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Pressure-Enthalpy and the Variable Refrigerant Cycle

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Presentation on theme: "Pressure-Enthalpy and the Variable Refrigerant Cycle"— Presentation transcript:

1 Pressure-Enthalpy and the Variable Refrigerant Cycle
Joe Cefaly OEM Applications Manager - CEM, LEED AP Mitsubishi Electric US Cooling & Heating

2 What is VRF? Variable Refrigerant Flow

3 Heat Pump VRF Systems COOLING HEATING

4 Heat Recovery VRF Systems
Outdoor Unit or Water-source Unit

5 Basic Refrigeration Cycle
RED = Higher Temp/Pressure BLUE = Lower Temp/Pressure

6 Basic Refrigeration Cycle
Evaporator High-Pressure Vapor High-Pressure Liquid Condenser Low-Pressure Liquid Low-Pressure Vapor

7 Basic Refrigeration Cycle
RED = Higher Temp/Pressure Subcooled Liquid Condensing Liquid Gas Expansion Cycle Liquid and Gas Compression Cycle Pressure Evaporating Superheated Gas BLUE = Lower Temp/Pressure Enthalpy

8 Accumulator Provide compressor protection from liquid slugging during startup Stores refrigerant not required in low load conditions Assures adequate vapor and oil return

9 Accumulator

10 Scroll Compressor Intake Compression Discharge Orbiting Scroll
Fixed Scroll Orbiting Scroll Assembled Scrolls Discharge

11 Inverter-Driven Scroll Compressors
What is an Inverter? A variable speed drive that changes the voltage and frequency being fed to the motor Think of the inverter as a throttle control Changes electrical frequency from 60 Hz to a varying range of 15 Hz to 125 Hz Frequency is affected by: Number of indoor units operating Outdoor unit model Outdoor unit target temps/pressures Greatly reduces energy usage To convert AC to DC is to rectify, a device that converts DC to AC is an inverter.

12 Compressor Evaporator High-Pressure Vapor High-Pressure Liquid
Condenser Low-Pressure Liquid Low-Pressure Vapor

13 Oil Separator Allows long piping runs Eliminates need to trap
Increases operating range

14 Oil Separator

15 Condenser Air or Water Refrigerant changes from gas to liquid

16 Segmented Heat Exchangers
Segments use valves Capacity control Improves efficiency Simultaneous heat/cool/heat recovery

17 Condenser Evaporator High-Pressure Vapor High-Pressure Liquid
Low-Pressure Liquid Low-Pressure Vapor

18 Linear Expansion Valve (LEV)
Controls refrigerant superheat or sub-cooling at evaporator Modulates by “pulsing” from Used on indoor units and in BC controller

19 Linear Expansion Valve (LEV)
Evaporator High-Pressure Vapor High-Pressure Liquid Condenser Low-Pressure Liquid Low-Pressure Vapor

20 Evaporator Fins Suction Header Feeder Tubes Refrigerant Distributor
Heat and moisture is removed from the air stream Refrigerant evaporates Fins Suction Header Feeder Tubes Refrigerant Distributor Evaporator Tubes

21 Evaporator Evaporator High-Pressure Vapor High-Pressure Liquid
Condenser Low-Pressure Liquid Low-Pressure Vapor

22 Indoor Unit Cooling Coil
Sensor (TH23) Heat Exchanger Airflow Sensor (TH21) Note: TH21 can also be located at the remote controller Pulse Sensor(TH22) LEV 1 1 1 8 7 1 1

23 “Smart Coil” Operating Parameters
Sub-cooled refrigerant Super-heated refrigerant Condensing High psi Pressure Expansion Cycle Refrigerant in liquid and gaseous states Compression Cycle Low psi Evaporating TH 22 TH 23 Superheat Differential Enthalpy

24 Cooling Coil – Max Capacity
High Fan Speed High Fan Speed Numbers are approximate for explanation purposes

25 Cooling Coil – Reduced Capacity
High Fan Speed Numbers are approximate for explanation purposes

26 Cooling Coil – Low Capacity
High Fan Speed Numbers are approximate for explanation purposes

27 Low or Extra-Low Fan Speed
Cooling Coil – Dry Mode Low or Extra-Low Fan Speed Low or Extra-Low Fan Speed Numbers are approximate for explanation purposes

28 Cooling Coil – Dry Mode Fan runs continuously Indoor LEV THERMOSTAT
ROOM TEMP ON OFF CALLING 82° or more 9 Minutes 3 Minutes 79° - 82° 7 Minutes 75° - 79° 5 Minutes 64° - 75° less than 64° -- Always SATISFIED 64° or more 10 Minutes We don’t sense humidity. You must either schedule dry mode or manual turn it on from the R/C. Only way to do it is to use a DIDO board to sense humidity and send signal to MNET. Fan runs continuously

29 Reversing Valve Reverses refrigerant flow when systems changes between heating and cooling

30 Branch Circuit Controller
Refrigerant “traffic cop” Gas/liquid separator Tube in tube heat exchangers LEVs Solenoid valves

31 Gas/Liquid Separator Hot gas is used for heating
Liquid is used for cooling

32 Tube-in-Tube Heat Exchangers
Provides sub-cooling in heating mode Provides super-heating in cooling mode

33 Solenoid Valves Block of valves used to control refrigerant direction

34 Full Port Valves Recommended at BC controller
Helps with evacuation during install Isolates branches for maintenance Allows additional branches for future use

35 VRF Piping Considerations
Keep pipe as straight as possible to avoid pressure drops Long bends instead of elbows when possible (90° ~ 1ft length) No refrigerant specialties/accessories/traps (minimize restrictions) Oil separator and accumulator in outdoor unit Selection program sizes piping for you Pipe length = pressure changes = capacity/performance Vertical difference between units: CU below Indoor units ft (CU to Indoor) CU above Indoor units ft (CU to Indoor) 131/196 ft length from BC controller to furthest indoor unit 49 ft height difference between indoor units and/or BC controller

36 Filter Drier Installed in liquid line
Filter foreign material from the system Desiccant core removes moisture and small dirt collected in refrigerant Internal screens filter any solid material NOT Required or recommended on new Mitsubishi systems when installation procedures are followed Used in replacements

37 Filter Drier Liquid Line Evaporator High-Pressure Vapor High-Pressure
This is an example of where the filter drier needs to be installed in refrigeration system. Condenser Low-Pressure Liquid Low-Pressure Vapor

38 Sight Glass In Liquid line
Visual indication whether system is contaminated with moisture Green is dry, Yellow is wet Shows bubbles which could indicate problem & assists in charging system NOT used in VRF equipment Refrigerant state is constantly changing

39 Sight Glass

40 Piping Considerations
Suction line velocity ~ 1200 ft/min Sized for minimum capacity Oil return is #1 concern Pitch piping towards compressor Trap with condenser above evaporator Help with oil return especially during off cycle Inverted trap with evaporator above condenser Helps to prevent slugging liquid Not required with pump down

41 Oil Traps Assist in oil return to compressor
Prevent oil accumulation in evaporator Installed in suction line when compressor is above evaporator Not required or recommended in VRF systems

42 Compressor Control Maintains evaporation temperature in cooling
Maintains condensing temperature in heating

43 Heat Exchanger Control
Heat exchanger is separated for capacity control Sections of heat exchanger are enabled/disabled as required Condenser fan modulates on air cooled units

44 Indoor Unit Control Auto Control

45 Indoor Unit Control Modulates LEV and fan speed based on setpoint
Open valve = more flow/capacity Close valve = less flow/capacity

46 Thank you for your time


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