Herrmidifier Load Calculator User Manual
Engineered Humidification Systems
Load Calculation Guide
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L o a d C a l c u l a t i o n G u i d e
TABLE OF CONTENTS
SECTION I PREFACE
Preface ...........................................................................................................................................................3
SECTION II BASIC INFORMATION
Denition Of “Relative Humidity” ....................................................................................................................4
“Dry Air” From Heating ....................................................................................................................................4
“Dry Air” From Cooling .................................................................................................................................... 4
The Psychrometric Chart ................................................................................................................................5
Equilibrium Moisture Content .........................................................................................................................5
“Regain” Of Hygroscopic Materials.................................................................................................................5
“Dry Air” And Comfort .....................................................................................................................................5
Humidity And Dust ..........................................................................................................................................6
Humidity And Its Effect On Bacteria And Virus Life ........................................................................................ 6
“Dry Air” And Static Electricity ......................................................................................................................... 6
“Dry Air” And Hygroscopic Materials ............................................................................................................... 7
Woodworking And Humidication ................................................................................................................... 8
Paper Products And Humidication ................................................................................................................8
Printing And Humidication.............................................................................................................................9
Textiles And Humidication .............................................................................................................................9
Food Storage, Processing And Humidication ............................................................................................... 9
Leather Processing And Humidication .......................................................................................................... 10
A Humidication Synopsis .............................................................................................................................. 10
SECTION III LOAD CALCULATIONS
The Psychrometric Chart ................................................................................................................................11
Heating Load ..................................................................................................................................................12
Cooling Load ..................................................................................................................................................14
Product Load ..................................................................................................................................................15
Process Reduction .........................................................................................................................................16
People Reduction ...........................................................................................................................................16
SECTION IV TYPES OF EQUIPMENT
Atomization .....................................................................................................................................................17
Evaporation ....................................................................................................................................................19
Steam .............................................................................................................................................................19
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Preface
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HERRMIDIFIER welcomes you to the world of engineered
humidication systems. HERRMIDIFIER was founded in
1945 and humidication is our only business. We are your
“Total Capability Humidication Resource.”
This Guide will familiarize you with both the need and the
benets of controlled humidication. It will also acquaint you
with the technical facets of accurately calculating humidication demand loads and the selection of the best and most
appropriate system for your application.
HERRMIDIFIER’s recognized leadership position within the
industry is borne from many reasons.
They include:
•Committed to Quality
•Broadest Range of Humidication Systems
-Electrode Steam Generators
-Electric Resistive Steam Generators
-Central Steam
-Steam to Steam
-Air/Water Atomizing Systems
-High Pressure Water Atomizing Systems
-In-Duct Systems
-In-Space Systems
-Water Pretreatment Systems
•Factory Trained Sales Force
-A nationwide network of factory-trained technical sales
representatives.
•Technical Support
-Or Engineering staff will custom design a system to ll
your specic needs.
•Technical Leadership
-State-of-the-art, engineered and patented energy efcient system development.
•Market Diversication Telecommunications
-Computer Rooms
-Electronic Manufacturing
-Textile
-Woodworking
-Printing
-Paper Storage
-Food Storage
-Hospitals
-Ofce Buildings
•Service
We trust this Guide answers your questions. We have more
engineering data for your use and we are ready to help you
solve your dry air problems. Give us a call!
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CU. FT.
7.80 Grains
CU. FT.
.78 Grains
SECTION II BASIC INFORMATION
Relative Humidity and Its Place in Environmental Control
“Dry Air” From Heating
Since the beginning of modern day engineering, environmental control in factories, ofces and homes has become
increasingly more important as its benets to personnel and
product alike were realized. There are three basic parts to
environmental control:
1) air quality-its cleanliness and purity,
2) temperature
3) relative humidity
Of the three, the most ignored is the level of relative humidity-probably because the effects of temperature and air quality are more easily seen and felt than the effects of relative
humidity. Relative humidity is important as it can affect human health and comfort, operation of production machinery,
quality and workability of production material. Proper control
of relative humidity can also be an important factor in the
total energy use and operating efciency of a factory. To develop an understanding of relative humidity and its effect, it
is rst necessary to dene some terms.
Denition Of “Relative Humidity”
HUMIDITY is dened as “the amount of moisture in the air.”
This moisture must be in the form of water vapor. Visible water droplets that have not evaporated to the vapor state do
not affect humidity. The term RELATIVE HUMIDITY is used
to describe “the amount of moisture in a given volume of
air as compared with the greatest amount of moisture that
that volume of air could contain at the same temperature,
expressed as a percentage,” so that:
%RH = (Ma/Mg)
Ma = Amount of moisture in the air
Mg = Maximum amount of moisture in the air
If that cubic foot of air is saturated at 1O°F (100% R.H.) and
raised to 69°F, without adding or subtracting any moisture,
it will now contain only 1/10 the amount of moisture it could
hold at saturation; thus it now has a relative humidity of
10%...2-1/2 times drier than the Sahara Desert!
This is essentially why, during the heating season, air is drier.
The cold, moist outdoor air, brought in by forced air makeup,
exhaust, or natural inltration is heated and becomes warm
dry air. To bring this air to an acceptable level of relative humidity, moisture must be added.
“Dry Air” From Cooling
Under certain conditions, cooling by air conditioning and
refrigeration can remove moisture from the air and reduce
its relative humidity to unsatisfactory low levels. This occurs
when the air is cooled below its DEW POINT-the temperature at which the air becomes saturated and if cooled further
the excess moisture will condense out of the air. For example: Air at 70°F and 75% R.H. will have about 6.08 grains of
moisture per cubic foot.
Air at 55°F can hold only 4.89 grains of moisture per cubic foot at saturation. Therefore, if the 70°F 75% R.H. air is
cooled to 55°F it will now be at 100% R.H. and will contain
a maximum of 4.89 grains of moisture per cubic foot having
lost the excess of 1.19 grains (6.08-4.89 = 1.19) by condensation. When this 55°F 100% R.H. air is discharged back into
the room and again warms to 70°F it will now have a relative
humidity of 60% since it now contains only 4.89 grains of
moisture per cubic foot instead of the original 6.08 grains.
1.19 grains of moisture per cubic foot must now be added to
return the air to its original level of 75% R.H.
The greatest amount of moisture that a given volume of air
can contain changes as the temperature of that air changes. The higher the temperature of that air, the greater the
amount of moisture it can hold when saturated. The key word
here is “temperature.” For example: a cubic foot of air at 69°F
can hold ten (10) times as much moisture as the same cubic
foot of air at 1O°F.
FIGURE 1
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69°F
10°F
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The Psychrometric Chart
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To further illustrate the moisture holding ability of air at various temperatures, following is a chart showing the grains of
water per cubic foot of saturated air, at various temperatures.
This chart was abstracted from the ASHRAE Handbook.
Table 1-A
GRAINS OF WATER PER CUBIC FOOT (AIR)
Saturated Air, Various Temperatures
°F Grains °F Grains
0 .475 60 5.795
5 .609 65 6.845
10 .776 70 8.055
15 .984 75 9.448
20 1.242 80 11.04
25 1.558 85 12.87
30 1.946 90 14.94
35 2.376 95 17.28
40 2.863 100 19.95
45 3.436 105 22.95
50 4.106 110 26.34
55 4.889 115 30.13
As you can see, from the above Table 1 -A, as the temperature of the air increases, so does its ability to hold moisture.
Determinations of MAXIMUM HUMIDIFICATION DEMAND
LOAD are made from this chart. To determine a heating humidication load, simply take the maximum indoor and minimum outdoor temperatures, refer to the chart above, and
write down the corresponding grains of moisture. Then multiply these times the percent of relative humidity desired. Use
the lowest design R. H. for the outdoor gure. Now subtract
the lower temperature gure from higher temperature gure
and insert the result into the following formula for Grains/
Cu. Ft., also inserting the cubic foot of air to be humidied
per hour:
LOAD = Grains/Cu. Ft. X Cu. Ft./Hr.
(Lbs. Water/Hr.) 7000/Grains/lb.
Other factors inuencing the maximum humidication demand load are:
• Natural Air Inltration
• Exhaust Equipment
• Make-up Air
• Construction of Building
• Air Conditioning or Refrigeration
• Vacuum Equipment
• Vapor Barriers
• Window Area
• Hygroscopic Material
Because of all the factors involved, humidication can be
simple or rather complicated. It is best to consult a humidication expert such as Herrmidier Co., Inc. and allow them to
conduct a humidication survey. (Free help can be obtained
by lling out Herrmidier’s form DI-5 and mailing it to us. This
form contains all necessary information for us to help you
design a project).
Equilibrium Moisture Content
Dry air pulls moisture from everything it contacts- HYGROSCOPIC materials (able to absorb or emit moisture), living tissues, etc. Conversely, moist air gives up moisture to
dry hygroscopic materials. An equilibrium will eventually be
reached when the moisture gain of a material equal its moisture loss. This is the EQUILIBRIUM MOISTURE CONTENT
OR “EMC.” This “EMC” changes with temperature, R.H. and
from material to material. The reaching of this “EMC” can
sometimes be detrimental as we shall see.
“Regain” Of Hygroscopic Materials
All hygroscopic materials-and a long list is so classied-take
on or give off moisture when the EMC is disturbed. At a given
level of R.H. a given hygroscopic material will hold a certain
amount of moisture. The weight of this moisture so help compared with the dry weight of the material is called “Regain”
and is expressed as a percentage. Regain varies with R.H.
for a given material. For example: EMC values for average
wood are 5.9% Regain with 30% R.H. air; 9.3% Regain with
50% R.H. air; 14% Regain with 70% R,.H. air; etc. A standard Regain is often specied for hygroscopic items sold by
weight. If the standard Regain is not attained, economic loss
to the seller results.
Variations in Regain cause hygroscopic materials to change
in dimensions, weight, quality, workability, etc.; therefore, it
is best to stabilize the Regain at the most desirable level for
manufacturing, processing, testing, storage, use, consumption, etc. To do this, the R.H. of the air in contact with the material must be stabilized at the proper level, as we shall see.
“Dry Air” And Comfort
Dry air pulls moisture from anything it contacts, including
the human body. Dry air will cause moisture to evaporate
more readily from the surface of the skin, causing a feeling
of chilliness-even at temperatures as high as 75°F! Dry air
also pulls moisture from living membranes, such as the nasal
passages, throat, eyes and ears, leading to the uncomfortable parched throat and sore eyes of winter. Proper control
of relative humidity can help to eliminate these problems.
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When moisture evaporates from the surface of the skin it
causes a degree of evaporative cooling. During the winter,
when heated air is dry, this evaporation occurs more readily,
causing a higher degree of evaporative cooling and a feeling of chilliness. Raising the temperature will help alleviate
the feeling of chilliness, but will actually aggravate the other
problems of dry, parched throat and eyes, because the air
at this higher temperature can now hold still more moisture
(refer to Table 1 -A), which causes the R. H. to drop and the
pull for moisture from body to air becomes even greater.
More comfort can readily be obtained by raising the level of
relative humidity. Often, by raising the R.H. the temperature
can then be lowered while maintaining the same comfort
level. The following Table 1 -B illustrates various comfort
levels possible. As you can see from the chart, raising
the R.H. could result in your being able to lower the temperature, thereby saving energy. In this age of expensive
energy, this could be a big boost for any industry, ofce or
home. In addition the annoying parched throat, sore eyes
and dry nose may be eliminated. Generally, R.H. levels of
35% to 50% are considered to be in the comfort range.
Table 1-B
Comfort Levels vs. Temperature/Humidity
Factory Ofce
°F % RH °F % RH
65 40 68 45
68 30 70 40
72 20 76 25
78 10 79 20
Humidity And Dust
Dust is not only a cleaning and maintenance nuisance but
a common vehicle for microorganisms. It is well known
that the R.H. of the air will signicantly affect the amount of
dust in the air. A higher level of R.H. (50%) will cause the
particles to settle out of the air.
Also, dry air will pull moisture from the bers of carpets and
rugs causing them to become brittle, break off and oat in
the air. By raising the level of R.H. in the air this problem
can be signicantly reduced. For example, in one study a
carpet cleaned weekly, under low levels of relative humidity, produced 3 to 4 bags of broken bers or “fuzz.” After the
R.H. in the ofce was raised to 50% the weekly cleaning
produced only a half bag of “fuzz.” Needless to say, the
carpet life was probably extended, as well as a reduction of
dust from the bers of the carpet achieved.
Humidity And Its Effect On Bacteria And Virus Life
Several studies on various bacterial strains and viruses
have shown that at R.H. levels close to 50% these microorganisms fail to survive for long periods of time. Possible
explanations of this are that at low levels of R.H. these microorganisms can enter a “dormant” state and simply oat
around in the air until such time as they contact a moist
surface where they can become “active” again. At high levels of R.H. there is enough moisture in the air that these microorganisms may be able to thrive “actively.” In the middle
levels of R.H., near 50%, there is enough moisture in the
air that these microorganisms cannot remain “dormant,” but
not enough that they can thrive “actively” either.
“Dry Air” And Static Electricity
Dry air permits the buildup of static electricity charges
on machinery, materials and people. These electrostatic
charges may cause production problems because of the
electrostatic attraction built up between materials, unpleasant shocks to personnel, and in some cases, explosion
hazards.
Static electricity charges are built up by movement of
machinery and materials, such as in a printing press or
a spinning machine, by people walking across carpeted
oors, etc. These charges are constantly being generated
and their buildup and discharge are affected by the level
of R.H. Relative humidity levels above 45% will serve to
eliminate electrostatic charge buildup and discharge. What
happens when R.H. is higher is that an invisible moisture
lm will form on the surface of materials and equipment.
This lm contains impurities, from the air, which allow it to
be a conductor. As electrostatic charges are generated, this
lm conducts the charges to ground before they can build
up sufciently high to cause a spark to jump.
Control of static electricity is important in many industries.
Printing plants need to eliminate the static electricity caused
problems of erratic feeding, sticking sheets, tacky ink and
misregistration of color. Textile mills can ill afford to have
huge electrostatic charges build up on spindles and cards.
Data Processing is especially sensitive to static electricity
as it can cause malfunction by improper feeding of cards
and paper, brittle tape and electrostatic discharges. Explosive production areas must be humidied. To chance a
static discharge in an explosive atmosphere is extremely
dangerous.
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“Dry Air” And Hygroscopic Materials
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HYGROSCOPIC materials (those able to take on or give
up moisture) are particularly sensitive to humidity changes
in their environment. Materials so classied would include
wood and wood products, paper and paper products, textiles, leather, ceramics, food and a long list of others.
These materials respond to their environment by taking on or
giving up moisture, thereby changing their REGAIN. When
these materials nally reach a balance, where they are stable and no longer take on or give off moisture, they are said
to have reached their EQUILIBRIUM MOISTURE CONTENT
(EMC).
When a hygroscopic material is stabilized at is EMC for a
particular temperature and R.H., there is little effect on the
material. The problems begin when the R.H. begins to drop
and the air pulls moisture from the material, upsetting its
EMC. When the material loses moisture it will shrink, warp,
crack, check, become thirsty for solvents, etc. This causes
problems not only with the material, but also with the machinery, nishing processes, coatings and so on. Weight and
texture are also affected.
Table 1-C
Hygroscopic materials lose moisture to dry air... pick up moisture from humidied air. This can materially affect your prot!
REGAIN OF HYGROSCOPIC MATERIALS
Moisture Content expressed in Percent of Dry Weight of the Substance at Various Relative Humidities - Temperature 75 °F
When the EMC is upset to the point of damaging a product (cracking, splitting, warping) and rendering it unsaleable,
economic loss results. This includes the loss of any and all
energy required to make that product, (from the raw material rening to the nished product) if the product must be
scrapped, the additional energy input and labor expense
if the product is reworked, down time when machinery is
jammed or damaged and higher per piece costs if machinery must be run slower than normal to prevent electrostatic
buildup. For example, one woodworking plant reported savings of $900 a week after introducing controlled humidity to
the plant. One investment castings company reported savings of $4,800 per week and the textile industry was even
more dramatic with $6,700 per week! These savings are realized from better product workability, faster machine operation and production of less non-saleable units. Following is
a charge listing the Regain for several materials, after which
we shall take a look at some industries in depth.
Industry Materials Relative Humidity %
10 20 30 40 50 60 70 80 90
Baking: Crackers 2.1 2.8 3.3 3.9 5.0 6.5 8.3 10.9 14.9
Flour 2.6 4.1 5.3 6.5 8.0 9.9 12.4 15.4 19.1
White Bread 0.5 1.7 3.1 4.5 6.2 8.5 11.1 14.5 19.0
Leather: Sole Oak, Tanned 5.0 8.5 11.2 13.6 16.0 18.3 20.6 24.0 29.2
Printing: Paper-Com. Ledger - 75% Rag., 1% Ash 3.2 4.2 5.0 5.6 6.2 6.9 8.1 10.3 13.9
Paper-M.F. Newsprint - 24% Ash 2.1 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6
Paper-White Bond Rag - 1% Ash 2.4 3.7 4.7 5.5 6.5 7.5 8.8 10.8 13.2
Paper-Writing - 3% Ash 3.0 4.2 5.2 6.2 7.2 8.3 9.9 11.9 14.2
Textile: Cotton - Absorbent 4.8 9.0 12.5 15.7 18.5 20.8 22.8 24.3 25.8
Cotton - American-cloth 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10.0 14.3
Cotton - Sea Isle-roving 2.5 3.7 4.6 5.5 6.6 7.9 9.5 11.5 14.1
Hemp - Manila & Sisal 2.7 4.7 6.0 7.2 8.5 9.9 11.6 13.6 15.7
Jute - Average grade 3.1 5.2 6.9 8.5 10.2 12.2 14.4 17.1 20.2
Linen - Dry Spun - yarn 3.6 5.4 6.5 7.3 8.1 8.9 9.8 11.2 13.8
Rayon - Cellulose - Acetate-ber 0.8 1.1 1.4 1.9 2.4 3.0 3.6 4.3 5.3
Rayon - Cupromonium - Average Skein 4.0 5.7 6.8 7.9 9.2 10.8 12.4 14.2 16.0
Rayon - Vicose Nitrocel 4.0 5.7 6.8 7.9 9.2 10.8 12.4 14.2 16.0
Silk - Raw Cheyennes - Skein 3.2 5.5 6.9 8.0 8.9 10.2 11.9 14.3 18.8
Wool - Australian - Marino - Skein 4.7 7.0 8.9 10.8 12.8 14.9 17.2 19.9 23.4
Cigarette 5.4 8.6 11.0 13.3 16.0 19.5 25.0 33.5 50.0
Wood: Timber - Average 3.0 404 5.9 7.6 9.3 11.3 14.0 17.5 22.0
Glue - Hide 3.4 4.8 5.8 6.6 7.6 9.0 10.7 11.8 12.5
Misc.: Charcoal - Steam Activated 7.1 14.3 22.8 26.2 28.3 29.2 30.0 31.1 32.7
Gelatin 0.7 1.6 2.8 3.8 4.9 6.1 7.6 9.3 11.4
Silica Gel 5.7 9.8 12.7 15.2 17.2 18.8 20.2 21.5 22.6
Soap 1.9 3.8 5.7 7.6 10.0 12.9 16.1 19.8 23.8
Starch 2.2 3.8 5.2 6.4 7.4 8.3 9.2 10.6 12.7
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