refrigeration heat load estimating

8/12/2019 Refrigeration Heat Load Estimating

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Refrigeration Heat LoadRefrigeration Heat LoadEstimatingEstimating

2008

Revision:Revision:

1. What are the 6 areas of load for cool /

2. Define K Factor.

3. Define U Factor.


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Learning Outcomes:Learning Outcomes:

Calculate the product load of a freezer

& cool room using data from relevant tables.

Learning Outcome 4:

freezer/cool room.

Content:Content:

- Calculate sensible, latent and respirationproduct heat loads.

- Calculate loads for products above and belowfreezing.

- Calculate the heat added to a room viamiscellaneous loads:

- Electrical Load- Human Load- Defrost Load- Machinery Load.


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Product LoadsProduct Loads

The product heat load is the heat to be

entering temperature to its final temperature.

Three stages may be involved-1. Cooling down to freezing point. (Sensible

heat).

3. Cooling the product below freezingtemperature. (Sensible Heat)

Cooling to freezing pointCooling to freezing point

Cooling down to freezing point, (Sensible Heat)

Q = M x C x TDTime

WhereQ = Capacity (Kw)

M = Mass (kg)C = Speci ic Heat J g.K A ove FreezingTD = Temperature Difference (K or C)Time = Pull down time (Seconds)


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ExampleExample Sensible Cooling above freezing.Sensible Cooling above freezing.

Calculate the product load in KW

Produce 3000Kg of fresh beef entering a room at25C and is cooled to -1.7 C.

Pull down time; 12 hours.

Freezing the Product,Freezing the Product,Latent Heat.Latent Heat.

,

Q = M x HTime

Where

= Ca acit KwM = Mass (Kg)H = Latent Heat (Kj/Kg)Time = Pull down time (Seconds)


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ExampleExample FreezingFreezing thethe ProductProduct

(Latent Heat)(Latent Heat)

Calculate the product latent heat load in KW.

3000Kg of fresh beef over a 12 hour period.

CoolingCooling below freezing point:below freezing point:

Sensible Heat Removal

Formula,Q = M x C x TD

TimeWhereQ = Capacity (Kw)

=C = Specific Heat (Above Freezing)TD = Temperature Difference (Kelvin or C)Time = Pull down time (Seconds)


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Cooling product below freezingCooling product below freezing

Calculate the roduct load in KW

3000Kg of fresh beef being cooled from freezingpoint (-1.7C) to -18 C storage temperature over12 hours.

Heat ofHeat of Respiration:Respiration:Fruit & vegetables are still alive after harvesting

.

The heat rejected by the product whilst instorage is called the respiration heat and must beconsidered as part of the heat load when storedabove freezing.

The uantit of heat re ected willdepend on the type of fruit or vegetable and thestorage temperature it is usually expressed inwatts/tonne.


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Heat of Respiration contHeat of Respiration cont

Formula,Q = M x RH

WhereQ = Capacity (kW)

=RH = Respiration Heat (W/kg), 1t = 1000Kg

Heat of Respiration contHeat of Respiration cont

of apples stored at 5C


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Miscellaneous HeatMiscellaneous Heat Loads:Loads:

Areas to be considered,

Occupant density or number.

Electrical Equipment.

Machinery Load.

Defrost Load.

Heat Equivalent of Occupancy:Heat Equivalent of Occupancy:

RoomTemperature

(C)

10 5 0 -5 -10 -15 -20 -25

Load, 210 240 270 300 330 360 390 420Watts Person

For intermediate temperatures the heat equivalent varies 6 Watts / C


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Heat Equivalent of OccupancyHeat Equivalent of Occupancy

Occupant Load = P x H x Hrs Occupied

24 Hours

P = No. Occupants

= ea qu va en a e

Hrs Occupied = Hours occupied per day

Occupant Heat LoadOccupant Heat LoadExample:Example:

a cu ate t e eat oa rom occupants t atworking 10hrs a day in a coolroom that ismaintained at 5C.


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LightsLights

simply add the loads up.Factors,Incandescent 1.0Fluorescent 1.25 (to allow for the ballast)Where the quantity of lights is not known we can

.

Lights = Wattage x Hrs Run

24hrs

Various types of lights are utilized in Cold rooms.

Incandescent, normal filament type globes ranging from

Lights contLights cont

- wa s, s recommen e a gconstruction) globes are used.

Fluorescent, Electronic or electro-mechanical.

Discharge Lamps, Mercury vapour, High pressure sodium.

Used in large rooms with high ceiling.

. . , .

All lighting should have the appropriate IP rating.

UV lights are utilised to reduce bacteria growth.


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Lights Example:Lights Example:

A cool room has 5off 100w incandescent lights and4off 36w fluorescent lights. The lights operate for12 hours a day.

Calculate the heat load from the lights.

Miscellaneous Electrical LoadsMiscellaneous Electrical Loads

Further to occupants and lights, commonly there are a number

of other electrical or machiner loads resent within

refrigerated spaces.

Generally the miscellaneous loads are intermittent and toavoid

over sizing the plant the load is spread over 24hr.

Q = WattageMISC x Hrs Run

Where,WattageMISC = Electrical load of the misc. loadHrs Run = Hours of operation per day


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Miscellaneous ElectricalMiscellaneous ElectricalLoads contLoads cont

These include;

Under floor heatin 16.5w m2

Heated Glass (inserts),

Low temp. rooms - 86w/m2

Low temp. (within A/C areas) - 65w/m2

Normal temp. rooms - 43w/m2

Fascia heaters,

Heater cables are generally 32w/m for low temp rooms and

18w/m for normal coolrooms. From this it can be assumed

that half of this load enters the refrigerated space.

Low temp rooms 16w/m of fascia

Normal temp rooms 9w/m of fascia

Glass Panel Cross Section

DoubleGlazed

DoubleGlazedHeated

TripleGlazed

Triple GlazedHeated

AmbientSide

AmbientSide

AluminiumSpacerbonded toglass

Transparent

TransparentHeat Film240volt

Heat Film240volt


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Normal Insert Door Sizes:Normal Insert Door Sizes:

Type: Size:

King Size 1596mm X 760mm

Jumbo 1857mm X 760mm

MiscellaneousMiscellaneous Electrical Loads:Electrical Loads:Additional Lighting,Insert doors normally have a fluorescent light fittedto each side of the door e . 1 door has 2 li hts & 2doors have 3 lights).These fluorescent lights are typically 36w per tube.

Defrost Load,When a room has a SET lower than 0C it is commonto have a defrost cycle. During this period the

evaporator fans will be turned off and electricelements turned on to defrost the coil/drain.The heat produced by the elements and the time thatthese elements are on each day needs to beconsidered for our heat load estimates.


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ForkliftForklift Loads:Loads:

An estimation of the load due to a forklift operating within the

space can be obtained from the information on the motor and

assuming 80% efficiency for battery powered and 33% for

internal combustion powered forklifts.

Q = MR x t

m x 24

Where,

= apac y w

MR = Motor Rating (w)

t = Time in use per day (hr)

m = Motor efficiency (80% battery & 33% internal combustion)

ForkliftForklift Loads:Loads:

Forklift Capacity Battery Powered IC Powered

900 4100

1800 6150 17,600

3600 7600 25,100


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Forklift Example:Forklift Example:

A cold storage facility has an electric forklift1800kg capacity operating for 12hr a day.

Calculate the heat load from the forklift.

Summary and conclusion:Summary and conclusion:

. product?

2. Explain Heat of Respiration

Wednesday & Thursday:

Beverage Chiller (IBC) loads.

In Class Exercise


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Beer Chilling Calculations:Beer Chilling Calculations:Beer room loads can be calculated as follows;

Q = L x B x F x 4.19 x TD

x .

Where;

L = External Length of Room (m)

B = External width of Room (m)

F = Factor for weight of beer per m2

2 -240kg/m2 for direct pull rooms)

4.19= Specific Heat of water

PDT = Pull Down Time (72hr)

Example: Beer RoomExample: Beer Room

A client has requested a Beer Room withdimensions of 4m long by 4m wide.

-room.

The beer kegs enter at 25C and are to bechilled to 10C prior to entering the IBCsat the bar.

decided.

Calculate the refrigeration capacity required.


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Instantaneous Beverage Chillers:Instantaneous Beverage Chillers:

The following table can be used forca cu ating eat oa s or IB s.

Type Number of fonts Load per head

Pre-chilledBeverage

2 Pull 1500W per head

3-4 Pu 800W per ea

Warm Beverage 2, 3 or 4 Pull 2300W per head

refrigeration heat load estimating

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