Reference Publication: McIlvaine, J., Mallette, M., Parker, D., Callahan, M., Lapujade, P., Floyd, D., Schrum, L., Stedman, T., Cumming, B., Maxwell, L., Salamon, M., "Energy-Efficient Design for Florida Educational Facilities," Prepared for the Florida Department of Education, Tallahassee, FL., September, 2000.
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.
Energy-Efficient Design for Florida Educational Facilities
Janet McIlvaine, Michele Mallette, Danny Parker, Michael
Callahan, Philippe Lapujade, David Floyd, Lynn Schrum,
Ted Stedman, Brian Cumming, Larry Maxwell, Milt Salamon
Solar Energy Center (FSEC), R. Douglas Stone Associates, Inc.,
Spacecoast Architects, Technical Editor
Performance of Individual Measures
Tables 1-3 show the predicted energy and economic performance of the individual energy conservation measures (ECMs) as simulated in Orlando, Florida. Performance is based on the energy savings of each ECM compared individually to the Base Case building prototype. Each of the three educational building prototypes are based on typical Florida construction practices. The various assumptions are described in detail in Appendix A. The costs are based on cost data collected for the study from the average of three bids obtained from local vendors who would supply the equipment. The relative benefit of each ECM is the net savings identified in the far right-hand column. A nominal discount rate of 8% (real rate = 3%) is used to represent the opportunity cost of capital. Both fuel price escalation and the general economic inflation rate is assumed to be 5%. Thus, energy prices are conservatively assumed to increase at the rate of general inflation.
Brandemuehl and Beckman (1979) have formulated an economic evaluation method that is comprehensive, quick, and very useful for life cycle analysis. Two economic parameters, P1 and P2, can be used to assess the life-cycle cost of any energy saving project. P1 is the ratio in years of the present value of the life-cycle fuel savings to the first-year fuel savings. It takes into account the inflation of fuel prices over time as well as the discounting of future fuel savings according to the opportunity cost of capital:
d = discount rate
iF = fuel price inflation rate
NE = analysis period (years)
C = flag for income producing venture
t = marginal tax bracket
PWF = present worth factor
The factor P2 is the ratio of the life-cycle cost incurred over the useful life of the project against the initial capital investment. It takes into account all of the parameters that affect the investment costs over time such as financing and taxes:
m = annual mortgage interest rate
i = general inflation rate
NL = term of loan
Nmin = years over which mortgage payments contribute to the analysis (usually the minimum of NE or NL)
ND = depreciation lifetime in years
N'min = years over which depreciation contributes to the analysis (usually the minimum of NE or ND)
t = property tax rate based on assessed value
D = ratio of down payment to initial investment
Ms = ratio of first-year miscellaneous costs (parasitic power, insurance and maintenance) to initial investment
V = ratio of assessed valuation of the ECM in first year to the initial investment in the system
Rv = ratio of resale value at the end of the period of analysis to initial investment
All economic parameters are given in their nominal terms (include inflation). The assessment allows the financial structure of an individual, firm, or institution to be assessed in the economic evaluation.
Economic Parameters Used
|General inflation rate (i)
Fuel price inflation rate (iF)
Discount rate (d)
Finance rate (m)
Property tax rate (t)
Marginal tax bracket (t)
Down payment (D)
Analysis period (NE)
Mortgage period (NL)
O&M fraction (Ms)
Resale value (Rv)
Electricity was assumed to cost $0.04/kWh with a monthly demand charge of $8 per kW. Natural gas was priced at $0.40/therm. These rates represent typical Florida energy costs in the second quarter of 1994. Measures were ranked by their net present value savings over the life of each individual option. The net present value savings is the difference between the life cycle savings of reduced energy use by a measure and the life cycle costs of the option (first cost amortized over its useful life along with any incremental operation and maintenance expenses).
The three tables below summarize the relative performance and economics
of the individual measures analyzed for the three prototype buildings as
compared with the initial base case. We caution that such an analysis cannot
be used to predict the performance of a group of measures since many of
the ECMs have significant interaction. For instance, addition of R-30 roof
insulation would greatly reduce the savings produced by later selecting
a reflective roof. Similarly, a number of the lighting options are mutually
exclusive. Also, note that some measures are sensitive to the input assumptions.
As example, the enthalpy recovery system (TERS) is not cost effective at
the current minimum ventilation rate of 5 cfm per student, but is quite
economic when the ventilation rate is increased to 15 cfm as recommended
by ASHRAE Standard 62-1989.
Technical Potential to Reduce Energy Use
Most energy efficiency improvements for educational facilities behave according to a law of diminishing returns. The fundamental characteristic is one of decreasing savings associated with the addition of each increment designed to reduce the building or machine thermal load. As a result, we analyzed the incremental energy savings associated with each energy conservation measure (ECM) for each building prototype. With this approach, optimization by steepest descent is used to determine the order in which measures were added. This means that the measure with the greatest savings is chosen first, and implemented in the Base Case building, before re-evaluating the remaining measures for the next choice. In this way, it is possible to determine a "technical optimum" series of ECMs ranked in terms of their performance at reducing energy use.
This assessment, obviously does not consider cost. Although a cost-effectiveness analysis is ultimately desirable, we wished to determine the most superior group of performance measures independent of cost since the expense of some newer high-technology options may change over time. Measures that appear promising, but are yet too expensive may be targeted for efforts to reduce their cost.
Tables 4-5 show the technical optimization results for each building prototype. The selected ECMs comprise the package of options determined to provide the maximum reduction in facility energy use under the assumptions used in our study. Different measure performance between the various prototypes depend, in large part, on the different occupancy densities and use schedules between the different buildings.
The analysis results show that energy use in the three prototypes can be potentially reduced by 46-62% using available technologies. Cooling system size can be lowered by 21-24%.
Table 4. Technical Optimization of ECMs - Classroom Building
|Run||Annual Energy Use Intensity||Annual Electric Consumption||Annual Gas Consumption||Annual Energy Cost||Cooling Capacity|
|F32, T-8 Electronic Ballast||33||31||133,962||97||11,220||44|
|Dimming Electronic Ballast||7||29||123,145||101||10,433||42|
|Double Pane Spectrally Selective Glazing||15||26||111,848||103||9,264||37|
|Enthalpy Recovery (ERS) at ventilation rate = 5 cfm||46||25||108,099||91||8,934||36|
|Optimal Start (Energy Management System)||48||24||102,230||74||8,444||35|
|Variable Speed Pumps (for Chiller)||39||24||100,739||72||8,339||35|
Table 5. Technical Optimization of ECMs - Administration Building
|Run||Annual Energy Use Intensity||Annual Electric Consumption||Annual Gas Consumption||Annual Energy Cost||Cooling Capacity|
|F32, T-8 Electronic Ballast||32||32||85,167||63||7,263||23|
|Dimming Electronic Ballast||7||30||85,167||65||6,773||22|
|Double Pane Spectrally Selective Glazing||15||19||82,367||58||6,404||19|
|Optimal Start (Energy Management System)||48||16||81,034||40||6,340||19|
Economic Optimization Analysis
Measures showing a positive life cycle net saving in the single-measure economic test were subjected to an incremental analysis to choose those which were cost effective under a more stringent criteria. As before, the system life cycle net savings was used to decide on the winning options. An incremental analysis is more rigorous since most conservation related improvements are subject to steadily diminishing returns. This analysis examines all measures competing against each other to determine their economic ranking relative. After all options are assessed, the winning incremental option is incorporated into the Base building after which all remaining options are then reassessed. The process of selecting measures and incorporating them into the building continues until all measures are included, or there are no longer any cost effective options remaining. Interactions are taken into account by the computer simulation of the measures as they are incorporated into the building in a step-wise fashion.
Tables 6-8 and Figures 48-50 show how overall building energy use and associated expenses over the life of the project is reduced as measures are added in an incremental fashion. Note that the lifecycle savings greatly outweigh the cumulative initial costs of the ECMs. Results are presented for each of the three prototypes. The package of selected measures with this procedure represents the optimum mix of ECMs based on our assumed costs, building and equipment parameters and operation related assumptions.
Obviously, the relative economics of the various options could vary greatly under differing cost or use assumptions. Thus, these results should be used to guide ECM selection, rather than to be seen as the final word in energy-efficiency for school design. It does, however, suggest how a package of ECMs can be chosen for the design of an educational facility to address the building's major energy end-uses. Also, the order in which the measures were selected in the optimization process provides useful information to design teams about the relative ranking of ECMs for capital constrained projects. Some measures, such as a more efficient chiller and low-shading coefficient windows, are shown to be uniformly cost effective and highly desirable in each analysis.
The results differ for the three building prototypes, primarily due to differences in occupant density and use schedules for the buildings. Perhaps the largest caveat regards the assumed ventilation rate for the buildings, which is 5 cfm/student under current Florida Department of Education 6A-2 regulations. It appears likely that the state may adopt ASHRAE Standard 62-1989 in the near future. This will require an outside ventilation rate of 15 cfm per student. Our analysis showed that if this ventilation standard is adopted, that use of enthalpy recovery systems, or other alternative means of controlling humidity and mitigating the standard's effects will immediately become very cost effective for Florida educational facilities.
Regardless, the analysis showed that it is possible to reduce energy
use in the three prototype facilities by 41-44% in a cost-effective fashion.
The same package of optimum energy-efficiency measures reduces the required
cooling system size by 22-24% resulting in additional project cost savings
that we did not include in our conservative assessment.
Applying What We Know
As this manual is new, specific application of its recommendations in new Florida educational facilities must await future projects. Currently, we are aware of one project, Celebration Middle School in Orlando, being designed by Schenkel Schultz Architecture/Interior Design who plan to incorporate some strategies explored in this manual.
We are also aware of several school districts pursuing retrofit energy
conservation with great success. Two HVAC retrofits are described here
to illustrate how some of the specific technologies can be incorporated
into existing educational facilities. Another case study explains Pasco
County's Comprehensive Energy Management Program. If readers are aware
of other such projects, we would appreciate receiving information on these
so that we might help document and dissiminate the results of these.
Renovation Of Existing School HVAC Systems In Humid Climates
R.Douglas Stone Associates, Inc.
Florida's hot, humid climate is typical for tropical and subtropical locations throughout the world. ASHRAE Standards 62-89 and 55-92 potentially have a tremendous impact on the initial cost, energy consumption costs, in such a climate. These two standards will especially affect schools which usually have a high occupant density and large swings in heat loads based upon time of day.
Since the late 1970's, most HVAC systems in Florida schools have been designed for a constant ventilation of 5 cfm/occupant. There have been many humidity problems even at this ventilation rate. Test and balance data in many schools has shown daily humidities of 60 to 80+ percent during fall and spring periods. These humidity levels have been recorded for all types of systems. However, high humidities are most prevalent in schools with HVAC systems that have constant volume supply air where unconditioned ventilation air is introduced into the return air duct or plenum, the supply fan runs continuously and the cooling compressor (or chilled water valve) cycles to meet space temperature. These systems include all single coil DX system types with no reheat, popular unit ventilators, PTAC, and fan coil systems. Psychometric analysis shows that these systems cannot maintain space humidities under 60% during part load conditions without the use of reheat.
Many indoor air quality (IAQ) complaints in schools arise because of high humidity, poor temperature control, and lack of fresh air. These are usually because the HVAC systems cannot maintain acceptable humidity levels at part load conditions even at 5 cfm/student. Many time ventilation dampers are closed by maintenance staff to reduce humidities at the hazard of increasing carbon dioxide levels, decreasing air quality, and increasing occupant illness.
ASHRAE Standard 62-89 recommends ventilation rates should be a minimum of 15 cfm/student in classroom spaces. Typical classrooms require about 900 to 1200 cfm of supply air at 55oF at peak conditions. Typically, there are about 30 students in a classroom which require about 450 cfm of ventilation air, or about 40% of the total air required. This poses unique challenges for the project engineer in order to successfully retrofit the existing school HVAC systems. There are two paths that can be used to retrofit school HVAC equipment:
1. Reusing Existing Equipment
If the airside equipment is relatively new and in good condition, it may be most economical to reuse existing HVAC equipment. Usually, the equipment cannot accommodate the increased ventilation cooling and heating loads. Therefore, the best means of augmenting ventilation is to add dedicated outside air systems which supply dehumidified, preconditioned outside air directly into the spaces or into the return of the existing equipment. These can be packaged DX outside air equipment or chilled water air handling units. Both types will require some means of reheat.
Since school occupancy densities are high, consideration should be given to provide the outside air directly to the space and distribute it uniformly while allowing the recirculating unit fan to cycle off with cooling to satisfy space temperature. This mode of operation eliminates re-evaporation of water on the coil to the supply air stream when the compressor is off. This is particularly important for unit ventilators, fan coil units, and constant volume systems. VAV systems will require the same approach to comply with 6-A2 requirements and ASHRAE Standard 62-89 requirements.
Exhaust systems will be required to provide the additional ventilation air. It is advised to provide one central exhaust system that is interlocked with the dedicated ventilation air handling system. Return air or exhaust plenums are strongly discouraged.
To minimize energy usage, new control points and sequences will be required to monitor and actively control humidity. CO2 levels may also require monitoring for verification of system function.
2. Replacing Complete HVAC System
This option should be exercised if the existing equipment is beyond it's useful life, damaged, or inadequate to meet the needs of the current occupancy. If it has been determined that existing ductwork requires replacement, the cost of adding new systems is usually justified.
Note that many previously used HVAC system types used with 5 cfm/occupant will not maintain humidities less than 60% during part load conditions. It is important to exercise caution in considering acceptable types of systems. System types considered should include constant volume DX with reheat (use of condenser heat to provide reheat), VAV with dedicated outside air, dual duct VAV (with pre-conditioned outside air as hot deck), and multizone systems.
The refrigerant phase-out issue will emphasize reduction of the number of refrigerant sources on school facilities. This will reduce exposure by reducing the number of potential refrigerant sources of leaks. Consideration should be made to replace multiple DX equipment with new central chilled water systems. Heat can be recovered off chillers to provide source of heat for reheat. Also replacing small, individual constant volume air handlers with larger, VAV type air handlers can reduce the maintenance requirements of each air system. It is also more flexible in cases where facility loads may grow in the future.
Boiler plants were commonly used in schools in Florida until the 1980's.
There has been a trend by maintenance departments to eliminate boiler systems
and use electric strip heating since there is minimal maintenance. However,
recent increases in demand charges and energy code requirements will probably
again make boiler plants the preferred choice in the future. Hot water
systems have excellent reheat applications. In addition, these systems
are more flexible for growing campus needs.
Seminole High School
Seminole County, Florida
A 13 million dollar project at Seminole High School included renovations to existing buildings and the addition of new classroom buildings and an administration building. The existing primary system was a four-pipe central chilled water and hot water system. Some existing buildings contained old DX units. R. Douglas Stone Associates, Inc. gave an indoor quality presentation to the owner to educate the staff on the merits of following ASHRAE Standards 62-89 and 55-92 guidelines. In addition, the refrigerant phase-out issue was discussed. It was determined to expand the chiller plant capacity by replacing one of the existing chillers with a new 600 ton high efficiency centrifugal chiller (0.55 kW/ton) including a heat recovery heat exchanger. Both chilled and hot water systems incorporated primary/secondary pumping with variable frequency drives (VFD) to conserve pump energy.
Air distribution systems included replacement of existing systems (fan coil, split DX, rooftop multizone, packaged constant volume) with central variable air volume (VAV) recirculating systems (no outside air) that modulate fan inlet vanes to maintain an optimized static pressure setpoint. (Limited budget did not allow VFD.) Typical classrooms required 1,200 cfm of 55oF supply air for peak cooling conditions. Ventilation requirements were 15 cfm/student or 450 cfm per classroom. VAV boxes were the cooling only type, which modulate airflow based on room temperature in cooling or heating mode. Ventilation air was provided thru a dedicated outside air system which was designed to dehumidify outside air and supplement the cooling capacity of the VAV system. The system provided preconditioned outside air directly to each space at constant volume. The temperature setpoint was 55oF during peak conditions. If any VAV box was 100% closed and the space temperature was below the cooling setpoint, the ventilation air temperature was reset upward to maintain temperature in the current critical space. Temperature setup was performed using 110oF hot water reheat from waste heat scavenged from the new main chiller. Return water can be as low as 80oF, which can increase chiller efficiency slightly under some conditions.
Dedicated outside air systems allowed direct digital (DDC) system to shutdown the ventilation systems during unoccupied periods while allowing VAV systems to provide unoccupied temperature and humidity control. The DDC control system included humidistats in rooms and control sequences that actively monitor and control humidity and ventilation systems.
The total mechanical bid cost was 3 million dollars, or $2,365 per ton.
This included extensive underground piping replacement ($400,000), DDC
controls ($500,000) and chiller plant renovations ($150,000). The project
was phased over a two year construction period, including after-hour work,
which added approximately 20% to the total mechanical cost. Lighting incorporated
standard ballasts with high efficiency fluorescent lamps. Unfortunately,
an add alternate bid for electronic ballasts was not accepted by the owner
due to budget constraints.
Lighting Retrofits and HVAC Fine Tuning
District School Board of Pasco County
One of the most ambitious efforts to improve the energy-efficiency of Florida educational facilities has been the effort of the District School Board of Pasco County. In 1992 Pasco County developed a comprehensive Energy Management Program. This has lead to an innovative effort where a revolving fund is being used to make retrofit efficiency improvements to the district's school buildings. Since Pasco County's energy committee estimates that approximately 35% of its energy use comes from lighting, the main emphasis thus far has been to improve these systems. Accomplishments in the 1993-1994 school year are summarized below:
Relamped 3,000 incandescent exit signs at various schools using flourescent retrofit kits. This is projected to save $22,000 annually.
Replaced incandescent bulbs in 586 recessed can fixtures with compact fluorescent lamps. Estimated annual savings of over $7,300.
Converted over 4,500 T-12 fluorescent lamps to either T-10 and T-8 lamp with electronic ballasts. Estimated annual savings of $81,000. The lamp replacements have resulted in a better perceived light quality and, in many cases, increased interior levels of illuminance.
Added 500 spring-loaded AC timers added as well as automatic scheduling controls for HVAC systems.
Upgraded equipment: replaced inefficient water heater, relocated thermostats for improved temperature control and adjusted outside air dampers for better ventilation performance.
Conducted comprehensive educational energy awareness program for students and teachers. An extensive series of guidelines are used to promote efficient operation of the facilities. There is also an incentive program for the facilities showing greatest improvement in reducing energy costs and developing innovative ways to achieve the savings.
The one-time expense of the measures over the school year was $110K with an expected simple payback of only nine months. The impact of the improvements has already been observed in the county's monthly energy costs. Using the Faser energy-accounting software, the school system's 1993-1994 monthly energy use for the involved facilities decreased by an average of 9.7% over the previous year. The seasonally adjusted annual savings is predicted to be approximately $400,000 for the total improvements made over the two year history of the program. Furthermore, in spite of adding 38 portable classrooms, two new health clinics, a new music suite, an entire classroom wing and four walk-in freezers, the school board's energy bills actually decreased overall during the year! Even more impressive is the fact that the school district is planning to reinvest a portion of the savings in further improvements to its facilities as well as more efficient design of new construction. In this way, Pasco county's novel self-perpetuating program aims to achieve the most efficient school facilities in the state by the turn of the Century.