Boise School District Retrofit

Figure 6. Weather monitoring system installation in the Boise portable classroom.

BAIHP staff located a portable classroom at the West Boise Junior High School in the Boise Idaho School District, occupied by a teacher who was interested in having the classroom monitored and retrofitted.  The teacher is also an Idaho State legislator active in education issues, so the chance of the project results having impact was increased.

BAIHP staff performed a field testing, and installed data logger monitoring equipment to track the classroom's energy use during Year 1.  In Year 2, the classroom was retrofitted with an efficient HVAC system (controlled by CO₂ sensors), lighting and envelope measures.  The classroom was then retested, and monitored for the rest of the year.

BAIHP staff worked with Pacific Northwest National Laboratories (PNNL) on the pre- and post-retrofit audits, and installation of the monitoring equipment.  In their capacity of providing energy management services to the school district, the local utility, Avista Corp., collected lighting and occupancy data. 

The classroom was retrofitted in the summer of 2001.  Monitoring data indicates a reduction of 58% in energy usage post-retrofit.  Blower door tests indicate a reduction in air leakage from 9 ACH at 50 PA to 5 ACH at 50 PA. See Figure 8.  The cost of the retrofit was $9,892.

Monitored CO₂ data suggests that the CO₂ sensor that controls the HVAC system is not correctly configured.  The system does seem to react to an increase in CO₂ levels early in the day, but does not remain on; CO₂ levels only begin to significantly dissipate after 1 p.m.  BAIHP staff have noted the difficulty of correctly configuring these sensors in other monitored classrooms.

Oregon Schools

Oregon BAIHP staff worked with the Portland Public School District to procure two energy efficient classrooms.  The classrooms were constructed to specifications determined by BAIHP staff.  The specifications include increased insulation levels in the envelope, high efficiency windows, transom windows designed to increase daylighting. BAIHP staff videotaped the construction process for one of the classrooms.

The classrooms were delivered and sited in September 2001.

Monitoring equipment was installed by PNNL staff.  Estimates using the software Energy-10 indicate a total energy consumption of 9200 kWh, or $583 per year at Portland energy rates.  Measured results showed the Oregon portable used about 6600 kWh for the monitored period.

Incremental costs for the energy efficiency measures were $6,705 over Oregon commercial code, including approximately $2,500 for the HVAC system.  This suggests a simple payback of 10-12 years.

Initial blower door tests indicate air leakage rates of 11.3 ACH at 50PA.  BAIHP staff also identified significant leakage through the T-bar dropped ceiling and up through the ridge vents.

Monitoring results indicate the same HVAC control problems exist with the Oregon classroom as with the others studied in this project.

Oregon BAIHP staff conducted a modeling study that determined the ideal daylighting set-up. Windows placed on each side of the portable classroom along with roof skylights or solar tube apparatus provided the highest level of daylight to the room.

A survey sent to teachers and maintenance staff indicates a high degree of satisfaction with the efficient portables; the teachers were most impressed with the improved indoor air quality and increased light levels due to the daylighting windows.

Outreach to other school districts included involvement in numerous meetings, including the Oregon School Facilities Managers annual meeting, and the Oregon Association of School Business Officials annual meeting.

Figure 9. Measured energy use in Oregon efficient portable classroom, compared to existing classrooms

The Energy Efficient model outperformed code level models in the Portland area.  The older the classroom, the more energy consumed.  Even compared with new code level models in the same year, the Energy Efficient model used 35% less energy. Conventional code level classrooms do not include energy efficient measures, greatly increasing operating costs.  Classrooms built more than 10 years ago use twice as much energy compared to the efficient model, and those older than 20 years consume more than 3 times the amount of energy.  High performance classrooms can save anywhere from $200 to $1000 dollars a year in energy costs when compared to less efficient models.

Additional Outreach

BAIHP staff authored and submitted an article on the portable classroom project for publication in the Rebuild America/Building America Partner Update newsletter.

BAIHP staff also worked with the North Thurston School District to troubleshoot a portable classroom in Lacey, Washington.  The classroom was experiencing high energy use and poor indoor air quality.  BAIHP staff tested the classroom, made recommendations including opening the supply dampers, install a wall side vent to better ventilate the classroom and discussed the specification development process with district staff. The North Thurston School District is now including most of the measures listed in the new procurement guidelines for all future purchases of portable classrooms. The school district will investigate the feasibility of installing an air/vapor above the T-bar dropped ceiling and will record costs.

Workshops

In Year 2, BAIHP staff hosted the Smart Portable Classroom Collaborative Workshop in Portland, Oregon.  This was the first opportunity for national experts in portable classroom design, construction, siting, and end use to come together and discuss energy-related issues.

No additional workshops were held in Year 3, as the specifications were still being developed.  In Year 4, BAIHP staff will meet with district procurement staff, maintenance personnel, administrators, manufacturers, suppliers, and other interested parties to disseminate the specifications once they are finalized.

Findings

Comparative Energy Usage in Portable Classroom Study

Figure 10. Comparative Energy Usage in Portable Classroom study.

Notes

• In the 2000-2001 school year, the teacher in Marysville, WA P5 (efficient classroom) brought in small portable heaters; this offset space heating, and made for excessive plug loads.  The portable heaters were not in use during the 2001-2002 school year.
• The two significant difference in space heating between P2 and P5 can be explained by the fact that P5 had major air leakage through the T-bar dropped ceiling and that thermostat in P2 was set-back manually at the end of the day during the 2001/2002 school year.  
• The Portland portable had the lowest energy use of all the portables monitored during this project, adjusted for climate (0.43 kWh/HDD ratio).
• The Boise Portable data shows a 58% reduction in space heating use due to the retrofit measures.
• Portable classrooms in the NW are occupied about 1225 hours per year, or about 14% of the total hours in a year.
• Most portable classrooms are constructed of standard materials at a construction facility that comprises low thermal mass in classrooms (chairs, desks, wallboard, carpeted flooring).
• The average number of occupants in the standard 28' X 32' portable classroom provide internal heat of about 480 kWh/yr, or 8 - 10 % of space heating requirements.
• Even though the portable classrooms in this study are not constructed to minimize energy loss they still have relatively low energy consumption due the items listed about. The energy use ranges from 4000kWh/yr to 9700 kWh/year.
• Most of the heat loss in portable classrooms manufactured after 1990 is by air leakage through T-Bar dropped ceilings that do not use a sealed air/vapor barrier. This phenomenon is due to the utilization of a dropped T-Bar ceiling in place of the more expensive sheet rock used in older portables. Air leakage is further aided by the use of an unsealed marriage line which is used as a low cost method of meeting the state ventilation requirements in attics.
• Because all portables tested in the project used a simple 7 day programmable thermostat, the HVAC systems are operating on vacations and holidays which greatly increases  electricity consumption.
• The energy codes in Washington, Oregon and Idaho are high enough to make beyond-code envelope measures non cost-effective.
• Older portable classrooms that are being considered for removal and disposal can be retrofitted with new energy efficiency measures at much less cost than a new portable classroom. Low e, vinyl framed windows; insulated doors; T-8 light fixtures; and caulking and sealing air leaks can all be cost-effective when refurbishing older portable classrooms. New HVAC systems being replaced in older portable classrooms will be the biggest single cost item and can cost anywhere from $4500 to $6500. A significant decrease in space heating can be attained by utilizing these measures.
• CO₂ sensors appear to be unreliable as a control strategy.  CO₂ sensors installed by the field crews and monitored by data loggers did not match the readings being shown by the CO₂ sensors that controlled the ventilation systems in the portable classrooms.  CO₂ sensors tested by staff at the Florida Solar Energy Center went out of calibration rather quickly after being installed.

Recommendations
Based on the data analysis the following measures are recommended:

• Install 365 day programmable thermostats in all existing portables and specify them for new construction. These types of units are available and have been designed for small buildings such as portable classrooms.
• In portable classrooms constructed with T-Bar dropped ceilings, install an air/vapor barrier above the T-Bar system and on the warm side of the insulation. Completely seal all edges and overlaps.
• If roof rafter insulation is used, seal the marriage line at the roof rafter joint with approved sealant such as silicon caulk or foam. Make sure there is adequate ventilation between the insulation and the roof.
• Conduct an audit of the older portables scheduled for disposal to determine if retrofitting them will be cost effective.
• Install occupancy sensors to operate the ventilation system.
• Specify new units be ordered with windows on opposite walls.
• Specify new units with the exhaust fans be placed on opposite side of classroom than the fresh air supply.

Guidelines
Based on the experiences of the project, BAIHP staff produced guidelines for procurement, set-up, and commissioning of new portable classrooms, as well as guidelines for the retrofit of existing classrooms.  These guidelines are included in this report as Appendix B.