Make-up air energy recovery ventilator

Abstract: In an air conditioning system designed to operate in relatively high humidity conditions, an auxiliary unit, including a complete and independent operating refrigerant circuit. is installed in air flow relationship therewith such that outdoor make-up air is caused to flow first through an auxiliary evaporator coil then through the system evaporator coil, and at least a portion of the return air is passed through an auxiliary condenser coil before being discharged outside. Energy is thereby recovered from the return air, and the make-up air is pre-conditioned to improve the dehumidifying effect of the system.

Description: This invention relates generally to air conditioning systems and, more particularly, to an improved method and apparatus for controlling the humidity in a space. With conventional air conditioning systems, little effort is made to control the humidity in the space being cooled and, as a result, in order to achieve the degree of desired comfort, it is necessary to bring the space down to a lower temperature than would otherwise be required. Such an "over cooling" function is relatively expensive and also may be cause for discomfort to one in the space being cooled. An improvement was made to the conventional air conditioning system by the addition of a subcooler on the downstream side of the evaporator as shown and described in U.S. Patent No. 5,622,057, issued on April 22, 1997. Here, the latent affect of the evaporator coil is enhanced by the added subcooler coil, and the humidity is substantially reduced. Another approach that has been taken to control humidity in a space is that of using desiccants to supplement the conventional air conditioning system. Such a system is shown in U.S. Patent 5,551,245, issued on September 3, 1996. Although such a desiccant system can provide even greater humidity control than that of the subcooler approach mentioned above, the fabrication and installation costs thereof are substantially greater. Because of the tight construction of buildings erected today, there is now the condition known as the "sick building" syndrome, wherein there is insufficient leakage of outside air into the building such that the same air is recycled over and over and becomes stale and stagnant. To avoid this problem, there is now an ASHRAE standard code establishing prescribed requirements for minimum replenishment of air volumes in public buildings. This is presently being accomplished by the use of economizers, but present systems will not accommodate the use of 100% outside air since the cooling capacity is generally not sufficient to do so. Similarly, a make-up air pre-conditioner is shown in U.S. Patent 4,281,522, wherein a supplementary system is used to pre-cool the outdoor air. Again, such a system is not capable of accommodating 100% outside air FR-A- 2 299 605 and DE-A-2 612 997 both disclose air conditioning systems having multiple circuits. It is an object of the present invention to provide an improved method and apparatus for the control of humidity in an air conditioned space. Briefly, in accordance with one aspect of the invention, there is provided an airconditioning system as claimed in claim 1. There is also provided a method as claimed in claim 5. Thus a complete refrigeration circuit, including a compressor, a condenser coil, an expansion device, and evaporator coil are installed in working relationship with an air conditioning system having its own such components. The ducting and flow of air by way of fans is arranged such that the outdoor make-up air is made to flow first through the auxiliary evaporator coil and then through the system evaporator coil. Also, at least a portion of the return air from the space is made to pass through the auxiliary condenser coil before it is discharged outside. In this way, the auxiliary system is made to be more efficient by use of the cooler return air rather than outdoor air, and the auxiliary evaporator coil brings the outdoor air closer to the dewpoint prior to its being passed through the evaporator to thereby increase the amount of condensation that occurs at the evaporator coil such that its latent effect is substantially enhanced to reduce the humidity of the air being passed to the space. Another portion of the return air passes through the system evaporator coil. Preferably, filters may be added upstream of both the auxiliary evaporator and the system evaporator coils. Preferably, a subcooler coil may be disposed downstream of the system evaporator coil to further enhance the latent cooling effect thereof. In the drawings as hereinafter described, a preferred embodiment is depicted; However, various other modifications and alternate constructions can be made thereto without departing from the scope of the invention. Figure 1 is a schematic, perspective illustration of an air conditioning system with the present invention incorporated therein; Figure 2 is a schematic, perspective illustration of an air conditioning system with a modified embodiment of the present invention incorporated therein; Figure 3 is a psychrometric chart illustration of the cycles for both the return air and the supply air flowing through the system. Referring now to Figure 1, the invention is shown generally at 10 as applied to an air conditioning system including a compressor 11, a condenser coil 12, an expansion device 13 and an evaporator coil 14 connected in serial flow relationship to operate in a conventional manner, with a fan 15 passing the return air from the space being cooled through the evaporator coil 14, and a fan 20 passing the outdoor air through the condenser coil 12. Although the present invention can be used in a heat pump system, it is most useful in an air conditioning system and will, for purposes of simplicity and description be described in terms of such a system, with the understanding that a reversing valve (not illustrated) could be included such that the system could operate in the heating mode. In accordance with the present invention, an energy recovery unit or auxiliary system 16 is combined with the conventional air conditioning system in such a way as to operationally interact therewith for the purpose of obtaining improved indoor air quality and comfort. The auxiliary system 16 includes a compressor 17, a condenser coil 18, an expansion device 19 and an evaporator coil 21. These auxiliary system components are designed to operate in a conventional closed circuit manner to cool the air passing through evaporator coil 21. While the system is primarily designed to operate in the cooling mode, it can also be used as a heat pump to warm the air passing through the coil 21 which is normally considered the evaporator coil but would be a condenser coil when operating in the heat pump mode of operation. For that purpose, a reversing valve 22 is provided to enable the selective change of refrigerant flow so as to allow either cooling or heat pump operation. Air moving apparatus is provided to move the air through both the auxiliary system and the base system in a manner as shown by the arrows. That is, in one air flow stream, the ambient, outdoor air (make-up air) is caused by the fan 15 to pass through the auxiliary evaporator coil 21 and then through the base system evaporator coil 14. As the ambient air passes through the auxiliary evaporator coil 21, the air is pre-conditioned by the lowering of its dry bulb temperature, thereby removing some moisture and bringing the air closer to its dewpoint. This enables the base unit evaporator 14 to become more effective in sensible cooling and removing moisture, thereby resulting in improved indoor air quality and comfort. If the outdoor air is at a lower temperature than the return air from the space, the reversing valve 22 of the auxiliary unit is switched over to a heat pump mode. Then the coil 21 acts as a condenser coil to thereby heat the air passing therethrough, prior to its passing through the base unit evaporator coil 14. As will be seen, a filter 23 is preferably provided upstream of the auxiliary evaporator coil 21 to screen out any particulate matter that may be entrained in the ambient air. Similarly, a filter 24 is preferably placed upstream of the system evaporator coil 14 to filter out any particulate matter that would otherwise pass through that coil. In addition to the circulation of the ambient air through the system as described hereinabove, there is also an air moving means, such as an electric motor driven fan 25, to circulate the return air through the system as indicated by the arrows. Here, all or a portion of the return air is passed over the condenser coil 18 to complete the condensation stage in the circuit of the auxiliary system. In this way, the system takes advantage of the relatively lower temperature of the return air (e.g. 80 DB/67 WD degrees F as compared with a typical 95 DB/75 WB degrees F outdoor temperature) to increase the efficiency of the auxiliary system. After passing through the auxiliary condenser coil 18, the air is then discharged to ambient. As will be seen in Figure 1, a portion of the return air is mixed with the make-up air coming from the evaporator coil 21 prior to being passed through the evaporator coil 14. This mixture may be selectively varied, depending on the ambient conditions and the desired conditions in the spaced to be cooled. It will be recognized that where the ambient temperature is lower than the desired temperature in the space, the reversing valve 22 may be switched over to the heat pump mode such that the condenser coil 18 acts as an evaporator coil, and the air passing therethrough is therefore cooled prior to being discharged to the outside. Referring now to Figure 2, an alternate embodiment of the present invention is disclosed wherein, a subcooler coil 26 is added for the purpose of selectively subcooling the liquid refrigerant prior to its being passed to the evaporator coil 14 in a manner shown in detail in U.S. Patent Appln. No. 5,622,057 assigned to the assignee of the present invention. A solenoid valve 27 is provided to allow the selective inclusion or exclusion of the subcooler coil 26 within the circuit. When the solenoid valve 27 is open, the refrigerant passes from the condenser coil 12, through the solenoid valve 27, through the expansion valve 13 and to the evaporator coil 14 in a manner as described hereinabove. When subcooling is desired, the solenoid valve 27 is closed so that the refrigerant passes along line 28 to the subcooler coil 26 where the temperature of the refrigerant is reduced. The cooler refrigerant then passes from the subcooler coil 26 along line 29 to a thermal expansion valve 31, where the pressure of the liquid refrigerant is reduced prior to entering the expansion device 13 and the evaporator coil 14. The thermal expansion valve 31 is controlled in a manner described in the above referenced patent. Referring now to Figure 3, there is shown a psychrometric chart illustration of the temperatures of the various air flows passing through the system on a day when the outdoor temperature is 90°F. Assuming the system is operating with 100% make-up air, ambient air is brought in at 95 DB/75 WB degrees F as shown at A. The air is cooled by the evaporator coil 21 to 73.4 DB/68 WB degrees F as indicated a point B. That air is then caused to pass through the evaporator coil 14 where it is further cooled to 59.6 DB/58.2 WB degrees F as shown at C. At this temperature, which is below the dewpoint, a substantial amount of condensation occurs to thereby reduce the humidity of the air being passed to the spaced being cooled. This condensate is drained off in a conventional manner. The cooled air is then passed through the subcooler 26, where it picks up heat from the refrigerant being pre-cooled, with a resulting air temperature of 65 DB/60.3 WB degrees F for delivery to the space being cooled. On the return air side, air coming from the space being cooled is at 80 DB/67 WB degrees F as shown at E in Figure 3. All of this air is then passed through the condenser coil 18, where it is applied to cool the refrigerant in the auxiliary unit 16 for the purpose of condensing it into a liquid. In the process, the air is heated to 109 DB/75.6 WB degrees F, and this relatively hot air is then discharged to the outside. It will therefore be recognized that the energy of the return air is recovered by the auxiliary unit 16 for the purpose of cooling the ambient air to a temperature level below the return air coming from the space.

Claims: An air conditioning system of the type having a compressor (11), a condenser coil (12), an expansion device (13) and an evaporator coil (14) connected in serial flow refrigerant circuitry and comprising an auxiliary refrigerant circuit (16) comprising an auxiliary compressor (17), an auxiliary condenser coil (18), an auxiliary expansion device (19), an auxiliary evaporator coil (21) and air moving means installed in operating relationship with the air conditioning system such that said air moving means causes: outdoor air to flow first through said auxiliary evaporator coil (21) and then through the system evaporator coil (14); and at least a portion of return air from a space being conditioned, to flow through said auxiliary condenser coil (18); characterised in that another portion of return air is caused to flow through said system evaporator coil (14). An air conditioning system as set forth in claim 1 wherein said auxiliary circuit (16) includes a filter (23) and wherein the outdoor air is caused to flow first through said filter (16) and then through said auxiliary evaporator coil (21). An air conditioning system as set forth in claim 1 or 2 wherein said air conditioning system includes a system filter (24) and wherein said an other portion of return air is caused to flow first through said system filter (24) and then through said system evaporator coil (14). An air conditioning system as set forth in claim 1, 2 or 3 wherein said air conditioning system includes a system filter (24) and wherein the outdoor air is caused to flow first through said auxiliary evaporator coil (21), then through said filter (24) and then through the system evaporator coil (14). An air conditioning system as set forth in any preceding and including a subcooler coil (26) disposed downstream of the system evaporator coil (14) and wherein the air passing through the system evaporator coil (14) is also caused to pass through the subcooler coil (26). An air conditioning system as set forth in any preceding claim 17 wherein the air that is passed through said auxiliary condenser coil (18) is subsequently caused to pass through said system condenser coil (12). An air conditioning system as set forth in any preceding claim and including a reversing valve (22) for selectively converting the system from a cooling unit to a heat pump unit whereby the functions of the auxiliary evaporator coil (21) and the auxiliary condenser coil (18) are reversed. A method of improving the performance of an air conditioning system of the type having an evaporator coil (14) and a condenser coil (12) comprising the steps of: installing an auxiliary refrigerant circuit (16) having an auxiliary compressor (17), an auxiliary condenser coil (18), an auxiliary expansion device (19), and an auxiliary evaporator coil (21); installing air moving means to cause outdoor air to flow first through said auxiliary evaporator coil (18) and then through the system evaporator coil (14); and installing air moving means to cause at least a portion of return air from a space being conditioned, to flow through said auxiliary condenser coil (18); characterised by the additional step of installing air moving means to cause another portion of return air to flow through said system evaporator coil (14).

Inventors: BUSSJAGER RUDDY C, MCKALLIP JAMES M, MILLER LESTER N, BUSSJAGER, RUDDY C., MCKALLIP, JAMES M., MILLER, LESTER N.
Applicants: CARRIER CORP, CARRIER CORPORATION
Application year: 1999
Main classification: F24F3
IPC codes: F25B13, F24F3, F25B40, F24F12