Energy Use in Refrigeration Systems

2012 Rocky Mountain ASHRAE Technical Conference Energy Use in Refrigeration Systems PRESENTED BY: Scott Martin, PE, LEED AP BD+C

Objectives Understand mechanical refrigeration terms Describe how heat is transferred and what methods are primarily used in the refrigeration cycle Describe the 4 principles of the refrigeration process Explain the function of the 4 system components Explain refrigerant properties Section 1 Introduction

Definition of Refrigeration re frig er a tion (n.) Mechanical refrigeration is the process of using a volatile fluid to absorb heat from a lower temperature place, raising the fluid s pressure and temperature so it can be rejected to a higher temperature place Section 1 Introduction

Basic Principals Heat is a form of energy First law of thermodynamics: Energy can neither be created or destroyed Heat flows from a higher temperature to a lower temperature Heat energy can move by one of three methods of heat transfer

Three Types of Heat Transfer Conduction Transfer by contact Convection May be natural or forced transfer by density currents and fluid motion Radiation Transfer by electromagnetic waves Mechanical refrigeration uses the first two. Section 2 Basic Principles

Two Forms of Heat Energy Sensible Heat Associated with molecular movement Measured with a thermometer Latent Heat Change of state Latent heat of fusion (solid to liquid) Latent heat of vaporization (liquid to gas) Latent heat of sublimation (solid to gas)

Sensible Heat of Water 212 132 Temperature F 100 42 32 0 0 10 100 Enthalpy (Btu/lb) 180 Section 2 Basic Principles

Latent Heat Total Heat (Enthalpy) = Sensible Heat + Latent Heat 212 F liquid 212 F gas Change of State Latent heat cannot be measured on a thermometer Section 2 Basic Principles

Change of State Latent Heat of Fusion Latent Heat of Vaporization 1 lb ice 32 F 144 Btu/lb 32 F 970 Btu/lb Section 2 Basic Principles

Temperature-Enthalpy Plot Temperature F 212 32 Ice Example: R-718 (water) 1 pound at standard barometric pressure Latent heat of fusion Liquid Subcooled Solid Latent Heat of Vaporization 970 Btu -176-144 0 180 1150 Enthalpy (Btu/lb) (Sensible + Latent Heat) Section 2 Basic Principles

Superheat Saturated Vapor @ 212 F Pressure is constant @14.7 psia Superheated Vapor @ 242 F 212 F Water Superheat t 2 t 1 = 30 F Section 2 Basic Principles

Temperature-Enthalpy Plot 242 Saturated Liquid Superheated Vapor Vapor Temperature F 212 32 Ice Subcooled Liquid Liquid Latent Heat of Vaporization Condensation Evaporation 1 Btu/lb 970 Btu/lb 0.45 Btu/lb Saturated Vapor -176-144 0 180 Enthalpy (Btu/lb) NOTE: THERE IS NO TIME ON THIS SCALE Section 2 Basic Principles 1150 1160

Rate of heat transfer Btu is a measure of quantity Btuh is a measure of quantity per unit of time (hour) 288,000 Btu 1 Day 1 Ton of Ice 1 Ton = 12,000 Btuh 12,000 Btu 1 hour 200 Btu 1 Min Latent heat of fusion 144 Btu 2000 lb = 288,000 Btu Section 2 Basic Principles

Four Laws of System Operation 70 70 No Flow Some Flow 70 Heat only moves from higher temperature to a lower temperature 212 70 More Flow 32 The greater the difference the greater the flow 70 Section 2 Basic Principles

Four Laws of System Operation 1. Heat only moves from a higher temperature to a lower temperature Sensible Heat 71 F 70 F 1 Btu / lb Section 2 Basic Principles

Four Laws of System Operation 1. Heat only moves from a higher temperature to a lower temperature 2. A large amount of energy is required to change the state of matter Latent Heat Saturated Vapor 212 F Change of state occurs at a constant temperature 212 F 970 Btu/lb Section 2 Basic Principles

Four Laws of System Operation 1. Heat only moves from a higher temperature to a lower temperature 2. A large amount of energy is required to change the state of matter 3. The temperature and energy required to change state are a function of pressure Section 2 Basic Principles

Pressure Affects the Boiling Point 0 psig 5 psig 50 psig 212 F 227 F 298 F 970 Btu/lb 960 Btu/lb 912 Btu/lb If we control the pressure, we control the boiling point Section 2 Basic Principles

Measuring Pressure Absolute Pressure Scales Compared psia in. Hg Abs 14.696 psia 29.921 in. Hg (sea level) 12.23 psia 24.9 in. Hg (5000 ft above sea level) PRESSURE PRESSURE 0 psia 0 in. Hg (no atmosphere) 0 psig = 14.696 psia MERCURY Section 2 Basic Principles

Refrigerant Boiling Points -40 F Water HFC-134a HCFC-22 HFC-410A 212 F -15 F -41 F -62 F Section 2 Basic Principles

Pressure Difference Creates Flow Flow may be caused by: Static pressure difference Pressure difference Mechanical work Static Suction Pressure Vapor Section 2 Basic Principles

The Mechanical Refrigeration Cycle

Four Components Are Required 3. Heat rejecting section 4. Pressure/ flow control valve 2. Vapor pump 1. Heat absorbing section Section 3 The Mechanical Refrigeration Cycle

An Open Cycle Refrigerant Under Pressure 14.7 psia AIR R410a -60.8 F Section 3 The Mechanical Refrigeration Cycle

The Closed Cycle Metering Device Evaporator Condenser Compressor Section 3 The Mechanical Refrigeration Cycle

2-Pressure Zone Typical conditions at peak load for: HCFC-22 HFC-410A 120 F / 431.6 psia 120 F / 274.7 psia Condenser (Rejects Heat) Metering Device Compressor Evaporator (Absorbs Heat) Hot Gas Line Suction Line High Side Low Side 45 F / 90.8 psia 45 F / 144.5 psia Section 3 The Mechanical Refrigeration Cycle

Pressure-Enthalpy Diagram Refrigeration Cycle Pc Saturated Condensing PRESSURE Ps SAT. LIQUID Saturated Suction SAT. VAPOR LIFT RE ENTHALPY Section 2 Basic Refrigeration Cycle

The Evaporator Absorbs Heat Liquid and Vapor 60 F All Vapor AIR 80 F Section 3 The Mechanical Refrigeration Cycle

Basic System Components Every system has four basic components Cold Mixture Evaporator Air out: 59.7 F db / 57.3 F wb 45 F 90.8 psia SET Air in: 80 F db / 67 F wb 55 F 90.8 psia Cold Vapor Evaporator Absorbs the heat from the space or the load Mostly liquid refrigerant boils (evaporators) in the tubes as the heat load is absorbed, changing to vapor often with some superheat Section 3 The Mechanical Refrigeration Cycle

Pressure-Enthalpy Diagram Refrigeration Cycle Pc Saturated Condensing PRESSURE Ps SAT. LIQUID Saturated Suction SAT. VAPOR LIFT RE ENTHALPY Section 2 Basic Refrigeration Cycle

Basic System Components Hot Vapor 120 F 274.7 psia SDT Every system has four basic components Evaporator Compressor SST Air out: 59.7 F db / 57.3 F wb Compressor Raises the pressure from the evaporator pressure to the condensing temperature and creates a pressure differential to cause refrigerant flow 45 F 90.8 psia Evaporator 55 F 90.8 psia SET Air in: 80 F db / 67 F wb Cold Vapor Section 3 The Mechanical Refrigeration Cycle

Pressure-Enthalpy Diagram Refrigeration Cycle PRESSURE Pc Tc TEMP SAT. LIQUID Saturated Condensing SAT. VAPOR HEAD LIFT Ps Saturated Suction Ts RE COMP ENTHALPY Section 2 Basic Refrigeration Cycle

Compressor Suction Suction Line Causes flow by creating a low pressure area HCFC-22 90.8 psia & 45 F SST 90.8 psia & 55 F actual HFC-410A 144.5 psia & 45 F SST 144.5 psia & 55 F actual Actual is the temperature with superheat Section 3 The Mechanical Refrigeration Cycle

Compressor Discharge Hot Gas Line Suction Line HCFC-22 274.7 psia & 120 F SDT 274.7 psia & 170 F actual HFC-410A 431.6 psia & 120 F SDT 431.6 psia & 170 F actual HCFC-22 90.8 psia & 45 F SST 90.8 psia & 55 F actual HFC-410A 144.5 psia & 45 F SST 144.5 psia & 55 F actual High Side Compresses the vapor to raise the pressure and temperature above the condensing temperature Low Side Section 3 The Mechanical Refrigeration Cycle

Basic System Components Condenser 108 F 274.7 psia SCT Air out: 115 F db 120 F 274.7 psia SDT Every system has four basic components Evaporator 45 F 90.8 psia Evaporator Air in: 95 F Compressor SST Air out: 59.7 F db / 57.3 F wb 55 F 90.8 psia SET Air in: 80 F db / 67 F wb Compressor Condenser Rejects the heat from the load and system losses Highly superheated refrigerant condenses in the tubes as heat load is rejected and changes back to a liquid and is subcooled Section 3 The Mechanical Refrigeration Cycle

Pressure-Enthalpy Diagram Refrigeration Cycle Condenser Pc Saturated Condensing PRESSURE SAT. LIQUID SAT. VAPOR LIFT Ps Saturated Suction RE COMP ENTHALPY Section 2 Basic Refrigeration Cycle

Example Air-Cooled (HCFC-22) (HFC-410A) 95 F Air SCT 120 F R-22 R-410A 274 psia 432 psia Actual Condensing 180 F Actual Liquid 108 F Subcooling =? F Section 3 The Mechanical Refrigeration Cycle

Example Water-Cooled Condenser LEAVING DIFFERENCE Hot Gas Line To Tower 95 F 105 F SCT Liquid Line 100 F Actual From Tower 85 F Section 3 The Mechanical Refrigeration Cycle

The Metering Device TXV: Thermostatic Expansion Valve HCFC-22 274.7 psia & 120 F SCT 274.7 psia & 108 F actual High Side HCFC-22 90.8 psia & 45 F SET 90.8 psia & 45 F actual Low Side HFC-410A 431.6 psia & 120 F SCT 431.6 psia & 108 F actual TXV: - Controls the refrigerant flow rate - Reduces the pressure of the refrigerant gas - Refrigerant gas temperature is reduced Section 3 The Mechanical Refrigeration Cycle HFC-410A 144.5 psia & 45 F SET 144.5 psia & 45 F actual

Refrigeration Cycle with Subcooling Pc SUBCOOLING tc PRESSURE Ps TXV SAT. LIQUID ts SAT. VAPOR Vgs h fc RE ENTHALPY h gs Section 2 Basic Refrigeration Cycle

Refrigeration Cycle with Subcooling Pc SUBCOOLING tc PRESSURE Ps SAT. LIQUID ts SAT. VAPOR Vgs RE Superheat h fc ENTHALPY h gs Section 2 Basic Refrigeration Cycle

Compressor Energy SCT SAT. LIQUID 97 Heat Rejection Pressure SST 82 42 Reduced Lift Refrigerant Effect (Capacity) Compression SAT. VAPOR Enthalpy

Basic System Components Condenser 108 F 274.7 psia SCT Air out: 115 F db 120 F 274.7 psia SDT Every system has four basic components Evaporator 45 F 90.8 psia Evaporator Air in: 95 F Compressor Metering Device SST Air out: 59.7 F db / 57.3 F wb 55 F 90.8 psia SET Air in: 80 F db / 67 F wb Compressor Condenser Metering Device Regulates the flow and decreases the pressure from condensing pressure to evaporator pressure Section 3 The Mechanical Refrigeration Cycle

Refrigeration Lines Liquid Line Evaporator Coil Condenser Coil Hot Gas Line Suction Line Section 3 The Mechanical Refrigeration Cycle

Other System Components In addition to the four basic components, refrigeration systems may have other components that enhance system safety, performance, or reliability: System protectors Storage devices Performance devices System pressure regulators Valves and solenoids Temperature and pressure controls Oil controls Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories System Protectors Filter-Driers Normally in the liquid line and sometimes in the suction line Removes particles,water, acids, solids and sludge Sight Glasses Located in the liquid line Indicates moisture and is sometimes used to determine charge Mufflers Located in the hot gas line Reduces gas pulsations Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories Storage Devices Accumulators In the suction before the compressor Used on heat pumps and long line applications Protects against liquid returning to the compressor Receivers In the liquid line after the condenser Not often used in comfort air conditioning Stores refrigerant Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories Performance Devices Desuperheaters In the hot gas line after the condenser Used in some heat pump systems Heats water for domestic use Subcoolers In the liquid line after the condenser Uses water to cool the liquid refrigerant Reduces flash gas and increases efficiency Economizers Located in the liquid line Reduces flash gas and increases efficiency Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories System Pressure Regulators Outlet Crankcase Pressure In the suction line after the condenser Controls maximum outlet pressure Used primarily in lowtemperature refrigeration Prevents compressor overload Inlet Evaporator Pressure In the suction line Controls minimum pressure Used primarily in refrigeration with multiple evaporators Maintains consistent suction pressure Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories System Pressure Regulators Hot Gas Bypass Located between the hot gas discharge line and the TXV outlet Admits a small amount of gas back to the evaporator without going to the condenser Provides stable low load operation Head Pressure Control Located in the liquid line at the condenser outlet Regulates the condenser capacity by allowing refrigerant to flood the condenser tubes Provides stable low ambient operation Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories Refrigerant Valves Many locations Controls flow Holds refrigerant for capacity control, off-cycle charge control, and service Hand Solenoid Valves Check Valves Relief Valves Special (defrost/heat reclaim) Section 3 The Mechanical Refrigeration Cycle

Refrigeration Cycle Accessories Temperature and Pressure Controls Many locations in the system For system control and safety Oil Controls Located in the hot gas line Assures oil return to the compressors Not often used in comfort AC Section 3 The Mechanical Refrigeration Cycle

Heat Pump System A heat pump system has the same four basic components but adds a Reversing Valve and Accumulator Evaporator Compressor Condenser Metering Device (2) Reversing Valve Accumulator Section 3 The Mechanical Refrigeration Cycle

Heat Pump System Check Valve Ball Valve TXV OUTDOOR COIL Filter Drier 4-Way Valve Compressor INDOOR COIL Accumulator TXV Accurator Cooling Mode Section 3 The Mechanical Refrigeration Cycle

Heat Pump System Check Valve Ball Valve TXV OUTDOOR COIL Filter Drier 4-Way Valve Compressor INDOOR COIL Accumulator TXV Accurator Heating Mode Section 3 The Mechanical Refrigeration Cycle

Refrigeration Lines Liquid Line Evaporator Coil Condenser Coil Hot Gas Line Suction Line Section 3 The Mechanical Refrigeration Cycle

Indoor Coil Loading - Tons Per Circuit Refrigerant velocity must be high enough to keep compressor oil entrained with refrigerant vapor. EVAPORATOR AIRFLOW TXV Minimum tons/circuit: 3/8 tubes = 0.4 tons/circuit 5/8 tubes = 0.6 tons/circuit Refrigerant paths Section 3 System Components

Indoor Unit Refrigerant Circuits Single Circuit Distributor Dual Circuit Solenoid TXV LIQUID LINE LIQUID LINE TXV Filter Drier Distributor Section 2 System Basics

Tons Per Circuit Example Model # of coil splits # of circuits/splits # of circuits total 007 008 012 014 016 024 028 034 1 1 2 2 2 2 2 2 Standard Unloaded capacity, 7 tons ACCEPTABLE 7 tons/18 circuits = 0.4 tons/circuit With additional unloading Unloaded capacity, 3.3 tons TOO LOW! 3.3 tons / 18 circuits = 0.2 tons/circuit Add capacity control solenoid valve ACCEPTABLE 12 15 9 9 12 13 15 18 Now 3.3 tons / 9 circuits = 0.4 tons/circuit 12 15 18 18 24 26 30 36 Section 3 System Components

Elevation UNIT 012 014 016 024 LIQUID LINE 1-2 ton UNITS MAX ALLOW. LIFT (ft) 65 67 82 87 Max Allow. Pressure Drop (psi) LIQUID LINE Max Allow. Temp Loss ( F) 7 2 NOTE: Data above is for units at 45 F saturated suction and 95 F entering air. LIQUID LIFT Section 6 Installation

Suction Riser Refrigerant velocity in suction riser must be high enough to entrain compressor oil with the refrigerant Double suction riser or reduced diameter riser may be required Consult manufacturer s recommendations Section 6 Installation

Refrigerant Piping (6-10 Ton, R-22) UNIT SIZE Refer to manufacturer s recommendations DO NOT bury refrigerant piping underground! Section 6 Installation

Maximum Length of Refrigerant Piping Piping length depends on the application Heat pumps 100 linear feet Consult manufacturer s recommendations Section 6 Installation

Long Line Applications LONG LINE = 75 LINEAR FEET OR LONGER Lift vs. Run RUN Long Lines Require: 1.Liquid line solenoid valve(s) 2.Suction line accumulator(s) LIFT Section 6 Installation

Refrigerants

What is a Refrigerant A refrigerant is a fluid that absorbs heat and changes from vapor to liquid phase at reasonable pressures and temperatures as encountered in mechanical refrigeration. PRESSURE psia F Water HCFC-22 HFC-410A HFC-134a CO 2 Propane -40 0.00186 15.26 26 7.43 145.77 16.1 0 0.0185 38.73 64 21.62 305.80 38.4 40 0.122 82.28 132 49.70 567.50 78.6 100 0.950 210.70 340 138.80 X 188.6 130 2.225 311.60 500 213.40 X 273.3 212 14.696 *CP *CP 587.20 X X *Critical Point, pressure psia Section 3 The Mechanical Refrigeration Cycle

What Makes a Good Refrigerant Safe Efficient Stable Cost Effective Compatible Section 4 Refrigerants 1. Non-toxic and non-flammable 2. Reasonable operating pressures 3. Leakage resistance 4. Large heat of vaporization 5. Relatively low specific volume 6. Low liquid specific heat (reduced flash gas) 7. Easy to detect leaks 8. Compatible with oils (vapor side) 9. High coefficient of heat transfer 10. Easy to handle and cost effective 11. Non-corrosive and chemically stable 12. No Ozone Depletion Potential (ODP) or Global Warming Potential (GWP)

Summary Discussed mechanical refrigeration terms Described how heat is transferred and which methods are primarily used in the refrigeration cycle Described the four principles of the refrigeration process Explained the function of the four system components Listed characteristics of a good refrigerant Section 5 Summary

2012 RM ASHRAE Technical Conference This completes the presentation.