Investigation of Propane Heaters for Northern Climate School Bus Applications · 2014-01-28 · Investigation of Propane Heaters for Northern Climate ... Northern Climate School Bus

Investigation of Propane Heaters for Northern Climate

School Bus Applications

Final Report

Prepared for:

1140 Connecticut Ave. N.W., Suite 1075

Washington, DC

Prepared by:

4351 Garden City Drive, Suite 600

Landover, MD

December 2007

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Investigation of Propane Heaters for December 2007 Northern Climate School Bus Applications Final Report

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Table of Content

Executive Summary ........................................................................................................................ 1 Introduction..................................................................................................................................... 4

Background ................................................................................................................................. 4 School Bus Market.................................................................................................................. 6 School Bus Idling Characteristics........................................................................................... 9 Health Effects........................................................................................................................ 10 Idle Reduction Technologies ................................................................................................ 12

Review of Similar Technology - Diesel Fuel Fired Coolant and Air Heaters .............................. 13 Air Heaters ................................................................................................................................ 13 Diesel Fuel Fired Coolant Heaters ............................................................................................ 14

Design and Operation ........................................................................................................... 14Advantages............................................................................................................................ 15 Hardware and Installation ..................................................................................................... 16Manufacturers and Products ................................................................................................. 17

Scholastic Series (Webasto).......................................................................................... 18 TSL 17 (Webasto)......................................................................................................... 19 Hydronics 10 (Espar) .................................................................................................... 20 Hydronics 16 (Espar) .................................................................................................... 21 X45 School Bus Edition (ProHeat)............................................................................... 21

Propane Heaters and Preliminary System Design ........................................................................ 23 Availability of Mobile Propane Heaters ................................................................................... 23 Preliminary System Design and Costs...................................................................................... 24

Hardware............................................................................................................................... 24 Propane Heater.............................................................................................................. 24 Water Pump .................................................................................................................. 26 Propane Tank ................................................................................................................ 26

Installation requirements and costs....................................................................................... 28 Operation and Safety............................................................................................................. 30

Market Characterization................................................................................................................ 31 Climate Data ............................................................................................................................. 31 Student Population and School Bus Data ................................................................................. 33 Propane Availability and Costs................................................................................................. 37Potential Market Analysis......................................................................................................... 40

Lifecycle Cost Analysis ................................................................................................................ 45 Introduction............................................................................................................................... 45 Model Description .................................................................................................................... 45

Temperature Submodel ......................................................................................................... 46Heat Transfer Submodel ....................................................................................................... 48Financial Submodel .............................................................................................................. 56

Results....................................................................................................................................... 58 Conclusions and Recommendations ............................................................................................. 63 Conclusions and Recommendations ............................................................................................. 63 Appendix....................................................................................................................................... 65


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School Bus Manufacturers........................................................................................................ 66 Thomas Built Buses .............................................................................................................. 67 IC Corporation ...................................................................................................................... 67 Blue Bird Corporation........................................................................................................... 68

RV-500 Propane Water Heater Specifications ......................................................................... 69 Propane Refueling Station and Pricing Data ............................................................................ 71

List of Tables

Table 1. North American School Bus Sales by Type (Source: School Bus Fleet Magazine) ........ 8 Table 2. Idle emissions without accessories ................................................................................. 10 Table 3. EPA Study Idle Emissions.............................................................................................. 10Table 4. Diesel Coolant Heater Specification Summary .............................................................. 22 Table 5. Select RV-500 Specification........................................................................................... 25Table 6. Twenty Largest North American School Bus Fleets (Source: School Bus Fleet Magazine) ..................................................................................................................................... 35 Table 7. Potential Candidate States .............................................................................................. 41 Table 8. Cold and Mild Period Temperatures for the Morning and Afternoon Scenarios ........... 47 Table 9. Model Matrix of Different Scenarios and Conditions .................................................... 47 Table 10. List of Potential Funding Opportunities for the Demonstration Phase......................... 64 Table 11. 2006 School Bus Manufacturers and their Models (Unit Sales Included for Type C&D)....................................................................................................................................................... 66

List of Figures

Figure 1. Schematic of the School Bus Coolant System with Propane Heater Components ......... 1 Figure 2. Potential Market for School Bus Propane Heaters .......................................................... 2 Figure 3. Cumulative Lifetime Cost Comparison of the Three Different Approaches .................. 3 Figure 4. Typical School Bus and its Passengers ........................................................................... 4 Figure 5. School Bus Diesel Exhaust.............................................................................................. 5 Figure 6. Large Fleet of School Buses............................................................................................ 6 Figure 7. North American School Bus Population and Ownership Type....................................... 7 Figure 8. Type A/B School Bus...................................................................................................... 7 Figure 9. Conventional or Type C School Bus ............................................................................... 8 Figure 10. Transit Style or Type D School Bus.............................................................................. 8 Figure 11. Children Boarding School Buses after School .............................................................. 9 Figure 12. Espar D8LC (Source: http://www.espar.com)............................................................. 13 Figure 13. Conventional Cooling System Schematic for a Type C School Bus........................... 15 Figure 14. Cooling System Schematic for a Type C School Bus with an Auxiliary Coolant Heater....................................................................................................................................................... 15 Figure 15. 3-D coolant line blueprint (Source: Webasto Scholastic Series Operating Manual) .. 17 Figure 16. Webasto Scholastic Series Heater Schematic (Source: Scholastic Operating Manual, Webasto) ....................................................................................................................................... 18 Figure 17. Webasto Scholastic Series Heater (Source: http://www.webasto-us.com) ................. 19

http://www.espar.com).............................................................13http://www.webasto-us.com).................19


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Figure 18. Webasto TSL 17 Heater Schematic (Source: TSL Operating Manual, Webasto) ...... 19 Figure 19. Espar Hydronics 10 Schematic (Source: Hydronics 10 Operating Manual, Espar).... 20 Figure 20. Espar Hydronics 16 (Source: http://www.espar.com)................................................. 21 Figure 21. ProHeat X45 School Bus Heater (Source: X45 Operating Manual, ProHeat) ............ 21 Figure 22. Hilton Cordless Heater (Source: http://www.cp.duluth.mn.us/~hilton/)..................... 23 Figure 23. Enviroharvest Heater (Source: http://www.servicemate.com).................................... 24 Figure 24. Precision Temp RV 500 (Source: http://www.precisiontemp.com)............................ 25 Figure 25. Schematic of typical tank-less heater (TwinTemp Operating Manual)....................... 26 Figure 26. Recirculatory pump (Source: http://www.precisiontemp.com)................................... 26 Figure 27. Vertical LP Tank (left) and Horizontal LP tank (right) (Source: http://www.go2marine.com) ......................................................................................................... 27 Figure 28. Blueprint of Propane Coolant System ......................................................................... 28 Figure 29. Schematic of the School Bus Coolant System with Propane Heater Components ..... 29 Figure 30. Schematic of Individual Components of the Propane Heater System......................... 29 Figure 31. U.S. Average January Temperatures ........................................................................... 32 Figure 32. U.S. Average School Year Temperatures.................................................................... 32 Figure 33. U.S. School Children Population................................................................................. 33 Figure 34. U.S. School Children Population Density ................................................................... 34 Figure 35. U.S. School Bus Population ........................................................................................ 36Figure 36. U.S. School Bus Population Density and 100 Largest Fleets...................................... 36 Figure 37. U.S. Propane Sales ...................................................................................................... 37 Figure 38. U.S. Propane Sales Density......................................................................................... 38Figure 39. U.S. October 2006 Propane Prices .............................................................................. 39 Figure 40. U.S. February 2007 Propane Prices............................................................................. 39 Figure 41. Temperature and Propane Sales Density Criteria Selection Based on Market Share . 40 Figure 42. Temperature and Propane Sales Density Criteria Selection Based on Market Share Increase ......................................................................................................................................... 41 Figure 43. Results of Potential Market Criteria Analysis ............................................................. 42 Figure 44. Potential Market for School Bus Propane Pre-Heaters ............................................... 43 Figure 45. Close-up of Potential Market for School Bus Propane Pre-Heaters ........................... 43 Figure 46. Daily Temperature Fluctuation.................................................................................... 46 Figure 47. Examples of Monthly Average Temperatures for Northeast ...................................... 47 Figure 48. Comparison of Temperature Profiles from the Model with Actual Data.................... 49 Figure 49. Temperature Profiles for the Engine Idle Approach during Morning Warm-up at 10F....................................................................................................................................................... 50 Figure 50. Temperature Profiles for the Engine Idle Approach during Morning Warm-up at 25F....................................................................................................................................................... 51 Figure 51. Temperature Profiles for the Diesel Heater Approach during Morning Warm-up at 10F............................................................................................................................................... 51 Figure 52. Temperature Profiles for the Diesel Heater Approach during Morning Warm-up at 25F............................................................................................................................................... 52 Figure 53. Temperature Profiles for the Propane Heater Approach during Morning Warm-up at 10F............................................................................................................................................... 52 Figure 54. Temperature Profiles for the Propane Heater Approach during Morning Warm-up at 25F............................................................................................................................................... 53

http://www.espar.com).................................................21http://www.cp.duluth.mn.us/~hilton/).....................23http://www.servicemate.com)....................................24http://www.precisiontemp.com)............................25http://www.precisiontemp.com)...................................26http://www.go2marine.com).........................................................................................................27


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Figure 55. Afternoon Temperature Profiles for the Engine Idling Approach at 30F and 45F .. 54 Figure 56. Afternoon Temperature Profiles for the Diesel Heater Approach at 30F.................. 54 Figure 57. Afternoon Temperature Profiles for the Diesel Heater Approach at 45F.................. 55 Figure 58. Afternoon Temperature Profiles for the Propane Heater Approach at 30F............... 55 Figure 59. Afternoon Temperature Profiles for the Propane Heater Approach at 45F............... 56 Figure 60. Diesel and Propane Fuel Prices ................................................................................... 57 Figure 61. Daily Operating Cost Comparison .............................................................................. 58 Figure 62. Annual Operating Cost Comparison ........................................................................... 59 Figure 63. Cumulative Lifetime Costs for the Low Cost Scenario............................................... 60 Figure 64. Cumulative Lifetime Costs for the High Cost Scenario.............................................. 60 Figure 65. Cumulative Lifetime Costs for the Low Cost Scenario with Propane System Cost Premiums ...................................................................................................................................... 61 Figure 66. Cumulative Lifetime Costs for the High Cost Scenario with Propane System Cost Premiums ...................................................................................................................................... 61 Figure 67. Freightliner C2 Chassis (Type C)................................................................................ 67 Figure 68. . IC Corporation's Type C School Bus - CE................................................................ 68 Figure 69. Blue Bird's Type C School Bus - Vision Model ......................................................... 68 Figure 70. Propane Refueling Stations in the U.S. ....................................................................... 71 Figure 71. U.S Propane Refueling Data........................................................................................ 71Figure 72. U.S. Propane Refueling Station Density ..................................................................... 72 Figure 73. Retail Propane Refueling Station Pricing ($ per gallon) ............................................. 72 Figure 74. Residential Propane Prices based on a Diesel Energy Equivalent Gallon .................. 73

Investigation of Propane Heaters for September 2007 Northern Climate School Bus Applications Draft Report

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Executive Summary

Over 24 million children ride on 480,000 yellow school buses every school day in the U.S. According to the U.S. Environmental Protection Agency, on average these children spend an hour and a half per day on a school bus. The yellow school buses are by far the safest means of student transport; however, it has been documented that diesel exhaust from these buses can be harmful to childrens health. To reduce childrens exposure to diesel fumes, extensive periods of idling, in the morning to warm up the bus and in the afternoon while waiting for students to board, have been identified as targets for diesel exhaust emission reduction. A number of proactive school districts have outfitted their diesel buses with auxiliary heaters to provide cabin heat and warm up the engine in lieu of prolonged idling. While diesel fired auxiliary heaters are currently the only alternative to engine idling in cold weather, this study investigated propane heaters as another, lower cost and cleaner option.

Due to unavailability of a commercial propane coolant heater that could be applied directly to school bus applications, an alternative design approach was developed as part of this study that combines a tank-less propane water heater and a water pump. At 50,000 BTU/hr the heat capacity of this system is comparable to those of diesel fired coolant heaters designed for school bus applications. The fuel efficiency of the propane heater is similar to those of diesel coolant heaters (80 percent). A water pump and an eight gallon propane cylinder approved by the Department of Transportation for onboard vehicle use completed the proposed propane heating system, as shown in Figure 1.

Figure 1. Schematic of the School Bus Coolant System with Propane Heater Components

Pump

HeaterSpace for PropaneTank


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Based on an extensive market analysis conducted in the study, fourteen mostly northeastern states were identified as good candidates for application of this technology based on propane availability, average school year temperatures, and school bus population. Figure 2 presents a map of the candidate states highlighted with white borders. This figure also shows the average school year temperatures, propane sales density and school bus populations for each state. While the best business case for the propane coolant heaters exists in the coldest climates, the number of school buses operating in these regions will drive the potential sales. Considering climate and school bus population, Michigan, New York and Pennsylvania are the top candidates for use of propane coolant heaters in school bus application.

Figure 2. Potential Market for School Bus Propane Heaters

With nearly 185,000 school buses in operation, the fourteen candidate states account for 39 percent of the total U.S. school bus market. Assuming that 50 percent of these buses would use auxiliary pre-heaters and 50 percent of those would be propane fueled (the others being fueled with the competing diesel technology), the potential market for propane pre-heaters would be comprised of more than 46,000 school buses. As the heat transfer school bus model developed for the study illustrated, on average a bus equipped with a propane coolant heater would consume upwards of 50 gallons of propane per school year (anywhere between 40 and 70 gallons depending on average ambient temperatures). This would result in potential propane sales of more than 2.3 million gallons (9.8 million pounds) per school year for the projected propane heater school bus market.

A lifecycle cost analysis was conducted in the study for comparing three approaches to school bus heating: diesel engine idling (baseline), diesel fuel-fired heaters, and propane-fired heaters.The results showed that coolant heaters in general (either diesel or propane) can recover their initial capital cost within the first eight years of the typical 12-year school bus life for even the most conservative scenario due to much lower operating costs when compared to the baseline


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engine idling case. Propane coolant heaters have slightly higher operating costs compared to those of diesel coolant heaters; however, when capital costs are accounted for, the propane coolant heaters reach the break even point faster than diesel coolant heaters when compared with baseline engine idling.

Figure 3 plots the low cost or minimal idle time scenario for the three approaches for a typical 12-year school bus life. Since there are no capital costs associated with the baseline case, the coolant heaters have much higher costs during the initial years. Due to lower capital and similar operating costs compared to the diesel version, the propane coolant heater is the lowest cost option, surpassing the engine idling baseline case after 5.5 years. The diesel coolant heater is the second best option, surpassing the baseline case at 8 years. In the high cost or maximum idle time scenario, both diesel and propane coolant heaters surpass the engine idling baseline much faster due to extensive idling periods, with propane only requiring 3 years and diesel 4.5 years.

Total Cost - Minimal Idle Time

$0

$1,000

$2,000

$3,000

$4,000

$5,000

$6,000

0 2 4 6 8 10 12Years

Diesel Baseline

Diesel-fired Heater

Propane-fired Heater

Figure 3. Cumulative Lifetime Cost Comparison of the Three Different Approaches

Based on the positive results of this study, a demonstration project in one of the three top candidate states would be warranted. The demonstration project would quantify the potential economic and environmental benefits of the propane coolant heater technology compared to the diesel versions and baseline engine idling. First, the exact design requirements for system installation on a school bus would be determined. The installation procedure would be documented so other school bus operators can replicate the installation. A series of laboratory tests to record the fuel use and emissions performance would be used to gather the necessary data. Laboratory testing would allow for controlling the ambient temperature and humidity to quickly simulate a wide range of environmental conditions. Regional universities with similar experience would be approached for participation in this project. The demonstration results would be presented in a final report.

Investigation of Propane Heaters for October 2007 Northern Climate School Bus Applications Draft Report

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IntroductionIn the U.S. there are over 24 million school children that depend on the fleet of almost 480,000 yellow school buses for transport to and from school every school day. According to the U.S. Environmental Protection Agency (EPA), on average these children spend an hour and a half per day on a school bus. However, there are some children that spend up to 3 three hours per day on a school bus. While the U.S. Department of Transportation figures have shown year after year that the yellow school buses are by far the safest means of student transport, the diesel exhaust of these vehicles can be harmful to childrens health. With the exception of outfitting school buses with the latest exhaust aftertreatment technology there is not much that can be done to reduce diesel school bus emissions while on route. However, extensive periods of idling, in the morning to warm up the bus and in the afternoon while waiting for students to board, have been identified as targets for reduction of exhaust emissions. Reduced fuel use and engine wear are additional benefits of reducing diesel engine idling. During winter months, a lot of school bus fleets need to idle their buses in the morning to warm up the engine and bus passenger cabins as well as in the afternoon to maintain comfortable cabin temperatures. A number of proactive school districts have outfitted their buses with auxiliary heaters to provide cabin heat and warm up the engine in lieu of prolonged idling. While diesel fired auxiliary heaters are currently the only alternative to engine idling in cold weather, this study investigated propane heaters as another, lower cost and cleaner option.

Figure 4. Typical School Bus and its Passengers

BackgroundThe yellow school bus fleet is the largest fleet of vehicles with identical mission and characteristics in the U.S. While these vehicles are the safest and most efficient way of transporting children to school, they are powered by heavy-duty diesel engines that are on average older than 9 years. Due to the longevity of diesel engines, it is estimated that about one-third of all diesel school buses now in service were built before 1990. Older buses are not equipped with today's pollution controls or safety features. They are estimated to emit as much as six times more pollution as the new buses that were built starting in 2004, and as much as sixty times more pollution as buses that meet the 2007 diesel emission standards. Starting in 2007 all of the heavy-duty vehicle diesel engines must be equipped with diesel particulate filters to limit soot emissions (i.e. black smoke).


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Figure 5. School Bus Diesel Exhaust

Unnecessary school bus idling pollutes the air, wastes fuel, and causes excess engine wear. Fortunately, it's easy to implement practices that reduce school bus idling. Idling school buses can pollute air in and around the bus. Exhaust gases from buses can also enter school buildings through air intakes, doors, and open windows. Typical school bus engines burn about half a gallon of fuel per hour of idling. School districts that eliminate unnecessary idling can save significant dollars in fuel costs each year. Newer school bus engines do not need to idle more than a few minutes to warm up. In fact, extended idling causes engine damage. Engine manufacturers generally recommend no more than three to five minutes of idling for recent model year buses. Caterpillar cautions drivers to avoid excess idling (more than 5 minutes) because it can cause carbon buildup. IC Corporation's engine manual states that excessive idling reduces fuel economy, and may decrease oil life. Cummins Engine Company suggests idling for only three to five minutes before operating with a load.

There are several concerns among school bus operators regarding the no idling policies in place or being considered in many jurisdictions. The first one is regarding the need for a long idle period, especially in cold weather. Today's school bus engines only require warm up times of several minutes. In fact, running an engine at low speed (idling) causes significantly more wear on internal parts compared to driving at regular speeds. Another concern is that the engine must be kept running in order to operate the school bus overhead flashing lights and other safety equipment. This is generally true; however, safety equipment can be operated without the engine running for up to an hour through re-wired circuitry with no ill-effects on the electrical system of the bus. Some newer buses already have circuitry wired this way. Fleets that have re-wired their safety equipment so that it can be used without the engine generally have not experienced problems with draining the battery or other issues. Lastly, idling is necessary to keep the cabin at a comfortable temperature, but depending on the weather, many buses will maintain a comfortable interior temperature for a while without idling. Idling is also not an efficient way to keep the cabin warm. Auxiliary heaters are a technology that can be installed to keep the cabin comfortable while the engine is not running.


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School Bus Market

School buses have become the primary mode of transportation for transporting children and adolescents to and from school. In North America, however, the school bus is itself a specific type of bus distinct from other buses. Canada and the United States have specially built, painted, and equipped school buses. They are commonly painted yellow (officially known as "National School Bus Chrome Yellow"), for purposes of visibility and safety, and are equipped with specialized traffic warning devices. Most school buses offer no standing room, no luggage space, and little in the way of luxury features. Specific safety features for school buses, in addition to their distinct color, are design and markings that make the bus recognizable, and warning lights and signs to warn traffic when children are getting in and out. Like the vast majority of commercial heavy-duty vehicles, school buses are also mostly diesel-powered. Full-size school buses can seat between 59 to 90 passengers, but in many districts smaller vehicles are used as well. Such smaller vehicles are commonly known as "short buses," and are often used for low-density routes associated with private schools and programs for developmentally-challenged students.

Figure 6. Large Fleet of School Buses

Most U.S. school districts purchase buses and hire their own drivers. Others engage the service of school bus contractors, such as Laidlaw, to perform this function. In the U.S. each year, approximately 480,000 public school buses travel more than 4 billion miles and daily transport more than 24 million children to and from schools and school-related activities. Figure 7 shows the historic totals for the number of school buses on North American roads as well as their type of ownership. More than half of the school buses are district owned while contractors own one quarter. School buses account for an estimated 10 billion student trips each year. That means approximately 54 percent of all K-12 students in the country ride yellow school buses.


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Number of School Buses in Operation

0

100,000

200,000

300,000

400,000

500,000

600,000

State Owned (18%)Contractor Owned (26%)District Owned (56%)

Figure 7. North American School Bus Population and Ownership Type (Source: School Bus Fleet Magazine Database)

There are several types of school buses available that meet federal motor vehicle safety standards:

The Type A school bus consists of a bus body constructed on a van-type or cutaway front-section vehicle with a left side driver's door, designed for carrying more than 10 persons. This definition includes two classifications: Type A-1, with a Gross Vehicle Weight Rating (GVWR) of 10,000 pounds or less, and a Type A-2, with a GVWR of 10,000 pounds or more.

Figure 8. Type A/B School Bus

The Type B school bus consists of a bus body constructed and installed on a front-section vehicle chassis, or stripped chassis, with a gross vehicle weight rating of more than 10,000 pounds, designed for carrying more than 10 persons. Part of the engine is beneath and/or behind the windshield and beside the driver's seat. The entrance door is behind the front wheels.

The Type C school bus, also known as a "conventional," is a body installed upon a flat-back cowl chassis with a hood and fenders. Its GVWR is typically between 23,500 and 29,500 lbs. and the bus is designed for carrying more than 10 persons. The whole engine is in front of the windshield and the entrance door is behind the front wheels.


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Figure 9. Conventional or Type C School Bus

The Type D school bus, also known as a transit-style, is a body installed upon a chassis, with the engine mounted behind the windshield and either beside the driver's seat (FC for "forward control), at the rear of the bus behind the rear wheels (RE for "rear-engine"), or mid-ship, between the front and rear axles. GVWR is typically between 25,000 and 36,000 lbs and the entrance door is ahead of the front wheels.

Figure 10. Transit Style or Type D School Bus

Table 1 shows the North American school bus sales data for the most recent 10 years. While school bus sales vary from year to year, recent figures are around 45,000 units per year. Type C school buses are the most popular and account for 60 percent of the total annual school bus sales. Type D and A/B buses account for approximately 20 percent of annual sales each. Therefore, Type C buses were selected as the focus of this study for integration of a propane coolant heater. More information about Type C bus manufacturers in the U.S. is presented in the Appendix.

Table 1. North American School Bus Sales by Type (Source: School Bus Fleet Magazine) Year Type A/B Type C Type D Total 1997 5,671 24,996 9,700 40,367 1998 8,750 23,064 9,835 41,649 1999 10,569 25,329 10,547 46,445 2000 10,190 26,521 11,115 47,826 2001 9,221 23,274 9,848 42,343 2002 9,535 25,551 8,949 44,045 2003 8,791 24,016 8,113 40,920 2004 9,089 27,965 7,791 44,845 2005 9,015 27,505 8,726 45,246 2006 9,507 30,600 7,740 47,847


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School Bus Idling Characteristics

School buses are often idled in the morning prior to their initial bus route and in the afternoon while waiting to pick up children to take them home. School bus idling occurs for the following reasons:

- To keep the engine and fuel warm in cold weather - To provide heat inside the bus in cold weather- To provide power for lighting for safety purposes

Heavy duty diesel engine idling results in costly fuel consumption and engine wear. Moreover, idling produces pollutants in the form of nitrous oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and particulate matter (PM), which may be avoidable with the reduction of unnecessary idling. Indeed, unlike mobile emissions, which can at best be reduced through a variety of costly exhaust aftertreatment technologies, idle emissions can be completely eliminated by eliminating unnecessary idling.

Figure 11. Children Boarding School Buses after School

Rowan University recently conducted a study that took a closer look at how school buses operate in the state of New Jersey. Their study found that on average school buses idle one hour per day. As part of this study, school bus idle experiments were conducted on several different model year school buses at the United States Army Aberdeen Test Center (ATC) in Aberdeen, Maryland. The results show that school buses consume an average of 0.5 gallons of fuel per hour1. Fuel consumption at idle for heavy-duty diesel engines can vary depending on the accessories used. Most school buses are not equipped with air conditioning devices, but are equipped with heaters for cold weather. The heater on a school bus contains at least three fans to evenly distribute heated air throughout the school bus. Operating these fans increases the total load on the vehicles engine, thereby increasing the engine speed at idle. The increase in engine speed in turn raises the fuel consumption. For the Rowan University experiments, the heater fans were not turned on.

1 Hearne, J. (2004). School Bus Idling and Mobile Diesel Emissions Testing: Effect of Fuel Type and Development of a Mobile Test Cycle. Master's Thesis, Rowan University.


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In addition to the fuel costs associated with idling, diesel exhaust contains a variety of chemical species that have adverse effects on human health and the environment. The health risks associated with school bus idling are of a particular concern since much of the idling occurs with children on or near the bus. Particulate matter caused by incomplete combustion is known to contain carcinogens. Also, NOx, CO and CO2 are criteria air pollutants responsible for ozone depletion and global warming. Engine idle emission levels without accessory loads are presented in Table 2 for the Rowan University study.

Table 2. Idle emissions without accessories Pollutant Emissions (g/hr)

CO 50 CO2 3800 NOx 75 HC 10 PM 1.2

A study released this year by the Region 2 of EPA, measured school bus idling emissions during wintertime operation in a northern climate2. The emissions were measured on buses of model years 1997 through 2004, all equipped with Caterpillar engines. Number 2 diesel fuel was used during the testing and all buses were equipped with diesel oxidation catalysts. Table 3 shows the comparison of average emissions released during a 20 minute idle period compared to emissions in a case of a warm engine start.

Table 3. EPA Study Idle Emissions 20 minute idle Restart and go

Pollutant Emissions Emissions Reduction (%) NOx 24 g 0.032 g 99.9 CO 10 g 0.081 g 99.2 PM 112 mg 19 mg 83

Particle Polycyclic Aromatic Hydrocarbons 0.48 mg 0.0071 mg 98.5

Health Effects

Diesel engine exhaust emissions rank among the air pollutants that EPA believes pose the greatest public health risk. Diesel exhaust emissions are composed of a number of compounds that can cause significant health impacts. Two of the most problematic are oxides of nitrogen (NOx) and particulate matter (PM). According to the EPA study National Emission by Source, vehicle emissions are responsible for 28 percent of the total PM emissions and 54 percent of nitrogen oxides emissions that form ground-level ozone. NOx is a respiratory irritant and precursor to the formation of tropospheric ozone, or smog. Smog can cause eye irritation,

2 Kinsey, J. et. all, Characterization of the Fine Particle and Gaseous Emissions from School Bus Idling, U.S. EPA Office or Research and Development, July 2007.


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sore throats, coughing, and long term exposure can cause lung damage, cancer, and premature death. PM is composed primarily of elemental carbon core and absorbed organic compounds. It consists of fine (2.5 microns or less) and ultrafine (0.1 microns of less) size particles and therefore can get deposited deep in the lungs. Additionally, the absorbed organic fraction of PM can be significantly toxic in nature, containing many mutagenic and carcinogenic compounds. For example, according to EPAs Health Assessment Document for Diesel Engine Exhaust published in 2002, polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, and oxidized PAH derivatives are present in the organic fraction of diesel PM, typically less than 1 percent of the PM mass. The EPAs Health Assessment Document went on to conclude that long-term exposure to diesel PM is likely to pose a cancer hazard, especially for exposure to pre-1995 diesel engines. Thus, EPA has designated diesel PM as a probable human carcinogen. Several other international health organizations have made similar designations including the National Institute for Occupational Safety and Health, International Agency for Research on Cancer, World Health Organization, California EPA, and the U.S. Department of Health and Human Services. Short-term exposure to PM was found to cause transient irritation and inflammatory lung conditions. Further, there is increasing evidence that diesel PM can exacerbate pre-existing allergic and asthma conditions. In general, PM can cause respiratory disease, decreased lung function, changes in lung tissue, cancer, and premature death.

One of the most worrisome sensitive populations to diesel exhaust emissions is children, because of their higher respiration rates and maturing lung tissue. It has been found that children living near highways and freeways have a higher rate of respiratory problems. In a recent study conducted by the University of Southern California, children living near highways had higher frequency of respiratory problems that can lead to asthma. The study, partially funded by the California Air Resources Board (CARB), the National Institute of Environmental Health Sciences, U.S. EPA, and the National Heart, Lungs, and Blood Institute, found that children that live near freeways develop pollution-related lung problems over time. According to the study, children living within 500 yards of the freeway had a 3 percent decrease in the amount of air they can exhale. Similar findings have been demonstrated in the New York City metropolitan area where hospitalization rates for children with asthma up to 14 years of age are double the national average. In the Bronx, the rate is highest at almost four times the national average.

Another significant diesel exhaust exposure scenario for children is school bus transportation. A 2002 Union of Concerned Scientists report, Pollution Report Card Grading Americas School Bus Fleets, essentially echoes EPAs findings concerning diesel exhaust emissions and its potential health impacts for children. There are almost 480,000 school buses in service across the country. The majority (about 85 percent) of these buses are diesel engine-powered. More than 24 million children in the U.S. ride a bus to and from school every day. Bus idling to warm bus interiors while waiting in school premises or designated parking areas can expose children to unhealthful levels of diesel exhaust. Buses may idle for several minutes to an hour waiting for commuting children. Under this scenario, diesel emissions permeate the interior space of the bus as well as gather in the immediate vicinity of the bus increasing the concentrations of toxic compounds to unhealthful levels. When buses idle in the school yard, the exhaust also can pollute the air inside the school building and pose a health risk to children throughout the day. In a study by Environment and Human Health, Inc. with collaboration from University of


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Connecticut and Yale University researchers, it was determined that children that ride school buses breath 5-10 times more diesel exhaust fumes than children that do not ride these buses.Several other studies by such organizations as NRDC, Coalition for Clean Air, and UCLA all concluded that peak diesel exhaust pollutant levels inside the bus often occur when idling since windows are often closed for interior heating.

Idle Reduction Technologies

To help reduce the health effects associated with diesel exhaust, school buses can be retrofitted with equipment that helps reduce idling. While some of this equipment is standard or optional on new buses, older buses are typically not equipped with it. Aftermarket auxiliary heaters can be used to warm up engines and passenger compartments in colder climates. This equipment runs off the school bus fuel tank or off electric outlets and includes a timer that can be programmed to automatically start the heating function. There are three types of heaters:

Electric Plug-in Block Heaters these heaters warm up the engine block by heating the engine coolant or oil. They are powered by electricity and are available in a range of voltages and watts, drawing between 1000 - 1500 watts per bus per hour. They include a timer that can automatically start or turn off the heater. A heater is mounted on the engine block of each bus and is plugged in when the bus is parked at the depot. Even in the coldest climates, engines will have a "warm start." Bus depots and garages can be designed or retrofitted to bring in the required electrical service. These heaters usually cost less than $100.00.

Engine Block Pre-Heaters these heaters have the same function as the electric plug-in block heaters, to heat the engine block for a warm start, with the difference being the energy source. Electric plug-in block heaters use the electrical energy from a 110V outlet to provide warm up the coolant while engine block pre-heaters use fuel stored onboard the vehicle (i.e., diesel, gasoline, natural gas or propane). Each block pre-heater uses only about 1/2 cup of diesel fuel per hour as opposed to at least a half-gallon of fuel per hour of idling. Block engine pre-heaters cost approximately $1200 - $1500, installed. Some of the reported benefits of these heaters are lower emissions and fuel savings, longer engine oil life, less wear-and-tear on the engine, and relatively easy installation and maintenance. They can be used in remote yards or other situations where electrical block heaters are not practical or possible to install and can be started by a timer, thus potentially saving time that would have been used to start and idle the buses.

Compartment/Engine Block Heaters these auxiliary heaters not only warm up the engine block but also provide heat to the passenger compartment at the same time. Due to this additional benefit of compartment/engine block heaters, they are more costly than the aforementioned two alternatives, approximately $2400 installed. The heaters use only about 1 cup of fuel instead of the half-gallon of fuel needed to idle for an hour. These heaters are especially useful for night time-activity buses and buses that transport very young and/or special-needs children. In addition, the radiant heat keeps the windows from frosting or fogging, which is a safety concern. Because of their multiple benefits and positive fleet responses, these heaters were selected as the focus for the remainder of this study.


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Review of Similar Technology - Diesel Fuel Fired Coolant and Air Heaters

Heavy-duty vehicles are used in a variety of applications, ranging from refuse collection vehicles with minimal cabin space to transit buses which can accommodate more than 100 people. Heavy-duty vehicles, whose primary function is people transport (i.e. school and transit buses), can not always relay solely on the heat given off from the diesel engine to keep the passenger compartment warm. To aid in keeping their passengers warm during cold winter months, school and transit bus fleets have resorted to the use of auxiliary heaters. There are generally two competing technologies for providing passenger space heating on heavy duty vehicles: air heaters and coolant heaters. Each technology is discussed below in relation to school bus application.

Air Heaters One auxiliary heater technology approach for school bus fleets is the use of air heaters. Diesel powered air heaters are a very effective and efficient way to heat the passenger compartment of a school bus and thus reduce idle time. Although they operate on engine fuel, air heaters are separate self-contained units that transfer heat from the combustion reaction that takes place within the heater to the air that gets circulated around the cabin by use of a fan or some other ventilation device. By heating the cabin they do reduce some of the idling that takes place, but because they cannot provide any heat to the engine, they do not totally eliminate the need for idling in school bus application. They have only a small draw on the battery and use a modest amount of fuel. Air heater prices range from $1,500 to almost $3,000, depending on the maximum BTU output, which ranges from 15,000 to 30,000 BTU/hr.

Figure 12. Espar D8LC (Source: http://www.espar.com)

One of the most capable and popular air heaters is the Espar D8LC model. This diesel-fueled model is very powerful, providing top of the range BTU output (27,300 BTU/hr) while consuming a very small amount of diesel fuel (0.26 gal/hr)3. The heater measures 25 inches in length, 10 inches in width and 10 inches in height which is about average for this type of auxiliary heater. It retails for nearly $3,700 which includes a $700 installation kit.

3 Technical Specifications Sheet, Espar website (http://www.espar.com)

http://www.espar.comhttp://www.espar.com)


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According to interviews with school bus fleet operators, approximately half of the bus idling time is due to the need to warm up the engine. The other half is spent mainly providing heat to the passenger cabin. Therefore, air heaters do not eliminate idling completely, but at best reduce idling by only 50 percent. Because school and transit bus fleets rely heavily on idling to pre-warm the engines in the mornings, air heaters are generally not used in these applications. They are typically used by over-the-road tractors in addition to block heaters, which provide engine heat. In the tractor application, air heaters are warming up a much smaller space to provide a comfortable environment during rest periods. Limited functionality and relatively high cost have lead to the conclusion that air heaters are not the most effective anti-idling technology for school bus application and thus will not be considered for the remainder of this study.

Diesel Fuel Fired Coolant HeatersDiesel fuel fired coolant heaters have been sold for over 40 years. They have evolved from bulky, inefficient, and unsafe units to the smaller, almost 85% efficient, and safe units that exist today. Their worth has been proven through several different studies showing that they do indeed reduce vehicle idle time, fuel consumption and emissions. Diesel fired coolant heaters are installed primarily on buses (school, transit and motor coaches) in order to pre-heat the engine coolant to reduce cold start emissions as well as to provide additional heat to the bus cabins during cold temperatures. This technology reduces idle time because the engine does not have to idle to provide heat to the cabin.

Design and Operation

With coolant heaters, the heater is inserted into the existing coolant line, draws diesel fuel from the fuel tank and electricity from the main vehicle batteries, and pumps heated coolant through the engine, radiator, and cabin heaters. The warmth generated by coolant heaters keeps defrosters working properly and passenger compartments at comfortable temperatures.

A schematic of a typically cooling system for a Type C school bus is shown in Figure 13. The engine cooling system circulates the coolant through the engine to remove excess heat and prevent the engine from overheating. After exiting the engine the coolant is at higher temperature due to the extra heat it picked up. The warm coolant exiting the engine is routed along the length of the bus to the cabin heaters (i.e. heat exchangers) located throughout the bus. There are typically several cabin heaters on a bus including a defroster for the front windshield, a heater for the driver by his feet and heaters in the middle and back of the bus to provide heat to the cabin.Each heater consists of a fan blowing air over coolant filled coils allowing the exchange of heat between the coolant and the air that is spread around the bus. After exiting the last heater, the coolant is returned to the radiator, which acts as a heat sink, where it is cooled by the engine fan before entering the engine again. While the main function of the cooling loop is to prevent the engine from overheating, it also provides the heat to the cabin of the bus. Since the coolant heat is typically used to warm up the passenger compartment, a conventional bus has no means of warming up the compartment while the engine is off.


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Figure 13. Conventional Cooling System Schematic for a Type C School Bus

Diesel fired coolant heaters are currently the only commercial technology that can provide heat to the engine and passenger compartment at the same time. They are integrated into the existing cooling system on the bus to provide heat to the engine and bus compartment when the engine is not running. A schematic showing the typical location of an auxiliary coolant heater is shown in Figure 14. When the engine is cold (i.e. after a long period of not running) the coolant heater warms up the coolant that is being circulated through the engine in order to warm up the engine and thus prevent startability issues as well as increased emissions associated with a cold start. With an auxiliary coolant heater present, the engine is not the only source of heat for the passenger compartment anymore. This allows the engine to be shutoff in certain instances where it would otherwise idle to maintain comfortable passenger cabin temperatures.

Figure 14. Cooling System Schematic for a Type C School Bus with an Auxiliary Coolant Heater

Advantages

Auxiliary coolant heaters are beneficial because they allow for the main diesel engine to be switched off during periods when it typically idles. The heaters reduce idling resulting in lower fuel consumption, emissions, and engine wear and tear. Diesel fuel fired coolant heaters use less fuel than the average school bus engine, to provide the same amount of heat. According to the EPA, the average school bus idles about an hour and a half a day, using about a gallon of diesel


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fuel during this time. Depending on the coolant heater used, it is possible to save almost a half gallon of diesel fuel a day, or around $270 per year per bus (at $3 per gallon fuel prices and 180 school days). Auxiliary coolant heaters have better fuel efficiency than diesel engines at idle due to much simpler system design. The main difference is that auxiliary coolant heaters are purposely designed to only provide heat to the coolant system, while the diesel engine primarily provides propulsion. A coolant heater consists of a combustion chamber surrounded by helical coils that contain coolant. This design allows for an exchange of heat from the combustion of diesel fuel to the coolant. This enables most of the combustion energy to be transferred, as heat, to the coolant. In comparison, the diesel engine is very in-efficient for providing heat at idle because it uses part of the fuel energy to overcome engine friction that the moving parts experience during reciprocating motion. Therefore, only a fraction of the total fuel energy released by combustion is transferred to the heating/cooling system. This difference in heating efficiency also allows some heaters to provide more heat to the cooling system than the diesel engine is capable of. This results in larger cabin heat capacity, and shorter engine warm up times.

As far as emissions are concerned, because the fuel fired heaters combustion process is more efficient than that of a diesel engine (i.e. requiring less fuel for the same heat output), fewer emissions are produced. Also, by not having to idle as long, which has been shown to be very taxing on engines from a reliability and longevity standpoint, school bus engines can last longer, diminishing the need for repairs and cutting maintenance cost. Less wear on the internal engine components also improves emissions because more deteriorated engines are less efficient and produce more harmful emissions.

While the aforementioned advantages make a strong case for diesel coolant heaters, they still consume diesel fuel and therefore, release some harmful toxins into the air. To avoid emissions associated with diesel fuel combustion and still retain the inherent benefits of auxiliary coolant heaters, this study investigates the use of propane fueled coolant heaters for school bus applications.

Hardware and Installation

Most of the heaters come with an installation package that includes a protective case, the controller, the wiring that connects the power source to the controller, the mounting brackets, and the fuel line to connect the heater to the fuel supply (i.e. vehicle fuel tank). In addition, for some of the heaters, the water pump that controls the flow of the coolant is specified separately, but is usually included in the coolant heater package. The installation process consists of splicing the coolant heaters inlet and outlet into the already existing coolant line on the drivers side of the vehicle. A direct fuel supply line must also be run from the fuel tank of the bus to the coolant heater. Additionally, wiring needs to be run from the power source, usually the buss batteries, to the heaters controller. An electrical connection must be made between the buss batteries and the coolant pump to provide the power for pump operation. The heater can be mounted onto the frame of the bus between the front and rear wheels, as there is plenty of space to allow for this installation as shown in Figure 15. Two air vents are required for the heater; one for the combustion air and the other for the exhaust. Individual installation instructions vary


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slightly for each aforementioned unit, but the general installation procedure is very similar. Labor costs may vary but given that the installation typically only takes a couple of hours, the cost should not exceed $250 (i.e., 5 hours @ $50 per hour labor rate).

Figure 15. 3-D coolant line blueprint (Source: Webasto Scholastic Series Operating Manual)

Manufacturers and Products There are three manufacturers of auxiliary diesel coolant heaters, including Webasto, Espar and ProHeat. All three manufacturers offer comparable models that range in heat output from 15,000 to 45,000 BTU per hour, similar to air heaters discussed at the beginning of this section.

Webasto is one of the two manufacturers of auxiliary diesel coolant heaters that offer a product specifically designed for school busses, the Scholastic Series. Webasto is a large company based out of Stockdorf, Germany, with U.S. facilities located in Michigan, Kentucky and California. Their product line includes both marine and road equipment, including coolant heaters for both applications. Webasto has been around for over 100 years. Since its creation, the company has evolved into a leading manufacturer of heating and cooling systems for the transportation industry. Their current products applicable to the school buses include the Scholastic Series and TSL 17 model.

Espar is also a large manufacturer of heating and cooling solution products. The company was established in North America in 1973 offering a wide array of heating and cooling solutions. It is based out of Mississauga, Ontario, Canada. Espar offers effective coolant heating products that, although they are primarily made for transit buses and specifically designed for school busses, would be effective in a school bus application. There are two Espar models that are applicable to school buses: Hydronics 10 and 16.


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Teleflex is the parent company to the ProHeat brand, which is based in Ontario, Canada and produces several heating solutions for motor vehicles. They offer truck auxiliary power units, coolant heaters for on road use, as well as military vehicle and train equipment. Their objective is to reduce idle time for motorized vehicles. Along with Webasto, they are one of the only two companies that offer a direct fired coolant heater specifically designed for school bus use, the X45 School Bus Edition.

Scholastic Series (Webasto)

The Scholastic Series is a direct fired diesel coolant heater specifically designed for school bus application. Shown in Figure 17, it is a modified version of the Webasto DBW2010 model that is designed to be integrated into the coolant system of a school bus. Its maximum heat output is 45,000 BTU per hour. At maximum output this heater consuming 0.4 gallons of diesel fuel per hour (greater than 80% efficiency). It draws 11 amperes of electrical current during maximum operation. The unit, including casing necessary for mounting, measures 24 long by 12 wide by 9 tall, and weighs about 60 lbs. The schematic, showing the internal components of the heater is shown in Figure 16. The unit operates on a timer, allowing for automatic start to preheat the engine at a pre-set time (i.e. prior to the arrival of the operator in the morning). The Scholastic Series heater retails for about $2,500 with installation kit, but if it is installed as an option on a new bus, the additional cost is only $1,800.

Figure 16. Webasto Scholastic Series Heater Schematic (Source: Scholastic Operating Manual, Webasto)


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Figure 17. Webasto Scholastic Series Heater (Source: http://www.webasto-us.com)

TSL 17 (Webasto)

The TSL 17 model is a smaller diesel fuel fired coolant heater that is capable of preheating the engine in a school bus application. However, it would take much longer, compared to a higher capacity coolant heater, to heat the coolant to a temperature sufficient for warming up the passenger compartment. TSL 17 produces 17,000 BTU per hour at maximum output while consuming 0.155 gallons of diesel fuel per hour (79% efficiency). Its current draw is a mere 2.1 amperes of electrical current. This is one of the smaller coolant heaters measuring only 9.25 in length, 6.4 wide and 4 tall. Similar to the Scholastic Series, it can be controlled manually by a switch or by using a programmable timer. The retail price of the unit, including the installation kit is $1,050, much lower than for the Scholastic Series. This coolant heater is primarily designed for use in over-the-road tractors, to keep the engine warm and provide heat to the sleeper cab while the driver is resting.

Figure 18. Webasto TSL 17 Heater Schematic (Source: TSL Operating Manual, Webasto)

http://www.webasto-us.com)


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Hydronics 10 (Espar)

The Hydronics 10 model manufactured by Espar provides up to 32,400 BTU per hour while only consuming 0.33 gallons of diesel fuel per hour. At maximum power, it draws 10.4 amperes of electrical current. The Hydronics 10 is available in two forms: a cased form that is easier to handle and install (16.75 long by 11.35 wide by 8.25 tall), or the universal form (13 long by 9.5 wide by 5.5 tall). The Hydronics 10 also utilizes the timer system that allows for automatic pre-heating at a pre-set time (i.e. before the driver arrives on cold mornings). The regular version, without the enclosure, is priced at $1,573; the unit with the enclosure costs $2,310. A separate installation kit is necessary to properly install the system, which costs an additional $241. Therefore, including the installation kit, the retail price of the Hydronics 10 is $1,814 for the case-less unit, and $2,651 for the cased system.

Figure 19. Espar Hydronics 10 Schematic (Source: Hydronics 10 Operating Manual, Espar)


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Hydronics 16 (Espar)

The Hydronics 16 model by Espar is typically used for large motor coach applications, and therefore, because of size similarities, would be applicable to school buses. Its maximum output is 55,000 BTU per hour while consuming 0.5 gallons of diesel fuel per hour. Its electrical current draw is 2.1 amperes. It is 24 long, 9 wide and 8.8 tall. This system retails for $1,843. Espar does not currently manufacture an installation kit for this unit, but if the installation parts were purchased separately, according to Espar representatives, it would cost around $300, bringing the total retail price to about $2,150.

Figure 20. Espar Hydronics 16 (Source: http://www.espar.com)

X45 School Bus Edition (ProHeat)

The X45 School Bus Edition is a very efficient and popular diesel fired coolant heater. It is specifically designed for use on school buses. The heater provides a maximum of 45,000 BTU/hr while consuming 0.33 gallons of diesel fuel per hour and drawing 7 amps of electrical current. Its dimensions are 20.5 in length by 12.5 in width and 11 in height. Like the aforementioned models, it is capable of using a programmable controller allowing for automatic starts on cold mornings. The unit itself, including the heating pump and controller, retails for $1,975. The installation kit must be purchased separately for an additional $190, bringing the total retail price of the system to $2,165.

Figure 21. ProHeat X45 School Bus Heater (Source: X45 Operating Manual, ProHeat)

http://www.espar.com


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Table 4 compares the most important parameters of the diesel coolant heaters presented in this section. Included in the table are: power output, power source, dimensions, diesel fuel consumption, overall system costs, and emissions (where available).

Table 4. Diesel Coolant Heater Specification Summary

Model Scholastic Series TSL 17 Hydronics 10 Hydronics 16 X45 School Bus Model Manufacturer Webasto Webasto Espar Espar ProHeat Power Output

(BTU/hr) 45,000 17,000 32,400 55,000 45,000

Power Source (V) 12 12 24 24 12

Dimensions (L X W x H) 24x12x9 13x7x9 10x4x7 24x9x9 21x13x11

Fuel Consumption (diesel gal/hr)

0.4 0.155 0.32 0.48 0.33

System Costs ($) 2,470 1,050

1,814 (regular) 2,651 (with case) 2,143 2,165

Emissions

32 ppm CO 10% by vol. CO2

70 ppm NOx


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Propane Heaters and Preliminary System Design

Availability of Mobile Propane Heaters Originally, it was planned for purposes of this study to conceptually design a propane fueled coolant heating system using an already existing, commercially available propane powered coolant heater. After lengthy investigation, only two potential products were discovered. These two products, however, do not provide sufficient heat for the school bus application, and are not readily available. Both of these products turned out to be very rare, meaning that they are not mass produced, nor widely advertised. There was very little information available for either product in terms of manuals, drawings or complete product specifications.

The only two manufacturers of commercial propane powered coolant heaters are Hilton and Enviroharvest. Neither manufacturer was able to provide sufficient information about their product though, as the actual products are rarely ordered and produced in very small quantities (i.e. special orders).

The Hilton Cordless Heater is capable of producing 6,500 Btu per hour while consuming 5.4 ounces of propane per hour. Its dimensions are about 13 inches in height with a diameter of 5 inches. Its retail price is about $700. Hiltons website lists another product, the B series, which has 2.5 times higher heating capacity (16,000 BTU/hr), but no further information on this product was available from the distributor or manufacturer. Due to the lack of information, as well as relatively low heating output capacity, this product is not appropriate for use in school bus application.

Figure 22. Hilton Cordless Heater (Source: http://www.cp.duluth.mn.us/~hilton/)

There was even less information available about the Enviroharvest Heater. This heater has a maximum output of 15,000 BTU per hour and its retail price is $750. Enviroharvest was contacted in order to obtain more information, but was unable to provide any. According to Enviroharvest, less than a dozen of these units are produced a year. This system was also deemed inadequate for purposes of this study because of the lack of information, its low availability as well as its low heating capacity.

http://www.cp.duluth.mn.us/~hilton/)


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Figure 23. Enviroharvest Heater (Source: http://www.servicemate.com)

As a result of the unavailability of an adequate commercial product, propane air heaters were also considered. While there are several propane air heaters commercially available, they would not meet the needs of this study. As previously mentioned in the diesel heater section of this report, school districts much prefer coolant heaters due to their ability to eliminate the idle time necessary to warm up the engine on cold mornings.

Although these two coolant heater systems were not adequate for the school bus application, comparing their limited specifications with those of similar capacity diesel fired coolant heaters led to determination that a propane fueled coolant heater would still be a comparable solution in terms of capital and operating costs and would produce lower emissions.

Preliminary System Design and CostsAfter the reviews of all the pre-existing propane coolant heaters yielded no viable choices for this study, an alternative design approach was developed combining a tank-less propane water heater and a water pump in order to create an adequate coolant heater. During the search of propane heaters for the Recreational Vehicle (RV) market, a combined system for heating the water supply and coolant was discovered. It is comprised of two almost identical heating loops (one for heating coolant and one for heating water). The BTU rates of the tank less water heaters that are currently available are comparable to those of diesel fired coolant heaters (i.e. ~50,000 BTU/hr). Under this alternative design, an additional water pump is necessary because the standard flow rates of tank-less heaters are not high enough to provide proper circulation of the coolant.

Hardware

Propane Heater

The best available heater is the RV500, manufactured by Precision Temp. The RV500 heater is the only one designed for use on a RV, meaning that it is the only heater designed for on-the-road use which assures that the unit will be able to handle the vibrations caused by driving, as well as be durable enough to be exposed to outdoor conditions. It also provides an adequate heat output, (44,000 BTU/hr) and is efficient enough (0.6 gallons/hr and 80% efficient), to operate for long periods of time on a reasonably small tank of fuel. The RV500 is also relatively inexpensive, retailing for $879. The unit measures 13.5" wide, 13.5" deep and 14.5" high. It weighs 35 pounds. Precision Temp staff indicated that this unit has been used successful for

http://www.servicemate.com)


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heating and circulating engine coolant in the past, and that staff, by modifying the controllers software, can optimize it for a given application. The disadvantage of using this unit, compared to diesel coolant heaters, is its shape and size. While the total volume of the unit is comparable to that of a typical diesel coolant heaters, its height may be problematic for vehicle packaging. While diesel coolant heaters generally have heights of less than 10 to fit between the skirt of the body and the frame rail, making the lowest point above both the rail and the skirt, the RV500 heater would likely have its lowest point several inches below the frame rail. Also, the current unit does not include a water pump, so a separate one will have to be installed in order for the coolant to be circulated. At an adequate flow rate, tank-less heater units were designed for in-home use were considered for this application, however due to their inability to handle the vibrations associated with onboard vehicle applications, as well as their lack of weatherproofing, they were deemed inadequate. Figure 12 shows a schematic of a typical tankless heater unit. Figure 12 illustrates the combustion chamber as well as the heat exchanger which heats the coolant wrapped around the chamber.

Figure 24. Precision Temp RV 500 (Source: http://www.precisiontemp.com)

Table 5. Select RV-500 Specification

Dimensions: 13.5" Wide x 13.5" Deep x 14.5" High Weight: 35 pounds

Burner: High primary air, 12 element, atmospheric type Aluminized steel body with stainless flame strips Heat Exchanger: Copper fin tube type with wrap for cooling

Connections: Electric: 18-2 x 2' lead.

Gas: brass 3/8" flare inside case rear or side accessible. Water: 1/2" OD copper tubing. Brass compression to 1/2"

Capacity: Max burn: 56,000 Btu input 44,000 Btu output (8.5 WCI pressure) Low burn: 15,000 Btu input 12,000 Btu output (1.2 WCI pressure) Fuel Consumption: Max burn: 2.55 lbs per hour

Power: 12 VDC at 1 amp. Operating range is 9 to 15 VDC Flue Gas Temperatures: Under 300F

Water Temperature: Can be adjusted from 90 to 135F

Gas Train: Burner is a 12 element high primary air, atmospheric type with stainless steel flame strips. Aluminum manifold with brass pressure tap.

Controls: Microprocessor, controlling ignition, flame proofing, safety systems and electronic gas modulation temperature control.

http://www.precisiontemp.com)


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Figure 25. Schematic of typical tank-less heater (TwinTemp Operating Manual)

Water Pump

Since the RV500 water heater does not include its own water pump, one needs to be installed. A pump was recommended by Precision Temp that is a high temperature water recirculation pump made for onboard vehicle application. It is 5 long with a diameter of 3. The pump is capable of circulating up to 5.5 gallons per minute of liquid at a maximum of 203 degrees Fahrenheit. It draws 2.25 Amperes of current. The retail price of this pump is $300.

Figure 26. Recirculatory pump (Source: http://www.precisiontemp.com)

Propane Tank

In the case of diesel coolant heaters, the fuel is obtained from the main fuel tank, requiring only installation of a fuel supply line. A propane coolant heater requires separate propane supply tank, unless it is installed on propane powered bus that already incorporates propane fuel tanks.Propane tanks come in two designs, horizontal and vertical mounted. Vertical mounted propane

http://www.precisiontemp.com)


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tanks are similar to those on most propane powered grills. Horizontal tanks are more expensive than their vertical counterparts, but are the preferred for a school bus application since they can be more easily fitted on the underside of school busses along the frame-rail. The critical dimension is the width and therefore horizontally mounted tanks could hold larger volumes.

Figure 27. Vertical LP Tank (left) and Horizontal LP tank (right) (Source: http://www.go2marine.com)

The size of the tank depends on several different factors. First, it must be small enough to fit into the available space (the frame rail height dictates the diameter size), but large enough to provide enough fuel to the heater so that it can be run as much as necessary under worst case conditions for several school days (i.e. below freezing temperatures). In addition, the United States Department of Transportations (DOT) prohibit vehicles carrying over 10 lbs of propane access to certain tunnels and bridges. This must be considered so as not to limit the travel routes of the bus. The tank also has to meet the Federal Motor Vehicle Safety Standards (FMVSS), meaning that it has to be certified for on road use. This specification could be met by using a tank that is actually designed for use on the road, such as a tank meant for use in an RV. Several different materials for tanks are available. Despite the weight advantage of aluminum and carbon fiber tanks, steel tanks are the best choice because of their much lower cost. The weight of the tank is not of primary importance in this application since the weight of the tank is trivial to that of the bus. Due to the aforementioned guidelines, a 40 lb (~ 7.1 gallon) steel horizontal mounted tank (go2marine.com) was selected as the best available tank for this study. Its dimensions are 23.5 long with a 12.15 radius. Its retail price is $217 and it is DOT approved for on-road use. Based on the heater selected, which at maximum output consumes 2.5 lbs/hr of propane, it was determined that 40 lbs of propane would meet typical school bus performance requirements, as it would provide 16 hours of use at maximum output. This is equivalent to the amount of fuel that the heater would use in a week. The tank comes with a gauge so that the fuel level of the tank can be maintained. The tank does not meet the federal standard size to allow access to certain tunnels, but as a rule, most school bus fleet applications in northern climates should not be impacted.

http://www.go2marine.com)


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Installation requirements and costs

The system could be installed along the frame rails of the bus, on the drivers side, in the same location as diesel fired coolant heaters, as shown in Figure 28. There is adequate room for the system, including the propane tank and the pump, in this location because the body of the bus does not protrude below the top of the chassis frame rails. Installation of the system is very similar to that of the diesel powered coolant heater. It will require that both the heater and the tank be mounted to the frame. The coolant line is connected to the inlet of the pump and routed to the inlet of the heater. The outlet of the heater is connected to the rest of the coolant system. Only 6 of hose is needed between the pump and the inlet of the water heater. The water heater (RV500) is connected to the propane tank with propane fuel line, and to the buss battery to provide the electricity needed to power the unit. There must be sufficient ventilation for the heater so that air can be pulled in to facilitate the combustion process as well as vacate combustion exhaust. Controls are also needed in order to turn the system on or off, depending on the status of the bus. These controls would be located in the cockpit of the bus, similarly to these on diesel coolant heater systems, and would only require a switch that would turn the electrical power to the pump and the heater on/off. Additionally, a timer could be placed on the heater and pump so that they could both be turned on automatically to pre-heat the engine and bus compartment prior to the arrival of the driver on cold mornings.

Figure 28. Blueprint of Propane Coolant System

The overall dimensions of the proposed system would be 14.5 tall, 40long and 13.5 wide. At this size, the length and depth are not an issue. The height, however, is slightly longer than preferred, hanging approximately 4 inches below the frame rail. This generally should not cause a clearance problem for the bus as other underside components typically hang lower than this level. The heater, the pump and the propane tank are sold with mounting hardware, although a mass-produced system for the school bus application would likely have specially-designed mounting hardware. The heater retails for $879 while the propane tank is $217. The water pump that is necessary to circulate the coolant costs $305. Installation should take less than 4 hours (2 hrs typically for diesel coolant heaters), so the cost of labor should be under $400 (at $50 per hour). The net price for the whole system presented in this section is approximately $1800. The system design is shown in the following two figures. Figure 29 demonstrates where


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in the bus the system would be installed. Figure 30 shows a close-up of the system, indicating where the fuel and coolant lines enter and, for the case of the coolant, where it leaves the heater.

Figure 29. Schematic of the School Bus Coolant System with Propane Heater Components

Figure 30. Schematic of Individual Components of the Propane Heater System

Pump

Heater Space for Propane Tank

Coolant Inlet Coolant Outlet

Propane Heater

Propane Fuel


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Operation and Safety

Since propane coolant heater uses pressurized propane gas as a fuel for its operation there will naturally be safety concerns when installing this system on a school bus that transports between 50 and 100 students every school day. As mentioned previously, the propane coolant heater requires a separate fuel tank, unlike the diesel coolant heater that just connects to the existing diesel fuel tank on the bus. Propane is stored under low pressure (~190 PSI) and is therefore relatively safe compared to compressed natural gas (3,000 to 3,600 PSI) or hydrogen (5,000 to 10,000 PSI) when used onboard a vehicle. The onboard propane storage tank meets the DOT Federal Motor Vehicle Safety Standards (FMVSS), meaning that it has to be certified for on road use. In addition, there are several other safety features built in the operation and design of the proposed propane coolant heater system.

When RV-500 is powered, the microprocessor activates the gas modulation valve and performs component diagnostics. The unit remains dormant until the rotary flow meter senses at least 0.4 GPM of coolant flow. The gas modulating valve will be set to its ignition value, the spark will be affected and the gas valve will open. Ignition will occur and the flame will be proofed. The microprocessor reads water flow rate and incoming water temperature, calculates the required gas flow to maintain set temperature and sets the gas modulation valve to the proper setting. The water temperature is then monitored by the thermistors midway and at the outlet to make any minor corrections in gas flow. If there is any change in water flow or incoming water temperature, the microprocessor recalculates and makes any required adjustments. The unit continues to produce hot water until water flow is stopped and the burner turns off.

Temperature control is maintained by microprocessor controlled gas modulation that delivers output water temperature within 2F by sensing water flow rate and three temperature inputs. There are three thermistors, one senses incoming water temperature (mounted on cold water line of heat exchanger), one senses temperature midway through heat exchanger (mounted in stainless probe with compression fitting on the heat exchanger), and one senses outlet temperature, (mounted to hot water outlet on the heat exchanger).

RV-500 has the following safety features incorporated in its design: The Model RV 500 is pilotless. There is no flame unless water flow is sensed. Flame rectification: Gas valve shuts off in 0.8 of a second if there is a flame outage. Redundant gas solenoid. Electronic high temperature shut-off (two). ECO high temperature shut off @ 165F with manual reset. Pressure relief valve at 100 PSI. Direct vent with combustion chamber sealed from inside of bus.


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Market Characterization When assessing the market potential for a certain technology, critical factors that are required for success in the market must be determined. These critical factors are used as criteria for market assessment. Based on these criteria the market is narrowed down and segments with the highest potential are identified. In case of the market assessment of propane heaters for school buses, the following critical factors were selected: climate, school bus population, and propane availability. The potential market for school bus coolant heaters is heavily dependent on the climate since bus heaters are primarily used during cold weather. As with any market assessment, customer concentration is also of great importance. In this case, school districts are the customers an

Documents

Investigation of Propane Heaters for Northern Climate School Bus Applications · 2014-01-28 · Investigation of Propane Heaters for Northern Climate ... Northern Climate School Bus