Size too small and the risk is obvious: a generator that trips when the chillers restart, or a site that cannot hold redundancy during maintenance. Size too large and you pay for capacity that runs lightly loaded, wets its exhaust and fails its own testing routine. Either way the downtime or the wasted capital lands on you.
A Sizing Method You Can Check Line by Line
We know you need a figure you can defend to your design team, your tenants and your finance committee. USP&E has delivered 150+ power projects in 45+ countries, with 25,000 MW contracted since 2002, including standby and prime power for data centres and other critical sites. Our systems are ISO 9001 and ISO 45001 certified. USP&E is a full-service EPC and O&M contractor, not a broker.
The method below is the one our engineers use. It does not replace a full design, but it shows you every step so you can see where the number comes from.
Step One: Build the Total Load
Start with the IT load at full design, not just day one. Then add everything else that must run on generator power: cooling plant, pumps and fans, UPS losses and battery charging, lighting, security, fire systems and building services. Cooling is often the largest addition, and on a hot day it can be a large share of the total.
Use real equipment data where you have it, and sensible allowances where you do not. Note which loads start with large motors, such as chillers and pumps, because those starts matter in step four. Note too which loads restart in sequence after a mains failure.
Plan for growth. If halls will be added in phases, decide whether generators are added per phase or sized for the final load from the start. The AI campus power requirements guide explains why loads are rising faster than many plans assumed.
Step Two: Choose Redundancy
Redundancy decides how many units you need. With N+1, you install enough sets to carry the load plus one spare. With 2N, you install two full systems. Some designs use distributed or block redundancy. The right choice depends on your tier target, tenant contracts and budget.
Remember maintenance. A site that needs to keep N+1 while one unit is down for service may need another set. Be clear whether your redundancy figure applies at all times or only when every unit is available.
Step Three: Derate for Your Site
Generator ratings are given at reference conditions. High ambient temperature, altitude and restricted air flow all reduce real output. Ask for the derated rating at your design day temperature and your site altitude. On hot or high sites, the gap can be large enough to change the number of units.
Check the rating type too. Many makers publish standby, prime and continuous ratings, and some publish a rating aimed at data centre duty. Make sure the rating you size against matches how long the sets will run and how the load varies.
Step Four and Five: Check Load Steps and Prove It
After a mains failure, loads come back in steps. Model each step and make sure the sets can accept it without voltage or frequency dropping outside UPS and equipment limits. Large chiller restarts are a common problem. Staggered restarts and soft starters can help. Check also how your UPS interacts with the generators, as some UPS designs need careful tuning to share power smoothly.
Finally, prove the size with a load bank test at commissioning and at regular intervals. Testing at realistic load protects the engines and gives you real data for the next phase. Our data centre power engineers can review your sizing, and you can see available generator inventory for near-term needs.
As campuses grow, sizing often moves beyond diesel standby, and hyperscale EPC/O&M teams plan AI gas turbines, hyperscale generators and gas turbines for compute, using gas turbine generators, used/new gas turbines, a remanufactured GE Frame 6B or natural gas engines/stations. USP&E offers the New USP&E FX-45 45MW Modular Gas Turbine for the Hyperscale Data Center sector in the USA.
Where USP&E Supports Your Compute Campus Power Project
If your compute campus black-start plan is in the United States, your first conversations run through USP&E’s US offices in Colorado Springs (1755 Telstar Dr, Suite 300) and Knoxville (800 S Gay St, Suite 700). They keep you close to developers, utilities, gas suppliers and US equipment sources, and they can walk your site before anything ships.
Johannesburg (22 Kildoon Rd, Bryanston) runs engineering, protection studies and project controls for black-start gensets, Frame 6B units and gas turbine generators, and Cape Town (31 Brickfield Road, Woodstock) adds design and commissioning support. London (162-168 Regent Street) structures the contract, insurance and financing file your lenders will read, while Wuxi, China (No. 1, Ningzhou Road, Wuxi) follows up China supply chain and manufacturing.
Sizing reviews for American campuses come out of Colorado Springs and Knoxville; African facilities are covered from Johannesburg and Cape Town, with London on commercial terms. Regions served: USA | AFRICA | UK | UAE | CHINA. USP&E has delivered 150+ power projects in 45+ countries, with 25,000 MW contracted since 2002, and is ISO 9001 and ISO 45001 certified.
Proof from Recent Compute Campus Power Projects
You want proof that USP&E can size and deliver critical power. These projects show that record.
- USP&E has refurbished seven GE Frame 6B gas turbines to zero hours in-house for major US hyperscale data-centre developers.
- A gold mine in West Africa: USP&E rebuilt more than 80 MW of Caterpillar CM32 engines and added 24 MW of new zero-hour capacity, delivering a 104 MW station with 300% greater reliability and availability than previously recorded at site. Read the case study.
- A giga-project developer in the Middle East: USP&E supplied three zero-hour Siemens SGT-400 gas turbines as the single technical and commercial interface.
How to Size Data Center Generators
Your 3-step plan: 1. Share your IT load, cooling design and redundancy target. 2. Receive a step-by-step sizing check with derating and load steps. 3. Supply, test and support the generators with one team.
- Start from the IT load and the design growth path.
- Add cooling, UPS losses and building loads.
- Choose the redundancy level for the site.
- Check site derating for heat and altitude.
- Check load steps and UPS interaction.
- Confirm the size with a load bank test.
Resources and live pathway
Data centres · EPC · O&M · About USP&E · Contact.
Generator Sizing FAQ for Data Centers
How do you calculate generator size for a data center?
USP&E starts with the full design IT load, adds cooling, UPS losses and building services, applies the redundancy target, then derates for site temperature and altitude. Load steps are checked last, and the result is proven with a load bank test at commissioning.
What is the difference between N+1 and 2N generators?
USP&E explains N+1 as enough generators to carry the load plus one spare, while 2N means two complete systems that can each carry the full load. 2N gives more resilience but costs more, so the choice follows tier targets, contracts and budget.
Why does derating matter for data center generators?
USP&E applies derating because heat, altitude and restricted air flow reduce real output below the reference rating. On hot or high sites the loss can change the number of generators needed, so sizing must use the derated figure at your design conditions.
Do UPS systems affect generator sizing?
USP&E checks UPS interaction on every sizing review. UPS losses and battery recharge add load, and some UPS designs need tuning to work smoothly with generators. Ignoring this can cause unstable voltage or frequency during transfer, even when the kW figure looks right.
Where are USP&E’s offices for data center work?
For American data centres, USP&E works from Colorado Springs and Knoxville, and London looks after commercial terms. Johannesburg and Cape Town support African projects, and Wuxi supports equipment sourced in China, so engineering help is available close to your site and in your time zone when a design review is due.
What has USP&E delivered for data center power?
USP&E has delivered 150+ power projects in 45+ countries. In data centre power, USP&E has refurbished seven GE Frame 6B gas turbines to zero hours in-house for major US hyperscale data-centre developers, and it supplies standby and prime generation for critical sites.
Is USP&E a generator broker?
USP&E is not a broker. USP&E employs the engineers who size, supply, test and maintain its generators, so nobody hands your sizing figure to a third party. The people who check the numbers are the people who answer for the sets later. You get one accountable contractor rather than a chain of resellers.
How quickly can USP&E review a generator sizing?
USP&E can review a sizing sheet as soon as you share your IT load, cooling design and redundancy target. Missing loads, derating and block-load response get flagged up front, which tells you whether the number survives before anything is ordered.
Size Once, Size Right
Size your generators from the full load, the right redundancy and the real site conditions and they will carry your halls through every outage. Guess, and you pay in trips or idle capacity. USP&E will help you size, test and support them with confidence.
Start now: send your load, site and fuel data through the contact page, phone +27 10 822 2324 or write to info@uspeglobal.com, and search current USP&E inventory while the team scopes your compute campus black-start plan.
Powering Possibility. Built for the Frontier.