Experimentally-Determined Characteristics of Radiant Systems for Commercial Buildings

PG&E operates a wide range of building energy efficiency programs designed to meet its energy and demand goals, both for the program cycles and in the longer term, for the big bold CA Strategic Energy Efficiency goals leading to Net Zero Energy building by 2030. Increasingly, utilities would like to explore shifting their programs from component-based solutions to more innovative integrated system solutions. However, the field performance of these integrated systems is more difficult to evaluate and quantify, which is one of the key motivations for the use of the FLEXLAB building test facility at Lawrence Berkeley National Laboratory (LBNL). FLEXLAB enables repeatable experiments in 600 ft2 test chambers that are representative of a perimeter zone in a commercial building. PROJECT GOAL The main goal of this Project was to characterize the behavior of radiant heating and cooling systems in order to provide information for designers that would reduce both the cost and the perceived risk associated with radiant systems. The aim is to improve energy and comfort performance by encouraging the appropriate adoption of radiant systems in both new construction and retrofit of commercial buildings in California. A secondary goal was to assess the benefits of integrated control of HVAC, active facades and daylight harvesting. PROJECT DESCRIPTION The systems studied, and particular aspects of their design and operation relating to performance and cost, were selected in conjunction with an Industrial Advisory Group consisting largely of California practitioners – see Appendix 1. Two systems were studied in FLEXLAB: • Radiant floor slab heating and cooling systems • Radiant ceiling panel heating and cooling systems Radiant slab systems have the ability to smooth and shift peak HVAC loads but are often difficult to retrofit and so are applicable primarily to new construction, although pipes embedded in a relatively thin topping slab can be installed on the structural slab in some cases. Radiant panel systems can be installed in suspended ceilings, and therefore are relatively easy to retrofit, but have no thermal storage capability. They have the disadvantage of being more expensive than radiant slab systems for new construction and so are more applicable to retrofit situations. To motivate the study of radiant system characteristics of relevance to designers, a simulation-based assessment of the savings potential of radiant ceiling panel systems relative to a conventional variable-air-volume (VAV) system was performed for a mediumsized office building in four California climates. Radiant slab systems respond relatively slowly and so their control, and their simulation, is not as straightforward as for the fastacting radiant panel systems. However, a field study comparing the performance of a radiant slab system to that of a conventional air-based system was been identified and its results are summarized in Section 4.6. Integrated control of HVAC, active facades and daylight harvesting was assessed using simulation for the same four climates, with a view to evaluating the technical potential of off-the-shelf integrated control products. The ability of radiant systems to address perimeter zone effects using simple controls was investigated, including the effect of ceiling fans, as was the ability of radiant floor slab systems to shift and smooth peak HVAC loads. Priorities for study topics were chosen in consultation with the Industry Advisory Group.