Portable Classrooms - Indoor Environment

Chapel Hill Middle School, Chapel Hill, North Carolina

The NC PERC, located at Chapel Hill Middle School in Chapel Hill, North Carolina was sited in November 2002. The North Carolina Solar Center partnered with FSEC to help monitor the performance of the NC PERC experiment. The experiment consisted of (2) end-to-end 24�-0� x 36�-0� modular classrooms sharing a common wall, corridor and bathroom totaling 1.724 sq feet. Each classroom was occupied during testing. The PERC was located next to the conventional built relocatable classroom and was expected to be 50% more energy efficient and have enhanced lighting levels. FSEC monitored energy performance in both classrooms. All data was downloaded daily to FSEC via modem.


Overall Results

Data collected from November 1, 2003 through March 8, 2004 showed that the modified classroom achieved overall energy savings of 50%.

Construction efficiency related differences between the two NC classrooms are listed in the table below.

Side-by-Side Study of NC PERC
Specifications of Standard and Energy Efficient Construction

Characteristic Standard Relocatable PERC
Floor Insulation R-11 R-15 Formaldehyde Free
Wall Insulation R-11 R-15 Formaldehyde Free insulation w/R-7 polyisocyanurate sheathing, Tyvek house wrap
Exterior Door Steel/steel knock down with 10�x10� view panel R=1.616 HM pressed steel knock down CECO with polystyrene core 10�x10� view panel R=14.8
Ceiling Insulation R-19 batt insulation R-38 blown (10.5 inches)
Roof Dark colored asphalt shingle Light colored asphalt shingle with Techshield radiant barrier
Windows Single pane, aluminum frame (U=1.10, SHGC= 0.86, Vt=0.90) Low-E Argon gas filled vinyl framed by Reynolds 200 Series (U=0.35, SHGC-0.38, Vt=0.58)
Lights 16 fixtures @ (2) T12 34W lamps + Bathroom (1) 60 incandescent bulb + (2) outdoor lights @ 60W=1,208 Total Installed Wattage 10 fixtures @ (3) T8 32 W lamps _ Bathroom (1) 13W CFL + (2) outdoor lights @ 13W CFL = 790 W Total Installed Wattage
Light Controls Manual controlled � one switch controls one half of the fixtures in the classroom and the other switch located on opposite wall controls other half of fixtures Occupancy sensor initially activates lights, photosensor maintains minimum 50fc light level with continuously dimming ballasts
Outdoor Light 60 Watt incandescent Manually controlled (2) 13 Watt CFL, photosensor controlled
Skylights None (6) SunOptics Skylights Model800IB (2348), curb mounted by power light louver
Interior Floor Finish Roll carpeting Non-permeable backing, Interface Cubic carpet tile, low VOC glue
Interior Wall Finish Vinyl covered gypsum Harmony High Performance Low Odor Latex Paint
Heating System 10kW electric resistance heat strip, 34,130 BTU Bard SH Series Heat Pump with ERV, HSPF 7.5, 5 kW heat strip
Cooling System Bard Central Air Conditioning 3.5 ton 43000 BTU cool SEER 10 3 ton Bard SH Series Heat Pump with ERV SEER 12
Ventilation System Fixed CFM during occupancy CO2 control for ventilation with 3-step fam speed with energy recovery ventilator
HVAC Controls Manual t-stat Bard CS2000 Energy Monitor
Bathroom Exhaust Fan Broan, 4 sonne, 100 CFM 2/60W incandescent light bulb Broan Ultrasilent model #S80Lu, 0.3 sonne, 50CFM with 13W cfl
Duct Leakage* CFM25out = 197 CFM25out = 182
Building Leakage* ACH50 = 9.08 ACH50 = 4.83
Building Leakage (nat)* ACH50 = 0.47 ACH50 = 0.25
Sound level of HVAC equipment (fam only) 46dB 44dB
Sound level of HVAC equipment (ac compressor on) 51dB 49dB
*Leakage Testing performed � October 22, 2003

Detailed Results

The graph below shows the predicted annual energy savings potential for typical modular classrooms in various climates. The 48% energy savings predicted for the NC PERC was on target with actual savings measured at 50%.

As indicated in the chart below, total electricity use averaged 64.9 kWh/day in the control portable against 32.3 kWh in the improved one for an overall energy savings of 50%.

The timing of the savings are shown in the average daily load profiles shown in the plot below.

Lessons Learned

  • Adjustments to the LCD lighting control module (ratio of dimming to the amount of daylight contributing to the illumination of the zone) can significantly contribute to energy savings without compromising indoor light levels.
  • Providing timely and easily understandable information to teachers and maintenance staff is a must.
  • Carefully designed and installed skylight wells are a must for natural light distribution in the classroom.
  • In mixed climates, such as Chapel Hill, North Carolina, insulation with a radiant barrier looks to be the best strategy for the roofing system as it helps control both heating and cooling needs. However, daylighting is quite attractive as it reduces lighting energy and substantially reduces space cooling. Insulation measures, duct leakage control and a more efficient heating system all look to be promising measures.
  • Specification of a heat pump is important to controlling heating costs.