In a data center with a well defined constant load, there is no penalty for a complete up-front build out of the infrastructure, and it is actually required. In this case, the scalability benefits of a modular architecture are irrelevant. However, many other benefits of modular design are still attractive, such as reduced engineering effort, the quality benefits resulting from the use of proven designs, and reduced lead time. When the IT load is constant and well defined, modular architectures tend toward large module sizes and centralized plants for many subsystems. In the case of a data center with slow growth and an uncertain growth plan, the benefits of scalability are a dominant factor in the design. There are huge potential penalties for a complete up-front build out: large investments in unused or underutilized capital equipment, maintenance costs associated with assets providing no value, unnecessary waste of energy due to over-provisioning, or even the possibility of writing down a large capital asset if the facility is abandoned partway through its life. In these cases, the ability to scale the data center infrastructure to match the IT load can dramatically affect the TCO of the data center and therefore the return on the investment. Modular data center architectures that minimize the upfront build out and maximize the modularization of the subsystems are the best choice in these cases. Design concept: Data centers with stable predictable loads will benefit from modular architectures based on central plants and large module sizes that are typically deployed all up front. Data centers with uncertain future loads and long growth plans will benefit from modular architectures centered around decentralized infrastructure and smaller module sizes. These are conflicting requirements requiring different architectural approaches.