Senior Design Team #18Senior Design Team #18

Lacey EdnoffLacey EdnoffBrianna BeconovichBrianna Beconovich

Jarimy PassmoreJarimy PassmoreJesse PoormanJesse Poorman

Presentation Overview Objective

Product Specifications

Design Concept

Component Analysis Theoretical & Experimental

Cost Analysis

Conclusion 3D Drawings & Bill of Materials

Future Plans

2

Objective Use the waste heat from a window AC unit to heat water in a 40 gallon tank

Heat the water initially from 70°F to 120°F in under 3 hours

Utilize customers existing 40 gal hot water heater

Working fluid is R-22

Assemble for less than $500

Commercially available parts

Easy installation & reproducible

3

External Heat Exchanger

CPVC piping

Coaxial Coil

System utilizes force convectionRequires a pumpMay need insulation

4

Douchette Model CX-H075

Pump

Component Analysis

Blue: Already performed, Red: To be performed prior to final presentation

5

Component Analysis Performed

AC Window Unit Minimum amount of heat required for system

External Heat Exchanger Analytical overall heat transfer coefficient, Experimentally measure mass flow rate, inlet and outlet Temperature & Pressure

Internal Heat Exchanger Analytical overall heat transfer coefficient, Experimentally measure mass flow rate, Inlet and outlet Temperature & Pressure

Piping & Fittings

Volumetric Flow rate, Velocity, Pressure Drop and Total Head

Pump System Curve for pump power

Table 1: System components to be analyzed

Selection of AC Window Unit Assumptions:

Hot water heater is well insulated i.e. no heat loss to surroundings All of the heat is transferred to the water

∆T : Temperature change equal to 50 °F

Cp : Specific Heat of Water

mh2o : Mass of water

ΔTCmQ poh 2

6

Total amount of heat transfer required to heat the water: Q = 16,667 BTUIn order to heat the water in 3 hours:

Final selection: Frigidaire Model Qdot = 8000 BTU/hr

7

Heat Transfer Assumptions The system is steady state

Closed system i.e. Heat loss from fluid 1 = heat gain by fluid 2

Thermal properties of the materials are constant

Air properties are constant and evaluated at the appropriate Temperatures

Resistance to heat flow within the copper tubing is negligible, so the temperature is uniform throughout

Goal is to determine if the chosen heat exchanger is sized correctly to efficiently transfer the heat from the R-22 fluid to the water

8

Heat Exchanger AnalysisRate of Heat transfer is governed by the overall Heat transfer coefficient, U

Compared the air-cooled system to the modified water-cooled systemMeasured Surface Temperatures of the AC unit System

Temp before and after condenser ( T

H

i

n

& T

H

o

u

t

) T

emp of ambient air and air after condenser( T

C

i

n

& T

C

o

u

t

)

For the Doucette CX-H075 Coaxial Coil Heat exchanger:Used manufactures operating Temperatures

Qdot UA LMTD( )

TH in

TC out

TH out

TC in

Fluid 1 (warm)

Fluid 2 (cold)

9

Volumetric Flow Rate for Water

TC

QV

pavg

Determined Volumetric Flow rate as function of ΔT Assumed a constant heat transfer rate Defined ΔT across the heat exchanger in increments of 5 deg

Piping Layout Divided into 3 sections due to difference

in in diameters of pump, heat exchanger, and hot water tank inlets

Section 1: Hot water heater to Heat exchanger ½” Schedule 40 CPVC

5 90 deg elbows

1 Ball valve

1”- ½” Reduction

Section 2: Heat Exchanger ½” - 5/8” Expansion

5/8”- 3/4” Expansion

Section 3: Heat exchanger back to Hot water tank ¾” Schedule 40 CPVC

4 90 deg elbows

10

1

3

2

11

Pressure drop across the piping

g

VK

D

fLz

g

V

g

Pz

g

V

g

PH

h 222

2

1

2

112

2

22

Assumptions:

For each section of piping Velocity remained constant

Modified Bernoulli Equation

The major and minor losses associated with each section of the piping were calculate individually to find the total pressure drop as a function of change in temperature

Used manufacture specifications for the pressure drop across the heat exchanger

This lead to the calculation of the total hydrostatic head which helped in determining an appropriate pump

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Hydrostatic Head as a function of Ball Valve Position

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4

Volumetric Flow (gpm)

Hea

d (

ft) System (a = 60 deg)

System (a = 50 deg)

System (a = 0 deg)

By changing the angle of the ball valve position, the head can be increased

Hydrostatic Head vs. Volumetric Flow

Pump Selection

Operatingpoint

RequiredPressure

Head

DesiredFlowRate

Pump curve was approximated from manufacture specsSelection based on cost and low volumetric flow rate

p/g

V

13

Cost AnalysisExternal Heat Exchanger Cost Analysis

Total Cost $421.46

$44.33 $8.98

$41.95

$97.20$169.00

$60.00 Fittings

Piping

Pump

Heat Exchanger

A/C Unit

R-22

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Conclusion

1 External Heat Exchanger2 ¾” CPVC elbow3 ½” CPVC elbow4 AC Unit5 Hot water heater6 Ball Valve7 ½” CPVC Pipe8 ½” Connector9 ¾” Connector10 1/2”-5/8”Compression Fitting 11 ¾”-5/8” Compression Fitting

15

Gnatt Chart

16

Future Plans Analysis of the internal heat exchanger design

Overall heat transfer coefficient, Inlet and Outlet Temperature of R-22

Length of tubing required

Mounting

Pump, A/C Unit

Thermostat

Assembly

Experimental Analysis of working Fluid R-22

Pressure, Temperature, Mass flow rate

Heat exchanger effectiveness, System efficiency

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References

Oak Ridge National Laboratory

http://www.ornl.gov/

Doucett Industries

http://www.doucettindustries.com

Janna, William. Design of Fluid Thermal Systems 2nd Edition. PWS Publishing Company 1998

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Special Thanks!!

Dr. Steve Van Sciver

Dr. Chang Shih

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