This split-screen designer pairs an interactive 3D model of a central-plant commercial HVAC system with a live loop diagram, so you can see the equipment and the hydronic schematic side by side. It models a water-cooled chilled-water plant — chillers, cooling towers, and primary/secondary pumps — feeding air-handling units and VAV terminal boxes sequenced by a building automation system. It's built for HVAC designers, plant operators, commissioning agents, and students studying chilled-water plant design to ASHRAE 90.1.
The designer covers a complete central plant and its air distribution, split between the 3D view and the system diagram:
• Chiller plant — water-cooled chillers producing chilled water (CHW), typically near 44 °F supply. • Cooling towers — rejecting condenser-water (CW) heat to atmosphere, with the tower approach set by wet-bulb temperature. • CHW and CW pumps — circulating water between chillers, towers, and coils, often in a primary-secondary arrangement. • Air-handling units (AHUs) — chilled-water cooling coils, supply/return fans, and economizer dampers. • VAV reheat boxes — modulating zone airflow and adding hot-water reheat at part load. • Hydronic loops and BAS — the CHW/CW piping plus the DDC controllers that sequence the plant.
Chillers cool a chilled-water loop that is pumped to cooling coils in the AHUs; the heat the chillers absorb (plus their compressor work) is moved by a condenser-water loop to the cooling towers, which reject it to the outdoor air. A primary-secondary pumping scheme decouples constant-flow chiller (primary) loops from variable-flow distribution (secondary) loops, letting pumps ride down on speed as load drops. When outdoor conditions are cool and wet enough, a waterside economizer can make chilled water through the towers and a heat exchanger with the chillers off. The BAS stages chillers, towers, and pumps to hold setpoints while chasing the lowest plant energy use, commonly following ASHRAE Guideline 36 sequences.
1. Drag to orbit the plant, scroll to zoom, and pan across the 3D model. 2. Click any chiller, tower, pump, AHU, or VAV box to highlight it in both the 3D view and the loop diagram. 3. Trace the chilled-water loop (chiller → CHW pumps → AHU coils → back) and the condenser loop (chiller → CW pumps → tower → back) to understand how heat moves out of the building.
Primary-secondary pumping splits the system into a constant-flow primary loop dedicated to the chillers and a variable-flow secondary loop that serves the building coils, joined by a hydraulic decoupler. This keeps a steady, minimum flow through each chiller for stable operation while letting the secondary (distribution) pumps slow down on variable-speed drives as the building load falls, saving pump energy.
COP (coefficient of performance) is the cooling delivered divided by the electrical power consumed — a dimensionless efficiency. Large water-cooled centrifugal chillers can reach full-load COPs around 6 or higher (roughly 0.5 kW per ton), and because they run mostly at part load, integrated metrics like IPLV/NPLV better capture real seasonal efficiency than a single full-load point.
Approach is the difference between the temperature of the water leaving the cooling tower and the ambient wet-bulb temperature. A smaller approach means a more effective tower and colder condenser water, which lowers chiller lift and energy use, but it requires a larger or more heavily ventilated tower. Approach — not the dry-bulb temperature — is the key tower design metric because evaporative cooling is limited by wet-bulb.
A waterside economizer uses the cooling tower and a heat exchanger to produce chilled water directly from cool outdoor conditions, allowing the chillers (compressors) to be shut off or unloaded. It works when the outdoor wet-bulb is low enough that the tower can make water cold enough to meet the cooling load, providing free cooling in winter and shoulder seasons.
A building automation system stages and unstages chillers, towers, and pumps; resets chilled-water supply temperature and differential-pressure setpoints; and controls AHU economizers and VAV airflow. Modern plants commonly implement standardized, high-performance logic such as ASHRAE Guideline 36, which defines repeatable sequences for plant staging and setpoint reset to improve efficiency and reduce commissioning errors.