Mechanical Systems Design Strategies for High Altitudes

Robert Thompson, SmithGroup, Inc.

Sustainable solutions to laboratory mechanical systems design are informed to a large degree by their environment. High altitude locations greater than 5,000 feet above sea level are characterized by low air density, increased heating hours, and reduced relative humidity levels. Often referred to as high deserts, these locations benefit from the limited dehumidification season, relatively low outdoor wet bulb conditions, and reduced cooling loads in summer.

The dry climate and high elevation translate to a limited window of elevated humidity. In the Denver area, for example, these elevated humidity levels are limited to a collective 2-3 weeks per year. Given this understanding, chilled water temperatures can for the most part remain elevated for improved energy efficiency and latent heat recovery solutions are less practical. A high-performance sensible energy recovery system can simplify maintenance while being very effective.

Underfloor air, displacement, and natural ventilation strategies are well suited to this environment. Direct and indirect evaporative cooling solutions can provide free cooling for most summer months but require a degree of control to maintain consistent supply temperatures. Pad-type direct evaporative cooling systems need to be zoned, while high pressure atomizing solutions provide the highest degree of control. Evaporative pre-cooling of exhaust air enhances the performance of sensible energy recovery systems in summer months.

The low outdoor wet bulb increases the opportunities from waterside economizer free cooling for large central chilled water systems for campuses. Moderately sized facilities may consider the application of variable-speed air-cooled chillers, taking advantage of elevated chilled water temperatures (with reduced relative humidity) and lower design temperatures in summer. Coupled with active chilled beam solution, these systems can be very effective while limiting water use.

Another characteristic of these arid climates is a large diurnal temperature swing, up to 30 degrees from daytime to nighttime. When factoring in temperature changes due to changing weather patterns, these locations can see an over 50-degree temperature swing over a 1-1/2 day period. Mechanical systems design needs to be responsive, and able to react to this dynamic environment.

The presentation will highlight the analysis and application of these systems to the high desert of Denver, Colorado, with examples from the National Renewable Energy Laboratory's (NREL) Energy Systems Integration Facility (ESIF), Denver Crime Lab, and the CSU/Denver Water Western Regional Center currently in design.

Learning Objectives

  • Understand the role of climate analysis in the design, planning, and selection of the mechanical systems employed in these high desert environments;
  • Learn about approaches to low energy mechanical systems design for high altitudes, their characteristics, and how they compare with one another;
  • Identify the resources from local climate models to building program elements that inform integration and establish a path forward for innovation; and
  • Understand the dynamic environment of the high desert, and how mechanical systems designs can accommodate rapid changes in environmental conditions.

Biography:

Robert Thompson is a principal and mechanical engineer at SmithGroup, and actively participates with their Science & Technology and Sustainability National Practice Groups. Robert is also a member of ASHRAE, ASPE, and I2SL, and has published articles for the ASHRAE Journal, Consulting-Specifying Engineer Magazine, and 7x24 Exchange Magazine.

 

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