Lawrence Berkeley National Laboratory, Davis Energy Group, American Modular Systems (a manufacturer of RCs), and two California school districts collaborated to perform a field study of four new, high-performance RCs. The results of this study indicate that it is possible to engineer solutions that simultaneously increase the indoor environmental quality (IEQ) and energy efficiency of RCs.
The benefits of energy efficiency are well known, and energy-efficient design is becoming increasingly important as building codes and standards require it. High IEQ in buildings is expected to improve occupant health and work performance and reduce absenteeism.
This study of high-performance RCs demonstrates technologies that can simultaneously improve energy efficiency and IEQ, and quantifies the results. RCs are well suited to this demonstration because they are self-contained and have dedicated heating, ventilation, and air conditioning (HVAC) systems and well-defined occupancies.
The IDEC supplies continuous ventilation at âä¥7.5 L/sec per person even when heating or cooling is not required. Compared to the standard heat pump system, the IDEC consumes as much as 70 percent less cooling energy, and, because it has a quieter fan and no compressor, its noise output is lower. The IDEC hybrid system includes an 85-percent-efficient (annual fuel utilization efficiency) gas-fired hydronic space-heating system and an efficient inlet filter system.
The high-performance RCs were sited side by side at each of the schools prior to the fall 2001 semester and used during the semester by 3rd- and 4th-grade classes of 20-30 students; each class had one teacher. During nine weeks of the 2001 summer/fall cooling season (August to October 2001) and nine weeks of the heating season (January-March 2002), the two RCs at each school were simultaneously operated with either the standard heat pump or the IDEC unit; the systems in use were switched weekly. Each RC was instrumented to measure a range of IEQ and energy parameters, including humidity, temperature, air velocity, sound level, indoor and outdoor CO2 concentrations, particulate matter (PM) counts, volatile organic compound (VOC) and formaldehyde concentrations, and energy use.
Table 1 summarizes indoor CO2, indoor-outdoor formaldehyde, and indoor PM concentrations. Indoor sound level and daily HVAC operation costs are also shown. These data are averaged across the study RCs by cooling and heating seasons and by HVAC system type. The PM concentrations are presented as mass concentrations in three nested size bin ranges: 0.3 Âµm, 0.3 - 1.0 Âµm, and 0.3 - 5.0 Âµm. These ranges were chosen to facilitate assessment of the inlet filter effectiveness and system operation.
The continuous ventilation provided by the IDEC system was effective for controlling the concentrations of indoor-generated pollutants, as demonstrated by the formaldehyde data. School-day formaldehyde concentrations in both the cooling and heating seasons were higher during HPAC weeks than during IDEC weeks.
The teachers' usage of the HVAC system during the heating season was similar to usage during the cooling season, but morning heating demands led to more consistent use of the IDEC. Mean heating season indoor CO2 concentrations were 1,370Â±630 ppm and 760Â±370 ppm for HPAC and IDEC weeks, respectively.
Indoor PM concentrations were generally higher than outdoor concentrations, indicating that occupant activities were a source of particles. During the cooling season when doors and windows were frequently open, there was increased infiltration of PM from outdoors. Indoor PM concentrations were lower on average during HPAC operation across the particle-size distribution, but concentrations occasionally reached high levels with both HVAC systems.
Sound levels in the RCs were consistent across HVAC system and season, averaging about 56 A-weighted decibels (dBA). A comparison of occupied and unoccupied time periods showed that most of the noise increase above background in the occupied classrooms was from the occupants themselves, with HPAC and IDEC system operation contributing up to 14 dBA and 8 dBA, respectively.
Classroom total energy use and HVAC energy consumption were measured throughout the field study, and the energy data were used to calibrate a DOE-2 energy simulation model. Using the calibrated DOE-2 model for 16 California climate zones, we compared the energy use of the HPAC and IDEC, assuming that each HVAC system was operated to meet minimum ventilation standards. The resulting statewide average energy impacts per classroom included an 80 percent reduction in annual electricity use, more than 70 percent reductions in peak electricity requirements during both summer and winter, an increase in natural gas use (for winter heating), and a $220 annual energy cost savings.
These results overall suggest that it is possible to use efficient engineering solutions to simultaneously reduce energy consumption and improve indoor environmental quality.
This study was conducted by: M.G. Apte, D. Dibartolomeo, T. Hotchi, A.T. Hodgson, S.M. Lee, D.G. Shendell, D.P. Sullivan, and W.J. Fisk of the Indoor Environment Dept., Lawrence Berkeley National Laboratory, Berkeley Calif.; S.M. Liff of Massachusetts Institute of Technology, Boston; and L.I. Rainer of Davis Energy Group, Davis, Calif.
Reprinted from the Environmental Energy Technologies Division News #15, Lawrence Berkeley National Laboratory, Berkeley, Calif. For more information, contact Michael G. Apte at 510-486-4669; 510-486-6658 (fax); MGApte@lbl.gov.
The full report may be downloaded at http://buildings.lbl.gov/hpcbs/s_arc.html.
This study was sponsored by the California Energy Commission through the Public Interest Energy Research program.
Publication date: 05/17/2004