Portable Classrooms - Indoor Environment

Cromwall Elementary School, Cromwall, New York

The NY PERC, located at Willow Avenue Middle School in Cornwall, New York was sited in September 2002. It was built by Design Space Modular, in McCrae, Georgia and consisted of (2) end-to-end 24�-0� x 36�-0� classrooms sharing a common wall, corridor and bathroom, totaling 1,724 sq. feet. During testing, each classroom was occupied. The PERCs were located next to the conventional built relocatable classrooms 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

Measured data shows that an overall savings of 36% were achieved for the combined heating and cooling loads. Good data collection periods were November 17, 2002 � June 20, 2003.

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

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

Characteristic Standard Relocatable PERC
Floor Insulation R-11 R-13 Formaldehyde Free
Wall Insulation R-11 R-19 Formaldehyde Free Insulation with polystyrene board
Ceiling Insulation R-19 R-30 @ roof deck, w/airspace between rafters for maintaining cold roof
Windows Season Shield Double Glazed Low-E Thermopane by Atrium
Note (U=0.24, SHGC � 0.38)
Lights  3,072 Total Installed Wattage 1,536 Total Installed Wattage
Skylights None 12 SunOptics skylights
Interior Floor Finish 26 oz. Rolled carpet Non-permeable backing, Interface carpet tile, low VOC glue
Heating System Board Electric Resistance Heat Bard Qtec Heat Pump, HSPF 7.5
Cooling System Bard Central Air Conditioning, SEER 10 Bard Qtec Central Heat Pump, SEER 12
Ventilation System Fixed CFM during occupancy CO2 control for ventilation with 3-step fan speed and energy recovery ventilator Bard CS200 Energy Monitor
Bathroom Exhaust Fan Broan, 4 sonne Broan Ultra Silent Fan, 1.0 sonne
HVAC Through Wall Install Standard gasket provided with unit-rough opening not addressed On site � sealed rough opening at HVAC wall connection with mastic and fiber tape
Duct Joints Industry Standard Sealed with Mastic (post construction)
Building Leakage* CFM25out = 3627 CFM25out = 3692
Building Leakage* ACH50 = 16.37 ACH50 = 16.66
*Leakage Testing performed � December 9, 2002

Detailed Results

Figure 1 shows a pie chart revealing how energy was used in the Control portable classroom over the year; Figure 2 shows the same data for the PERC portable revealing a 36% energy savings. The clear message of the data is that energy use in portable classrooms is dominated by heating, cooling and ventilation. Lighting consumption is very much a secondary issue and other end-uses are virtually unimportant.


The graph at right shows the average shape of the energy savings over the entire school year over a 24 hour cycle from November 2002 � June 20th of 2003. The measured overall energy savings of the more energy efficient experimental model was 48 kWh/day or 36%. Most of the savings were concentrated in the evening and early morning hours when the heating season was operating at its maximum. Note that the average peak electrical demand of the experimental unit at 8 AM is more than 2 kW (20%) lower than the control.

Figure 3 shows how the HVAC savings varied over the winter months. Savings from November - March averaged 47% even with a difficult to resolve problem with the control thermostat in the PERC portable. This occurred when the system would refuse to turn off the HVAC system during unoccupied periods and would maintain abnormally high temperatures. A series of trial and error procedures were used to isolate the problem which eventually turned out to be a thermostat compatibility issue with the automated (CS-2000) control system. This was only resolved near the end of the project; savings would be considerably higher in a second year of monitoring. Regardless, the success in resolving this problem was reflected in more successful projects in North Carolina and Florida.

Figure 3

Lessons Learned

  • In cold, heating dominated climates such as Rochester, New York, insulation measures and duct air leakage control measures look to be the most important.
  • Results further suggest that ground source heat pumps or natural gas heating may be attractive alternatives to air-source heat pumps.
  • Daylighting, while producing savings in lighting energy, tends to increase heating budgets and is not as attractive as insulation and heating system measures. It appears important that a successful daylighting strategy in 12 such locations utilize highly insulated glazing (double glazed low-e was assumed) in order to be successful.
  • Floor and wall insulation is important.
  • Solar control glass is counterproductive.