You are the facility engineer of a 1 MW data hall: chillers, a chilled-water loop, UPS batteries and a standby generator. Heat flows from servers to air to water to the outdoors — and every watt you spend on cooling shows up in the PUE.
What you will learn
How heat moves through a facility, and why the chilled-water loop buys you minutes in a crisis.
Why chillers get less efficient on hot days (Carnot COP) and what PUE and WUE really measure.
How UPS batteries and generators hand over during a grid outage.
Simulator
Time 0 min
Inlet < 24 °C
Inlet ≥ 27 °C
Inlet ≥ 32 °C
◎Chiller running
⟳Chiller starting (5 min)
✕Chiller tripped (latched until reset)
Controls
Chiller #1…#n. A newly started chiller needs 5 min before it cools.
Warmer water = better chiller efficiency, but warmer server inlets.
Batch jobs postponed to later: less heat and power now.
Uses cold outdoor air through a dry cooler when it is cold enough.
Evaporates water to cool condenser air: better efficiency, water use.
Only needed if the automatic start fails. Takes 3 min.
Clears a chiller safety trip once the fault has been checked; accepted from 15 min after the trip.
Indicators
Server inlet temperature
22.4°C
normal
PUE
1.34
normal
Facility power
1076kW
UPS battery
100%
normal
Chilled-water temperature
14.0 °C
Chiller COP
5.1
IT load
803 kW
Chillers running
2
Chillers available (not tripped)
3
Chillers tripped (latched)
0
Trip reset possible in
0 min
WUE
0.00 L/kWh
CO₂ emissions
484 kg/h
Trend
Crisis scenarios
Level 1 · Chiller trip at peak
A hot afternoon, 32 °C outside. IT draws 850 kW on two of three chillers, and the chilled water runs at 16 °C to save energy — which leaves the server inlets only about 2 K below the ASHRAE recommended limit. One chiller is about to trip. Keep the inlets inside the recommended range, keep the IT work running, and get the plant back to full redundancy.
Inlet never above 27 °C
Inlet ≤ 25 °C at the end (back to normal)
Average IT load ≥ 750 kW (do not just switch servers off)
All three chillers available again at the end (tripped unit reset)
Level 2 · Heatwave and a demand-response call
Outdoor temperature climbs from 30 °C to 42 °C. Chillers lose capacity and efficiency. Then the grid operator issues a demand-response request: keep this site’s facility power under 900 kW for half an hour.
Inlet never above 27 °C
Average facility power ≤ 900 kW during the request
Average IT load ≥ 720 kW over the scenario
Level 3 · Grid outage, generator fails to start
The grid drops. The generator should pick up within ten seconds — this time it does not. Servers are on UPS batteries with roughly ten minutes of energy, and the chillers are dark.
No IT outage
Battery never below 72 %
Inlet never above 25 °C
Basis — the model behind the numbers
Every relation the simulator uses, with its source. Constants marked as assumptions are illustrative calibrations.
Air node energy balance: servers heat the air, cooling coils move heat into the chilled water.
C_air · dT_air/dt = P_IT + P_fans − Q_CRAH, Q_CRAH = UA · (T_air − T_chw)[4][11]Assumption: capacitances, coil conductance, chiller size and battery energy are illustrative values for a 1 MW hall.
Water node energy balance: the loop’s thermal mass buffers the gap between heat load and chiller capacity.
Chiller efficiency as a fixed fraction of the Carnot limit — it falls as outdoor air gets hotter. The evaporator temperature follows the actual chilled-water loop temperature (2 K below it), not the setpoint, so a loop that warms after a trip briefly raises the COP.
COP = 0.45 · T_evap / (T_cond − T_evap), T_evap = T_chw − 2 K, T_cond = T_air,out + 12 K [K][5]Assumption: capacitances, coil conductance, chiller size and battery energy are illustrative values for a 1 MW hall.
Power usage effectiveness: total facility power over IT power (1.0 is the ideal).
UPS battery energy drains with the protected load until the generator takes over.
E_batt(t+Δt) = E_batt − (P_IT + P_fans + P_pumps)/η_UPS · Δt (energy balance); generator ≤ 10 s[6]Assumption: capacitances, coil conductance, chiller size and battery energy are illustrative values for a 1 MW hall.
After any power transfer the chillers stop and must restart.
chiller restart after any power transfer = 5 min (quick-start; typical 10–15 min)[11]
Emissions from grid electricity intensity, or from diesel when the generator runs.
CO₂ = P_facility × grid intensity (≈450–650 g/kWh in the scenarios); diesel ≈ 2.69 kg CO₂/L[9][10][13]
Other operating constants used by the model.
chillers 3 × 450 kW, derate 2.5 %/K above 35 °C · adiabatic effectiveness 70 % · loop P-gain 150 kW/K · IT shutdown at 40 °C inlet · manual generator start 3 min · chiller trip reset accepted 15 min after the trip · battery 150 kWh (≈10 min at full load), recharge 10 %/h · UPS η 95 %Assumption: capacitances, coil conductance, chiller size and battery energy are illustrative values for a 1 MW hall.
Randomness: a seeded mulberry32 generator; distributions used — uniform, exponential (inverse CDF), normal (Box–Muller), Poisson (Knuth). The seed is shown and shareable.