This simulator models a computer-room air handler (CRAH) — a filter bank, chilled-water coil, control valve and fan wall that cool recirculating room air by exchanging heat into a chilled-water loop. Adjust air and water flow, chilled-water setpoint and coil capacity, then watch leaving-air and server-inlet temperatures respond.
• Facility laboratory tab: a real-time 3D workbench of the CRAH unit — filter cassette, exposed fin-and-tube cooling coil, EC fan wall and water-flow control valve/assembly — with Home view, Focus selected part, Show full enclosure/exploded view toggle, Auto rotate, Expand and a clickable component list with callouts; live stats (server inlet, hot return air, coil leaving air, heat removed, chilled water supply, water return); an operating-sequence readout; and experiment controls — Pause/advance simulation (10 ms or 1 s steps), playback speed, and sliders/toggles for IT load, air volume flow at full fan, fan speed multiplier, water mass flow, chilled-water setpoint, coil/chiller capacity, and pump-running. • Curves & measurements tab: a temperature history chart (server inlet, return air, water supply) and a heat-flow chart (IT heat, coil heat removal, chiller electricity), the underlying model equations (Qcoil = ε·Cmin·(Treturn−Twater) limited by rated capacity; Qwater = ṁwater·cp,water·ΔTwater; room and water thermal-mass balances; Pchiller = Qchiller/COP) and snapshot measurements. • Experiments tab: guided scenarios (rated coil operation at 80 kW room heat, restricted water flow down to 0.5 kg/s, a stopped pump removing forced water cooling, and a coil-capacity limit case applying 200 kW to a 100 kW coil), a model verification bench (Run model checks) against independent fresh models, and a timestamped event log with a trial-report export. • Learn & assess tab: lessons on the air-treatment sequence (filter, coil, fan wall), two-fluid heat exchange, the effect of reducing water flow, and why leaving-air is a distinct measurement from server-inlet, a knowledge-check quiz with reset, and a scope/references note.
A CRAH — chilled-water air handling — draws warm room-return air through a pleated filter, across a fin-and-tube cooling coil supplied with chilled water, and pushes the cooled air back out through an EC fan wall. Unlike a CRAC (which has its own refrigerant compressor), a CRAH depends entirely on a central chilled-water plant delivering cold water through a control valve. In this model, heat transfer across the coil is limited both by the water- and air-side heat-capacity rates and by the coil's finite effectiveness — it is not simply proportional to the temperature difference alone.
The water-flow control assembly lets you throttle the water mass flow, which changes the water-side heat-capacity rate: reduce it and the coil becomes water-side limited, so leaving-air temperature rises even though the air side is unaffected. Stopping the pump entirely sets forced water-side cooling to zero in this teaching model — the coil then cannot remove heat via water circulation.
Coil-leaving-air temperature is the sensor reading right after the coil, distinct from the mixed server-inlet temperature reported elsewhere in the Data Centers labs (that mixing is modeled in the hot/cold aisle containment lab). Watch how a lower water mass-flow rate or a stopped pump widens the gap between return-air and coil-leaving-air temperature: the coil is now able to remove less heat per unit time, and the heat-flow chart's coil-removal trace flattens or drops toward zero even as IT heat input stays constant.
When commanded IT load exceeds the coil/chiller capacity setting, the model cannot remove all the incoming heat, so the room's thermal mass keeps absorbing the surplus and return-air temperature keeps climbing rather than settling — a direct illustration of a coil operating beyond its rated duty. The Run model checks bench validates the underlying water-side and air-side heat-balance equations against independent fresh instances, leaving your live trial untouched. This is a lumped sensible-heat model (400 kJ/K room thermal mass, 850 kJ/K water-loop mass, cp,air = 1.005 kJ/kg·K, cp,water = 4.186 kJ/kg·K) that fixes containment at 0.9 and uncontained recirculation at 0.2 — it excludes CFD, humidity/condensation, the refrigeration cycle and a full hydraulic network.
CRAH stands for computer-room air handler — it cools air by exchanging heat into a central chilled-water loop through a coil, with no refrigerant compressor of its own. A CRAC (computer-room air conditioner) instead contains its own direct-expansion refrigeration cycle. This simulator models the chilled-water CRAH path, including the coil, filter, fan wall and water-flow control valve.
Heat transfer at the coil depends on both the air-side and water-side heat-capacity rates, not just the temperature difference. Reducing water mass flow lowers the water-side heat-capacity rate, making the exchange water-side limited, so less heat is removed from the air per pass and leaving-air temperature rises.
With the pump stopped, this teaching model sets forced water-side heat transfer to zero — the coil can no longer remove heat via water circulation, and the room and water-loop temperatures will rise as IT heat accumulates.
It is a lumped sensible-heat model with fixed room and water thermal masses that fixes containment effectiveness at 0.9 and recirculation at 0.2 so you can isolate the water- and coil-side variables. It excludes CFD, humidity and condensation, the refrigeration/chiller cycle physics, and a detailed hydraulic network — adjust airflow and containment variables in the dedicated hot/cold aisle containment lab.