Trends, changes in data center HVAC design
Several trends are pushing the HVAC systems in data centers in different directions
- Bill Kosik, PE, CEM, BEMP, Senior Energy Engineer, DNV, Oak Brook, Illinois
- Matt Koukl, DCEP, Principal, Market Leader Mission Critical, Affiliated Engineers Inc., Madison, Wisconsin
- Kenneth Kutsmeda, PE, LEED AP, Global Technology Leader – Mission Critical, Jacobs, Philadelphia
- Ben Olejniczak, PE, Senior Project Mechanical Engineer, Environmental Systems Design Inc., Chicago
- Brian Rener, PE, LEED AP, Mission Critical Leader, Smith Group, Chicago
- Jonathan Sajdak, PE, Senior Associate/Fire Protection Engineer, Page, Houston
What unique cooling systems have you specified into such projects?
Ben Olejniczak: Most of the projects I’ve worked on lately surround direct evaporative or indirect evaporative technology. Depending on the application, there are benefits and drawbacks to each technology. Some of my most recent project work focuses on direct evaporative technology and its application across a broad number of data centers across the country. Depending on local climate, economization hours can be maximized — upward of 8,000+ hours a year. Difficulties arise when you start to consider local geography and things like arid climates where dirt may become an issue or areas where water is scarce. These areas present unique challenges that we tackled with enhanced filtration and unique water quality provisions which allow us to run at higher cycles of concentration given poor incoming water to maximize water use effectiveness.
Matt Koukl: Designing data center facilities in Southeastern U.S. have unique challenges due to the heat and moisture content in the air. While it is possible to design data centers in this region, the approach to the cooling system design becomes critical balancing efficiency, cooling supply water temperatures and water and power use. In many cases, the use of a waterside economizer is difficult and/or economically unfeasible due to the limited number of hours for traditional economizing. However, with the ability to raise the facility supply water temperatures in certain types of systems, the hours of economization can be increased to become economically viable to have a waterside economizer.
Describe a project in which the building used free cooling. Outline the building’s location, size, efficiency and other HVAC needs.
Bill Kosik: Free-cooling is right at the top of the energy savings design list. If you compare free-cooling strategies for data centers and an office building (each having a central chilled water plant), the data center will use the free-cooling much more of the year. Why? Data centers should be using 65°F or higher supply water temperatures. Typical chilled water supply temperature in an office is 55°F (required for comfort cooling). Depending on the climate zone, the extended hours available to the data center yields a tremendous savings.
Matt Koukl: AEI has experience with multiple different types of economizers (free cooling systems) and have implemented these technologies on multiple buildings to decrease the use of mechanical cooling and power usage. Most recently we used a water-side economizer for a high-performance computing facility in Idaho that is achieving a power usage effectiveness of 1.1 or better. We can’t take credit for the climate or the fact that the facility uses a majority of equipment with direct to chip liquid cooling where we can leverage higher water temperatures for a chillerless cooling solution. The facility is planned for about 8 megawatts of computing capacity in approximately 10,000 square feet of computing space.
Ben Olejniczak: We recently worked on a data center located on the East Coast using direct evaporative systems. The building supported approximately 75 megawatts of IT capacity and spanned approximately 1 million square feet. Using the direct evaporative technology and a generous operating envelope within the data hall, we are theoretically able to realize over 8,000+ hours of compressorless cooling using outside air and water for evaporation. Annualized power usage effectiveness and water usage effectiveness metrics are approximately 1.1 and 0.056, respectively.
How have you worked with HVAC system or equipment design to increase a building’s energy efficiency?
Ben Olejniczak: Some of the systems that we’ve worked on lately can automatically optimize water usage or power usage, depending on the ambient characteristics throughout the year. From an energy efficiency perspective, the system can use more water to enhance the number of hours we run the system wet and limit the number of hours we use compressor-based mechanical cooling equipment. Having this flexibility gives the owner the options they need to optimize the operating characteristic of the system based on what’s going on outside of the building at any given point in time.
What best practices should be followed to ensure an efficient HVAC system is designed for this kind of building?
Ben Olejniczak: First and foremost is to know your local climate and understand how you can use it to your advantage. Understand the operating envelope of your data hall and cross-reference that with the local climate through a bin data analysis. If you find that a high percentage of annual bins fall within the envelope of your space, direct outside air systems may be a suitable candidate for the basis of design. This also helps you in identifying how many economization hours are available for your mechanical system and thereby how many hours throughout the year you can operate without the need for mechanical cooling. Also, it is critically important to fully understand your non-IT loads. Oversized loads can lead to inefficient equipment operation. Traditionally, rules and assumptions govern certain aspects of the non-IT load calculation. The more refined you can be with your calculations, the better. Engage your electrical counterparts to understand actual equipment loads and non-IT electrical loads given the electrical distribution topology selected and input that information back into your HVAC load calculations.
What type of specialty piping, plumbing or other systems have you specified recently?
Ben Olejniczak: Recently, our team was tasked with designing a reverse osmosis system to enhance water quality for use in the facility and to protect the proprietary heat exchanger technology used in the design. This technology is very sensitive to fluctuations in water quality so a mechanism to control this through the heat exchanger was critical. The system was arranged in an N+1 configuration and was comprised of fully stainless-steel construction. Centralized water storage was provided on a per data hall basis as an additional resiliency measure for periods of the year when water may be scarce or water quality was expected to be poor.
What are some of the challenges or issues when designing for water use in such facilities?
Ben Olejniczak: Water quality is one of the biggest challenges I see from a water use perspective. Water quality has a huge impact on a facility operation and can drastically influence how much water is used throughout the year. Managing water quality effectively can open opportunities to increase cycles of concentration, thereby limiting the amount of water consumed by the facility’s mechanical systems. Filtration and chemical treatment are also critical to mitigate detrimental impacts to equipment and biological growth. Managing each of these items effectively prolongs the life span of the system and allows for safe, efficient operation over the course of the facility’s useful life.
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