REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - cooler/reefer tonnage capacity

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REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - cooler/reefer  tonnage capacity 

PROBLEM:

An 8 x 20 ft sea container reefer walkin cooler has an hourly load of 22,500 Btu/hr and operates 24 hours a day. The defrost system runs for 15 minutes every hour. Calculate the tonnage capacity in Tons of Refrigeration and in Kilowatts.

Given

22,500 Btu/hr hourly load

24 hours operation 

15 minutes defrost per hour

Unknown 

Reefer capacity in tons and KW

SOLUTION:

Total defrost time

= 15 minutes x 24

= 360 minutes

= 6 hours

Total Run-Time

= 24 - 6

= 18 hours

Q = hourly load 

       x 24/run time 

Walk in Cooler Condensing Unit capacity

= ( Hourly Load x 24 hr ) / 18 hr Run-Time

= ( 22,500 x 24 ) / 18

= 30,000 Btu/hr

Tonnage capacity = 30,000/12,000 = 2.5 tons

Capacity in Kilowatts = 2.5 x 3.5 = 8.8 KW

*

REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - water flow rate of chiller

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REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - water flow rate of chiller

PROBLEM:

A chiller has a capacity of 75 tons with a heat rejection ratio (HRR) of 1.3. If the change in temperature is 10F, solve for the water flow rate in US gallons per minute and imperial gallons per minute.

Given

chiller capacity = 75 tons

heat rejection ratio = 1.3

delta T = 10F

Unknown

US gpm

imperial gpm

SOLUTION:

Converting tons to Btu/hr 

Q = 75 tons x 12,000 Btu/hr per ton = 900,000 Btu/hr

Incorporating the HRR and rearranging the main equation,

US gpm = Q x HRR/(500 x delta T)

US gpm = 900,000 x 1.3/(500 x 10)

US gpm = 234 US gallons

To solve for imperial gallons, change the constant to 600

imperial gpm = Q x HRR/(600 x delta T)

imperial gpm = 900,000 x 1.3/(600 x 10)

imperial gpm = 195 imperial gpm

*

REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - water temperature entering chiller

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Eternalson17

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REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - water temperature entering chiller

PROBLEM:

A 60 ton chiller circulates 160 US gallons of water. What is the temperature rise? If the water supply temperature is 45F, determine the temperature of the water entering the chiller.

Given

Cooling capacity = 60 tons 

gpm = 160 US gallons

suppy temperature = 45F

Unknown

Temperature rise = ? or change in temperature (delta T)

Temperature of water entering chiller = ? or return temperature

SOLUTION:

Converting tons to Btu/hr 

Q = 60 tons x 12,000 Btu/hr per ton = 720,000 Btu/hr

Rearranging the main equation Q = 500 x gpm x delta T 

delta T = Q/(500 x gpm)

delta T = 720,000/(500 x 160)

delta T = 9 F

return temperature = delta T + supply temperature

return temperature = 9 + 45

return temperature = 54 F

*

REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - chiller cooling capacity (tonnage)

 

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 Eternalson17

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REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - chiller cooling capacity (tonnage) PROBLEM: Calculate the tonnage of a water chiller having a water flow rate of 240 US gallons with a supply temperature of 45F and a return temperature of 55F.

Given gpm = 240 US gallons supply temperature = 45F return temperature = 55F Unknown Q = ? cooling capacity in tons of refrigeration

SOLUTION: Q = 500 × gpm x delta T Q = 500 × 240 x (55 - 45) Q = 500 × 240 x 10 Q = 1,200,000 Btu/hr

The conversion is 1 Ton = 12,000 Btu/hr, so the final answer is, Tonnage = 1,200,000/12,000 Tonnage = 100 tons *

REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - walk in freezer hourly load

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REFRIGERATION HVAC MECHANIC RED SEAL LICENSE EXAM REVIEWER - walk in freezer hourly load

PROBLEM:

A 3 ton walkin freezer operates 24 hours a day and the defrosting system runs for 10 minutes every hour. Determine the hourly load in Btu/hr.

SOLUTION:

Total defrost time

= 10 minutes x 24

= 240 minutes

= 4 hours

Total Run-Time

= 24 - 4

= 20 hours

Walk in Freezer Condensing Unit capacity

= ( Hourly Load x 24 hr ) / 20 hr Run-Time

3 x 12,000 = Hourly Load x 24/20

Hourly Load = 36,000/1.2

Hourly Load = 30,000 Btu/hr

*

Walk-in cooler wiring diagram, walk in freezer, domestic refrigerator wiring

                                         
                                           Walk-in cooler mechanical diagram:

                               Walk-in freezer electrical wiring diagram with heater

                             Walk in freezer with defrost - electrical wiring diagram

                         Walk-in cooler with pump down - electrical wiring diagram

 
                          Walk in freezer with electric defrost - electrical wiring diagram

                              Domestic refrigerator - simple electrical wiring diagram

Watch Youtube video:
https://www.youtube.com/watch?v=bCs-NAi4uhA

REFRIGERANT R134A SAFETY

Purpose/Why: Provide knowledge & safety awareness of R134a Refrigerant

Where can you use this knowledge: Workplace, in the field, Home, Office

Definition, use, characteristics

What is a refrigerant?

Refrigerant = a substance that is used to transfer heat energy.

What is R134a?

R134a is a refrigerant that is primarily used in domestic refrigeration and automobile air conditioners.

My fridge at home uses R134a refrigerant

My car's A/C uses R134a refrigerant as well

Chemical name: Tetrafluoroethane

Characteristics: Non-flammable, Non-explosive, Non-toxic, Colorless, Odorless  gas

Hazards

1.       Frost bite – may result when it contacts your skin

2.      Eye damage – may result when it contacts your eyes

3.      Inhalation of too much vapour can cause headaches, unconsciousness, or suffocation.

­First Aid

1. Skin contact:

·         Take off all contaminated clothing immediately.

·         Flush skin with lukewarm water.

·         Call a physician.

2. Eye contact:

·         Flush eyes with plenty of water for at least 15 minutes.

·         Get medical attention.

3.Inhalation:

·         Move away from exposure to an area of fresh air.

·         Keep the patient warm and at rest.

·         Consult a physician.

Safety Precautions

1.       Always wear PPE.      ---  (Safety glasses, gloves)

2.      Avoid breathing vapours or mist.

3.      Avoid contact with skin and clothing.

4.      Ventilate work area. Provide sufficient air exchange and/or exhaust.

Storage of Refrigerant Cylinders:

5.      Keep cylinder upright and valves tightly closed.

6.      Store cylinders in cool, dry well ventilated place.   (Temperature:  45 C/113 F)

Conclusion

R134 is a useful refrigerant in domestic refrigeration and automobile air conditioners, however there are also hazards that we need to be aware of. To minimize injuries, all safety precautions must be followed.

R134a other info:       

Zero Ozone Depletion Potential (ODP): 0
Global Warming Potential (GWP): 1.2

Other uses:

• Domestic air-conditioners
• Commercial refrigeration
• Aerosol propellant in pharmaceutical, pesticide, cosmetics and cleaning industry
• Flame retardant
• Blowing agent

Chemical formula	CH2FCF3
Molar mass	102.03 g/mol
Appearance	Colorless gas
Density	0.00425 g/cm3, gas
Melting point	−103.3°C (−153.9°F; 169.8 K)
Boiling point Boiling point	−26.3 °C (−15.3°F; 246.8 K)
Solubility in water	0.15 wt%
Hazards
Main hazards	Asphyxiant
Flash Point Flash point	250°C (482°F; 523 K)