US 3064952 A
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Description (OCR text may contain errors)
Nov. 20, 1962 R. w. BROWN AIR CONDITIONING SYSTEM Filed Aug. 4, 1960 2 IN VEN TOR. Rummy I I T B120 WN.
.ATTY- 3,964,952 AIR CDNDHKONHNG SYSTEM Ronaid W. Brown, Toiedo, fihio, assignor to Midland- Ross Qorporation, Toledo, @hio, a corporation of Gino Filed Aug. 4, 1969, Ser. No. 46,613 4 Claims, (ill. 261-3) This invention relates to an improved air conditioning system of the type which includes apparatus to contact a stream of air being conditioned with a stream of hygroscopic solution. More particularly, this invention relates to an air conditioning system for conditioning the air for a plurality of chambers wherein it is desired to maintain the relative humidity at or above a minimum desired value.
This invention also relates to an improved apparatus for adding moisture to an aqueous hygroscopic solution to compensate for the moisture added to the air from the solution during those periods when the air conditioning unit must humidify the treated air to maintain the air, at or above, the minimum desired humidity conditions for safety reasons, human comfort, or industrial process requirements.
In the art of air conditioning a plurality of spaces from a central air treating unit of the type which utilizes an aqueous hygroscopic solution as an air treating medium, there are many schemes for controlling the temperature and moisture conditions of the treated air. Perhaps the simplest control scheme involves controlling the moisture and temperature conditions or" the treated air from the central air treating unit in response to humidity and temperature conditions in one of the several conditioned spaces. This control scheme is satisfactory only in applications where the sensible and latent heat loads of the several spaces will normally be relatively proportional to each other or in those applications where relatively Wide deviations from optimum temperature and humidity conditions are tolerable in the other spaces.
In systems for conditioning a plurality of operating rooms in a hospital, however, a deviation below the optimum humidity conditions may not be tolerated in any of the operating rooms. It is essential that a minimum relative humidity be maintained in each operating room to suppress the formation of static electricity charges which are capable of igniting explosive mixtures of anesthetic gases. I have found that a plurality of operating rooms may be safely and conveniently conditioned by treating the air in the conditioning unit to constant conditions of temperature and humidity and by then heating at a point remote from the conditioning unit, when necessary the air streams to the individual operating rooms in response to temperature conditions within the respective rooms.
To obtain the optimum constant conditions of temperature and humidity in the air from the conditioning unit may require that the air be either cooled or heated and either dehumidified or humidified in the air treating unit. It is, of course, old in the air conditioning art to contact a stream of air with an aqueous hygroscopic solution, such as an aqueous solution of lithium chloride, and to utilize the moisture vapor pressure difference between the air and hygroscopic solution streams as the mechanism for creating a moisture interchange between the contacted streams. Apparatus for accomplishing this moisture interchange is shown in a simplified form in FIG. 3 of United States Patent 2,798,570 to Kelley. Such equipment normally operates to dehumidify the air stream and it is the usual practice to provide an additional contacting chamber in which the spent or diluted hygroscopic fluid is de-watered or regenerated by heating the fluid and passing it into contact with a scavenging gas at a lower E,%d,%2 Patented Nov. 29, 11962 moisture vapor pressure thus maintaining the hygroscopic solution at a relatively constant concentration.
The humidification of the treated air by the hygroscopic solution, as is frequently required in hospital applications of the type described, poses certain problems not inherent in the operation of prior art dehumidifying apparatus. Since it is difficult to construct a regenerator capable of transferring moisture to the hygroscopic fluid from the scavenging gas, a problem of avoiding overconcentration of the hygroscopic fluid arises during these periods when the air conditioning unit is functioning to add moisture to the air being treated. Such a condition can, in aggravated cases, lead to salting-out of the hygroscopic material if provisions are not made to add a compensating amount of moisture to the hygroscopic solution. It is, in View of the present state of the art, an obvious expedient to add Water in the liquid state to the hygroscopic solution during such periods. This may be accomplished either manually or automatically, as in response to a signal indicative of the solution concentration such as a float-type level measuring device. It is desira ble to use demiueraiized or distilled water or pure steam condensate for this purpose since the use of tap water creates the problem of precipitation of dissolved impurities in the system, especially in heated portions of the air conditioning unit such as in the regenerator. Because the equipment needed to maintain an independent body of pure make-up for this purpose is quite expensive, it has been the practice, in certain installations, to bleed steam condensate from a nearby steam heating system and add this condensate to the hygroscopic fluid sump. This expediency, however, involves the danger that the steam heating system may not be able to supply a sufficient quantity of condensate when needed for this purpose, as during those periods when there is no heating load on the steam system. Another expedient which has been practiced by some prior artisans involves the addition of live steam from a steam heating system directly to the hygroscopic solution in the sump. This method, which is illustrated in United States Patent 2,159,276 to Lawless, has an advantage over the method of adding steam condensate in that the availability of steam in a given heating system is less dependent on the heating load of the heating system than is the availability of condensate. However, live steam tends to violently agitate the hygroscopic solution thereby causing excessive splashing and noise.
It is, therefore, the object of my invention to provide an air conditioning system which is capable of humiditying a stream of air for sustained periods by evaporation of moisture from a stream of hygroscopic solution.
It is a further object of my invention to provide an air conditioning system which is capable of humidifying or dehumidifying and Warming or cooling the incoming air as its properties require, to provide treated outlet air at fixed conditions of temperature and moisture content.
It is a further object of my invention to provide novel means for adding make-up water to a hygroscopic liquid air conditioning system during periods when the system is operating to humidity the treated air. It is a further object of my invention to incorporate in such means the advantage of increased availability that live steam in a steam heating system has over steam condensate in the same system together with the advantages that can be realized by adding make-up water to the air conditioning system in the liquid state rather than in the vapor state.
It is a further object of my invention to indirectly transfer, to a stream of hygroscopic solution, a quantity of heat proportional in value to the heat required to evaporate moisture from the hygroscopic solution and to utilize such heat transfer steps as the means to condense steam whereby to obtain make-up water to replenish the moisture evaporated from the hygroscopic solution. It is a further object of my invention to obtain the advantages inherent in performing such heat transfer step within the contact chamber of the air conditioning unit.
For a consideration of what I believe to be novel and my invention attention is directed to the following portion of the specification, the drawing, and the appended claims.
In the drawing:
FIGURE 1 illustrates apparatus embodying this invention;
FIGURE 2 illustrates a fragmentary portion of a distribution system for distributing and consuming the air stream conditioned in accordance with this invention.
In accordance with the invention as is illustrated in FIGURE 1, the air to be conditioned is admitted, through pre-heat chamber 11, to contact chamber 12 wherein the air is treated by intimately contacting it with an aqueous solution of a hygroscopic material, such as lithium chloride, over extended surface cooling coil 13 to which a coolant, preferably chilled water, may be admitted by means of control valve 14. This treated air, which is delivered from chamber 12 through header 15 to a plurality of conditioned spaces by means of blower 16 is brought to controlled conditions of temperature and humidity in chamber 12 by controlling the concentration of the hygroscopic solution the cooling effect of cooling coil 13, and the heating effect of coil 17.
Pre-heat chamber 11 is equipped with a coil 17 to which steam is admitted through control valve 18. Such a pre-heat chamber is old in the art with the operation of valve 18, in prior art devices, normaly being thermally responsive to a thermostat immediately downstream of the pre-heat chamber, as at point 19. In connection with air conditioning applications which frequently require humidification of the treated air, however, it is expedient to make the operation of valve 18 responsive rather to the outlet air dry bulb temperature as sensed by thermostat 23 in header 15. This modification to the prior art preheat control schemes, While serving to decrease to a degree the sensitivity of the pre-heat chamber to fluctuations in inlet air temperature, permits ready compensation for those fluctuations in outlet air temperature as caused by adiabatic chilling of the air during periods of air heating and humidification. It would, of course, be possible to devise an elaborate control system to control the operation of valve 18 in response both to thermostat 23 and in response to a thermostat at point 19. However, the expense of such an elaborate control system could rarely be economically justified.
It is to be noted that a control system for the apparatus, as thus far described, should safeguard against the simultaneous operation of heating coil 17 and cooling coil 13. This may be achieved by making control valve 14 a normally-closed valve adapted to open only when the outlet air dry bulb temperature, as sensed by thermostat 23, exceeds the preselected dry bulb temperature by some reasonable differential, say 2 F. Similarly, control valve 18 may be a normally open valve adapted to close when the outlet air dry bulb temperature is below the preselected value by 2 F. or some other reasonable differential.
The aqueous hygroscopic solution which is delivered to contact chamber 12 from sump 25 by means of conduit 26, pump 27, conduit 28, conduit 29, metering orifice 31 and spray nozzles 32, is returned to sump 25 through conduit 33, by gravity, in a more or less concentrated condition depending on whether the incoming air is humidified or dehumidified in bringing it to the desired humidity conditions. Provisions must, therefore, be made to add or subtract an equivalent amount of moisture from the hygroscopic solution to maintain the solution at the desired vapor pressure. Apparatus for regenerating or removing moisture from a hygroscopic solution is old in the art and comprises regenerator chamber 34 to which a stream of hygroscopic solution is charged from conduit 28 through branch conduit 35 containing metering orifice 36, normally open valve 37, and spray nozzles 38. This stream of hygroscopic solution is contacted with a stream of scavenging air, supplied by blower 46 driven by blower motor 47 over the extended surface of heating coil 39. Coil 39 is heated by steam which is admitted through valve 41.
The degree of regeneration imparted to the hygroscopic solution within regenerator 34 must be regulated to control the water absorbing capacity or vapor pressure of the solution. Accordingly, means sensitive to a condition of the solution indicative of its vapor pressure is provided to control the heating effect of steam coil 39 (the amount of moisture transferred to the scavenging gas being proportional to the temperature to which the solution is heated). A condition which is widely used as an indication of solution vapor pressure is solution concentration which, in a given system, can be determined by measuring solution volume. Solution volume can be conveniently sensed by a commercial float-type modulating level control valve 42. Level control 42 is adapted to increase the flow of steam through valve 4-1 when the solution level in sump 25, as sensed by float portion 42a, rises above a pre selected level.
Apparatus as thus far described, with the exception to the modification of pre-heat chamber 11 pointed out above, has been widely used in the air conditioning art to dehumidify an air stream. The heart of this invention, however, is directed to the improvement in such apparatus which will render the apparatus suitable to humidify the incoming air stream by transferring moisture thereto by evaporation from the aqueous hygroscopic solution. While this improvement is described in the setting of a simplified air conditioning device it is to be expressly pointed out that the improvement is also applicable to more complex air conditioning devices such as those illustrated in United States Patent 2,935,154 and Figures 1 and 2 of Patent 2,798,570, both to Kelley.
The condition of moisture transfer from the hygroscopic solution to the treated air tends to cause an increase in concentration of the solution thereby leading to a falling liquid level condition in sump 25 which is sensed by level control 42. A signal from control 42 representative of such a condition is utilized to open normally-closed valve 43 thereby admitting steam from an external source to steam condensing coil 44 located within contact chamber 12 in amounts substantially equal to the rate of moisture transfer from the solution. The steam within coil 44 is readily condensed by the streams of hygroscopic solution and air which pass thereover. This condensed steam is delivered to the hygroscopic solution in sump 25 by means of conduit 45 and serves to maintain the concentration of the hygroscopic solution at the desired value. As an added refinement of my invention I have found it desirable, as an economy measure, to provide means to shut down regenerator unit 34 during air humidification periods, i.e., those periods in which steam is being condensed within coil 44. Regenerator unit 34 may be shut down by using a signal from control 42 to close valve 37 and shut off motor 47. Thus, a falling sump level condition, as sensed by control 42 and which is indicative of an increasing solution concentration, will cause valves 41 and 37 to close; motor 47 to shut down; and valve 43 to open.
It would, of course, be structurally feasible to locate steam condenser 44 in the solution in sump 25 rather than within contact chamber 12. Such a construction would, however, involve a number of undesirable features. If the steam condenser were located in the sump it would require that the surface area of cooling coil 13 be appreciably increased to provide the requisite surface area for efficient contacting of the streams of air and hygroscopic solution. Also, the submergence of condenser 44 in sump 25 would cause the Whole volume of solution in sump 25 to be heated by the condensing steam thereby increasing the thermal losses from solution pipes 28 and 29.
The latent heat of condensation of the steam which is condensed in coil 44 is recovered by the passing streams of air and hygroscopic solution and is utilized to oflset the latent heat needed to evaporate moisture from the hygroscopic solution to bring the air stream to the desired humidity level. During periods when the apparatus is functioning to both warm and humidity the treated air stream it is desirable to provide, in addition to the latent heat furnished to the hygroscopic solution by the steam as it condenses within coil 44, a secondary source of heat for the incoming air stream. This is so because of the phenomenon that the heat of vaporization of water in solution with any of several hygroscopic salts is increased significantly by virtue of the chemical heat of solution. Thus, the latent heat given up by one pound of condensing steam is insufiicient to evaporate one pound of moisture from an aqueous solution of lithium chloride. At equilibrium conditions then, i.e., where the mass rate of steam condensation is equal to the mass rate of moisture transfer from the hygroscopic solution to the treated air, the air stream would naturally be adiabatically chilled to a dry bulb temperature somewhat below the control point temperature of a thermostat at point 19. It is for this reason that the operation of coil 17 was made responsive to the outlet air temperature as detected by thermostat 23 rather than to a thermostat at point 19. No other special provisions are required to inhibit adiabatic chilling during periods when the unit is both cooling and humidifying the air stream. A small degree of adiabatic chilling will serve only to reduce the cooling load on coil 13. A large degree of adiabatic chilling may ofiset completely the cooling load on the unit in which event valve 14 would close and valve 18 would open.
Referring to FIGURE 2, there is illustrated a fragmentary portion of a distribution system for distributing the treated air from the air conditioning apparatus of FIG- URE 1. Treated air is delivered from contact chamber 12 to distribution header at constant conditions of humidity and temperature by means already described The treated air in header 15 is delivered to a number conditioned spaces, including space 48, by means of individual distributing ducts including duct 49. Each distributing duct includes an after-heat chamber 51 containing a steam heating coil 52. Steam is admitted to coil 52 through normally closed valve 53 which is adapted to open in response to a signal from thermostat 54 indicative of low temperature conditions in space 48.
As would be apparent to one skilled in the art, various modifications can be made in the apparatus illustrated and described without departing from the scope of the invention as defined in the appended claims. For instance, the operation of valves 43, 37, 41, and motor 47 could be responsive to a condition indicative of solution vapor pressure other than solution concentration, Thus a humidistat adapted to sense the humidity of the treated air, as at duct 15, could readily be substituted as a substantial equivalent for control valve 42.
It is also to be noted that the broad concept of a steam condenser within the contact chamber is also applicable in simple air humidifying devices. The use of a hygroscopic solution as an air humidification expedient, although more expensive than simple spray-type air humidifiers, is becoming increasingly popular by virtue of the bacteriostatic action of many hygroscopic salts including lithium chloride.
1. A system for conditioning air to a predetermined humidity comprising, in combination:
a. sump means containing a hygroscopic solution;
b. a contact chamber;
c. means for passing a first stream of solution from the sump means through the contact chamber and back to the sump means;
a. means for passing a stream of air to be conditioned through said contact chamber in intimate contact with the first stream of solution whereby to promote the interchange of moisture between the contacted streams from that stream which is at the higher moisture vapor pressure to the other stream;
. a regenerating chamber; heating means within the regenerating chamber;
g. first control means responsive to a condition indicative of the moisture vapor pressure of the first stream of solution for controlling the heating efiect of the heating means in such a manner as to increase the heating effect of the heating means as the moisture vapor pressure of the first stream of solution surpasses a preselected value;
h. means for passing a second stream of solution from the sump means through the regenerator, over the heating means, and back to the sump means;
1'. means for passing a stream of scavenging medium through the regenerator in contact with the second stream of solution;
j. an indirect heat exchanger disposed within the system in heat exchange relationship with the hygroscopic solution;
k. means for delivering condensed steam to said sump by way of said heat exchanger comprising means for delivering steam to said heat exchanger for condensation therein by virtue of heat transfer to hygroscopic solution;
I. and second control means responsive to a condition indicative of the moisture vapor pressure of the solution for controlling the admission of steam to said heat exchanger in a manner to increase the admission of steam thereto when the moisture vapor pressure of the first stream of solution drops below a preselected value.
2. A system according to claim 1 wherein said heat exchanger is disposed within said contact chamber in heat exchange relationship with the first stream of solution.
3. A system according to claim 1 wherein said heating means comprises a steam coil and wherein said first control means comprises a modulating valve adapted to modulate the admission of steam to the steam coil.
4. A system according to claim 3 wherein the condition indicative of the moisture vapor pressure of the first stream of solution to which the first and second control means operates is the concentration of solution in said sump means and further comprising a float valve for detecting this concentration.
References Cited in the file of this patent UNITED STATES PATENTS 2,116,093 Anderson et a1. May 3, 1938 2,548,665 Grant Apr. 10, 1951 2,555,528 Angelery June 5, 1951 2,681,182 McGrath June 15, 1954 2,739,792 Blum Mar. 27, 1956 2,798,570 Kelley July 9, 1957