Design of a Device to Protect Humidistats Against

Home , Mercury switch

DESIGN OF A DEVICE TO PROTECT HUMIDISTATS

AGAINST DUST IN ANIMAL HOUSING

SENIOR PROJECT BY

FRANCOIS GRANGER

PRESENTED TO

PROFESSORS

S. BARRINGTON s

E. NORRIS

MACDONALD COLLEGE OF McGILL UNIVERSITY

DEPARTMENT OF AGRICULTURAL ENGINEERING

APRIL 1988 ABSTRACT

The suggested design is oriented towards the protection of commercially available humidistats. Actually , no humidistats can withstand the environmen tal conditions in animal housing. lt is believed that protection against dust alone could be enough to greatly expend their life expect~ncy. In this project, importance is given only to dust and effects of gases on the humidis tats are not dealth with. The device would consist of three filtering tubes in a closed suction enclosure. The humidistat would be placed in this enclosure on the suction side of a blower. Altough no prototype and experimentation has been done, it is felt t.hett the suggested design would provide a good solution for the problem of automatic humidity control in animal housing. The cost of the device would be around $100 • The price for a nylon ribbon humidistat is about $200. This would make a total unit of $300 • This is half the price of an industrial humidity sensor equiped with a controller. The suggested device is worth trying as it would provide more insight on dust properties in animal housing. Also, this could serve as a prototype to design a fabric filtering system for air cleaning in animal housing. TABLE OF CONTENT

ACKNOLEDGEHENTS ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 11

LIST OF FIGURES ••••••• " ••••••••••••••••••••••••••••••••••••••• I I •• I I •• I I •• iii

LIST OF TABLES •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• IV

INTRODUCTION •• I •••••••••••••••••• I •••• I •••••••••••••••••••••• I ••••••••• I •• I

OBJECTIVES ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• G •• 5

LITERATURE REV I EN ••••••••• I I I I •••••••••••• I ••• I I ••••• I ••••• I I • I ••• I I • I I ••• 6

DESIGN DESCRIPTION •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 20

c0 Nc L us I 0 Ns • • • • • • • . . • . . . . • • . • . • . • • • • • • • • . • . . . I . I I . . . . I . I I . . I I . . I . . . . I . I I I I 30

RECOHHENDATIONS ••••• ...... 3 2

REFERENCES ...... 34

APPENDIX A •••••••••• IIIIII····················~···············~~~·~~~··~··A

APPENDIX 8 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 8 ACKNOWLEDGEMENTS

The author would like to thank the two advisors for this project;

S. Barrington and E. Norris, both professors at Macdonald College for the

Department of Agricultural Engineering.

Also, the following persons contributed considerably to brainstorming and technical help needed throughout this project;

-R. Nattress: technician in electronics and electricity at Macdonald College.

-C. Vignault: agr. eng. for agr. Canada in St-Jean Que. and Ph.D. student at

Macdonald College.

-C. lemelin : private electronic consultant in Henryville Que.

-J.C. Desrosiers: technician in agr.eng. for agr. Canada , St-Jean , Que.

-S. Burgoyne: B.sc. student in agr. eng. at Hacdonald College.

-M. lvanic McGill radar station staff , Ste-Anne-de-Bellvue,Que.

Gratitude is expressed towards professor E. Barber of University of Saskat chewan who kindly sent a copy of his paper presented at the 1987 ASAE summer meeting held in Baltimore.

Finally, special thanks are adressed to Nathalie Gaulin who gave precious time and efforts to help in typing this report.

11 LIST OF FIGURES

Figure l. Ventilation rates vs ambient temperature curves •...... Al

Figure 2. Protection nf an aspirated psychrometer

with a fabric filter (Hou9ley & Fryer 1976) ..••.•..•...... • ~1

Figure 3. Protection of an aspirated psychrometer

with an automobile air filter

Figure 4. Model SP aspirated psychrometer (Gu & al.19B7> •••••••.•••••••.•• A3

Figure 5. Model 110 aspirated psychrometer

Fig~re 6. Closed suction bag house ••••••••••••••••••••••••••••.••.•..•••.• AS

Figure 7. Dust layer formation on fabric filters ••••.••••...... AS

Figure 8. Technical data for blower R90-18/0n

of Pamotor and other fans & blowers •.•••••••.••••....•...... A6

Figure 9. Electric circuit & components

for the suggested design ••••••••••••••••••••••••••••.••••.•••••• A7

Ill LIST OF TABLES

Table l. Characteristics of various types

of fabrics used in industrial filtration ••••••••••••••••.•.•••.•• ~8

Table 2. Components and cost analysis for the suggested design ••••••••••••••••••••••••••••••••••.•••••• A9

IV INTRODUCTION

Need for Moisture Control

Underst~nding of humidity effects on animal health has significantly in creased over the decade. The concern for more efficient humidity control has grown with it.

High humidity, above 807., causes problems in both hot and cold environment.

These _problems however, are less apparent in temperate conditions. In hot conditions, a rise in humidity of the air reduces the evaporation on the animal skin. This in turn reduces the rate of heat loss and increases the heat stress on the animal, (Sainsbury & Sainsbury,1967) ,

Several authors stated that for leghorn chickens at high temperatures, 30 C and 35 C, an increase in relative huaidity from 40 to 90 percent has resulted in an overall decline of 777. in the respiratory evaporative heat loss. They also stated that the production decreased as the humidity increased, but only for hiqh temperatures-

At cold temperatures, a rise in the relative humidity causes dampness of the coat, bedding and the floors and walls so that evaporation of vapour from these surfaces may be expected to increase the unfavourable effect of cold,

(Sainsbury & Sainsbury,1967).

1 Further•ore, high humidities also affect the animal's health indirectly by encouraging conditions conductive to the propagation of various disease caus ing organisms and skin fungi, CStarr,1981)9.

However, too low hu•idity levels also affect animal health. C onsi~tently low hu~idity levels, below 407., increase the danger of respiratory disease due to excessive dehydration of the mucous membranes allowing invasion by the pathogens, CSainsbury,l974)4. The recomaended relative humidity range for animals is between 507. and BOX to control airborn bacteria and dust during the humidity control regi~e,CChristian$on & Fehr,1983) 14 • Usually, humidity control is of greater concern during cold seasons due to lower ventilation rates.

In addition to animal health problems, high humidities within the animal shelter can cause serious deterioration of the building itself. Even with adequate insulation and a good vapor barrier. Very high humidity levels, above 907., can cause tond~nsation on and within inside surfaces of the build ing. Condensation on walls and ceiling surfaces or in attic spaces can be damaging to the structure or its contents. Condensation within walls can cause paint ~listering, sev!re ~tructural damage and can greatly r~dut~ the

3 value of some insulation materials,

2 Actual Method for Moisture Control

In cold weather, the actual •ethod for controlling relative humidity is by

ventilation and heating. A continous ventilation rate is det~rmined in cold

conditions. This is done by dbing both heat and moisture balances for the warm

building. Ventilation rates for temperature and moisture control are found.

The highest nf the two is used as the winter ventilation rate. However, the

chosen rate must be ab~ve or equal to the continuous ventilation rate

required for gas and odor control. The ventilation rate for pollution con-

trol prevails over the rates for humidity and temperature control.For a com

plet~ description of ventilation design, the reader is referred to Hellickson

~ Walker,l983 and Anonymous,l983 3 •

Figure 1 shows the ventilation rate versus the outside temperature. For

ideal control over the environment, one chooses the highest rate required at any temperatures under the maximum practical rate. This is shown by the fat

line.

The major problem associated with this method, is that the initial conditions for heat and moisture balance may change. This means that the ventilation rates "ill need to be adjusted for varying conditions. It may be due to changes in waste ~anagement or species produced. For temperature control, there is no big problems for adjusting the ventilation rates with temperature chan9es within the building. The ventilation rate and heating are adjusted automatically by •eans of thermostats. When the ventilation rate for pollu-

3 tioo is too high for temperature control, heat is supplemented by heaters con trolled by thermostats.

For moisture cantrol, there is usually no probl~m as long as the ventila tion rate is greater than that required for controlling the moisture.

Problems occur when the v~ntilation rate or heating are smaller than required for Aoisture ·control. lt would be of great help if ~uaidistats could be used to adjust automatically the ventilation rate or the heat with changes in rela tive humidity.• Actually no relia~le, inexpensive device is available to sense and automatically control the humidity, within an agricultural building. The humidity level must be measured periodically and the ventilation rate adjusted

4 accordingly",

14 Fehr,1983) • A study on air contaminants in dairy barns was done by Clark &

McQuitty in 1985. They reported the relative humidities for six commercial barns in Alberta. Although the average humidity levels were within 70'l. to BB'l.

RH, the ranges varied from 447. to lOO~ RH. This shows how badly needed humidistats are in some cases.

Problem

The problem with humidistats, is that the sensors used are not reliable in dusty environments and may be affected by gases. For example the wick in aspirated psychrometers will quickly become contaminated by dust pollutants in

.4 the house atmosphere. And consequently, the instrument will require regular and conscientious maintenance,(Clark & Cena,1981}~. Commercially available huaidistats have life expectencie5 of only a few month5 in dusty environments.

They are all calibrated individually and their sensors can not be replaced.

Nhen they fail, the whole unit has to be replaced,

(Honeywell,l9BB>,

& Cena,l981) 9 .But nothing else was found on the effects of gases on other sensors.

OBJECTIVES OF THE DESIGN

The main objective of this work is aiming the direct use of commercial huaidistats in animal housing. The primary concern is protection against dust as short term exposure to gases will be neglected. However, the humidistats to be used should be tested in air containing ammonia and hydrogen sulfide

_5 A design is suggested to protect humidistats against dust in animal hous ing.The criterias for the design are as follows;

l) simplicity

2) high protection efficiency

3) continous operation

4) no sainte~ance

5) low cost protection

In addition, the device giving prot~ction to the humidistat should be as compact as possible and easy to install.

LITERATURE REVIEW

A sound design soluti~n requires a fairly good knowledge of the air contaminants in the livestock housing. This review looks at dust and gases that have a deterioration potential on equipment. Also, it looks at previous ef forts to solve the dust problem for aspirated psychrometers.

Dust

Carpenter, 1986, states that dust in livestock buildings is almost en tirely organic and originates fro~ feed, skin and feathers, bedding and dried feces.

6 The organic nature of dust implies that it has the ability to absorb moisture. In fact, Avey,1970, found a direct relationship between dust weight and relative humidity. As the percent relative humidity increases the weight of dust increases proportionately.

Carpenter,19B6, states that airborn- particles, in livestock buildings, are smaller or equal to 10 micrometers. Most of the mass of dust consists of particles greater or equal to 3 micrometers while the highest number of par ticles is below 1 micrometer. Bundy & Hazen,1975, found that about 60 7. of the particles in suspension are between 0.5 micrometers or larger. Carpen ter,l98b,states that dust concentrati~n were between 1 to lOO mg/m 3 in pig geries, 32 mg/m 3 for broiler on litter, and 18 and b mg/m~ for layer in lit ter and in cage respectively. Carpenter,198b, gives particles counts ranging from 2 E6 to 158 Eb particles/m3 for non-viable and viable particles in live stock housing. For particles greater or equal to 0.5 micrometer, in an empty swine confinment building, Bundy & Hazen,1975, found particle counts ranging from 0.7 Eb to 10.6 Eb particles/m3 with a mean of 3.06 E6 particles/m~. Other information on dust characteristics or properties for animal housing,could not be found in the literature.

Gases

The gases which may causes damage to the sensor of a humidistat in live stock housing are; hydrogen sulfide •

. 7 Both gases are soluble in water, H2S is heavier than the air while NH~ is

1 ighter than the air

Sensor damage is suspected because of their effects on animals. Scott &

al•".,1983, state that a few days exposure to NH~ at contentrations of 65 and

105 pp~ caused eye irritation in talves. One week exposure to a concentration

of 20 ppm of H2S caused tissus damaged to the cornea in calves. Hany other

authors also state the negative effects of H2S and NH 3 on

animals,(Anonymous,l983)~,

a few .However, no information was fbund relating to equipment damage by these gases.

Bundy & Hazen,1975, reported test results on the effect of S02 on the rusting of iron in moist air. The test showed that the rusting of iron in moist air containing S02 is greatly accelerated by the presence of dust. But the iron showed little tendency to rust in the same air without dust.

The quantity of H2S and NH3 produced in an animal building varies with the species of animal and the waste management. For the most sensitive ani•als like poultry and young livestock, an ~aximum li•it for tolerance is 40 ppm for NH3 and 20 ppm for H2S (Christianson Fehr, 1983) 14 and

(Anonymous,l983) 3 • Esmay & Dixon,1986, give maximum allowable concentrations of SO ppm for NH3 and 10 pp• for H2S for workers in 8 to 10 hour periods.

8 Usually, the concentration of both gases are lower than above with continous ventilation for pollution control. The above values however can be used as a tolerance criteria for humidity sensors.

Previous Work

Few protective devices have been designed for the protection of humidity sensors in animal housing environment. Rather, more emphasis has been given to the initial design of the ventilating and heating system of a building using temperature sensors. To control both temperature and humidity.

So•e devices have been designed by Moulsley and Fryer ,1976, and Gu and al. ,1987, for aspirated psychrometers in dusty environments. Figures 2 & 3 show two eodels of aspirated psychrometers using fabric filters. The results obtained by Gu and al.,l997,in a swine weanling barn, showed that the filter and the wi~k had to be changed or cleaned every 2 weeks. However, their other

•odels, shown in figures 4 & 5 , required Maintenace at only one occasion each, in every three months. The •aintenance required was to unplug the nozzle for model SP and to reposition the wick on the model MO.

The first ai• of the above psychro~eters was to give regular humidity

Geasurements for barn operators. They were tried on 12 hours cycles and 5 minutes cycles. The 5 minutes cycles were used to simulate continous operation if the psychrometers were to be used as controls for ventilation and

9 heating. According to their conclusion, all psychrometers tested could provide accurate measurements with proper ~aintenance.

The main advantages of aspirated psychrometers are their low cost and the facility to replace the wick with no need for calibration. Calibration is needed only once at the begining of the operation of the instrument. For con tinous operations however, the ~aintenance required even for the best designs

~ay still be high. This is because a continous supply of water should be provided to the wick and the quality of water varies from farm to farm. The wick replacement needs will be greater in barns where the mineral content of the water is high. Used as a control, the cost of the psychrometer may greatly increase as the signals given by the thermocouples must be interpreted by sophisticated m~ans. A signal must be interpreted for each temperature sensors. Th~ wet bulb and dry bulb temperature must then be compared to give the relative humidity. This is usually done with an analog to digital con- verter and a computer. Another disadvantage, is that aspirated psychrometers require relatively high air velocities on the sensors. The ANSI/ASHRAE stand ard 41.6-1982, asks for 4 +_ 1 ~/s and 2 + 0.5 ~/s for transverse and axial flow across the sensors respectively. But Gu and al.,l987, found that 1.3 m/s was sufficient for relative humidities above 35Y.. The high air speed implies that large quantities of dust are involved. However, one could go around this by placing the s~nsors in a narrow section of an enclosure with a large inlet area.

1() . DESIGN OF THE PROTECTION DEVICE

To provide a good protection for hu~idistats against dust, their require-

•ents and weaknesses must be known. The infor~ation available from the eanufacturers of humidistats is not very satisfying. Technical sheets give physical di~ensions, operating humidity and temperature ranges, electrical data and instructions about installation. The exact circulation rate or air velocity over the sensor is not given. All that is known is to provide good circulation at average te~perature, i.e. not to install the humidistat in a stagnant zone. The tile of response is not given. In addition, the sen- sitivity of various sensors to different gases like ammonia and hydrogen sulfide is not known. Thi~ is because they are made for clean atmospheres and are therefore not tested.

The most limiting asset of hu•idity sensors used in humidistats is that each instrument is calibrated in~ividually at the company. This implies that when a humidistat sensor fails, the whole unit ~ust be replaced by a new one, as •entioned earlier. The price for a humidistat with a nylon ribbon sensor is around t200, (Honeywell,1988). The ANSI/ASHRAE standard 41.6-1982, gives a list of all hu•idity sensors used in hu1idistats with their mode of operation and characteristics.

11 "ethods of Protection Considered

Since high efficiencies of dust protection are required, three methods were investigated. Those using fabric filtration,wet scrubbing and electrostatic precipitation. However, electrostatic precipitation was soon rejected because of its complexity, higher cost and high electrical shock hazards. This method implies very high voltages, 15 to 70 kV, and the design of an electrostatic precipitator can hardly be done by theory. Rather it is designed by com parison between what it will be designed for and an actual application in similar conditions (Oglesby ~ Nichols,l978). Also, there is a chance that a good part of the water molecules be removed out the air stream,

Electrostatic precipitators also require cleaning of the collecting electrode at periodic intervals, because the dielectric property of the air decreases as th~ thickness of the dust layer increases. And arcing can occur between the two electrodes. The cleaning is usually done with water jets or rapping

Wet scrubb.ing was also rejected because of the volume of dust to handle.For continuous operation,this method would not have been very practical as the liquid scrubbing the air would also have to be cleaned or replaced. This liq uid could not have been water, because it would have change the readings.This further complicated this method. Theodore & Buonicore,1976, give a good

12 description of industrial wet scrubbers.

Fabric filtration was chosen because fabric filters are easy to manipu- late, safe and of low cost. Their efficiency is also almost as high as for electrostatic precipitators. Theodore &Buonicore,1976, state that they are capable of providin~ high collection efficiencies for particles as small as

0.5 micrometers and that they will remove a fair quantity of particles as small as 0.01 micrometers. Although no fabric filters can be made 1007. efficient, adequate sizing, good design and proper fabric selection can give ef ficiencies 4S high and above 90I, (Warring,198l). lt is also possible to use fabric filters in continous operation with automatic cleaning intervals. For the design, it was decided to use a miniaturized version of actual closed suction bag houses used in industry as shown in figure 6,

Buonicore,1976) and (Warring,l98l).

Fabric Filter Theory

For a complete discu~sion on fabric filters the reader is referred to

Theodore & Buonicore,197b,Warring,198l and Anonymous 2 ,1983. The filtration mechanisms of fabric filters are direct filtration by the filter medium and filtration by the particles deposited on and in the filter medium,

Buonicore,l976). The later mechanism is the one providing high filtration efficiencies. As more and more particles are collected by the filter, pore

13 space decreases with an increasing dust layer, this is shown in figure 7.

This dust layer is usually referred to as filter cake,

Buonicore,l976). Although the effieciency is greatly increased by the filter cake, resistance to air flow becomes a problem as this layer thickens. Thil is why for maintenance free continous operation an automatic cleaning system must be provided. But it is important to keep enough of the filter cake to benefit form its advantage.

Several cleaning mechanisms for bag houses are described by Theodore &

Buonicore,l97b and Warring,l98l. For closed suction baghouses the usual method of cleaning the filter bags is, to shake them. Mechanical shaking is the simplest way to do it.

To find the pressure drop across the fabric and the filter cake, emperical models are used. The use of these models is very much limited by the avaibility of emperical data on the type of fabric used and the type of particles to be removed. This is because the number of variables required to design a fabric filter is very large. Theory alone is not sufficient to try to predict the performance and the design of a filtering unit. It must be coupled with some experimental data.

The total pressure drop across the filter medium and the filter cake is equal to;

= ( 1 )

14 where: 6 p = total pressure drop

~ P• = pressure drop across filter

~Pc =pressure drop across cake

and J ~ P4 = ( u L/KA ) g

~Pe: = ( u C/.fJKA 2 ) VO

where; u = gas viscosity

L = thickness of filter medium

K = permeability coefficient for filter medium and caJ:e

A = ar~a of filter available to gas stream

g = gas volumetric flow rate c = particle concentration at inlet I = bulk density of filter cake V = volume of gas filtered for deposited tickness

The deposisted thickness on the filter is;

Z = VC I .1' A

let; B = u C/ ./' KA 2 )

C = ( u L/ KA )

then the total pressure drop through the filter is;

15 ~ p = ( BV + C ) Q ( 2)

For constant pressure operation, the flowrate Q is a function of time;

Q(t) = dV I dt

Substituting in equation 2 yields;

~)dt = dV

Integrating from 0 to t and from 0 to V gives;

6p = . ( BV 2 I 2t) + (CV I t) (3)

The values of B and C are usually found experimentally. But a first ap

proximation of B and C can be obtained by rewriting equation (3) as;

t I V = (B I 26p ) V + CC I ~ p )

and plotting t I V. vs V. This yields a straight line of slope

16 For constant flow rate operation, Equation (2) can be interperted as a

function of time knowing that;

dQ I dt = 0

Q(t) = dV I dt = constant

so; V = Qt

then~ 6P = B Q2 t + C Q ( 4)

A plot of p vs t gives a straight line of slope (BQ 2 ) and intercept (CQ).

At time, t = O, the resistance to flow is that of th~ fabric filter alone. But

the pressure drop is a linear function of time. As time increases, the resis

tance to flow due to the dust cake may predo•inate.

Equations 3 & 4, may prove very useful for determining the rate of cleaning for the filter and selecting the fan. However, some of the variables involved in this equation must be determined experimentally. The variables which must be experimentally determined are K, C, and ~ For dust in animal housing, only data for dust concentration (C) were found in the literature. Rough es- timates could be made using feed and grain dust data for swine confinment building. But ideally, data on dust characteristics should be found for various type of animal production.

17 For pressure-volume relationships across the filter medium and filter cake, a simpler equation form is used in Anonymous,l983 2 • This is based on the fact that laminar flow prevails through the fabric and the dust. This means that the increasing resistance to flow will be directly proportional to the ap proach velocity;

.6p = k V t W (5)

where; ~p = pressure drop or resistance to flow

k = permeability of fabric & cake

v, = approach velocity to the fabric (m/s)

W = mass of the dust cake (g/m 2 )

In this equation, only Wand Kneed to be determined experimentally. The mass of the dust cake could be determined using dust concentration data in ani•al housing with the following assumption:

All the dust entering the filter is collected and retained on the fabric.

The mass of the dust cake would be determined as follows;

W = QCt I A = v~Ct

where; Q = flow rate through the filter (m 3 /s)

C = dust concentration in air (g/a~)

. 18 t ~ time of filtration (s)

A ~ filtering area (m~)

V~ a velocity through filter (m / s)

The permeability K through the fabr i c and the dust cake still need to be

determined experimentally. It is a function of particle size distribut i on .

Permeability will be higher for coar~e particles than for fine particles .

This is because K is expressed with presseure units and lowering the per 

meability increases the resistance to flow through the filter. The only us e

ful value found for K, which could be applied for animal housing application was that for oats dust for particleg smaller than 45 micrometers. This value es 13.7 kPa/gram of dust per m~lmls, and was converted to SI units from

Theodore and Buonicore l97b. This value is expected to at leas t double for particles smaller then 10 micrometers. However, this value can probably not be used for the pres~nt design applications. This is because, it i s a valu• derived from industrial applications having much greater flow rates through the filters and more powerful! fans. Hence, the resistance of the filter i s likely to be much higher in industrial applications than in the present design. Warning is given to the reader that some discrepencies were encoun tered when comparing Anony~ous 2 (1983) to Theodore and Buonicore <1976) for the units of K. The di~crepencies were corrected to the knowledge of the author.

19 DESCRIPTION OF THE DESIGN

The device would consist of 3 filtering tubes, a shaking mechanism to clean them and a fan providing negative pressure inside the filtering enclosure.

The latter would be made of wood. All joints in the enclosure should be sealed. Two gasketed panels would be provided for access to the filters and the humidistat.

T~e dimensions of the device should be as small as possible to keep it compact. At the same ti~e, efforts are made to give a large enough filtering area. For this reason, the effective length of the filtering tubes was choosen to be 30.5 cm,

This diameter is considered reasonable for the tube length and the shaking required to remove the dust cake. The tube material would be of woven cloth.

Operation

The air enters the botto~ of the filtering tubes and comes out through their ·sides when the fan runs. The air passes around the humidistat before being exhausted. When the fan stops, the shaker starts and the dust fall by gravity through the tube inlets. Hopefully, most of the dust will fall on the floor. This would be better for continous operation than having to provide a hopper. A hopper would prevent reintrainment of the dust into the filter if it stays airborn.

20 The use of a timer was considered to control the operation of the fan and

the shaker. However, it was felt that a better control would take into ac-

count the conditions inside the protective enclosure. So, the control

designed consists of a mercury switch, a RC (resistive-capacitive) time con-

stant circuit and a relay. As the pressure drops in the enclosure, the mer-

cury rises towards the enclosure until it closes the circuit to stop the fan

and start the shaker. In order for the shaker to operate during a long enough

time, the current must pass through a delay circuit. This delay is provided

by the RC time constant circuit which in turn controls the relay. A few

seconds is allowed before the shaker stops and the fan starts again.

Selection of the Fan

Waring (1991) gives initial resistance and recommended final resistance for various types of air filters. The range given is between 25 Pa (0. l in water> and 249 Pa <1.0 in water) for the initial resistance and between 97 Pa <0.35 in water) and 995 Pa (4.0 in water) for the recommended final resistance.

This is with a average face velocity of 2.54 m/s <500 ft/min> through the fil ter. But no wover fabric cloth were specified. Obviously, if the face velocity is reduced, the initial resistance of the filter will be reduced also. The recommended maximum velocity through filters is 0.015 m/s for fine dust removal in industry.

21 In this design, only small flowrates are needed. Also for compactness the

fans used should be as small as the design permits. Some small AC and DC fans

and blowers were looked at. The dimensions of interest for the housing were

2 in the range between 6 f 6 cm <2.36 * 2.36 in 2 ) and 12 * 12 cm 2 (4.75 * 4.75

The air dekivery at zero static pressure varied from o.00425 m~/s (9 cfm) to 0.059 m3 /s (125 cfm}.

Some of the fans can operate at maximum static pressures up to 0.124 kPa

(0.5 in water). But most are listed for maximum static pressures under 0.075

kPa (0.3 in water). For blowers, the maximum static pressure varies from 0.1

kPa (0.4 in water) to 0.248 kPa <1.0 in water). However, the bl~wer~ are more expensiv~ than the fans. This technical information was taken from the 1986

Newark catalogue number 108. The data contained in this catalogue shows also that as the static pressure increases the air delivery drops dramatically.

The use of the previous equations could help to choose the right fan or blower. But here, these equations can not be used to determine the static pressure inside the enclosure. This is because the permeability coefficient of the filters and dust cake is not known for dust in animal housing. And also because data from large industrial bag houses cannot be used for such a small application. In addition, the time interval for filtration can not just be guessed while using these equations. It has to be monitored along with other variables otherwise the results obtained may be way off from that of reality.

22 The choice of a readily available fan or blower would help to keep the cost of the device low.

For the design, it was decided to choose a blower because it has a larger

static pressure range. This ch~racteristic is important for the proper opera tion of the mercury switch.

The choosen blower is the Pamotor model RL90-1B/OO from the 1986 Newark

catalog no 108. The size of the frame is 12f12cm 2 (4.75f4.75in~) with a depth

of 3.8cm (l.Sin). It runs on llSVAC and bOHz.It's free air delivery is

.0118m~/s (25cfm). The air delivery drops to .002Bm~/s

H20> static pressure. Figure 8 shows the static pressure vs air flow for this

blower.

Because it runs on 115 VAC, no transformer is needed. This also reduces the

cost.

Selection of the Filtering Material

The filtering material should be a cloth of synthetic continuous filament spun yarn. This is because this type of cloth has a co~pletely smooth surface which is an advantage for easy dust cake release. The regularity of the fila nent yarn permits the construction- of a very closely woven lightweight cloth which is capable of retaining the particles. High tensile strenght also

23 results from the continuous fiber

For the filter tubes, the material to be used is either polypropylene or polyethylene. These are chosen because of their low moisture absorption, adaptation to shaking and relative low cost. Unfortunatelly, no technical data was found for these fabrics. Other types of fabric ~re listed in Table

Efforts have been made to evaluate the initial permeability required for the filtering material. This would have permitted to choose the best theoretical filtering material for the blower operationg pressure range. But the equations ~entionned previou$ly were of no use because no adequat ex perimental data was available.

The flow rate will vary with t~e pressure drop through the filters. And the pressure drop will vary with the accumulation of the dust layer on the filter. Although the filtering area is constant, the voids area through the fabric and dust will vary with the dust layer on the filter. lt is the reduc tion in the void area that is responsible for the increasing efficiency of the filter, the increase in pressure drop and the reduction of the flow rate. The dust accumulation on the filter will vary with time.

Many variables are involved, and they are interrelated, so no set of as sumptions can satisfactory replace the lack of data. To theoretically evaluate

K dust proprieties such as the radius of the the permeability coefficient, '

24 particles

porosity, £,

For animal housing dust, this is not the case actually.

So to choose the right thickness and porosity for the filtering material , one will have to use technical data provided by fabric manufacturers. The choice will also depend on the desired range of flowrate and on the pressure drop accross the filters.

Selection of the Shaking Mechanism

The heart of the shaking mechanism is the •otor. This motor is choosen for compactness and it must operate on the same voltage as the blower to simplify the electric circuit. It must turn fast enough to shake well the filters.

Because of the dusty conditions and because the motor should not turn for a long time, about 30 secondes, it was choosen to take a totally enclosed motor.

The one retained is designed for air-oven fan equipment such as kitchen ex haust fans.

The motor choosen is a Dayton model for kitchen exhaust fans. The model is not known, but the stock number is 3H552 in the 1987 Oayton Electric Mfg.Co.

Catalog, titled "Equipment and Supplies for Industry, Farm and Home". It is a 115 VAC at 60Hz motor with a power of 7.46 W (1/100 HP). It is listed at

1550 RPM and 0.73 Amps at full load. It also has thermal protection. The

25 overall lenght of the motor is 7.6 cm (3 in) and the diameter is 8.4 cm (3

5/16 in).

The force required to shake the filters. is going to be very small. The supports of the tubes hooks on a small plate mounted on a track. The contact between the plate and the track could be nylon sliders. The amplitude of motion of the plate is limited by the space between the enclosure and the tubes,

1.9 cm (0.75 in). The total movement for one cycle is 3.8 cm <1 l/2 in). The radius for the point of attachement of shaker arm on the motor plate is 1.9 cm

(0.75 in).

Selection of the Control Circuit

Figure 9 shows a diagram of the electric circuit designed. The RC time constant circuit will operate on 9 VDC to keep the other components of that circuit small. Th~ relay, fan and motor circuit will operate on 115 VAC.

The mercury switch (manometer) is inclined at tto degree from the horizon- tal, as shown on the plan. This provides a motion of about 0.5 cm from 24.8

Pa to 124 Pa pressure drop. It implies that care must be taken to properly install the device on the wall so it is leveled. The mercury switch consist of a neoprene tube with two needles put into it and connnected to the RC cir cuit.

26 All components required for the circuit are listed on figure 9.

Costs

Table 2 lists the various components and their price found in various catalogs.

The cost of the device is not as low as it was expected. For estimation purposes, a 407. addition to the known price was assumed for the components for which no price was found. The prices may vary a lot from one store to the other. Here most electronic components were choosen to the lowest prices found. The blower and the motor are the most expensive parts of this design. If this project was to be experimented, further efforts should be put into finding t~e lowest price possible for these components. Other models of blowers and motors could be looked at.

In general, most of the prices were choosen on the low side. A 100 $ budget would be reasonable to built this device. However, this does not in clude the humidistat itself which costs about 200 f. This would make a com plete functional unit for controling humidity for about 300 !, which is not cheap. Considering that if the design fails the humidistat may have to be re placed at full cost, the above sum of •oney would be spent on a high risk in ~ vestment.

27 Anticipated Problems

Ideally, a fan or a blower having a low flow rate, at low and high static pressure, should be used. This would lower the cleaning frequency of the filters since less dust would be collected in a given time. Because no s~ch fan or blower was found, one readily available blower was choosen. rts flowrate is relatively high at low static pressures. The reccomended velocity of 0.015 m/s through the filtering medium for fine dust removal,

1976), can not be achieved initially with the present design. It was estimated that the velocity through the fabric and the dust layer should be about five times greater due to the present filtering area available. In creasing the filtering area would solve the problem, but would imply a much bigger design which is not wanted.

The velocity that would exist through the filter was roughly estimated as follows:

- the filtering area is 0.2 m2

- the assumption is made that initially the flowrate through the filter is

0.0108 m3 /s at 24.8 Pa pressure drop

- the area of interest is the •void area• which can be found using the conti-

nuity Equation;

28 Q = V Av

where; Q = the flowrate m~/s

V = the velocity through the filter mls Av = the void area to let ait through mz

If the recommended velocity would prevail, then

Av = 0.0108 I 0.015 = 0.72 m2

This is about 3 112 times the actual filtering area.

Using 5 times the recommended velocity yields;

Av = 0.0108 I 0.075 = 0.144 m2

which is about l.4 times smaller than the actual filtering area.

Because the available equations could not be used in this design, one can not predict Khat the void area and the filtering velocity will be at various points in time. However, the void area should definitely be smaller than the actual filtering area. This means that the velocity through the filter will be larger than the recommended velocity for a given flowrate. Hence, some fine particles may not be collected on the fabric and dust layer medium.

29 Another problem will be to choose the right filtering material. If the porosity is too large the efficiency of the filters will be small. If the porosity is too small , the pressure will drop very quickly and maybe a con tinous cleaning condition will develop. In addition, a new fabric will have a low efficiency as the humidistat may have to be protected until the dust layer on the fabric provides a reasonable efficiency.

In addition, water absorption by the dust layer on the filter will tend to slow the response of the humidistat. In continuous air circulation, this may not be too much of a problem, but extent of it is not known.

The air tightness of the enclosure may also create a problem. To avoid this problem, all joints should be carefully sealed. Also the access panels should be provided with a good gasket.

CONCLUSIONS

In theory, the design will provide efficient protection against dust for humidistats, and no maintenance should be required. However, the cost of the device added to the cost of a humidistat is higher than expected. This is not a very cheap- device for controlling humidity.

30 Although experimentation is required to really evaluate this design, it has favourable advantages. The idea behind the design can be applied to protec

tion of other type of equipment, even to filter the entire air volume of a building. The present design could be adapted for psychrometer use , by nar- rowing the cross section area where the hu•idistat is to be. This would provide adequat air speed on the sensors. The use of a mercury switch ensures that the filters will be cleaned when needed. And the design is quite simple, so easy to built and experiment.

But, is it worth it to try this device and to use it in a near future ?

If a huaidistat which is not sensitive to the actual gas contaminants in ani•a1 housing is used, the answer is yes. This is because it is at least half the cost Chuaidistat included) of the cheape!t humidity sensor for in dustrial conditions equiped with a controller, to the knowlegde of the author.

It is also expected that most of the problems anticipated will be overcome during experimentation. And finally, the cost will be much paid for by a more opti•al and better controlled environment in the animal housing. Moreover, it would ~robably reduce the costs of excessive heating and ventilating in cold weather.

31 RECOMMENDATIONS

- The various humidistats that could be used with this device, should be

tested for their tolerence to NH~ and H2 S for short and long exposure.

- A fan or blower providing small flowrates at low and high static pres

sure should be used. If it exists at reasonable dimensions.

-More data on dust properties should be collected from various type of

animal housing. This is a critical need when designing with fabric

filters.

- If possible, a cheaper fan or blower and motor for the shaker should be

used to lower the cost of the device.

Finally, dust Mill always be a problem with humidistats. Even if the air in

the barn is kept cleaned, at feeding time there will always be a risk of dust

contamination on the instruments. The ideal solution would be to come up with

a humidistat with a replacable washable sensor that would be cheap. No

recalibration should be required and long time between replacement ar washing

of the sensor should be allowed. Futher efforts in humidistat design should

be oriented to bringing industrial quality at low cost to the farm.

One type of sensor that seems to have some potential in this area is the

1 hygroscopically coated quartz cristal (Anonymous 1982> • Comparison of frequency between a wet and a dry cristal is made to determine the humidity.

ASHREA indicates that humidistats using that concept exist for measurments and

32 . •

control, but no information was found on companies that make these. Neverthe less, usually crystals are cheap and if they could be standardized for this application then they would be very promissing.

33 REFERENCES

l. Anonymous, 1982. Standard methods for measurment of moist air properties.

ANSI /ASHRAE standard 41.6-1982. The American Society of Heating,

Refrigerating and Air Conditionig Engineers Inc. Atlanta, GA, USA

2. Anonymous, 1983. ASHRAE Handbook : Equipment. American Society of Heating,

Refrigerating and Air Conditioning Engineers Inc. Atlanta, GA, USA

3. Anonymous, 1983. Structure and Environment Handbook. Mid West Plan Service

Eleventh Edition. Iowa state University, Ames Iowa, USA.

chap. 632 and 633

4. Anonymous, 1974. livestock environment effects on Production, Reproduction

and Health. Proceedings of the internatio~al livestock environment

symposium. American Society of Agricultural Engineers. St-Joseph,

Mtchigan, USA. pp 4-13

5. Avey H.R, 1970. Swine barn dust as related to heat exchanger application.

H.Sc Thesis McGill University. Macdonald College Agricultural Engi

neering department. Ste-Anne de Bellevue, Que. Canada. chap 4.

6. Bundt 0.5 and T.E Hazen, 1975. Dust levels in swine confinment systems

associated with different feeding methods. Transaction of the ASAE

vol. pp 137-39 and pp 144.

34 8. Carpenter G.A, 1986. Dust in livestock buildings- Review of some aspects.

Review paper. Journal of Agricultural Engineering Research, vol 33, pp 227-241.

9. Clark J.A, 1981. Environmental aspects of housing for animal production.

Butterworth publishing.

10. Clark P.C and J.B McQuitty, 1985. Air quality in commercial dairy barns

in Alberta. Paper presented at the 1985 annual meeting of the Canadian

Society of Agricultural Engineering. Paper No 85-410 CSAE.

11. Curtis S.E, 1983. Environmental management in animal agriculture. The [owa

state University press~ pp273-76.

12. Esmay H.L and J. Di~on, 1986. Environmental control for agricultural buil

dings. Ayi publishing Company Inc. Wesport, Connecticut, USA.

13. Gu D, E.M Barber and R. Bannerman, 1987. Development of a low maintenance

psychrometer for use in dusty environments. ASEA paper No 87-4035.

Presented at the 1987 summer meeting of the ASEA in Baltimore MD. USA.

14. Hellickson N.A ·and J.N Walker, 1983. Ventilation of agricultural struc

tures. monograph No 6 in a series published by th ASEA.

35 15. Honeywell Company, 1988. Personnal communication with sale persons.

16. Inter Technology, 1988. Personnal communication with Hr.Maurice Gaboury

17. Housley L.J and J.T Fryer, 1976. A resistance thermometer psychrometer.

Journal of Agricultural Engineering Research. vol 21 pp 101-102.

lB. Oglesly S.Jr and G.B Nichols, 1978. Electrostatic precipitation. No 8 in

the series Pollution Engineering and Technology. Marcel Decker [ne.

New York and Basel.

19. Raber R.R, 1986. Fluid filtration: Gas. A symposium sponsored by ASTM

Committee F-21 on Filtration and the American program Committee of the

filtration Society. Philadelphia. USA. ASTH special technical publica

tion 975.

20. Reist P.C, 1984. Introduction to aerosol science. Hacmillan publishing cie

21. Sainsbury D and P. Sainsbury, 1967. Animal health and housing. William and

Wilkins Co. Baltimore.

22. Theodore L and A.J Buonicore, 1976. Industrial air pollution control equi

pment for particulates. CRC press

23. Warring R.H, 1981. Filters and filtration Handbook. Gulf publishing cie.

36 Catalogs Consulted

1. Active Electronics, 1988. 2 stores in Montreal

2. Addison Electronics, 1988. Montreal

3. Dayton Electric Hfg.Co., 1987. Equipment and supplies for industry farm and

home. Industrial electric motors(lebo) ltd. Montreal

4. lntertechnology, 1977. Consulted at Macdonald College

5. Newark Electronics, 1986. Catalog number 108

37 APPENDIX A

FIGURES S TABLES

A loiAXIMU" PIIACTICAL VI!'NTILATJON RAT!!' FOil loiAJNTAINJN(, (OOI~OAT

,.INIMUM VENT I I.. AT ION" Tc loiAINTAIN OPTIMAL ENvtAONM£NT TI!'-I!'IIATUAI!

FIGURE I. VENTILATION RATES vs AMBIENT TEMPERATURE CURVES 14 ( CHRISTIANSON a FEHR 1983 )

E E c E r I I I I I

I. ·120mm .I A. THERMOMETER B. FAN C. ELECTRIC MOTOR D. PLASTIC JAR E. FILTER PAD F. WICK

FIGURE 2. PROTECTION OF AN ASPIRATED PSYCHROMETER WITH A FABRIC FILTER ( MOUSLEY a FRYER 1976)

Al ~ ~0

~~ CT V- - ' I I . . I I \1/~ · ~ W1 ~ 0.... en ~ N 1/ I 25.4 - \ ~~K! I I Ll ~ 11 6 11 :,-L Ar t ~fA I!/v v- 1'1 """' if ~ ~ {I I - ~ I - I i ~T.~~ CD • I ~ ~ ~ - I I .._ _j/4 ~~/" ij ,., n -=--- - -ci:l N 0 ~ CD r . t::::::{ -}C)

I l l- I 12 0 ' l l 146 A-A

1. Automobile air-cleaner filter 5. Water reservoir 2. Dry-bulb temperature sensor 6. Wick 3. Wet-bulb temperature sensor 7. Plywood housing 4. Instrument fan

FIGURE 3. PROTECTION OF AN ASPIRATED PSYCHROMETER WITH AN AUTOMOBILE AIR FILTER. ( GU a AL. 1987)

A2 280

-7

-6

!I I~ I I I t 5 !tl ~ ~ I 0 (D ~ - 11 ~ - f ~ I I

I f-1-

120

1. Instrument fan 5. Wet-bulb temperature sensor 2. Dry-bulb temperature sensor 6. .Solenoid valve 3. Flexible water line 7. Plywood housing 4. Nozzle

FIGURE 4. MODEL SP ASPIRATED PSYCHROMETER < Gu a AL. 1987)

A3 420

----·

0 - .. - _A_ A 146 - I - 120

203

1. Linear actuator 7. Wick 2. Relay 8. Water reservoir 3. Foam rubber gasket 9. Water intake valve 4. Wet-bulb temperature sensor 10. Instrument fan 5. Dry-bulb temperature sensor 11. Plywood housing · 6. Overflow port

FIGURE 5 . MODEL MO ASPIRATED PSYCHROMETER ( GU a AL. 1987)

A4 DIRTY GAS ----""'==~ FROM PROCESS

FIGURE 6. CLOSED SUCTION BAG HOUSE ( THEODORE a BUONICORE 1978 )

IAI

IBI

FIGURE 7. DUST LAYER FORMATION ON FABRIC FILTERS

A) INITIAL CONDITIONS 8) DUST CAKE FORMED ( THEODORE a BUONICORE 1978 )

AS PAMOTOR AC ·& DC Fans and Blowers

· MODEL 1124K MODEL Altd-11124 .so ,....--.,...--..,..---""'f"'"--f~ll "'-=- !} .30 ...... =--1~~-.f---+-- - f~ u: j: ~ .20 t----f"'o.~ --~~--4----+----=::::-ZI c: = . 10r--~~--~~~~~~~---J

Stock No. 50-11 Stock No. 50.H ~F4042 35.22 ~F4041 41.31 AC Fans and Blowers Quick Selection Guide

Type

ShadM Pole Fane lh8dM Pole F.,. (contlnLI Id) 25005 115 50160 115 85000 115 S0/60 40 25505 230 50160 115 4-~ Sq.x2 0 85000P 115 S0/60 40 4800X 115 50160 120 8508" 115 50160 40 4800XP 115 50/60 120 85500 230 . S0/60 40 3~ sq.x1\AI D 4606X" 115 50160 120 85560 ~ 230 S0/60 40 88000 115 50180 27 4850X · 230 50160 120 . ""'"• ecpc 1·~ D 4656X" 230 '50/60 120 88500 230 50180 27 4800X 115 50/60 70 4850X 230 50160 70 900t 24-42 50180 20-27 3-Yt dla.xH'J D 76005 .115 50160 240 Radial Blower 7606° 115 50160 240 78505 230 50160 240 e c1a.x2~. o RL90-18100 I 115 :Jk:150J80 I 25 4-Ve sq.x1~ 0 7656° 230 • 50160 240 fMOdii 900 reqlafes an · eapaatOi UL lnd moat IN CSA and VD! ·approved. "High temperature bal bearing models JWCOtnlad, Certified

MODELS 2500S/2550S . ~r--~--~-~-- "' .SO 1:----+--+---+-- Ill . 30t----'~~--+---+-- a::_ ll:_ ~ON .40 t::---3looolio.,.....---+---l---lt §} .25 t--=.r--~llr--+----+-- "'% f: - ~~~~--~--~~--+--+--~ f : .20 w.-_J_-=~~~~~ u% u% i=u i=~ . 20~-~-~~~~~-~~~~-~ c! . 15t---+-~.r---+---+-~~+---t c: ~ . 10~--4--~---~~~~~~-~ =- . 10t---+--+---t~::..:.U...... --~r--~ 0 0~--M~-~~~-~---~~-+~~~ - ~~--+--+---t---+-~r--+-~~

AIR VOLUME lcfml 00~-~M~--~~--~~--~~-~-~ AIR VOLUME lcfml I Year Werranty

Stock No. 50-11· 57F2600 11.13

AIR VOLUME lcfml o~~~+-+-,~o~~~-*~~~~~~ Stock No. I Type I 1·1 I 10.24 25-41 50.H AIA VOLUME lcfml 57F2603 I 900 I 20.10 I 11.11 11.31 14.17 1·11 100.241 Stock No. 50·il 57F2601 I .1011 I I 3.71 3.45 57F1002 23.11 714 NEWARK

FIGURE 8. TECHNICAL DATA FOR BLOWER R90-18/00 AND OTHER PAMOTOR FANS a BLOWERS (NEWARK CATALOG 108, 1988)

A6 ,-----, I relay

(RC TIME CTE CIRCUIT)

mercury switch

2.2K!\ 9VDC IIGAC . 600ttF • • 8 = blower M= motor

FIGURE 9. ELECTRIC CIRCUIT FOR THE DESIGN SUGGESTED

A7 Yes

Yes

Nt, No

Yes

amines.

Supports

combustion

pot:assium

temper.uures

ketones,

cost

1.0

elevated

2.5 3.2 1.15

sodium 2.75

2.8 8

5.5 2.0

30.0

100.0

Relative

{approximate)

affected

good

salts.

FILTRATION

and

resistance

good-

good good-

adve~ly

sodium l:hloride;

Flex abrasion

excellent

resistance

exceUent

poor

excellent

Fair-good

Fair

Very Fair--good

Very Fair

Very

Very Fair

Poor

Good

zinc

most

has

halogens;

for

acid;

good

most

attacked

Alkali

good-

;

good-

resistance

resislance

INDUSTRIAL

excellent

exceUent

Fair--good

Poor-fair

Very

Excdlent

Good-very Fair Fair-sood

Excellent Excdlent Fair

Excdlent Very

poor

aiTected

chlorosulfuric

to IN

dewpoint)

and

fair

acid

Auoride

Poor acid Poor--fair

Poor

Poor resiswxe Poor

Poor-fair

Poor-fair Good Poor

Poor-fair -

above

alkalies;

USED

hydroxide,

nitric

Media

and

good

good-

Acid

&ood

excelJent

sodium

resistance excellent

Poor

Very Fair Excellcnt

Good-very

Fair Good- Fair-sood Good Excdlent ExceHent

Filter Very

abrasion

environments

acid.

strength

temper.uures

FABRICS

fair

nitric

twc

tensile

Common

Mcsltins

resistance

decomposes

softens OF softens high decomposes decomposes

302"

elevated

572°chars 325" 333° 1,470" 480" 750" - 482" 700" 482" 2.550-2,650"

tempera

(generally

has

concentrated

acid

and

exceJlent

Properties

(min) .

perioda

attaded

with

TYPES

215.

250" 250"

240" 275° 325" - 250'" 500" 500" - 600"

sulfuric

times

hydrocarbons. fiber

Short

for

attaded

Typical

abrasion.

rc:sistance "F

temperatures

collector

temperature

1978)

absorption;

ruggc:d

high

rc:sistance

range,

stability~

cal

chlorinatc:d

periods

(months)

fungi;

VARIOUS

resistance

btion-type

temper.&ture

recommc=ndc=d used Maximum

moisture

and

chemt

and

be time

180" Lone 18

1,400-1.500" 20

not

good

low

OF in

can

dimensional

excellent

mildew

aromatics

fiber.

BUONICORE exceUc=nt

solvents; and

strength

spun spun spun spun spun spun spun spun

brasion;

selection

with

a excellent

strong

yam

Type to

tenslle

used possesses

and

common stability.

Filament Filament Filament bulked Filament - Staple Filiunent Filament Filament Staple Filament Spun

unaffected

:and

excellc=nt

high

alkalic=s;

filterability.

vulnerable:

not

and

fungi~

resistance

harmed

c=lasticity;

good

dimensional .

and

fiber fiber

resistance.

hence

polylUllide acids

aromatic ,

not

names

temperatures

;

THEODORE

Generic th

olefin olefin

good

to good

abrasion CHARACTERISTICS cetone

(

temperatures.

cotton;

protein cellulose

rature

mildew nt

NaturaJ NaturaJ Nylon e Poly Modacrylic Acrylic Fluoroarbon - Polyester Nylon Poly

Gbss

temperatures;

of .

stren

a l

i h~h

eleV!lted

moisture

temp

strength.

high strength.

res

to g

those

mely

none, e

hanic

stecik

a h

used

chemic.&land tr

ide 304)

conditions ®

tensile

® resist tensile

propylene&!

Fabric

ethylene

ctd

High

Poor (type

low

bsimilar

Dyncj®d Dacron®s 11 cyclohex hydro (Resistanc in Fiberglaui echemically Nylon..: Nomex dGood kF<¥ Poly houtst:andin ican TABLE 'High j Woolb Orlon®f Poly StainJess Couon Teflon

Q) TABLE 2 . COMPONENTS a COST ANALYSIS FOR THE DESIGN

COMPONENT COST (f)

PLYWOOD 6 450 SQ CM 5.50

GLASS 450 SQ CM 2.50

BLOWER 32.00

MOTOR 55.00

FILTER MATERIAL 2500 SQ CM

NEOPRENE TUB! 10 CM

MERCURY 800 ML

R!LAY 5.00

TRANSISTOR .50

CAPACITOR .10

RESISTORS • 20

POTENTIOMETER I, 00

TRANSFORMER 8.00

TOTAL 85.80

OTHER COSTS ( 20% OF TOTAL) 17.11

HUMIDISTAT (NYLON RIBBON ) 200.00

TOTAL FOR UNIT ~ 505.00

A9 APPENDIX 8

PLANS

8 ~ .._

.. - -·... -· . . - · - - ilf

...... 125 :,.._ _ . ·--··-- 256 13 I I A ~13 _ I

-~ -l I 40' I

r ' 1-- .15\ I f,-4 [ - I ! +- @ 108

l ;;. :.1- I I I(, ' \~· I /1 \ lJ ! I f, ' I •'/ I ! I ~ / I tiff~ I / I I ! I I I 300 108 1. humidistat

4oa ~' JF f-l 2. blower if' I tl Ill I ;: \ \ \ \ ~ t I 3. motor 371. 4.filter tube 5. mercury switch f Ill I I I \ (!V l;l ~~ ' ! cp():· 6. RC time cte circuit I 7. relay I I I I I I I _f ' ·~' I 8. transformer I ~--- I I --,__.., r-Jf7' I 9. track : C1 I L~·_;• I 115 VAC 152 10.nylon slid er I I I 11.fitter support I I r-- 12.motor support ' L_ _ ~~.ea~115VAC J _ -- _J L __ I JI 13. plywood _l. 1L..wir(? & hook for filter 15.etectric outl(?t tor humidistot I . 16. rubber membrane to seal shaft -70 _J - ~19r , ~ 17.rigid plastic tube u.o A 18.collar __., 19. sealant 325 242 -- · ·- 6.5 20.gasket /sealant A-A 21. panel 22.glass window 23. slot for air flow

MACOONALD COLLEGE OF McGILL UNIVERSITY agr. eng. dept.

-DEVICE TO PROTECT HUMIOISTATS AGAINST DUST

- SENIOP PROJECT SPRING 1988 DRAWING NUMBER p.l of 1