Paul class Flashcards
(59 cards)
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
