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Energy Use in Refrigeration Systems

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Energy Use in Refrigeration Systems 2012 Rocky Mountain ASHRAE Technical Conference EnergyEnergy UseUse inin RefrigerationRefrigeration SystemsSystems 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 212 132 100 42 Temperature °F 32 0 0 10 100 180 Enthalpy (Btu/lb) Section 2 – Basic Principles Latent Heat TotalTotal HeatHeat (Enthalpy)(Enthalpy) == SensibleSensible HeatHeat ++ LatentLatent HeatHeat 212°F liquid 212°F gas Latent heat cannot be measured on a thermometer Change of State Section 2 – Basic Principles Change of State Latent Heat of Fusion Latent Heat of Vaporization 1 lb ice 32° F 970 Btu/lb 32° F 144 Btu/lb Section 2 – Basic Principles Temperature-Enthalpy Plot Example: R-718 (water) 1 pound at standard barometric pressure 212 Latent Heat of d Latent heat i Vaporization iqu of fusion L Temperature °F 970 Btu 32 e Ic Subcooled Solid -176 -1440 180 1150 Enthalpy (Btu/lb) (Sensible + Latent Heat) Section 2 – Basic Principles Superheat Saturated Vapor Pressure is constant @ 212 F @14.7 psia Superheated Vapor @ 242 F 212° F Water Superheat t2 –t1 = 30 F Section 2 – Basic Principles Temperature-Enthalpy Plot 242 Superheated r Saturated o Liquid Vapor ap V 212 Latent Heat of d Saturated i Vaporization Vapor Subcooled iqu Liquid L Condensation Evaporation Temperature °F 32 e c 1 Btu/lb 970 Btu/lb 0.45 I Btu/lb -176-144 0 180 1150 1160 Enthalpy (Btu/lb) NOTE: THERE IS NO TIME ON THIS SCALE Section 2 – Basic Principles 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” = 12,000 Btu 1 hour 1 Ton of Ice 12,000 Btuh 200 Btu 1 Min Latent heat of fusion 144144 BtuBtu 20002000 lblb == 288,000288,000 BtuBtu Section 2 – Basic Principles Four Laws of System Operation No Flow 70 70 Heat only moves from S higher temperature to om e a lower temperature 70 Flow Mor 32 e The greater the difference 21270 Flow the greater the flow 70 Section 2 – Basic Principles Four Laws of System Operation 1. Heat only moves from a Sensible Heat higher temperature to a lower temperature 71 F 70 F 1 Btu / lb Section 2 – Basic Principles Four Laws of System Operation 1. Heat only moves from a Latent Heat higher temperature to a lower temperature Saturated Vapor 2. A large amount of energy 212 F is required to change the Change of state of matter 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 Water 212° F HFC-134a -15° F HCFC-22 -41° F -40 F HFC-410A -62° F 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 4. Fluid flow only occurs if a pressure difference exists 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 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 4. Fluid flow only occurs if a pressure difference exists Section 2 – Basic Principles The Mechanical Refrigeration Cycle Four Components Are Required 3. Heat rejecting section 4. Pressure/ flow control 2. Vapor valve pump 1. Heat absorbing section Section 3 – The Mechanical Refrigeration Cycle An Open Cycle Refrigerant Under Pressure 14.7 R I psia A 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 120° F / 431.6 psia at peak load for: 120° F / 274.7 psia HCFC-22 Condenser HFC-410A (Rejects Heat) Hot Gas Line Compressor High Side Metering Low Side Device Evaporator (Absorbs Heat) Suction Line 45° F / 90.8 psia 45° F / 144.5 psia Section 3 – The Mechanical Refrigeration Cycle Pressure-Enthalpy Diagram Refrigeration Cycle Saturated Condensing Pc . R T O A P S A V . D LIFT T I A U S Q I L PRESSURE Saturated Suction Ps RE ENTHALPY Section 2 – Basic Refrigeration Cycle The Evaporator Absorbs Heat 60° F Liquid and Vapor R All Vapor AI 80° F Section 3 – The Mechanical Refrigeration Cycle Basic System Components Every system has four basic components Evaporator Absorbs the heat from the space or the load Mostly liquid refrigerant boils (evaporators) in the tubes as the heat load is absorbed, Air out: 59.7° F db / 57.3° F wb changing to vapor often Cold with some superheat Mixture 55° F 45° F 90.8 psia 90.8 psia SET Cold Evaporator Vapor Air in: 80° F db / 67° F wb Section 3 – The Mechanical Refrigeration Cycle Pressure-Enthalpy Diagram Refrigeration Cycle Saturated Condensing Pc . R T O A P S A V . D LIFT T I A U S Q I L PRESSURE Saturated Suction Ps RE ENTHALPY Section 2 – Basic Refrigeration Cycle Basic System Components Hot Vapor Every system has four 120° F basic components 274.7 psia SDT Evaporator Compressor Compressor Raises the pressure from the evaporator SST pressure to the condensing temperature and creates a pressure differential to Air out: 59.7° F db / 57.3° F wb cause refrigerant flow 55° F 45° F 90.8 psia 90.8 psia SET Cold Evaporator Vapor Air in: 80° F db / 67° F wb Section 3 – The Mechanical Refrigeration Cycle Pressure-Enthalpy Diagram Refrigeration Cycle Saturated Condensing Pc . Tc R T O A P S A V . D HEAD T I A U TEMP S LIFT Q I L PRESSURE Saturated Suction Ps Ts RE COMP ENTHALPY Section 2 – Basic Refrigeration Cycle Compressor Suction Suction Line HCFC-22 90.8 psia & 45° F SST CausesCauses flowflow byby 90.8 psia & 55° F actual creatingcreating aa lowlow HFC-410A pressurepressure areaarea 144.5 psia & 45° F SST 144.5 psia & 55° F actual ActualActual isis thethe temperaturetemperature withwith superheatsuperheat Section 3 – The Mechanical Refrigeration Cycle Compressor Discharge Hot Gas Line Suction Line HCFC-22 HCFC-22 274.7 psia & 120° F SDT 90.8 psia & 45° F SST 274.7 psia & 170° F actual 90.8 psia & 55° F actual HFC-410A HFC-410A 431.6 psia & 120° F SDT 144.5 psia & 45° F SST 431.6 psia & 170° F actual 144.5 psia & 55° F actual High Side Low Side CompressesCompresses thethe vaporvapor toto raiseraise thethe pressurepressure andand temperaturetemperature aboveabove thethe condensingcondensing temperaturetemperature Section 3 – The Mechanical Refrigeration Cycle Basic System Components Condenser Air out: 115° F db Every system has four 108° F 120° F basic components 274.7 psia 274.7 psia SCT SDT Evaporator Air in: 95° F Compressor Compressor SST Condenser Air out: 59.7° F db / 57.3° F wb Rejects the heat from the load and system losses Highly superheated refrigerant 55° F condenses in the tubes as heat load is 45° F 90.8 psia 90.8 psia SET rejected and changes back to a liquid and is subcooled Evaporator Air in: 80° F db / 67° F wb Section 3 – The Mechanical Refrigeration Cycle Pressure-Enthalpy Diagram Refrigeration Cycle Condenser Saturated Condensing Pc .
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