1. Pressure Regulators
KVR + NRD Presentation , Jbm - Page 1

2. Pressure Regulators Overview
CONDENSER PRESSURE REGULATORS
EVAPORATOR PRESSURE REGULATORS
CRANKCASE PRESSURE REGULATORS
HOTGAS BY-PASS REGULATORS
Direct feed of hot gas
Use of Liquid/Vapour mix
KVR + NRD Presentation , Jbm - Page 2

3. Some Functions of Regulators
Maintain required temperatures through control of pressure
Maintain pressure to components that are within operating envelopes
Ensure adequate pressure differential across metering devices in all ambients
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4. Condenser Pressure Regulators
(CPR)
Application Information
The main purpose of a condenser pressure regulator is to maintain sufficient pressure at the TEV during low ambient (Outdoor) temperatures
KVR + NRD Presentation , Jbm - Page 4

5. Location of CPR Condenser Used in the liquid line before the receiver
KVR + NRD Presentation , Jbm - Page 5

6. Condenser Pressure Regulator
Condensing Temperature = 110 Fahrenheit
90 degree Fahrenheit Air Inlet Temperature
Condensers are designed for a certain difference between the outside ambient temperature and the condensing temperature
Because the condenser must be able to reject heat even at high loads, the condenser must be large enough to reject this heat even when it is hot outside i.e. 90F
KVR + NRD Presentation , Jbm - Page 6

7. Condenser Pressure Regulator
When the outdoor temperature is lower, the condenser acts like it is a lot larger
Temperature = 90F
Temperature = 20F
KVR + NRD Presentation , Jbm - Page 7

8. Condenser Pressure Regulator
When the condenser effectively becomes larger, the condensing pressure can drop substantially ,causing the TEV to operate erratically
The CPR acts by reducing the area available for heat rejection, effectively making the condenser smaller
KVR + NRD Presentation , Jbm - Page 8

9. Condenser Pressure Regulator
This the way the condenser behaves when liquid is backed up in it
Only a portion of it can reject heat
The CPR accomplishes this by backing up the liquid in the condenser, using up free volume
The condenser then has a smaller area available to reject heat from the refrigerant
KVR + NRD Presentation , Jbm - Page 9

10. Reduction in Latent Heat Capacity
If the coil is full of liquid, then the majority of the coil is only capable of sensible heat removal
This can reduce the capacity of the condenser by 300%
Sub-cooled liquid outlet
Hot discharge gas inlet
KVR + NRD Presentation , Jbm - Page 10

11. Heat Energy - Enthalpy Temperature Heat (Energy) Enthalpy
Enthalpy is the heat in BTUs per pound added to or removed from a substance, in this case water.
superheating
vapor
212 °F
boiling water
(liquid + vapor)
Temperature
heating
water (liquid)
970 BTU/lb
Heat (Energy)
Enthalpy
180 BTU/lb
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12. CPR Functionality
The CPR closes on a fall in inlet pressure and opens on a rise in inlet pressure
The regulator is in turn set to operate over a given pressure range or Proportional band (P-band) with the opening pressure controlled by a chosen setting
Capacity in %
100 75 50 25
psi 75
150
225
300
375
Factory setting
P-band
KVR + NRD Presentation , Jbm - Page 12

13. Relation of Capacity and P-band
Capacity in %
100 75
Below are the values between the start of the valve opening and the valve being fully open 50 25
psi 75
150
225
300
Factory setting
P-band
KVR + NRD Presentation , Jbm - Page 13

14. Relation of Capacity and P-band
Capacity in %
100
By subtracting the value of the opening pressure from the fully open we arrive at the P-band 75 50 25
psi 75
150
225
300
Factory setting
P-band
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15. Relation of Capacity and P-band
Capacity in %
100
= 75 psi
The P-band is 75psi 75 50 25
psi 75
150
225
300
Factory setting
P-band
KVR + NRD Presentation , Jbm - Page 15

16. Relation between Capacity and Offset
Capacity in %
100 75
Offset is the permissible difference between the operating pressure and the minimum pressure allowed. 50 25
psi 75
150
225
300
Factory setting
Offset
KVR + NRD Presentation , Jbm - Page 16

17. Relation between Capacity and Offset
Capacity in %
100 75
In this example the operating pressure is 175 psi and the minimum pressure desired is 155 psi 50 25
psi 75
150
225
300
Factory setting
Offset
KVR + NRD Presentation , Jbm - Page 17

18. Use of Pressure Differential Valve
-10 F with ambient air movement
Under very low ambient conditions, even back filling the condenser with liquid may not be adequate to maintain sufficient condensing pressure
KVR + NRD Presentation , Jbm - Page 18

19. Differential Pressure Valve
(DPV)
The DPV uses a pressure differential to inject hot gas into the receiver to boost it’s pressure
It opens when the pressure difference between the compressor discharge and the receiver is greater than the spring pressure holding the valve closed
KVR + NRD Presentation , Jbm - Page 19

20. Differential Pressure Valve
(DPV)
A pressure differential of 20 psi will begin to open the DPV. It will inject hot gas into the receiver to boost it’s pressure.
The valve will be 100% open when the differential pressure is 43psi.
KVR + NRD Presentation , Jbm - Page 20

21. Location of CPR Condenser
Hot gas is injected directly into the receiver
KVR + NRD Presentation , Jbm - Page 21

22. SIZING THE KVR + NRD Conditions Refrigerant R-22
Capacity BTU/hr
Application Liquid line
Desired Pressure drop 3 psi
Evaporating temp. 20 F
Condensing temp F
Liquid temp F
Connection KVR ½” flare
NRD ½” solder
KVR + NRD Presentation , Jbm - Page 22

23. Using the Application Guide
The capacity chart is based on rated capacities which assume certain conditions
In reality, the conditions are likely to be different and these differences need to be taken into consideration
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24. Using the Application Guide
The actual required capacity must be determined by using a correction factor for actual evaporating temp
= .97 X = BTU/hr = ~6.6 tons
KVR + NRD Presentation , Jbm - Page 24

25. Using the Application Guide
The selection is made by locating the correct condensing temperature and the desired pressure drop across the valve and then picking the corrected capacity from the table
KVR + NRD Presentation , Jbm - Page 25

26. Using the Application Guide
The final code number selection is determined by the family model that fits the connection requirements
In this example it is the 034L0091 with 1/2” flare connetions
KVR + NRD Presentation , Jbm - Page 26

27. KVR & NRD Summary
The KVR & NRD maintain sufficient condensing pressure during low loads and low ambient conditions
They help to maintain a sufficient pressure differential across the TXV so it reliably controls according to it’s specifications
KVR + NRD Presentation , Jbm - Page 27

28. Crankcase Pressure Regulators
KVR + NRD Presentation , Jbm - Page 28

29. Crankcase Pressure Regulators
Evaporator
The KVL limits the amount of refrigerant returning back to the compressor
It is primarily used with low temperature compressors as they are designed for low density suction gas
KVR + NRD Presentation , Jbm - Page 29

30. Crankcase Pressure Regulators
During high loads, the returning gas can be at a high pressure and density and can damage the compressor motor
The KVL will close on a rise in inlet pressure, limiting the amount of refrigerant that returns to the compressor
KVR + NRD Presentation , Jbm - Page 30

31. Crankcase Pressure Regulator Selection
Below are conditions from a system that we can use to make an example selection
System capacity is 8000 btu/hr or .65 tons
Refrigerant R404a
Suction temperature is -10F
Liquid temperature is 110F
Desired pressure drop across valve is 3 psi
Maximum suction pressure is 40 psi
Connection size is 7/8 sweat
KVR + NRD Presentation , Jbm - Page 31

32. Crankcase Pressure Regulator Selection
Tons
The capacities given in this code number table is based on certain assumptions about the conditions of the system (rated conditions)
Actual system conditions may be very different so the table capacities must not be used to make a selection
KVR + NRD Presentation , Jbm - Page 32

33. Crankcase Pressure Regulator Selection
Below are the steps that we need to take to make a selection
Does this capacity exceed the required capacity?
If yes, then choose the code number for the valve from the code number selection table based on the size and type of connections required
If not, then go down to the next size of valves and repeat the process
KVR + NRD Presentation , Jbm - Page 33

34. Crankcase Pressure Regulator Selection
Here we see the correction table that corrects for the temperature of the liquid ahead of the TXV
If the liquid temperature is different than 100F, then we need to use the appropriate conversion factor to correct the system capacity
KVR + NRD Presentation , Jbm - Page 34

35. Crankcase Pressure Regulator Selection
To correct the system capacity, we multiply this capacity by the correction factor
Corrected capacity is .65 tons x 1.10 = .72 tons
.72 tons is the capacity we use to make a selection from the capacity table
KVR + NRD Presentation , Jbm - Page 35

36. Crankcase Pressure Regulator Selection
Step 1
Find the evaporator temperature
Step 2
Find the desired pressure drop
Using the system condition provided and the corrected capacity, make the selection from the capacity table
KVR + NRD Presentation , Jbm - Page 36

37. Crankcase Pressure Regulator Selection
Find the maximum suction pressure
Select the capacity that is above the required capacity
Step 4
Step 3
KVR + NRD Presentation , Jbm - Page 37

38. Crankcase Pressure Regulator Selection
Choose the code number for the valve from the code number selection table based on the size and type of connections required and the valve type
The correct code number is 034L0045
KVR + NRD Presentation , Jbm - Page 38

39. Evaporator Pressure Regulators
An EPR is designed to maintain a desired pressure (temperature) in an evaporator
It can be used with a single evaporator or in multiple evaporator arrangements
An EPR will open when the inlet pressure rises to the desired set-point and it will close if it falls below the set point.
KVR + NRD Presentation , Jbm - Page 39

40. EPR with Single Evaporator
Single Evaporator Application
The KVP is located between the evaporator and the compressor and is designed keep the evaporator at a desired temperature
Compressor
EPR
KVR + NRD Presentation , Jbm - Page 40

41. EPR with Multiple Evaporators
Multi Evaporator Application
Evap #1
Evap #2
10F at 12psi
35F at 30psi
The EPR will keep evaporator Evap # 2 at it’s desired set-point regardless of the temperature of Evap #1
KVP
KVR + NRD Presentation , Jbm - Page 41

42. KVP Pipe Diagram Multi Evaporator Application Evap #1 Evap #2
10F at 12psi
35F at 30psi
The compressor suction pressure will be equal to the non-regulated evaporator (Evap #1)
KVP
12psi
12psi
KVR + NRD Presentation , Jbm - Page 42

43. Hot Gas Regulator
The KVC is designed to maintain a minimum pressure at the compressor suction inlet
This is important when the compressor capacity is greater than minimum load requirements
It opens when the outlet pressure drops below the desired set-point and it will close when the pressure rises above the set point.
KVR + NRD Presentation , Jbm - Page 43

44. Simple Hot Gas System
This image shows the hot gas regulator controlling hot gas from the compressor discharge to the inlet of the evaporator
Check valve to protect TXV
Compressor
This adds a false load onto the compressor
KVR + NRD Presentation , Jbm - Page 44

45. Example of Capacity Control - Air Drying
The suction pressure will follow the load on the evaporator, dropping on low load until the low pressure cut-out shuts off the compressor
Compressor on.
Compressor off.
Suction Pressure
Suction pressure varies
The compressor cycles frequently on low pressure cut-out.
Time
KVR + NRD Presentation , Jbm - Page 45

46. Example of Capacity Control - Air Drying
By utilizing hot gas bypass, the addition of the discharge gas raises the suction pressure to a level where the low pressure control will not trip and cycle the compressor.
Suction pressure without hot gas bypass fluctuates with evaporator load
Suction Pressure
Suction pressure is relatively steady.
The compressor does not cycle.
Time
KVR + NRD Presentation , Jbm - Page 46

47. Capacity Control in Air Drying Applications
In reality, there is a limit to the amount of additional load that can be added to the suction side of the system
As the suction gas cools the compressor, an important limitation is the maximum allowable suction temperature of the compressor
180 F discharge
280 F discharge
30 F
80 F
KVR + NRD Presentation , Jbm - Page 47

48. IMPORTANT!
Artificial load is often used in air driers without liquid injection, but remember :
If the artificial load exceeds 50 % of the total system load, it will normally be necessary to cool the suction gases.
This is done by injecting refrigerant into the suction line via a TEV, in series with a EVR solenoid valve mounted as close as possible to the TEV.
The TEV valve must be set to max. superheat and with sensor on suction line.
KVR + NRD Presentation , Jbm - Page 48

49. Liquid & Hot Gas Mixing Compressor
Liquid from the TEV maintains the suction gas temperature.
Liquid Gas Mixer
TEV sensing bulb controls superheat to compressor
Compressor
KVR + NRD Presentation , Jbm - Page 49

50. P-band and Offset
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