Post on 24-Apr-2018
Energy Use in
Refrigeration Systems
PRESENTED BY:
Scott Martin, PE, LEED AP BD+C
2013 Rocky Mountain ASHRAE Technical Conference
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
Conduction – Transfer by contact
Convection – May be natural or forced transfer by density currents and fluid motion
Three Types of Heat Transfer
Radiation – Transfer by electromagnetic waves
Mechanical refrigeration uses the first two.
Convection
Conduction
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
42
132
100
32
0 180 0 10 100
Tem
pera
ture
°F
Enthalpy (Btu/lb)
212
Latent Heat Total Heat (Enthalpy) = Sensible Heat + Latent Heat
Change of State
212°F liquid 212°F gas
Latent heat cannot be
measured on a thermometer
Change of State
32° F
1 lb ice
32° F
Latent Heat of Fusion Latent Heat of Vaporization
970 Btu/lb
144 Btu/lb
Temperature-Enthalpy Plot Te
mpe
ratu
re °F
32
212
-144 1150 -176
970 Btu
Latent heat of fusion
Enthalpy (Btu/lb) (Sensible + Latent Heat)
0
Subcooled Solid
Example: R-718 (water) 1 pound at standard barometric pressure
180
Latent Heat of Vaporization
Superheat Saturated Vapor @ 212° F
Pressure is constant @14.7 psia
Superheated Vapor
@ 242° F
212° F Water
Superheat t2 – t1 = 30° F
Temperature-Enthalpy Plot Te
mpe
ratu
re °F
32
212
0.45 Btu/lb
Subcooled Liquid
Enthalpy (Btu/lb) 1150 1160
Condensation
Latent Heat of Vaporization
1 Btu/lb 970 Btu/lb
Superheated Vapor
242
-144 -176 0 180
Evaporation
Saturated Liquid
Saturated Vapor
NOTE: THERE IS NO TIME ON THIS SCALE
Rate of heat transfer Btu is a measure of quantity Btuh is a measure of quantity per unit of time (hour)
1 Ton of Ice
144 Btu ∗ 2000 lb = 288,000 Btu
200 Btu 1 Min
1 Day 288,000 Btu
12,000 Btu 1 hour
Latent heat of fusion
1 “Ton” = 12,000 Btuh
70° 212°
No Flow
Four Laws of System Operation
Heat only moves from higher temperature to a lower temperature
The greater the difference the greater the flow
70° 70°
70°
32°
70°
Four Laws of System Operation
71° F
70° F
1 Btu / lb
Sensible Heat 1. Heat only moves from a higher temperature to a lower temperature
Four Laws of System Operation Latent Heat
Saturated Vapor 212° F
212° F
970 Btu/lb
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
Change of state occurs at a constant temperature
Four Laws of System Operation
3. The temperature and energy required to change state are a function of pressure
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
Pressure Affects the Boiling Point
960 Btu/lb
5 psig
227° F
50 psig
298° F
912 Btu/lb
212° F
0 psig
970 Btu/lb
If we control the pressure, we control the boiling point
Measuring Pressure Absolute Pressure Scales Compared
MERCURY
PRES
SUR
E
PRES
SUR
E 12.23 psia (5000 ft above sea level) 24.9 in. Hg
14.696 psia 29.921 in. Hg (sea level)
0 psia 0 in. Hg (no atmosphere)
0 psig = 14.696 psia
psia in. Hg Abs
Refrigerant Boiling Points
-40° F
Water
HFC-134a
HCFC-22
HFC-410A
212° F
-15° F
-41° F
-62° F
3. The temperature and energy required to change state are a function of pressure
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
4. Fluid flow only occurs if a pressure difference exists
Four Laws of System Operation
Pressure Difference Creates Flow
Pressure
Vapor
Static Suction
Flow may be caused by: • Static pressure difference • Pressure difference • Mechanical work
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
Four Laws of System Operation
The Mechanical Refrigeration Cycle
Four Components Are Required
4. Pressure/ flow control
valve 2. Vapor pump
1. Heat absorbing section
3. Heat rejecting section
An Open Cycle Refrigerant Under Pressure
R410a
-60.8°F
14.7 psia
The Closed Cycle
Compressor Condenser
Evaporator
Metering Device
2-Pressure Zone
Condenser (Rejects Heat)
Hot Gas Line
45° F / 90.8 psia
Typical conditions at peak load for: HCFC-22 HFC-410A
High Side Metering Device
Compressor
Suc
tion
Line
Low Side
120° F / 274.7 psia 120° F / 431.6 psia
45° F / 144.5 psia
Evaporator (Absorbs Heat)
Pressure-Enthalpy Diagram Refrigeration Cycle
LIFT
Saturated Condensing
Saturated Suction
PR
ES
SU
RE
RE
Pc
Ps
ENTHALPY
The Evaporator Absorbs Heat
Liquid and Vapor
All Vapor
60° F
80° F
Air out: 59.7° F db / 57.3° F wb
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
Basic System Components
Cold Mixture
Cold Vapor Evaporator
45° F 90.8 psia SET
Every system has four basic components
Evaporator
55° F 90.8 psia
Air in: 80° F db / 67° F wb
Pressure-Enthalpy Diagram Refrigeration Cycle
LIFT
Saturated Condensing
Saturated Suction
PR
ES
SU
RE
RE
Pc
Ps
ENTHALPY
Raises the pressure from the evaporator pressure to the condensing temperature and creates a pressure differential to cause refrigerant flow
Basic System Components
Compressor
120° F 274.7 psia
Hot Vapor
Cold Vapor
Air out: 59.7° F db / 57.3° F wb
Evaporator SET
SST
SDT
Every system has four basic components
Evaporator
Compressor
45° F 90.8 psia
55° F 90.8 psia
Air in: 80° F db / 67° F wb
Pressure-Enthalpy Diagram Refrigeration Cycle
HEADLIFT
Saturated Condensing
Saturated Suction
PR
ES
SU
RE
TEM
P
RE
Pc
Ps
ENTHALPY
COMP
Ts
Tc
Compressor Suction
Causes flow by creating a low pressure area
Suction Line
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
Compressor Discharge
Hot Gas Line Suction Line
High Side Low Side Compresses the vapor
to raise the pressure and temperature above the
condensing temperature
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
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
Evaporator
55° F 90.8 psia
Basic System Components
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 SET
SST
SDT SCT
Every system has four basic components
Evaporator
Compressor
Condenser
45° F 90.8 psia
108° F 274.7 psia
Air in: 80° F db / 67° F wb
Air out: 59.7° F db / 57.3° F wb
Compressor Air in: 95° F
Air out: 115° F db Condenser
120° F 274.7 psia
Pressure-Enthalpy Diagram Refrigeration Cycle
LIFT
Saturated Condensing
Saturated Suction
PR
ES
SU
RE
RE
Pc
Ps
ENTHALPY
COMP
Condenser
Actual Liquid 108° F
Example – Air-Cooled
(HCFC-22) (HFC-410A) 95° F Air
R-410A R-22
Actual Condensing
180° F SCT 120° F
Subcooling = ? °F
LEAVING DIFFERENCE
Example – Water-Cooled Condenser
Liquid Line
Hot Gas Line
100° F Actual
105° F SCT
To Tower 95° F
From Tower 85° F
HCFC-22 90.8 psia & 45° F SET 90.8 psia & 45° F actual
The Metering Device TXV: Thermostatic Expansion Valve
High Side Low Side
HFC-410A 144.5 psia & 45° F SET 144.5 psia & 45° F actual
HCFC-22 274.7 psia & 120° F SCT 274.7 psia & 108° F actual
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
Refrigeration Cycle with Subcooling
SUBCOOLING
ts
tc
hfc hgs
PR
ES
SU
RE
ENTHALPY
Pc
Ps Vgs
RE
TXV
Refrigeration Cycle with Subcooling
SUBCOOLING
ts
tc
hfc hgs
PR
ES
SU
RE
ENTHALPY
Pc
Ps Vgs
RE Superheat
SAT. LIQUID
SAT. VAPOR
Refrigerant Effect (Capacity)
Heat Rejection
Enthalpy
SCT
Reduced Lift
Pres
sure
42
82
97
SST
Compressor Energy
Basic System Components
Air in: 80° F db / 67° F wb
Air out: 59.7° F db / 57.3° F wb
Evaporator
Compressor
120° F 274.7 psia
Air out: 115° F db Condenser
108° F 274.7 psia
Metering Device
Air in: 95° F
SET
SST
SDT SCT
Every system has four basic components
Regulates the flow and decreases the pressure from condensing pressure to evaporator pressure
Metering Device
Evaporator
Compressor
Condenser
45° F 90.8 psia
55° F 90.8 psia
Suction Line
Hot Gas Line
Refrigeration Lines Liquid Line
Evaporator Coil
Condenser Coil
Other System Components
• System protectors
• Storage devices
• Performance devices
• System pressure regulators
• Valves and solenoids
• Temperature and pressure controls
• Oil controls
In addition to the four basic components, refrigeration systems may have other components that enhance system safety, performance, or reliability:
• Filter-Driers – Normally in the liquid line
and sometimes in the suction line • Removes particles,water, acids, solids and sludge
Refrigeration Cycle Accessories System Protectors
• 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
• Receivers – In the liquid line after the condenser – Not often used in comfort air conditioning
• Stores refrigerant
• Accumulators – In the suction before the compressor – Used on heat pumps and long line applications
• Protects against liquid returning to the compressor
Refrigeration Cycle Accessories Storage Devices
Performance Devices
Refrigeration Cycle Accessories
• 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
• Outlet Crankcase Pressure – In the suction line after the condenser – Controls maximum outlet pressure – Used primarily in low-
temperature 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
System Pressure Regulators
Refrigeration Cycle Accessories
• 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
Refrigeration Cycle Accessories
• 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
System Pressure Regulators
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)
– Many locations in the system – For system control and safety
Refrigeration Cycle Accessories
Oil Controls – Located in the hot gas line – Assures oil return to the compressors – Not often used in comfort AC
Temperature and Pressure Controls
Heat Pump System A heat pump system has the same four basic components
but adds a Reversing Valve and Accumulator
Accumulator
Evaporator
Compressor
Condenser
Metering Device (2)
Reversing Valve
Heat Pump System
Cooling Mode
Accumulator
Compressor
4-Way Valve
Filter Drier
OU
TDO
OR
CO
IL IN
DO
OR
CO
IL
Accurator
TXV
TXV
Check Valve Ball Valve
Heat Pump System
Heating Mode
Accumulator
Compressor
4-Way Valve
Filter Drier
OU
TDO
OR
CO
IL IN
DO
OR
CO
IL
Accurator
TXV
TXV
Check Valve Ball Valve
Suction Line
Hot Gas Line
Refrigeration Lines Liquid Line
Evaporator Coil
Condenser Coil
Refrigerant velocity must be high enough to keep compressor oil entrained with refrigerant vapor.
Refrigerant paths
TXV
Indoor Coil Loading - Tons Per Circuit
Minimum tons/circuit: 3/8” tubes = 0.4 tons/circuit 5/8” tubes = 0.6 tons/circuit
Indoor Unit – Refrigerant Circuits Single Circuit
TXV
LIQUID LINE
Distributor
LIQUID LINE
TXV
Filter Drier
Solenoid
Distributor
Dual Circuit
With additional unloading – Unloaded capacity, 3.3 tons 3.3 tons / 18 circuits = 0.2 tons/circuit
Standard – Unloaded capacity, 7 tons 7 tons/18 circuits = 0.4 tons/circuit
Add capacity control solenoid valve Now 3.3 tons / 9 circuits = 0.4 tons/circuit
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
12 15 9 9 12 13 15 18
12 15 18 18 24 26 30 36
Tons Per Circuit Example
ACCEPTABLE
TOO LOW!
ACCEPTABLE
Elevation LIQUID LINE – 1-2 ton UNITS
UNIT MAX
ALLOW. LIFT (ft)
LIQUID LINE
Max Allow. Pressure
Drop (psi)
Max Allow.
Temp Loss (°F)
012 014 016 024
65 67 82 87
7 2
NOTE: Data above is for units at 45° F saturated suction and 95° F entering air.
LIQUID LIFT
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
Refrigerant Piping (6-10 Ton, R-22)
DO NOT bury refrigerant piping underground! Refer to manufacturer’s recommendations
UNIT SIZE
Maximum Length of Refrigerant Piping
• Piping length depends on the application
• Heat pumps – 100 linear feet
• Consult manufacturer’s recommendations
Long Lines Require: 1.Liquid line solenoid valve(s)
LONG LINE = 75 LINEAR FEET OR LONGER
Lift vs. Run
Long Line Applications
LIFT
2.Suction line accumulator(s)
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 CO2 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
What Makes a Good Refrigerant
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)
Safe • Efficient • Stable • Cost Effective • Compatible
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
2013 RM ASHRAE Technical Conference
Thank You This completes the presentation.