Air handling unit temperature control

The brief

Client

Maple Court Offices

Site

Air handling unit AHU-1

Work order

MC-2615

Industry

Building services

Task code

PLC-15

Difficulty

Intermediate

Type of work

Programming

Hold the supply air of an air handling unit near a set point with a proportional heating valve and a dead band, prove the airflow before heating, and protect the coil from frost.

What you do

1. Read the client brief and the tag table: 11 tags, 7 inputs and 3 outputs.
2. Write the logic in ladder, Structured Text or SFC.
3. Press Simulate and watch the plant answer your program.
4. Run the factory acceptance test and fix what fails.

Skills you practise

• Proportional control with SUB, MUL and DIV
• Dead band
• Airflow proving with a timer
• Frost protection latch
• Set point selection

What the test checks

The factory acceptance test runs 6 numbered tests against your program. The numbers in the brief are drawn per learner. The tests are:

• The set point follows the occupancy selector
• The valve follows the error in whole numbers
• Dead band around the set point
• The valve opens only with the fan running and airflow proven
• Frost protection by the coil thermostat
• Frost protection by low air temperature

In this lab

• Ladder, Structured Text and SFC in one studio
• A plant that answers: motors, tanks, conveyors
• Numbered tests mark your program