Solar-Assisted Water Heater

Chen, Cheng-Han

Yu, Ssu-Chieh

Motivation

• Solar Energy is “clean”

• It saves the money

• Solar-assisted water heat becomes more and more popular in low-latitude country

• It is quite safe

Background

• It heats water by solar energy

• It works during day time &with enough sun light

• Domestic

• Hotel

• School

• Other use

Schematic Diagram

Solar Collector

Two main kinds of solar collector

1. Flat-plate collectors

2. Evacuated tube collectors

Glazed Flat Plate Solar Collectors

• Moderate cost

• Higher temperature operation

• Can operate at mains water pressure

• Heavier and more fragile

Photo Credit: NRCan

Evacuated Tube Collectors

• Higher cost

• No convection losses

• High temperature

• Cold climates

• Fragile

• Installationcan be more complicated

• Snow is less of a problem

Photo Credit: NRCan

Photo Credit: Nautilus

Tube Developed and Manufactured in China

Solar Collectors Pros Cons

Flat-platecollectors

•Capable to deliver moderate

temperature hot water

•Lower cost when compared

with the evacuated tube

collectors

•Heavier collector weight

•Large wind load under wind

condition

•More susceptible to

blockage and leakage

•More complicated in

maintenance issue

Evacuatedtube

Collectors

•Lower heat loss to the

surrounding

•Capable to deliver to high

temperature water

•Lighter support structure

•Simplicity in maintenance

•Higher capital cost

compared with flat-plate

collector

Model Assumptions

• Steady State

• Close & Open Loop

• Consider Pressure Drop Loss

• Isolation in the tank

• Qin is averaged

Model Parameters

Results

• Efficiency is about 45-55%, which is close to the solar collector efficiency

• Outlet temperature is over 40C,which is enough for domestic use (34 C)

Conclusion• System performance highly depends on solar input (isolation level)

• System efficiency mostly depends on solar collector efficiency

• Ambient temperature is influential to thermal efficiency of the system

• Inlet flow rate is related to outlet temperature

• Pump works against the pressure drop

• Pressure drops is not important to system efficiency

• Good business model may help this industry grow faster

• The cost of the product is important to costumers due to electric bill they

may save after several years

• Control engineering is also important to this system

Future Work

• Exergy Balance

• Cost

• Geography

• Tilt angle

• Working fluid

Reference

• http://www.pipeflowcalculations.com/pressuredrop/index.htm

• http://www.builditsolar.com/References/Calculators/Collector/ColEfic.htm

• Solar water heating project analysis,

Retscreen international

• Solar thermal collector for water heating, Energy Efficiency Office, Electrical and Mechanical Services Department, HK

THANK YOU