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Page 2: The LHG and Fuel-Fired / Fuel-Operated Heaters (FFH/FOH)

How the LHG Makes Heat


OK, this gets a little technical, but it’s pretty cool stuff – well, hot stuff, really.

The LHG uses the physics of fluid dynamics to generate heat within a liquid. The engine's motion (kinetic energy) is transferred to the LHG through the engine’s belt system while the engine coolant gets piped through the LHG's innards. Inside the LHG, the coolant liquid passes between a rotor and stator (mechanical things), which creates friction within the liquid.


As we all know here in Michigan, from rubbing our cold hands together in the winter, friction generates heat. So, the hydraulic friction within the liquid (in this case, the coolant) heats instantaneously.


Gotta love that physics!

Finally, by using a clutch and dynamically adjusting various aspects of the liquid flow, the LHG controls the liquid dynamics and the amount of heat generated.

Engine ISO 2-EDITED.jpg
Compare LHG to FFH FOH bus heaters.

Why the LHG Is More Efficient
than Fuel-Fired Heaters (FFH/FOH).

Two reasons: the diesel engine itself and some more physics... Unlike a fuel-fired heater that directly draws diesel from the tank and burns it, the LHG draws a small amount of energy from the engine itself - and only when it is expedient to do so.

Diesel engines are very efficient at creating motion (lots of power and lots of torque), and hydraulic friction is very efficient at generating heat. The engine burns fuel to run, and the LHG (when engaged) puts very little load on the system - drawing off a small amount of that power and torque.  


The slight load placed on the system by the LHG produces heat with an efficiency of up to 98%. So, while the engine will burn a little more fuel when the LHG is engaged. it is only a fraction of what a much less efficient fuel-fired / fuel-operated heater demands.

As a matter of fact, a field study done for presentation to NYSERDA showed that a bus engine running at idle with the LHG engaged had almost no effect on fuel consumption compared to running without the LHG. There were other efficiencies too. Download a summary using the link on this page.

Why the LHG Is Much Cleaner
than a Fuel-Fired Heater (FFH/FOH)

First, the LHG is better at producing heat, so it uses less fuel overall (see above). More importantly, exhaust from the small amount of additional fuel used by the engine when turning the LHG is put through the engine's after treatment system - cleaning it up considerably. ( see: "About Advanced Diesel Tech." and "Do Diesel Engines Produce Less..." for more on diesel emissions)

On the other hand, fuel-fired / fuel-operated heaters use diesel to feed a flame and then expel the exhaust directly from under the bus. There is no attempt to clean or treat the FFH exhaust, making the LHG considerably cleaner. 

FFH Exhaust Graphic.png

Untreated exhaust from a fuel-fired heater is expelled directly into the air around the bus.

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The LHG (highlighted here mounted on a school bus engine) has a small footprint and does not directly burn fuel or emit exhaust.

Ventech's LHG kits are available for Thomas Built, Blue Bird, and IC Buses for end-user or dealer installation.

If you need a supplemental heat solution for your fleet and your model is not available through our online store, or you're looking for an OEM partner to give your buses an edge, let's talk. Use the contact link below or give us a call.

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