DESIGN AND VALIDATION OF A SOLAR DOMESTIC HOT WATER HEATING SIMULATOR

Department of Mechanical EngineeringBaylor University

Thomas Cemo

April 29, 2009

OUTLINE

Introduction

Background

Assumptions

Theory

Apparatus

Results

Conclusions

INTRODUCTION:GOALS

To accurately simulate efficiency ratings provided by the Solar Rating and Certification Corporation (SRCC).

To create a platform for testing modifications to domestic solar hot water heating systems.

BACKGROUND:DOMESTIC HOT WATER HEATING

The home is the second largest non-commercial consumer of energy, behind transportation.

14% to 25% of domestic energy is demanded by water heating.

Solar thermal water heating has a tremendous opportunity to reduce this demand.

BACKGROUND:SOLAR RATING AND CERTIFICATION

CORPORATION (SRCC)

Arab Oil Embargo of the 1970s Federal tax credits motivated a rush to hastily

install solar thermal systems. The market was flooded with poor designs and

craftsmanship.

Solar Rating and Certification Corporation (SRCC) Founded in 1980 Reassures consumers of quality products. Efficiency ratings will be used to validate our

hardware simulation.

BACKGROUND:DOUBLE TANK SYSTEMS

Double Tank System

Water is heated as it is circulated through a collector.

Energy is transferred to thermal storage and auxiliary heating if necessary.

Hot water is then drawn for domestic uses such as dishwashing.

ASSUMPTIONS: SOLAR DAY

How to accurately model the energy available during a typical day?

Standardized weather profile provided by the SRCC.

All calculations occur in an adjusted time frame known as Solar Time.

Solar Night Solar Day Solar Night

Insolation (Whr/m2)

THEORY: SOLAR ENERGY FACTOR

auxpar

del

QQ

QSEF

Qdel : Thermal energy delivered to the domestic hot water load.

Qpar : Energy required by parasitic devices such as pumps and controllers.

Qaux : Energy required by auxiliary resistive heating elements.

Average SEF:2.0 - 5.0

THEORY: QDEL DELIVERED ENERGY

Solar ‘Day’ Draw Schedule

THEORY:SOLAR FRACTION

SEF

EFSF 1

SF: Portion of hot water provided by solar energy.

EF: Energy factor for a conventional electric hot water heater (0.9).

SEF: Solar Energy Factor.

Average Solar Fractions:0.50 - 0.75

APPARATUS

Mains Chiller

Auxiliary Storage Tank

Solar Storage Tank

Solar Thermal Collector Simulator

APPARATUS: SOLAR THERMAL COLLECTOR SIMULATOR

(STCS)

Simulates thermal collector absorbing insolation during a solar day within 10% accuracy.

LabVIEW Control Software calculates the useful power from the simulated collector array.

Modified Seisco on-demand hot water heater.

Resistive heating elements deliver power to circulated water.

APPARATUS:LABVIEW CONTROL SOFTWARE

APPARATUS:LABVIEW CONTROL SOFTWARE

APPARATUS:MAINS CHILLER

Test conditions require 14°C.

Baylor water mains temperaturerange from 15°C to 22°C.

Closed loop that circulated water through 60ft of copper submerged in an ice bath.

19 gallons were cooled to 14°C in approximately 25 min.

Temperatures maintained within 0.4°C.

Pump controls

Ice bath

Chiller tank

RESULTS:DOUBLE TANK CONFIGURATION

Test SEF Difference

SRCC 3.0

Test 1 2.44 -18.6 %

Test 2 2.84 -5.5 %

Average 2.64 ± 0.043 -12 %

Solene Double Tank Drainback System

RESULTS:DOUBLE TANK CONFIGURATION

Test Parasitic (kJ) Time (hr) Auxiliary (kJ) Time (hr)

Test 1 3564 7.4 13,732 1.25

Test 2 3456 7.19 11,767 1.1

•Average Solar Fraction of 0.65•Solar Savings =30,155 kJ/day

•8.3 kWh/day•Average Electricity cost $0.13/kwh*

Yearly Savings: $388

auxpar

del

QQ

QSEF

* Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State, EIA

RESULTS:DOUBLE TANK CONFIGURATION

Double Tank TestSolar Tank Temperatures vs. Time

30

35

40

45

50

55

60

0 5 10 15 20

Time from start of test (hr)

Tan

k T

emps

(°C

)

Tlow in

Ttop suf

Solar Day

RESULTS:DOUBLE TANK CONFIGURATION

Double Tank TestAuxiliary Tank Temperature vs. Time

40

45

50

55

60

65

0 5 10 15 20

Time From Start (hr)

Tan

k T

emp

erat

ure

(°C

)

Solar Day

CONCLUSIONS

Constructed a test platform for future research into solar domestic water heating.

Calculated accurate and repeatable results verified by SRCC data.

Test SRCC BU

Double SEF 3.0 2.64 ± 0.043 -12 %

RECOMMENDATIONS

Incorporate a Differential Temperature Controller

Utilize location specific weather data

Construct an array of thermocouples to be inserted into the tanks.

ACKNOWLEDGMENTS

Departments of Mechanical and Electrical Engineering for providing the means to continue this research.

Dr. Van Treuren, Dr. Gravagne, and Dr. Lehr

Mr. Ashley Orr and Mr. Dan Hromadka

QUESTIONS?