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Pressure Enthalpy without Tears. Presented by Eugene Silberstein Suffolk County Community College. HVAC EXCELLENCE EDUCATORS CONFERENCE Imperial Palace, Las Vegas, Nevada March 8-10, 2009. If we change the way we look at things, the things we look at change. LINES OF CONSTANT ENTHALPY.

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Slide1 l.jpg

Pressure Enthalpy

without Tears

Presented by

Eugene Silberstein

Suffolk County Community College

HVAC EXCELLENCE EDUCATORS CONFERENCE

Imperial Palace, Las Vegas, Nevada

March 8-10, 2009



Slide4 l.jpg

LINES OF CONSTANT ENTHALPY at change

LINES OF CONSTANT PRESSURE

Pressure

(psia)

PRESSURE DROPS

PRESSURE RISES

HEAT CONTENT DECREASES

HEAT CONTENT INCREASES

Heat Content

Btu/lb


Slide5 l.jpg

Pressure at change

(psia)

SATURATION CURVE

Heat Content

Btu/lb

Btu/lb


The saturation curve l.jpg
THE SATURATION CURVE at change

  • Under the curve, the refrigerant follows the pressure-temperature relationship

  • The left side of the saturation curve represents 100% liquid

  • The right side of the saturation curve represents 100% vapor

  • For non-blended refrigerants, one pressure corresponds to one temperature


Slide7 l.jpg

Pressure at change

(psia)

LINES OF CONSTANT TEMPERATURE

Heat Content

Btu/lb


Slide8 l.jpg

Pressure at change

(psia)

LINES OF CONSTANT VOLUME (ft3/lb)

Heat Content

Btu/lb


Slide9 l.jpg

Pressure at change

(psia)

LINES OF CONSTANT ENTROPY

Heat Content

Btu/lb


Slide10 l.jpg

Pressure at change

(psia)

LINES OF CONSTANT QUALITY

Heat Content

Btu/lb


Slide11 l.jpg

PUT IT ALL TOGETHER… at change

Pressure

(psia)

Heat Content

Btu/lb


Slide12 l.jpg

Pressure-Enthalpy (p-h) Diagram for R-12 (Simplified) at change

Pressure (psia)

160°F

140°F

221

120°F

172

100°F

132

80°F

99

60°F

72

40°F

52

20°F

36

0°F

24

12 2025 31 35 8 8 8 8 8 9 9 9 9 9 1 1 1 1 1

0 2 4 6 8 0 2 4 6 8 0 0 0 0 0

Enthalpy in btu/lb (Heat Content)

0 2 4 6 8


Slide13 l.jpg

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified) at change

Pressure (psia)

160°F

140°F

352

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

20°F

58

0°F

39

15 24 31 40 46

110

112

119

123

Enthalpy in btu/lb (Heat Content)


Slide14 l.jpg

Liquid at change

Vapor

High Pressure High Temperature

High Pressure High Temperature

Low Pressure Low Temperature

Low Pressure Low Temperature

Liquid

Vapor

CONDENSER

METERING DEVICE

COMPRESSOR

EVAPORATOR


Slide15 l.jpg

Subcooled Liquid at change

Saturated Refrigerant

Superheated Vapor

CONDENSER

METERING DEVICE

COMPRESSOR

EVAPORATOR


Slide16 l.jpg

Pressure at change

Subcooled Region

Superheated Region

Saturated Region

Heat Content


Slide17 l.jpg

Pressure at change

Heat Content


Slide18 l.jpg

Pressure at change

(psia)

Heat Content

Btu/lb


Slide19 l.jpg

Height Above Saturation at change

Saturation

VAPOR

LIQUID


Slide20 l.jpg

Saturation at change

VAPOR

LIQUID

Distance Below Saturation


Slide21 l.jpg

Pressure at change

(psia)

Heat Content

Btu/lb


Slide22 l.jpg

PUT IT ALL TOGETHER… at change

Pressure

(psia)

A

E

B

C

D

Heat Content

Btu/lb


Slide23 l.jpg

PUT IT ALL TOGETHER… at change

Pressure

(psia)

A

A

E

E

B

B

C

C

D

D

Heat Content

Btu/lb

E to A: CONDENSER (Including discharge and liquid line)

A to B: METERING DEVICE

B to C: EVAPORATOR

C to D: SUCTION LINE

D to E: COMPRESSOR


Slide24 l.jpg

A at change

E

D

NET REFRIGERATION EFFECT

The portion of the system that provides the desired cooling or conditioning of the space or products being treated.

B

C


Net refrigeration effect l.jpg
NET REFRIGERATION EFFECT at change

  • The larger the NRE, the greater the heat transfer rate per pound of refrigerant circulated

  • NRE is in the units of btu/lb

  • Cooling effect can be increased by increasing the NRE or by increasing the mass flow rate

  • The cooling effect can be decreased by decreasing the NRE or by decreasing the rate of refrigerant circulation through the system


Nre example l.jpg
NRE Example at change

  • Heat Content at point B = 35 btu/lb

  • Heat Content at point C = 85 btu/lb

  • NRE = C – B = 85 btu/lb – 35 btu/lb

    NRE = 50 btu/lb

  • Each pound of refrigerant can therefore hold 50 btu of heat energy

  • How many btu does it take to make 1 ton?


How many btu 1 ton l.jpg
How Many btu = 1 Ton? at change

  • 12,000 btu/hour = 1 Ton = 200 btu/min

  • From the previous example, how many lb/min do we have to move through the system to get 1 ton?

  • 200 btu/min/ton ÷ 50 btu/lb = 4 lb/min

  • We must circulate 4 pounds of refrigerant through the system every minute to obtain one ton of refrigeration

  • Mass Flow Rate Per Ton


Nre and mfr ton l.jpg
NRE and MFR/ton at change

  • The NRE determines the number of btu that a pound of refrigerant can hold

  • The larger the NRE the more btu can be held by the pound of refrigerant

  • As the NRE increases, the MFR/ton decreases

  • As the NRE decreases, the MFR/ton increases

  • NRE = Heat content at C – Heat content at B

  • MFR/ton = 200 ÷ NRE

  • Cool, huh?


Slide30 l.jpg

A at change

E

B

D

THE SUCTION LINE

The line that connects the outlet of the evaporator to the inlet of the compressor. This line is field installed on split-type air conditioning systems.

C


Suction line l.jpg
SUCTION LINE at change

  • The suction line should be as short as possible

  • The amount of heat introduced to the system through the suction line should be minimized

  • Damaged suction line insulation increases the amount of heat added to the system and decreases the system’s operating efficiency

  • Never remove suction line insulation without replacing

  • Seal the point where insulation sections meet


Slide32 l.jpg

A at change

E

E

B

D

D

C


Slide33 l.jpg

A at change

E

B

C

D

HEAT OF COMPRESSION

The quantity, in btu/lb that represents the amount of heat that is added to the refrigerant during the compression process.


Heat of compression hoc l.jpg
HEAT OF COMPRESSION (HOC) at change

  • The HOC indicates the amount of heat added to a pound of refrigerant during compression

  • As the pressure of the refrigerant increases, the heat content of the refrigerant increases as well

  • Heat gets concentrated in the compressor

  • As HOC increases, efficiency decreases

  • As HOC decreases, efficiency increases

  • HOC = Heat content at E – Heat content at D


Slide35 l.jpg

A at change

E

B

C

D

TOTAL HEAT OF REJECTION

The quantity, in btu/lb that represents the amount of heat that is removed from the system. THOR includes the discharge line, condenser and liquid line.


Total heat of rejection thor l.jpg
TOTAL HEAT OF REJECTION (THOR) at change

  • THOR indicates the total amount of heat rejected from a system

  • Refrigerant (hot gas) desuperheats when it leaves the compressor (sensible heat transfer)

  • Once the refrigerant has cooled down to the condensing temperature, a change of state begins to occur (latent heat transfer)

  • After condensing, refrigerant subcools

  • THOR = Heat content at E – Heat content at A

  • THOR = NRE + HOC


Subcooling flash gas l.jpg
SUBCOOLING & FLASH GAS at change

  • Subcooling is a good thing, right?

  • Flash gas is a good thing, right?

  • Are flash gas and subcooling related?

  • How can we tell?

  • Stay tuned...


Slide38 l.jpg

A at change

E

B

C

D

HIGH SUBCOOLING....

(Only a slight Exaggeration)

What happened to the amount of flash gas?


Slide39 l.jpg

A at change

E

B

C

D

LARGE AMOUNT OF FLASH GAS....

(Only a slight Exaggeration)

What happened to the subcooling?


Subcooling flash gas40 l.jpg
SUBCOOLING & FLASH GAS at change

  • Subcooling and flash gas are inversely related to each other

  • As the amount of subcooling increases, the percentage of flash gas decreases

  • As the percentage of flash gas increases, the amount of subcooling decreases


Slide41 l.jpg

A at change

E

High-side pressure

Low-side pressure

B

C

D

COMPRESSION RATIO

Determined by dividing the high side pressure (psia) by the low side pressure (psia)


Compression ratio l.jpg
COMPRESSION RATIO at change

  • Represents the ratio of the high side pressure to the low side pressure

  • Directly related to the amount of work done by the compressor to accomplish the compression process

  • The larger the compression ratio, the larger the HOC and the lower the system MFR

  • The larger the HOC, the lower the efficiency

  • Absolute pressures must be used


Absolute pressure l.jpg
ABSOLUTE PRESSURE at change

  • Absolute pressure = Gauge pressure + 14.7

  • Round off to 15, for ease of calculation

  • Example 1

    • High side pressure (psig) = 225 psig

    • High side pressure (psia) = 225 + 15 = 240 psia

    • Low side pressure (psig) = 65 psig

    • Low side pressure (psia) = 65 + 15 = 80 psia

    • Compression ratio = 240 psia ÷ 80 psia = 3:1


Low side pressure in a vacuum l.jpg
Low Side Pressure in a Vacuum? at change

  • First, convert the low side vacuum pressure in inches of mercury to psia

  • Use the following formula

     (30” Hg – vacuum reading) ÷ 2

  • Example

    • High side pressure = 245 psig

    • High side pressure (psia) = 245 + 15 = 260 psia

    • Low side pressure = 4”Hg

    • Low side (psia) = (30”hg – 4”Hg) ÷ 2 = 13 psia

    • Compression ratio = 260 ÷ 13 = 20:1


Meet tammy l.jpg
Meet Tammy… at change


Slide46 l.jpg

90 at changeth Floor

2 Lawyers + 1 Tammy = Wasted Time

2nd Floor


Tammy s 8 hour day l.jpg
Tammy’s 8-Hour Day at change

  • 9am – 10 am Work on 2nd Floor

  • 10am – 11am Walk up

  • 11am – 12 noon Work on 90th Floor

  • 12 noon – 1pm Walk down

  • 1 pm – 2pm Lunch

  • 2pm – 3 pm Work on 2nd Floor

  • 3 pm – 4 pm Walk up

  • 4pm – 5 pm Work on 90th Floor


Hmmmmmmmmmmmm l.jpg
Hmmmmmmmmmmmm at change

  • What if the law firm moves its 90th floor office to the 3rd floor?

  • How will this affect Tammy’s productivity?

  • Will she do more work? Less?

  • What the heck does this have to do with air conditioning?

  • How many licks does it take to get to the chocolaty center of a Tootsie Pop?


If tammy s office moves from the 90 th floor to the 3 rd floor we get something like this l.jpg
If Tammy’s office moves from the 90 at changeth floor to the 3rd floor, we get something like this….


Tammy s 8 hour day58 l.jpg
Tammy’s 8-Hour Day at change

  • 9:00 am – 10:00 am Work on 2nd Floor

  • 10:00 am – 10:05 am Walk up to 3rd Floor

  • 10:05 am – 11:05 noon Work on 3rd Floor

  • 11:05 am – 11:10 am Walk down to 2nd Floor

  • 11:10 am – 12:10 pm Work on 2nd Floor

  • 12:10 pm – 1:10 pm Lunch

  • 1:10 pm – 1:15 pm Walk up to 3rd Floor

  • 1:15 pm – 2:15 pm Work on 3rd Floor

  • 2:15 pm – 2:20 pm Walk down to 2nd Floor

  • 2:20 pm – 3:20 pm Work on 2nd Floor

  • 3:20 pm – 3:25 pm Walk up to 3rd Floor

  • 3:25 pm – 4:25 pm Work on 3rd Floor

  • 4:25 pm – 4:30 pm Walk down to 2nd Floor

  • 4:30 pm – 5:00 pm Work on 2nd Floor


Office comparison l.jpg

2 at changend Floor  90th Floor

4 hours of work

3 hours of walking up and down the stairs

1 hour lunch

Day ends on the 90th Floor

2nd Floor  3rd Floor

6 ½ hours of work

30 minutes of walking up and down the stairs

1 hour lunch

Day ends on the 2nd Floor

Office Comparison

Which is better?


Compression ratio60 l.jpg
COMPRESSION RATIO at change

  • Lower compression ratios  higher system efficiency

  • Higher compression ratios  lower system efficiency

  • The closer the head pressure is to the suction pressure, the higher the system efficiency, all other things being equal and operational


Causes of high compression ratio high side issues l.jpg
Causes of High Compression Ratio (High Side Issues) at change

  • Dirty or blocked condenser coil

  • Recirculating air through the condenser coil

  • Defective condenser fan motor

  • Defective condenser fan motor blade

  • Defective wiring at the condenser fan motor

  • Defective motor starting components (capacitor) at the condenser fan motor


Causes of high compression ratio low side issues l.jpg
Causes of High Compression Ratio (Low Side Issues) at change

  • Dirty or blocked evaporator coil

  • Dirty air filter

  • Defective evaporator fan motor

  • Dirty blower wheel (squirrel cage)

  • Defective wiring at the evaporator fan motor

  • Closed supply registers

  • Blocked return grill

  • Loose duct liner

  • Belt/pulley issues


Theoretical horsepower per ton l.jpg
THEORETICAL HORSEPOWER PER TON at change

  • Determines how much compressor horsepower is required to obtain 1 ton of cooling

  • The ft-lb is a unit of work

  • The ft-lb/min is a unit of power

  • 33,000 ft-lb/min = 1 Horsepower

  • The conversion factor between work and heat is 778 ft-lb/btu

  • 33,000 ft-lb/min/hp ÷ 778 ft-lb/btu =

    42.42 btu/min/hp


Theoretical horsepower per ton64 l.jpg
THEORETICAL HORSEPOWER PER TON at change

  • THp/ton = (MFR/ton x HOC) ÷ 42.42

  • For example, if we had a system that had an NRE of 50 and a HOC of 10, the THp/ton would be:

THp/ton = (200/NRE) x HOC ÷ 42.42

THp/ton = (200/50) x 10 ÷ 42.42

THp/ton = 4 x 10 ÷ 42.42

THp/ton = 40 ÷ 42.42

THp/ton = 0.94


Thp ton example l.jpg

5 TONS at change

1 TON

3.8 TONS

25 TONS

16 TONS

THp/ton Example

  • If we had a 20-Hp reciprocating compressor and the THp/ton calculation yielded a result of 2 hp/ton, what would the expected cooling capability of the system be?

20 TONS

3,492 TONS

10 TONS


What affects the thp ton number l.jpg
What Affects the THp/ton Number? at change

  • The Net Refrigeration Effect (NRE)

  • The Heat of Compression (HOC)

What Affects the NRE and HOC?

  • Suction pressure

  • Discharge pressure

  • Compression Ratio

  • Airflow through the coils

  • Blowers and fans

  • And so on, and so on, and so on, and so on….


Slide68 l.jpg

Get the Picture? at change


Mass flow rate of the system l.jpg
MASS FLOW RATE OF THE SYSTEM at change

  • The amount of refrigerant that flows past any given point in the system every minute

  • Not to be confused with MFR/ton

  • MFR/system is the actual refrigerant flow, while MFR/ton is the flow per ton

  • MFR/system can be found by multiplying the MFR/ton by the number of tons of system capacity, or

MFR/system = (42.42 x Compressor HP) ÷ HOC


Cool stuff l.jpg
COOL STUFF at change

  • As the HOC increases, the MFR/system decreases, and vice versa

  • As the Compression Ratio increases, the HOC increases

  • As head pressure increases, or as suction pressure decreases, the Compression Ratio increases

  • As the MFR/system decreases, the capacity of the evaporator, condenser and compressor all decrease

  • Let’s take a closer look…


Evaporator capacity l.jpg

Evaporator Capacity = MFR/system x NRE x 60 at change

Btu Lb Btu 60 Min

Hour Min Lb Hour

EVAPORATOR CAPACITY

  • A function of the MFR/system and the NRE

  • The MFR/system is in lb/min, the NRE is in btu/lb and the capacity of the evaporator is in btu/hour


Evaporator capacity72 l.jpg
EVAPORATOR CAPACITY at change

  • If the NRE or the MFR/system decreases, the evaporator capacity also decreases

  • The “60” is a conversion factor from btu/min to btu/hour, given that there are 60 minutes in an hour

  • Divide the evaporator capacity in btu/hour by 12,000 to obtain the evaporator capacity in tons


Condenser capacity l.jpg

Condenser Capacity = MFR/system x THOR x 60 at change

Btu Lb Btu 60 Min

Hour Min Lb Hour

CONDENSER CAPACITY

  • A function of the MFR/system and the THOR

  • The MFR/system is in lb/min, the THOR is in btu/lb and the capacity of the condenser is in btu/hour


Compressor capacity l.jpg

Compresser Capacity = MFR/system x Specific Volume at change

ft3 Lb ft3

Min Min Lb

COMPRESSOR CAPACITY

  • A function of the MFR/system and the Specific volume of the refrigerant at the inlet of the compressor

  • Calculated in cubic feet per minute, ft3/min


Coefficient of performance cop l.jpg
COEFFICIENT OF PERFORMANCE (COP) at change

  • The ratio of the NRE compared to the HOC, assuming a saturated cycle

  • If the cycle is not saturated, add the suction line heat to the HOC

  • If the HOC remains constant, any increases in NRE will increase the COP

  • If the NRE remains constant, any decrease in HOC will increase the COP

  • The COP is a contributing factor to the EER of an air conditioning system

  • COP is a unitless value


Cop example 1 l.jpg
COP EXAMPLE #1 at change

  • Heat content at point B = 35 btu/lb

  • Heat content at point C = 104 btu/lb

  • Heat content at point D = 104 btu/lb

  • Heat content at point E = 127 btu/lb

  • NRE = 104 btu/lb – 35 btu/lb = 69 btu/lb

  • HOC = 127 btu/lb – 104 btu/lb = 23 btu/lb

  • COP = 69 btu/lb ÷ 23 btu/lb = 3

  • Notice that the “3” has no units


Cop example 2 l.jpg
COP EXAMPLE #2 at change

  • Heat content at point B = 35 btu/lb

  • Heat content at point C = 105 btu/lb

  • Heat content at point D = 110 btu/lb

  • Heat content at point E = 140 btu/lb

  • NRE = 105 btu/lb – 35 btu/lb = 70 btu/lb

  • HOC = 140 btu/lb – 110 btu/lb = 30 btu/lb

  • SL superheat = 110 btu/lb – 105 btu/lb = 5 btu/lb

  • COP = [70 btu/lb] ÷ [30 btu/lb + 5 btu/lb] = 2


Energy efficiency ratio eer l.jpg
ENERGY EFFICIENCY RATIO (EER) at change

  • A ratio of the amount of btus transferred to the amount of power used

  • In the units of btu/watt

  • The conversion between btus and watts is 3.413

  • One watt of power generates 3.413 btu

  • For example, if a system required 50,000 btu of heat, 14,650 watts of electric heat (14.65 kw) can be used


Energy efficiency ratio eer cont d l.jpg
ENERGY EFFICIENCY RATIO (EER), Cont’d. at change

  • The efficiency rating of an air conditioning system is the COP

  • For each btu/lb introduced to the system in the suction line and the compressor, a number of btus equal to the NRE are absorbed into the system via the evaporator

  • To convert the COP to energy usage, we multiply the COP by 3.413


Eer example l.jpg
EER EXAMPLE at change

  • The NRE of a system is 70 btu/lb

  • The HOC of the same system is 20 btu/lb

  • The COP is 70 btu/lb ÷ 20 btu/lb = 3.5

  • The EER = COP x 3.413

  • EER = 3.5 x 3.413

  • EER = 11.95


Seasonal eer seer l.jpg
SEASONAL EER (SEER) at change

  • Takes the entire conditioning system into account

  • Varies depending on the geographic location of the equipment

  • Ranges from 10% t0 30% higher than EER

  • So, if the EER is 10, the SEER will range from 11 to 13


From the p h chart we can find l.jpg

Compression Ratio at change

NRE

HOC

HOW

THOR

COP

MFR/ton

THp/ton

MFR/system

Evaporator Capacity

Condenser Capacity

Compressor Capacity

EER of the System

SEER

From the P-H Chart, We Can Find

Okay, Okay, Okay… How do I plot one of these things?


An r 22 a c system l.jpg
An R-22 A/C System… at change

  • Condenser saturation temperature 120°F

  • Condenser outlet temperature 100°F

  • Evaporator saturation temperature 40°F

  • Evaporator outlet temperature 50°F

  • Compressor inlet temperature 60°F

  • Compressor Horsepower: 4 hp


Slide84 l.jpg

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified) at change

Pressure (psia)

180°F

160°F

140°F

352

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide85 l.jpg

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified) at change

Pressure (psia)

180°F

160°F

140°F

352

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide86 l.jpg

A at change

B

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified)

Pressure (psia)

180°F

160°F

140°F

352

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

C

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide87 l.jpg

A at change

B

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified)

Pressure (psia)

180°F

160°F

140°F

352

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

C

D

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide88 l.jpg

A at change

B

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified)

Pressure (psia)

180°F

160°F

140°F

352

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

C

D

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide89 l.jpg

A at change

B

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified)

Pressure (psia)

180°F

160°F

140°F

352

E

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

C

D

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


Slide90 l.jpg

A at change

B

High: 275 psia

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

Pressure-Enthalpy (p-h) Diagram for R-22 (Simplified)

Pressure (psia)

180°F

160°F

140°F

352

E

0.7

120°F

275

100°F

211

80°F

159

60°F

117

40°F

84

C

D

20°F

58

0°F

39

-20°F

25

-40°F

3 4 4 5 1 1 1 1 1

2 0 6 3

1 1 1 2 2

0 2 7 1 5

Enthalpy in btu/lb (Heat Content)


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HIGH SIDE PRESSURE (psia) at change

LOW SIDE PRESSURE (psia)

High: 275 psia

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

COMPRESSION RATIO

COMPRESSION RATIO = 275 psia ÷ 84 psia = 3.27:1


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

HEAT OF COMPRESSION

HEAT CONTENT AT “E” – HEAT CONTENT AT “D”

HEAT OF COMPRESSION= 125 btu/lb – 112 btu/lb = 13 btu/lb


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

NET REFRIGERATION EFFECT

HEAT CONTENT AT “C” – HEAT CONTENT AT “B”

NRE = 110 btu/lb – 40 btu/lb = 70 btu/lb


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

MASS FLOW RATE PER TON

200 ÷ NRE

MFR/ton = 200 ÷ NRE =200 ÷ 70 btu/lb = 2.86 lb/min/ton


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

TOTAL HEAT OF REJECTION

HEAT CONTENT AT “E” – HEAT CONTENT AT “A”

THOR = 125 btu/lb – 40 btu/lb = 85 btu/lb


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

THEORETICAL HORSEPOWER PER TON

[MFR/ton x HOC] ÷ 42.42

THp/ton = 2.86 lb/min/ton x 13 btu/lb ÷ 42.42 = 0.88 Hp/ton


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

COEFFICIENT OF PERFORMANCE

NRE ÷ [HOC + SL]

COP = [70 btu/lb] ÷ [15 btu/lb + 2 btu/lb] = 4.12


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

MASS FLOW RATE OF THE SYSTEM

[42.42 x Compressor HP] ÷ HOC

MFR/system = [42.42 x 4] ÷ 13 btu/lb = 13.05 lb/min


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

CAPACITY OF THE EVAPORATOR

NRE x MFR/system x 60

CAP/evap = 70 btu/lb x 13.05 x 60 = 54,810 btu/hour

CAP/evap = 54,810 btu/hour ÷ 12,000 btu/hour/ton = 4.57 tons


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

CAPACITY OF THE CONDENSER

THOR x MFR/system x 60

CAP/cond = 85 btu/lb x 13.05 x 60 = 66,555 btu/hour

CAP/cond = 66,555 btu/hour ÷ 12,000 btu/hour/ton = 5.55 tons


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

CAPACITY OF THE COMPRESSOR

MFR/system x Specific Volume

CAP/comp = 13.05 x 0.7 = 9.13 ft3/min


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High: 275 psia at change

Low: 84 psia

“A”: 40 btu/lb

“B”: 40 btu/lb

“C”: 110 btu/lb

“D”: 112 btu/lb

“E”: 125 btu/lb

ENERGY EFFICIENCY RATIO

COP x 3.413

EER = 4.67 x 3.413 = 15.94

SEER (low end) = 1.1 x EER = 1.1 x 15.94 = 17.5

SEER (high end) = 1.3 x EER = 1.3 x 15.94 = 20.7


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Heat Content “A” = 40 btu/lb at change

Heat Content “B” = 40 btu/lb

Heat Content “C” = 109 btu/lb

Heat Content “D” = 111 btu/lb

Heat Content “E” = 125 btu/lb

High side pressure = 267 psig

High side pressure = 282 psia

Low side pressure = 70 psig

Low side pressure = 85 psia

Compressor Hp = 2.5 Hp

Specific Volume = 0.7

NRE = 69 btu/lb

HOW = 14 btu/lb

HOC = 16 btu/lb

THOR = 85 btu/lb

Comp. Ratio = 3.32

MFR/ton = 2.9 lb/min/ton

THp/ton = 0.96 Hp/ton

COP = 4.3

MFR/system = 7.58 lb/min

CAP/evap = 31,381 btuh

CAP/cond = 38,658 btuh

CAP/comp = 5.3 ft3/min

EER = 14.68

SEER = 16.15 – 19.1

Properly Operating System

A/B C D E


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Heat Content “A” = 39 btu/lb at change

Heat Content “B” = 39 btu/lb

Heat Content “C” = 112 btu/lb

Heat Content “D” = 118 btu/lb

Heat Content “E” = 134 btu/lb

High side pressure = 226 psig

High side pressure = 241 psia

Low side pressure = 59 psig

Low side pressure = 74 psia

Compressor Hp = 2.5 Hp

Specific Volume = 0.9

NRE = 73 btu/lb

HOW = 16 btu/lb

HOC = 22 btu/lb

THOR = 95 btu/lb

Comp. Ratio = 3.26

MFR/ton = 2.74 lb/min/ton

THp/ton = 1.03 Hp/ton

COP = 3.3

MFR/system = 6.63 lb/min

CAP/evap = 29,039 btuh

CAP/cond = 37,791 btuh

CAP/comp = 5.97 ft3/min

EER = 11.26

SEER = 12.39 – 14.64

Clogged Cap Tube System

A/B C D E


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Contact Information... at change

Eugene Silberstein

Suffolk County Community College

1001 Crooked Hill Road

Brentwood, NY 11717

(631) 851-6897

E-mail: [email protected]


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