Reference Publication: Callahan, M. P. and D. S. Parker (1998). Energy Efficient Florida Educational Facilities. Improvements to a Portable Classroom. FSEC-CR-1008-98. Florida Solar Energy Center, Cocoa, FL 32922.
Disclaimer: The views and opinions expressed in this article are solely those of the authors and are not intended to represent the views and opinions of the Florida Solar Energy Center.
Efficient Florida Educational Faclities.
Improvements to a Portable Classroom
P. Callahan and Danny S.
Florida Solar Energy Center (FSEC)
An ambitious project by the Florida Solar Energy Center (FSEC) and sponsored by the Florida Department of Education (FDOE) is monitoring the energy use of two adjacent portable classrooms to see how they might be made more energy efficient in a hot-humid climate. These classrooms have been monitored for one year to collect baseline data before the energy efficient measures are installed. These measures include an efficient lighting system, a new air conditioner, and a reflective white metal roof.
Figure 1. Photograph of the portables being monitored
at Silver Sands Middle School.
Portable 035 is on the right and portable 096 is on the left. Each has a conditioned space of 720 ft2.
The purpose of this study is to determine if portable classrooms can be made more energy efficient either by retrofit or at the time when new portables are constructed. We also want to determine which measures are the most effective and most affordable so that both energy savings and costs will be tracked. Retrofits include:
Portable 035 was chosen for the initial retrofits since during the year of collecting baseline data, the HVAC has performed poorest of the two.
An ever-expanding number of portable classrooms is a growing fact of life in the Florida school system. Where these relocatible classrooms were once thought to be temporary structures, it is now accepted that they are more or less permanent. One of the main problems of portable classrooms is that they are often poorly received by the community (Brown 1995). They are frequently judged as substandard educational facilities (Florida 1993) and have been called "eyesores" and "monotonous and uninspiring"(Educational Facilities Lab 1964). These perceptions have to do mainly with the portable's bland coloration and their non-permanent appearance (Brown 1995).
Florida schools, on average, have 9.9 portables with 836 ft2 of floor area per portable (Callahan et al. 1997). In addition, studies show that each portable classroom uses approximately 30 kWh/day (Sherwin and Parker 1996) or 10,840 kWh per year (Callahan et al.1997). Portables account for 11.1 % of the energy budget for Florida public schools. Recent research shows that the energy use at Fellsmere Elementary is 360 kWh/day for 12 portables (Sherwin and Parker 1996).
The Florida Solar Energy Center, in conjunction with the Volusia County School Board and the Florida Department of Education, chose Silver Sands Middle School for the study. Silver Sands is located in Port Orange south of Daytona and has 39 portable classrooms.
Portables 035 and 096 have been chosen for the study. These portables are side by side and identical in dimensions and configuration. They are 36 ft. x 20 ft. in an east-west orientation with North and South facing windows. The windows are 4.1 ft. x 6.1-6.9 ft. with three on both the North and South side of the portables. Total glazed area is 162.6 ft2 on each side of the portable.
Each portable was fully instrumented. Metering equipment consists of thermocouples that measure interior air temperatures and relative humidity, roof surface temperature, attic air temperature, and decking temperature. The portables are also wired to measure how long the doors are opened and provided with CO2 sensors. The rooms are also configured to measure total portable kWh, air conditioning (AC) kWh, and lighting kWh. There is also a weather station at the site that measures wind speed, ambient temperature, relative humidity, and solar insolation over a 24 hour period. Instruments are scanned every ten seconds with integrated averages output to logger storage every 15-minutes. All this instrumentation is poled by a Campbell CR10 data logger that is accessed by FSEC at night.
Lighting represents about 13% of the total annual energy consumption for Florida schools (Sherwin and Parker 1996). This does not take into account the heat produced by lighting. Lights increase the sensible AC load by an average of 23% annually (Floyd et al. 1995). Schools typically have T12 lamps with magnetic ballasts in classrooms because they are the most inexpensive. However, it has been shown in previous studies (Sherwin and Parker 1996, Parker et al. 1996a, McIlvaine et al. 1994) that slim-line T8 lamps with electronic ballasts performed best in both commercial buildings and educational facilities. These T8 lamps combined with electronic ballasts consume less energy (122 W versus 155-180 W for the T12 lamps with magnetic ballasts), are brighter than T12s (109 decalux for T12s and 158 decalux for T8s), and run cooler (McIlvaine et al. 1994).
This is the concept behind retrofitting the lighting system in portable 035. The 24 fixtures in the with the old magnetic ballasts were replaced with 12 electronic ballasts. The F40CW T12 lamps were then replaced with F32 T8 lamps.
The A-frame roofs currently in place consist of gray asphalt shingles over 3/4" plywood decking. One segment is 36' 3" x 11' 9" and the other is 36' 3" x 15' 9". This longer half provides an overhang for a handicap accessible entranceway on the South side of the building. The replacement roof is a reflective white metal roof. We decided to replace the roof because previous research has shown that roof colors significantly impacts space cooling energy use (Givoni 1976). In fact, a white roof has been shown to reduce cooling loads by approximately 13,000 kWh per year (10%) at Our Savior's School (Parker et al. 1996b). Asphalt shingles are known to have poor reflectivity. The reflectivity of gray asphalt shingles is 22%, black asphalt shingles is 5%, but for a white metal roof it is 67% (Anderson et al. 1991, Parker et al. 1993). A white reflective roof can decrease residential cooling requirements by an average of 20% (Parker et al. 1996b).
Heat, Ventilation and Air Conditioning (HVAC)
Both inefficient lighting and roof solar absorptance can significantly increase cooling loads. Generally, HVAC use makes up one-third of a school's energy budget. A poorly sized HVAC - or a poorly maintained system, can lead to major problems with indoor air quality, bacterial contaminants, viruses, mold, spores, and pollen (Brown 1995).
HVAC's are sometimes oversized by contractors in order to avoid future complaints (Vieira et al. 1996). The HVAC currently in place is a Crispaire AVP36HPA 3 ton wall mount unit. It has been replaced by a more efficient Bard WH301-A 2.5-ton wall mount unit. Bard manufacturing has donated the model for our research project.
Results and Discussion
The portable classrooms had the traditional T12 lamps with magnetic ballasts in place. This type of lighting system puts out a great deal of heat and is not as bright as the T8 lamps with electronic ballasts which they were replaced with. The old system also had greater energy consumption than did the new system as seen in Figure 2.
Figure 2. Graph of lighting demand over the course
of a day for portable 035.
Pre-retrofit average demand is 0.60 kW and post retrofit average demand is 0.45 kW.
The lighting energy comparison pre and post retrofit in Figure 3 highlights the energy savings. The average energy demand on May 20, 1998 prior to the retrofit is 0.60 kW while the average energy demand after the retrofit (May 27, 1998) is 0.45 kW. This represents a energy savings of 25%, which is higher than in previous studies (Sherwin and Parker 1996). This savings is considerable since the data shows that lighting energy for portable 035 is 26% for May 20 while on May 27 the energy use was only 19% of total portable energy use.
Figure 3. Energy consumption comparison for portable 035 on a typical school day. Pre-retrofit lighting energy demand is 26% of total energy demand while post retrofit energy demand is reduced to19%.
Figure 4 is an infrared thermograph of the lighting system at Silver Sands Middle School pre-retrofit. The darker colors represent the cooler areas while the lighter colors represent the hotter areas. It is very easy to see that the lighting fixtures heat up to over 93o F (white).
Figure 4. Infrared thermograph of heat gain from the lights and ceiling in portable 035 pre-retrofit.
The temperature range is from 75.2oF to 93.2oF. The afternoon surface temperature of the ceiling tiles is 86-87oF.
On June 17th the existing Cripsaire AVP36HPA wall unit was replaced with the new 2.5-ton system with an energy recovery ventilator. It would be premature to attempt to analyze data from the AC retrofit, due to the school year ending before the recent installation. With the end of the school year and the subsequent install, the AC has either been turned off altogether or the schedule has changed significantly. When school resumes in late August and the AC is once again run for most of the day, a savings analysis can be performed. Figures 5 and 6 examine preliminary data for this retrofit. This data has been gathered from two matched days with very similar outdoor temperatures.
It can be seen that the average temperature within the portable post retrofit is very similar to the pre-retrofit temperature, but that the total energy use by the AC system is 2.8 kWhs less (14%), even though the Bard unit is a 2.5-ton unit versus 3 tons for the old unit. Figure 6 also points out that through the hottest part of the day, the demand post retrofit was approximately 500 watts less than pre-retrofit.
Figure 5. AC energy demand data for two matched days.
Pre-retrofit total kWh = 22.4: post retrofit total kWh = 19.6
Figure 6. Interior air temperatures for two matched days.
Pre-retrofit average temperature = 88.09: post retrofit average temperature = 88.13
Air side problems of the old system can be observed in Figure 7. The infrared thermograph demonstrates leakage around the connecting of the cooling system supply duct to the conditioned space. The HVAC on portable 035 runs constantly (with a demand consistently over 5 kW per hour for 6-7 hours during the hottest part of the day) but does not effectively pull down the temperatures (75oF to over 80oF during the same time period). Part of this problem is that the portable loses cooling energy because the AC cools the exterior wall of the portable (blue to violet colors).
Figure 7. Infrared thermograph of the old HVAC of portable 035. The temperature range
is 76.9o F to 94.8oF with the darker colors being cooler and the lighter colors being hotter.
Note supply air leakage at the connection to the building.
The old gray asphalt shingle roofing system is scheduled to be replaced by June 30, 1998 so no comparison can be made at this time. However, the current roofing system data is available for analysis.
Figure 8 demonstrates the temperatures associated with portable 035. The roof gets extremely hot reaching temperatures topping 130oF over the course of the day. Figure 9 is a graphical representation of the roof temperatures. While the ambient temperature averages 73.8oF, both the attic air and roof surface temperatures are quite a bit higher (86.02oF and 86.83oF on average respectively) and are much higher during the hottest part of the day (10:00 am - 4:00 pm). This is primarily due to high solar absorptance of the roof. This reduces the efficiency of the HVAC system because the ducts are in the attic and also get very hot. This, in turn, increases the interior temperatures even though the HVAC is continually running. When the roof is replaced with a reflective white metal roof, the differences in temperatures can be completely analyzed.
Figure 8. Infrared thermograph of portable 035 at Silver Sands Middle School.
The temperature range is from 65.1oF (darkest colors) to 101oF (lightest colors).
Figure 9. Graph of the temperatures associated with the gray asphalt shingle roof system. Average ambient temperature = 73.8o F; average attic temperature = 86.02o F; average roof surface temperature = 88.83o F; average interior temperature = 73.89o F and average interior relative humidity = 61.64.
Portable 035 will have all the retrofits installed withing a few weeks. This will allow portable 096 to serve as a control for comparison. Later, portable 096 will have the retrofits installed over time in order to fully observe the individual effects of the changes on energy usage.
The Silver Sands Middle School portable classroom project has been underway for approximately one year. We have collected a year of baseline data concerning energy use, weather data, and roof system temperatures for portables 035 and 096. We are in the process of retrofitting portable 035 with more energy efficient measures than are currently in place. The old T12 lamp magnetic ballast lighting system has been replaced with a T8 electronic ballast lighting system and has yielded an energy savings of approximately 25%. The old Crispaire AVP36HPA 3-ton wall unit has been replaced with a more efficient Bard WH301-A2 2.5-ton wall unit. However, due to the recent replacement no data analysis is available at this time. In addition, the new reflective white metal roof is scheduled to be retrofitted towards the end of June. Results of this work will be reported in Phase VI of our contract with FDOE.
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Florida Department of Education
Office of Educational Facilities
325 W. Gaines St., Rm. 1054
Tallahassee, FL 32399