Hvac Experiment 4o1a2l

German Jordanian University School of Applied Technical Sciences Mechatronics Engineering Department ME 3431 Automatic Control systems Lab

EXPERIMENT 9 HVAC Trainer

Objectives:  

To be familiar with HVAC system. Control the temperature of the system using both On/Off, and PI controller.

Introduction: HVAC stands for “Heating, Ventilation and Air Conditioning”, three functions often combined into one system in today's modern homes and buildings. Warmed or cooled or dehumidified air flows through a series of tubes - called ducts - to be distributed to all the rooms of the building. The principles of Heating, Ventilation, and Air Conditioning (HVAC) are based on: a. Thermodynamics b. Fluid mechanics c. Heat transfer HVAC trainer that is used in this experiment, consist of plexiglass duct, with a heater in one end and a blower in the other end. The heater is a halogen lamp and the blower is a variable-speed fan. There is a thermistor sensor placed inside the duct to measure the temperature of the chamber and another thermistor sensor outside the chamber to measure the room temperature.

Figure1 : Heating and Ventilation Trainer (HVAC)

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The temperature measured at the thermistor inside the chamber is to be controlled using the heater voltage while the fan is ran at a constant speed. Heat is transferred to the thermistor by radiation from the heater and by convection from the air stream. Radiative heat transfer is highly nonlinear and it is therefore difficult to model the system by first principles. As a result, empirical tuning will be used to control the system. This heat transfer plant is very similar to the systems that are used to control wafer temperature in semiconductor manufacturing. HVAC Trainer Components: The components comprising the Heating and Ventilation Trainer are labeled in Figure 2, and described in Table 1.

Figure2 : HVAC Chamber Components

Table 1

ID # 1 2 3 4 5

Description Halogen light bulb (heater) Fan: The blower is a 24-Volt variable-speed fan (For Cooling) Thermistor chamber temperature sensor Chamber (Duct) Thermistor ambient temperature sensor

In this experiment, two types of control will be used:  On/Off Control  PI control

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PART I : ON/OFF CONTROL

On-off control is one of the simplest control types. It is usually used in many basic controls, such as heating and cooling buildings to regulate temperature. In this experiment, on/off controller will be used to control the temperature inside the chamber. In the loop used in HVAC, a temperature sensor continuously measures the temperature inside the chamber. This continuous measurement is critical because it allows the HVAC system to react to disturbances to maintain a stable temperature.

Principle of Operation: The HVAC system is activated when the temperature outside is outside the desired range, and deactivate while within the range. The heater is switched on when the temperature is lower than the desired value, and switched off when the temperature is higher than the desired value. A block diagram of a system with relay is shown in Figure 3.

Figure3 : Block Diagram of the Heater System

To perform this control process, a sensor measures the current temperature and compare it to the set point. And so, the HVAC system would turn on or off to reach this point. This is one of the simplest temperature control systems. However, this type of controller generally produces oscillations in the output; meaning that room’s temperature goes too high and too low continuously, this could be avoided by using PID based control.

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HVAC Trainer’s Interface ( Front ): The HVAC On-Off Control virtual instrument implements a relay to control the temperature of the chamber. This instrument can also be used to model the dynamics between the heater voltage and the temperature. Table 2 lists and describes the main elements of the HVAC On-Off Control virtual instrument’s interface. Every element is uniquely identified through an ID number as located in Figure 4.

16 14 1 3

2

17

15

12

4 5 6 7 8

13

9 10 11

Figure4 : HVAC On/Off Control Interface

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Table 2: HVAC On/Off Control Interface Components

ID # 1

Label Chamber Temp.

Symbol Tc

2

Ambient Temp.

Ta,m

3

Ta

4

Calibrate

5

Signal Type

6

Amplitude

7

Frequency

8

Offset

9 10 11

Vh_amp Vh_off Δ Th

Vh,amp Vh,off Δ Th

12

Temperature

Tc , Tr

13 14 15 16 17

Voltage Device Sampling Rate Stop Heater OFF

Vh

Description Temperature inside chamber numeric display. Temperature outside chamber numeric display (i.e. measured room temperature). Latched ambient temperature that is added to reference temperature from Signal Generator. Sets the red latched ambient temperature to the measured ambient temperature. Type of signal generated for the input voltage signal. Generated temperature reference signal amplitude input box. Generated temperature reference signal frequency input box. Generated temperature reference signal offset input box. Heater voltage amplitude input box. Heater voltage relay offset input box. Heater relay width. Scope with reference temperature (in blue) and measured chamber temperature (in red). Scope with applied heater voltage (in red). Selects the NI DAQ device. Sets the sampling rate of the VI. Stops the LabVIEW VI from running. Enables heater when pressed in.

Unit ⁰C ⁰C ⁰C

⁰C Hz ⁰C V V ⁰C ⁰C V V

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Procedure: a. Calibration After Powering up ELVIS, and before running any of the labs, follow this procedure to calibrate the system. 1. Open the QNET_HVACT_On_Off_Control.vi. 2. The cooling fan is automatically activated when the “Prototyping Board Power” (on the ELVIS unit) is switched on. 3. Make sure the correct Device is chosen. 4. Run the QNET_HVACT_On_Off_Control.vi.by pressing the arrow symbol below the menu bar. 5. Let the actual temperature Tc in the temperature scope settle, then adjust the temperature scope scales to see both the actual temperature signal. 6. Calibrate the temperature sensors by clicking on the Calibrate button. This will align the chamber temperature ,Tc, to the measured ambient temperature, Ta.

b. On/Off Control After calibrating, the control will be activated by pressing on Heater OFF button.

Exercise 1: Fixed Set-Point 1. Click on Heater OFF button, to activate control. 2. Examine the actual temperature (in red), and reference temperature (in blue) responses in the Temperature (C) scope, and observe the voltage scope with time. 3. Export both Temperature & Voltage charts with time. (Right-Click on each chart, then choose “Export >> Export simplified image”. 4. Find both upper & lower limits, using the saved charts. Upper Limit = -------------------------, Lower Limit = ----------------------5. Vary the relay width (ΔTh) from control parameter section between 0.01 to 1 ⁰C. Observe the Temperature chart, what do you notice on the upper & lower limits?

6. Vary the offset in the signal generator gradually, between 0.5 and 2. Observe the Temperature chart, what do you notice?

7. Click on stop button to stop running the process.

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PART II : PI CONTROL

PI control uses a proportional – integral control loop, the oscillations that occur with on/off control can be avoided by using a linear proportional and integrating controller. This type of controller used when more exact conditions are required, such as: laboratories, manufacturing plant, or processing centers.

Figure5 : Block Diagram of Heater PI Closed-Loop System

Procedure: a. Calibration As Explained in Part I. b. PI Control After calibrating, the control will be activated by pressing on Heater OFF button.

Exercise 2: Qualitative PI Control 1. Observe the control parameters and set the amplitude of signal generator to zero. 2. Click on Heater OFF button, to activate control. 3. Examine the actual temperature (in red), and reference temperature (in blue) responses in the Temperature (C) scope, and observe the voltage scope with time. Click on “Stop” button. 4. Export both Temperature & Voltage charts with time. (Right-Click on each chart, then choose “Export >> Export simplified image”. 5. Compare both scopes with ones in On/Off control. 6. Click on “Stop” button. 7. Set Ki to 0, and change the proportional gain Kp to 2. 8. Click on the arrow to start the process. Observe the temperature response then export the chart. 9. Set Kp to 10 and repeat the previous step.

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10. Attach both charts, and compare the temperature response at low Kp, and at high Kp. Explain the effect of the proportional gain on the temperature response. 11. Set Kp to 0.5, and change the integral gain Ki between 0.25 and 2. 12. Attach two charts, one of them for temperature response at low Ki, and the other at high Ki. Explain the effect of the integral gain on the temperature response.

Exercise 3: Design PI Controller a. Find the proportional gain [Kp], and integral gain [Ki] needed to satisfy the following specifications, then set the calculated values in control parameters section, export temperature scope: 𝒔𝟐 + 𝟎. 𝟏𝟐𝟓𝒔 + 𝟑. 𝟗𝟎𝟔𝟐𝟓𝒙𝟏𝟎−𝟓

Hint: C.S equation = s2 + 2 ζ ωₒ s + ωₒ2 𝑲𝒑 =

𝟐𝜻𝝎ₒ 𝑲𝒗

𝝎ₒ𝟐 𝑲𝒊 = 𝑲𝒗 Where Kv = 0.00625 ⁰C/(V.S), Kv: HVAC model gain

b. Tune the controller by changing the values of control parameters to achieve better response. Hint: Take “0.5” as a step for Ki values and “2” for Kp values. Export Temperature scope after 2 cycles.

Requirements 1. For each part, you should follow the procedures and answer all question. 2. Attach all charts with discussion. 3. Tell me your opinion about this experiment and give one suggestion to improve it.

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