US2149990A - Humidity control for refrigerated spaces - Google Patents

Description

March 7, 1939. w. H COOK 2,149,990

HUMIDITY CONTROL FOR REFRIGERATED SPACES Filed Nov. 22, 1937 2 Sheets-Sheet l mm vm ooooooo o ooooooo \woaooooo w. H COOK 2,149,990

Filed Nov. 22, 1937 2 Sheets-Sheet 2 Fig.5

HUMIDITY CONTROL FOR REFRIGERATED SPACES March 7, 1939.

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Patented Mar. 7, 1939 I HUMIDITY 'coN'moL F 11. REFR'IGERATED' smos William Harrison Cook, Ottawa, Ontario, Canada Application November 22, 1937, Serial No. 175,852

12 Claims.

This invention relates to a method and means for maintaining and controlling humidities of the atmosphere in refrigerated storage compartments.

An object of the invention is to provide a method and means 'for maintaining and controlling the humidity in refrigerated spaces with the vminimum addition of heat to the refrigeration load.

A further object is to increase the efllciency of heat transfer from surfaces of the cooling elements to the atmosphere in refrigerated spaces by maintaining these surfaces free from ice by means of liquid flowing over them. The prevention of ice formation on the cooling surfaces also avoids the addition of the-latent heat of fusion of such ice to the refrigeration load. Broadly the invention consists in spraying a suitable liquid over the cooling elements to prevent moisture freezing thereon and to collect condensed moisture, collecting this liquid for recirculation, and causing a portion of the liquid to be boiled in an insulated heater to provide watervapor which is discharged into the refrigerated space when high humidities are desired, or which is exhausted externally of the refrigerated space when lower humidities are desired.

The invention will be described with reference to the accompanying drawings, which are more or less diagrammatic and in which,

Figure 1 is a sectional view of an apparatus embodying the invention as applied to a cold storage space,

Figure 2 is an end sectional view of the apparatus, the intervening wall of the storage space being omitted,

Figure 3 is a partial end sectional view of a modified form of apparatus,

Figure 4 is a side sectional view of another 4 form of heater arrangement and Figure 5 is an, end sectional view of the arrangement shown in Figure 4.

In the drawings, I" is the refrigerated space having insulated walls 2, and 3 the cooling coils, 45 containing a refrigerant, preferably positioned in the upper portion of thespace.

Means for preventing ice formation on the cooling coils as a result of. freezing of condensed moisture thereon comprise a spray pipe 4 located above the coils in a position to spray the same, a pipe 5 for supplying spraying liquid thereto, a tank 6 containing a suitable liquid, and a pump 1 with motor 8 for circulating the liquid through the pipe. A valve 9 and a screen III for the liquid may be provided adjacent'the inlet of pipe 5. A

pressure release for the liquid in pipe 5 consists of a pipe ll leading into the tank provided with a relief valve l2.

The liquid employed must be capable of dissolving, ice at the temperature of the cooling surfaces of the refrigeration coils, and also of yielding only an aqueous vapor when heated. Brines, for instance, calcium chloride, are suitable, as are also solutions of ethylene glycol. Qbviously' the liquid used will have a lower vapor pressure 1 than that of ice at the temperature of the refrigeratingsurfaces and the vapor pressure, which varies with concentration of the liquid, makes dehumidification possible when the aqueous vapor is exhausted externally. V

Means for collecting'the sprayed liquid and returning it to the tank comprise drip pans l3, insulated'on the under side where necessary and located below the coils, louvers II at the side of the coils for directing the liquid into the pans 2 and a return pipe l5 leading from the pans to the tank. A space I6 is provided between the pans to ensure necessary air circulation around the coils, baiiles I1 being provided above the space to direct the sprayed liquid into the pans. A tank overflow pipe l8 may be provided.

Means for maintaining a suitable humidity in the refrigerated space comprises a heater l9 "preferably positioned outside the space, as shown in .Figure 1, and having an electrical heating element within a casing 2| surrounded with insulation 22. Liquid is supplied to the heater by means of a pipe 23 having a valve, a return pipe 25 having a valve 26 being provided for the liquid. Water vapor formed in the heater rises through an insulated channel 21 for escape through an outlet ,28 to the refrigerated space when a higher humidity is required therein or, by means of a flap .valve 29, through an outlet 30 to the exterior of the space when a lower hu- I 40 midity is required. In large refrigeratedspaces, itmay be necessary to provide a distributing fan for the vapor at the outlet 28.

- A circulation of the liquid through the heater and back to the tank must be provided to prevent accumulation of the non-aqueous portion in the heater. Since the concentration of the liquid with respect to the non-aqueous phase must be changed to accord with the temperature of the cooling surfaces, the rate of circulation should be varied accordingly. For instance a highly concentrated solution necessitates a greater volume of liquid in circulation through the heater than with dilute solutions if accumulations of the.non-,

aqueous portion therein are to be avoided. Ac-

. cording to the invention the circulation between the heater and the tank is preferably restricted to .the minimum neediul tor the operation so that the minimum. amount of sensible heat is added to the tank. It is obvious that the sensible heat addedtothetankisaddeddireotlytothereirlg-'- eratingloadwhi'chispreferablykeptaslowas possible.

The restriction andcontrolor the circulation areaccolnplished by a particular arrangementoi thetank and heater without strlctlons in the pipe line. The tank is divided intoan upper or auxiliary iliary compartment, and the return pipe. 28, which communicates with a standpipe 34 through a heat exchanger Si in the heater, empties into' the main compartment. The return pipe il from upward through. a vertical portion or pipe ll, to

the drip empties into. the auxiliary, oompartment and the level or liquid therein is controlled by means of an adjustable standpipellleading from the auxiliary to the main compartment. The heater is so positioned-adjacent the tank that it willbe ted byigravity with liquid from the auxiliary compartment ii, the inlet pipe 2] communicating-with the bottom oi the heater casing 2i. It ,will be observed that the inlet or standpipe N is the inlet to pipe 23 in the compartment SI and at substantially the same level as the outlet oi pipe ll. A head or liquid is thus provided to control the flow or the portion oi liquid to be circulated through theheater. Therateoiiiowthroughtheheater is determined bythe difl'erence inflevel between the standpipe II and the level in the auxiliary compartl'nent Sh-which latter level is regulatable by the adjustable standpipe a. In order to conveniently odate the heater adjacent th'tank, it may be inclined somewhat as shown inl 'lgure 2.' I

. The stand pipe 34 in-the heater communicates with return pipe II through the heat exchanger. )5. v When the apparatus is in operation liquid 'ilows down the heat exchanger, 'where as much as possible of the heat is removed,- then prevent air locks, and finally discharges into the main compartment of the tank 8!, ate. level substantially the same as that of the heater standpipe. as. Valves H, in the supply pipe 28, and it, in return pipe II, are provided for servicing:

"'mater'ialintheheaterw- Means are provided for automatically discon-' or for the ilow temporarily in an emergency. The liquid entering the supply pipe ll ir'on the auxiliary compartment ll is preierably screened as at- It to prevent choking oi the lines and undesirable accumulations of insoluble necting ,theheater from its heating circuit when for any reason the circulation oi liquid in the spraying system, is" stopped, as for. instance, through failure oi the pump. Asillustrated, this means comprisu a small unrestricted opening Il leading i'romthe auxiliary compartment to the main compartment --of the tank through which the liquid in the. auxiliary compartment may drain and afloat ll connected to actuate a switch a in the heating circuit 40' when the liquid levelcaches the bottom or the auxiliary compartshown diagrammatically in Figure 2. 8 illustrates an alternativearrangement .9m ment, as Figure I or the inlet and outlet'pipes oi the heater. As

shown, the liquid isdelivered firstly to the heat euchanger Ilbyaninletpipell andthentothe II and a lower or main compartment 82; As shown, the inlet pipe 23 for the heater leads iron the aux-1 heater through standpipe u. the return flow uring place through a standpipe. 4 2 communicating with the base of the heater. In this arrangethe heater is controlled as previously described by adjusting the standpipe 33 to give the desired level in the auxiliary compartment II. In this 'ment the restriction oi the rate or flow through arrangement the outlet level oithe heater standi e .must be below the liquid level in the heater as fixed by the outlet level of the return standpipe 12, and this latter level is below thstilned by adiustable standpipe 33.

Figures 4 and 5 illustrate another embodiment of the heater arrangement, the spraying system being the same as that previously'described. As

' shown, the tank 6 comprises but a single compartment, a minimum level 0! liquid as indicated at, being maintained therein. A heater ll,

closely similar to heater l9, comprises a casing 46 with'an insulated covering 46, a heating element 41, a water vapor channel-48, vaporoutlet 49 to reifrigera'ted space and vapor-outlet 50 to exterior ot the space-controlled by avalve II.

The heater ll may be mounted adjacent the tank within the refrigerated spaceand a liquid inlet 52, with valve-i3, communicates with the bottom thereof. The heater is so positioned, ,as shown.

that't'he liquid level therein will be maintained,

by gravity, at substantially'the same liquid level as the tank. This heater is also inclined with respect to the tank for convenience-oi arrangement.- A return pipe 54 with a valve 55 for the liquid is providedv just slightly below the level of liquid in the tank and heater. The retu'rn pipev 54 is provided with u restricted passage it of such a sizethat the circulation of liquid through the heater isadequate for preventing troublesome concentration or the non-aqueous part oi! the liquid in: the heater and is preferably restricted so .that a minimum amount of sensible heat is added to the tank. "The valve Il may also be used for controlling the circulation. r I

The liquid inlet 5.2 may be provided with a screen 51.

While the heater .is shown outside the refrigerated space .in. the embodiment of Figure 1 and within the space in the embodiment of Figure 4, it will be readily understood that the position 01' the heater is entirely dependent upon the par I 'ticuiar installation being made. I! placed within the space,'th e necessity oi. heavy insulation there-. for is more important.

required at low temperature, 1. e., or the order oi 0' I". or lower. Under these conditions, the eir culatingmedium must be quite concentratedto prevent theiormation or ice, and this requires the circulation of a relatively large-volume oi the medium in relation to the amount of water evaporated; There being no restricted passages in the shown in Figures 1 and 2 is v letter embodiment, choking of the lines by 'crys-J tallization oi the non-aqueous portion 01' the liquidis avoided; even when a concentrated brine I solution is employed. The embodiment shown in 'Figures 1 and 2 also requires less liquid to maintain the'minii'n'um levels necessary'in operation.

This is important it expensive liquid such as ethylene glycol is used. '1

The humidity in the refrigerated W may be controlled either manually or automatically by controlling the heat input to the heater. Most of the present commercial devices used for the automatic control of relative humidity are slow in response and comparatively insensitive at tained in a closed space below the freezing point with constancy with practically no adjustment of Fluctuations in the outside temthe apparatus. perature and other changes affecting the amount of heat to be eliminated from the space cause slight, but generally insignificant, fluctuations in the relative humidity. Where the space is not closed but subject to periodic opening of doors and the like, a loss or gain in the total moisture content will occur, with consequent slight changes in the concentration .of the aqueous medium in the tank. The concentration of the liquid medium may be adjusted periodically, for instance, by exhausting water vapor formed;by the heater outside the refrigerated space or by adding water or the non-aqueous phase as required.

It will be observed that the heat required for humidification is reduced to a minimum by arranging to have the highest possible proportion of the heat supplied as latent heat in the form of water vapor, instead of as sensible heat..

As previously stated, the described method of and means for humidity control in refrigerated spaces, is capable of maintaining and. controlling humidities in the vicinity -of saturation, which is the condition usually required in refrigerated spaces held at temperatures below the freez point of water. It is well known that most perishable food stuffs require the surrounding refrigerated atmosphere to bekept at a relative humidity of 95% or higher in order to avoid desiccation with consequent deterioration in quality and value. These high relative humidities cannot be obtained by the mere addition of Water vapor torefrigerated spaces, owing to the dehydrative effect of the refrigerating surfaces, which become coated with ice, thus leading -to a second effect previously mentioned, namely, a decreased efiiciency of heat transfer.

In actual trials of the apparatus described, it has been found that-the humidity was raised to over 95% and maintained at these values with the air temperature at 14 F., with the mean temperature of the refrigerating surfaces at 1 F. The heat transfer efliciency of these surfaces was relatively 50% greater with than without the humidity control described. The relative humidity in the space without the present control never exceeded 80%, a condition which caused severe, desiccation of the stored perishable food commodities.

The method and means described are applicable wherever distribution of brine or other suitable liquids over cooling refrigerating, surfaces and collection 'of the same can be arranged.

It may be noted that the invention is applicable for increasing or decreasing the relative humidity in storage or like spaces at temperatures well above and well below the freezing point.

It will be understood that the means for carrying out the invention may vary widely without departing from the scope thereof. Moreover,

, the water vapor such means will necessarily be altered to meet varying conditions of installation.

I claim:

1. A method of controlling the humidity in a closed space having cooling elements which comprises applying an aqueous spray to the surfaces of the cooling elements to prevent moisture freezing thereon and to collect condensed moisture, recovering the aqueous spray withits accumulatedmoisture, continuously vaporizing water in a portion of the recovered sprayand delivering within or without the space as required.

, ,2..,A method of controlling the humidity in a closed space having cooling elements which comprises applying" an aqueous spray to the surfaces of the cooling elements to prevent moisture freezing thereon and to collect condensed moisture, recovering the aqueous spray with its accumulated moisture, continuously circulating a portion of the recovered spray through a heater to vaporize a portion of the water therein and delivering the vapor within or without the space as required.

3. Humidity control for refrigerated spaces having cooling elements with a refrigerant circulating therethrough comprising means for spraying an aqueous liquid upon the surfaces of the cooling elements, said liquid having a freezing point below the temperature of said surfaces, means for recovering the sprayed liquid, a constant level tank adapted to receive the liquid, a heater disposed adjacent thereto and having a liquid inlet communicating therewith, said heater being adapted to boil the liquid therein to form water vapor, a standpipe in the heater adapted to withdraw liquid from the heater, said standpipe having an inlet at a level below that of the constant level tank, and means for delivering the vapor within or without said space.

4. Humidity control for refrigerated spaces having cooling elements with a refrigerant circulating therethrough comprising means for spraying an aqueous liquid upon the surfaces of the cooling elements, said liquid having a freezing point below the temperature of said surfaces, means for recovering the sprayed liquid, a constant level tank adapted to receive the liquid, a main tank adapted to receive the overflow from saidconstant level tank, means for adjusting the level in said constant level tank, a heater disposed adjacent the constant level tank and hav ing a liquid inlet communicating therewith whereby liquid is supplied to the heater by gravity, said heater being adapted to boil the liquid therein to form water vapor, a standpipe in the spraying an aqueous liquid upon the surfaces of the cooling elements, said liquid having a freezing point below the temperature of said surfaces, means for recovering the sprayed *liquid, a tank adapted to receive the recovered liquid, a heater disposed adjacent the tank and having a liquid inlet leading from the tank to the lower portion thereof, said heater being adapted, to vaporize a portion of the moisture in said liquid, a liquid outlet leading from the upper portion of the 4 heater to metank, said outlet having a restricted orifice to control passage of liquid through the outlet, and means for delivering the vapor by the heater within or withoutthe space.

6. Humidity control for closed'spaces having cooling elements with a refrigerant circulating therethrough which comprises means for supplying an aqueous fluid having a freezing point" -below the temperature of the cooling element surfaces, means for spraying said fluid upon said surfaces, means for recovering said sprayed fluid,

means forcontinuously and reguiatably frac- I tionally dividing said recovered fluid, a' heater adapted and arrangedto vaporize a portion of the water of oneof such fractional divisions, means for delivering the water vapor within or without said space andtmeans for returning the concentrated fluid to,said fluid supply.

freezing point below the temperature of said surfaces, recovering the aqueous spray with its accumulated moisture, continuously vaporizing a part of the recovered spray and delivering the 'water vapor to the space.

I 8. A method of maintaining the humidity in' a closed space having cooling elements adapted to provide a temperature of 32 F. or lower in said space which comprises supplying an aqueous" liquid for-continuous application in the form of a spray to the surfaces of the cooling elements to prevent moisture freezing thereon and to collect condensed moisture,.said aqueous liquid hav ing a'freezing point below the temperature of said surfaces, recovering the sprayed liquid-with its accumulated moisture, continuously circulating a portion of the recovered spray through a heater to vaporize a portion of the water there- .in, and delivering the water vapor to the space,

surfaces, recovering the sprayed liquid with itsaccumulated moisture, continuously and regulatably fractlonally dividing'said recovered liquid, vaporizinga portion of the water of one of such fractional-divisions delivering the water vapor formed within or without the space as required andreturning the concentrated liquid totiie aqueous liquid supply.

10. Humidity 'control for refrigerated spaces having cooling elements witharefrigerant circulating therethrough comprising means for spraying an aqueous liquid-upon'ithe surfaces of the cooling elements, said liquid having a freezing point below the temperature of said surfaces, means for recovering the sp yed liquid, aconstant level tank adaptedt o receive the recovered liquid, a heater having aliquid inlet communieating with theconstant level tank, said heater being adafp the liquid therein and to vaporize water from saidiliquid, a; liquid outlet leading from theheater, means for controlling the flow of liquid through said heater, and means for delivering ted to receive therefrom a portion of the vapor formed by the heater within or without said space. a

ll. Humidity control for closed spaces having cooling elements with a refrigerant circulating therethrough which comprises means for sprayingan aqueous liquid upon the surfaces of the cooling elements, said liquid having a freezing point below the temperature of said surfaces. means for recoveringthe sprayed liquid, a constant level tank adapted to receive the recovhaving cooling elements with a refrigerant cir- I culating therethrough comprising means for spraying an aqueous liquid upon'the surfaces of the cooling elemients to prevent moisture freezing thereon and to collect condensed moisture, said liquid having a freezing point below the temperature of said surfaces, means for recovering the sprayed liquid, a heater having-inlet means providing a constant supply of said recovered liquid thereto, said heater being adapted to vaporize a portion of the water in the liquid supplied thereto, said heater having liquid out"- let means adapted to maintain a continuous circulation of liquid through the'heater, means for controlling the rate of flow of liquid through the heater, and means for delivering the vapor within or without'said space.

' WILLIAM HARRISON COOK.

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