPERATION

Heat pipe operation is generally similar to the operation described in aforementioned U.S. Pat. No. 2,350,348. Heat pipe areas 40a within duct 28 are subjected to 30.degree. air, while heat pipe areas 40b in duct 30 are subjected to higher temperature air, for example 60.degree. F. The cold airstream in duct 28 causes the liquid in the pipe 40a interior lining 58 to be condensed, while the hotter airstream in duct 30 causes the condensed liquid in the 40b interior lining 58 to be evaporated. A suitable tube charging liquid is selected that will provide an intended economic temperature conductance between 30.degree. and 60.degree. under the pressure chosen for the tube 56 chamber.

Each heat pipe has a central space 61 which allows vapor from section 40b to move longitudinally into section 40a; meanwhile the capillary porous lining 58 functions to pump condensed liquid from section 40a into section 40b. The overall operation involves a cyclic mass transfer and heat transfer between section 40a and section 40b.

Preferably the heat pipes 40 are arranged with their axis substantially horizontal or slightly pitched so that section 40a is slightly elevated above pipe section 40b, the purpose being to enable gravitational forces to assist or at least not interfere with capillary flow of liquid from section 40a to section 40b. However this preferred pitching, as I understand, is not of significant importance in the heat pipe theory of acceptable performance.

OPERATION OF THE REFRIGERATION MACHINE

FIG. 4 illustrates in chart form the general operation of a refrigeration machine having a condenser 42 and evaporator 50. Compressor operation involves the adiabatic compression of refrigerant vapor from condition C along line C-D. Refrigerant condensation in condenser 42 involves the isothermal condensation of super-cooled refrigerant along line D-A. The usual restrictor (capillary tube or expansion valve) is interposed between condenser 42 and evaporator 50 so that evaporation of refrigerant occurs adiabatically along line A-B; line A-B measures the useful cooling produced by the evaporator. Efficiency of the refrigeration cycle is improved by super-cooling the refrigerant in the condenser but, more beneficially by the reduction of the compression and resultant condensing energy requirement thus producing line C'-D'. The super-cooling causes line D-A to be displaced leftwardly, thereby somewhat increasing the length of useful cooling line A-B. The lower condenser coil entry (purge) air temperature reduces the compressor input power requirement (compressor size) to line B-C' and results in a lowering of the condenser coil work load and relevant size to line C'-D'. The added effect of the heat pipe onto intended replenish airstream can be diagrammatically illustrated in relative respect, by the h BTU/lb. increase by line A-A'.

In the arrangement of FIGS. 1 and 2 the air supplied to condenser 42 is at a relatively low temperature, for example 60.degree. F., so that condenser 42 is able to achieve more super-cooling of the refrigerant and require less work effect than if the air were supplied at a higher temperature, for example 85.degree. F. The cooling of the air in duct 30 by heat pipes 40 reduces the heat load on coil 50 and thus decreases the mass refrigerant flow requirements through the evaporator, thereby appreciably reducing the operating costs and refrigerant cycle component sizes for compressor operation. In a typical installation it is estimated that operational savings might be on the order of 50 percent of the cost based on units wherein heat pipes 40 supplemental to mechanical refrigeration are not employed. It is an apparatus that not only recovers the potential cold content of the purged contaminated air but, by using the same air moving devices normally needed for air purge and replenish, also transfers or uses the cold content in the incoming airstream and the crossflow-arranged refrigeration coils.

DIFFERENTIATION OVER PRIOR PRACTICE

The described apparatus in operation differs from known methods of enclosure air purge and replenish primarily in the respect that it returns makeup air at relatively the same temperature as purged. Known conventional methods of accommodating contaminated air purge is by thermowheel equipment, having porous rotating cell(s) that embrace the two air systems, having mechanical seals and subject to air bypass. The thermowheel, requiring a deep cell or banks of in-parallel cells for effective heat recovery at large .DELTA.t, does not lend itself in practical nature to low-refrigerated enclosure temperature use. Also, the thermowheel can never return replenish air at the same or even near same dehumidified air temperature as the enclosure purge air exhausted. The introduction of nondehumidified replenished air can cause psychrometric vaporization within the enclosure, in the form of frost vapor, in excess, can cause stalactite formation within the enclosure, but also can sanitarily affect the stored product, say beef, by causing sliming or bacteria formation. The thermowheel's intent is for air conditioned or heated enclosure use whereas this invention is an apparatus intended for refrigeration use.

There are no known devices that this invention parallels or duplicates in its intended use or scope.

UNIT ORIENTATION

As shown in FIGS. 1 and 2, casing 10 is disposed on the roof top of the building or enclosure so that elbow ducts 36 and 54 are both located at the same end of the casing. This arrangement may have some advantage in reducing erection costs because a single large opening in the roof top can then be used to contain the duct work which connects with the two elbows 36 and 54. Normally a curb structure or framework must be formed for each duct elbow which enters the building; the cost of a single subdivided curb structure is probably somewhat less than the cost of two separate curb structures located at opposite ends of the casing.

It is not essential that the unit be rooftop mounted. For example, casing 10 can be mounted on a slab outside the building, in which event the inlet 37 for duct 28 and the outlet 52 for duct 30 can connect with the building through a common subdivided opening. The unit can also be mounted in the building or enclosure, in which event outlet 44 for duct 28 and inlet 46 for duct 30 would connect with a common subdivided opening in the building wall; duct 44 might in that case be located in end wall 22.

The illustrated unit 10 is a cool-only unit wherein duct 30 supplies only cool replenish air to the building. The unit 10 can be made as a heat-cool unit by substituting a reversible heat pump refrigeration machine for the described machine. In that event coils 50 and 42 would function both as evaporators and as condensers. During regular cycle operation, coil 50 would function as an evaporator while coil 42 would function as a condenser. During reverse cycle operation, coil 42 would function as an evaporator and coil 50 would function as a condenser; a refrigerant flow reversing valve would of course be used to enable the two coils to perform the dual evaporation-condenser functions. During reverse cycle operations, supplemental heat could be added to the duct 30 airstream by a conventional gas-fired heater or oil-fired heater. Such a reverse cycle unit operation could be used, but not limited to, say banana ripening vaults.

Heat pipes 40 are able to reversibly transfer heat, either from duct 28 to duct 30 or from duct 30 to duct 28, depending on the prevailing temperatures in the two ducts. Therefore heat pipes 40 are adapted to summertime operation or wintertime operation without adjustment or structural change.

Claims

I claim:

1. In a cold air replenishment unit for an enclosed cold storage space comprising a first duct for withdrawing stale air from the space; a second duct for supplying fresh air to the space; and a refrigerating machine comprising a refrigerant condenser in the first duct, and a refrigerant evaporator in the second duct: the improvement comprising sealed container means spanning the two ducts to exchange heat with both duct airstreams; said container means containing a heat transfer liquid that undergoes condensation due to thermal contact with the outgoing stale air and vaporization due to thermal contact with the incoming fresh air; said container means having the portion thereof spanning the first duct located upstream from the condenser; said container means having the portion thereof spanning the second duct located upstream from the evaporator.

2. The unit of claim 1 wherein the two ducts are parallel and adjacent one another; said ducts having a common divider wall, and said sealed container means comprising hollow pipes extending through said common wall normal to the duct axis.

3. The unit of claim 2 wherein the two ducts are horizontal ducts arranged in a common horizontal plane; said hollow pipes extending horizontally crosswise of the ducts; each pipe having a wick lining for capillary pumping of condensed liquid longitudinally along the pipe.

4. The unit of claim 3 wherein the inlet for the first duct and the outlet for the second duct are in a common plane for connection with the building through a common opening.

5. The unit of claim 1 wherein the two ducts are parallel and adjacent one another, said ducts having their respective inlets and outlets at opposite ends of the unit so that the duct streams flow countercurrent to one another.

6. The unit of claim 1 wherein the unit is arranged for rooftop mounting on the building; the two ducts extending parallel and adjacent one another in counterflow relation so that the inlet for the first duct and the outlet for the second duct are in a common vertical plane; said unit being connected to the building via two elbow ducts arranged between the roof and respective ones of the aforementioned inlet and outlet.

7. The unit of claim 1 wherein the enclosed building space takes the form of a cold space for storing perishable commodities at temperatures below about 30.degree. F.