Lesson learned in portable classrooms.
Thirty-six percent of the nation's schools use portable classrooms. (1) Many school districts intend to use them temporarily, but units are seldom removed. Although our research may contradict past stereotypes, portables are perceived to provide a substandard quality of learning environment. (2) Built to minimum code requirements because of budget issues, typical specifications for relocatable classrooms do not offer high performance or durability strategies. They also are large energy users and are often blamed for indoor air quality problems.Several studies have evaluated potential improvements to portable classrooms. Washington State University and the Oregon Office of Energy conducted a study that examined the cost effectiveness of energy improvements to Pacific Northwest (PNW) relocatable classrooms. (3)
These studies concluded that opportunities for energy efficiency existed, with on-site commissioning during set up being particularly cost effective. (4)
Research conducted by Lawrence Berkeley National Laboratory examined modifications to save energy but also evaluated the volatile organic compound (VOC) emissions from typical interior finish materials used in the manufactured modular industry. This analysis not only verified energy savings but also revealed that the transportation of classrooms to their respective sites often resulted in increased outgassing of interior materials, thereby reducing VOC concentrations. (5)
A much-discussed study done for the Pacific Gas and Electric Company suggested a correlation between classroom daylight levels and improved student academic performance and attendance levels. (6) However, a more recent study shows weaker association, with window views and the acoustic environment being more important than daylighting. (2)
In previous work, the Florida Solar Energy Center (FSEC) studied retrofits in two existing portable classrooms in central Florida demonstrating the potential to reduce measured energy use by 40%. This was achieved by improving heat pump efficiencies, integrating ERV (enthalpy recovery ventilator) and changing to a highly reflective roof. (7) In separate simulation analysis, FSEC evaluated potential improvements to new portable classrooms across U.S. climates. (8) A building energy simulation tool was created to model the energy performance of relocatable classrooms in varied climates in the United States. Modeling results were used within this demonstration project to determine the most effective modifications for testing.
Specifications of Experimental Classrooms
These three case studies described in this report were side-by-side comparisons in three climates and became known as the performance enhanced relocatable classrooms (PERC) project. This research looked at specifically designed modular classrooms constructed in a factory and delivered to school sites. They are designed to use less energy, potentially improve indoor air quality, and provide enhanced levels of natural lighting. The research consisted of three different case studies in three different climates, requiring three different sets, of specifications. All exceeded the minimum building and energy code. Most relocatable classrooms in the United States are 24 ft x 40 ft or 24 ft x 36 ft (7 m x 12 m or 7 m x 10 m) units with a conditioned floor area of 860 to 960 [ft.sup.2] (80 [m.sup.2] to 89 [m.sup.2]). However, regional and local building codes create different specifications.
FSEC located matched pair units in three different climates. One pair of classrooms is in Cornwall, N.Y. (cold climate), Chapel Hill, N.C. (mixed climate), and Orlando, Fla. (hot-humid). The standard classroom is typical in specifications for each location. In contrast, the experimental PERC unit used the research strategies mapped out from the previous analysis. (8) The New York and Florida portables were elementary classrooms, while those in North Carolina were occupied by high school students. Within each location, the hours occupied and occupancy levels between the side-by-side comparisons exhibited little deviation.
Monitoring Results
Beginning in fall 2002, six classrooms (two in each climate) were constructed, sited, instrumented, and monitored for performance. Detailed 15-minute data were obtained including end-use energy, meteorological conditions, and interior classroom conditions for temperatures, humidity, C[O.sub.2] concentrations, and light and noise levels. As is typical, all of the classrooms were all-electric with measured end-uses including total classroom electrical demand, lighting loads, air conditioner, strip heat/heat pumps and bathroom heaters where applicable (each classroom has a bathroom). Miscellaneous electricity used for plug loads were obtained by differencing the total recorded site electrical use from the recorded energy use of the various submetered major appliances.
NEW YORK EXPERIMENT
The portables are located side-by-side at Willow Avenue Middle School in Cornwall, N.Y., about 50 miles north of New York City. These units consist of two classrooms each (24 ft x 34 ft [7 m x 10 m]) attached end-to-end. The control and experimental portables are 24 ft x 68 ft (7 m x 20 m) with 1,632 [ft.sup.2] (151 [m.sup.2]) of conditioned floor area. Cornwall, N.Y., is a heating-dominated climate with 30-year normals showing 6,848 heating-degree days and 507 cooling-degree days.
Energy Savings. Figure 1 shows the average electrical load shape describing the energy savings for the entire school year over a 24-hour cycle from November 2002 to June 20, 2003. The measured overall energy savings of the PERC was 48 kWh/day or 36%. Most of the savings were concentrated in the evening and early morning hours when the heating system was operating at its maximum. Note that the average peak electrical demand of the experimental unit at 8 a.m. is more than 2 kW (20%) lower than the control. The slightly greater demand around 4 p.m. is due to a difference in the lighting controls systems.
HVAC. All the enhanced portables were equipped with heat pumps, whereas conventional practice in portable classrooms typically uses strip heating. While this incurred an incremental cost (including additional cost for improved SEER), this translated into energy savings, especially in the New York and North Carolina comparisons where heating is a greater part of the annual HVAC loads. Figure 2 shows how the heating, energy savings varied over the winter months. Savings from November to March averaged 79 kWh or 47% even with a problem with the control thermostat in the PERC portable. This occurred when the system did not turn off the HVAC during unoccupied periods and maintained abnormally high temperatures. Other difficulties were experienced with the control of the auxiliary strip heat, which was always activated with the heat pump. Trial and error procedures isolated the problem as a thermostat compatibility issue with the automated control system. This was resolved near the end of the project. Savings likely would have been higher in a second year of monitoring (the units were vacant in 2003-2004).
Lighting. Figure 3 shows the lighting demand profile evaluated over the year. Performance was disappointing as the experimental unit had a lower installed connected lighting load, as well as the daylighting system, which should have reduced lighting energy use. However, the teacher in the control classroom often turned on only half of their lighting for use with an overhead projector, reducing comparative systems. Also, due to hardware troubles, we never achieved satisfactory daylighting responsive controls in the experimental unit.
Even so, we showed about an 8% lower average daily lighting use (1.2 kWh/day) in the PERC unit, largely due to lower lighting during evening hours due to the occupancy controls in the experimental unit. The occupancy controls increased lighting use around 3 p.m. to 4 p.m. after school is out. This seemingly contradictory result comes from the janitorial staff activating the lighting (due to occupancy sensing) in the experimental unit, whereas the lights are manually turned off in the control. Our trouble with the daylight dimming system emphasized the need to ensure that such controls operate from the outset. The importance of lighting control commissioning has been observed in previous projects. (9)
Subjectively, the interior lighting quality in the PERC was significantly improved. This is visually apparent in Photos 1 and 2, comparing daytime interior illumination in the two units with lights off. Although labor intensive to install, daylight distribution was improved by retrofitting a reflective enclosure around the skylight's wells. This increased desktop light levels by 10% to 15% after the retrofit.
NORTH CAROLINA EXPERIMENT
The matched pair portable classrooms in Chapel Hill have a mixed heating and cooling climate. The 30-year normals show 3,733 heating-degree days and 1,294 cooling-degree days. Each are 24 ft x 36 ft (7 m x 10 m) units with 864 [ft.sup.2] (80 [m.sup.2]) of conditioned floor area. The typical classroom used in this school district is a wood-framed structure with gypsum ceiling, unlike the Florida and New York typical classrooms, which used acoustic tile t-grid ceilings.
Energy Savings. During the school year from Nov. 1, 2003, through May 12, 2004, data showed that the modified classroom achieved an overall energy savings of 46%. Total electricity use averaged 51.1 kWh/day in the control against 27.3 kWh in the PERC (Figure 4). The relative proportions of the daily energy end uses in the conventional control are shown in the pie chart in Figure 5, illustrating that space heating and cooling dominates portable classroom energy use.
Lighting. Photo 3 shows the improved aesthetic quality of the PERC with the integrated skylights and flared skylight wells. Not surprisingly, the teachers at the school preferred the lighting quality and interior appearance of the daylit classroom.
FLORIDA EXPERIMENT
Florida has approximately 25,000 relocatable classrooms. (10) The Florida PERC experiment was located in hot and humid Orlando, which has 580 heating-degree days and 2,428 cooling-degree days. Specifications were based on experiences with the New York experiment and for climatic differences. In designing for climate, rather than greater insulation levels, reflective surfaces were specified for the roof. A major difference between the Florida PERC and those in New York and North Carolina was the insulation of the roof deck rather than the ceiling. This has the advantage of reducing plenum heat gain and bringing the duct system inside.
Energy Savings. Measured data from November 2003 to May 2004 showed an overall savings of about 81% or 45 kWh/day (Figure 6). The higher savings experienced in this project appeared related to the insulated roof deck system with the white roof, which reduced cooling loads by reducing heat gain to the duct system and greatly lowering building air infiltration.
Lighting. From the New York experiment, we learned the difficulty of integrating skylights into classrooms with acoustical ceiling tiles. The gypsum ceiling solution used in North Carolina was effective, but expensive to fabricate. In Orlando we implemented an alternative daylight integration strategy to simplify installation and reduce labor costs. Round 21 in. (533 mm) diameter skylights provided an effective solution. We also simplified the lighting controls. The tubular daylighting system has continuously dimming ballasts with photocell sensors to harvest daylighting savings. A dampered louver system is controlled with a simple twist timer used when the teacher must close the skylights. Figure 7 shows the lighting energy savings achieved by using more efficient fixtures, with occupancy controls and daylight integration. Figure 8 illustrates the increases desktop illuminance levels produced by the skylights: more than twice that in the control unit between 9 a.m. and 3 p.m.
Reducing Building and Duct Leakage. The PERC had a white reflective roof against the black single-ply membrane in the control, helping to lower roof/ceiling heat gains. The experimental unit also had icynene foam insulation applied to the roof deck to bring the duct system within the insulated envelope and lower air infiltration. Unlike the other sites, the attic or plenum space in the Florida portable is sealed, rather than ventilated. Blower door and tracer gas decay testing suggested this is a significant factor in reducing building and duct system leakage in the experimental model. The blower door test showed 23.2 ach at a 50 Pa pressure for the control against only 9.6 ach for the experimental unit. Similarly SF6 tracer gas tests showed 2.60 ach with the air handler operating in the control versus only 0.66 ach for the PERC unit. We also know from previous projects that moving the duct system inside the conditioned zone benefits HVAC system efficiency by lowering duct heat gains. This fact is reinforced by the excellent comparative performance observed in the Florida PERC.
Preliminary Economics
The experimental PERC classrooms had higher incremental costs associated with increased insulation, high performance windows skylight integration, automated controls, higher efficiency HVAC systems and improved interior finishes. These costs are likely much higher than what could be actually realized in mass manufacture due to the unique experimental nature of our project. With these caveats understood, Table 4 shows the incremental costs, energy savings and payback periods for each classroom. Note that savings per unit floor area were fairly similar between the North Carolina and New York units, although the North Carolina portable had considerably greater cost. However, the Florida PERC clearly shows the best overall electric savings performance.
Energy Consumption
Tables 5 and 6 show the measured energy consumption for the three experimental classrooms compared with the standard unit, as well as interior conditions prevailing over the measured period. The period monitored is from Nov. 17, 2002 to June 20, 2003 for the New York units and from Nov. 1, 2003 through May 12, 2004 for the North Carolina and Florida units.
Conclusions
In the PERC project, comparison experiments were conducted with energy efficient units compared with standard units in three locations. An assessment was performed on the integration of various climate-specific energy-efficiency improvements in each experimental portable compared with a conventional side-by-side twin. In each location the units' annual energy requirements were dominated by heating and cooling end-use. Lighting was only about 10% to 15% of the total. The monitored long-term measured energy savings of the PERC models were 36% in New York, 46% in North Carolina, and 81% in Florida. The large level of HVAC-related savings were due, not only to envelope-related measures, but also to the use of heat pumps versus strip heat in conventional units, reduced duct leakage and ERVs with C[O.sub.2] controlled demand ventilation.
Superior interior lighting with integrated skylights in the experimental model was demonstrated at each site. Lessons learned should allow integration of identified technologies in a more cost-effective fashion. For instance, the combination of tubular skylights with a sealed attic plenum with insulated roof deck system covered by a reflective roof in the Florida portable showed superior performance at potentially lower costs.
New York
Willow Avenue Elementary School, Cornwall, N.Y.
1,724 [ft.sup.2] (160 [m.sup.2])
Total cost of building: $56,160 (enhanced relocatable)
Florida
Shingle Creek Elementary School, Orlando, Fla.
864 [ft.sup.2] (80 [m.sup.2])
Total cost of building: $56,900 (enhanced relocatable)
North Carolina
Chapel Hill High School, Chapel Hill, N.C.
864 [ft.sup.2] (80 [m.sup.2])
Total cost of building: $49,300 (enhanced relocatable)
LESSONS LEARNED
* Skylights. Careful integration is necessary to incorporate skylights into the lighting plan. Consider tubular skylights to simplify integration.
* Daylighting Controls. Select daylight dimming controls that can be verified by the vendor to operate as indicated. Best results were with continuously dimming ballasts with a pull timer to temporarily close off skylighting. Require in the specification that these controls be commissioned.
* HVAC. Downsize auxiliary strip heat on heat pumps to prevent excessive inefficient morning use of inefficient resistance heating. Use outdoor temperature control to lock out strip heat above specified temperatures, and use ramp-up thermostats to reduce strip heat during morning warm-up. This also helps to avoid thermostat "overshoot" during morning thermostat recovery. Warn HVAC contractors of the exact specification to avoid confusion and compliance issues.
* Ducts. The ducts in all experimental portables were sealed with mastic, reducing leakage rates substantially (see specifications). The ducts were located in the insulated, ventilated attic in the control and experimental portables for the North Carolina and New York portables. The Florida PERC has spray foam insulation at the roof deck providing sealed and "conditioned" space for the ductwork. Based on comparison with the North Carolina PERC, this construction/insulation technique appeared to yield superior performance.
* Controls Integration. Verify that the thermostats are compatible with occupancy controls. Also verify compressor operation in heating mode and termination of auxiliary strip heat after temperature recovery. Commission occupancy controls for lighting and HVAC.
* Roof/Plenum Insulation. Evidence from the New York project suggests that acoustic ceiling tiles with a ventilated plenum leads to leaky buildings with excessive heating and cooling. Either sheetrock ceiling or sealed attic/plenum construction with an insulated roof deck is preferred. The Florida PERC with an insulated foam roof deck under a highly reflective roof with a sealed plenum was significantly tighter than the other portables. It also had the duct system within the insulated envelope under a reflective roof, leading to much lower heating and cooling energy use relative to the other types.
* Form Follows Function. Although the typical relocatable classrooms are stigmatized by their metal or TI-1 1 clad, square, low roof, box reputation, this project was funded to primarily research the effects of energy efficiency and indoor air quality improvements. It was also important to maintain a duplicate design to ensure the control and experimental models were compared accurately. This research is also relevant to "learning cottage," or vernacular architecture, for future modular classroom construction. However, forms are limited if cost-effective fabrication is to remain off site in a controlled factory.
Acknowledgments
FSEC expresses appreciation to the National Association of State Energy Officials (NASEO) and the U.S. Department of Energy for project funding and support. This research is detailed in an earlier report. (11)
References
(1.) Lewis, L., et al. 2000. Condition of America's Public School Facilities: 1999, U.S. Department of Education, NCES-2000-32.
(2.) Heschong Mahone Group, 2003. "Windows and Classrooms: A Study of Student Performance and the Indoor Environment." P50003-08Z-A-7, PIER Buildings Program, State of California.
(3.) Brown, G.Z., et al. 1997. "Design and Evaluation of Energy-Efficient Modular Classroom Structures, Phase II." University of Oregon and Modern Building Systems, Inc.
(4.) Klure, J., M. McSorley, 2002. "Northwest portable classrooms energy data study." Conference Proceedings 2002 State Energy Program/Rebuild America National Conference.
(5.) Apte, M.G. 2002. "Energy and Indoor Environmental Quality in Relocatable Classrooms." LBNL-49581, Lawrence Berkeley National Laboratory, Berkeley, Calif.
(6.) Heschong, L., R.L. Wright, and S. Okura. 2002. "Daylighting impacts on human performance in schools." Journal of the Illuminating Engineering Society, Summer.
(7.) Callahan, M.P., et al. 1999. "Evaluation of Energy Efficiency Improvements to Portable Classrooms in Florida." FSEC-CR-1133-99, Florida Solar Energy Center.
(8.) Parker, D.S., P. Fairey. 2001. "Preliminary Evaluation of Energy-Efficiency Improvements to Modular Classrooms." FSECCR-1272-01, Florida Solar Energy Center.
(9.) Floyd, D.B. and D.S. Parker. 1995. "Field Commissioning of a Daylight Dimming Lighting System." FSEC-PF-283, Florida Solar Energy Center.
(10.) Callahan, M.P. 1997. "Energy Efficiency for Florida Educational Facilities: The 1996 Energy Survey of Florida Schools." FSECCR-951-97, Florida Solar Energy Center.
(11.) Thomas-Rees, S., D. Parker, J. Sherwin. 2004. "Preliminary Evaluation of Performance Enhanced Relocatable Classrooms in Three Climates." FSEC-PF-382-04, Florida Solar Energy Center.
By Stephanie Thomas-Rees, Danny Parker, Associate Member ASHRAE; and John Sherwin
Stephanie Thomas-Rees is a research architect, Danny Parker is a principal research scientist, and John Sherwin is a senior research engineer at the Florida Solar Energy Center in Cocoa, Fla.
Table 1: New York standard and PERC specifications. Characteristic Standard Relocatable Floor Insulation R-11, Standard Wall Insulation R-11, Standard Ceiling Insulation R-19, Standard Windows Season Shield, Double Glazed Lighting 14 Fixtures at (4) T12 34 W Lamps Plus 1 Fixture With (2) T12 Each; 15 Ballasts; Other: Bathroom (2) 60 W Incandescent Bulb Plus (4) Outdoor Lights at 60 W; Connected Lighting Load = 2,264 W Skylights None Interior Floor 26 oz. Rolled Carpet Finish Heating System 10 kW Electric Resistance Heat Cooling System 3 ton Air Conditioner, SEER 10 Ventilation System Fixed cfm During Occupancy Bathroom Exhaust 4 Sone Fan HVAC Through Wall Standard Gasket Provided With Unit. Rough Install Opening Not Addressed Duct Joints Industry Standard Duct Leakage cfm25out = 458 Building Leakage ACH50 = 16.37 Characteristic PERC Floor Insulation R-13 Formaldehyde Free Wall Insulation R-19 Formaldehyde Free Insulation With 0.5 in. Polystyrene Board Ceiling Insulation R-30 at Roof Deck, With Airspace Between Rafters for Maintaining Cold Roof * Windows Low-e (U = 0.24, SHGC = 0.38) Lighting 12 Fixtures at (3) T8 32 W Lamps Plus 1 Fixture With (2) T8 Each; 25 Ballasts; Other: (2) 15 W CFL for Bathroom, (4) 60 W Outdoor; Connected Light Load = 1,422 W Skylights 12 Skylights with Site Modified Skylight Wells Interior Floor Nonpermeable Backing, Interface Carpet Tile, Finish Low VOC Glue Heating System Heat Pump, HSPF 7.5 With 10 kW Auxiliary Strip Heat Cooling System 3 ton Heat Pump, SEER 12 Ventilation System C[O.sub.2] Control for Ventilation With 3-Step Fan Speed and Energy Recovery Ventilator Bathroom Exhaust 1 Sone Fan HVAC Through Wall Sealed Rough Opening at HVAC Wall Connection Install With Mastic and Fiber Tape (On Site) Duct Joints Sealed With Mastic (On Site) Duct Leakage cfm25out = 271 Building Leakage ACH50 = 16.66 * The intended airspace between air barrier and the roof deck was not constructed as specified. The manufacturer made a substitution that was not approved and could not be mediated after the unit was constructed. Table 2: North Carolina standard and PERC specifications. Characteristic Standard Relocatable Floor R-11, Standard Insulation Wall Insulation R-11, Standard Exterior Door Honeycomb Core R = 1.626 Ceiling R-19 Batt Insulation Insulation Roof Dark Colored Asphalt Shingle Windows Single Pane, Aluminum Frame (U = 1.10, SHGC = 0.86, Vt = 0.90) Lighting 16 Fixtures at (2) T12 34 W; 16 Ballasts; Other: Bathroom (1) 60 W Incandescent Bulb Plus (2) Outdoor Lights at 60 W; Connected Lighting Load = 1,268 W Light Controls Manual Outdoor Light Manually Controlled Skylights None Interior Floor Roll Carpeting Finish Interior Wall Vinyl Covered Gypsum Finish Heating System 10 kW Electric Resistance Heat Strip Cooling System 3.5 ton Air Conditioner, SEER 10 Ventilation Fixed cfm During Occupancy System HVAC Controls Manual Thermostat Bathroom 4 Sone, 100 cfm Exhaust Fan Duct Leakage cfm25out = 197 Building ACH50 = 9.08 Characteristic PERC Floor R-15 Formaldehyde Free Insulation Wall Insulation R-15 Formaldehyde Free Insulation with R-7 Isocyanurate Sheathing, House Wrap Exterior Door Polystyrene Core R = 4.8 Ceiling R-38 Blown Insulation Roof Light Colored Asphalt Shingle with Barrier Decking Windows Low-e Argon Gas-Filled, Vinyl Framed (U = 0.35, SHGC = 0.38, Vt = 0.58) Lighting 10 Fixtures at (3) T8 32 W Lamps Plus 3 Fixtures With (1) T8 each; 20 Ballasts; Other: Bathroom (1) 13 W CFL Plus (2) Outdoor Lights at 13 W CFL; Connected Lighting Load = 1,065 W Light Controls Photosensor Controls Continuous Dimming Ballast With Manual Override Outdoor Light Photosensor Controlled Skylights (6) Skylights Interior Floor Nonpermeable Backing Carpet Tile, Low VOC Glue Finish Interior Wall Low Odor Latex Paint Finish Heating System Heat Pump, HSPF 7.5, 5 kW Auxiliary Heat Strip Cooling System 3 ton Heat Pump With ERV, SEER 12 Ventilation CO2 Control for Ventilation With 3-Step Fan System Speed With ERV HVAC Controls Energy Monitor Bathroom 0.3 Sone, 50 cfm Exhaust Fan Duct Leakage cfm25out = 182 Building ACH50 = 4.83 Leakage Table 3: Florida standard and PERC specifications. Characteristic Standard Relocatable Floor R-14 Unfaced Insulation Wall Insulation R-11 Faced Exterior Door Honeycomb Core R = 1.5 Ceiling R-19 Faced Insulation Roof Standard Dark Roof; 0.45 mm Black EPDM Over V2 in. Roof Board Windows 1/8" Nontempered Bronze Tint Glass (U = 1.03, SHGC = 0.84, Vt = 0.77) Lighting 14 Fixtures at (2) T12 34 W Lamps Plus 3 Fixtures With (1) T12 each; 17 Ballasts; Other: Bathroom (1) 60 W Incandescent Bulb Plus (2) Outdoor Lights at 60 W; Connected Lighting Load = 1,234 W Outdoor Light 60 W Incandescent Manually Controlled Skylights None Interior Floor 26 oz. Rolled Carpet Finish Heating System Strip Electric Heat 10 kW Heat Strip Cooling System Central AC 3.5 ton With ERV, SEER 10 Ventilation Fixed cfm During Occupancy System Bathroom 4 Sone, 100 cfm Exhaust Fan Duct Leakage cfm25out Supply = 426 Building ACH50 = 23.2 ach Leakage * SF6 Tracer Gas Infiltration Air Handler On: 2.60 ach Decay Infiltration Air Handler Off: 0.27 ach Characteristic PERC Floor R-14 Unfaced Formaldehyde Free Insulation Wall Insulation R-14 Unfaced Formaldehyde Free Insulation With Vfe in. Gypsum Board With 3/4" Polyisocyanurate Foam Insulation Board Exterior Door Polystyrene Core R = 4.8 Ceiling R-30 Spray Foam Insulation at Roof Deck Insulation Roof Reflective Roof; 0.45 mm White EPDM Over 5/8 in. Roof Board Windows Low-e Argon Gas-Filled, Vinyl Framed With 60 Glass (U = 0.28, SHGC = 0.39, Vt = 0.71) Lighting 8 Fixtures at (3) T8 32 W Lamps Plus 3 Fixtures With (1) T8 Each; 20 Ballasts; Other: (3) 15 W CFL, Photosensor Controlled; Connected Lighting Load = 915W Outdoor Light 15 W CFL, Photosensor Controlled Skylights (6) 21 in. Diameter Skylights Interior Floor Nonpermeable Backing Carpet Tile, Low VOC Glue Finish Heating System Heat Pump, HSPF 7.5, 5 kW Strip Heat Cooling System Heat Pump With ERV, SEER 12 Ventilation C[O.sub.2] Control for Ventilation With 3-Step System Fan Speed and Energy Recovery Ventilator, Energy Monitor Bathroom 1.3 Sone, 190 cfm Exhaust Fan Duct Leakage cfm25out = 274 Building ACH50 = 9.6 ach Leakage * SF6 Tracer Gas Infiltration Air Handler On--0.66 ach Decay Infiltration Air Handler Off--0.05 ach * Building air changes under 50 Pa blower door test pressure. Table 4: Preliminary economics. Incremental Incremental Energy Cost ($) Cost ($/ Electric Savings [ft.sup.2]) Rate ($) (kWh/Day) N.Y PERC $23,160 $14.20 $0.11/kWh * 48 N.C. PERC $22,300 $14.20 $0.08/kWh * 24 Fla. PERC $24,400 $28.20 $0.09/kWh * 45 Energy Annual Payback Savings Savings Period (Wh/Day/ ($) [ft.sup.2]) N.Y PERC 29.4 $1,930 12 years N.C. PERC 27.8 $700 17.6 years Fla. PERC 52.1 $1,480 16.5 years * These were the utility rates at the time the project was conducted. Rates today are higher. Therefore, annual savings are expected to be more and the payback period less. Table 5: Total measured long-term energy consumption for portable classrooms. Parameter N.Y. N.Y. N.C. Control PERC Control Total (kWh/Day) 134.3 86.0 51.1 HVAC (kWh/Day) 118.8 71.9 45.0 Lighting (kWh/Day) 14.9 13.6 3.9 DHW (kWh/Day) 0.2 0.4 1.0 Other (kWh/Day) 0.4 2.7 1.2 Savings (kWh/Day) -- 45.7 -- Interior C[O.sub.2] 777 788 746 (ppm) Interior Temperature 71.3 70.4 68.9 (°F) Interior Relative 32 30 42 Humidity (%) * Parameter N.C. Fla. Fla. PERC Control PERC Total (kWh/Day) 27.3 55.5 10.4 HVAC (kWh/Day) 19.9 49.6 8.5 Lighting (kWh/Day) 1.3 4.2 1.3 DHW (kWh/Day) 0.9 -- -- Other (kWh/Day) 5.2 1.7 0.6 Savings (kWh/Day) 23.8 -- 45.1 Interior C[O.sub.2] 628 531 744 (ppm) Interior Temperature 67.5 70.7 70.7 (°F) Interior Relative 38 50 49 Humidity (%) * * Weekdays, 8 a.m.--3 p.m. Table 6: Total measured long-term energy consumption for portable classrooms, Btu/[ft.sup.2] per day. Location Control PERC Cornwall, N.Y 280.8 Btu/[ft.sup.2] 179 Btu/[ft.sup.2] Chapel Hill, N.C. 201.8 Btu/[ft.sup.2] 107 Btu/[ft.sup.2] Orlando, Fla. 219.2 Btu/[ft.sup.2] 41 Btu/[ft.sup.2] Location Savings Btu/ % Savings [ft.sup.2] Per Day Cornwall, N.Y 101 36 Chapel Hill, N.C. 94 46 Orlando, Fla. 178 81 Figure 5 (left): Measured average electricity end-uses in control portable. Lights (8%) Hot Water (2%) Other (2%) HVAC (88%) Note: Table made from pie chart.
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| Author: | Thomas-Rees, Stephanie; Parker, Danny; Sherwin, John |
|---|---|
| Publication: | ASHRAE Journal |
| Article Type: | Report |
| Geographic Code: | 1USA |
| Date: | May 1, 2009 |
| Words: | 4478 |
| Previous Article: | Using time-of-day scheduling to save energy. |
| Next Article: | Commissioning high performance buildings. |
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