Data center cooling: 1 MW IT load on warm-water free cooling

A 1 MW data hall cooled the way modern halls are: a warm-water loop — chilled-water supply at 27 °C rather than the legacy 7 °C — picks up the IT heat (10 K rise at 24 kg/s), hands it across a plate exchanger to a condenser-water loop, and an evaporative cooling tower rejects all of it to an 18 °C wet bulb with a 6 K approach. No chiller runs: that is free cooling, and it is only possible because the supply is warm — a 7 °C loop cannot be served by a tower whose water cannot get below the wet bulb plus its approach, which is the whole reason the industry moved to warm-water and ASHRAE's wider allowable envelopes. The tower reports the numbers a data-center operator is judged on: 24.6 mol/s (0.44 kg/s) of evaporation and 32.8 mol/s of makeup water at four cycles of concentration — the water-usage effectiveness (WUE) story. Sweep the IT load and watch the makeup water scale with it. Honest scope: the IT load is a specified duty (no per-rack or airflow model); both loops are drawn open, supply to return, where a plant recirculates with makeup; the tower is a heat and water balance with a Merkel characteristic, not a fill-vendor rating; and a thermal_storage block on the chilled loop would give the ride-through buffer a real hall carries for a chiller or tower trip.