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Thermoelectric Heat Pump Geothermal Scale Model. E. Kimball Perley February 2013 ELM Senior Projects. What is Geothermal Heating?. Extracts heat from the ambient ground temperature Can be closed or open loop Can run off well water or an installed ground loop. Traditional Heat Pumps.

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Thermoelectric Heat Pump Geothermal Scale Model

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Thermoelectric Heat Pump Geothermal Scale Model

E. Kimball Perley

February 2013

ELM Senior Projects

What is Geothermal Heating?

• Extracts heat from the ambient ground temperature

• Can be closed or open loop

• Can run off well water or an installed ground loop

Expansion Valve

Evaporator

Heat moves from the hot side to the cold side, this is Q

Condenser

Compressor

The compressor is powered with electricity.

Thermoelectric Modules

• When a thermoelectic module is powered, it acts as a heat pump.

• One side becomes warmer and the other cooler based on the polarity of the power.

Heat moves from the hot side to the cold side, this is Q

The module is powered with electricity.

Hot Side

Cold Side

Ground Water

Coefficient of Performance

Q Heat Moved

COP =

Power into pump

Electric Heat has a natural COP of 1

Traditional Geothermal has a COP of >1

Thermoelectric COP is dependent on the operating range

The Advantages of Thermoelectrics

• No moving parts

• Ease of maintenance

• Quiet

• Scalable

• Ease of Installation

• Variable heat transfer

Client Requirements

• Table top scale model

• Uses a thermoelectric heat pump

• Takes heat from tap water at constant flow

• Transfers heat to hot water tank

• Maintains hot tank temperature at 100-110 Fahrenheit

• Controls the power to the thermoelectric module

System Diagram

Laptop

Water in

Sensor Box

T3

Flow regulator

T4

Flow out

Power Control Circuit

Cold

Thermoelectric

Module

T1

Hot Water Tank

T2

Software Design

• The entire system will be controlled by a Lab View user interface.

• The computer will both record all of the relevant data and calculate derived values such as power and COP

• The user will need to input some data and turn the system on and off

• The software will drive the module at a current dependent on the Dt of the system to increase performance.

Laptop

Sensor Box

Mechanical Design

• The system will use a module from HiZ

• The max hot water tank size based on this module is 1 liter

Water in

T3

Flow regulator

T4

Flow out

Cold

Thermoelectric

Module

T1

Hot Water Tank

T2

COP Requirements

Max DT for COP > 1; 34 C

Max DT for COP > 1 at 1.5 A

22C

Sizing Calculations

20 Watts = 20 J/s

20 J/s * .238cal/J = 4.78 cal/s

4.78 cal/s * 3600 s/h = 17208 cal/h

20 Watts

17208 cal/h / 1000ml/l = 17C/h

8 Watts

Moving 20 Watts of heat in an hour this module could raise the temperature of 1 liter of water by 17C.

Electrical Design

The National Instruments sensor box will power and read all four temperature sensors.

It will also use 0-5 Volts to drive the power control circuit for the module.

It will take readings of the power circuit to calculate the power being used.

These readings are all necessary for the COP and other calculations done by the software.

Sensor Box

Power Control Circuit

Thermoelectric

Module

T4

T2

T3

T1

Power Control Circuit

• A Power MOSFET transistor will control the flow of current through the Module.

• Increasing the Voltage into the Gate of the MOSFET allows more current to flow, increasing the power to the Module

Power Supply

(25 Watts)

Thermoelectric

Module

MOSFET

D

G

0-5v

Signal from NI sensor box

R

Resistor

S

Budget

Other components:

Power supply

NI USB 6008

Laptop Computer

Flow controllers

Micsleds, resistors, sensors, transistors, wiring