Designing Refrigeration Systems |
1.Load Calculations
-Above or below freezing
2. Equipment Selection
-Condensing unit
-Evaporator
-Accessories
3.Refririgerant pipe sizing
-Liquid Line
-Suction Temp
Electrical Components
-Over current selection
-Overload protection
-Conductor Sizing
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Load Is Always Calculated On aA 24 Hour Basis From The Following Sources: |
1.The wall or transmission load
-How much heat escapes into the cooling zone
-{(SQ. FT wall area) x (BTU/ 24 Hour Factor)}
2. The Air change or ventilation load
-{(Room Volume) x (Air Changes/HR) x (Air Change Factor)}
3. The Product Load
-{(Weight of the product) x (Sp. Heat x Temp. Difference)}
-{(Weight of the product) x (Latent Heat)}
4. Miscellaneous Loads
-Load in Watts x 3.412
-Occupant Load
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Equipment Selection |
-The first component selected from a commercial load calculation is the condensing unit. Selection is based on:
-Condensing medium required
-Type of compressor
|-Type of refrigerant
-Temp application
-Required space humidity
-Voltage required
-Preferred equipment manufacture
-*Note: Once all the above has been determined the condensing unit will be selected as close to the actual calculated load as possible
Evaporator Coil
-Based on the following criteria
-Capacity required- Same as condensing unit capacity
-Application + location of coil
-Type of defrost method preferred
-Voltage required
-Coil TD required
-Preferred equipment manufacture
-*Note: Coil capacity must be the same as the selected condensing unit capacity
-Formula for actual coil TD:
(Actual Condensing unit capacity) ÷ (Coil capacity at design TD) x 10
-Formula for finding coil Capacity for Selected TD
(Actual Condensing unit capacity) ÷ (Desired TD) = Coil Capacity at 10°F TD
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Refrigerant Pipe sizing |
Suction Line Sizing
-Based on the following
-Type of refrigerant used
-Condensing temp.
-Evaporator temp
-Subcooling (Standard)
-Superheat (Standard)
-Cooling Load
-Desired tube diameter: Suction service valve + outlet of evaporator size
-Equivalent length of pipe obtained from: The actual length of run, number of elbows, accessories used in line
-*Note: Once the above has been calculated(on computer software) check the following: Min velocity obtained, Max velocity obtained, Max press drop exceeded (2°F)
- Suction line
-Max velocity: 4000FPM
-Min FPM Horizontal: 500 FPM
-Min FPM Vertical: 1300 FPM
-Velocity important for oil return
Liquid Line Sizing
-Based on the following
-Type of refrigerant used
-Condensing temp.
-Evaporator temp
-Subcooling (Standard)
-Superheat (Standard)
-Cooling Load
-Desired tube diameter: Receiver outlet size + Inlet to TXV size
-Equivalent length of pipe obtained from: The actual length of run, number of elbows, accessories used in line
-*Note: Once the above has been calculated(on computer software) check the following: Min velocity obtained, Max velocity obtained, Max press drop exceeded (2°F Max)
-Liquid line must not exceed 360 Feet/ Min
- If liquid line exceeds 360 FPM liquid hammering may occur
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Calculation Of Equivalent Length Of Pipe |
-Must look in mechanical engineering book
-Each elbow/ drier/ solenoid/ valve… has an equivalent number of feet added to the actual run of the pipe. This total is called equivalent length.
Calculation of Equivalent length of pipe |
Desired diameter 3/8" |
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Actual length of run |
20' |
6 Short radius elbows |
30' |
1 Filter drier |
3' |
1 Sight glass |
2' |
1 Liquid line solenoid |
4' |
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Total = 59' |
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Equipment Selection |
-Once the condensing unit and evaporator have been selected you must select the accessories required for proper operation
Expansion Valve
-Based on the following
-Type of refrigerant
-Capacity required
-Temp application
-Body style
-Inlet + outlet sizes required
-Internal + external equalized
-Preferred Equipment manufacture
-*Note: Expansion valve capacity should never be selected with a lower capacity than the coil it is feeding
-*Note: When selecting internally and externally equalized expansion valves look in wholesaler manuals at the selected evaporator and it will tell you if the TXV is internal or external equalized
Accessories
-Based on the following
-Temp application of system: High, Medium, Low
-What components come with selected condensing units
-Water valve
-High/ low pressure switch
-Crankcase heater
-Suction accumulator
-Sight glass/ moisture indicator
-Direr
-When getting a CPR(Crankcase Pressure Regulator)
-Look at the compressor capacity
-May be 0°F to -40°F SST
-Convert 0°F to -40°F to the refrigerant (being used) pressure and then set the CPR to that pressure.
-*Note: Can also set a CPR to compressor RLA amperage…
-Solenoid Selection
-Coil Voltage must match that of condensing unit or power supply
-The valve must match/ be applicable to the tonnage
-Find this out by taking the condensing unit load/ capacity and convert to tons: (÷ 12000)
-Make sure PSI of system does not go above the solenoid capacity
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Commercial Load Calculation Questions |
Exercise Requirements
1. Prepare a Load calculation
2. Select equipment from wholesaler catalog
3. Determine correct line size requirements
4. Determine conductor size, overcurrent and overload protection
5. Sketch a basic pipe layout (Not to scale)
6. Sketch a electrical schematic of the electrical devices selected |
| Application |
Meat Cooler |
| Product |
800 lbs of fresh Beef |
| Design Ambient Temp Outside |
85 °F and 60% RH |
| Room Storage Temp |
40 °F |
| Room Dimensions |
Width: 20 ft
Height: 8 ft
Length: 10 ft |
| Insulation Used |
4 " Cork |
| Product Data |
Meat arrives at 75 °F |
| Miscellaneous Loads |
2 Motors at 0.25 HP each
3 Lights at 100 Watts each
2 Person @ 2 hours a day |
| Equipment Information |
Condensing unit located on back side of walk in cooler and the available voltage is 120/ 208 volts 1 phase. Water is not available |
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| Application |
Meat Freezer |
| Product |
1500 lbs of fresh Beef |
| Design Ambient Temp Outside |
85 °F and 60% RH |
| Room Storage Temp |
-10 °F |
| Room Dimensions |
Width: 20 ft
Height: 8 ft
Length: 20 ft |
| Insulation Used |
8" Cork |
| Product Data |
Meat arrives at 35 °F |
| Miscellaneous Loads |
2 Motors at 0.25 HP each
3 Lights at 100 Watts each
2 Person @ 2 hours a day |
| Equipment Information |
Condensing unit located on back side of walk in cooler and the available voltage is 120/ 208 volts 3 phase. Water is available |
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| Application |
Ice storage |
| Product |
4500 lbs |
| Design Ambient Temp Outside |
85 °F and 60% RH |
| Room Storage Temp |
-10 °F |
| Room Dimensions |
Width: 25 ft
Height: 8 ft
Length: 20 ft |
| Insulation Used |
8" Cork |
| Product Data |
Ice arrives at 32 °F |
| Miscellaneous Loads |
4 Motors at 0.25 HP each
3 Lights at 100 Watts each
2 Person @ 6 hours a day |
| Equipment Information |
Condensing unit located on back side of walk in cooler and the available voltage is 120/ 208 volts 3 phase. Water is available |
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