Energy Use in Refrigeration Systems...Energy Use in Refrigeration Systems PRESENTED BY: Scott Martin, PE, LEED AP BD+C 2013 Rocky Mountain ASHRAE Technical Conference Objectives •

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°


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


3. The temperature and energy required to change state are a function of pressure



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




4. Fluid flow only occurs if a pressure difference exists


Pressure Difference Creates Flow

Pressure

Vapor

Static Suction

Flow may be caused by: • Static pressure difference • Pressure difference • Mechanical work




4. Fluid flow only occurs if a pressure difference exists


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


LIFT


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


Compressor

120° F 274.7 psia

Hot Vapor

Cold Vapor

Air out: 59.7° F db / 57.3° F wb

Evaporator SET

SST

SDT


Evaporator

Compressor

45° F 90.8 psia

55° F 90.8 psia



HEADLIFT


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


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


Evaporator

Compressor

Condenser

45° F 90.8 psia

108° F 274.7 psia


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


LIFT


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



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


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


• 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

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


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.

Documents

Energy Use in Refrigeration Systems...Energy Use in Refrigeration Systems PRESENTED BY: Scott Martin, PE, LEED AP BD+C 2013 Rocky Mountain ASHRAE Technical Conference Objectives •