Logic Diagram Tool
Ball Room AHU Discharge Temperature Control
This logic diagram is associated with the Ballroom Air Handling System at the fictitious Hijend Hotel that is the facility associated with the SketchUp model based training exercises we use and make available on our SketchUp Models page. There are several opportunities associated with the system that can be captured by low-cost/no-cost modifications to the control logic
- The change dry bulb change over set point for the economizer was higher than it should have been given the targeted ball room conditions and the local climate. This was addressed by making a simple adjustment to the changeover set point based on a technique that is discussed in the functional testing guide which you will find referenced at this link and as illustrated below.
- The system could be challenging to start in extreme weather due to nuisance freezestat trips. This was solved by improving the mixed air temperature measurement system and adding a mixed air low limit cycle. Originally, the system had a single point mixed air sensor and the freezestat element had not been properly installed (left below). The project added averaging mixed air sensors and an additional freezestat with all of the elements arranged to fully cover the plenum (right) along with repairing damper blade seals and adding a baffle to improve mixing.
Before
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After
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The logic diagrams illustrate the logic that existed before and after the improvements were made.
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The system diagram for this unit is illustrated below.
