Humidification and ventilation management in textile industry ppt

8.4 AirBell air outlet 1149.2 Operation and problems associated with air washer systems 1309.3 Efficient use of humidification plants 136 9.6 Problems of not getting required conditions

in textile industry

B Purushothama completed his B.Sc (Textiles) in 1969 and then M.Sc(Textiles) in 1974 from Bangalore University He is a postgraduate in BusinessAdministration from St Joseph’s College of Business Administration,Bangalore He associated with The Textile Association (India) in 1973 andgot Fellowship of The Textile Association (India) in 1985, and Fellowship ofInstitute of Engineers in 2009 He is a Lead Auditor in ISO 9000 since 1994and a Certified Quality Analyst from Tata Quality Management Services Hetook extensive training in Total Quality Management from M/s Win Researchand Consultants, Mumbai He got trained by Tata Quality Management Servicesfor the JRD QV (The Quality System named after late JRD Tata and nowcalled as TBEM, i.e Tata Business Excellency Model) and Malcolm BaldrigeNational Quality Awards He worked as an examiner for TBEM for 5 yearsand has trained thousands in Total Quality Management, Malcolm BaldrigeQuality Awards and in various technical aspects of textiles.

B Purushothama, in his service of 40 years in the textile and garmentindustry, has worked in various capacities in Spinning, Maintenance, Projects,Quality Assurance, and in Research He has published over 50 papers in varioustechnical and management areas, and has presented papers in variousconferences and seminars Some of his publications include Fundamentals ofTextile Mill Management, Guidelines to Process management in Textiles,Quality management in Garment Industry, Winning Strategies, In theWonderland of Problems, etc He has guided hundreds of students fromdifferent universities and colleges in their project works

He is an active member of The Textile Association (India) and has served

as Joint Secretary, Secretary, Management Committee Member, and Chairman

of Ichalkaranji Miraj Unit He is also a member of Spinning Advisory committee of BTRA (Bombay Textile Research Association, Mumbai) Hewas a member of TX-30 sub-committee of Bureau of Indian standards, dealingwith Industrial textiles and Geo textiles He has also served as a member ofsyllabus committee for Shivaji University for B.Text He is a member ofvarious associations like Quality Council of India, Gokak ManagementAssociation and Asian technology group, which work for the spread ofknowledge

sub-He is also active in Kannada Literature and has written novels, poems, anddevotional songs in Kannada, and several books on Management, Hilarious

talks, etc Huchchuraamana Muktakagalu and Kareyutide Yasha Shikhara are books on Management written in Kannada Huchchana vichaaradhaare, a hilarious book of philosophy; Tumula, Kaalada hakki, Ayyo Huchchumundede, Miss Maala and Jagadodharana are social novels; Gaardhabha Maartanda and Banni Makkale Kathe Heltini are short stories for children; Sumamaale, light poems; and Gana stuti and Devaranaamagalu are devotional songs.

Humidification and ventilation

management in textile

industry

B Purushothama

New Delhi ● Cambridge ● Oxford

Woodhead Publishing India (P) Ltd., G-2, Vardaan House, 7/28, Ansari RoadDaryaganj, New Delhi – 110 002, India

www.woodheadpublishingindia.com

Woodhead Publishing Limited, Abington Hall, Granta Park, Great AbingtonCambridge CB21 6AH, UK

www.woodheadpublishing.com

First published 2009, Woodhead Publishing India (P) Ltd

© Woodhead Publishing India (P) Ltd., 2009

This book contains information obtained from authentic and highly regardedsources Reprinted material is quoted with permission Reasonable efforts havebeen made to publish reliable data and information, but the authors and thepublishers cannot assume responsibility for the validity of all materials Neitherthe authors nor the publishers, nor anyone else associated with this publication,shall be liable for any loss, damage or liability directly or indirectly caused oralleged to be caused by this book

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Woodhead Publishing India (P) Ltd ISBN 13: 978-81-908001-2-9

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Typeset by Sunshine Graphics, New Delhi

Printed and bound by Raj Press, New Delhi

1.7 Protection of electronics and equipments 10

4.2 Supplying air to air washer plants 454.3 Air filter construction and cleaning system 49

6.2 Air distribution needs in nonwoven industry 966.3 Material air-conditioning and spot air-conditioning 98

7.5 After-sales service: trouble-free operation 109

8.1 Need for localised humidification control 110

8.4 AirBell air outlet 114

9.2 Operation and problems associated with air washer systems 1309.3 Efficient use of humidification plants 136

9.6 Problems of not getting required conditions 153

9.8 Guidelines to select supply outlets and return grilles 156

10 Auxiliary units to make humidification

10.1 Building design to have effective control of humidity 162

12.5 An integrated approach for the textile industry 204

14.2 Fundamental of energy and resource-efficient HVAC design 213

15 Definitions of terms used in humidification

Appendix 1 Some of the commercial humidification plants 253Appendix 2 Cooling and heating systems 308Appendix 3 Fogging fans and Jets 317Appendix 4 Spray nozzles and mist eliminators 346

Appendix 6 Dampers and diffusers 373Appendix 7 Sensors and data loggers 387

Appendix 9 Fume and dust control, air ventilation 424

hose and ductsAppendix 10 Filters and dust collectors 431

The importance of maintaining and managing humidity and temperature

in a textile mill is not a new concept, but understanding the requirements,the equipment capabilities and utilizing them to get the best results is achallenge the technicians face all the time Now the systems have changedfrom manually operated to fully automatic; however, unless one knowshow to monitor, he shall still have the problem Some guidelines are neededfor the shop floor technicians relating to maintenance of humidity andmonitoring the air

The idea of writing a book on Managing of Humidity came from myfriend Ananth Harnahalli I hesitated first, as I was only a TextileTechnologist and not a Humidification Engineer Ananth reminded me that

I had faced lot of problems due to improper maintenance of humidity whileworking on the shop floor and had struggled a lot to get required conditions.The problems faced were always unique as the systems were gettingchanged, materials were getting changed and also the working conditions.Ananth told that the purpose of this book should be to guide the shop floortechnicians and engineers in maintaining required conditions and to act inadvance They need the basic concepts and the choice available in themarket to update their humidification plants; hence this book

An attempt is made to collect and provide information starting from thebasic concepts, developments, varying needs of the industry, the problemsassociated with maintenance of plants to get the required conditions,designing of plant capacity, modification or designing of building to getthe best results, various issues of health and hygiene, the pollution controlissues, various models available in the market, etc However, it should benoted that it is practically impossible to explain all the equipments andgive details of all manufacturers Hence, efforts are made to explain atleast one unit in each type

I am thankful for all the information providers, without which this bookwould not have come out Also I am thankful to all my friends who

encouraged me to write this book, and the family members for theircomplete cooperation My special thanks are to Ravindra Saxena and SumitAggarwal for the initiations taken to publish this book so that it couldreach masses.

B Purushothama

Need for maintaining humidity

Spinning of yarn from cotton and then weaving or knitting cloth from theyarn is known to mankind for millenniums It is probably one of the firstcrafts developed as men’s thought of civilisation As this primitive craftflourished in tune with civilisation, the ancients learnt that if water issprayed on the floor on the hot days or if wet cloth is kept over the warp,the working is easier because of less yarn breakage This was the state ofaffairs till 200 years back, but as the industrial revolution took place andmass production was aimed, different methods were developed to providemoisture to the material in process As more people were concentratedunder one roof along with number of machines working at a pace, thegeneration of temperature also added to the problem Though frequentuse of water cans for humidity, and wide windows for fresh air wereprovided, it did not help in improving the working conditions The increase

in speed of machinery also liberated fibrous dust

Air is an important element for every human being Man’s capacity forwork and his general health may seriously be impaired by defectiveventilation The purity of air, the temperature and the movement of air arefew of the many factors to be considered The comfort of an occupiedspace depends as much on its condition as on its freshness Althoughhumidity is invisible to our eyes, we can easily observe its effects In humanterms, we are more comfortable and more efficient with properhumidification In business and industrial environments, the performance

of equipment and materials is enhanced by effectively applying humiditycontrol Maintaining indoor air quality through humidity management canlower the energy costs, increase productivity, save labour and maintenancecosts, and ensure product quality Controlled humidification helps to protecthumidity-sensitive materials, personnel, delicate machinery and equipment.Beyond the important issues of comfort and process control, humidity

1

control can help safeguard against explosive atmospheres In short,humidification can provide a better environment and improve the quality

of life and work

Air free from dirt, debris and fibres that is closely maintained withinfixed limits of temperature and humidity is a vital necessity to the textileindustry It is not only because of the changes in dielectric properties andtensile properties of fibres due to varying humidity and temperature, butalso for maintaining a clean working environment The generation of staticelectricity while processing in spinning and weaving creates dust and fibrefly (fluff) Higher moisture content lowers the insulation resistance andhelps to carry off the electrostatic charge Hence, relative humidity needs

to be maintained above the lower limit, specified for various textileprocesses so as to avoid the problems of yarn breakage in dry and brittlecondition and also minimise the build up of static charge so as to reducedust and fibre fly (fluff)

1.2 Relation of humidity to working in the textile

mills

Correct ambient conditions are essential to prevent degradation of textilematerials during a series of operations right from beating in blow room toweaving fabric at loom shed or knitting the fabric or producing non-wovensheets Fibres should have requisite properties so that the final productretains its basic shape, size and strength Above certain moisture limit, i.e.above the upper limit of relative humidity for the fibre and the process,fibres tend to stick and lead to formation of laps on the rolls which disruptthe production process Removal of laps is not only a manual and time-consuming process, but results in the damage of machine parts, especiallythe rubber coatings Fibres become brittle and store electric chargesgenerated because of friction between the fibres during theirindividualisation process when atmospheric relative humidity is very low

In case of weaving, as the warp yarns are coated with size film, theenvironment should be suitable for the size film on the yarn Too lowhumidity makes size film brittle resulting in cracking of the film, where astoo high humidity makes the beam soft

Modern spinning equipments are designed to operate at high spindlespeed; however, the increase in ambient temper ature curtails the speedlimits of operation Moreover, the sophisticated electronic controls inmodern textile machinery also require controlled temperature which shouldnot exceed 33°C or so It is also necessary to limit the range of temperature

to which the textile machinery is exposed, since the steel and aluminiumparts of machinery which expand at different rates with temperature rise

(due to difference in co-efficient of thermal expansion) will be subjected

to mechanical stress Hence, along with the maintenance of stable relativehumidity conditions, recommended for different textile processes, it is alsodesirable to maintain the temperature level within a range, withoutfluctuation

Mechanical properties of fibres and yarns also depend on thesurrounding temperature conditions to which these are exposed duringthe textile process Apart from the dust levels, the stickiness in some ofthe cottons also demands controlled weather When cotton is sticky, higherhumidity creates sticking of fibres to rollers and other parts of the machine.The general reasons for controlling temperature and humidity in a textilemill are as follows:

● Dry air causes lower regain and this contributes to poor quality andlower productivity

● Yarns with low moisture content are weaker, thinner, more brittleand less elastic, create more friction and are more prone to staticelectrification

● Materials at optimum regain are less prone to breakage, heating andfriction effects; they handle better, have fewer imperfections, are moreuniform and feel better

● Higher humidity reduces static problems Reduced static makesmaterials more manageable and increases machine speed

● Textile weights are standardised at 60% RH and 20°C Low humiditycauses lower material weight and lowered profits

● Low humidity causes fabric shrinkage Maintained humidity permitsgreater reliability in cutting and fitting during garment creation andcontributes to the maintenance of specification where dimensionsare important, such as in the carpet industry

● Humidification reduces fly and micro-dust, giving a healthier andmore comfortable working environment

Adequate yarn humidity (moisture in yarn) is needed to enhance thestrength and the elasticity and to have smooth yarn surface Both tensilestrength and elasticity depend on fibre and spinning characteristics, onwarp pre-treatment (slashing) and increase with moisture content of theyarn being fed into the weaving process Hairiness depends on the spinningsystem, speed, humidity and the fibre quality Higher spindle speed, lowerhumidity and abrasion while spinning are the major reasons for increasedhairiness It is reduced by slashing, as fibres protruding from the yarn areglued to it Moisture content smoothens the hairs and lubricates the yarnsurface Abrasion between yarns, mainly in the shed area, removes shortfibres (lint) and size dust from the warp yarn Adequate yarn moisturereduces the fall out

While weaving, the yarn adsorbs water from the air Lint and dust fallingout from the yarn are incorporated into the room air Power consumed bythe loom and other devices in the room is converted into heat andincorporated into the room air This heat evaporates the moisture fromyarn Previous results show that yarns perform best in weaving machineswhen their moisture content is 7–9% (parts of water in 100 parts of dryyarn) Less moisture reduces strength, elasticity and smoothness Highermoisture may make the size glue the warp yarns together Therefore, there

is a need to humidify the area with suitable controls

Maintaining adequate high RH levels provides the most effective andeconomical means of preventing the build-up of static charges With high

RH, an invisible film of moisture forms on surfaces in the room Thepresence of normal impurities makes this film a conductor that carriesstatic electricity harmlessly to the ground before it can harm A relativehumidity of at least 45% is needed to reduce or prevent the accumulation

of static charges, although some materials such as wool and certainsynthetic fabrics may require higher RH levels Similarly, heat-generatingmachines may require higher RH to provide sufficient moisture in proximity

to the machine to dissipate static charges

Due to high heat dissipation from spinning as well as weaving andknitting equipment, there is a significant increase in temperature conditionsparticularly in the vicinity of the machinery and their driving motors Thenatural wax covering cotton fibres softens at these raised temperatureconditions, thereby adversely affecting the lubricating property of waxfor controlling static and dynamic friction

Increase in temperature beyond the design limit also reduces the relativehumidity condition near the processing elements of the machinery Hencetextile air-engineering design has to take care of controlled air flow withinthe textile machinery for dissipating heat generated at the source and it iscustomary to carry the waste heat along with the return air to the return airtrench The quantity of return air going to exhaust or re-circulation isregulated for controlling the inside design conditions

The requirement of humidity is lower at blow room at around 45–50%,moderate at spinning processes from carding to ring spinning at around55%, around 65% in winding and warping, where as weaving rooms needhigh relative humidity of 80–85% at the warp sheet level, i.e at ‘loomsphere’, whereas it would suffice to maintain general humidity condition

in the room at around 65% RH Knitting operation also requires a stablerelative humidity condition at 55±5% for precise control of yarn tension.Hence it is important to maintain stable relative humidity conditions withinthe prescribed tolerance limits at all steps of textile processing

Workers are a part of manufacturing process Therefore, the conditionsmaintained in the shed should not only be comfortable for the process and

the product but they should also be comfortable to the people Followingtable gives generally recommended humidity levels in a textile mill:

Table 1.1 General recommendations of RH% in a textile mill

Department Cotton Man-made Department Wool (%)

(%) fibres (%) Opening and picking 45–60 50–55 Raw wool storage 50–55 Carding 50–55 50–60 Mixing and blending 65–70 Silver lapping 55–60 55–65 Carding – worsted 60–70 Ribbon lapping 55–60 55–65 Carding – woolen 60–75 Combing 55–65 55–65 Combing – worsted 65–75 Drawing 50–60 50–60 Drawing – worsted –

Roving 50–60 50–60 Bradford system 50–60 Spinning 45–60 50–65 French system 65–70 Winding and spooling 60–65 60–65 Spinning – Bradford Worsted 50–55 Twisting 60–65 50–65 French (mule) 75–85 Warping 55–70 50–65 Woolen (mule) 65–75 Knitting 60–65 50–60 Winding and spooling 55–60 Weaving 70–85 60–70 Warping – worsted 50–55

Similar to the requirement of humidity, the temperature also plays avery important role in the textile processes Following are the normaltemperature levels followed in textile mills

Table 1.2 Normal temperature levels followed in textile mills

Department Minimum temperature Maximum temperature

Cotton dust is defined as dust present in the air during the handling orprocessing of cotton, which may contain a mixture of many substances

including ground up plant matter, fibre, bacteria, fungi, soil, pesticides,non-cotton plant matter and other contaminants which may haveaccumulated with the cotton during the growing, harvesting and subsequentprocessing or storage periods Any dust present during the handling andprocessing of cotton through the weaving or knitting of fabrics, and dustpresent in other operations or manufacturing processes using raw or wastecotton fibres and cotton fibre by-products from textile mills are consideredcotton dust within this definition The workers are exposed to such workingenvironment and inhale fibrous particles and dust whole day Generallyair suction system exists in all departments to maintain certain humidityand to remove air contaminants; however, at some places it workseffectively, but at certain areas improper air exchange results intosuffocation and inconvenience for the workers In a weaving mill, fibrousparticles in small quantity are present in the working environment, whichare inhaled by most of the workers These small fibrous particles aregenerated during weaving activities and disperse in occupational air It istherefore essential to have sufficient circulation of filtered air Air washersand ventilation systems are very essential for this.

All textile manufacturing processes, except garment making, generateenvironmental pollution During cotton spinning and weaving, dust andfly are released into the air streams of the production departments Most

of the modern textile mills are equipped with automatic waste removal,dust filtration and humidification plants The dust and fly released by themachines are sucked away by suction nozzles and ducts The dust ladenair is filtered, humidified and re-circulated The number of air changesper hour is optimised in each department to keep the air streams clean andhygienic to prevent any risk to the health of the workers The normal airchanges are as follows:

Table 1.3 Normal air changes per hour

Department Number of air changes

per hour Blow room, drawing, combing and roving 15

Twisting, warping, sizing and weaving 20

To minimize risk of industrial diseases such as byssinosis (lungdisease) among the workers, the US Occupational Safety and HealthAuthority (OSHA) has specified concentration limits of dust in the airstreams of production rooms for compliance by the concerned industries

as follows:

● 0.5 mgm per cubic metre, from blowing to roving preparation andfor manufacture of nonwovens.

● 0.2 mgm per cubic meter, for spinning, twisting, winding and warping

● 0.75 mgm per cubic metre, for sizing and weaving

With the industrial growth, the quality of air has been considerablydeteriorated Atmospheric air contains lot of aerosol This has created theneed for air-conditioning, which implies fresh air supply, removal ofaerosols and heat, and air motion for cooling and refreshing Compliancewith the above listed limits for air cleanliness brings in economic benefitsfor the textile mills in the form of improved worker attendance, productquality, process efficiency, reduced end-breakage rate in spinning andweaving mills and improved yield of yarn

Because of this need, the textile industry is one of the largest industrialusers of air-washing equipment Similar equipment is used in otherindustries such as automotive industry spray paint booths, tobacco industry,hospital surgery and nursery rooms, photographic film manufacturingplants and aircraft industry’s clean rooms Each of these industries normallyuses water in a gas scrubbing device to clean and process air so that itmeets their particular clean air standards The use of air-washing equipment

in the textile industry is more difficult to understand than in other industries

as there are many different processes and different combinations ofprocesses in one plant Air washers are utilised throughout the variousprocesses in cotton mills where raw cotton is processed into woven cottonfabric They are also used in blending plants where raw cotton is processedand blended with synthetic staple into yarn and then woven into blendedfabric Man-made fibre plants producing nylon or polyester yarn also useair washers Fibreglass plants producing fibreglass yarn for tyre cord andother industrial uses also utilise air washers extensively Some of theseplants have gas-scrubber systems which double as plant air washers andwhich present some of the most difficult water-treatment problems Airwashers are found extensively in knitting plants including ladies’ hosieryplants, and in carpet mills where carpet yarn is processed and dyed, aswell as in the carpet weaving plants Dyeing, finishing, and bleachingprocesses generally do not require air washer systems; but these processesare often located in the same plant as one or more of the previouslydescribed processes For example, a plant blending cotton with syntheticstaple to produce drapery material may have another section of the plantwhere they dye this material, finish it, and possibly run it through a printingprocess Although dyeing and finishing operations do not require airwashers, they have started using various types of smoke-abatement

equipments to control vapours emanating from the plant from some ofthese finishing processes.

1.4 Control of air pollution

The textile industry is plagued by air pollution problems which must beresolved In particular, smoke and odour arising in the process requireabatement The major air pollution problem in the textile industry occursduring the finishing stages, where various processes are employed forcoating the fabrics After the coatings are applied, the coated fabrics arecured by heating in ovens, dryers, tenter frames, etc A frequent result isthe vapourisation of the organic compounds into high molecular weightvolatile organic (usually hydrocarbon) compounds (VOCs) In terms ofactual emissions, the industry must also deal with larger particles,principally lint The other problem is the creation of VOCs, which takethe form of visible and invisible smoke, and objectionable odour Smoke

is basically made up of tiny solid or liquid particles of VOCs less than onemicron in size that are suspended in the gaseous discharge When thesmoke/gas mix goes up the stack, the Environmental Protection Agency(EPA) measures the density or opacity of the emission using an officialtransparent template, and labels the opacity as ranging from 0 to 100%.The more opaque the smoke, the more visible it is Opacity of smoke isactually related to the quantity, rather than the weight, of particles present

in the gas

The problem with odour is that it is not practically measurable It is asensation originated by interaction between molecules of hydrocarbonsand ten million nerve fibres in the human olfactory membranes The humannose can differentiate between 4000 different odours The odoursassociated with textile plant emissions are usually caused by hydrocarbonswith molecular weight less than 200, and fewer than 15 carbon molecules(C1 to C14) These odorous molecules attach themselves to the particles

of smoke and can be carried at great distances from their point of origin,causing complaints Proper system for collecting the polluted air anddirecting it for suitable treatment is an important aspect of air controlling

in textile industry

The number of air change is an important factor to ensure that air is cleanand safe The number of air changes required depends on the type of activitybeing taking place Following table gives the specified air changes fordifferent levels of air controls:

Table 1.4 Specified air changes at different levels of air control

ISO Controls Air velocity Air changes HEPA coverage class at table level rate per hour as % of ceiling

The method used to calculate CFM requirements for a given fan or fans

is based on complete number of changes of air in a structure or room in agiven period To determine the CFM required, the room volume (in cubicft.) is divided by the appropriate ‘minutes per air change’ In textile industrythe minutes per air change ranges from 5 to 15 Additional considerationsare local code requirements on air changes, specific use of the space andthe type of climate in the area Air changes are required more when thepeople working in a section, the generation of heat, or the generation ofdust is more and the maximum dust level is allowed in the air

When considering air purification systems, it is typical to evaluate thefilter media, product efficiency claims, and the size and portability of theunit The most important factor in the success of any system is the frequency

of air changes per hour (ACH) that the system can create The rate ofACH determines the rate at which the total volume of air in the room iscleaned by an air purification system, which is a major factor in the degree

of air cleaning that can be achieved

Providing ideal indoor air quality includes air purity, temperature andmoisture level A low humidity level can be as unhealthy and uncomfortable

as excessive humidity Dry air causes dry, rough and flaky skin becausethe skin’s outer layers lose moisture to the surrounding air Respiratorypassages such as the nose and throat also lose moisture from theirmembranes causing dryness and irritation Low levels of humidity canalso contribute to respiratory infections, allergic and asthmatic symptomsand an increase in airborne dust and allergens If the humidity level is toolow, bacteria, viruses, respiratory infections and allergic asthma willincrease If the humidity level is too high, dust mites and fungi/mold willproliferate and allergic asthma will also increase

Numerous studies done by ASHRAE and other indoor air quality experts,suggest an optimum RH range of 40–60% Dryer or wetter causes differentkinds of problems, at each extreme See the chart below, based on ASHRAEsponsored research The shaded portions indicate problems For example,bacterial problems shall be less at 26–60% RH and viral problems from

43 to 70% Most of the problems are not there between 45% and 55%, ascan be seen from the table

000000000000 000000000000 000000000000 00000000000 00000000000 00000000000

000000000000 000000000000 000000000000 00000000000

00000000000 000000000000 000000000000 00000000000 00000000000 00000000000

000000000000 000000000000 000000000000 00000000000 00000000000 00000000000

000000000000 000000000000 000000000000 00000000000 00000000000 00000000000

000000000000 000000000000 000000000000 00000000000

00000000000 000000000000 000000000000

RH

1.1 Comfortable levels of humidification (ASHRAE findings)

The last 2 decades have seen a major shift in the technology adopted intextile industry The manual operations are being replaced by automationscontrolled by programmed electronic logic systems It is not only the casewith testing laboratories; but monitoring of speeds, settings, temperature,humidity and various other factors are also controlled by electronic gadgets.Central to all electronic circuits today is the IC (integrated circuit) or ‘chip’.The heart of the IC is a wafer-thin miniature circuit engraved insemiconductor material Electronic components and chips in particularcan be overstressed by electrical transients (voltage spikes) This may causecratering and melting of minute areas of the semiconductor, leading tooperational upsets, loss of memory or permanent failure The damage may

be immediate or the component may fail sooner than an identical part notexposed to an electrical transient A major cause of voltage spikes iselectrostatic discharge (ESD) Although of extremely short duration,transients can be lethal to the wafer-thin surfaces of semiconductors.Electrostatic discharge may deliver voltage as high as lightning, and it

strikes faster In addition to the risk of damage to electronic devices fromstatic electricity charges, there are grave risks associated with sparks fromstatic charges in many process applications Static electricity is extremelydangerous in the presence of gases, volatile liquids, or explosive dustssuch as is found in munitions plants, paint spray booths, printing plants,pharmaceutical plants, and other places Many static control products(special mats, carpeting, sprays, straps, etc.) are available, but they cannotreplace the work done by humidification, which is a passive static control,which means working to control static all the time However, care should

be taken to ensure that there are no condensations on electronic parts The

RH preferred is from 40 to 70%

Conclusions

The need for providing conditioned and controlled air, monitoring the airmovement in textile industry is very essential not only from the point ofview of product quality and productivity, but also for the consideration ofthe health of employees and the community around Extensive works havebeen done to design the best possible combination considering theeffectiveness and the cost implications It is not possible to discuss all theavailable systems, but some of the widely used systems are discussed inthe further chapters

The concept of modern air conditioning was first established by anAmerican Mr Stuart W Cramer in the beginning of 20th century Theterm ‘air conditioning’ was coined by him and defined it as a process oftreating the air so that its temperature, humidity, cleanliness and distributionwith in the room are controlled simultaneously He was exploring ways toadd moisture to the air in his textile mill Cramer coined the term airconditioning as an analogue to ‘water conditioning’, then a well-knownprocess for making textiles easier to process He combined moisture withventilation to ‘condition’ and changed the air in the factories, controllingthe humidity so necessary in textile plants Willis Carrier further developedthe system, and in 1906 the first Buffalo humidifier and air washer plantwas designed He adopted the term and incorporated it into the name ofhis company This evaporation of water in air, to provide a cooling effect,

is now known as evaporative cooling

Early commercial applications of air conditioning were manufactured

to cool air for industrial processing rather than personal comfort Modernair conditioning emerged from advances in chemistry during the 19th12

century, and the first large-scale electrical air conditioning was inventedand used in 1902 by Willis Haviland Carrier Designed to improvemanufacturing process control in a printing plant, his invention controllednot only temperature but also humidity The low heat and humidity were

to help maintain consistent paper dimensions and ink alignment Later,Carrier’s technology was applied to increase productivity at the workplace,and the Carrier Air Conditioning Company of America was formed to meetrising demand Over a time air conditioning came to be used to improvecomfort in homes and automobiles Residential sales expanded dramatically

in the 1950s

Early textile mills had north light roofing to get a uniform sunlight.Further there used to be windows and number of openings so that the aircould move freely However, these buildings were not able to protect thetemperature and humidity inside the working area Any change in outsidetemperature or humidity was affecting the work Normally there used to

be problems in the evenings when temperature was changing, and also inthe afternoons when out side temperature was high The supervisors hadthe main task of getting water sprinkled on the floor in the afternoons, andgetting all windows closed in the nights There used to be closed steampipes to heat the section when the temperature was low Heating lamps ondraw frames, speed frames and combers was a common feature Theexperience of the technician and the speed at which he could monitor thefacilities was very important for smooth working After the false ceilingswere introduced, the effect of outside humidity and temperature gotreduced, and also the amount of air to be controlled became less Thewindows were permanently closed, which helped further to control thetemperature and humidity

As the speed of machinery increased, the precision in controllingtemperature and humidity became prime necessity The central air washerplants with automatic controls became an inseparable part of textile mills.Just a few years ago, textile air washers were designed primarily aslow-air-velocity, non-chilled water systems They were so large that air-washer rooms were an integral part of the building housing the textileoperation Lint and fibre screens ahead of the washers were non-existent

in many cases, and the washer rooms were typically filled with cotton lint.The warm water in the washer was a perfect environment for bacteria.Lint, dirt, and other suspended matter in the water continually plugged airwasher spray nozzles, reducing the efficiency As the industry began toinstall air conditioning equipment, these units were upgraded and modified

to perform properly with chilled water

2.2 Unit humidifiers

Unit humidifiers came into picture in the middle of last century, whichalmost became an integral part of textile mills Unit humidifier or Semi-Central Duct Unit is a combination of axial flow fan, one or morecentrifugal atomisers, air mixing chamber with interconnected fresh airand return air dampers to take fresh air as well as to re-circulatedepartmental air, a set of large area V-shaped air filters and fabricateddistribution duct with eliminator-type grills If required, steam heating coilscan also be mounted on return air damper of the mixing chambers

-2.1 Unit-type plant.

Different models with various fan capacities from 12000 to 25000 cfm areavailable in the market Unit humidifiers are normally fitted at the topnear the ceiling The ducts normally shall be extended up to 50 ft (15.2 m)

2.3 Central station-type plant

Early system of air cooling consisted of a cooling coil arrangement inwhich supply air was cooled and dehumidified by indirect heat exchangewith cold water pumped through tubing Willies Carrier, the developer ofair washers, surmised that an alternative design using direct contactbetween the air and chilled water might improve performance In his earlyair-conditioning systems, he observed that although the air came in contactwith water on the cooling coil surface, dehumidification occurred In a

typical air washer, water droplets are brought into direct contact with theair resulting in the exchange of heat and mass (moisture) from the air tothe water droplets If the temperature of supplied water is below the enteringair dew-point temperature, moisture from the air will condense onto thewater droplets; thereby, dehumidifying the supply air stream If theincoming air is hot and dry, it takes up the moisture and increases thehumidity.

Air washer plants are big centralised units which use water spray from

a bank of nozzles on air moving with a force The water spray not onlyadds humidity but also cleans the air from dust by making them wet andheavy, which fall down A set of eliminators prevent the movement ofwater droplets and the dust particles along with the humidified air Hence,the production area gets humidified clean air

2.2 Semi-central humidification unit.

2.3 Air-washer plant developed by Willies Carrier.

The central station-type plants have two units The main plant consisting

of a fan, air washer and other accessories is located in a plant room, which

is out side the conditioned space Only the air distribution system is inconditioned area The distribution duct is connected with the plant, but isnot an integral part of it The fan, air washer and circulating pumps arenormally at floor level and have an easy access, where the ducts are atroof level

The circulating fan may be either centrifugal type or an axial flow type.The fan may be installed before the air washer or after the air washer Thefirst type is called as blow- through where as the second one is called assuck-through

Central station plants are more costly than the unit plants But they aremore reliable and easily accessible for inspection and maintenance The life

of these plants is also longer Air coming out of air washer plants is normally

at 95%, where as in unit plants it is above 100%, and some moisture iscarried with the air in the form of fine mist Therefore, for the same quantity

of air handled, the Unit humidifiers give more evaporative cooling However,dry bulb temperature shall normally be higher inside the department because

of less air circulation in case of Unit humidifiers The central station type is

0000 0000 0000 0000

Heater

Fan

Air washer Eliminators

more suitable for refrigerative cooling as chilled water can be added asrequired Also dehumidification is possible by supplying water with atemperature less than the dew point temperature of the air.

As the requirement of air with predetermined temperature and humiditybecame need of the day, air heaters and air coolers were developed andinstalled along with the humidification plants Normally, closed steamradiators or steam coils were installed in the path of air flow after thehumidification unit Later electrical heating coils with thermostat controlswere introduced In case of steam coils, the steam pressure was manuallyadjusted and monitored, where as with thermostat the temperature iscontrolled automatically A combination of controls of humidity,temperature and circulation of air led to the concept of air conditioning.Most of the air-conditioning systems perform the functions of providingthe cooling and heating energy required, conditioning the supply air, that

is, heat or cool, humidify or dehumidify, clean and purify, and attenuateany objectionable noise produced by the HVAC&R equipment, distributingthe conditioned air containing sufficient outdoor air to the conditionedspace and controlling and maintaining the indoor environmental parameterssuch as temperature, humidity, cleanliness, air movement, sound level,and pressure differential between the conditioned space and surroundingswithin predetermined limits

In central hydronic conditioning systems, also called as central conditioning systems, air is cooled or heated by coils filled with chilled orhot water distributed from a central-cooling or -heating plant It is mostlyapplied to large buildings with many zones of conditioned space An airsystem, which is called as air-handling system, is used to condition,transport and to distribute the conditioned or re-circulated air, get outdoorair or exhaust air to control the indoor environment according to therequirement The major components of an air system are the air-handlingunits, supply/return ductwork, fan-powered boxes, space diffusion devices,and exhaust systems

air-Different types of air-handling units are now available which are made for the industry or the purpose for which it is applied Thehumidification and ventilation systems used in textile industry can begrouped in different categories However, the control of desired conditions

tailor-at the work area requires a scientific knowledge of the properties of airand the competency of the equipment being used If we are just running aplant without understanding the basic properties of air and its relationswith water and water vapour, we shall not be able to achieve the requiredresults, but might end up with more losses The ventilation requirementvaries widely depending upon the type of industries and nature of work

In certain industries, beside normal ventilation, air pressurisation is alsorequired

2.4 Supplementary humidification

With the season changing, the out side temperature and humidity conditionshall be continuously varying If the air washer capacity is designed tohandle the driest weather, the plant has to be under utilised in other seasons.Therefore, the plants are designed considering the normal weatherprevailing for maximum number of days in a year The deficiency incapacity can be supplemented by direct water atomisation units especiallyfor use in dry summer days Bahnson L-type centrifugal fans were widelyused earlier, but because of its problem of letting coarse drops of water,its usage is reducing The pneumatic atomisers are becoming popularbecause of good atomisation and better distribution

Where high relative humidity levels are to be maintained as in the loomshed, the common practice was to provide supplementary systems Themain plant can provide around 60% RH, and the remaining 20% is provided

by Bahnson L-type fans It is possible to achieve the required 80% humiditywithout using supplementary humidification, but by increasing the number

of air changes Use of two systems such as central unit and supplementaryunits is called as split system as the responsibility of providing requiredconditions is split into two units The system eliminating supplementaryunit and managing with only central units are called as all-air system Aircirculation capacity of the main plant in the case of all-air system should

be quite high, around three times, as compared to split system This results

in very high capital cost as well as operational cost However, the all-airsystem provides uniform humidity throughout the department compared

to supplementary humidification Further the water droplets that arecondensed in split humidification can corrode machine parts The studieshave shown that with air-air system the loom efficiency is higher compared

to supplementary humidification This increase in efficiency compensatesthe increased capital expenses and the running expenses

Although the air washer plants are supposed to provide 95% humidity

at the diffusers, it fails in a number of cases to reach even 80% With air system, the provision for supplementing the humidity by additionalhumidifiers is not possible Hence while designing a plant this point needs

all-to be considered

The recent developments in humidification are mainly concentrating onenergy savings and pollution control Helmut Stueble’s invention (US

Patent No 283026 dated 5th March 1996) relates to a process for the coolingand conditioning of a waste air generated in a textile room from machinescarrying out a textile process The process comprises of drawing the heatedwaste air from the textile room and passing the air through a liquid mediumheat exchanger; drawing a liquid cooling medium at a desired temperaturefrom a constant source and passing the liquid cooling medium through theheat exchanger to cool the heated waste air, the liquid cooling mediumthereby being heated by the heated waste air; recycling at least a portion

of the cooled air exiting the heat exchanger back to the textile room; anddirecting the heated liquid cooling medium from the heat exchanger to anoperative location in the textile process requiring a separate medium ofapproximately the temperature of the heated liquid cooling medium, andusing the heated liquid cooling medium at the location as a source of theseparate medium to reduce the overall energy consumption of the textileprocess Open waters, well and/or tap water of the water supply networkare used for the heat exchange, whereby this water is used after utilisation

in the heat exchange at other locations for the cooling of the process and/

or as hot water for further utilisation in the process

SITRA–PCRA Climo Control, developed in 2005, was sponsored bythe Petroleum Conservation Research Association (PCRA) It helps saveenergy to the tune of 25–60% in the existing condition with a pay-backperiod of 18 months Climo Control consists of three different modules tovary the speed of supplier fan, exhaust fan and water pump in thehumidification plant based on the outside climate SITRA also developedenergy saving overhead cleaners in the same year and is named ‘SITRA–PCRA Ener Optimisers’ SITRA has developed five different methods andbased on this, the investment would vary from 0.4 to 5 millions with apay-back period ranging from 4 months to 5 years

Arun Shourie, chairman of PackPlast India, a pioneer in energy savingprojects in textile mill humidification developed Auto Return Air Cleanserwhich cleans the return air of textile mill and reuses it, reducing the airpollution as well as conditioning cost

An apparatus and a method for humidifying a continuous textile materialare described in European Patent EP1428923 by Bertoldo, Franco 06/16/

2004 The apparatus comprises a rotatable drum having an internal cavity,the side wall of which is formed externally by a side surface and a tankfacing the side surface A conveying means for conveying the textilematerial through the tank and means for supplying into the tanksubstantially saturated steam at a pressure Pv and at a temperature Tv andfor supplying into the internal cavity substantially saturated steam at apressure Pc and at a temperature Tc The conveying means comprise apermeable belt for pushing the textile material into direct contact with theside surface at least in the zone of tank, the steam supplied into the internal

cavity being kept at a pressure Pc less than steam pressure Pv inside thetank by a certain value so as to cause partial and controlled condensation

of the steam supplied into the tank onto the side surface and onto thetextile material

In a very recent development (Patent Application No 28/MUM/2007Adated 26th Jan 2007) by Rakesh Pramodbhai Shah, Nilesh PrafulchandraVaria and Devand Prafulchandra Varia, steam generated in the steamgenerator is injected into the moist air generating chamber through theinsulated pipeline and water is sprayed in the chamber through nozzles.Humidifier and conditioner chamber is connected with moist air generatingchamber through the insulated pipeline Velocity of moist air andtemperature in the humidifier and conditioner chamber is controlled byelectronic control panel

Geiger Stephan, LEU Karl and SUBUIS Robert (Ref International PatentWO/2007/090313 dated 16th Aug 2007 Application No PCT/CH2007/000064) developed a device for evaporation of water

2.5 Device for evaporation of water.

In this device for the evaporation of liquid, in particular for water, anevaporation mat is used which is wetted with the liquid on which the liquidevaporates The evaporation mat comprises a textile fabric having fibres,wherein the surface of the fibres is coated with a covering (which comprises

a cured reaction product of a polyamine and a polyalkylene glycol etherifiedwith end groups of the structure X-CH2[CH(OR)]WCH2–, in which structure

w is an integer from 0 to 1 and, when w is 0, X is a halogen; and when w

is 1, X is halogen and R is hydrogen, or X and R together are –O–.Preferably, the evaporation mat is a consolidated non-woven which containsfibres made of a synthetic thermoplastic which are bonded to one another

by means of thermoplastic hot-melt glue at their intersection points Thedevices are used for air humidification, for concentrating solutions, or forevaporative cooling

3 Different types of humidification

There are several ways to add moisture to air Adding thermal energy tovapourise the water and simply spraying water through misting nozzlesare the two popular categories The best method depends on how muchwater needs to be vapourised; how quickly and what equipments are alreadyavailable to help distribute the moisture In case of very cold and dryweather, direct injection of steam is used which gives immediate relief.However, it is not suggested if the temperature is above normal humanbody temperature, as it can cause uneasiness among the operators Thesystems adopted for humidifying differ significantly Humidifying ahospital operating room is different than those for a textile mill, an officebuilding, or even a laboratory Different types of operations havesubstantially different requirements for the achievement of proper relativehumidity These requirements determine what means of humidificationone should use

Steam, evaporative pan and water spray are the popular humidifyingsystems used conventionally Each has particular advantages andlimitations which determine its suitability for a particular application.Steam is ready-made water vapour that needs only to be mixed with theair With evaporative pan humidification, air flows across the surface ofheated water in the pan and absorbs the water vapour Both steam andevaporative pan humidification do not affect the temperature of thehumidified air Water spray humidification disperses water as a fine mistinto the air stream where it evaporates As it evaporates it draws heatfrom the air and cools it

22

3.1.1 Direct steam injection

Water is heated to the boiling point where it turns to steam vapour Thesteam is allowed to rise from the unit without the aid of a motorised fan.This can be used virtually at all commercial, institutional and industrialapplications Where steam is not readily available, self-contained steamgenerating units or central system steam humidifiers are used Steamhumidifiers use natural fuels like coal, wood, husk, bagasse, furnace oil,diesel etc., or developed fuel such as electricity to generate steam droplets

It produces the noisy sound of boiling water Although the product may becheaper, but it costs more to operate than the impeller and ultrasonic typehumidifiers due to the high consumption of electricity used to heat thewater

3.1 Direct steam humidification.

The early industrial systems used space heating steam boilers forhumidification If there were not enough steam system leaks to meethumidification needs, additional steam would be vented into the space.When air handlers came along, various steam injection systems weredeveloped for large scale controlled humidification Generally, the samesteam was used that provided space heat and perhaps ran industrialprocesses However, this steam contained boiler-water-treatment chemicals.During the initial days of indoor air quality concerns people were scared

of using boiler chemicals In some special cases, more environmentallychemicals were used; but in more cases, dedicated boilers were needed.This became expensive to install, especially for small facilities and for the

Direct Stream Humidification

Cross Section of Manifold

facilities that would otherwise not even have a boiler This gave rise to theelectric humidification technology The most recently developedtechnology is the direct-fired gas humidification unit Steam systems arethe most economical, when there is an existing boiler and the applicationrequires a lot of volume Since boiler chemicals are still a concern in mostcommercial applications, steam-to-steam heat exchangers have beendeveloped This way, the low operating cost of the central boiler is obtained,and there is a lower first cost than buying a dedicated boiler system Thereare also chemicals that are certified safe for humidification applications.Direct fired natural gas humidifiers produce steam directly They aredesigned to operate with no extra steam pressure build-up and deal withhard water fouling without the use of treatment chemicals Direct firedunits are the most economical systems for large applications where there

is no existing boiler

The first direct fired unit was introduced by DriSteem, and is called theGTS Humidifier (Gas to Steam) It resembles a large fat-fryer with waterinstead of oil in the tank Units are available from 75 to 600 lbs h-1 steamoutput and 100000 to 800000 BTUs per hour gas input

3.2 Direct fired natural gas humidifier.

Direct steam injection was normally practiced in dry cold winters, as itgive both temperature and humidity, almost instantly However, there wereproblems of the steam getting condensed when it came in contact withcold roof, and water drops used to fall down This was very dangerouswhen water drops fell on running material or on the machine parts, resulting

in jamming, lapping and breakdown of machines Some times this led tostains on the fabrics Before refilling the water tank, the remaining waterincluding mineral deposits collected should be tipped out Depending onthe water hardness the insert must be de-scaled once or twice a month byusing de-scaling agent The deposits can also be scraped off with a tool,e.g., a screw driver.

The main advantages of steam humidification are favourable price, ahigh humidification performance and little maintenance The vapourisationprinciple guarantees absolutely germ, bacteria and mineral-freehumidification as residues remain in the tank

Immersion humidifiers incorporate electric heating elements in a reservoir

of water to provide humidification Immersed heating elements raise thetemperature in a tank, boiling the water and generating steam that is sent

to a dispersal unit for absorption into the air This type of humidifier isslow to react to humidity changes if it has been off for a while, and typicallydoes not control the amount of minerals from the water that get introducedinto the air This method is generally not recommended for data-centreapplications

3.1.3 Steam canister

Steam canister humidifiers use electrodes inserted into the water reservoir

to pass current through the water, causing it to boil and to discharge puresteam at 212°F at atmospheric pressure through a steam distributor Thisapproach provides greater application flexibility than the infrared sincethe canister does not need to be mounted in the conditioned air stream, but

it cannot react to changes in humidity as quickly if it has been off for awhile The canister portion of the humidifier can be installed inside the airconditioner or outside the air conditioner on ducts, on walls or in otherlocations The distributor can be mounted in the air conditioner, in ductwork or with a special blower box for free discharge in the space Thepiping for the distributor is specifically sized to match the humidifier’scapacity and must be located to avoid condensate blockage duringoperation A steam canister humidifier must bring the water in the canister

up to boiling temperature before it is at full capacity, a process that cantake several minutes It does this by passing an electrical current throughthe water between electrodes The mineral content in the water providesthe conductivity for this to occur The unit is consuming energy duringthis time, and the relative significance of this energy consumption variesbased on how many times the unit turns on and off Consequently, if

operation is intermittent, steam canister systems will operate less efficientlythan anticipated, and the efficiency of the system may be reduced overtime as the system ages and the electrodes are consumed.

3.3 Steam canister.

As moisture is conveyed into the air unit’s air stream, efficiency can beaffected by losses in the hose and distributor system The amount of lossdepends primarily on the length of the hose and number of bends Forexample, if the canister is generating 20 lbs h-1 of moisture at the canisterand 4 lbs h-1 is lost due to condensation, the net output is reduced to 16 lbs

h-1 emission This loss is evidenced by water running back down the hose

to the drain or back into the bottle Efficiency can also be negativelyimpacted if the distributor is located close to the cold metal surfaces onthe leaving side of the evaporator coil because some of the hot steam willcondense on the metal rather than being absorbed into the air Anotherconsideration for steam canister systems is water quality They requirewater conductivity levels of between 200MM (micromho) and 500MMfor optimal performance Higher levels may result in excessive arcing,and at levels below 060MM, there is insufficient conductivity for current

to flow between the electrodes The water quality and number of hours ofoperation determine the life of the electrodes, which are part of thereplaceable canister assembly The minerals in the water cause theconsumption of the electrodes, and accordingly, canisters can last forseveral weeks or several months This is typically the only maintenanceitem in the system

3.1.4 Infrared humidification

Infrared humidifiers are typically installed within precision air conditioningunits Infrared humidifiers use high intensity quartz infrared lamps over astainless steel humidifier pan The infrared radiation from the lamps breaks

the surface tension of the water, allowing the air flowing across it toevaporate and carry the moisture away as a particle-free vapour This

provides very precise and fast humidification The number and wattage of

the lamps depends on the size of humidifier and voltage utilised Whenhumidification is called for, heat energy from the lamps is reflected ontothe water in the pan The infrared radiation breaks the surface tension ofthe water, allowing the air flowing across it to evaporate and carry themoisture away as a particle-free vapour The process takes less than sixseconds from turning on the bulbs to achieving full capacity, makinginfrared humidifiers very responsive The only time capacity is reduced is

if a bulb fails, but it can be easily and quickly replaced

Because they do not depend on boiling water for evaporation to occur,and because there is no loss due to condensation, infrared units typicallyprovide full rated capacity when operating But because airflow for aninfrared humidifier comes from the precision air unit through a bypass,the precision air unit’s airflow must be at the recommended level for thehumidifier to operate at full capacity Water quality as measured inmicromho (MM) and total dissolved solids (TDS) has a negligible effect

on the performance and effectiveness of infrared humidifiers Infraredhumidifiers can be used at any micromho level, even where waterconductivity levels are less than 060MM The minerals in the water arenot evaporated into the air stream in the infrared process Instead, they areflushed through the system and either go down the drain or settle out inthe bottom of the pan Serviceability of infrared humidifiers is simple,with all components easily accessible for periodic cleaning The quartzlamps are located above and away from the water in the pan, minimisingthe possibility of corrosion and burnout The water pan must be cleaned

or changed out periodically because sediment drops out of the water andscales on the pan Most users simply keep two or more pans on hand thatcan be changed out as necessary and cleaned as maintenance resourcespermit

3.1.5 Steam-to-steam humidifiers

Steam-to-steam humidifiers use a heat exchanger and the heat of treatedsteam to create a secondary steam for humidification from untreated water.The secondary steam is typically at atmospheric pressure, placing increasedimportance on equipment location Maintenance of steam-to-steamhumidifiers is dependent on water quality Impurities such as calcium,magnesium and iron can deposit as scale, requiring frequent cleaning.Response to control is slower than with direct steam because of the timerequired to boil the water

Solids in water driven down to bottom

out

Reflector Infra red lamps

3.4 Infrared humidifier.

3.1.6 Electronic steam humidifiers (electrode)

Electronic steam humidifiers are used when a source of steam is notavailable Electricity and water create steam at atmospheric pressure.Electrode-type units pass electrical current through water to provideproportional output Use with pure demineralised, de-ionised or distilledwater alone will generally not provide sufficient conductivity for electrodeunits Water quality affects the operation and maintenance of electrode-type humidifiers Use with hard water requires more frequent cleaning,and pure softened water can shorten electrode life Microprocessor-baseddiagnostics assist with troubleshooting Electrode units are easily adaptable

to different control signals and offer full modulated output However, theneed to boil the water means control will not compare with direct-injectionunits

3.1.7 Electronic steam humidifiers (ionic bed)

Ionic bed electronic humidifiers typically use immersed resistance heatingelements to boil water Since current does not pass through water,conductivity is not a concern Therefore, ionic bed technology makes the

humidifier versatile enough to accommodate various water qualities Theseunits work by using ionic bed cartridges containing a fibrous media toattract solids from water as its temperature rises, minimising the build-up

of solids inside the humidifier Water quality does not affect operation,and maintenance typically consists of simply replacing the cartridges Ionicbed humidifiers are adaptable to different control signals and offer fullmodulated output Control is however exercised by the need to boil thewater

Evaporative pan humidification can increase dry-bulb temperature asmeasured on the psychrometric chart This unwanted temperature changemay occur as air is forced across the warmed water in the pan The increase

in DB can cause damaging results in process applications and increase theneed for humidity control The psychrometric chart helps illustrate thatevaporative pan humidification is not a constant DB process

Maintenance of evaporative pan humidification systems demands regularcleaning of the heating coils and pan, which are subject to ‘liming up’.The use of chemical additives added either automatically or manually tothe water in the pan can reduce this problem by as much as half Response

to control with the evaporative pan method is slow due to the time requiredfor evaporation to take place before humidified air can be circulated Output

is determined by water temperature and surface area Evaporative panhumidifiers can sustain bacteria colonies in the reservoir and distributethem throughout the humidified space High water temperatures, watertreatment, and regular cleaning and flushing of the humidifier help tominimise the problem, however