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.
Results
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.
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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.
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