Examining government, state, municipal, federal, and military facilities: HVAC
- Roger Chang, PE, LEED Fellow, Principal, DLR Group, Washington, D.C.
- Shem Heiple, PE, LEED AP, Associate Principal, Senior Mechanical Engineer, Interface Engineering, Portland, Ore.
- Dalrio Lewis, PE, Project Engineer, RTM Associates, Orlando, Fla.
- Spencer Morgenthau, CPSM, LEED AP, Director of Business Development, Southland Energy, a division of Southland Industries, Sterling, Va.
CSE: What unique heating and cooling systems have you specified in such projects? Describe a difficult climate in which you designed an HVAC system.
Chang: We are seeing significant interest in ground-source heating and cooling systems, which can be adapted to a wide range of climates but require a clear understanding of ground properties and a building’s heating- and cooling-load balance. The increasing adoption of heat pump technology is tied to the benefits of electrification, as utility-grid-delivered electricity is made up of a higher percentage of renewable sources.
Heiple: We recently designed a facility in Niger with outdoor-air temperatures exceeding 120°F, frequent dust storms, and unreliable water and power utilities. Extensive load and energy analysis was conducted to provide design guidance on HVAC system performance integration with the building envelope. We used inertial filtration and sand louvers to address dust and indoor-air quality. Due to the dry air during continuous hot conditions, humidification was beneficial to maintain expected low humidity levels that also provided significant energy savings.
CSE: What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Heiple: We recently designed a courtroom building with diverse space requirements that used active chilled beams and displacement ventilation with thermally activated slabs to meet energy goals and comfort requirements.
Chang: We are seeing a continued move to the use of dedicated outdoor air systems (DOAS) where ventilation-air delivery is decoupled from space heating and cooling. This requires additional care to meet the economizer provisions in the IECC/ASHRAE 90.1. The increasing use of distributed VRV fan coil units and fan-powered VAV boxes with cooling comes with a challenge of decentralized filter-change requirements. We have included polarized media-type filters on a major government project to decrease filter-change intervals.
CSE: What types of air economizers or other strategies are owners and facility managers requesting in government, state, municipal, federal, and military facilities?
Heiple: Recently, DOAS have gained acceptance in many government design standards. The major energy efficiency advantage to these systems is the ability to use air-to-air heat recovery, but the trade-off is that they are not capable of providing full economization because they are typically not sized to provide outside air rates exceeding minimum ventilation standards. For some projects, and depending on the climate, we have proven through analysis that full air-side economizer systems are more beneficial for energy conservation and indoor air quality than dedicated outside air systems, and we were allowed an exception to the design standards.
CSE: How have you worked with HVAC system or equipment design to increase the building’s energy efficiency?
Chang: Design assumptions for process load have a significant impact on zone-level heating and cooling system design, especially given increasing stringency for building envelope and lighting performance. While process-load density has dropped significantly in the past decade, due to increasing use of LED monitors and laptops, the unpredictability of process loads results in the use of prescriptive assumptions. Early and frequent dialog on assumptions allows better sizing of equipment, which allows improved fit, reduced first-cost investment, and better performance at low and part-load demand.