The U.S. Department of Defense (DoD) is interested in improving their facilities in a variety of aspects, including enhancing energy performance and reducing potential for mold and mildew formation. To this end, the DoD funded a research effort focused on a pair of single-story, brick-clad administrative facilities (Buildings 1540A and 1540B) at Fort Detrick, MD. Building 1540A was the focus of facility improvements, and building 1540B served as the control for comparison.
Military facilities experience many problems with mold and mildew formation, especially in hot, humid locations. DoD installations are also mandated to reduce energy consumption. The main objective of this project is to simultaneously reduce energy consumption, maintain occupant comfort, and reduce the potential for mold and mildew formation with a heating, ventilating, and air-conditioning (HVAC) system that is easily operated and maintained and is life-cycle cost (LCC)-effective.
This demonstration was conducted in two closely connected buildings, which were approximately 20 years old, of separate but nearly mirrored construction, and had the separating space between them enclosed to enable a continuous roof, though the two buildings retained their separate conditioned envelopes. Each building contained its own HVAC and boiler systems. During this demonstration, Bldg 1540A was retrofitted with three complementary and innovative technologies that collectively addressed the aforementioned concerns. These technologies were:
- Improved building envelope air tightness to minimize unconditioned outdoor air infiltration.
- A dedicated outdoor air system (DOAS) to properly condition makeup air.
- A ceiling-mounted radiant heating and cooling system.
These technologies are complementary in a number of ways. Improved air tightness of building envelopes reduces unconditioned air infiltration and the amount of makeup air required to maintain a slight positive air pressure in the building interior. A dedicated outdoor air system ensures delivery of proper volumes of conditioned outdoor air to meet the building’s ventilation/makeup air requirements. The tightened building envelope combined with the dedicated outdoor air system makes it possible to maintain proper humidity levels within the building. Maintaining proper interior humidity levels facilitates use of radiant heating and cooling systems without the concern of developing condensation on cool radiant surfaces. Hydronic radiant heating/cooling systems should be able to deliver heating and cooling energy more efficiently than all-air systems.
The team installed these technologies in Bldg 1540A and repaired/recommissioned Bldg 1540B to bring it into conformance with its original design. The energy performance of both buildings were measured, recorded, analyzed, and compared.
These demonstrated technologies were considered successful even though they did not entirely meet some of their aggressive objectives. Building envelope sealing efforts decreased air infiltration from 0.82 to 0.39 cfm/ft2 at 75 Pa. While this did not meet the envelope air tightness objective, it was a 52% reduction in building air leakage. The DOAS satisfactorily dehumidified the outdoor air used to both ventilate the space and to supply building makeup air. The temperature of the conditioned space was managed by the radiant heat transfer of water flowing through the ceiling panels—absorbing heat and cooling the space during cold water flow and emitting heat and warming the space during hot water flow. The combined DOAS and ceiling-mounted radiant panel systems demonstrated their long-term ability to satisfy American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 55 (2010). The 95th percentile of Bldg 1540A space temperatures and RH values during occupied hours (6:00 a.m.–6:00 p.m.) were between 62 and 78°F, and 28 and 58% RH, respectively. These RH values also satisfied the aim of reducing mold and mildew potential. Energy reduction goals were also achieved. Overall, Bldg 1540A consumed 46% less energy compared with the prior fiscal year, and 20% less energy than Bldg 1540B during this fiscal year. An absence of maintenance concerns demonstrated the system’s O&M success; however, the system’s 26.7-year simple payback exceeded the 5-year objective.
This project resulted in several significant findings:
- It is feasible to significantly improve the air tightness of an existing building envelope without implementing major changes or disruptions to the interior or exterior surfaces of the building envelope.
- Radiant heating and cooling systems can adequately maintain comfort conditions in administrative buildings in locations with significant heating and cooling loads.
- Radiant cooling systems, when combined with a DOAS to properly dehumidify outdoor air and maintain proper space humidity conditions, can operate without condensation forming on the surface of the radiant cooling panels.
- Radiant heating and cooling systems are capable of improved energy efficiency compared to conventional all-air HVAC systems.
- Radiant systems are easily maintainable and require no special skills for HVAC technicians.
The radiant system installed in this project did not prove to be cost competitive with respect to a conventional all-air HVAC system. Considering first cost, energy savings, and reduced maintenance costs, the demonstrated system was calculated to have a long simple payback of 26.7 years. Nevertheless, it may be possible that using different approaches and technologies could cause a radiant system to compete favorably with traditional all-air HVAC systems.
Installing ceiling-mounted radiant panels in an existing ceiling grid proved to be very challenging. In retrospect, completely replacing the existing ceiling grid would have been a less-challenging approach. The team also found it difficult to coordinate installation of these radiant panels with the location of existing ceiling-mounted light fixtures and sprinkler heads. If this had been a new construction project, it might have been possible to better coordinate the location of the radiant ceiling panels with ceiling light fixtures and sprinkler heads.
This project was deliberately sited in a location characterized by hot and humid conditions, which required significant dehumidification and cooling capacity. In more mild climates, the economics of the demonstrated systems might be more favorable. As with any system, before deciding to design/install a radiant system, one should perform a thorough economic analysis to determine the most cost-effective alternative.