ASHRAE Journal -November 2012 - 64

Data Centers

Cooling as a Service
I
By Donald L. Beaty, P.E., Fellow ASHRAE

Data Center Cooling Considerations

n October’s column we compared data center cooling to comfort cooling from the perspective of occupant requirements. Data centers focus

on electronic equipment and software requirements (Thermal Guidelines for Data Processing Environments, 3rd ed.), while many other commercial uses focus on human requirements (ASHRAE Standard 55). This month the comparison is between data center cooling and comfort cooling from the perspective of service versus system.
In comfort cooling applications, it is common to think in terms of cooling equipment and cooling systems. A variety of people design and operate data centers; many of them build upon their experience, which is often a previous comfort cooling project. As a result, they continue to think in terms of cooling equipment and cooling systems even though it is more useful to consider cooling a “service.” This column will explain why data centers benefit significantly from taking a cooling as a service (CaaS) approach. party is as a “service provider” and a “service consumer.” However, in most applications, cooling is rarely considered a service. There is no interface point or meter; no upstream point beyond the cooling equipment itself. The HVAC design capacity is known and finite for the life of the building because the internal “plug loads” don’t vary significantly over the life of various occupant changes. In contrast, for data centers the “plug load” is commonly 90% or more of the total load and subject to many changes as the software and electronic equipment change. Subsequently, the cooling design capacity must change to accommodate this, hence the concept of “cooling as a service.” As mentioned in last month’s column, unlike most buildings, the cooling load for a data center is subject to frequent and prolific change due to the ever changing software applications and associated hardware upgrades over the lifetime of a data center facility. In short, data center cooling systems must be designed to be capable of meeting IT equipment requirements, both now and in the future.
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In addition, the interface between the supplier of a cooling service (e.g., a data center facilities operations department) and the consumer of that service (e.g., an internal or external IT operations department) requires a common understanding that transcends the inwardly focused knowledge of both departments.

Why Data Centers Treat Various Aspects as a Service
Information technology (IT) function, department or business units represent the data center equipment and the data center occupants (software/applications). This is different than the building/facility function, department or business unit. Often, IT and building/facility are separate departments and may not even be in the same business unit. A good way to define the responsibilities and expectations of each is through a service level agreement (SLA). This can be an agreement between IT and building/facility in the same company or between the data center user that is renting data center space from a landlord. In the data center industry, the use of the words landlord and tenant are uncommon. Rented facilities are typically called colocation facilities (multiple tenants) or “build to suit.” There has been an increasing trend of companies outsourcing their data center operations to a provider (called a landlord in most commercial scenarios) or “service provider.” Cloud computing (also known as “on demand computing” or “utility computing”) is essentially a rented computing service. Years ago, rented computing services were called “time sharing.” Data centers are very capital intensive and, in these financially challenging times, there is an increasing temptation
November 2012

What Defines Something “…as a Service”?
Public utilities, such as water, gas and electricity, are readily accepted as being a service. The interface or demarcation point for how the service is delivered is typically a meter and very little attention or interest is paid to the details upstream of that meter (Figure 1). The customer simply assumes that the capacity provided by the service provider is unlimited and that service (for the most part) is uninterrupted. In the data center industry, a good way to describe each
64 ASHRAE Journal

ASHRAE Journal -November 2012

Table of Contents for the Digital Edition of ASHRAE Journal -November 2012