Project – "Mackerel Deck"

An HMI Mockup and Corresponding PLC Program Written in Ladder Logic for the Allen-Bradley / Rockwell Automation Platform

HMI

RSLogix LAD 2

This software is intended to control a fan coil unit (FCU) providing air condition to a occupied space used for food processing.

Problem

Liquid sub-cooled (-40˚F) refrigerant is supplied to the FCU evaporator via a pump at 45psi. This limits the total evaporator pressure to about 40psi via a back pressure regulator with a corresponding temperature of 25˚F and causes rapid FCU ice-up. No defrost functionality is installed.

Solution

Add ability to the FCU's PLC program that allows the refrigerant supply solenoid valve to cycle open/close at settable intervals (while the FCU's fans continue to run) only permitting refrigerant flow for sort durations – preventing ice build-up. Anticipated effective cycle time – approx. 3 minutes on / 12 minutes off.

Mockup Link