When a busnut says “Webasto”...
by Buswarrior
When a busnut says “Webasto” or “Proheat” or “Espar” or “Aqua Hot”, the sky is the limit as to what the words are being used to describe. For the novice researching the archives, it may be a little confusing.
Is it the brand name component being referred to? Which style? Is it referring to the underlying system that the brand component it is attached to? How do I compare these different examples of installations? What various design strategies have been employed?
You can be sure that no two busnut installations, choice of parts, or design criteria, will be the same! Neither will be the things that these words are meant to describe.
So, here are a few more words to try and help:
On the brand name and product line front, Webasto, Teleflex Thermal System’s Proheat, Eberspacher’s Espar and Aqua Hot/Hydro Hot (formerly Vehicle Systems) all make a wide variety of diesel-fired devices suitable for a busnut's needs, and some, perhaps not. Roughly speaking, from as small as 5000 BTU/h (1.5 kW) for the smallest air heater, all the way to 150,000 BTU/h (44kW) for the biggest coolant boiler, you can see that the conversation will change dramatically depending on which device is being referred to.
Further to confuse us, a brand name of a device gets used to describe some greater combination of the systems that the named device has been installed in. Without the details of the system involved, the word “Webasto” or the others, when seen on the board is widely misunderstood, to the point that it becomes meaningless, without further details.
So, let’s see if we can clear things up a bit:
First, these devices are rated by their capacity to make heat, measured in BTU/h (British Thermal Units per hour). Depending on what devices you are comparing and what heating/cooling calculations you are using to estimate your demand, take care you aren’t mixing up BTU and BTU/h. When making comparisons with lesser products, you need to be aware. Some marketers may quote the rating of the fuel input and not the heat output of the device. Compare the heat outputs, not the fuel inputs.
A few definitions:
Bunk Air heater:
A diesel fired device that heats air and has a small fan in it. These are commonly used to heat the sleeper cabs of highway trucks, and are robust units.
Some brand names:
Webasto Air Top;
Proheat Air;
Espar Airtronic.
Coolant boiler:
A diesel fired device that heats liquids that are circulated through it, popularly some form of automotive antifreeze mixture, if not the engine coolant. Some brand names:
Webasto:
Thermo;
TSL;
DBW.
Proheat:
X45;
M series;
Bravo;
XL.
Espar:
Hydronic;
D series.
Aqua-Hot/Hydro-Hot:
These are more complete turn-key systems in a box, relieving the busnut from designing and sourcing many of the controls and valves for multiple zones. Before you let sticker shock distract you, in comparing prices, be sure to include the costs of valves, controls and your engineering with another choice. This system may close the gap quickly in your calculations.
Furnace:
On purpose, I try not to use this word anymore in reference to these systems, to reduce the confusion with other components. I reserve this word to describe a unit that is self contained, large enough to be the only source of heat aboard, that burns fuel, heats air and is fan forced. For instance, the popular propane fired RV style furnaces, which mimic what you might find in a house.
I will not be discussing propane RV furnaces here. There are many, many busnuts using propane RV furnaces and there are many sources of good info for their use and installation elsewhere.
Depending on the device in question, being diesel fired, in the design stage, the busnut needs to consider the safe routing of fuel lines, for most, a supply and a return, and what to do with the hot exhaust to route it to a desirable location.
The exhaust carries the usual dangerous by-products of combustion, is quite hot close to the source, and many think it stinks. Simply dumping it out the side will not be well regarded by close neighbours. An up-pipe of some sort will be desirable. Keeping the business end of the device accessible for maintenance is also a common oversight. These things, like the rest of the coach, need periodic maintenance to stay operating in top shape.
Now as to what might make economic or efficient sense... we must remember that in all things busnut, an existing component, or one that is free or inexpensive makes for a compelling compromise from what might be “best”, so don’t worry about getting it just right if you have some bits and pieces available to you. In developing your design, include some thought as to what the back-up plan will be if you are a little off in your calculations, or what limitations you will willingly accept with acquired components, and share your thoughts on the BNO Bulletin Board System.
So, how about an air heater?
The use of bunk air heaters by busnuts, judging from the activity on the bulletin board, appears to be fairly small. It may be due to the unavailability of good used units, as truckers snap them up if they have any life left in them. They may also be considered to be rather pricey in comparison to the amount of heat you get. As the heating capacity of these is typically smaller than the total potential heating needs of a bus conversion, they are commonly used by a busnut in a layered approach: the busnut installs more than one, or has a number of smaller capacity heating solutions, adding more devices to the mix as the temperature drops. This strategy can be argued to be more efficient and has redundancy. Small devices running steady might use less fuel than a large device cycling on and off to maintain interior temperature. Busnuts seem to enjoy designing redundancy into their coaches; an especially good thing when we employ discarded commercial parts with no known history.
In deciding if a coolant boiler is for you:
What do you want to heat, and how big do you need?
Popular choices are: coach engine pre-heat, generator engine pre-heat, domestic hot water supply, coach interior, storage bay/waste/water tanks, in the arctic, fuel heating, and the hardy alternative fuel folks may also warm their fryer fuel.
Mix in that some components become heat sources when operating, instead of heat recipients: engine, generator, domestic hot water tank, and other purposefully installed devices, and your choices as to what you want to include, and what you want to ignore, grows quickly.
As for sizing, you need to do a bit of research on how much heat energy you might need for the intended climate, and refer to the archives here on the bulletin board to see what sizes others are using, and why.
For instance, the 40,000 BTU/h (12kW) size are popular, a smaller capacity unit may require some thought as to how to extract the desired performance in colder climates, or your design may leave you cold, or dissatisfied with the length of time for warm up.
Some of the highway truck folks use ones in the 17 000 BTU/5kW with a focus on engine pre-heat using a timer to start it ahead of time and little else.
On the other hand, a larger one will give you quick warm up, but will short cycle on and off quite frequently in warmer climates. My own 100,000 BTU/h (30kW) unit that came with the coach, engine off, can feed the stock HVAC, sucking in fresh air, enough heat to make it toasty in -25F/-30C. But it burns on and off too quickly when it is above freezing, even with the engine block in the loop, and the incoming fresh air to help waste the heat. The higher fuel bill is a fine trade off for an infrequent camper, and for quick Canadian winter warm-ups, but it certainly would be an expensive compromise for extended above freezing living.
Then there are the decisions as to how you will go about distributing this heat, and how you choose to integrate or isolate the bits and pieces. You will find the bulletin board is full of opinions and options as to what each busnut thinks or has done. You get to choose what you think you’d like to do. That’s why we build our own!
Typically, there will be some system of pipes, hoses, pumps, valves and thermostats that circulate and direct the heated liquid to the coach interior and the other equipment, as needed, to heat it.
For interior heating, you might find radiant in-floor loops, wall mounted finned radiator types, fan forced heat exchanger types, or some home-brewed interpretation and combination.
Some busnuts integrate the engine coolant system and use its antifreeze as the liquid; others choose to isolate the two systems, being free to use the liquid of their choice in the coolant boiler system. Be sure that an isolated system has some sort of freeze protection and corrosion inhibitor for the metal bits.
Some busnuts design bypass systems on a single fluid system; some just run a big loop. Continually heating the engine block does cost!
Some busnuts prefer to keep the systems separate to defend against catastrophic failure by a single hose clamp, others attach less concern to that possibility. Some wish to consider the lighter load on pumps that a smaller isolated system will have. Others consider that the isolated systems do not require the more expensive engine anti-freeze, and maintaining the SCA’s, and will not require as frequent flushing and re-filling as the engine system, a definite cost issue depending on the capacity of the finished systems.
If the busnut chooses to keep engine and coolant boiler systems isolated, some use a plate style heat exchanger to transfer heat between the engine system and the boiler system to facilitate engine pre-heat in one direction, and using the "free heat" from the engine while driving, in the other direction. The generator may be similarly plumbed for pre-heat/ waste heat capture.
Domestic hot water can be done a number of ways. A note of safety right up front: Proudly spend the big dollars necessary on a blending valve to protect everyone from scalding, and set it no hotter than is safe to put your hand under. You don’t need water any hotter than that at the tap. These systems, after going for a drive, will be at least 180 degrees!
There are specially made hot water tanks that have built in heat exchangers. Typically these are referred to as “marine” hot water tanks, which have attachments for coolant lines in order to scavenge the heat from the running engine to heat the water. Others use house type electric tanks and rig up a circulating system using an external heat exchanger. Others use a propane powered hot water tank with some variation of the above. It really gets entertaining when you rig it so that the hot water tank can be used as a heat source to heat the rest of the system, as well as being the recipient of the heating.
How to use your coolant boiler in the execution of a fryer veggie oil fuel system for the coach or the generator would be better described by those with the passion for it!
As you can see, there are many variables involved in slinging around the words Webasto, Proheat, Espar & Aqua-Hot!
Happy coaching!
Buswarrior
Copyright © 2010. All rights reserved. Reproduced with permission of the author.
