Too Efficient?
All combustion engines generate heat. And while some heat is necessary for proper functionality, much of the heat generated by combustion engines is discarded as waste. The purpose of radiators, for example, is to help remove this “waste heat” (excess energy produced through the combustion process that is not converted into motion or used to assist with proper combustion).
In cold conditions, some of this excess heat can be put to good use, defrosting windows and keeping the operator and passengers comfortable.
Efficiency is the process of using as much consumed energy (horsepower, heat, etc.) as possible to achieve the goal (moving a vehicle). As automotive engines have become more efficient, more energy (fuel) is used to move the vehicle, and less energy (fuel) is expelled as waste heat.
Not enough waste?
Over the years, diesel engines have become more and more efficient. They use less fuel and create less waste heat.
For example, Thomas Built Bus (TBB), Detroit Diesel engines have become so efficient that, in cold weather conditions, the engines no longer produce enough waste heat to quickly and consistently defrost the windows while supporting passenger comfort. In 2021, Thomas Built Bus was looking for a way to cleanly, quickly, and efficiently add heat to their buses in the Northern US and Canada.
This was good because the TBB/Detroit Diesel engines use less fuel compared to other engines, but it led to a new challenge of providing enough heat to warm the driver and students and to defrost the windows. Also, it is important for the engine and after-treatment systems to maintain optimal operating temperature.
How could TBB maintain exceptional engine efficiency while ensuring the highest level of passenger safety and comfort?
The Old Way: Burn Stuff
Buses have large cabin spaces that require heat. They can lose much of that heat during passenger ingress and egress (even more so when special-need lifts are involved). Buses also tend to have higher-than-normal idle time caused by picking up and dropping off children, combined with slow urban and suburban traffic. For most buses in northern climates, the engine (even less efficient engines) cannot create enough extra heat to provide for quick defrosting and passenger comfort.
For this reason, there have been, and are, traditional supplemental heat systems for buses. These are often referred to as “fuel-fired heaters” or “hydronic heaters.” This older heating technology draws and burns diesel fuel which is tapped from the bus’s fuel tank. The tapped fuel is burned in a raw flame, and the flame is used to heat coolant that is pumped through a heat exchanger. The untreated diesel exhaust from the hydronic heater’s flame is then vented directly out from under the bus.
These fuel-fired/hydronic heaters take some time (over 30 minutes) to generate enough heat to defrost a bus’s windows and even longer to heat the passenger compartment. They are not very efficient, require regular maintenance, and cannot provide the engine with instant supplemental heat when required by environmental conditions. (VentechLHG Student Transportation)
Yes, there is a better way.
As we worked together, TBB quickly realized that the Ventech LHG (Liquid Heat Generator) technology is the solution.
Faster heat production.
Faster defrosting.
No fuel tap.
No flame.
No untreated exhaust.
The New Way: Liquid Heat
How does the LHG bring a superior approach to heating buses? The LHG does not pre-heat the bus over a long period like a traditional fuel-fired heater. Instead, it delivers amazingly fast and efficient heat generation.
The LHG rapidly heats the bus in concert with the engine. The LHG, by itself, can produce 45,000 BTU/hr., equaling or beating any fuel-fired heater available for buses. However, because the LHG also loads the engine, the system delivers twice the heat. By working together with the engine, the available heat is DOUBLED to 90,000 BTU/hr. because the bus’s engine generates an equal amount of heat when the LHG is engaged. All the heat produced by the LHG and the engine working together goes directly into the coolant, which is, in turn, used to defrost and warm the bus. Preheating becomes unnecessary as the bus will defrost and warm to comfort during the time it takes the driver to perform the initial safety checks before setting off. This rapid initial heating saves fuel and personnel time.
No attitude towards altitude. While not an issue for most bus operators, if you drive at higher altitudes, some fuel-fired/hydronic heaters simply can’t work efficiently. There are special high-altitude modules (at an additional cost), but then those don’t work efficiently if the bus comes down from higher altitudes. The Ventech LHG doesn’t have an altitude attitude. It will function just as well up high, down low, and in between.
Engine health and exhaust after-treatment health. The Ventech LHG benefits the engine and after-treatment systems, reducing maintenance issues and promoting longevity. This has been seen over decades in the field as the LHG is used by many generator manufacturers to prevent “wet stacking” and other maintenance issues. Thousands of generators have been equipped with LHGs. Spanning a variety of markets and models, both as original equipment from the factory and as aftermarket improvements. On generators, the main purpose of an LHG is to protect and preserve the engine. Obviously, generators have no windows to defrost or passengers to keep warm. Instead, generator manufacturers use the LHG to ensure that the generator’s diesel engine maintains optimal operating temperature and load. Enhancing exhaust gas temperatures (EGT) and promoting proper after-treatment conditions. As with a diesel generator, proper engine load and added EGT help a bus’s engine run properly when idling, protecting the bus’s engine and after-treatment systems.
Environmentally-friendliness. Traditional fuel-fired/hydronic heaters burn diesel fuel and emit raw diesel exhaust. On the other hand, the LHG siphons no fuel and has no flame. The LHG is driven by the bus’s engine. Why is this important? The bus’s engine has undergone intense scrutiny by such agencies as the EPA and CARB and has been fitted with emissions control systems to ensure that harmful emissions are minimized and, in some cases, eliminated entirely. The same cannot be said for fuel-fired/hydronic heaters. Even when they are at optimal performance, fuel-fired/hydronic heaters belch untreated diesel exhaust fumes.
Extremely Reduced Maintenance. The LHG requires no regular maintenance. fuel-fired/hydronic heaters require frequent and ongoing maintenance. More importantly, failure to perform maintenance on fuel-fired/hydronic heaters leads to decreased heat output and noticeably higher emissions. Of course, maintenance adds additional cost.
Economics, Performance, Sustainability
The LHG is the right technology at the right time for the right reasons. Together, Ventech and Thomas Built Bus distributed and installed over 1,000 units in just over a year, to the delight of tens of thousands of warm, comfortable students, their drivers, and their transportation team.
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