Data centre design reference

Generic reference designs for power, cooling, controls and operations

Sizing calculator

A sizing calculator for early design: enter a few parameters and read rounded results.

On this page
  1. What this calculator is for
  2. Calculator
  3. How each number is worked out
  4. What this calculator does not do

What this calculator is for

This calculator gives order-of-magnitude numbers for the early design of a data hall: how many power blocks, UPS systems, batteries, generators and cooling distribution units a given IT load needs, how much water and heat that implies, and how much of the heat could be reused. It is meant for the first conversation, before drawings exist.

Every assumption is a visible input and every input can be edited. Each result is shown with the formula that produced it and the numbers that went into it, so you can check the arithmetic or reproduce it in a spreadsheet. The defaults describe a 16 MW hall in four blocks with direct-to-chip liquid cooling. They are starting points, not recommendations.

It is not a design. The numbers are sizing estimates under simple rules. A real design needs the studies listed under “What this calculator does not do”.

Calculator

Load

Pumps, CDUs, fans and losses; used for backup sizing.

Power
Backup generators
Cooling

One spare CDU (N+1) is added per block.

Water. A glycol mix has a lower cp, so the flow for the same heat is higher.

Energy and heat reuse

W32 supply (32 °C) plus the 10 K rise.

Results

How each number is worked out

Symbols are the ones used in the input labels. Power is in MW unless a unit says otherwise.

Blocks
N_b = ceil(P_it / P_b): the IT load divided by the block size, rounded up to a whole block. IT per block = P_it / N_b, so the blocks are equal and none is larger than P_b.
UPS systems and rating
2N: two systems per block, each rated for the block load, so 2 × N_b systems and twice the IT load installed.
Block redundant N+1: one system per block plus one reserve system shared by all blocks, so N_b + 1 systems, each rated for one block.
Distributed redundant 4/3: blocks are taken in groups of up to three. In each group four systems share the group load L, each rated L/3, so one system can fail and the other three carry L. The number of groups is ceil(N_b / 3). Blocks are whole and equal, so the fullest group holds ceil(N_b / groups) blocks, and every system is rated for that group: rating = ceil(N_b / groups) × (P_it / N_b) / 3. Installed capacity is 4/3 of the IT load only when the blocks divide evenly into groups, for example 3, 4 or 6 blocks. Otherwise it is higher: 5 blocks in 2 groups put 3 blocks in the fullest group, so the installed capacity is 1.6 times the IT load.
Installed capacity / IT load = systems × rating / P_it. UPS modules per system = ceil(rating / m_ups). The rating covers the block's IT load only; the reference block also puts critical cooling (CDU and facility-water pumps) on UPS, so add that load before choosing modules.
Battery energy
E = rating × t_bat / 60 / η_inv × k_bat, in MWh per UPS system: the system carries its full rating for the autonomy time, the inverter loss is added, and the margin covers ageing and low temperature. Multiply by 1000 for kWh.
Backup generators
P_bk = P_it × (1 + k_mech): the IT load plus the mechanical and electrical load that must also run on generators. Usable output per generator = S_gen × pf_gen × d_gen / 1000. n_gen = ceil(P_bk / usable output) + 1 for N+1, or + 2 for N+2.
Heat to liquid and to air
Q_liq = P_it × f_liq. Q_air = P_it × (1 − f_liq) + P_it × k_mech × 0.5. The last term is an assumption: half of the overhead is taken to end up as heat in the room. Change k_mech or f_liq to see the effect.
Facility water flow
Mass flow m = Q_liq / (cp × ΔT), with Q_liq in kW, cp in kJ/(kg K) and ΔT in K, giving kg/s. Volume flow V = m / ρ × 3600, in m³/h. For 1 MW at 10 K and water properties this is 23.9 kg/s or 86.4 m³/h.
CDUs
CDUs per block = ceil(Q_liq per block / Q_cdu) + 1, where Q_liq per block = Q_liq / N_b and the +1 is one spare unit. Total = per block × N_b. With no liquid cooling (f_liq = 0) the count is 0.
Racks and tap-offs
Racks = ceil(P_it / p_rack). Usable tap-off capacity = √3 × V × I_tap × loading limit / 1000, in kW, taking the power factor as 1. Racks per tap-off = floor(capacity / p_rack). A result of 0 means one rack is larger than one tap-off can feed, so the rack needs more than one tap-off or a higher-rated one.
Annual energy and heat reuse
E_yr = P_it × LF × 8760 × PUE, in GWh per year. Heat available for reuse H_yr = Q_liq × LF × 8760, in GWh per year.
Heat-pump COP = η_c × (T_dh + 273.15) / (T_dh − T_ret): a fraction of the ideal (Carnot) value for lifting heat from the facility water return temperature to the district-heating supply temperature. District heat delivered = H_yr × COP / (COP − 1), because the delivered heat is the source heat plus the compressor work.

What this calculator does not do

  • No short-circuit, selectivity (protection coordination), harmonic or transient studies. Cable, busbar and breaker ratings are not checked.
  • No hydraulic network: no pipe sizes, pressure drops, pump duty, balancing or control valve selection. Water flow is a heat balance only.
  • No site climate: no outdoor design temperatures, free-cooling hours, dry-cooler or chiller sizing, and no water use.
  • No cost, space, schedule, maintainability or failure-rate analysis.
  • Redundancy counts follow simple rules on equal blocks. They do not show that a given failure case is survivable.

Treat the output as a check on whether a concept is the right size, then confirm each part with a proper study.