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Federal lab cost-effectively eliminates diesel idling to condition Class 8 sleeper cabs
Written by Paul Weissler
You see them atthe side of roads, in parking lots and pull-off areas of highways Class 8 over-the-road trucks with their diesel engines idling through the night to runthe heating or air conditioning that assure comfort in the resting drivers" sleeper compartments. A lot of fuel might be saved and CO2 emissions reduced with energy-efficient alternatives to extended idling. The NationalRenewal Energy Laboratory, a federal facility based in Golden, CO, took on thechallenge. The idle fuel-usagestudies it found were from 2005; the outdated figuresestimated idling is 7% of total diesel fuel consumption, so NREL focused onindividual Class 8 trucks, proposing a package of technologies that can annually save 774 gallons on A/C cooling loadalone compared with an idling truck; at $3 per gallon for diesel fuel, full payback of aninvestment in sleeper cabin climate-control equipment would come in about three years. Only about halfthe states in the U.S. currently restrict idling for over-the-road trucks and laws often are observed in the breach, as someanswers raise cost and reliability issues. Driver comfort important The trucking industry and regulators know there"s a clear opportunity to save fueland improve air quality. But restingdrivers can"t be confined to cocoon-like compartments with an occasional wispof cool air in summer and/or wrapped in heavy blankets in winter. Today"s sleepercompartments make driver comfort and convenience high priorities. Volvo VNL Class 8 series single-bed units are118 ft /3.34 m with a flat roof, andtwo-driver models with high roofs (77 in/1955 mm) have bunk beds in a 371 ft /10.5 m livingspace considerable area to beclimate-controlled. NREL"s namepoints to its research in such areas as photovoltaics, wind and biosciences,but much of its work is on cost-effective solutions to real-world"lower-tech" problems. It hasprovided considerable study on climate-control related electric-vehicle range issuesand at the recent SAE World Congress explained its extensive research into reducing Class 8truck idling fuel consumption. There are alternative approaches for climate control insleeper cabs to avoid extensive idling, includingbattery-powered auxiliary A/C, fuel-fired or electric heaters and small diesel engines that serve as auxiliary power units (APUs). The popularity of diesel APUs peaked someeight years ago and the adoption rate today represents just 9%, explainedJason Lustbader, NREL senior research engineer. NREL looked atmany aspects of what it proposes as "complete cab solutions,"with emphasis on low-cost additions or substitutions. "The project goal was to reduce cabthermal loads to enable smaller, lighter and more cost-effective idle-off climate-control equipment," explainedLustbader. The goal: a 30% reduction inbig-rig sleeper climate-control loads with no-idle solutions that pay backwithin three years or less. The NREL projectevaluated four aspects in an integrated strategy: the solar envelope (as overall A/C energy use is in theequation), heat and cold conductive pathways into the sleeper, efficientequipment and the volume of the sleeper. In this effort, NREL works with industry partners, particularly VolvoGroup NA, PPG and Aearo Technologies, which makes energy/sound absorbingmaterials. 35.7% reduction in A/C load NREL testingshowed its complete cab solution exceeded the goal, with its most advancedapproach producing a 35.7% reduction in A/C load and 43% decline in heating load, withan even greater reduction of 53% with a more advanced approach toinsulation. Translating those savings into dollars, NREL found that with the complete cab solution toreduce loads and adding a battery-powered A/C system for the sleeper, 774 gallon of fuel per year could be saved. Savingsand cost analysis for heating the cabin is still underway, although somepreliminary data was announced. Prior testing byNREL indicated the best bang for the buck was in specific insulation, interior curtains, window shades and paints. Although all the actual testing was done atNREL headquarters in Golden, CO, the data was plugged into NREL"s own loadestimating software, CoolCalc, to give the results a nationwide scope. The process provides fuel-use estimation bycombining thermal loads with an A/C performance model to calculate anelectrical demand. The load was combinedwith modeling to be able to determine fuel use from recharging the battery pack. Because long-haul trucks operate across thecountry, the model used the 200 most representative weather stations nationwideto calculate total fuel saved. Details that led to NREL"s quantified results: Thinsulate in "plus" package Baselineinsulation consists of foam attached to the door and body trim panels of thesleeper. The advanced package insteaduses one- and two-inch insulation blankets with a thermal conductivity rating of0.03-0.05 W/m-K. In addition to thatadvanced package is a "plus" addition of 0.25-in layer of Thinsulate,which has a reflective radiant barrier installed between the interior trimand the structure of the sleeper. The three levelsof insulation for the sleeper were combined with three different packages ofprivacy shades for the cab glass and sleeper curtains between the cab andsleeper: standard insulation withadvanced shades and curtains, advanced insulation with standard shades andcurtains and a package of fully advanced insulation, shades and curtains. The first two packages produced almost thesame reduction in UA (heating load): 20.6% and 20.7%. The fully advanced setup resulted in a 43%reduction. "Advancedplus" insulation also was evaluated against standard shades and curtains, advancedshades and open curtains and advanced shades and curtains. This"Complete Cab Plus" configuration yielded the greatest reductionin UA at 53%. However, evenwith Plus insulation and advanced shades, leaving the sleeper curtains open to avoid aclaustrophobic-feeling sleeper caused theheating load reduction to drop markedly to just 21.6%. No-idle equipment A Dometic no-idle7000-BTU A/C system was installed. This truck sleeper system is battery-operated, has a three-speed blower and will run for more than11 hours, the company claims. The system was powered by the laboratory"s 120-v A/C fortesting to obtain the most accuratedata. However, the analysis assumed the use of104 A-h AGM (absorbent glass mat) batteries that would recharge while thetruck is in operation. For heating,NREL chose a forced-air heater with the diffuseroriented to avoid air stratification. The heater was operated at 90 F (32 C) to provide a sufficient gap compared withambient temperate for accurate measurement of the heat transfer coefficient (clearly muchhigher than would be used solely for sleeper comfort). A fuel-fired heater will be evaluated infuture testing and it is expected to enhance the overall results. Paint-color effect Exterior paint color affects sleeper thermal loads only when the sun is out for along time and intensity is high, typically in summer. However, because it does affect the total vehicle A/C load, the chosen white color was found to deliver a 20.8% load reduction compared with black. As an alternative, solar-reflective blue wascompared with conventional blue and showed a 7.3% saving. The white color combined with theNREL Complete Cab Plus package to deliver the lab"s 35.7% cut in overall A/C energyconsumption. NREL"s completesolution delivered results that equate to operating the trucks in year-round moderate temperatures. Modeling with CoolCalc showed majorreductions in the number of both heating and cooling days in all parts of thecountry. This seems to provide an opportunity to save by downsizing the batterypack and other components in a fully optimized Class 8 climate-control system.
Date written: 12-May-2016 12:23 EDT
More of this article on the SAE International Website
ID: 3384
Written by Paul Weissler
You see them atthe side of roads, in parking lots and pull-off areas of highways Class 8 over-the-road trucks with their diesel engines idling through the night to runthe heating or air conditioning that assure comfort in the resting drivers" sleeper compartments. A lot of fuel might be saved and CO2 emissions reduced with energy-efficient alternatives to extended idling. The NationalRenewal Energy Laboratory, a federal facility based in Golden, CO, took on thechallenge. The idle fuel-usagestudies it found were from 2005; the outdated figuresestimated idling is 7% of total diesel fuel consumption, so NREL focused onindividual Class 8 trucks, proposing a package of technologies that can annually save 774 gallons on A/C cooling loadalone compared with an idling truck; at $3 per gallon for diesel fuel, full payback of aninvestment in sleeper cabin climate-control equipment would come in about three years. Only about halfthe states in the U.S. currently restrict idling for over-the-road trucks and laws often are observed in the breach, as someanswers raise cost and reliability issues. Driver comfort important The trucking industry and regulators know there"s a clear opportunity to save fueland improve air quality. But restingdrivers can"t be confined to cocoon-like compartments with an occasional wispof cool air in summer and/or wrapped in heavy blankets in winter. Today"s sleepercompartments make driver comfort and convenience high priorities. Volvo VNL Class 8 series single-bed units are118 ft /3.34 m with a flat roof, andtwo-driver models with high roofs (77 in/1955 mm) have bunk beds in a 371 ft /10.5 m livingspace considerable area to beclimate-controlled. NREL"s namepoints to its research in such areas as photovoltaics, wind and biosciences,but much of its work is on cost-effective solutions to real-world"lower-tech" problems. It hasprovided considerable study on climate-control related electric-vehicle range issuesand at the recent SAE World Congress explained its extensive research into reducing Class 8truck idling fuel consumption. There are alternative approaches for climate control insleeper cabs to avoid extensive idling, includingbattery-powered auxiliary A/C, fuel-fired or electric heaters and small diesel engines that serve as auxiliary power units (APUs). The popularity of diesel APUs peaked someeight years ago and the adoption rate today represents just 9%, explainedJason Lustbader, NREL senior research engineer. NREL looked atmany aspects of what it proposes as "complete cab solutions,"with emphasis on low-cost additions or substitutions. "The project goal was to reduce cabthermal loads to enable smaller, lighter and more cost-effective idle-off climate-control equipment," explainedLustbader. The goal: a 30% reduction inbig-rig sleeper climate-control loads with no-idle solutions that pay backwithin three years or less. The NREL projectevaluated four aspects in an integrated strategy: the solar envelope (as overall A/C energy use is in theequation), heat and cold conductive pathways into the sleeper, efficientequipment and the volume of the sleeper. In this effort, NREL works with industry partners, particularly VolvoGroup NA, PPG and Aearo Technologies, which makes energy/sound absorbingmaterials. 35.7% reduction in A/C load NREL testingshowed its complete cab solution exceeded the goal, with its most advancedapproach producing a 35.7% reduction in A/C load and 43% decline in heating load, withan even greater reduction of 53% with a more advanced approach toinsulation. Translating those savings into dollars, NREL found that with the complete cab solution toreduce loads and adding a battery-powered A/C system for the sleeper, 774 gallon of fuel per year could be saved. Savingsand cost analysis for heating the cabin is still underway, although somepreliminary data was announced. Prior testing byNREL indicated the best bang for the buck was in specific insulation, interior curtains, window shades and paints. Although all the actual testing was done atNREL headquarters in Golden, CO, the data was plugged into NREL"s own loadestimating software, CoolCalc, to give the results a nationwide scope. The process provides fuel-use estimation bycombining thermal loads with an A/C performance model to calculate anelectrical demand. The load was combinedwith modeling to be able to determine fuel use from recharging the battery pack. Because long-haul trucks operate across thecountry, the model used the 200 most representative weather stations nationwideto calculate total fuel saved. Details that led to NREL"s quantified results: Thinsulate in "plus" package Baselineinsulation consists of foam attached to the door and body trim panels of thesleeper. The advanced package insteaduses one- and two-inch insulation blankets with a thermal conductivity rating of0.03-0.05 W/m-K. In addition to thatadvanced package is a "plus" addition of 0.25-in layer of Thinsulate,which has a reflective radiant barrier installed between the interior trimand the structure of the sleeper. The three levelsof insulation for the sleeper were combined with three different packages ofprivacy shades for the cab glass and sleeper curtains between the cab andsleeper: standard insulation withadvanced shades and curtains, advanced insulation with standard shades andcurtains and a package of fully advanced insulation, shades and curtains. The first two packages produced almost thesame reduction in UA (heating load): 20.6% and 20.7%. The fully advanced setup resulted in a 43%reduction. "Advancedplus" insulation also was evaluated against standard shades and curtains, advancedshades and open curtains and advanced shades and curtains. This"Complete Cab Plus" configuration yielded the greatest reductionin UA at 53%. However, evenwith Plus insulation and advanced shades, leaving the sleeper curtains open to avoid aclaustrophobic-feeling sleeper caused theheating load reduction to drop markedly to just 21.6%. No-idle equipment A Dometic no-idle7000-BTU A/C system was installed. This truck sleeper system is battery-operated, has a three-speed blower and will run for more than11 hours, the company claims. The system was powered by the laboratory"s 120-v A/C fortesting to obtain the most accuratedata. However, the analysis assumed the use of104 A-h AGM (absorbent glass mat) batteries that would recharge while thetruck is in operation. For heating,NREL chose a forced-air heater with the diffuseroriented to avoid air stratification. The heater was operated at 90 F (32 C) to provide a sufficient gap compared withambient temperate for accurate measurement of the heat transfer coefficient (clearly muchhigher than would be used solely for sleeper comfort). A fuel-fired heater will be evaluated infuture testing and it is expected to enhance the overall results. Paint-color effect Exterior paint color affects sleeper thermal loads only when the sun is out for along time and intensity is high, typically in summer. However, because it does affect the total vehicle A/C load, the chosen white color was found to deliver a 20.8% load reduction compared with black. As an alternative, solar-reflective blue wascompared with conventional blue and showed a 7.3% saving. The white color combined with theNREL Complete Cab Plus package to deliver the lab"s 35.7% cut in overall A/C energyconsumption. NREL"s completesolution delivered results that equate to operating the trucks in year-round moderate temperatures. Modeling with CoolCalc showed majorreductions in the number of both heating and cooling days in all parts of thecountry. This seems to provide an opportunity to save by downsizing the batterypack and other components in a fully optimized Class 8 climate-control system.
Date written: 12-May-2016 12:23 EDT
More of this article on the SAE International Website
ID: 3384
