The ArmstrongHumidification

Handbook

Handbook HB-501

2Although humidity is invisible to our eyes,we can easily observe its effects. Inhuman terms, we are more comfortableand more efficient with proper humid-ification. In business and industrial environ-ments, the performance of equipmentand materials is enhanced by effectivelyapplying humidity control.

Maintaining indoor air quality throughhumidity management can lower energycosts, increase productivity, save laborand maintenance costs, and ensureproduct quality. In short, humidificationcan provide a better environment andimprove the quality of life and work.

Armstrong has been sharing know-howin humidification application since 1938.Through the design, manufacturing, andapplication of humidification equipment

Humidification Plays an Essential Role

Controlled humidification helps protecthumidity-sensitive materials, personnel,delicate machinery, and equipment.Beyond the important issues of comfortand process control, humidity controlcan help safeguard against explosiveatmospheres. You cant afford NOTto humidify. And the best way to protectyour investment is through provenhumidification strategies and solutionspioneered by Armstrong.

Armstrong has led the way to countlesssavings in energy, time and money.Armstrong also provides computersoftware, video tapes, and other educa-tional materials to aid in humidificationequipment selection, sizing, installation,and maintenance.

Armstrong offers the newly updatedHumidification Handbook as a problem-solving, educational aid for those involvedwith the design, installation, and mainten-ance of environmental control systemsin all types of buildings. In addition, youmay request a free copy of ArmstrongsSoftware Program 2 (Humidifier Sizingand Selection) for step-by-step sizing ofyour own installation.

Your specific humidification questionscan be answered by your ArmstrongRepresentative. Additional support fromArmstrong International humidificationspecialists is available to assist withdifficult or unusual problems.

1995 Armstrong International, Inc.

3Why Humidification is Important 4-7

How Humidity Affects Materials 8-9

Determining Humidity Requirements of Materials 10

How Psychrometrics Help in Humidification 11-13

How Humidifiers Work 14-17

Considerations in Selecting Steam Humidifiers 18-21

Basic Application Principles 22-25

Sizing Considerations 26-28

Steam Humidifiers in Central Systems 29-34

Installation Tips 35

Application of Unit Humidifiers for Direct Discharge 36-38

Conclusion 39

Table of Contents

4Humidity and TemperatureHumidity is water vapor or moisture contentalways present in the air. Humidity isdefinable as an absolute measure: theamount of water vapor in a unit of air. Butthis measure of humidity does not indicatehow dry or damp the air is. This can onlybe done by computing the ratio of theactual partial vapor pressure to thesaturated partial vapor pressure atthe same temperature. This is relativehumidity, expressed by the formula:

vpa

= actual vapor pressurevp

s= vapor pressure at saturation

t = dry-bulb temperature

For practical purposes, at temperaturesand pressures normally encountered inbuilding systems, relative humidity isconsidered as the amount of water vaporin the air compared to the amount the aircan hold at a given temperature.

At a given temperature is the key tounderstanding relative humidity. Warm airhas the capacity to hold more moisture thancold air. For example, 10,000 cubic feet of70F air can hold 80,550 grains of moisture.The same 10,000 cubic feet of air at 10Fcan hold only 7,760 grains of moisture.

Humidification is simply the addition ofwater to air. However, humidity exerts apowerful influence on environmental andphysiological factors. Improper humiditylevels (either too high or too low) cancause discomfort for people, and candamage many kinds of equipment andmaterials. Conversely, the proper type ofhumidification equipment and controlscan help you achieve effective, economi-cal, and trouble-free control of humidity.

As we consider the importance of humidityamong other environmental factorstemperature, cleanliness, air movement,and thermal radiationit is important toremember that humidity is perhaps theleast evident to human perception. Mostof us will recognize and react more quicklyto temperature changes, odors or heavydust in the air, drafts, or radiant heat.Since relative humidity interrelates withthese variables, it becomes a vitalingredient in total environmental control.

If the 10,000 cubic feet of 10F air held 5,820grains of moisture, its relative humidity wouldbe 75%. If your heating system raises thetemperature of this air to 70F with no moistureadded, it will still contain 5,820 grains of

Why Humidification is Important

Relative Humidity(RH):The ratio of the vapor pressure (ormole fraction) of water vapor in the airto the vapor pressure (or mole fraction)of saturated air at the same dry-bulbtemperature and pressure.

Sensible Heat:Heat that when added to or taken awayfrom a substance causes a change intemperature or, in other words, is sensedby a thermometer. Measured in Btu.

Latent Heat:Heat that when added to or taken awayfrom a substance causes or accompa-nies a phase change for that substance.This heat does not register on a ther-mometer, hence its name latent orhidden. Measured in Btu.

Dew Point:The temperature at which condensationoccurs (100%RH) when air is cooled ata constant pressure without adding ortaking away water vapor.

Evaporative Cooling:A process in which liquid water isevaporated into air. The liquid absorbsthe heat necessary for the evaporationprocess from the air, thus, there is areduction in air temperature and anincrease in the actual water vaporcontent of the air.

Enthalpy:Also called heat content, this is the sumof the internal energy and the productof the volume times the pressure.Measured in Btu/lb.

Hygroscopic Materials:Materials capable of absorbing orgiving up moisture.

Phase:The states of existence for a sub-stance, solid, liquid, or gas (vapor).

moisture. However, at 70F, 10,000 cubic feetof air can hold 80,550 grains of moisture. Sothe 5,820 grains it actually holds give it arelative humidity of slightly more than 7%.Thats very dry...drier than the Sahara Desert.

70F80,550 Grains

10F7,760 Grains

RH =vpavps

Glossary

t

5Evaporative CoolingWeve discussed the effects of changingtemperature on relative humidity. AlteringRH can also cause temperature to change.For every pound of moisture evaporatedby the air, the heat of vaporizationreduces the sensible heat in the air byabout 1,000 Btu. This can be moistureabsorbed from people or from wood,paper, textiles, and other hygroscopicmaterials in the building. Conversely, ifhygroscopic materials absorb moisturefrom humid air, the heat of vaporizationcan be released to the air, raising thesensible heat.

Dew PointCondensation will form on windowswhenever the temperature of the glasssurface is below the dew point of the air.Table 5-2, from data presented in theASHRAE Handbook & Product Directory,indicates combinations of indoor relativehumidity and outside temperature at whichcondensation will form. Induction units,commonly used below windows in modernbuildings to blow heated air across theglass, permit carrying higher relativehumidities without visible condensation.

Air Movement and HumidityAnother variable, air movement in theform of infiltration and exfiltration from thebuilding, influences the relationship betweentemperature and relative humidity. Typically,one to three times every hour (and manymore times with forced air make-up orexhaust) cold outdoor air replaces yourindoor air. Your heating system heats thiscold, moist outdoor air, producing warm,dry indoor air.

Per lbDry AirF

-10- 5

05

10

1520253031

3233343536

3738394041

4243444546

474849

Table 5-1. Grains of Water per Cubic Foot of Saturated Air and per Pound of Dry Airat Various Temperatures. (Abstracted from ASHRAE Handbook)

Percu ft

0.284660.369170.475000.6090.776

0.9841.2421.5581.9462.033

2.1242.2032.2882.3762.469

2.5632.6602.7602.8632.970

3.0813.1963.3153.4363.562

3.6923.8263.964

Per lbDry Air

3.21864.22105.50007.129.18

11.7715.0119.0524.0725.21

26.4027.5228.6629.8331.07

32.3333.6234.9736.3637.80

39.3140.8842.4844.1445.87

47.6649.5051.42

FPercu ft

Per lbDry Air

Percu ftF

Per lbDry Air F

Percu ft

4.4074.5614.722

525354

57.5859.7461.99 82

83848586

11.75

12.1112.4912.8713.27

166.4

172.1178.0184.0190.3

5150 4.106 53.38

4.255 55.45

5.2345.4155.602

6.1966.4076.622

7.3087.5717.798

8.5888.8679.153

575859

626364

676869

727374

69.2371.8274.48

83.0286.0389.18

99.19102.8106.4

118.2122.4126.6

77 10.06 140.4

78798081

9.4489.749

7576

131.1135.7

8.0558.319

7071

110.2114.2

6.8457.074

6566

92.4095.76

5.7955.993

6061

77.2180.08

4.8895.060

5556

64.3466.75

87

949596

104

13.67

16.7917.2817.80

22.32

196.7

247.5255.6264.0

341.5105 22.95 352.6

97

98

18.31

18.85

272.7

281.799

100101102

103

19.3919.9520.5221.11

21.71

290.9300.5310.3320.4

330.8

106 23.60 364.0

93 16.31 239.5

88 14.08 203.389909192

14.5114.9415.3915.84

210.1217.1224.4231.8

10.3810.7111.0411.39

145.3150.3155.5160.9

440.4454.5469.0483.9

566.5

1250.91473.51743.02072.72480.8

3664.54550.75780.67581.0

112113114115

120

145150155160165

175180185190

27.8128.5729.3430.13

34.38

64.0471.9980.7790.43101.0

125.4139.2154.3170.7

375.8387.9400.3413.3

107 24.26108109110

24.9325.6226.34

426.4111 27.07

662.6774.9907.9

1064.7

125130135140

39.1344.4150.3056.81

2996.0170 112.6

10493.015827.0

195200

188.6207.9

Double Glass(Storm Windows

or Thermal Glass)

38%42%49%56%63%71%

SingleGlass

11%16%21%28%37%48%

OutdoorTemperature

-100

+10+20+30+40

Table 5-2. Relative Humidities at WhichCondensation Will Appear on Windows at70F When Glass Surface is Unheated

6Energy ConservationWith Controlled RHIndoor relative humidity as we havecomputed it is called Theoretical IndoorRelative Humidity (TIRH). It virtually neverexists. RH observed on a measuringdevice known as a hygrometer will almostalways exceed the TIRH. Why? Dry air isthirsty air. It seeks to draw moisture fromany source it can. Thus it will soak upmoisture from any hygroscopic materials(such as wood, paper, foodstuffs, leather,etc.) and dry out the nasal passages andskin of human beings in the building.

But is this free humidification? No, it isthe most expensive kind there is whentranslated into terms of human comfort,material deterioration, and productiondifficulties. Moreover, it requires the sameamount of energy whether the moistureis absorbed from people and materialsor added to the air by an efficienthumidification system.

The true energy required for a humidificationsystem is calculated from what the actualhumidity level will be in the building, NOTfrom the theoretical level. In virtually allcases, the cost of controlling RH at thedesired level will be nominal in terms ofadditional energy load, and in some casesmay result in reduced energy consumption.

A major convention center in the CentralUnited States reported that it experienceda decrease in overall steam consumptionwhen it added steam humidification. Fromone heating season with no humidificationto the next with humidifiers operating, thesteam consumption for humidificationwas 1,803,000 lbs, while the steam forheating decreased by 2,486,000 lbs in thesame period. The decreased (metered)

consumption occurred despite 7.2% colderweather from the previous year. Therecords from this installation indicate that itis possible to reduce the total amount ofsteam required for environmental control bymaintaining a higher, controlled relativehumidity.

Lets examine a theoretical system usingenthalpy (heat content) as our base.n Assume a winter day with outside

temperature of 0F at 75% RH.n The enthalpy of the air is .6 Btu/lb dry

air (DA).n If the air is heated to 72F without

adding moisture, the enthalpy becomes18 Btu/lb DA.

n Theoretical relative humidity becomes3.75%, but actual RH will be about 25%.

n At 72F and 25% RH the enthalpy is22 Btu/lb DA.

n The additional moisture is derivedfrom hygroscopic materials andpeople in the area.

But what about the additional energythe difference between the 18 Btu/lb DAand 22 Btu/lb DA? This 22% increase mustcome from the heating system to compen-sate for the evaporative cooling effect. If ahumidification system is used and moistureadded to achieve a comfortable 35% RH,the enthalpy is 23.6 Btu/lb DA.

This is only a 7% increase over theinevitable energy load of 22 Btu/lb DAsubstantially less than the theoreticalincrease of 31% from 3.75% RH (18 Btu/lbDA) to 35% RH (23.6 Btu/lb DA) at 72F.If the temperature was only 68F at 35%RH (because people can be comfortableat a lower temperature with higher humiditylevels), the enthalpy is 21.8 Btu/lb DA, ora slight decrease in energy.

Problems With Dry AirDry air can cause a variety of costly,troublesome, and sometimes dangerousproblems. If you are not familiar with theeffects of dry air, the cause of theseproblems may not be obvious. You shouldbe concerned if you are processing orhandling hygroscopic materials such aswood, paper, textile fibers, leather, orchemicals. Dry air and/or fluctuatinghumidity can cause serious productionproblems and/or material deterioration.

Static electricity can accumulate in dryatmospheric conditions and interfere withefficient operation of production machineryor electronic office machines. Where static-prone materials such as paper, films,computer disks, and other plastics arehandled, dry air intensely aggravates thestatic problem. In potentially explosiveatmospheres, dry air and its resultantstatic electricity accumulations can beextremely dangerous.

Why Humidification is Important, Continued...

F F

INDOOR OUTDOOR

120

100

80

60

40

20

0

20

40

120

100

80

60

40

20

0

20

40

50

40

30

20

10

0

10

20

30

40

C

7Humidity and Human ComfortStudies indicate people are generally mostcomfortable when relative humidity ismaintained between 35% and 55%. Whenair is dry, moisture evaporates more readilyfrom the skin, producing a feeling of chillinesseven with temperatures of 75F or more.Because human perception of RH is oftensensed as temperature differential, itspossible to achieve comfortable conditionswith proper humidity control at lowertemperatures. The savings in heatingcosts is typically very significant over thecourse of just a single heating season.

The Need for HumidityControl in TodaysElectronic WorkplaceElectronics are revolutionizing the wayyour office and plant floor operates,communicates, collects data, and main-tains equipment. In the office, xerographiccopies, phone systems, word processors,and typewriters, even wall thermostats areelectronically controlled. Personal computersand CRT access points are sproutingeverywhere. Whats more, office decorhas far more work stations incorporatingwall panels and furniture with natural andsynthetic fabric than ever before.

In manufacturing areas, more machinesare electronically controlled. In fact, yousee more control rooms (just to houseelectronic control systems) than in previousyears.

All this means that the nature of todaysbusiness makes proper humidification avirtual necessity.

Why Improper HumidificationThreatens SensitiveElectronic EquipmentCentral to all electronic circuits today isthe IC (integrated circuit) or chip. Theheart of the IC is a wafer-thin miniaturecircuit engraved in semiconductormaterial. Electronic componentsandchips in particularcan be overstressedby electrical transients (voltage spikes).This may cause cratering and melting ofminute areas of the semiconductor,leading to operational upsets, loss ofmemory, or permanent failure. Thedamage may be immediate or thecomponent may fail sooner than anidentical part not exposed to an electricaltransient.

A major cause of voltage spikes iselectrostatic discharge (ESD). Althoughof extremely short duration, transients canbe lethal to the wafer-thin surfaces ofsemiconductors. ESD may deliver voltageas high as lightning, and it strikes faster.

ESD is a particularly dangerous phenom-enon because you are the source of thesetransients. It is the static electricity whichbuilds up on your body. The jolt you getfrom touching a doorknob or shakingsomeones hand is ESD. Table 7-1 belowshows voltages which can be generatedby everyday activities.

Voltage accumulates on surfaces (in thiscase, the human body), and when thesurface approaches another at a lowervoltage a discharge of electrical voltageoccurs. Note the humidity levels at whichthese voltages may be generated. As thelevel of humidity rises, voltages arereduced because a film of moisture forms Figure 7-1.

Effect of humidity on electrostatic voltages

Integrated circuit damaged by ESD.(Photo courtesy of Motorola Semiconductor, Inc.)

on surfaces, conducting the charges to theground. Although the 65%-90% RH citedin Table 7-1 is impractical for office areas,any increase in humidity will yield asignificant reduction in ESD events.

ESD Damage is Not OnlyPossible but ProbableA study of personnel ESD events in apoorly controlled room with a wool carpetwas conducted for 16 months. Thestrength of the ESD event was measuredin current (amps). Results indicate, forexample, that a current discharge of 0.3amps is 100 times more likely to occurat 10%-20% RH than at 45%-50% RH.In other words, the higher the relativehumidity, the lower the occurrence andseverity of ESD.

In addition to the risk of damage toelectronic devices from static electricitycharges, there are grave risks associatedwith sparks from static charges in manyprocess applications. Static electricity isextremely dangerous in the presence ofgases, volatile liquids, or explosive dustssuch as is found in munitions plants, paintspray booths, printing plants, pharmaceuti-cal plants, and other places.

While many static control products(special mats, carpeting, sprays, straps,etc.) are available, bear in mind thathumidification is a passive static-controlmeans. It is working to control static all thetimenot just when someone remembers.

Walking across carpetWalking over vinyl floorWorker at benchVinyl envelopes for work instructionsCommon poly bag picked up from benchWork chair padded with polyurethane foam

Means of StaticGeneratioo

35,00012,0006,0007,000

20,00018,000

1,500250100600

1,2001,500

Electrostatic Voltages

10%-20%Relative Humidity

65%-90%Relative Humidity

Table 7-1. Effect of Humidity on Electrostatic Voltages

8Paper and Paper ProductsEvery production superintendent in thepaper industry is, by experience, familiarwith the excessive scrap losses andcustomer complaints that can result fromthe following wintertime headaches:

1. Curling of stock.2. Cracking or breaking at creases of

folding boxes, cartons, corrugated andsolid fiber containers.

3. Loss of package and containerstrength.

4. Production delays when sheets fail togo through machines smoothly due tostatic electricity.

5. Gluing failures.

All of the above wintertime problemshave a common causedry or curlingpaper caused by low indoor relativehumidities.

Whenever you heat air, without addingmoisture, its RH drops. Table 8-1 showsthat 0F outside air at 75% RH will have a

How Humidity Affects MaterialsWhy Humidification is Important, Continued...

Figure 9-1. Effects of moisture content infolding paper. Sheet on left has propermoisture. Sheet on right lacks enoughmoistureis dry and brittlebreaks on fold.

relative humidity of only 4.4% when heatedto 70F indoors. Even though the theoreti-cal RH should be 4.4% in your plant, theactual observed humidity will be muchhigher because of the moisture given off bythe paper. This type of humidification is veryexpensive in terms of stock and production.

The RH of surrounding air governs themoisture content of paper, as shown inTable 9-1. The fibrils in paper take onmoisture when the paper is drier than thesurrounding air and give up moisture whenthe conditions are reversed.

A paper moisture content range of 5%-7%is essential to maintain satisfactory strengthand workability of paper. This requires anindoor RH of about 40%-50%, dependingupon the composition of the paper.

Moisture contents of different types of paperswill vary slightly from those shown in thetable but will follow an identical pattern.

Changes in moisture content thus causepaper to become thicker or thinner, flatteror curlier, harder or softer, larger orsmaller, limp or brittle.

Effect of Indoor Heating Upon RH andMoisture Content of Kraft Wrapping Paper.

NOTE: This table assumes an outdoor relativehumidity of 75%. When outdoor RH is less,as is common, indoor RH will also be less.

Indoor temperatures higher than 70F will alsocause lower relative humidities.

Indoor Temperature 70F

OutdoorTemperature

Degrees

-20-10010203040506070

IndoorRelative

Humidity %

1.52.54.47.211.618.126.838.354.075.0

Approx.Moisture

Content ofPaper

0.50.81.22.23.34.35.36.48.011.6

Table 8-1. How Indoor Heating ReducesIndoor RH and Dries Out Paper

9PrintingThe dry air problems found in papermanufacturing are equally common tothe printing industry.

Paper curling, generally caused by theexpansion and contraction of an unpro-tected sheet of paper, takes place whentoo dry an atmosphere draws moisturefrom the ex-posedsurfacewhichshrinksand curls.The curlwill be withthe grain ofthe sheet. Thistrouble is most pronounced with verylightweight stocks or with cover stocks,and coated-one-side papers.

Wood Products, Woodworking,and Furniture ManufactureLike all hygroscopic materials, wood takeson or gives off moisture as the RH of thesurrounding air varies. When, at any giventemperature and relative humidity, thewood finally stops absorbing or liberating

moisture, it is said to havereached its equilibriummoisture content (EMC).The moisture in the

wood is then in balancewith the moisture in the air.

It is generally not practical to holdindoor RH as high during the cold months

as it is during the warm months. However,when the cold season sets in, humidifierspermit a gradual reduction of RH andEMC to a practical minimum working level.Under this controlled condition, warpingand cracking will not occur.

Leather ProcessingRH maintained uniformly in the 40%-60%range (higher in muller rooms) reducescracking, minimizes loss of pliability, helpsmaintain quality and appearance, andreduces the dust problem in the plant.

OfficesRH maintained at 30%-40% stopssplitting, checking, shrinkage, and gluejoint failure in paneling and furnishings,adds life to carpeting and draperies.Electronic office equipment such ascomputers, xerographic copiers, andphone systems require a constant RHof 40%-50% to guard against harmfulelectrical transients (see page 7).

Libraries and MuseumsRelative humidity maintained uniformly at40%-55% in storage rooms, vaults, andgalleries prolongs the life of valuablecollections by stabilizing the pliability ofglue, starch and casein. The embrittle-ment of fibers in paper, canvas, papyrus,leather bindings, etc., is minimized.

Relative Humidity %Material Description

10 20 30 40 50 60 70 80 90

M.F. Newsprint Wood Pulp 24% Ash 2.1 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6HMF Writing Wood Pulp 3% Ash 3.0 4.2 5.2 6.2 7.2 8.3 9.9 11.9 14.2White Bond Rag 1% Ash 2.4 3.7 4.7 5.5 6.5 7.5 8.8 10.8 13.2Com. Ledger 75% Rag 1% Ash 3.2 4.2 5.0 5.6 6.2 6.9 8.1 10.3 13.9Kraft Wrapping Coniferous 3.2 4.6 5.7 6.6 7.6 8.9 10.5 12.6 14.9

Table 9-1. Moisture Content of Paper at Various Relative Humidities

10

moisture loss and materials deteriorationand/or production problems that result.

vary greatly from one material to the next.We will discuss typical hygroscopic materialswhich require specific RH levels to avoid

Determining Humidity Requirements of MaterialsNo single level of relative humidity providesadequate moisture content in all hygroscopicmaterials. Moisture content requirements

Table 10-1. Recommended Relative Humidities

Abstracted from the ASHRAE Handbook Systems and Applications

TeaPackaging 65 65

TobaccoCigar & cigarette making 70-75 55-65Softening 90 85-88Stemming & stripping 75-85 70-75Packing & shipping 73-75 65Filler tobacco casing

& conditioning 75 75Filter tobacco storage

& preparation 77 70Wrapper tobacco storage

& conditioning 75 75

PharmaceuticalsPowder storage (prior to mfg)* *Manufactured powder storage

& packing areas 75 35Milling room 75 35Tablet compressing 75 35Tablet coating room 75 35Effervescent tablets & powders75 20Hypodermic tablets 75 30Colloids 75 30-50Cough drops 75 40Glandular products 75 5-10Ampoule manufacturing 75 35-50Gelatin capsules 75 35Capsule storage 75 35Microanalysis 75 50Biological manufacturing 75 35Liver extracts 75 35Serums 75 50Animal rooms 75-80 50Small animal rooms 75-78 50

* Store in sealed plastic containers in sealed drums.

Photographic ProcessingPhoto Studio

Dressing room 72-74 40-50Studio (camera room) 72-74 40-50Film darkroom 70-72 45-55Print darkroom 70-72 45-55Drying room 90-100 35-45Finishing room 72-75 40-55

Storage roomb/w film & paper 72-75 40-60color film & paper 40-50 40-50

Motion picture studio 72 40-55

Static Electricity ControlTextiles, paper, explosive control > 55

Clean Rooms & Spaces 45

Data Processing 72 45-50

Paper ProcessingFinishing area 70-75 40-45Test laboratory 73 50

Switchgear:Fuse & cutout assembly 73 50Capacitor winding 73 50Paper storage 73 50

Conductor wrapping with yarn75 65-70Lightning arrester assembly 68 20-40Thermal circuit breakers

assembly & test 75 30-60High-voltage transformer repair79 55Water wheel generators:

Thrust runner lapping 70 30-50Rectifiers:

Processing selenium &copper oxide plates 73 30-40

FurStorage 40-50 55-65

GumManufacturing 77 33Rolling 68 63Stripping 72 53Breaking 73 47Wrapping 73 58

LeatherDrying 68-125 75Storage, winter room temp. 50-60 40-60

Lenses (Optical)Fusing 75 45Grinding 80 80

MatchesManufacture 72-73 50Drying 70-75 60Storage 60-63 50

MushroomsSpawn added 60-72 nearly sat.Growing period 50-60 80Storage 32-35 80-85

Paint ApplicationOils, paints: Paint spraying 60-90 80

PlasticsManufacturing areas:

Thermosetting moldingcompounds 80 25-30

Cellophane wrapping 75-80 45-65

PlywoodHot pressing (resin) 90 60Cold pressing 90 15-25

Rubber-Dipped GoodsCementing 80 25-30*Dipping surgical articles 75-80 25-30*Storage prior to manufacture60-75 40-50*Laboratory (ASTM Standard) 73.4 50*

* Dew point of air must be below evaporationtemperature of solvent

Residences 70-72 30

Libraries & MuseumsArchival 55-65 35Art storage 60-72 50Stuffed fur animals 40-50 50

Communication CentersTelephone terminals 72-78 40-50Radio & TV studios 74-78 30-40

General Commercial & Public Buildings70-74 20-30

(including cafeterias, restaurants, airport terminals,office buildings, & bowling centers)

Hospitals & Health FacilitiesGeneral clinical areas 72 30-60Surgical area

Operating rooms 68-76 50-60Recovery rooms 75 50-60

ObstetricalFull-term nursery 75 30-60Special care nursery 75-80 30-60

Industrial Hygroscopic MaterialsAbrasive

Manufacture 79 50Ceramics

Refractory 110-150 50-90Molding room 80 60-70Clay storage 60-80 35-65Decalcomania production 75-80 48Decorating room 75-80 48

CerealPackaging 75-80 45-50

DistillingStorage

Grain 6 35-40Liquid yeast 32-33

General manufacturing 60-75 45-60Aging 65-72 50-60

Electrical ProductsElectronics & X-ray:

Coil & transformer winding72 15Semi conductor

assembly 68 40-50Electrical instruments:

Manufacture& laboratory 70 50-55

Thermostat assembly& calibration 75 50-55

Humidistat assembly& calibration 75 50-55

Small mechanisms:Close tolerance assembly72 40-45Meter assembly & test 75 60-63

PROCESS OR PRODUCT Temp.F %RH PROCESS OR PRODUCT Temp.F %RHPROCESS OR PRODUCT Temp.F %RH

11

How Psychrometrics Help in Humidification

Psychrometrics is the measurement ofthermodynamic properties in moist air.As a problem-solving tool psychrometricsexcel in clearly showing how changes inheating, cooling, humidification, anddehumidification can affect the propertiesof moist air. Psychrometric data is neededto solve various problems and processesrelating to air distribution.

Most complex problems relating to heating,cooling and humidification are combina-tions of relatively simple problems. Thepsychrometric chart illustrates these pro-cesses in graphic form, clearly showing howchanges affect the properties of moist air.

One of the reasons psychrometric data isparticularly important today is traceable tothe way most new buildings (and manyolder ones) are heated. The lower ducttemperatures (55F and below) used innew buildings make accurate humidity

control more difficult to achieve. (This isbecause low duct temperatures have alimited ability to absorb moisture. Addingmoisture via the central air handlingsystem must compensate for reheatingof air before it leaves the duct.)

For such applications, booster humid-ification must sometimes be accomplishedin the duct of the zone after it has reachedits final temperature (reheated).

To maintain typical conditions of 70F and50% RH, duct humidities will be very high(75% RH and above). To keep the ductfrom becoming saturated, a duct high limithumidistat is used, and becomes in thesecases the main controller of the humidifier.Since this humidistat is in close proximityto the humidifier, and air is constantlymoving, and must be controlled close tosaturation, the humidifier output controlmust be fast, accurate and repeatable.

TOTAL HEATH

TS E N S I B L E H E A T

Hs

ENTHALPYh

HUMIDITY RATIOW

500

0-1

000

~200

0

50003000

2000

1500

1.0

0.8

0.6

0.5

0.4

0.3

0.2

0.1

1.0

2.04.08.0

-8.0-4.0-2.0-1.0

-0.5-0.4-0.3-0.2-0.1

6050

4030

2010

0

120110

10090

8070

2015105

05

1015

25

3035

4045

C

F

5

295

315

30

1020

1010990

980

970

960

950

10301040

MILLIBARS

INCHES

6050

4030

20

10090

8070

5545

3525

15

65

7585

95

HUMIDITY

%RELATIVE HUMIDTY

2810

BAROMETER

1000

THERMOMETER

SATU

RATIO

N TEM

PERA

TURE

F

12.5

13.0

13.5

14.0

14.5 VOLUME CU

. FT

. PER LB

. DRY AIR

15.0

90%

80%

70%

60%

50%

40%

30%

20

10 RELATIVE HU

MIDITY

120

115

110

105

100

DRY

BULB

TEM

PER

ATUR

E

F

95908580757065605550454035

65

60

55

5045

40353025

70

75

80 WET BULB TEMPERATURE

85

90

3540

45

50

55

60

65

70

75

80

85

15

15 20 25

30

35

40

45

50

55

60

6055

10

20

25

30

35

40

45

50

ENTH

ALPY

(h) BT

U PER

BOUN

D OF D

RY AIR

ENTHALPY (h) BTU PER BOUND OF DRY AIR

.028

.026

.024

.022

.020

.018

.016

.014

.012

.010

.008

.006

.004

.002

HUM

IDIT

Y RA

TIO

(W)

POU

NDS

MOIS

TURE

PER

POU

ND D

RY A

IR

12

The psychrometric chart is a graphicalrepresentation of the thermodynamicproperties which impact moist air.

It consists of eight major components:

Using the Psychrometric Chart

1. Humidity ratio values are plottedvertically along the right-hand margin,beginning with 0 at the bottom andextending to .03 at the top.

2. Enthalpy, or total heat, is plotted withoblique lines, at intervals of 5 Btu/lb of dryair, extending from upper left to lower right.

3. Dry-bulb temperature lines areplotted vertically at 1F intervals.

4. Wet-bulb temperature lines areindicated obliquely and fall almost parallelto enthalpy lines. They are shown at 1Fintervals.

5. Relative humidity lines curve acrossthe chart from left to right at intervals of10%. They begin at the bottom at 10%and end at the top with the saturation curve(100%).

7. Two-phase region includes a narrow,cross-hatched area to the left of thesaturation region indicating a mixture ofcondensed water in equilibrium.

6. Volume lines indicating cubic feet perpound of dry air are plotted at intervalsof .5 cubic foot.

8. The protractor at the upper left of thechart contains two scales. One is for theratio of enthalpy difference. The other isfor a ratio of sensible heat to the totalheat. The protractor establishes the angleof a line on the chart along which aprocess will follow.

How Psychrometrics Help in Humidification, Continued...

0.030

0.028

0.026

0.024

0.022

0.020

0.018

0.016

0.014

0.012

0.010

0.008

0.006

0.004

0.002

0 HUM

IDIT

Y RA

TIO,

POU

NDS

MOI

STUR

E PE

R PO

UND

DRY

AIR

10

15

20

25

30

35

40

45

50

55

ENTH

ALPY

(H) B

TU pe

r pou

nd of

dry a

ir

35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 12025 30 35

4045

5055

60

65

70

75

80

85

90

90%

80%

70%

60%

50%

40%

30%

20%

10%

100%

14.5Volum

e(cubic

feet per poundof dry

air)15.0

14.0

13.0

13.5

12.5

Satur

ation

Temp

eratur

e F

TOTAL HEATH

TS E N S I B L E H E A T

Hs

ENTHALPYh

HUMIDITY RATIOW

500

0-1

000

~200

0

50003000

2000

1500

1.0

0.8

0.6

0.5

0.4

0.3

0.2

0.1

1.0

2.04.08.0

-8.0-4.0-2.0-1.0

-0.5-0.4-0.3-0.2-0.1

13

SATU

RATIO

N TEM

PERA

TURE

F

12.5

13.0

13.5

14.0

14.5 VOLUME CU

. FT

. PER LB

. DRY AIR

15.0

90%

80%

70%

60%

50%

40%

30%

20

10 RELATIVE HU

MIDITY

120

115

110

105

100

DRY

BUL

B TE

MPE

RAT

URE

F

95908580757065605550454035

65

60

55

5045

40353025

70

75

80 WET BULB TEMPERATURE

85

90

3540

45

50

55

60

65

70

75

80

85

15

15 20 25

30

35

40

45

50

55

60

6055

10

20

25

30

35

40

45

50

ENTH

ALPY

(h) BT

U PER

BOUN

D OF D

RY AIR

ENTHALPY (h) BTU PER BOUND OF DRY AIR

.028

.026

.024

.022

.020

.018

.016

.014

.012

.010

.008

.006

.004

.002

HUM

IDIT

Y RA

TIO

(W)

POU

NDS

MOIS

TURE

PER

POU

ND D

RY A

IR

SATU

RATIO

N TEM

PERA

TURE

F12.5

13.0

13.5

14.0

14.5 VOLUME CU

. FT

. PER LB

. DRY AIR

15.0

90%

80%

70%

60%

50%

40%

30%

20

10 RELATIVE HU

MIDITY

120

115

110

105

100

DRY

BULB

TEM

PER

ATUR

E

F

95908580757065605550454035

65

60

55

5045

40353025

70

75

80 WET BULB TEMPERATURE

85

90

3540

45

50

55

60

65

70

75

80

85

15

15 20 25

30

35

40

45

50

55

60

6055

10

20

25

30

35

40

45

50

ENTH

ALPY

(h) BT

U PER

BOUN

D OF D

RY AIR

ENTHALPY (h) BTU PER BOUND OF DRY AIR

.028

.026

.024

.022

.020

.018

.016

.014

.012

.010

.008

.006

.004

.002

HUM

IDIT

Y RA

TIO

(W)

POU

NDS

MOIS

TURE

PER

POU

ND D

RY A

IR

TOTAL HEATH

TS E N S I B L E H E A T

Hs

ENTHALPYh

HUMIDITY RATIOW

500

0-1

000

~200

0

50003000

2000

1500

1.0

0.8

0.6

0.5

0.4

0.3

0.2

0.1

1.0

2.04.08.0

-8.0-4.0-2.0-1.0

-0.5-0.4-0.3-0.2-0.1

Example 1Given the conditions of 75F drybulb and 50% RH, determine the dewpoint, volume and humidity contentin grains per cubic foot of dry air.

Solution:1. Locate the state point, where the

75F dry-bulb line intersects the50% RH line. Call this state pointnumber 1.

2. Project horizontally to the left tothe saturation curve and read 55F(dew point).

3. Project horizontally to the right andread .0092 pounds of moisture perpound of dry air.

4. Draw a line through the state pointparallel to 13.5 volume line andestimate a volume of 13.68 cubicfeet per pound of dry air.

5. Solve for grains per cubic foot byconverting:

0.0092 x 7,000 13.68 = 4.71 grains/cu ftSee also Table 27-5 for quick values.

Example 2Determine resultant RH when 55Fair at 80% RH is heated to a tem-perature of 75F.

Solution:1. Locate the state point where 55F

dry-bulb line intersects 80% RHline. Call this state point number 2.

2. Project horizontally to the right tointersect the 75F dry-bulb line at40% RH. Call this state point 3.

3. Observe that if air is delivered toa system at state point 2, that areheat operation can deliver it toan area at state point 3.

4. If state point 1 (example 1) isdesired in the area, then boosterhumidification is needed.

TOTAL HEATH

TS E N S I B L E H E A T

Hs

ENTHALPYh

HUMIDITY RATIOW

500

0-1

000

~200

0

50003000

2000

1500

1.0

0.8

0.6

0.5

0.4

0.3

0.2

0.1

1.0

2.04.08.0

-8.0-4.0-2.0-1.0

-0.5-0.4-0.3-0.2-0.1

No. 3No. 2

No. 1

14

Steam HumidificationUnlike other humidification methods,steam humidifiers have a minimal effecton dry-bulb (DB) temperatures. The steamhumidifier discharges ready-made watervapor. This water vapor does not requireany additional heat as it mixes with the airand increases relative humidity. Steam ispure water vapor existing at 212F (100C).This high temperature creates a percep-tion that steam, when discharged into theair, will actually increase air temperature.This is a common misconception. In truth,as the humidifier discharges steam intothe air, a steam/air mixture is established.In this mixture steam temperature willrapidly decrease to essentially the airtemperature.

How Humidifiers Work

Direct Steam InjectionHumidifiersThe most common form of steamhumidifier is the direct steam injectiontype. From a maintenance point of view,direct steam humidification systemsrequire very little upkeep. The steamsupply itself acts as a cleaning agent tokeep system components free of mineraldeposits that can clog water spray andevaporative pan systems.

Response to control and pinpoint controlof output are two other advantages of thedirect steam humidification method. Sincesteam is ready-made water vapor, it needsonly to be mixed with air to satisfy thedemands of the system. In addition, directsteam humidifiers can meter output bymeans of a modulating control valve. Asthe system responds to control, it canposition the valve anywhere from closedto fully open. As a result, direct steamhumidifiers can respond more quickly andprecisely to fluctuating demand.

The high temperatures inherent in steamhumidification make it virtually a sterilemedium. Assuming boiler makeup wateris of satisfactory quality and there is nocondensation, dripping or spitting in theducts, no bacteria or odors will bedisseminated with steam humidification.

Corrosion is rarely a concern with aproperly installed steam system. Scaleand sedimentwhether formed in the unitor entrained in the supply steamaredrained from the humidifier through thesteam trap.

Steam-to-Steam HumidifiersSteam-to-steam humidifiers use a heatexchanger and the heat of treated steam tocreate a secondary steam for humidificationfrom untreated water. The secondarysteam is typically at atmospheric pressure,placing increased importance onequipment location.

Maintenance of steam-to-steam humidifiersis dependent on water quality. Impuritiessuch as calcium, magnesium and ironcan deposit as scale, requiring frequentcleaning. Response to control is slowerthan with direct steam because of thetime required to boil the water.

Electronic Steam Humidifiers(Electrode)Electronic steam humidifiers are usedwhen a source of steam is not available.Electricity and water create steam atatmospheric pressure. Electrode-type unitspass electrical current through water toprovide proportional output. Use with puredemineralized, deionized or distilled wateralone will generally not provide sufficientconductivity for electrode units.

Water quality affects the operation andmaintenance of electrode-type humidifiers.Use with hard water requires more frequentcleaning, and pure softened water canshorten electrode life. Microprocessor-based diagnostics assist withtroubleshooting.

The psychrometric chart helps illustratethat steam humidification is a constant DBprocess. Starting from a point on any DBtemperature line, steam humidification willcause movement straight up along theconstant DB line. The example illustratesthat 70F DB is constant as we increaseRH from 30%-50%. This is true becausesteam contains the necessary heat(enthalpy) to add moisture withoutincreasing or decreasing DBtemperature. Actual resultsutilizing high pressure steamor large RH increases(more than 50%) increaseDB by 1 to 2F. As a result,no additional heating or airconditioning load occurs.

70 DB

50%

30%

Cross Section of Manifold

Dry Steam

Direct Steam HumidificationFigure 14-1.

Steam-to-Steam HumidificationFigure 14-2.

15

Electrode units are easily adaptable todifferent control signals and offer fullmodulated output. However, the need toboil the water means control will notcompare with direct-injection units.

Electronic Steam Humidifiers(Ionic Bed)Ionic bed electronic humidifiers typicallyuse immersed resistance heating elementsto boil water. Since current does not passthrough water, conductivity is not aconcern. Therefore, ionic bed technologymakes the humidifier versatile enough toaccommodate various water qualities.These units work by using ionic bedcartridges containing a fibrous media toattract solids from water as its temperaturerises, minimizing the buildup of solidsinside the humidifier. Water quality doesnot affect operation, and maintenancetypically consists of simply replacing thecartridges.

Ionic bed humidifiers are adaptable todifferent control signals and offer fullmodulated output. Control is affected bythe need to boil the water, however.

Water SprayThe water spray process can createpotential temperature control problems. Inorder to become water vapor or humidity,water requires approximately 1,000 Btuper pound to vaporize. This heat must bedrawn from the air, where it will hopefullyvaporize. If not enough heat is availablequickly enough, the water remains aliquid. This unvaporized water can result inoverhumidification, and the water canplate out on surfaces, creating a sanita-tion hazard.

Water spray contains virtually none of theheat of vaporization required to increasethe RH of the air to desired conditions.For this reason, water spray humidificationis a virtually constant enthalpy process.However, as the psychrometric exampleillustrates, DB temperature changes as weincrease RH from 30%-50%. The result ofthis loss of DB temperature is an in-creased heating load to maintain 70F.

Water SprayFigure 15-2.

70 DB

50%

30%

ENTHALPY

70 DB

50%

30%

Heat Taken From AirTo Evaporate Moisture

Water SupplyUnder Pressure

Water Mist

Response of water spray humidifiersto control is slow due to the need forevaporation to take place before humidi-fied air can be circulated. On/off controlof output means imprecise response tosystem demand and continual dangerof saturation. Water spray systems candistribute large amounts of bacteria, andunevaporated water discharge cancollect in ducts, around drains and drippans, and on eliminator plates, encour-aging the growth of algae and bacteria.Corrosion is another ongoing problemwith water spray humidification. Scaleand sediment can collect on nozzles,ductwork, eliminator plates, etc., leadingto corrosion and high maintenance costs.

Evaporative PanThe evaporative pan method uses steam,hot water or electricity to provide energyfor heating coils which in turn heat waterand create water vapor. This method ismost effective when installed in smallercapacity environments either in the airhandling system or individually withinthe area(s) to be humidified.

Evaporative pan humidification canincrease dry-bulb temperature as mea-sured on the psychrometric chart. Thisunwanted temperature change may occuras air is forced across the warmed waterin the pan. The increase in DB can causedamaging results in process applicationsand increase the need for humidity control.The psychrometric chart helps illustratethat evaporative pan humidification is nota constant DB process. This exampleshows DB temperature increasing as wemove from 30%-50% RH. To maintain aconstant DB of 70F some cooling load(air conditioning) is required.

Figure 15-1.Electronic Steam Humidification

16

How Humidifiers Work, Continued...

Cost ComparisonsTo fairly evaluate the costs of selecting ahumidification system, you should includeinstallation, operating, and maintenancecosts as well as initial costs. Total humidi-fication costs are typically far less thanheating or cooling system costs.

Initial costs, of course, vary with the sizeof the units. Priced on a capacity basis,larger capacity units are the mosteconomical, regardless of the type ofhumidifier, i.e.: one humidifier capable ofdelivering 1,000 pounds of humidificationper hour costs less than two 500 lbs/hrunits of the same type.

Direct steam humidifiers will provide thehighest capacity per first cost dollar; waterspray and evaporative pan are the leasteconomical, assuming capacity needs of75 lbs/hr or more.

Installation costs for the various typescannot be accurately formulated becausethe proximity of water, steam and electricityto humidifiers varies greatly amonginstallations. Operating costs are low fordirect steam and slightly higher for steam-to-steam. Water spray and evaporative panoperating costs are also low. Energy costsare higher for electronic humidifiers.

Direct steam humidifiers have the lowestmaintenance costs. Ionic bed electronichumidifiers are designed specifically tominimize maintenance while adapting tovarious water qualities. Maintenance costsfor other types can vary widely, dependingon water quality and applications.

These are the principal considerations inselecting a humidification system. Table16-1 summarizes the capabilities of eachhumidifier type.

Heated Water

Water Pan

Water VaporFloatValve Steam, Hot Water

Or Electricity In

Auto Valve

Evaporative PanFigure 16-1.

Maintenance of evaporative pan humid-ification systems demands regularcleaning of the heating coils and pan,which are subject to liming up.

The use of chemical additives addedeither automatically or manually to thewater in the pan can reduce this problemby as much as half.

Response to control with the evaporativepan method is slow due to the timerequired for evaporation to take placebefore humidified air can be circulated.Output is determined by water tempera-ture and surface area.

Evaporative pan humidifiers can sustainbacteria colonies in the reservoir anddistribute them throughout the humidifiedspace. High water temperatures, watertreatment, and regular cleaning andflushing of the humidifier help to minimizethe problem, however.

Table 16-1. Comparison of Humidification Methods

Maintenance frequency

Subject to severe corrosion and

bacteria problems

Pan subject to corrosion; bacteria

can be present

Effect on temperature

Unit capacity per unit size

Vapor quality

Response to control

Control of output

Sanitation/corrosion

InstallationOperatingMaintenance

Evaporative Pan Water SpraySmall

temperature riseSubstantial

temperature dropSmall Small

Poor

Slow Slow

Weekly to monthly

HighLow

Direct Steam

Small to very large

Excellent

Immediate

Good to excellent

Sterile medium; corrosion free

Annual

Low

Low

Maintenance difficultyCosts: Price (per unit of capacity)

Low

High

Steam-to-Steam

Virtually no change

Small

Good

Slow

Below average

Bacteria can be present

Monthly

High

LowHigh

Medium

Electronic Steam

Small to medium

Good

Fair

Average

Programmed to not promote bacteria

Monthly to quarterly

High

MediumVaries with availability of steam, water, electricity, etc.

Medium

Low

Ionic Bed Electronic Steam

Small to medium

Good

Fair

Average

Programmed to not promote bacteria

Quarterly to semi-annually

Low to medium

Medium

Medium

Good

Average

High

LowHigh

Average

Weekly to bimonthly

High

Medium to high

LowVery high

17

Recommended ApplicationsSteam: Recommended for virtually allcommercial, institutional and industrialapplications. Where steam is not avail-able, small capacity needs up to 50-75lbs/hr can be met best using ionic bed typeself-contained steam generating units.Above this capacity range, central systemsteam humidifiers are most effectiveand economical. Steam should bespecified with caution where humidificationis used in small, confined areas to addlarge amounts of moisture to hygroscopicmaterials. We recommend that youconsult your Armstrong Representativeregarding applications where theseconditions exist.

Evaporative Pan: Recommended onlyas an alternative to self-contained steamgenerating unit humidifiers for small loadcommercial or institutional applications.Generally not recommended where loadrequirements exceed 50-75 lbs/hr.

Water Spray: Recommended for industrialapplications where evaporative cooling isrequired; typical application is summer-time humidification of textile mills in thesouthern U.S.

The evidence supports the conclusion thatsteam is the best natural medium forhumidification. It provides ready-madevapor produced in the most efficientevaporator possible, the boiler. There isno mineral dust deposited, and becausethere is no liquid moisture present, steamcreates no sanitation problems, will notsupport the growth of algae or bacteria,has no odor and creates no corrosion orresidual mineral scale. Unless there areparticular requirements to an applicationthat can only be met with evaporativepan or water spray methods, steamhumidification will meet system needsmost effectively and economically.

Strainer

Safety Relief Valve

Packaged Steam Generator

AutomaticBlowdownSystem

Trap

To Drain

To AdditionalHumidifiers

SteamHumidifier

To Drain

Auto Fill Valve

Figure 17-1. Typical Piping for Boiler-Humidifier InstallationDesign GuidelinesBoiler-Humidifier Combinations

1. Boiler gross output capacityshould be at least 1.5 times thetotal humidification load.

2. Water softeners should be usedon boiler feedwater.

3. Condensate return system is notnecessary (unless required bycircumstances).

4. Boiler pressure should be at15 psig or less.

5. An automatic blowdown systemis desirable.

6. All steam supply piping shouldbe insulated.

7. No limit to size or number ofhumidifiers from one boiler.

With these advantages in mind, engineersspecify steam boilers and generatorssolely for humidification when the buildingto be humidified does not have a steamsupply. The minimum humidification loadwhere this becomes economically feasiblefalls in the range of 50-75 lbs/hr. Steamgenerator capacity is generally specified50% greater than maximum humidificationload, depending on the amount of pipingand number of humidifiers and distributionmanifolds that must be heated. Typicalpiping for boiler-humidifier installations isshown in Fig. 17-1.

Level Control &Low Water Cutoff

18

Considerations in Selecting Steam Humidifiers

Electronic Steam HumidifiersWhen steam is not available, self-contained electronic humidifiers can meetlow-capacity requirements. The primaryconsideration in selecting this typeof humidifier is its ability to work withwide ranges in water quality. Ionic bedelectronic humidifiers are frequentlyselected for this capability.

Direct InjectionSteam HumidifiersAn evaluation of three performancecharacteristics is essential to understandthe advantages steam holds over otherhumidification media:

n Conditioningn Controln Distribution

The humidifier must condition the steamso that its completely dry and free ofsignificant particulate matter. Responseto control signals must be immediate,and modulation of output must be precise.Distribution of steam into the air mustbe as uniform as possible. Inadequateperformance in any of these areasmeans the humidifier will not meet thebasic humidification requirements.

Direct injection steam humidifiers areavailable in three basic types: speciallydesigned steam grids, steam cups andthe steam separator.

Specially designed steam grid systemsincorporate advanced engineering inaddressing unique applications wherevapor trail is of prime concern.

Steam cup humidifiers receive steamfrom the side of the cup which theoreticallypermits the condensate to fall by gravityto the steam trap. However, in practicea great deal of the liquid moisture in thesteam goes into the air flow, and thesteam itself is poorly distributed.

The steam separator is a moresophisticated device which, whenproperly designed, meets essentialperformance criteria.

Figure 18-3. Steam Separator Type Humidifier

Integral Control Valve

Drying Chamber

Separating Chamber

InvertedBucketSteamTrap

Condensate Deflected Downward

Steam JacketedDistribution Manifold

Pneumaticor ElectricOperator

STEAM SUPPLY AT SUPPLYPRESSURE

STEAM AT ATMOSPHERICPRESSURE

CONDENSATE

KEY

Drain

Drain

Strainer

Trap

NOTE: Condensate cannot be lifted or dischargedinto pressurized return.

From Boiler

Figure 18-1. Steam Grid Humidifier

Figure 18-2. Cup Type Steam Humidifier

Drip Leg

1"/12" Slope

1" Air Gap

Header

Air Flow

Control Valve

19

Figure 19-1. Parabolic Plug Metering Valve

Steam ConditioningAs steam moves through supply lines,scale and sediment may be entrained inthe flowa Y-type strainer is required toremove larger solid particles. Similarly, thecondensation that occurs in the supplylines permits water droplets or even slugsof condensate to be carried into thehumidifier.

Several steps within the humidifierare required to positively prevent thedischarge of liquid moisture and finerparticulate matter along with thehumidifying steam.

The separating chamber in the humidifierbody should provide the volume requiredfor optimum velocity reduction andmaximum separation of steam fromcondensate. Properly separated, the

Chart 19-1. Desirable modified linearcharacteristic curve for valves used undermodulating control. The modification of truelinear characteristics provides more precisecontrol when capacity requirements are verylow and the valve is just cracked off the seat.

7/32"

9/32"5/16"11/32"3/8"

13/32"

15/32"1/2"9/16"5/8"3/4"7/8"

EquivalentDiameter

Rangeability

Ratio ofFlow

Max: Mii

Minimum Flowas % of

Maximuu

Valve Size

1"

11

1

63:169:161:153:144:133:1123:1105:197:185:175:164:170:159:149:140:131:124:118:159:137:128:121:115:110:1

1.61.41.61.92.33.00.80.91.01.21.31.61.41.72.02.53.24.25.61.72.73.54.86.9

10.0

Table 19-1.Steam Humidifier Valve Rangeabilities

1/2"1/4"1/8"

7/16"

1/4"

3/16"5/32"1/8"7/64"3/32"5/64"1/16"

Humidifier control must provide immediateresponse and precise modulation in orderto accurately maintain the required relativehumidity. Faulty control can make itdifficult to provide the desired humiditylevel, and can lead to overloading theducts with moisture and the creation ofwet spots.

Two design factors affect the accuracy ofhumidifier control that can be achievedthe metering valve and the actuator thatpositions the valve.

Precise flow control can be achievedwith a valve designed expressly for thepurpose of adding steam to air. Parabolicplug type valves have been established asbest for this service. They permit a longerstroke than comparable industrial valves,and the plug normally extends into theorifice even with the valve in full openposition. This facilitates full and accuratemodulation of flow over the completestroke of the valve.

The Control ValveThe parabolic plug design also providesexceptionally high rangeability. Range-ability is the ratio between the maximumcontrollable flow and the minimumcontrollable flow of steam through thevalve. The higher the rangeability of avalve, the more accurately it can controlsteam flow. Rangeabilities of the parabolicplug valves used in Armstrong Series9000 Humidifiers shown in Table 19-1 aretypical of the ratios that can be achievedwith this type of valve.

condensate carries a substantial portion ofthe significant micronic particulates withit to be discharged through the drain trap.

Steam from the separating chamber canstill carry liquid mist which must beremoved. Humidifiers equipped with aninner drying chamber that is jacketed bythe steam in the separating chamber caneffectively re-evaporate any remainingwater droplets before steam is discharged.Similarly, the control valve should beintegral with the humidifier. Both thehumidifier and the distribution pipe shouldbe jacketed by steam at supply pressureand temperature to prevent condensationas steam is discharged.

Only proper design of the humidifier forconditioning of steam can assure theessential levels of sanitation and a cleanatmosphere. These guidelines contributeto better comfort conditions and ensurethat the humidifier meets the vitalphysical requirements of the system.

Control of OutputAs discussed, the duct high-limit humidistatcan become the controlling humidistat dueto psychrometric conditions in the duct. Intypical duct air flow rates, the high limithumidistat senses humidifier output inone second or less. In most applica-tions, humidifiers consistently operateat a fraction of maximum output.

100

90

80

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90 100

PERCENT OF FULL STROKE

PER

CENT

OF

FULL

CAP

ACIT

Y

3/4"Stroke

3/8"

3/8" 3/8" 3/8"

9/32" 7/32"

20

The actuator is another important compo-nent in humidity control. Several types areavailable to provide compatibility withvarious system types. The actuator mustbe able to position the valve in very nearlyidentical relationship to the seat on bothopening and closing strokes. This isessential to provide consistent, accuratemetering of steam discharged by thehumidifier.

By their design, electric motor modulatingactuators provide true linear positioningcharacteristics on both opening andclosing cycles. Pneumatic actuators mayor may not be able to provide the precisepositioning and holding characteristicsessential to accurate control. Rollingdiaphragm type pneumatic actuators arerecommended, providing they meet thefollowing criteria:

Distribution of SteamThe third essential factor in proper humidifierdesign is distribution. Steam must bedischarged as uniformly as possible intothe air to permit the fastest possibleabsorption without creating damp spotsor saturated zones.

In normal ducts, a single distributionmanifold installed across the long dimen-sion will provide good distribution of steam.In large ducts or plenum chambers, it maybe necessary to broaden the pattern ofvapor discharge to achieve the requireddistribution, thus requiring multiple mani-folds from single or multiple humidifiers.

Humidification for industrial areas withoutcentral air handling systems is customarilyachieved with unit humidifiers dischargingsteam directly into the atmosphere. Propermixing of steam and air can be accom-plished in two ways. A dispersing fan maybe mounted on the humidifier or a unitheater can be positioned to absorb anddistribute the water vapor.

Considerations in Selecting Steam Humidifiers,Continued...

Figure 20-1.

Distribution Manifold

Duct Cross Section

SingleDistributionManifold in aNormal Duct

DistributionManifold

Duct Cross Section

Multiple DistributionManifolds in a LargeDuct or Housing

11

10

9

8

7

6

5

4

Opening StrokeClosing Stroke

0 10 20 30 40 50 60 70 80 90 100

CONT

ROL

AIR

PRES

SURE

TO

ACT

UATO

R-PS

IG

PERCENT OF FULL STROKE

Chart 20-1. Desirable OperatingCharacteristic for Pneumatic ActuatorsPosition of valve is very nearly identical onboth opening and closing strokes at any givenair pressure to the actuator.

1. Large diaphragm area22 sq in ormoreto provide ample lifting force.This permits the use of a spring heavyenough to stabilize both the hysteresiseffect and the flow velocity effect on thepositioning of the valve stem versus airpressure to the actuator.

2. Diaphragm material highly resistantto wear or weakening from continuouscycling.

3. Actuator stroke long enough (inconjunction with valve plug and seatdesign) to provide high rangeabilityratios.

All modulating actuators, whether electricor pneumatic, should incorporate a springreturn. This is necessary to ensure closingthe valve if there is an interruption of poweror control air to the unit.

For industrial in-plant operation and forvery limited duct applications, a solenoidactuator may be used to provide simpleon-off operation. This type of actuatorshould not be specified for duct applica-tions without a detailed analysis of thesystem.

Strainer

Inlet

Drain

Temp.Switch

Trap

SolenoidValve

Steam Out

C

E

Unit Humidifier for Direct Dischargeinto Area Humidified

Figure 20-2.

21

SilencingMaterial

D. The stainless steel metering valve shallbe a parabolic plug, with a full 3/4" stroke.This valve shall provide the high range-abilities required to achieve full andaccurate modulation of steam flow overthe entire stroke of the valve.

E. The internal drying chamber shallreceive total steam flow at essentiallyatmospheric pressure and be jacketedby steam at supply pressure.

F. The silencing chamber shall be steamjacketed and utilize a stainless steelsilencing medium.

G. The distribution manifold shall provideuniform distribution over its entirelength and be jacketed by steam atsupply pressure to assure that vapordischarged is free of water droplets.A full length stainless steel internalsilencing screen shall be provided.

H. Humidifier shall be equipped with aninterlocked temperature switch toprevent the humidifier from operatingbefore start-up condensate is drained.

Suggested Specification:Steam humidifiers for pneumatic orelectric modulating control: humidifier shallbe the steam separator type providing fullseparation ahead of an integral steamjacketed control valve. Steam shall bedischarged through an internal steamjacketed drying chamber, a silencingchamber and a steam jacketed distributionmanifold.

A. Humidifier shall receive steam atsupply pressure and discharge atatmospheric pressure. It shall befurnished with inlet strainer andexternal inverted bucket steam trap.

B. Separating chamber shall be of avolume and design that will disengageand remove all water droplets and allparticulate matter larger than 3microns when humidifier is operatingat maximum capacity.

C. The stainless steel metering valveshall be integral within the body of thehumidifier, and shall be jacketed bysteam at supply pressure and tempera-ture to prevent condensation.

Operating NoiseIn addition to these crucial performancecharacteristics, operating noise is aconsideration in selecting steam humidifi-ers for areas where quiet operation isessential or desirable, i.e., hospitals, officebuildings, schools, etc.

Figure 21-1. Figure 21-2.The noise of escaping steam is generated atthe control valve. Muffling materials around thevalve are necessary to minimize this noise.

Steam moving at high velocity through thedistribution manifold can create loud, high-pitched whistling as it passes the dischargeholes. An internal silencing screen or similarmaterial is required to interrupt the air flow andprevent whistling.

Stainless SteelMesh

22

Several basic principles must be consid-ered in the application of steam humidifi-cation equipment to avoid potentialoperating problems.

Vapor dissipation in air ducts is one ofthese considerations. In the steamhumidification process, pure water vaporat 212F is mixed with air at a lowertemperature. The mixing of hot steam withcooler air results in heat transfer. Any timeheat is transferred from steam, conden-sation takes place. This condensation isreferred to as visible vapor. When steamis discharged from a manifold in an airduct, it quickly changes from an invisiblegas into visible water particles, and thendissipates to become invisible again.

Basic Application Principles

Visible vapor indicates an area of super-saturation, where the invisible steam gasis condensing into water particles. Whencondensation occurs, the steam gasreleases its latent heat of vaporization(about 1,000 Btu/lb of vapor) to duct air.Then, as the vapor completely mixes withthe duct air, the latent heat previouslygiven off is reabsorbed, converting thevisible vapor back into invisible gas withessentially no change in DB temperature.(See Fig. 22-1).

Clearly, the vapor dissipation in air ductsis very important to proper location oftemperature or humidity controllers. Anycontroller located in or near the visiblevapor pattern will produce inaccurateresults because of pockets of saturatedair. Under typical duct conditions, allcontrollers should be located at least 10 to12 feet downstream of a manifold.However, the following system character-istics will affect the visible vapor pattern,and therefore should be considered incontroller location:

1. Aspect Ratio of Duct. The ratio ofduct height to width is a factor thatinfluences the visible vapor pattern.Fig. 22-2 shows two ducts with equalcross section areas, but with differentaspect ratios. Air velocities, tempera-tures, RH and vapor output from themanifolds are all identical. However,in the taller duct the manifold is shorterand its vapor output comes in contactwith a much smaller percentage of ductair, causing a longer visible vapor pattern.

Figure 22-1. Figure 22-2.Typical dry-bulb (sensible) temperaturevariations within a duct near the humidifiermanifold. As the latent heat of vaporizationis released, the temperature increases (inor near the visible vapor the temperaturemay rise as much as 20 to 30F).However, as the visible vapor mixes andre-evaporates in the air flow, the heat ofvaporization is reabsorbed and the duct airtemperature returns to its former level.

Visible Vapor

60F 60F

ControllerHumidifier Heat Released

Heat Reabsorbed

10 to 12 ft

Visible Vapor

Vapor Contacts 25% of Duct Air

Visible Vapor

Vapor Contacts 75% of Duct Air

Air Flow

Duct Cross Sections

Duct Cross Sections

23

2. Duct Air Temperature. The tempera-ture of the air flow in the duct alsoaffects the length of the visible vaporpattern. Warmer air produces shortervapor pattern, as shown in Fig. 23-1.All other conditions are the same. In75F duct air, the average vapor outputfrom a manifold produces a visiblevapor pattern shorter than 12 inchesin length.

3. Duct Air Velocity. As the duct airvelocity increases, the length of the visiblevapor pattern increases. Fig. 23-2shows two sections of air ducts with airvelocities of 500 fpm and 2,000 fpm

respectively. Other conditions are thesame: temperature, duct air humidity,duct dimensions and the amount ofsteam released from the identicalmanifolds. The length of the visiblevapor pattern is approximately propor-tional to the velocity of the air in the duct.

4. Number of Manifolds in Duct.In a large duct section requiring thedischarge capacity of two humidifiers,better vapor distribution is achieved byusing two manifolds full across the ductand vertically spaced to divide the ductsection into thirds. The same effect isachieved by using multiple distributionmanifolds from a single humidifierthat has adequate capacity to meet

the requirements. When a quantity ofvapor is distributed among multiplemanifolds, the amount released througheach manifold is smaller, and more of theduct air comes into contact with thevapor. This effect is shown in Fig. 23-3.

5. Duct Air RH. Relative humidityin the duct also affects the visiblevapor. The higher the relative humiditydownstream of the humidifier discharge,the longer the visible vapor trail. Thecloser duct conditions are to saturation,the longer the vapor trails are likely tobe. Fortunately, duct air RH may becontrolled with a duct high-limithumidistat, as shown in Fig. 25-2.

Figure 23-1. Figure. 23-2. Figure 23-3.

Visible Vapor

Duct Air 75 F

Air Flow

Visible Vapor

Air Flow 500 FPM

Air Flow

Visible Vapor

Duct Air 55 F

Visible Vapor

Air Flow 2,000 FPM

24

Basic Application Principles,Continued...

Since the use of multiple manifoldsreduces the length of visible vapor, theiruse should be considered whenever anyof the following conditions exist at thehumidifier location:

A. Duct air temperature is below 65For relative humidity is above 80%.

B. Duct air velocity exceeds 800 fpm.

C. Final or high efficiency filters arelocated within 10 feet downstreamfrom humidifier.

D. Height of duct section exceeds 36".

E. Visible vapor impinges upon coils,fans, dampers, filters (not final),turning vanes, etc. located down-stream from humidifier.

Table 24-1 and Fig. 24-1 show atypical number of manifolds and typicalspacing between them when duct heightexceeds 36".

Consult your Armstrong Representativefor specific recommendations regard-ing your needs.

The piping arrangement for humidifierswith multiple manifolds varies with thelocation of the manifolds.

When all manifolds are located abovethe humidifier inlet, manifold piping shouldbe as shown in Fig. 24-2.

When one or more manifolds are locatedbelow the humidifier inlet, the manifoldsshould be trapped separately, as shownin Fig. 24-3.

Smaller manifolds, when possible touse, reduce the cost of multiple manifoldinstallations. Care must be taken that thehumidifier capacity does not exceed thecombined capacity of the multiple mani-folds. Piping arrangement is shown inFig. 25-3.

6. Humidifier Manifold too Closeto High Efficiency Filter. Many airhandling systems require the use ofhigh efficiency filters (also calledabsolute or final filters). These filtersremove up to 99.97% of all particles0.3 micron in diameter, and up to 100%of larger particles. The significance ofthese filtering qualities is shown in thefollowing table, where particle sizes ofcommon substances are compared.

Strainer

Inverted BucketSteam Trap

ManifoldPipe Adapters

Duct Cross Section

Strainer

Inverted BucketSteam Trap

X Equals DuctHeight Divided By

Number of Manifolds

Duct Cross Section

Strainer

InvertedBucket

Steam Trap

F&T TrapDuct Cross Section

Pipe Insulation is Recommended

Manifold Pipe Adapters Standard Pipe With ThreadsOne End OnlyPipe Insulation is Recommended

Standard Pipe With ThreadsOne End Only Standard Pipe With ThreadsOne End Only

X/2

X

X

X/2

Figure 24-1. Figure 24-2. Figure 24-3.

No. of manifolds tobe installed from oneor more humidifiers

Duct height athumidifierlocation

2345

37" to 58"

59" to 80"81" to 100"

101" & Over

Table 24-1. Typical Number of Manifoldsfor Various Duct Heights

Consult your Armstrong Representative forspecific recommendations.

Manifold Pipe Adapters

Particles visible to human eye

Human hair

Dust

Pollen

Fog (visible steam vapor)

Mist (water spray)

Industrial fumes

Bacteria

Gas molecules (steam gas)

Particle Sizein MicronsMaterial

10 or more100

1 to 10020 to 502 to 40

40 to 5000.1 to 10.3 to 100.0006

Table 24-2.Typical Particle Sizes of Common Substances

25

StandardPipe WithThreadsOne End

OnlyInverted Bucket

Steam Trap

F&T TrapDuct Cross Section

Manifold Pipe AdaptersStrainer

Figure 25-3.

Since water particles present in visiblevapor range from 2 to 40 microns, theseparticles are trapped by high efficiencyfilters. Some types of filters absorbmoisture and expand, reducing air flowthrough the filter material. As a result,the static pressure in the duct rises fromnormal (about 1" water gauge) to as highas 40" wg. When the filter absorbs moisture,it also releases the latent heat of con-densed steam into the duct air.

Header

Strainer Control Valve

CondensateReturn

F&TTrap

Drip Leg Trap

InactiveTubes

ActiveTubes

F&TTrap

MountingFrame

NOTE: Condensate cannot be liftedor discharged into pressurized return.

Figure 25-4. Steam Grid System

Specially Designed Steam Grid SystemsFor applications with particularly limiteddownstream absorption distances, customengineered systems may be considered.The system includes a separator/headerand multiple dispersion tube assemblypackaged with a control valve, strainer,steam supply drip trap and one or twoheader drain traps. Each system iscustomized to provide uniform distributionand shortened wettable vapor trail(See Fig. 25-4.)

When a humidifier manifold is located tooclose to an absolute filter, the filter collectswater vapor, preventing the moisture fromreaching the space to be humidified.Placing the humidifier manifold fartherupstream allows the water vapor tochange into steam gas, which will passunhindered through an absolute filter.

Under most circumstances, the watervapor will dissipate properly if the humidi-fier manifold is located at least 10 feetahead of the final filter. However, if theduct air temperature is low, air velocity ishigh or the duct is tall, multiple manifoldsmay be installed to speed the mixing ofsteam with the duct air. For additionalprotection, install a duct high-limit controllerjust ahead of the final filter to limit themaximum humidity to approximately 90%.(See Fig. 25-2.)

Figure 25-1.

Air Flow

+ +++++

+ ++ ++

+ ++++

+++

++

++++

+

++++

+++

+

+

++++ ++

+++++

++++

++++

+++ ++++++++++++

++++

+++ ++

+++++

+

++

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+++

+ + + + ++ ++

+++

+

+ +++++

+ ++ ++

+ ++++

+++

++

++++

+

++++

++++++ ++

+++++

++++

++++

+++ ++++++++++++

++++

+++ ++

+++++

+

+

+

+

+++

+ + + + ++ ++

++

+

++

+

+ ++

+ +

+

+

+

+

++

+

+

+ +

+ +

+

+ +

+

+++

+

+

+

+

+

+

+

+

+

Active

Condensate

Inactive Tubes(Baffle Tubes)

Steam Nozzle

+

+

+

+

+

+

+

+

+

+

++

+

+

+

+

+

+

+

+

+

+

+ +

+

+

+

+

+

+

++

+

+

+

+

+

+

+

+

+

++

+

+

+

+

+

+

+

+

+

Not Here

At Least10 ft

HumidifierHigh-Limit Controller

Mounts Here

Preferred Location

Alternate Location

Figure 25-2.

How Steam Grid Systems ShortenImpingement DistancesDry steam enters each of the dispersiontubes and flows through stainless steelsteam nozzles which extend from thecenter of each tube, before dischargingthrough orifices into the airstream.

Air flow first encounters baffle tubes(See Fig. 25-1) which influence itsflow pattern and increase its velocity.Air traveling around each set of baffletubes encounters opposing flow ofhigh velocity steam exiting the orifices.The result is more uniform distributionand faster absorption of moisture intothe air, resulting in shorter impingementdistances than experienced withtraditional manifolds or dispersion tubes.

26

However, short-cut methods for makingthese calculations or for checking psychro-metric calculations are described below.

Sizing for Primary HumidificationIn sizing duct humidifiers for air handlingsystems, you should know:CFM of air.Design outdoor air temperature andrelative humidity.Required indoor temperature and relativehumidity.Humidifier steam supply pressure.

The formula for load calculation is:

Humidification Load in lbs/hr

Where:CFM = air flow of unhumidified air at

moisture condition R1R2 = moisture content of required

indoor condition air in gr/ft3R1 = moisture content of air to be

humidified (from outdoor condi-tion) in gr/ft3

7,000 = gr/lb conversion60 = min/hr conversion

EXAMPLE, assume:6,800 CFM of outdoor air.Design outdoor air temperature 0F.Steam pressure 10 psig.Required 40% RH at 70F.Air controls used.

From Table 27-1, for 70F final temperature,read 2.456 under 40% and opposite 0F.This is pounds of vapor per hour for 100 CFM.Then 68 x 2.456 = 167.01 or, call it 167 lbs perhour required for design conditions.

A single humidifier can provide this capacityalthough sequence control for two humidifiersmight be needed to avoid duct condensationon very light loads. Length of distributionmanifold is governed by width of duct wherethe humidifier is to be located.

Sizing Considerations

Psychrometric Considerationsin Ducted SystemsIn practice you may find that areas needhumidification but cannot be satisfactorilyhumidified through the central air handlingsystem. These are often areas havinghigh sensible heat loads that must bebalanced with low duct air temperatures tomaintain design temperature conditions inthe area. Typical examples are dataprocessing rooms or hospital operatingrooms where duct air temperatures maybe held as low as 50F to maintain adesign condition of 75F in the room.These low duct air temperatures preventadding enough moisture to the air to meetdesign RH requirements in the roomsay, 55% RH.

Using these conditions as an example,duct air at 50F and 90% RH holds slightlyless than 3.7 grains of moisture per cubicfoot. At 75F the same 3.7 grains ofmoisture yield a relative humidity of 39%.To achieve design conditions of 55% RHat 75F, the air must contain 5.2 grains ofmoisture per cubic foot1.5 grains morethan it psychrometrically can hold at ductair temperature.

For such applications, booster humid-ification must be accomplished in the airof the area after it has reached its finaltemperature. Evaporative pan humidifiersmay be used for this purpose, although wewould recommend using combined steamhumidifier-fan units which can be installedeither within the humidified space orremote ducted to the space. For hospitalapplications, steam humidifier-fan unitsshould include an integral high efficiency(95%) filter to satisfy code requirements.

Determining HumidificationLoads for Air Handling SystemsMost engineers prefer to determinehumidification requirements psychro-metrically on the basis of design condi-tions and humidification requirements.

Sizing for Booster HumidifierAssume that a primary humidifier providesair that will have 40% RH at 70F, but youwant to maintain 60% RH in a laboratorysupplied with 900 CFM of the air at 40%at 70F. Refer to Table 27-3 and read 1.38under 60% and opposite 70F40%.9 x 1.38 = 12.42 lbs. The humidifier mustbe able to provide this capacity at steamsupply pressure.

Special ConditionsWhen relative humidities must be figuredfor temperature conditions other thanthose given in Tables 27-1 through 27-3,Table 27-5 will prove helpful.

New Condition55% RH at 77F.Makeup Air35% RH at 70F.From Table E-23:Grains per cu ftNew Condition 5.54Less Grains per cu ft,Makeup Air 2.82Grains to be added 2.72Assume 800 CFM

800 x 2.72 x 60 7,000

NOTE: .857 lb of steam per hour will add1 grain to 100 CFM. Use of this factor simplifiesthe above equation to: 8 x 2.72 x .857 = 18.65.

Where Table 27-5 is used for outdoor airmakeup, assume 75% RH for the outdoorair at 0 to -20F.

Room to Duct ComparisonsWhen high humidity is needed in a room(70F-60% RH) and the duct temperatureis lower than the room temperature (50F),the duct high-limit humidistat often actsas the controlling stat. Duct high-limithumidistats should be set between 70%and 90% RH. We do not recommendsetting the high-limit stat any higher than90% RH. Table 27-4 shows the maximumroom humidity that can be achieved for thegiven duct conditions.

= 18.65 lbs/hr

CFM (R2 - R1) 607,000

=

27

Table 27-3. Booster Humidification Pounds of vapor per hour per100 CFM to secure desired relative humidity with no change in air temperature

Relative Humidity DesiredInitial Condition

RH 40% 45% 50% 55% 60% 65% 70%Temp.

70

70

72

72

75

75

35%40%35%40%35%40%

.345

.368

.405

.690

.345

.728

.368

.810

.405

1.03.69

1.10.73

1.22.81

1.381.031.461.101.621.22

1.721.381.831.462.031.62

2.071.722.201.832.432.03

2.422.072.572.202.842.43

Relative Humidity DesiredOutdoor

emp.

*30

20

10

0

-10

-20

35%

1.1651.6181.9182.1112.2332.309

40%

1.5101.9632.2632.4562.5782.654

45%

1.8552.3082.6082.8012.9232.999

50%

2.2002.6532.9533.1463.2683.344

55%

2.5452.9983.2983.5913.6133.689

60%

2.8913.3443.6443.8373.9594.035

65%

3.2363.6893.9894.1824.3044.380

70%

3.5814.0344.3344.5274.6494.725

Table 27-1. 70F Primary Humidification Pounds of vapor required perhour per 100 CFM to secure desired RH at 70F (outside air 75% saturated)

*30

20

10

0

-10

-20

1.5842.0342.3342.5292.6522.727

1.9892.4392.7392.9343.0573.132

2.3942.8443.1443.3393.4623.537

2.7993.2493.5493.7443.8673.942

3.2043.6543.9544.1494.2724.347

3.6094.0594.3594.5544.6774.752

4.0144.4644.7644.9595.0825.157

4.4194.8695.1695.3645.4875.562

Table 27-2. 75F Primary Humidification Pounds of vapor required perhour per 100 CFM to secure desired RH at 75F (outside air 75% saturated)

Relative Humidity DesiredOutdoor

emp. 35% 40% 45% 50% 55% 60% 65% 70%

Grains per cu ft atRelative Humidity Specified

75%65%60%55%50%45%40%35%

Grainscu ft

SaturatedAir

Temp.

Table 27-5. Grains of Water Vapor per cu ft of Air at VariousTemperatures and Relative Humidities

8.288.037.797.557.317.096.866.656.446.246.045.134.353.673.082.151.46.93.58.36.21.12

7.186.966.756.556.346.145.955.765.585.415.244.453.773.182.671.861.26.81.50.31.19.11

6.626.436.236.045.855.675.495.325.154.994.834.113.482.932.461.721.17.75.47.29.17.10

6.075.895.715.545.365.205.034.884.724.584.433.763.192.692.261.571.07.68.43.26.16.09

5.525.365.195.034.874.724.584.434.294.164.033.422.902.442.051.43.97.62.39.24.14.08

4.974.824.674.534.394.254.123.993.863.743.623.082.612.201.851.29.78.56.35.21.13.07

4.424.284.154.033.903.783.663.553.443.333.222.742.321.961.641.15.68.50.31.19.11.07

3.863.753.633.523.413.313.203.103.012.912.822.402.031.711.441.00.58.43.27.17.10.06

11.0410.7110.3810.069.7499.4489.1538.8678.5688.3198.0556.8455.7954.8894.1062.8631.9461.242.776.475.285.166

807978777675747372717065605550403020100

-10-20

Steam required to add 1 gr per cu ft to 100 CFM:100 x 60 = 6,000 cu ft per hour or 6,000 grains per hour.

You respond to the questionsoften witha single keystrokeand the SoftwareProgram 2 can:

n Calculate humidification load.n Determine correct humidifier

model number.n Determine correct orifice size.n Indicate psychrometric properties

of air.n Calculate equivalent room humidity

from known duct conditions.n Print the complete humidification

application specification.

= .857 lb/hr

For a free copy of Armstrong SoftwareProgram 2, contact Armstrong or yourArmstrong Representative.

Table 27-4. Maximum Room RH for Given Duct Conditions