Arduino HVAC Temperature Controller

Objectives• To create a simulation of a Constant Air Volume Box with PWM

Floating Control (Duct)• To create a temperature controller that will control a simulated CAV

box HVAC unit. • To create a wiring diagram of the operating system.• Incorporate data logging into the system.

Devices and Control Points• Setpoint- User-Set Desired Temperature; Variable in simulation.• Controlled Devices- 12 V Fan and heating coil(s).• Control Point- Duct supply temperature in degrees Celsius.• Differential- Temperature difference in degrees Celsius between the

setpoint and the sensor temperature in the duct.• Controlled Variable- Temperature the sensor reads after coil in the

simulated CAV box duct.

Single Line Diagram

SD

C

ard

Display and Control unit

Ardruino

HeatingAnd Fan

Control

Ardruino

Display And

Data Logging Control

120V AcTo

12V DCAdapter

Computer

SD CardReader

Temperature Sensor, Heating and Fan Control Line

Display and Data Logging Control Line

USB

USB

Relay Board

TemperatureSensor

Heating CoilFan

Duct Unit

Arduino Code Explanations“Power” Code:

Arduino Code Explanationscon’t.

“Fan Code”

Arduino Code Explanationscon’t.

“Heat” Code:

Arduino Code Explanationscon’t.

“Temperature Sensor” Code:

Arduino Code Explanationscon’t

“Setpoint” Code:

Arduino Code Explanationscon’t

“Duty Cycle” Code:Example: • If ∆T > 10°C, Relay Closed for 10/10 seconds Coil Heating for 10/10 seconds. • If ∆T > 5°C, Relay Closed for 5/10 seconds, Coil Heating for 5/10 seconds. • If ∆T = 0°C, Relay Closed for 0/10 seconds, Coil Heating for 0/10 seconds.

Flow ChartPower Button

Fan Switch

Heat Coil Switch

Heat Delay

Coil Duty Cycle

SetpointTemperature Sensor

ON

ON

ON

ON ΔT

OFF

OFF

OFF

°C°C

Datalog Button

Data SD CARD

ON

OFF

Fan Knob

Fan Speed

0%-100%

Wiring DiagramDisplay and Control unit

LCD Display

Power Button

Pot Dial

LED’s

Menu Button

Fan Switch Heat Switch

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

“Heating”Arduino UNO

+5VGND

USB

A0A1A2A3A4A5 D0

D1D2D3D4D5D6D7D8D9

D10D11D12D13

“LCD Display”Arduino UNO

+5VGND

USB

A0A1A2A3A4A5 D0

D1D2D3D4D5D6D7D8D9

D10D11D12D1312V

DC

12

34

56

78

910

1516

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

All 220 Ohm

1112

1314

Datalog Button

220 Ohm

8

7

8

7

8

7

10k Ohm

6 5

6

5

6

5

10k Ohm

10k Ohm

4

3

2

1

4

3

2

1

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

220 Ohm

Temperature Sensor

1

2

3

1

2

3

1

2

1

2

10k Ohm

GN

DIN

4IN

3IN

2IN

1N

OC

OM

NC

NO

CO

MN

C

NO

CO

MN

C

NO

CO

MN

C

R4 R3 R2 R1

Relay Board

FanHeat xxx xxx

Heating Coil Fan

24VDC12VDC

Connection from LED’s to Arduino Board

Connection from LED’s to Arduino Board

Problems Encountered• Cooling system was extremely hard to simulate and replicate in a

small scale simulation, so we chose not to implement one. • Arduino voltages and currents were sometimes not sufficient for the

simulation so alternative sources of power were needed.• Staging the fan speed and heating coil together.

Frying an Arduino Board + Wifi Shield

• The 12V line that was supplying power to the fan was live during a test; it touched a chip on one of the Wifi-Shields.

• The USB connection from both the Shield + connected Arduino Board was instantly lost, never to be regained…

• Good Lesson for working with 5V electronics: NEVER HAVE LIVE 12V LINES NEAR THE COMPONENTS!