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3rd Year Refrig Sait 2019 > Paul class > Flashcards

Paul class Flashcards

1
Q

4 criteria’s for pipe sizing

A

Cost
Oil return
Temperature penalties
Noise

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2
Q

6 pieces of information required for pipe sizing

A 
Saturated evaporator temp (sst)
Saturated discharge temp (sdt)
System capacity
Type of refrigerant
Length of pipe run
Number of fittings and valves
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3
Q

Minimum/ maximum velocity required for suction lines

A

700 horizontal min
1500 vertical min
3000 max

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4
Q

Temperature penalty formula

A

2 F degrees X actual Pressure drop
——————————
Saturated Pressure equal to 2 F degrees

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5
Q

4 disadvantaged to reduced pipe size

A

Larger pressure drop
Higher temp penalty
Reduced system capacity
More horsepower required

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6
Q

Max velocity in liquid line

A

300 ft/min

Greater than 300 ft/min causes liquid hammering at LLSV

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7
Q

Purpose of inverted trap at condensor

A

To prevent liquid draining back to compressor during off cycle

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8
Q

2 disadvantages of over sized pipe

A

More refrigerant charge needed

Higher cost on install

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9
Q

At what temperatures are oil separators manditory

A

-50F

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10
Q

Pressure drop formula for change in elevation

Static pressure

A

.5psi / ft

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11
Q

Maximum condensate line velocity

A

120 ft/min

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12
Q

Multiplier when estimating pipe design

A

1.5 for over 100ft

2 for under 100 ft

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13
Q

Actual pressure drop formula

A

Chart (psi/100) x (X/actual length)

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14
Q

Temperature penalty formula

A

TP =
2 deg x actual p drop
———————
Suction psi equivalent to 2 F degrees

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15
Q

Wall thickness in pipe K vs L

A

K has thicker wall
OUTSIDE diameter does not change
Type L will carry more volume

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16
Q

Max TP allowed

A

2 F degrees suction

1 F degree discharge and liquid line

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17
Q

5 steps to plotting line size on chart

A

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

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18
Q

Slope of suction pipe

A

1/2” per 10 ft in direction of flow

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19
Q

Purpose of smallest P trap possible

A

To limit amount of oil sitting in trap

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20
Q

Purpose of inverted trap on double suction riser

A

To prevent oil draining back to inactive riser

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21
Q

Purpose of double suction risers

A

To ensure proper velocity and oil return during compressor unloading

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22
Q

4 steps to sizing double suction risers

A

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

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23
Q

Average velocity formula for double suction riser

A

(Flow area suction line) x (velocity suction line)
_____________
(Flow area large riser + flow area small riser)

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24
Q

When do you install a hot gas binding line

A

During installs where the receiver can be warmer than the condensor

25
Q

Trapping for Copeland

A

Traps required for a rise of 3-4 ft
Trap every additional 20 ft

Think
(20-3-4)

26
Q

Trapping for industry standard

A

Trap required for rise of 5 ft or more

Additional trap every 10 ft

27
Q

Pipe expansion/contraction formula

A

(Length in inched) x delta T x 0.0000104

28
Q

Where do you install pipe offsets for expansion / contraction

A

Center of pipe run

29
Q

Hanger support spacing

A

Based on pipe size. Best practice is every 8 ft

30
Q

Result of evap TD below 8 F degrees

A

Mold and bacteria

31
Q

When adding 3 evaps with different TD to obtain average

A

Use proportional ratios of each at desired average TD then add togeather

32
Q

3 formulas for finding U value

A 
K= C x thickness
Thickness = R x K
1 = RT x U
33
Q

Transmission load formula

A

Qt= U x Area x Temp diff x 24h

“Quat 24!”

34
Q

Other names for transmission load

A

Leakage and wall load

35
Q

Service factor values for air changes

A 
Light = 0.6
Normal = 1
Heavy = 2
36
Q

Infiltration load formula

A

Qi = Volume x Average air changes x service factor x heat removed

37
Q

Calculating run time for motors in misc load

A

If cooler, x 24

If freezer, 24 - defrost time

38
Q

When to add latent load to product load

A

Before total is divided by pull down time

39
Q

When to add heat of respiration

A

After product load is divided by pull down time then multiplied by 24

40
Q

Product load calculation (typical)

A

Total loads/ run time

X 24

41
Q

Heat load capacity is calculated how

A

Add total loads, multiplied by safety factor (unless other wise stated is 1.1), then divide by run time
Divide by 12000 for tonnage

42
Q

Heat load calculations. What is run time for different set ups

A 
Ac = 24 hrs
Freezer with HGBP = 20
Freezer with electric defrost = 18
Cooler with positive defrost = 18
Cooler with off cycle defrost = 16
43
Q

What temperature kills enzymes

A

Above 170F

Reduced temp only slows rate of decay

44
Q

Bacteria reproduces at what temp

A

75-85F

45
Q

Seafood storage temp

A

38F or colder

46
Q

Frozen food storage temp

A

0 F

47
Q

Ice cream storage temp

A

-10 F

48
Q

Meat storage

A

32F(ideal) to 40F max

Keep TD low

49
Q

What must be kept in mind when refrigerating and storing fruits and vegetables

A

Product is “still alive”
Must breath (holes in bags)
Susceptible to dehydration (misters)

50
Q

Humidity during mixed storage

A

Keep it low

51
Q

Why is quicker freezing desired over a slower freezing process after harvesting

A

Promotes smaller ice crystals, less freezer burn

52
Q

What is sharp freezing

A

Low temp slow freezing with low velocity air

53
Q

3 types of quick freezing methods

A

Immersion (low temp brine on seafood)
Contact (evaporator plates)
Blast ( low temp high velocity)

54
Q

What causes ice crystal formations on product

A

Temperature fluctuations (7-11 ice cream)

55
Q

Specific heat and latent heat of water in different states

A 
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
56
Q

How many pounds in 1 US gal

A

8.33 lbs

57
Q

What temp is milk heated to and for how long to kill bacteria

A

72C for 16 sec

58
Q

Another name for expansion loop

A

Cold sprung

59
Q

4 requirements for oil separator

A

Ammonia
Long pipe runs
Multiple compressors
-50

3rd Year Refrig Sait 2019 (5 decks)

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