16th Air-conditioning Day, organised by the Portuguese Association of Engineers in Lisbon, 20th October 2016. Nalini’s speech on ‘Air humidity control’ underlines the need for correct humidity control to ensure personal comfort, correct preservation of artworks and food and optimisation of industrial processes. This presentation looks at isothermal and adiabatic systems, the two main humidification processes.

1. AIR HUMIDIFICATION
Technical, health and energy aspects
Luigi Nalini
Lisbon, October 20th, 2016

2. IN CASE OF INTEREST, THE SLIDES SHOWN
TODAY MAY BE REQUESTED AT THE FOLLOWING
E‐MAIL ADDRESS:
media.relations@carel.com

3. LIFE ON EARTH DEPENDS ON WATER
ALL KNOWN LIFE FORMS DEPEND ON THE PRESENCE OF WATER THAT MAKES POSSIBLE
THE METABOLIC PROCESSES.
MANY OTHER SUBSTANCES AND PRODUCTS, BOTH ORGANIC AND INORGANIC,
CONTAIN WATER THAT AFFECTS HEAVILY THEIR PHYSICAL, CHEMICAL AND
DIMENSIONAL PROPERTIES.
THE CONTENT OF WATER IN BODIES OR MATERIALS IS THE RESULT OF A BALANCE
BETWEEN INTAKE AND LOSS AMONG THE BODIES THEMSELVES AND WHAT
SURROUNDS THEM, INCLUDING THE ATMOSPHERE.
ON A PLANETARY SCALE THIS BALANCE IS MAINLY DETERMINED BY THE
HYDROLOGICAL CYCLE THAT CAUSES THE CONTINUOUS CHANGE OF STATE AND
MOVEMENT OF WATER ON THE SURFACE OF THE EARTH AND ABOVE IT.

4. THE HYDROLOGICAL CYCLE
THE PROVISION OF WATER NECESSARY FOR THE EXISTENCE OF LIFE AND THE
CONSERVATION OF SUBSTANCES OR BODIES ON EARTH HAPPENS THANKS TO THE
ATMOSPHERE THAT ABSORBS THE VAPOR ORIGINATED FROM THE LIQUID MASSES AND
PROMOTES THE GENERATION OF CLOUDS WHICH THEN FALL UNDER LIQUID OR SOLID
FORM TO THE GROUND.

5. THE DISTRIBUTION OF RAINWATER THROUGH THE RIVERS AND THE SOIL INFILTRATION, IS
THE MAIN SOURCE OF HYDRATATION OF THE PLANT KINGDOM AND THUS OF ALL LIVING
SPECIES, HOWEVER A SUBSTANTIAL PART OF WATER STANDS IN THE ATMOSPHERE IN THE
FORM OF VAPOR, SPREADING ITS MOLECULES THROUGH THE AIR.
THE CONTENT OF WATER VAPOR MOLECULES IN THE AIR IS DEFINED HUMIDITY.
ANY AIR CONTAINING WATER VAPOR MOLECULES IS CALLED HUMID AIR.

6. THE CIRCULATION AND THE DISTRIBUTION OF WATER WITHIN THE HYDROLOGICAL
CYCLE ARE MADE POSSIBLE BY THE TWO MAJOR TRANSFORMATIONS:
 EVAPORATION (PASSAGE FROM LIQUID STATE TO VAPOR STATE);
 CONDENSATION (FROM VAPOR STATE TO LIQUID STATE).
THE PASSAGE FROM ICE/SNOW INTO WATER AND VICE VERSA PLAYS AN IMPORTANT
ROLE BUT NOT IMMEDIATELY TIED WITH THE HYDRATATION OF THE EARTH

7. ACCORDING TO THE MOLECULAR KINETIC THEORY, AS ANY ELEMENT WATER ASSUMES
THE SOLID, LIQUID, GASEOUS STATE IN FUNCTION OF THE INTERNAL ENERGY OF ITS
MOLECULES , WHICH OCCURS AS VIBRATIONAL, ROTATIONAL, TRANSLATIONAL MOTION
AND RECIPROCAL COLLISIONS.
TEMPERATURE IS A MEASURE OF THE AVERAGE INTERNAL ENERGY AND THEREFORE
THE HIGHER THE TEMPERATURE, THE GREATER THE INTERNAL ENERGY OF THE WATER
MOLECULES.
IN LIQUID WATER THE INTERNAL ENERGY OF
MOLECULES IS NOT HIGH ENOUGH TO BREAK THE
RECIPROCAL ATTRACTION: UNLIKE SOLID ICE, IN
WHICH MOLECULES MOVE AROUND THEIR FIXED
POSITION, LIQUID WATER HAS A DEFINED VOLUME
BUT NO CONSISTENCY AND THUS, DUE TO GRAVITY
OR CAPILLARITY, TAKES THE SHAPE OF ITS
CONTAINER.
THE THREE PHYSICAL STATES OF WATER

8. UPON A SUFFICIENT ENERGY INPUT – UNDER HEAT FORM – THE MOLECULES OF
LIQUID WATER INCREASE THEIR AVERAGE INTERNAL ENERGY; PART OF THEM REACH
AN ENERGY LEVEL SUFFICIENT TO ENTER IN THE EVAPORATION PROCESS,
OVERCOMING THE ATTRACTIVE FORCES OF THE BULK OF THE LIQUID, PASSING TO
THE GASEOUS STATE AND SPREADING IN THE AVAILABLE SPACE AROUND.
ON THE CONTRARY, IF THE MOLECULES OF
WATER CONTAINED IN THE AIR TRANFER SOME
HEAT (FOR EXAMPLE COMING IN CONTACT WITH
A COLD SURFACE), THEIR INTERNAL ENERGY MAY
BECOME INSUFFICIENT TO ENABLE THEM TO
REMAIN AT THE GASEOUS STATE: IN THIS CASE
TAKES PLACE THE CONDENSATION PROCESS IN
WHICH THE VAPOR TURNS INTO LIQUID.
EVAPORATION AND CONDENSATION OF WATER

9. THE AVERAGE KINETIC ENERGY OF VAPOR MOLECULES
DETERMINES DIRECTLY THE MACROSCOPIC PRESSURE THEY
EXERT OVER THE ADJACENT BODIES, IN PROPORTION TO THE
NUMBER AND THE FORCE OF THE COLLISIONS.
AS WELL AS THE INTERNAL ENERGY, ALSO VAPOR PRESSURE
DEPENDS JUST ON TEMPERATURE.
ENTERING INTO THE ATMOSPHERE THE VAPOR MOLECULES MUST «COMPETE» WITH
THE PRESSURE EXERTED BY THE OTHER GASES: INFACT, ACCORDING TO THE GAS LAWS,
THE INDIVIDUAL PRESSURE OF ANY GAS (CALLED ALSO PARTIAL PRESSURE) IN THE
MIXTURE IS PROPORTIONAL TO ITS VOLUMETRIC FRACTION.
THE DIAGRAM SHOWS THE PRESSURE
EXERTED BY THE VAPOR MOLECULES vs
TEMPERATURE JUST AT THE SURFACE OF
LIQUID WATER (i.e.: 3170 Pa @ 25°C).
THE SURFACE VAPOR PRESSURE, SINCE IN
EQUILIBRIUM BETWEEN LIQUID AND VAPOR,
IS THE MAXIMUM POSSIBLE AT THAT
TEMPERATURE AND THEREFORE IS DEFINED
SATURATION PRESSURE PVS. 0 5 10 15 20 25 30 35 40 45 50
14000
12000
10000
8000
6000
4000
2000
0
temperature ‐ °C
Vaporpressure ‐Pa
SATURATION PRESSURE VPS OF WATER vs TEMPERATURE
3170
WATER VAPOR PRESSURE

10. THE NUMBER OF MOLECULES OF WATER
CONTAINED IN THE AIR IS PROPORTIONAL TO
THE PARTIAL PRESSURE THEY EXERT.
THE MAXIMUM QUANTITY IS GOT WHEN THE
VAPOR PARTIAL PRESSURE EQUALS THE
SATURATION PRESSURE VPS; IN THIS CASE,
THE AIR IS SAID SATURATED WITH VAPOR.
kPa20,5 76,6 0,97 3,17 0,07 101,3
22,6% 74% 1,33% 1,97% 0,11% 100%weight
PROPORTION OF ATMOSPHERE MAIN COMPONENTS WITH
WATER VAPOR AT SATURATION WHEN TEMPERATURE = 25°C
BUT, DIFFERENTLY FROM PERMANENT GASES
(N2, O2, AR) WHOSE PERCENTAGE IS STABLE,
WATER VAPOR CONCENTRATION VARIES
WITH GEOGRAFIC LOCATION, TEMPERATURE
AND WEATHER: IF THE CONTENT OF VAPOR
IN THE AIR IS NOT ENOUGH FOR SATURATION,
THE VAPOR PRESSURE PV IS ALSO LOWER
THAN THE SATURATED PRESSURE PVS.
THE RATIO BETWEEN THE ACTUAL PRESSURE
AND THE SATURATED PRESSURE IS DEFINED
RELATIVE HUMIDITY RH:
RH = PV / PVS [%]
VAPOR PRESSURE OF WATER vs TEMPERATURE AND RH
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30 35 40
temperature ‐ °C
Vaporpressure ‐Pa
25
PVS = 3170
PV = 1270
VAPOR PRESSURE
DEFICIT
ATMOSPHERIC PRESSURE (101,325 Pa)
ATMOSPHERIC RELATIVE HUMIDITY

11. SOME “MISTERIOUS” STAINS OF MOLD IN
THE CORNERS OF A HOUSE ARE GENERALLY
CAUSED DURING COLD SEASONS JUST BY
THE MIGRATION OF VAPOR FROM THE
KITCHEN OR FROM THE BATHROOM WHERE
IT IS GENERATED TO THE COLDER SPOTS
WHERE IT CONDENSES.
THE ATMOSPHERIC AIR IS A FUNDAMENTAL
VEHICLE FOR THE TRANSPORTATION OF
ACCORDING TO DALTON’S LAW EVERY GAS IN A MIXTURE BEHAVES INDEPENDENTLY
OF THE OTHER ONES AS IT WAS ALONE AT ITS OWN PARTIAL PRESSURE.
FOR THIS REASON IF TWO CONTIGUOUS AREAS HAVE AN UNEQUAL MOISTURE
CONTENT, DUE TO THE PARTIAL PRESSURE DIFFERENCE THE VAPOR WILL PASS FROM
THE SPACE WITH THE HIGHER MOISTURE CONTENT TO THE OTHER.
WATER VAPOR MIGRATES THROUGH THE ATMOSPHERE
MOISTURE AND FOR THE WATER BALANCE OF LIVING BEINGS AND BODIES OR
MATERIALS – ORGANIC AND INORGANIC – WHOSE PROPERTIES ARE INFLUENCED BY
THEIR WATER CONTENT NOT ONLY WITHIN CLOSED ENVIRONMENTS BUT ALSO IN IN
VAST OUTDOOR SPACES AS IN DESERTIC AREAS WHERE RAINS ARE VERY RARE

12. THE TRANSFER OF MOISTURE
WILL CONTINUE UNTIL THE
TWO PRESSURES WILL
EQUALIZE; DUE TO THE HUGE
DISPARITY IN MASS, THE FINAL
VAPOR PRESSURE IN THE ROOM
WILL BECOME VERY SIMILAR TO
THE EXTERNAL ONE, UNLESS
THERE IS AN INDOOR PROCESS
OF HUMIDITY CONTROL.0 5 10 15 20 25 30
35 40
25
20
15
10
5
0
DRY BULB TEMPERATURE ‐ °C
ABS. HUMIDITY ‐gV/kgA
VAPOR PARTIAL PRESSURE ‐KPA
1
2
3
0
0,49
2,5
1,5
3,5
2,53
15,9
3,0
24
Win
Wout
Sin Sout
22
VAPOR MIGRATES FROM INDOOR TO OUTDOOR AND VICEVERSA
IF THERE IS A DIFFERENCE IN PARTIAL PRESSURES, THE MIGRATION OF VAPOR TAKES
PLACE ALSO FROM AN ENCLOSED SPACE TO THE OUTDOOR AIR OR VICEVERSA
THROUGH CRACKS – OFTEN UNNOTICED – ON BUILDING WALLS, DOORS, WINDOWS.
HOWEVER IF THE TEMPERATURE OF THE TWO AMBIENTS ARE DIFFERENT, ALSO
RELATIVE HUMIDITIES WILL BE AFFECTED.
AS SHOWN IN THE ABOVE DIAGRAM, THE INDOOR RELATIVE HUMIDITY WILL
NORMALLY BE DRIVEN TO HIGH VALUES IN SUMMER AND TO LOW ONES IN WINTER:
BEYOND ACCEPTABLE LIMITS A CLIMATIC CONTROL SYSTEM BECOMES NECESSARY

13. STRATUM CORNEUM
STRATUM GRANULOSUM
STRATUM SPINOSUM
WATER
WATER
TRASPIRATION OF ANIMAL EPIDERMIS TRANSPIRATION OF WOODTRASPIRATION OF
VEGETAL CELLS
THE WATER CONTAINED IN ANY BODY OR MATERIAL HAS A SURFACE VAPOR PRESSURE
EQUAL TO THE SATURATION VALUE PVS AT ITS TEMPERATURE.
IF THE SURROUNDING AIR HAS A LOWER VAPOR PRESSURE, AN EVAPORATION OF
WATER FROM THE BODY OR MATERIAL INTO THE AIR WILL START.
ON THE OPPOSITE, THE PRESSURE DIFFERENCE WILL CAUSE THE TRANSFER OF VAPOR
FROM THE AIR INTO THE BODIES OR MATERIALS THAT ABSORB IT.
THE BELOW DRAWINGS SHOW THE «TRANSPIRATION» OF SOME ORGANIC MATTERS
VAPOR MIGRATES FROM BODIES TO AIR AND VICEVERSA

14. DRY BULB TEMPERATURE ‐ °C
VAPOR PARTIAL PRESSURE ‐KPA
1
2
3
2,5
1,5
3,5
20 25 30 35 40
25
20
15
10
5
ABS. HUMIDITY ‐gV/kgA
CAUTION: HEAT CRAMPS AND
HEAT EXHAUSTION POSSIBILE
DANGER: HEAT CRAMPS AND
HEAT EXHAUSTION LIKELY
PROBABLE HEAT STROKE
DUE TO METABOLISM, HUMAN BODY GENERATES HEAT
THAT, IN ORDER TO KEEP THE INTERNAL TEMPERATURE
AT 36‐37°C, MUST BE NECESSARILY RELEASED: OUR
PERCEPTION OF "HOT" OR "COLD" IS CAUSED BY THE
CAPABILITY TO TRANSFER THE METABOLIC HEAT RATE
MORE THAN BY ENVIRONMENTAL CONDITIONS.
AS AMBIENT TEMPERATURE RAISES, THE HEAT
TRANSFERRED BY CONVECTION OR RADIATION
DECREASES AND OUR BODY SPONTANEOUSLY SWEATS
HUMAN BODY PERCEIVES INDIRECTLY HIGH RELATIVE HUMIDITY
UPON AN INCREASE OF HUMIDITY,
SWEATING GROWS CREATING A
SENSE OF UNEASE WITH NO BENEFIT.
BEYOND CERTAIN TEMPERATURE/HUMIDITY LIMITS
THE METABOLIC HEAT CANNOT BE RELEASED,
CAUSING A SEVERE RISK OF A "HEAT STROKE" AND
EVEN PUTTING AT RISK THE SURVIVAL.
SO TO IMPROVE THE HEAT DISSIPATION THROUGH
EVAPORATION.

15. BEING NOT EQUIPPED WITH SENSORY RECEPTORS SUITABLE TO FEEL DIRECTLY THE
MOISTURE CONTENT OF THE AIR ‐ WHICH, IN ADDITION, IS FULLY TRANSPARENT ‐
HUMAN BODY IS LESS SENSITIVE TO LOW RELATIVE HUMIDITY.
LOW HUMIDITY IS MOSTLY PERCEIVED ONLY FOR ITS SIDE EFFECTS THAT, ALTHOUGH
POSSIBLY UNNOTICED IN THE SHORT TERM, COULD BE OBSERVED AFTER A CERTAIN
PERIOD OF TIME; HOWEVER THE CONSEQUENCES CAN BE UNPLEASANT AND OFTEN
HARMFUL ECONOMICALLY, TECHNICALLY AND PATHOLOGICALLY.
LET US FOCUS ON THE EFFECTS OF LOW ENVIRONMENTAL RELATIVE
HUMIDITY, ON THE RECOMMENDED MINIMUM LIMITS IN THE VARIOUS
AMBIENTS AND CIRCUMSTANCES AND ON THE DEVICES USED TO FACE IT.
LIMITED SENSIBILITY OF HUMAN BODY TO LOW RELATIVE HUMIDITY

16. normal nasal
mucosa
irritated nasal
mucosa
OVER TIME, EXPOSURE TO LOW HUMIDITY CAN DRY OUT
THE MUCUS MEMBRANES LOCATED IN THE NOSE AND
THROUGH THE RESPIRATORY TRACT, WHICH ARE A
NATURAL BARRIER TO INFECTION: BECOMING DRY, THEY
LOSE THEIR ELASTICITY AND CRACK GIVING A DIRECT PATH
FOR GERMS AND BACTERIA TO ENTER THE BLOODSTREAM.
MOREOVER, DRY AIR DRAWS MOISTURE OUT
OF THE SKIN CAUSING SMALL CRACKS ON ITS
SURFACE AND PROVIDING AN ENTRYWAY FOR
POTENTIAL DANGEROUS PATHOGENS.
(GUGGENBICHLER ET AL., 2007) CARRIED OUT
EXPERIMENTAL AND CLINICAL STUDIES AND
CONCLUDED THAT FOR A GOOD MECHANICAL
CLEARANCE OF THE AIRWAYS A HUMIDITY OF
AT LEAST 30% ( BETTER 45%) IS REQUIRED.
EFFECT OF LOW HUMIDITY IN HEALTH AND WELLNESS
germs
Rough, cracked,
pertially
inflamed skin
due to damaged
barrier
corneal layer
lipids (fats)
spinous
layer
basal layer
ONE OF THE FIRST COMPLAINTS STATED BY PERSONS EXPOSED TO PROLONGED DRY AIR
IS THE IRRITATION OF THE EYES ARISING IN CASE OF A BREAKDOWN OF THE TEAR FILM.
LOW HUMIDITY IS ONE OF THE REASONS PEOPLE MAY BECOME SICK.
THIS IS IMPORTANT PARTICULARLY FOR ESPECIALLY EXPOSED PERSONS SUCH AS
PEOPLE IN HOSPITALS AND NURSING HOMES.

17. EFFECT OF LOW HUMIDITY ON WOOD AND PAPER
MANY SUBSTANCES AND PRODUCTS CONTAIN WATER THAT
AFFECTS THEIR PHYSICAL AND DIMENSIONAL PROPERTIES.
THE LENGTH OF WOOD TANGENTIAL FIBRES INCREASES APPROX
0,04% PER %RH THUS, IF RH VARIES FROM 40% TO 50%, A
WOODEN BOARD OF 500 mm LENGHTENS OF 2 mm.
A RAPID CHANGE OF THE WATER CONTENT – AS OCCURS WHEN
water content ‐% weight
10% 30% 50% 70% 90%
0
5
10
15
20
25
air relative humidity @ 20°C
WOOD
PAPER
THE AIR HUMIDITY IS FAR FROM THE BALANCE WITH THE WOOD ‐ IMPLIES DIMENSIONAL
VARIATIONS WHICH CAN LEAD TO THE BOWING OF THE BOARDS UP TO GET A CRACKING.
THE CONTAINMENT OF THE AMBIENT RELATIVE HUMIDITY BETWEEN 35% AND 55% IS
RECOMMENDED FOR ITS LOWER INFLUENCE ON WATER CONTENT IN THESE MATERIALS.
REGARDING PAPER, A CHANGE OF RELATIVE HUMIDITY OF 10%
IMPLIES A DIMENSIONAL VARIATION BETWEEN 0.1% AND 0.2%: ON
A A4 SHEET IT MEANS NOT LESS THAN ½ mm.
IN ADDITION, IN A STACK OF PAPER OR IN A BOOK THE VARIATION
IN LENGTH TAKES PLACE INITIALLY IN THE PERIMETER PART, AND
ONLY AFTER A LONGER TIME IN THE CORE, GIVING RISE TO
FOLDING AND CORRUGATION OF THE SHEETS: THUS, BESIDES THE
ABSOLUTE VALUE, THE RELATIVE HUMIDITY STABILITY IS VERY
IMPORTANT.
Pressroom = 75% RH
Paper stack = 50% RH
Pressroom = 35% RH
Paper stack = 50% RH
TIGHT EDGES
WAVY EDGES

18. GENERALLY A HUMIDITY LEVEL BETWEEN 40% AND 60% IS MOSTLY SUITABLE FOR
HUMAN COMFORT AND TECHNICAL PROCESSES (WITH SEVERAL EXCEPTIONS AS IN
THE CONSERVATION OF MANY FOODS AND SUBSTANCES REQUIRING HIGHER VALUES).
HOWEVER AIR HUMIDIFICATION IS AN ENERGY CONSUMING PRACTICE BECAUSE THE
EVAPORATION OF 1 kg OF WATER REQUIRES AN INPUT OF APPROX 0,72 kWh (THE
SAME REQUIRED TO RIDE BY BIKE 25 km IN ONE HOUR).
IN ANY APPLICATION THE MINIMUM RELATIVE HUMIDITY THRESHOLD SHOULD BE A
COMPROMISE BETWEEN THE ACTUAL NEEDS – PREVENTING MOISTURE DROPPING
BELOW POTENTIALLY HARMFUL LEVELS ‐ AND THE RELEVANT COST INCURRED.
THE MOST INFLUENTIAL CONSEQUENCES OF A LOW RELATIVE HUMIDITY ON OUR LIVES
AND COMMON ACTIVITIES ARE:
1) THE ABSORPTION BY THE AIR OF THE WATER CONTAINED IN LIVING BEINGS AND
IN MATERIALS, PARTICULARLY THE ORGANIC ONES;
2) THE BUILD‐UP OF STATIC ELECTRICITY WITH A RESULTING "SHOCK" FOR INVOLVED
PEOPLE OR DAMAGES IN OBJECTS AND PRODUCTS.
MINIMUM RELATIVE HUMIDITY THRESHOLD IS A COMPROMISE

19. THE SENSITIVITY OF MATERIALS TO ENVIRONMENTAL HUMIDITY IS ONE OF THE MAIN
CAUSE OF DETERIORATION OF ARTWORKS MADE WITH HYGROSCOPIC MATERIALS.
DIMENSIONAL ALTERATIONS MAY GENERATE CRACKS IN WOODEN SCULPTURES AND IN
ANTIQUE FURNITURE OR IN MANUSCRIPTS WITH LOSS OF ELASTICITY AND BRITTLENESS.
MATERIALS LIKE OIL, GESSOES, TEMPERA PAINTS HAVE A LOWER RESPONSE TO AIR
RELATIVE HUMIDITY BRINGING TO CRAQUELURES IN PAINTINGS ON WOOD OR ON
FRAMED CANVAS IN THE CASE OF WIDE CHANGES IN AMBIENT CONDITIONS.
ACCORDING TO THE GUIDELINES OF THE SMITHSONIAN MUSEUM CONSERVATION
INSTITUTE THE RELATIVE HUMIDITY FOR EXHIBITION AND STORAGE SPACES SHOULD BE
INCLUDED BETWEEN 45% AND 55%, IN ANY CASE NOT LOWER THAN 37%.
EVEN MORE IMPORTANT IS THAT HUMIDITY FLUCTUATIONS IN THE SHORT TERMS
SHOULD NOT EXCEED A DEFINED TOLERANCE (TYPICALLY ± 5%).
EFFECT OF LOW HUMIDITY IN ART GALLERIES, MUSEUMS, LIBRARIES
“LA GIOCONDA” BY LEONARDO DA VINCI
PAINTING ON POPLAR TABLE (LOUVRE)
FRENCH WOOD SCULPTURE
(16TH CENTURY)
PAINTING ON CANVAS
(19TH CENTURY)

20. EFFECT OF LOW HUMIDITY IN FOODSTUFF PRESERVATION
TEMPERATURE AND RELATIVE HUMIDITY ARE FUNDAMENTAL FACTORS FOR A PROPER
FOOD CONSERVATION.
FRESH MEATS SHOULD BE STORED AT A TEMPERATURE NOT HIGHER THAN 2°C WITH A
RELATIVE HUMIDITY AROUND 70%; A HIGHER HUMIDITY WOULD BE RISKY FOR A
MICROORGANISMS GROWTH, BUT A LOWER ONE WOULD CAUSE A LOSS OF WEIGHT.
THE MATURATION OF RAW HAMS OR DRY SAUSAGES REQUIRES CONTROLLED AIR
HUMIDITY, STARTING FROM 90–95% AND, AFTER A CERTAIN PERIOD, FINALIZING THE
PROCESS AT 70–75% AT 6‐10°C.
A LOWER RELATIVE HUMIDITY WOULD CAUSE A COSTLY LOSS OF WEIGHT: THE WATER
CONTAINED IN A PATANEGRA HAM MAY COST MORE THAN 100 €/LITER !!
FRUITS AND VEGETABLES OPTIMAL STORAGE TEMPERATURE IS AROUND 2‐4°C WITH
A HUMIDITY HIGHER THAN 90% (WITH EXCEPTIONS LIKE BANANAS, MELONS, CITRUS,
PINEAPPLES AND OTHERS REQUIRING 10‐15°C AND A SLIGHTLY LOWER RH).
ALSO THE STABILITY OF THERMOHYGROMETRIC CONDITIONS IS VERY IMPORTANT: A
FREQUENT FLUCTUATION EVEN OF FEW °C OR HUMIDITY PERCENT PROVOKES WATER
ASBORBING/DESORBING CYCLES FROM FOOD THROUGH CELL MEMBRANES WHICH
CAUSES A SORT OF «FATIGUE» WITH A FASTER VISUAL AND QUALITY DETERIORATION.

21. EFFECT OF LOW HUMIDITY IN WINERY CELLARS
THE HUMIDIFICATION OF THE WINE CELLAR IS CRUCIAL
BOTH DURING THE AGING OF WINE IN OAK BARRELS
AND DURING STORAGE OF THE BOTTLES PLACED
HORIZONTALLY.
THE WINE WITHIN BOTTLES OR WITHIN BARRELS HAS A
VAPOR PRESSURE EQUAL TO THE SATURATION VALUE
HOWEVER THE CELLAR, ALTHOUGH AT THE SAME
TEMPERATURE, IS NORMALLY FAR FROM 100% RELATIVE
HUMIDITY: THUS, DUE TO PRESSURE DIFFERENCE,
WATER VAPOR IS PUSHED TO ESCAPE THROUGH THE
BOTTLE CORK OR THROUGH THE BARREL STAVES,
PARTICUARLY IF THEY ARE NOT PERFECTLY TIGHT.
IN ORDER TO MINIMIZE THE RISK TO DEHYDRATE AND DRY THE CORKS OR TO
DESSICATE THE BARREL STAVES, IN WHICH CASE THE WINE WOULD EVAPORATE AND
LET AIR ENTER ALTERING THE ORGANOLEPTIC PROPERTIES AND THE STRUCTURE OF
THE WINE, IN A WINE CELLAR THE RELATIVE HUMIDITY SHOULD BE MAINTAINED AT
75%‐80%.

22. EFFECT OF LOW HUMIDITY ON WATER‐BORNE PAINTING
COATINGSTHE USE OF WATER‐BASED COATINGS IS INCREASING ‐ PARTICULARLY IN AUTOMOTIVE
AND AEROSPACE INDUSTRIES ‐ DUE TO LEGISLATION ON THE EMISSION OF VOC
(VOLATILE ORGANIC COMPOUND) REPLACING MANY SOLVENT‐BASED COUNTERPARTS.
HUMIDITY AND TEMPERATURE HAVE A SIGNIFICANT EFFECT ON
HOW FAST WATER‐BORNE PAINT FLASHES OFF: THE WATER IS
REMOVED FROM THE SURFACE OF THE PAINT VIA
EVAPORATION, MIGRATING TO THE SURFACE UNTIL ALL OF IT
HAS RISEN TO THE SURFACE AND EVAPORATED.
THE TIME IN WHICH THE COATING IS DRY IS BASED ON THE
AMOUNT OF WATER TO BE REMOVED AND THE EVAPORATION
RATE, DEPENDENT UPON THE VAPOR PRESSURE DIFFERENCE
BETWEEN THE WATER IN THE COATING AND THE AIR HUMIDITY
IN ADDITION TO AIR VELOCITY.
THE FINAL QUALITY IS BASED ON THE THERMOHYGROMETRIC
CONTROL OF THE AIR RECIRCULATED IN THE SPRAY BOOTH ALL
OVER THE YEAR, IRRESPECTIVE OF SEASONAL CONDITIONS.
THE DESIGN RELATIVE HUMIDITY (50‐70%) DEPENDS ON THE
PAINTING MATERIAL AND THE PROCESS; THE ACCURACY
REQUIRED FOR HUMIDITY CONTROL IS AS LOW AS 2‐3%.
High humidity causes an excessive
diluition of the enamel deposited
onthe body and formation of
minuscule blister of liquid
Low humidity causes an early
evaporation of the water
contained in the paints, so
fluidity and covering capacity
decrease

23. STATIC ELECTRICITY IS USUALLY CAUSED WHEN CERTAIN MATERIALS ARE RUBBED AGAINST
EACH OTHER; IT IS ALSO CAUSED WHEN MATERIALS ARE PRESSED AGAINST EACH OTHER
AND PULLED APART: THIS CHARGE MAY BE TRANSFERRED FROM THE MATERIAL TO NEXT
GROUNDED OBJECT, CREATING AN ELECTROSTATIC DISCHARGE (ESD) WITH A SPARK.
BEYOND THE MATERIALS, THE AMOUNT OF CHARGE IS AFFECTED BY THE AREA OF
CONTACT, THE SPEED OF SEPARATION AND RELATIVE HUMIDITY.
IN DRY AIR, WHERE THE IMBALANCED CHARGES HAVE
NOWHERE TO GO, TYPICAL VOLTAGE LEVELS MAY EASILY ARRIVE
TO 30.000‐ 40.000 VOLTS.
TYPICAL ENERGY RELEASED BY A SPARK RARELY EXCEEDS 160 mJ
WHICH, WHILE WELL BELOW THE RISKY LIMIT OF 5 J, CAUSES
ANYWAY PHISICAL AND EMOTIONAL TROUBLES TO PEOPLE.
AN ESD WITH A VOLTAGE AS LOW AS 15‐30 V CAN CAUSE VERY
OFTEN A DESTRUCTIVE DAMAGE TO AN INTEGRATED CIRCUIT.
HOWEVER AIR WITH A RELATIVE HUMIDITY HIGHER THAN 30‐35% SERVES AS A NATURAL
CONDUCTOR THAT ALLOWS CHARGES TO LEAVE OBJECTS. MOLECULES OF WATER TOUCH
THE OBJECT AND ABSORB THE CHARGE AND, IN TURN, COME INTO CONTACT WITH OTHER
MOLECULES OF VAPOR, CAUSING THE EXCESS CHARGES TO SPREAD AWAY.
EFFECT OF LOW HUMIDITY ON ELECTROSTATIC DISCHARGES (ESD)

24. EFFECT OF LOW HUMIDITY ON SEMICIRCULAR LIPOATROPHY (LS)
THE SEMICIRCULAR LIPOATROPHY IS A BENIGN AND REVERSIBLE
DISORDER OF THE SUBCUTANEOUS FAT THAT IS OFTEN
MANIFESTED WITH A COLLAPSE IN THE ANTERIOR AND LATERAL
THIGH SURFACE AND IN THE FOREARMS; USUALLY AFFECTING
FEMALE OFFICE WORKERS, IT MAY BE PRESENT BOTH IN ONE
EXTREMITY (UNILATERAL) OR BOTH (BILATERAL) AND CAN BE
ACCOMPANIED BY ITCHING, CHANGES IN THE SENSITIVITY OF
THE AREA AND, LESS FREQUENTLY, BY DISCOMFORT AND PAIN.Environmental risks
Electronic
devices
Conductive floor
Conductive
desks
95% of subjects
are women
Thighs
and
forearms
are the
most
affected
72 cm:
height of office
desks matching
with the level of
affected areas
THIS DISEASE APPEARED IN EPIDEMIC FORM IN FEBRUARY 2007 IN BARCELONA, AND
SINCE THEN IN A GREATER NUMBER OF CASES IN DIFFERENT OFFICES IN THE COUNTRY.
DESPITE STILL FAIRLY UNKNOWN, LS HAS TO DO WITH THE
POSITION IN FRONT OF A DESK WITH UNGROUNDED
METAL FRAMES, AND WITH A LOW RELATIVE HUMIDITY
WHICH FAVORS ELECTROSTATIC DISCHARGES (ESD).
IN OFFICES WHERE LS LESIONS HAVE BEEN IDENTIFIED
MAGNETIC FIELDS WERE ALWAYS SIGNIFICANTLY HIGH
AND THE RELATIVE HUMIDITY WAS BELOW 30%‐35%.
IN ORDER TO PREVENT LS THE ENVIRONMENTAL
RELATIVE HUMIDITY SHOULD NOT BE LOWER THAN 35%
LS: depression on the thighs in
the form of semi‐circular band

25. COMFORT IN OCCUPIED SPACES INDUSTRIAL ENVIRONMENTS
OFFICES, SHOP MALLS, THEATERS 30%‐35% (1) AUTOMOTIVE PAINTING BOOTH 50%‐70% ± 2%
HEALTH CARE FACILITIES
CELLOFANE WRAPPING 45%
CERAMIC FACTORIES 60%
CRITICAL & INTENSIVE CARE 30% ELECTRICAL PRODUCTS 40%
NEWBORNE NURSERY ROOMS 30% GUM 45%
RECOVERY ROOMS 30% (2) LEATHER WORKINGS 40%
OPERATING ROOMS 30% (3) LENS GRINDING 80%
ART GALLERIES, MUSEUMS, LIBRARIES
PAPER WORKING 45%
PAINT 80%
ART GALLERIES, MUSEUMS 40% PHOTO STUDIOS 40%
LIBRARIES 40% PHOTOGRAPHIC MATERIAL FACILITIES 30%
DATACOM FACILITIES
PLYWOOD HOT PRESSING 60%
PRINTING PLANTS 45%
DATA CENTERS 30%‐35% (4) SEMICONDUCTORS FACTORIES 35%‐40% ± 2%
TELECOMMUNICATION FACILITIES 20% TEXTILE PLANTS – KNITTING 45%
CLEAN ROOMS ‐ LABORATORIES
TOBACCO SOFTENING 85%
TOBACCO CIGAR/CIGARETTE MAKING 55%
CLEAN ROOMS 40%‐50% ± 5% WOOD WORKING 45%
LABORATORIES 35%‐50%
FOODSTUFF CONSERVATION
HOTEL, MOTEL, DORMITORIES FRUITS 70%‐90%
HOTEL, MOTEL 30% HAM ‐ SAUSAGES 75%
DORMITORIES, JAILS 30% MEAT 70%
ANIMAL AND CROP FARMS
TEA 65%
TOBACCO 65%
ANIMALS 40‐50 40% VEGETABLES 90%
ENVIRONMENTAL CONTROL FOR PLANTS 50% WINERIES >75%‐80%
1) ANSI/ASHRAE STANDARD 55‐2013 does not specify a minimum humidity level for thermal comfort. Non‐thermal comfort factors , such as skin drying, irritation
of mucus membranes, dryness of the eyes, and static electricity generation, may place limits on the acceptability of very low humidity environments.
2) ANSI/ASHRAE/ASHE 170‐2013 suggests no lower limits: see above.
3) ANSI/ASHRAE/ASHE 170‐2013 suggests a limits of 20%; a higher value is advisable for older electronic equipment and for risk of gas explosion.due to sparks.
4) Lower values (i.e.: 20%) are allowable for servers rooms; a limit of 30% is recommended for personnel health reasons.
RECOMMENDED MINIMUM RELATIVE HUMIDITY LIMITS

26. HUMIDIFICATION TECHNOLOGIES
TYPE OF HUMIDIFIERS

27. ISOTHERMAL HUMIDIFIERS
THE VAPOR GENERATION CAN BE
OBTAINED BY PROVIDING EXTERNAL
ENERGY THAT IS USED TO HEAT THE
WATER TO BOILING TEMPERATURE
AND THEN TO OBTAIN ITS CHANGE
OF STATE.
THE HOT STEAM PRODUCED IS
DISPERSED IN THE AIR WHOSE
TEMPERATURE IS RAISED TO A SMALL
EXTENT; FOR THIS REASON THE
PROCESS IS CALLED ISOTHERMAL.
THE HUMIDIFIERS OF THIS TYPE ARE
COMMONLY ENERGIZED WITH ELECTRICITY AND THEREFORE HAVE AN OPERATING COST
WHICH OFTEN RESTRICTS THEIR APPLICATION TO LIMITED CAPACITIES.
FOR HIGHER RATES ARE AVAILABLE EQUIPMENT BASED ON THE COMBUSTION OF
METHANE OR LPG.
ISOTHERMAL HUMIDIFIERS ARE FAIRLY SIMPLE TO INSTALL, ENSURE THE HYGIENIC
PROPERTIES OF LIVE STEAM AND CAN BE USED BOTH FOR DIRECT DISTRIBUTION IN THE
ROOM OR IN DUCTED AIR HANDLING UNITS.
0 5 10 15 20 25 30 35 40
25
20
15
10
5
0
DRY BULB TEMPERATURE ‐ °C
ABS. HUMIDITY ‐gV/kgA
VAPOR PARTIAL PRESSURE ‐KPA
1
2
3
0
0,5
2,5
1,5
3,5
1,82
21,2
11,3
4,3
0,72
Isothermal humidifcation of air to bring the absolute humidity from 4,3
g/kg (@ 20°C ‐ 30% RH) to 11,3 g/kg (introduction of 7 g/kg of dry air)

28. 1 Water fill valve 8 Cylinder full probe
2 Flow restrictor 9 Electrode leads
3 Filling pipe 10 Electrodes
4 Cylinder fill pipe 11 Steam cylinder
5 Overfill pipe 12 Bottom filter
6 Conductivity probe 13 Drain valve or pump
7 Fill cup
IT IS A SIMPLE AND LOW PRICED TYPE OF EQUIPMENT IN
WHICH TWO OR MORE METAL ELECTRODES CONNECTED
TO ELECTRICAL MAINS USE WATER AS A RESISTIVE
ELEMENT, HEATING IT UP TO BOILING POINT.
THE CAPACITY CONTROL IS GOT BY VARYING THE DEPTH
OF IMMERSION OF THE ELECTRODES BY MEANS OF THE
FILLING AND WATER DRAINAGE SOLENOID VALVES.
IMMERSED ELECTRODE HUMIDIFIERS SHOULD BE FED
WITH NORMAL DRINKING WATER: THE ONLY REQUIRED
MAINTENANCE IS CLEANING OR REPLACEMENT OF THE
CYLINDER WHEN ELECTRODES ARE COVERED WITH LIME.
THEY ARE AVAILABLE IN A RANGE FROM 1 TO 130 KG/H.
IMMERSED ELECTRODE HUMIDIFIERS
STEAM CYLINDER

29. 1 Antifoaming sensor 11 Drain tempering pipe
2 Overfill diaphragm 12 Drain tempering valve
3 Filling diaphragm 13 Filling valve
4 Filling tank 14 Drain pump
5 Conductivity probe 15 Antiadhesive film
6 Equalizer pipe 16 Overtemperature PTC
7 Fill cup 17 Heaters
8 Filling pipe 18 Water temp. sensor
9 Level sensor 19 Thermal insulation
10 Overflow pipe
WITH THE ABILITY TO ELECTRONICALLY MODULATE THE
POWER OF THE HEATERS BY MEANS OF SOLID STATE
RELAYS, ADVANCED DEVICES ALLOW VERY HIGH LEVELS
OF ACCURACY (± 1%) IN CONTROLLED HUMIDITY.
THEY CAN OPERATE WITH NORMAL TAP DRINKING
WATER HOWEVER THE USE OF DEMINERALIZED WATER
REDUCES MAINTENANCE VIRTUALLY TO ZERO.
THE POWER RANGE ARRIVES UP TO 80 KG/H.
IMMERSED HEATER HUMIDIFIERS
THESE DEVICES INCLUDE RESISTIVE ELEMENTS
WHICH ARE SUPPLIED WITH ELECTRICITY TO
BOIL THE WATER THAT IS MAINTAINED AT A
CONSTANT LEVEL IN A TANK.
HEATING
ELEMENT

30. 1 Water on‐off tap 13 Gas line
2 Filling valve 14 Gas on‐off tap
3 Antifoaming sensor 15 Gas burner(s)
4 Steam outlets 16 Drain valve
5 Boiler 17 Filter
6 Flue gas 18 Drain pump
7 Electrical panel 19 Drain network
8 Gas temp. sensor 20 Conductivity meter
9 Level sensor 21 Drain pipe
10 Preheat sensor 22 Water line
11 Heat exchanger(s) 23 Safety thermostat
12 Air inlet 24 Bottom drain pipe
THE PRINCIPLE OF OPERATION OF THESE DEVICES, IN
WHICH NATURAL GAS OR LPG ARE BURNED INSIDE
OF A STAINLESS STEEL HEAT EXCHANGER IMMERSED
IN THE WATER, IS SIMILAR TO THAT OF THE
ELECTRICAL HEATER ONES; STEAM PRODUCTION IS
FINELY MODULATED BY ADJUSTING THE GAS SUPPLY.
THE MAIN ADVANTAGE STANDS IN THE LOWER COST
OF ENERGY SOURCE COMPARED WITH ELECTRICITY.
THEY CAN OPERATE BOILING DRINKABLE MAINS
WATER OR DEMINERALISED WATER, IN THIS CASE
DRASTICALLY REDUCING REGULAR MAINTENANCE.
THE AVAILABLE RANGE CAN REACH UP TO 360 KG/H.
GAS FIRED HUMIDIFIERS
HEAT
EXCHANGER

31. ADIABATIC HUMIDIFIERS
ALTERNATIVELY, THE EVAPORATION
CAN TAKE PLACE IN ADIABATIC
MODE, i.e. WITHOUT THE NEED OF
EXTERNAL ENERGY.
THE HEAT REQUIRED FOR THE
EVAPORATION IS SUPPLIED FROM
THE AIR THAT IS BEING HUMIDIFIED,
SO THAT IT GETS COLDER
FOLLOWING AN ISENTALPIC LINE
LIKE THE BLUE ONE IN THE
PSYCROMETRIC DIAGRAM.
FOR THIS REASON, IN ORDER TO
MAINTAIN THE FINAL TEMPERATURE
AT THE DESIRED VALUE, IT IS OFTEN NECESSARY A PREHEAT PROCESS (RED LINE).
ADIABATIC HUMIDIFIERS PROVIDE A WIDE AREA OF INTERFACE BETWEEN THE AIR AND
THE LIQUID WATER, WHICH EVAPORATES SPONTANEOUSLY. THE MAIN ADVANTAGE OF
THE ADIABATIC HUMIDIFICATION STANDS IN THE ENERGY CONSUMPTION: THE ONLY
POWER REQUIRED BY THE EQUIPMENT IS THAT FOR ATOMIZING OR RECIRCULATING THE
WATER ACCORDING TO THE TECHNOLOGY USED.
0 5 10 15 20 25 30 35 40
25
20
15
10
5
0
DRY BULB TEMPERATURE ‐ °C
ABS. HUMIDITY ‐gV/kgA
VAPOR PARTIAL PRESSURE ‐KPA
1
2
3
0
0,5
2,5
1,5
3,5
1,82
38,1
11,3
4,3
0,72
PREHEAT PROCESS ADIABATIC HUMIDIFICATION
Adiabatic humidifcation of air to bring the absolute humidity from 4,3
g/kg (@ 20°C ‐ 30% RH) to 11,3 g/kg (introduction of 7 g/kg of dry air)

32. IN THIS KIND OF ADIABATIC HUMIDIFIERS
THE AIR IS PASSED THROUGH MODULAR
PADS, I.E.: HONEYCOMB STRUCTURES OF
RESIN‐IMPREGNATED CELLULOSE OR GLASS
FIBER OFFERING A WIDE INTERFACE AREA.
THE PADS, PLACED VERTICALLY, ARE KEPT
WET BY A WATER FLOW DRAWN FROM A
BOTTOM TANK BY A PUMP AND
DISTRIBUTED ON THEIR UPPER EDGE.
WET MEDIA HUMIDIFIERS
ONLY PART OF THE WATER DISTRIBUTED ONTO THE PADS EVAPORATES WHEN THE REST IS
RECIRCULATED; THE EVAPORATION PROCESS INCREASES THE CONCENTRATION OF SALTS
WHICH MAY BUILD UP ON THE SURFACE, FORCING TO CLEAN OR REPLACE THE PADS
WHEN CLOGGED; FURTHERMORE THEY SHOULD BE PERIODICALLY CONTROLLED
BECAUSE THE PRESENCE OF A WARM WATER RECIRCULATION POTENTIALLY PROMOTES A
RISKY BACTERIAL GROWTH.
LAST BUT NOT LEAST, THE AIR SIDE PRESSURE DROP OF THE PADS REQUIRES AN
ADDITIONAL ENERGY CONSUMPTION EVEN WHEN NO HUMIDIFICATION IS REQUIRED.
THEIR USE, WIDESPREAD FOR THE LIMITED PRICE, SHOULD BE CAREFULLY EVALUATED
LOOKING ALSO AT THE OPERATING COSTS.

33. HIGH PRESSURE ATOMISING SYSTEMS
THESE DEVICES ARE EQUIPPED WITH A VOLUMETRIC PUMP WHICH PRESSURIZES THE
WATER TO VALUES BETWEEN 70 AND 100 BAR AND DELIVERS IT TO SMALL NOZZLES THAT
PRODUCE A FINE MIST (DROPLETS OF 10‐15 MICRON) EASILY ABSORBED BY AIR STREAM(*).
(*) the surface offered by 1 liter of water atomized at 15 micron is as high as 400 square meters
THE DISTRIBUTION PIPING NETWORK THAT SUPPORTS AND SUPPLIES THE NOZZLES IS
POSITIONED IN AN AIR DUCT OR PLACED DIRECTLY INTO THE ENVIRONMENT TO HUMIDIFY.
THESE DEVICES MAY REACH AN EXCELLENT LEVEL OF ACCURACY (± 2%) OF THE HUMIDITY IN
THE CONTROLLED SPACE AND VERY HIGH CAPACITIES WITH A NEGLIGIBLE ELECTRIC
CONSUMPTION ABSORBED BY THE PUMP (<4 W PER LITER OF SPRAYED WATER).
THEY ARE HYGIENICALLY SAFE WITH NO BACTERIAL GROWTH BECAUSE THE QUANTITY OF
NON ABSORBED WATER ‐ USUALLY VERY SMALL, IF ANY ‐ IS DRAINED OFF.
THE USE OF DEMINERALISED OR SWEETENED WATER IS RECOMMENDED TO PREVENT
CLOGGING OF THE NOZZLES.
THESE ATOMISING SYSTEMS MAY REACH A CAPACITY OF MANY THOUSANDS OF KG/H
PUMPING STATION ATOMIZING NOZZLE NOZZLE RACK NOZZLE RACK IN AHU SECTION SUSPENDED TYPE

34. 1 Air filter 9 Float level sensor
2 Rear fans 10 Tank
3 Atomised water 11 Driver
4 Diffuser 12 Piezo transducer
5 Atomisation chamber 13 Power supply
6 Fill valve 14 Front fans
7 Overflow pipe 15 Laminar air flow
8 Drain valvce
ULTRASONIC HUMIDIFIERS PROVIDE AN EXTRA FINE
ATOMIZATION OF WATER (≈ 3 μm) BY MEANS OF THE HIGH‐
FREQUENCY VIBRATION (CLOSE TO 1,7 MHZ) OF A
PIEZOELECTRIC ELEMENT OR MORE, IN PARALLEL.
N.B.: the surface offered by 1 liter of water atomized at 3 micron is 2000 square meters
BEST ULTRASONIC HUMIDIFIERS REACH EXCEPTIONAL
LEVELS OF PRECISION (± 1%) IN THE ENTIRE RANGE OF
THEIR RATED CAPACITY AND, THANKS TO THE HIGH
EFFICIENCY OF ABSORPTION, THEY ARE SUITABLE FOR THE
DISTRIBUTION OF THE PRODUCED MIST DIRECTLY INTO THE
ROOM AS WELL AS IN DUCTED SYSTEMS.
DUE TO SIZE AND COST THEY ARE CONVENIENT FOR SMALL
AND MEDIUM INSTALLATIONS (0,5 TO 15 kg/h).
FOR ULTRASONIC HUMIDIFIERS THE USE OF
DEMINERALISED WATER IS HIGHLY RECOMMENDED.
ULTRASONIC HUMIDIFIERS
STAND ALONE UNIT SMALL SIZE UNITDUCTED TYPE UNIT

35. VAPOR PRODUCTION
< 2 kg/h 2‐20 kg/h 20‐100 kg/h > 100 kg/h
ISOTHERMAL
HUMIDIFIERS
IMMERSED ELECTRODES
HIGH ELECTRICAL
ENERGY INPUT
IMMERSED HEATERS
HIGH ELECTRICAL
ENERGY INPUT
GAS FIRED TOO SMALL
ADIABATIC
HUMIDIFIERS
HIGH PRESSURE ATOMISERS TOO SMALL
ULTRASONIC TOO LARGE TOO LARGE
WET MEDIA TOO SMALL TOO SMALL
HYGIENIC
PROPERTIES
DISTRIBUTION SYSTEM
DIRECT IN ROOM DUCTED
ISOTHERMAL
HUMIDIFIERS
IMMERSED ELECTRODES
IMMERSED HEATERS
GAS FIRED
ADIABATIC
HUMIDIFIERS
HIGH PRESSURE ATOMISERS
WITH NO
RECIRCULATION
WITH DISTRIBUTED
TERMINALS
ULTRASONIC
IF EQUIPPED WITH
AUTOMATIC DRAINAGE
WET MEDIA
REGULAR INSPECTION
REQUIRED
NOT PRACTICAL
GENERAL SUITABILITY TABLE

36. MANY THANKS FOR
YOUR ATTENTION
luigi.nalini@carel.com