US2086385A - Air conditioning apparatus - Google Patents

Description

F. MANNING Er Al. 2,086,385 AIR CONDITIONING APPARATUS' Filed oct. 2, 1955 4 sheets-sheet 1 NNW m Ar i m ik F July 6, 1937. I

1N VENTORS July 6, 1937. F. MANNING Er AL 2,086,385

AIR CONDITIONING APPARATUS Filed 001:. 2, 1935. 1 4 Sheets-Sheet 2 INVENTORS Lw-MLM Mr I BYM my@ 1s, am

7&5; ATTORNEY.

July 6, 1937. F. MANNING ET AL 2,086,385

AIR CONDITIONING APPARATUS Filed Oct. 2, 1935 4 Sheets-Shn-z'e'fl 3 ATTORNEY.

ya l lNyENToR BY Q6. CM@

July 6, 1'937. -F. MANNING ET AL 2,086,385

AIR, CONDITIONING APPARATUS .4 Sheets-Sheet 4 Filed Oct. 2, 1935 Ia Pl lll .mf

RNEY.

S i ,i LNVENTOR [l w ATTO Patented July 6, 1937 UNITED STATES PATENT OFFICE I AIR lC-NDITIONING APPARATUS Fowler Manning, Bronxville, and Robert D. Lambert, North Pelham, N. Y., assignors/ to American Radiator Company, New York, N. Y., a corporation of New Jersey Application October 2, 1935, Serial No. 43,204

5 Claims. (Cl. 2611) This invention relates to. methods of conditioning air in heated room spaces and more particularly to a method of providing proper humidity conditions in room spaces during` the heating g ture being raised. As the outside air is the ultimate source of all of the air in the room, there is always a deciency of moisture in the heated room spaces during the heating season.

The optimum range of relative humidity values for room spacesof hou'ses during" the heating .season is generally understood to be between 30% and 70%. If no means are provided foradding moisture to the room spaces, the actual relative humidities will fall well below the 30%. This, of course, will depend upon the` prevailing outside climatic conditions; the number of people occupying the room spaces and the amount of moisture supp-lying operations suchvas cooking, washing, bathing, etc., done in the house.

It is an object of the present invention to provide an improved, dependable and inexpensive method of providing a proper humidity of the air in room spaces throughout the range of prevailing outside dry -bulb temperatures during the heating season, without objectionable condensation -of moisture on the inside surfaces of the windows and other surfaces most readily affected by the dry bulb temperature ofthe outside air, and without the use of humidity responsive control instruments. The invention consists in the series of-steps forming the method more fully described here- `inafter, and the novelty of which will be paticularly pointed out and distinctly claimed.

In the accompanying drawings, to be taken as a part oflthis specification, we have illustrated two alternative forms of apparatus for performing the novel steps of our method, in which drawings:

A Fig. 1 is a fragmentary vertical sectional view of a conventional dwelling house,.showing apparatus installed therein which performs the several steps of our improved method;

Fig. 2 is a horizontal sectional view taken on the line 2-2 ofFig. 1, and showing a portion of the aprniratusl for performing thesteps of our method;- l

Fig. 3 is a `vertical sectional viewtaken on the line 3--3 of Fig. 1, and also showing'a'portion of the apparatus;

Fig. 4 is a perspective view of "an"y alternative form of apparatus for performing the Vsteps oi.' our improved method; and I y Fig. 5 is .a graph showing bya-ourve the actual humidityv conditions maintained over a'inormal range of outdoor temperatures, in ,the room spaces of a conventional dwelling house vwhere our improvedv method was practiced, and also showing by a curve the amount of humidity lthat can be maintained without deposition of` moisture on the windows of that house for the same range tof outdoor temperatures.

In accordance with one specific aspect of our invention, our improved method comprises supplying heat to the air in a room space to maintain the dry bulb temperature of the air contained therein within a comfortable range; withdrawing from the room space a predetermined xed quantity per unit of time of the heated air; taking from the outside air a predetermined fixed quantity'per unit of time of air at its prevailing dry bulb temperature; mixing the withdrawn air with said quantity of outside air; increasing the humidity of the mixture by an amount 4,which is' a predetermined substantially fixed part of the diierence between the amount of moisture in grains per pound the mixture holds p rior to hav- ,ling its humidity increased and the amount of moisture the mixture could" hold if saturated at its wet bulb temperature, so that.the humidii'led mixture has at all times relative humidities which vary directly as a function of the dry bulb temperature of the outside air; increasing the 'dry bulb temperature of the humidied mixture to a ,point where its admission to the .room space will not result in discomfort to the occupants;

and introducing the heated and humidied mixture intol the room. By performing the method steps as just outlined, the air in the room space may be always maintained at a comfortable dry bulb temperature and the air will always contain a proper, comfortable and healthful amount of moisture, which amount is automatically varied with the changing outside dry bulb temperatures so that -moisturein objectionable amounts will notbe;

The steps of our improved method may be carried out by a variety ofv apparatus without departing from the spirit of the present invention. In the drawings, we have illustrated two forms of apparatus which we have found to operate effectively in maintaining the proper condition of the air in room spaces.

Referring rst to apparatus disclosed in Figures 1 t o 3, inclusive, it will be observed that we have shown such apparatus as installed in a conventional dwelling house which includes a room space I0 dened in part by an outside wall II, an inside wall I2 and a floor I3. A window I4 is provided in the outside wall II. Beneath the room I0 is a basement space I5 dened in part by side walls I6 and a oor I'I.

In accordance with one aspect of our invention, we have provided apparatus for maintaining the dry bulb temperature of the room space within a comfortable range to the individuals occupyingsuch space. 'I'his apparatus is shown as being a conventional oil red boiler unit I8 having an off-take 'steam main I9 connected by means of a pipe 20 to a radiator 2| installed within the room space. end of the radiator with a return main 23 leading to the boiler I8. We have shown a thermostat 24 mounted on the inside wall I2 and operating to control theoperation of an oil burner (not shown) disposed within the lower portion of the boiler unit I8. The heating apparatus shown is well known and needs no further explanation.

Other -forms of heating apparatus may be used without departing from the scope of the present invention. 'I'he reference character 30 indicates an apparatus which draws in a mixture-of` room air and outdoor air; lters the mixture; humidifles the mixture; and increases the dry bulb temperature of the mixture above that of the room and then forces such mixture into the room at a substantially xed' volume rate.

'Ihe apparatus 30 comprises an outer casing 3I having upstanding deiining Wal1s32 and a vertical partition wall 33 dening a U-shaped passage for the ilow of mixture therethrough. 'Ihe v partition 33 divides the casing 3I into a down coming leg 34 and an up-going leg 35.

Arranged above the apparatus 30 is a manifold casing 36 which may be suspended from the basement ceiling and is divided by a vertical partition 31 into an air inlet chamber 3 8 and an air outlet chamber 39 (see Fig. 2), lwhich communicate,

respectively, with the down-coming leg 34 andl the up-going leg 35 of the apparatus 30. A ilexible section connects the manifold casing 36 with the apparatus 30' and the sectiony 40 is also provided with a vertical partition 4I which is so arranged with respect to the 'partition 31 and the partition 33 as to provide the connection just explained between the casing 36 and the apparatus 30. The exible section may be formed of any suitable material, such for example, as can,

vas which may be readily cut to' suit the partlcular distance between the suspended manifold 36 and the apparatus 30 resting on the oor of the `basement. The canvasl also .functions as a sound deadening means. y

'rne inlet chamber sa is provided with piu- A pipe 22 connects the return i 2,086,385 z r the inlet chamber ss. The other three inlet openings 42 are connected to the room spaces to be humidied by ducts 44 communicating with grille- `covered openings 46 in the floor of the room openings 52 through the floor of the room spaces.`

A damper 53 is disposed within each of the inlet openings 42 of the inlet chamber 38, and are operated respectively, by suitable lever arms 54 arranged on the outside of the respective'flange portion 43. By regulating the dampers 53, the proportions of outside air and room` air drawn into the mixing inlet chamber 38 may be varied. As will later appear, the proper proportions are first determined and the dampers then remain in their selected positions, without further adjustment being required.

Disposed across the upper portion of the downcoming leg 34 of the apparatus 30 are a pair of lters 55 which are suitably arranged in the form of an inverted V and function to take outof the incoming air mixture substantially all of the foreign matter and dirt entrained therein.

Arranged below the lters 55 is a humidifying chamber 56 which forms a part of the down-coming leg 34 and has installed therein a plurality of spray nozzles 57 suitably connected to the city water supply by a pipe 58. In the extreme lower lower end of the down-coming leg 34 and extends entirely across the leg 34 so that all of the air mixture passes therethrough.

'I'his eliminator 60 may be constructed in any suitable fashion and of any suitable material. 'I'he eliminator shown comprises a relative shallow rectangular frame 6I havingk its opposite sides formed Aof spaced metallic screens 62, between which is disposed a suitable vaporizing and moisture eliminating mat'63; suchl for example, as layers of spun glass,` metal wool, or the like. The mat is so constructed as to provide.a multitude of interstices and tortuous passages for the air owing therethrough. The surfaces of the mat are kept wet by water from the sprays, and the air in passing therethroughcontacts with the exposed surfaces-of the water particles on the surfacosof the mat and effects evaporation of the water and humidiilcation of the air in a manner well knownin the art. Due t'o the balding effectl caused by the ltortous passages,l any Ifree moisture entrainedin the air mixture will be taken out land will ow downward through the mat and into a sump 64. A suitable drain 64aI is4 provided for conducting away the excess water.

The sprays may be adjusted to vary ftheir humidifying characteristics and thereby Kvary the extent to which the mixture is humidifled. The humidifying characteristics are'temperature,

pressure, flow and degree of neness of the spray; and, with the exception of temperature, these characteristics may be varied by suitable regulating screws 65 disposed on the upper end of each of the nozzles, and also by varying the pressure of the water against the nozzles by regulating a suitable Valve 66 in the pipe 58 connected to the city water supply line. As will later appear, when the desired values of these characteristics are once determined, they remain fixed during the operation of the apparatus. 'I'he temperature of the city water will, of course, vary within a small range, but the range is so small that its eifect on the operation of the method will not make sufcient diiference to justify its regulation.

Arranged within the lower portion of the upgoing leg 35 of the apparatus 30, is a blower B1, comprising a casing B8 and a rotating element 69. The casing 68 is provided with a pair of inlet openings 10 communicating with the space 1I on the down stream side of the eliminator 60, there being one opening through each side of the casing 68. The casing B8 is provided with an outlet opening 'l2 connecting with a diverging passage I3 which forms a part of the up-going leg 35 of the apparatus. ably driven by an electric motor which is connected by a belt 'I6 with a pulley on the shaftof the rotating element.

Arranged across the upper end of the up-going leg 35 is a radiator I8 consisting of a plurality of pipes 19 with fins 80 secured thereto for the purpose of promoting heat transfer. The radiator 'I8 is connected to the supply and return mains I3 and 23 of the boiler unit I8 by pipes 8l and 82, respectively.

The radiator 18 serves to raise the dry bul temperature of the air mixture above that of the room, so that when the lmixture is introduced into the room, it will not result in discomfort to the occupants. For example, in a case where the rooms are maintained at a dry bulb temperature approximating 72 F. by or in conjunction with a suitable heating system, we have found that it is desirable to temper the humidied air' to a temperature ranging between 79 F. and 85 F. It i`s to be understood that, While we have elected to disclose in the preferred embodiment of our method, the step of heating the room space by a conventional heating method and the step of merely tempering Aor raising the temperature of the humidied mixture prior to entering the room, our invention in all of its aspects is not to be considered as vbeing so limited; for, in so far as certain ofthe broader aspects of our method are concerned, all of the heating of the humidied mixture and the air inthe room may be effected either by the conventional room heating equipment or by a unit like the radiator 18 of suii'icient capacity and arranged in the path of the air coming from the humidifier.

The structure shown in Figs. 1, 2, and 3 and as just described operates to perform the several steps of our improved method and will maintain in the room space I0 properhumidity values,

without the objectionable deposition of moisture I on the window panes and Without any deposition of moisture on lthe ceilings or walls of the room` A Space. y

The temperature of the v-inside surfaces of the4 mains at a substantially uniform value. depend- The rotating element 69 is suitthe inside surfaces of the windows and similarlyA affected surfaces when the temperature of these surfaces is below the dewpoint temperature of the air in the room space.

The amount of moisture which air Will take up 1 in passing through a humidifier of the type shown varies directly as a function of the dry bulb temperature of such air before entering the humidier. With the blower 61 operating at a constant rate of 'speed and with the dampers 53 at fixed positions, xed proportions of room air and outdoor air will flow into the mixing inlet chamber 38, and this mixture will pass through the humidifying chamber 56 at a substantially uniform volume rate. The dry bulb temperature of the mixture inthe chamber 38 is a resultant of the dry bulb temperature of its room air constituent and its outdoor air constituent, and therefore varies directly as a function of the changing outdoor dry bulb temperature.A Therefore, with the humidifying characteristics of the sprays being xed and the volume rate'of air flow through the sprays and eliminator being fixed, the amount of moisture added to the mixture will vary directly `as a function of the dry bulb temperature of the outdoor air. We have found that vmoisture will be added tc the mixture in amounts which are a substantially xed part of the diiference between the amount of moisture in the mixture,

prior to entering the humidifying chamber 56 and the amount the mixture could hold were it saturated at its wet bulb temperature. The humidifying efficiency of the sprays and eliminator is the relationship between the amount added to the mixture and the amount the mixture could hold were it saturated at its wet bulb temperature.

The measure of the humidifying efficiency is the Value of the aforementioned part by which the moisture content of the mixture is increased.

From' the above, it is apparent that, with the proportions of room and outdoor air substantially constant and the humidifying efficiency substantially constant, and with the volume rate of air passing through the apparatus 30 and into the room substantially constant, the moisture content, and consequently the dewpoint temperature of the air in the room, will vary directlyas afunction of the changing outdoor dry bulb temperature and the inside window surface temperature.

Therefore, by predetermining and xingthe proportions of room'air and outdoor air, the humidification efficiency, and the volume rate of air flow with respect to the humidilcation requirements of a particular house, the dewpoint temperature of the air in the rooms can be made to vary with the inside surface temperature of the windows and never exceed a point where objectionable condensation will occur on these surfaces.

It is to 'be noted that, according to ourmethod, the desired humidity condition is maintained in the room, without objectionable condensation; and that this result is continuously and automatically obtained without the necessity. of further changing the proportions of outdoor and room air and the humidifying eiciency. AFor this rea-4 son, ourmethod has a distinct advantage over prior art humidifying methods using instruments and control systems to regulate the pro-- portions of room and outdoor air and/or to regulate the humidifying emciency. Such instruwind velocities, and will vary slightly up or down ments and control systems are lcostly and are at least of questionable durability and accuracy.

Fig. 5 of the drawings, is a graphl showing the actual results obtained in a conventional dwelling house in the area around -New York city, wherein apparatus of the type shown in Figs. 1, 2 and 3 was installed. This house has a cubic foot capacity of approximately 25,000, and the apparatus was of a size to introduce into the room about 900 cubic feet ofhumidied air per minute. It will be appreciated, of ceurse, that the capacity of the apparatus will'be varied to suit the capacity and conditionsof the particular house where it is installed.

The dotted line curve inv Fig. l", shows the humidity values that can be maintained in this house for the normal range of outside dry. bulb temperatures during the heating season without condensation of moisture on the window panes. We have elected to call this curve the uallowable relative humidity curve. This curve indicates the relation just explained with normal outside on the graph between no wind condition and' high Wind velocities, respectively.

In this particular house, the windows have single panes, and n'o storm windows are installed. With storm windows, the allowable relative hu'- midity curve would be substantially the same shape as that shown, but would be higher on the graph, as higher relative humidities could be maintained inv the room spaces without condensation on the window, because of the resulting higher inside surface temperatures of the win-- dows, the spaces between the storm windows and customary windows acting as a heat insu- 'lator from the outside dry bulb temperatures,

and also acting to nullify the effect of high wind velocities, which produce lower inside Window surface temperatures.

The full lin'e curve'on the graph indicates the mean actual humidities maintained in this house during the heating season by following the steps of our improved method. The curve shows the results obtained whenthe proportions of outside to inside air used were set at 1 to 3 and the efficiency of the humidifying chamber was approximately 40%, that is to say, when the humidifying chamber added to the air 40% of the dference between the absolute humidityof the mixture prior to entering the chamber and the absolute humidity of the mixture if saturated at its wet bulb temperature.

From an examination of Fig. 5, it will be observed that for temperatures below 20 above 0 F., the relative humidities maintained were 30% and slightly less, and that the curve show- 'ing the actual relative humidities maintained in the room crossesthe allowable relative humidity curve at 10 above 0 F. Therefore, for temperathe accepted optimum of 30% relative humidity was maintained; and for temperatures below 10 above 0 F. a slight fog or frost appeared on the window panes, butnot to such an extent as to cause moisture to run down the window pane and result in puddles. t"

Variations of tle actual relative humidity curve were obtained byusing different proportions of foutside and inside airand using a difmidity curve; but, in so doing, the amount of fresh air added to the rooms would, of course,

increase the heating load on the house. It was.

also found that if the efciency of the humidifying chamber were raised to 60%'with a 1 to 3 proportion of outside and inside air, the actual f relative humidity curve would be approximately the same shape as the one shown, but would cross the-allowable relative humidity curve ata higher outside dry bulb temperature. Frost appeared on the. windows at a higher outside the humidifying Veilciency may be selected to' maintain the` humidity condition desired by the .occupants of a particular house, and, when once determined, such humidity condition will be maintained automatically in the manner heretofore explained. The adjustments may be such that the relative humidity of the air at the house is maintained within the optimum range of 30% to 70%, and the deposition of moisture on the window panes will not be objectionable at the low temperatures. We have found that in reality it is not absolutely necessary, in order to have a refreshing and healthful condition, for the relative humidity tobe maintained at a minimum of 30%. Therefore, in cases where the occupants do not like to have a deposition of fog or frost on the window at thev low 4temperatures the adjustment may be such that proper, or healthful and` refreshing humidity conditions may be secured without the deposition of moisture in the form of frostor fog. The operation and range of results and conditions indicated on the graph in Fig. 5 are considered by us to be satisfactory. However, asjust explained,in ac cordance with our method they may be varied to `suit the conditions and the particular desires of.

our improved method also keeps the air in motion in the room spaces and maintains therein an even and positive supply of clean and fresh air withoutv objectionable drafts.' The `room spaces are kept under a slight positive pressure,

I due to the fact that more' air is supplied than is withdrawn, and this condition tends to prevent the entrance of dust and dirt from the outside through cracks and crevices around `the windows and'doors in the house. The latter, in conjunction with the cleansing of all of the air supplied to theroom, keeps the room spaces relatively room spaces is concerned, there is a decided advantage over methods not employing positive ventilation, `for in houses Where the amount of fresh air supplied depends upon the infiltration of outside air through cracks( around windows and doors, too much air is supplied when there are high wind velocities on the outside and too little ventilation is provided when there is4 no wind.

In Fig. 4 of the drawings, we have shown an alternative form of apparatus which performs the several steps of our improved method pre' viously explained. The apparatus is indicated by the reference numeral |00 and comprises a casing IDI suspended from the basement ceiling. At one end of the casing is provided a pair of clean. In so far as the fresh air condition of the municate respectively with the outside air and with the room spaces. The ducts |02 and |03 are provided with dampers |04 and |05 respectively, which serve to properly proportion the amounts of outside air and room air drawn into the casing ing |0| is provided three air supply ducts, which are indicated by the reference character |06 andare Aadapted to be connected to grille-covered openings in the oor of a room space in the same manner as the ducts of the previously described apparatus. A

The fresh air inlet duct |02 and the recirculating air duct |03 communicate with an air inlet chamber |01 provided in the adjacent end of the casing |0|, which'chamber serves to mix the room air and fresh air. The side ofthe chamber lute humidity of the mixture prior to entering the chamber and the absolute humidity of the mixture if saturated at its wet bulb temperature.

Humidificationis effected by a` plurality of water nozzles I arranged in the chamber 0 and supplied with water from a suitable pipe 2 connectedto the city water supply. The nozzles |I| are of the type which provide a very small, high velocity stream of water which strikes a surface of a suitable breaker plate and as a result the stream is broken up into minute particles which fill the chamber ||0 and are taken up by the air stream flowing through the chamber H0.

The breaker plates against which the jets Aof Water strike are indicated by the reference character H3, there beingone plate for each jet.

The plates ||3 are secured to the ends of arms ||4 which are carried by a rotatable shaft ||5 A suitably journalled in the sidewalls of the casing |0|. `A lever ,H6 is provided for rotating the shaft and for positioning the plates ||3 with respect to the jets. istics and hence the humidifying efficiency of the chamber l0 may be varied by rotating the shaft ||5 and thereby varying the angle at which streams of water strike the plates and the distances between the plates and the nozzles.-

Disposed across the side of the humidifying chamber I0 opposite to the filter |08 is an evaporater-eliminatorV |20 which is constructed and functions in a manner similar to the evaporatoreliminator 60 of the previously described apparatus. The eliminator |20 performs the functions of eliminating'any free moisture entrained in the air mixture owing from the chamber ||0 and of promoting evaporation of :moisture and the humidication of such air mixture.

Behind the evaporator is arranged a motor blower unit |25 which comprises a motor 26 hav- I3 which receive the humidifled air mixture flowing through the eliminator |20, and without- At the opposite end of the casi portions respectively, of the radiator.

meral |36.

The humidifying characterlets which are in communication with an air tempering chamber |33.

A suitable steam or hot Water radiator |34 is installed lin the air tempering chamber |33 and functions to raise the temperature of the air mixture to a point'where its entrance into the room spaces will not be uncomfortable to the occupants. For the purpose 'of preventing eddying of the air flowing from the blowers and through the radiator, asplitter vane |35 is provided which divides the flow of the air as itv comes-'from the blower and directs it to the upper and lower The opposite surfaces of the splitter vane, as well as the inside surfaces of the casing defining the tempering chamber, are lined with a sound absorbing material 'indicated by the reference nu- As was the case ofthe apparatus 30 shown in Figs. l, 2 and 3, the apparatus |00 withdraws a predetermined xed amount-of air per unit of time from the room spaces and takes in a predetermined fixed amount of air per unit of time from the atmosphere. The air from both sources is mixed, filtered, and passed through a humidifying chamber which adds to the air moisture in amountswhich area predetermined fixed part of the difference between the absolute humidity .of the mixture prior to being humidifed and the absolute humidity of the mixture were it saturated at its wet bulb temperature. The temperature of the humidified mixture is then raised by passing through a radiator and the air is then forced into the room space.

What we claim and desire to secure by Letters Patent of the United States is:

1. A/method of conditioning air in a room space during the heating season, without objectionable condensation on those internal room surfaces which are more readily aiected by changes in outdoor dry bulb temperature, which comprises mixing substantially unvarying proportions of thermally and hygrometrically untreated outdoor air and air of substantially xed dry bulb temperature drawn from the room space; passing such mixture at its resultant mean dry bulbV temperature and at a substanv tially fixed volume rate through a humidifying zone having a substantially xed humidifying eiciency; and introducing the humidiiied mixture into the room space, so that the dewpoint temperature of the air in the room space varies directly as a function of the changing outdoor vdry bulb temperature; the substantially fixed values of the proportionate amounts of room and outdoorl air, the volume rate of the air mixture, and the hurnidifying efficiency of the zone being sojrelated to one another and to the humidiflcation requirements of the room space, that the dewpoint temperature of the air in the room space does not exceed a point where objectionable condensation would occur on said internal room surfaces.

2. A method of conditioning air in aroom space during the heating season, without objectionable condensation on those internal room surfaces which are more readily affected by changes in outdoor dry bulb temperature, which comprises heating the air in the room space to provide a desired comfort condition; mixing substantially unvarying proportions of thermally and hygrometrically untreated outdoor air and heated air from. the room space; passing such mixture at its resultant mean dry bulb temperature and at a substantially fixed volume rate through a humidifying zone ciency; and introducing the humidified mixture into the room space so thatithe dewpointI temperature of the air in the room space varies directly as a function of the changing outdoor dry bulb temperature; the substantially fixed values of the proportionate amounts of room and outdoorair, the volume rate of the air mixture, and

' the humidifying eiliciency of the zone being so related to one another and tothe humidiflcation requirements of the room space, that the dewpoint temperature of the air in the roo`m space does not exceed a point Where objectionable condensation would occur on saidinternal surfaces.

3. A method of conditioning air ina room space during the heating season, Without objectionable condensation on those internal room surfaces whichare more readily affected by changes in outdoor dry bulb temperature, which comprises heating the air in the room space to provide a desired comfort condition; mixing substantially 'unvarying proportions of thermally and hygrometricall'y untreated outdoor air and heated .air

l midifying zone having a substantially fixed hu.

from thefroom space; passing such mixture at its resultant mean dry bulb temperature and V at a substantially xedvolume rate through a humidifying eiliciency; increasing the dry bulb temperature of the humidified mixture above that of the air in the room space; and introducing the humidied mixturev into the room space so -that the dewpoint temperature of the air in the room space varies directly as a function of the changing outdoor dry bulb temperature; the substantially fixed values of the proportionate amounts of room and outdoorl air, the volume rate of the air mixture,- and the humidifying' efliciency of the zone being so related to one another and to the humidication, requirements of the room space, that the dewpoint temperature of the air having a substantially lixetl humidifying eiliits resultant mean dry bulb temperature and at a substantially fixed volume rate through a humidifying zone having a substantially fixed humidifying efllciency; and introducing the humidied mixture into the room space so that the dewpoint temperature of the air in the room space varies directly as a function of the changing outwhich are more readily affected by changes in outdoor dry bulb temperature, which comprises establishing and maintaining a stream of air iiowing at a' substantially xed volume rate and composed of substantially fixed proportions of thermally and hygrometrically untreated outdoor air, and air of substantially fixed dry bulb temperature drawn from the room space; continually increasing the moisture content of such air stream by an amount which is equal to a substantially fixed part of the difference' between the amount of moisture the air stream contains before its moisture content is increased and the amount of moisture the air stream could hold were it saturated at its wet bulb temperature;

l introducing the humidified stream into the lroom `space, so that the dewpoint temperature of the airv in the room space varies directly as a fu'ncjr tion of the changing outdoor dry bulb temperature; the substantially fixed values of the proportionate amounts of room and outdoor air ccmposlng the air stream, of the volume rate ofthe air stream, and of the part by which the moisture content of the air stream is increased, being so related to one another and to the humidification requirements of the room space, that the dewpoint `temperature of the air in the room space does not exceed a point where objectionable condensation would occur on said internal room surfaces.

` FOWLER MANNING.

ROBERT D. LAMBERT.

Images