Paul class Flashcards
4 criteria’s for pipe sizing
Cost
Oil return
Temperature penalties
Noise
6 pieces of information required for pipe sizing
Saturated evaporator temp (sst) Saturated discharge temp (sdt) System capacity Type of refrigerant Length of pipe run Number of fittings and valves
Minimum/ maximum velocity required for suction lines
700 horizontal min
1500 vertical min
3000 max
Temperature penalty formula
2 F degrees X actual Pressure drop
——————————
Saturated Pressure equal to 2 F degrees
4 disadvantaged to reduced pipe size
Larger pressure drop
Higher temp penalty
Reduced system capacity
More horsepower required
Max velocity in liquid line
300 ft/min
Greater than 300 ft/min causes liquid hammering at LLSV
Purpose of inverted trap at condensor
To prevent liquid draining back to compressor during off cycle
2 disadvantages of over sized pipe
More refrigerant charge needed
Higher cost on install
At what temperatures are oil separators manditory
-50F
Pressure drop formula for change in elevation
Static pressure
.5psi / ft
Maximum condensate line velocity
120 ft/min
Multiplier when estimating pipe design
1.5 for over 100ft
2 for under 100 ft
Actual pressure drop formula
Chart (psi/100) x (X/actual length)
Temperature penalty formula
TP =
2 deg x actual p drop
———————
Suction psi equivalent to 2 F degrees
Wall thickness in pipe K vs L
K has thicker wall
OUTSIDE diameter does not change
Type L will carry more volume
Max TP allowed
2 F degrees suction
1 F degree discharge and liquid line
5 steps to plotting line size on chart
1) Look up tonnage capacity
2) Go down to evap temp
3) Go over to line size
4) Go down to condensor temp
5) Obtain velocity and check allowable perameters
Slope of suction pipe
1/2” per 10 ft in direction of flow
Purpose of smallest P trap possible
To limit amount of oil sitting in trap
Purpose of inverted trap on double suction riser
To prevent oil draining back to inactive riser
Purpose of double suction risers
To ensure proper velocity and oil return during compressor unloading
4 steps to sizing double suction risers
1) Use chart to size capacity at unloaded state (eg 33% of 3 ton system is 1 ton)
2) Size small riser with acceptable velocity
3) Subtract FLOW AREA of small riser from suction line
4) Size large riser but DO NOT EXCEED remaining FLOW AREA required
Average velocity formula for double suction riser
(Flow area suction line) x (velocity suction line)
_____________
(Flow area large riser + flow area small riser)
When do you install a hot gas binding line
During installs where the receiver can be warmer than the condensor
Trapping for Copeland
Traps required for a rise of 3-4 ft
Trap every additional 20 ft
Think
(20-3-4)
Trapping for industry standard
Trap required for rise of 5 ft or more
Additional trap every 10 ft
Pipe expansion/contraction formula
(Length in inched) x delta T x 0.0000104
Where do you install pipe offsets for expansion / contraction
Center of pipe run
Hanger support spacing
Based on pipe size. Best practice is every 8 ft
Result of evap TD below 8 F degrees
Mold and bacteria
When adding 3 evaps with different TD to obtain average
Use proportional ratios of each at desired average TD then add togeather
3 formulas for finding U value
K= C x thickness Thickness = R x K 1 = RT x U
Transmission load formula
Qt= U x Area x Temp diff x 24h
“Quat 24!”
Other names for transmission load
Leakage and wall load
Service factor values for air changes
Light = 0.6 Normal = 1 Heavy = 2
Infiltration load formula
Qi = Volume x Average air changes x service factor x heat removed
Calculating run time for motors in misc load
If cooler, x 24
If freezer, 24 - defrost time
When to add latent load to product load
Before total is divided by pull down time
When to add heat of respiration
After product load is divided by pull down time then multiplied by 24
Product load calculation (typical)
Total loads/ run time
X 24
Heat load capacity is calculated how
Add total loads, multiplied by safety factor (unless other wise stated is 1.1), then divide by run time
Divide by 12000 for tonnage
Heat load calculations. What is run time for different set ups
Ac = 24 hrs Freezer with HGBP = 20 Freezer with electric defrost = 18 Cooler with positive defrost = 18 Cooler with off cycle defrost = 16
What temperature kills enzymes
Above 170F
Reduced temp only slows rate of decay
Bacteria reproduces at what temp
75-85F
Seafood storage temp
38F or colder
Frozen food storage temp
0 F
Ice cream storage temp
-10 F
Meat storage
32F(ideal) to 40F max
Keep TD low
What must be kept in mind when refrigerating and storing fruits and vegetables
Product is “still alive”
Must breath (holes in bags)
Susceptible to dehydration (misters)
Humidity during mixed storage
Keep it low
Why is quicker freezing desired over a slower freezing process after harvesting
Promotes smaller ice crystals, less freezer burn
What is sharp freezing
Low temp slow freezing with low velocity air
3 types of quick freezing methods
Immersion (low temp brine on seafood)
Contact (evaporator plates)
Blast ( low temp high velocity)
What causes ice crystal formations on product
Temperature fluctuations (7-11 ice cream)
Specific heat and latent heat of water in different states
Latent heat of evaporation is 970 Latent heat of freezing is 144 Specific heat of steam is 0.46 Specific heat of water is 1 Specific heat of ice is 0.5
How many pounds in 1 US gal
8.33 lbs
What temp is milk heated to and for how long to kill bacteria
72C for 16 sec
Another name for expansion loop
Cold sprung
4 requirements for oil separator
Ammonia
Long pipe runs
Multiple compressors
-50
