chapter 07 - electricty for cooling

8/11/2019 Chapter 07 - Electricty for Cooling

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ELECTRICITY FORELECTRICITY FORCOOLINGCOOLINGbyby

Engr Engr . Alexis T.. Alexis T. BelonioBelonio

Department of Agricultural Engineering andDepartment of Agricultural Engineering andEnvironmental ManagementEnvironmental ManagementCollege of AgricultureCollege of Agriculture

Central Philippine UniversityCentral Philippine UniversityIloilo CityIloilo City

[email protected]@yahoo.com


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Provide proper ventilation for various farmProvide proper ventilation for various farm

structures such as poultry, dairy, otherstructures such as poultry, dairy, othercrop conditioning enterprises.crop conditioning enterprises.

Provide a better environment for farmProvide a better environment for farmhouses and offices.houses and offices.


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Principles of RefrigerationPrinciples of Refrigeration

Refrigeration has something to do withRefrigeration has something to do with

removing of heat so as to maintain theremoving of heat so as to maintain thetemperature of a substance or space at atemperature of a substance or space at atemperature lower than it is normallytemperature lower than it is normallywould be.would be.Refrigeration systems basically removeRefrigeration systems basically removeheat from an enclosed space and releaseheat from an enclosed space and releasethe heat outside the space.the heat outside the space.


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RefrigerantRefrigerant

It is the agent which conducts the heatIt is the agent which conducts the heat

from the refrigerated coils and releases itfrom the refrigerated coils and releases itto the outside air.to the outside air.Sources of RefrigerantsSources of Refrigerants

Ammonia Ammonia oldest and widely used for largeoldest and widely used for largeinstallationinstallation

Methyl chlorideMethyl chlorideSulfur dioxideSulfur dioxideFreonsFreons commonly used for refrigerationcommonly used for refrigeration

system now a days.system now a days.


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Properties of Some RefrigerantsProperties of Some Refrigerants

RefrigerantRefrigerant RefrigeratingRefrigeratingEffect, BTU/.lbEffect, BTU/.lbstandard cyclestandard cycle

RemarksRemarks

Ammonia Ammonia 475.5475.5 Highly toxic, flammableHighly toxic, flammable

Carbon dioxideCarbon dioxide 55.555.5 Nontoxic, nonflammable,Nontoxic, nonflammable,high operating pressurehigh operating pressure

Methyl chlorideMethyl chloride 150.3150.3 Somewhat toxic,Somewhat toxic,flammableflammable

Sulfur dioxideSulfur dioxide 141.4141.4 Very toxic,Very toxic,nonflammablenonflammable

Freon 12Freon 12 51.151.1 Nontoxic, nonflammableNontoxic, nonflammable




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EvaporationEvaporation

Evaporation makes liquid to change toEvaporation makes liquid to change to

gas.gas.To cause evaporation, heat must beTo cause evaporation, heat must beadded to the refrigerant.added to the refrigerant.

Evaporation of refrigerant cools theEvaporation of refrigerant cools thesurrounding area.surrounding area.

The evaporator is located inside theThe evaporator is located inside therefrigerated space (to pick up the heat)refrigerated space (to pick up the heat)


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CondensationCondensation

It makes the gaseous refrigerant into liquid.It makes the gaseous refrigerant into liquid.

Heat must be absorbed from the refrigerant inHeat must be absorbed from the refrigerant inorder to cause condensation.order to cause condensation.The cooler space subtracted heat from theThe cooler space subtracted heat from therefrigerant thereby causing condensation.refrigerant thereby causing condensation.Condenser are located outside the refrigeratedCondenser are located outside the refrigerated

space (to release heat)space (to release heat)


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Refrigeration CycleRefrigeration Cycle

It is the complete series of eventsIt is the complete series of events

occurring in order as the refrigerantoccurring in order as the refrigeranttravels the route.travels the route.


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ExpansionExpansion high pressure liquid escapeshigh pressure liquid escapesthrough the valve into low pressure pipe andthrough the valve into low pressure pipe andrefrigerant expands.refrigerant expands.EvaporationEvaporation liquid refrigerant begins toliquid refrigerant begins toevaporate and secures necessary heat from theevaporate and secures necessary heat from theair inside the refrigerated room.air inside the refrigerated room.CompressionCompression allows the refrigerant to give upallows the refrigerant to give upthe heat picked up from the refrigerated room bythe heat picked up from the refrigerated room bydrawing it with the compressor.drawing it with the compressor.CondensationCondensation highhigh --pressure high temperaturepressure high temperaturegaseous refrigerant is forced out by thegaseous refrigerant is forced out by thecompressor to the condenser.compressor to the condenser.


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Refrigeration Cycle


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Electrical Control forElectrical Control for

Refrigeration SystemRefrigeration SystemManual Disconnect SwitchManual Disconnect Switch for servicing andfor servicing and

safety purposessafety purposesTime Delay FusesTime Delay Fuses added protection in additionadded protection in additionto the builtto the built --in overload control that is oftenin overload control that is often

included in the motor.included in the motor.ThermostatThermostat controls the operation of thecontrols the operation of thesystemsystemSolenoid ValveSolenoid Valve controls the flow of refrigerantcontrols the flow of refrigerantPressure SwitchPressure Switch controls the low and highcontrols the low and high

pressure side of the evaporator and compressorpressure side of the evaporator and compressorpiping.piping.

Manual


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CondenserCompressor

Expansion Valve

Evaporator

Solenoid Valve

Thermostat

Motor

Pressure Switch

Pressure Switch

DisconnectSwitch

Electrical Circuit forRefrigerated System


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Quantities in RefrigerationQuantities in RefrigerationHeat to Removed for Cooling the ProductHeat to Removed for Cooling the Product

It is the heat required to remove when lowering theIt is the heat required to remove when lowering thetemperature of the producttemperature of the product

Heat to Remove for Cooling the SpaceHeat to Remove for Cooling the SpaceHeat transferring from the outside to the inside of wallHeat transferring from the outside to the inside of wallfloors, ceiling, and loose fitting joints.floors, ceiling, and loose fitting joints.Heat lost when door is opened.Heat lost when door is opened.Heat lost due to electric light or appliancesHeat lost due to electric light or appliancesHeat lost due to persons working inside the cooler.Heat lost due to persons working inside the cooler.


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Specific Heat of Farm ProductsSpecific Heat of Farm ProductsProductProduct Sp Ht aboveSp Ht above

FreezingFreezing(BTU/lb(BTU/lb --F)F)

Sp Ht belowSp Ht belowFreezingFreezing

(BTU/lb(BTU/lb --F)F)

FreezingFreezingPointPoint

(F)(F)

Latent HeatLatent Heatof Fusionof Fusion(BTU/lb)(BTU/lb)

StorageStorageTempTemp

(F)(F)

Apples Apples 0.900.90 0.490.49 28.528.5 122122 3535 --4040

OrangesOranges 0.900.90 0.470.47 2828 124124 4040 --4545

CabbageCabbage 0.930.93 0.470.47 0.310.31 132132 3535 --4040

Beef Beef 0.750.75 0.400.40 2727 9898 3535 --4040

PorkPork 0.680.68 0.380.38 2828 8787 3434 --3838

PoultryPoultry 0.790.79 0.370.37 2727 106106 2828 --3030

Butter Butter 0.640.64 -- 7373 -- 4545 --5050

EggsEggs 0.760.76 0.400.40 2727 100100 4040 --4545

MilkMilk 0.930.93 0.490.49 3131 124124 3535 --4040

CheeseCheese 0.640.64 0.360.36 1717 7979 4040 --4545

f l hH R f C li h


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Heat to Remove for Cooling theHeat to Remove for Cooling the

SpaceSpaceFor chill room (35For chill room (35 --40F) having a volume of 30040F) having a volume of 300to 400 ftto 400 ft 33 and 4 in. cork insulation on all surfacesand 4 in. cork insulation on all surfacesuse 6.5 BTU/ftuse 6.5 BTU/ft 22 --hr hr For zeroFor zero --degree rooms having a volume of 300degree rooms having a volume of 300to 400 ftto 400 ft 33 and 5 in. of cork insulation on alland 5 in. of cork insulation on allsurfaces, use 8.5 BTU/ftsurfaces, use 8.5 BTU/ft 22 --hr hr

Select the refrigeration that will remove theSelect the refrigeration that will remove therequired number of BTU/hr by operating only 2/3required number of BTU/hr by operating only 2/3of the time.of the time.


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Rating of Refrigerating SystemRating of Refrigerating System

The total amount of heat that must be removedThe total amount of heat that must be removedcan be obtained by adding the product load andcan be obtained by adding the product load andthe space load express in BTU/hr.the space load express in BTU/hr.Tons of refrigeration can be obtained by dividingTons of refrigeration can be obtained by dividingthe total amount of heat required with 12,000the total amount of heat required with 12,000BTU/hr.BTU/hr.Rule of thumb giving the relationship between theRule of thumb giving the relationship between the

horsepower and the ton of refrigeration ishorsepower and the ton of refrigeration is1 hp = 1 ton refrigeration if dealing with chill rooms1 hp = 1 ton refrigeration if dealing with chill rooms2 hp = 1 ton of refrigeration if dealing with a zero2 hp = 1 ton of refrigeration if dealing with a zero --degree roomdegree room


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Sample CalculationsSample Calculations

Determine the size of refrigerationunit for a proposed walk-in coolerhaving a floor space of 6 x 8 ft anda height of 7 ft. It is to have 4 in.of cork insulation on all surfaces

and an inside temperature of 35 F.The product to be cooled are:cabbage, 100 lb/day, and fresh

beef, 200 lbs/day. Assume theproducts are to be cooled from 85to 35 F in 24 hours.


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Product load:

0.9 x 100 x (85-35)/24 = 187 BTU/hr

0.75 x 200 x (85-35)/24 = 312 BTU/hr

Space Load:6 x 8 + 6 x 7 x 2 + 8 x 7 x 2 + 6 x 8 = 292 ft 2

Using 6.5 BTU/ft 2 -hr

292 ft 2 x 6.5 BTU/ ft 2-hr = 1,898 BTU/hr

Total Load:

187 + 312 + 1,898 = 2,397 BTU/hr


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Room Air ConditioningRoom Air Conditioning

Types are (1) console, (b) builtTypes are (1) console, (b) built --in unit, and (c) windowin unit, and (c) windowmodel.model.

General recommendations for selecting the proper sizeGeneral recommendations for selecting the proper sizeis given in table below.is given in table below.Electrical provision of the installation should include anElectrical provision of the installation should include an

individualindividual --equipment branch circuit.equipment branch circuit.Individual circuit makes the installation safe, assureIndividual circuit makes the installation safe, assureproper unit operation, and minimizes the chances of lightproper unit operation, and minimizes the chances of lightflicker and circuit overload.flicker and circuit overload.Safe operation requires that the air conditioner should beSafe operation requires that the air conditioner should beprovided with groundprovided with ground

Condenser


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Evaporator

Condenser

Compressor


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Selection Data for Air Conditioner Selection Data for Air Conditioner

HP sizeHP size Room AreaRoom AreaSun on 2 walls,Sun on 2 walls,

uninsulateduninsulated(Ft(Ft 22 ))

Room AreaRoom AreaNight operation, insulatedNight operation, insulated

walls and ceilingwalls and ceiling(Ft(Ft 22 ))

1/31/3 Up to 120Up to 120 Up to 200Up to 200

1/21/2 120120 -- 180180 200200 300300

3/43/4 180180 -- 280280 300300 420420

11 280280 -- 400400 420420 540540

11 --1/21/2 400400 -- 500500 540540 -- 660660


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Rule of Thumb for AirRule of Thumb for Air


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Rule of Thumb for AirRule of Thumb for Air

Conditioning DesignConditioning DesignFor every floor area of 20 m2 with a heightFor every floor area of 20 m2 with a height

of 8 ft and room temperature of 27 C, oneof 8 ft and room temperature of 27 C, onehp air conditioning system is required.hp air conditioning system is required.


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References:References: Althouse Althouse , A.D. and C. H., A.D. and C. H. TurnquistTurnquist . 1952. Modern Electric and. 1952. Modern Electric andGas Refrigeration. Fifth Revised and Enlarged Edition. TheGas Refrigeration. Fifth Revised and Enlarged Edition. The

GoodheartGoodheart --WillcoxWillcox Company, Inc. Publisher, Chicago. 945pp.Company, Inc. Publisher, Chicago. 945pp.Boast, M. 1991. Refrigeration.Boast, M. 1991. Refrigeration. SatishSatish Kumar Jain for CBSKumar Jain for CBS

Publishers & Distributors 485, JainPublishers & Distributors 485, Jain BhawanBhawan BolaBola NathNath Nagar Nagar ,,Delhi. India449pp.Delhi. India449pp.

Brown, R. 1956. Farm electrification. McGrawBrown, R. 1956. Farm electrification. McGraw --Hill BookHill BookCompany. New York. 367pp.Company. New York. 367pp.

chapter 07 - electricty for cooling

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