Webasto Heating System

[Jcparmley]

Hello All

I have been thinking about a heating system for OTR as well as a secondary heat system while parked in my MCI 102dl3.  I am going to remove the OTR HVAC except for the drivers heat and defrost.  I removed the floor and have cleaned out all the ducts. The floor will be installed over the duck outlets.  I drew a rough draft of the system so I can get my head around the major components.  Please take a look and give me some advice on what is missing.  Thanks

[buswarrior]

Your heat exchangers are arranged in parallel. The header says series?

How are you going to balance the flow to all the exchangers?
Fluid will choose the path of least resistance, so the longer and twistier will see less than shorter and straighter.

How are you going to prevent overheating the engine, if the plate exchanger doesn't remove enough heat from the coolant?

Have you budgeted a power source for all these electric fans, pumps and the boiler, for camping use? Meaning, How much power is it going to need to keep you warm for a day, or overnight?

In abandoning the duct work, don't leave any "accidental air intakes" which you cannot control, drafts, hot or cold, will screw up your underway HVAC attempts.

Happy coaching!
Buswarrior

[richard5933]

Without some way to remove the engine from the system when, you'll struggle to ever get any heat from this when using it for interior heat when camping. The engine will just become a huge heat sink hanging out in the cold and suck all the heat away.

Why not have the Webasto main loop provide for the interior heat/defrost. If you include a surge tank in that loop, it can be run by itself. When you want to preheat the engine or tap into the engine heat to provide interior heat, you can open the engine loop and connect the two systems.

[Utahclaimjumper]

 Your still not reading the original post,,,He is NOT interested in heating "the interior",,Only a few lower storage bays,, the generator,, and engine.. Even then he is only interested in eliminating the possibility of freezing in those areas.>>>Dan

[Jcparmley]

I will have heat pumps in the ac system for heat when it's not that cold.  I also have a 42k BTU propane furnace when boondocking.  My main point of the hydronic system will be for heat while going down the road and for engine preheat, etc. 

Yes, the drawing is in parallel.  The heading (series) was not cropped out when I copied and pasted from the original illustration.  What is the best way to balance the flow?  In regards to engine overheating I need some suggestions.  Would it be better to have the system in the same big loop rather than isolating the engine loop with the plate exchanger?  Can someone point out where are the "air intakes" might be so I can address air infiltration.  Thanks for the help with this.

Your heat exchangers are arranged in parallel. The header says series?

How are you going to balance the flow to all the exchangers?
Fluid will choose the path of least resistance, so the longer and twistier will see less than shorter and straighter.

How are you going to prevent overheating the engine, if the plate exchanger doesn't remove enough heat from the coolant?

Have you budgeted a power source for all these electric fans, pumps and the boiler, for camping use? Meaning, How much power is it going to need to keep you warm for a day, or overnight?

In abandoning the duct work, don't leave any "accidental air intakes" which you cannot control, drafts, hot or cold, will screw up your underway HVAC attempts.

Happy coaching!
Buswarrior

[Jcparmley]

Ok, so I drew another diagram this time in series.  Is this a better way to do the heat?  It's simpler but I was worried that it wouldn't be as efficient due to the cooling of the fluid as it goes through each exchanger.  Wouldn't this produce uneven heat distribution?  How much heat would be left for the engine?  Is this how most of you plumb your system?

[richard5933]

Your still not reading the original post,,,He is NOT interested in heating "the interior",,Only a few lower storage bays,, the generator,, and engine.. Even then he is only interested in eliminating the possibility of freezing in those areas.>>>Dan

Sorry, but it appears differently in his recent posts and in the drawings being posted. Your point was valid on the earlier thread, but now it appears that the system will also be used to warm the interior, at least some of the time. The heat exchange units labeled as 'kitchen', 'bathroom', and 'bunkhouse' are certainly part of the interior.

Here's how this thread began...

...I have been thinking about a heating system for OTR as well as a secondary heat system while parked...

[Jcparmley]

Sorry for the confusion.  There is actually two of us posting on the forum asking about Webasto heating. 

The other poster (not me) wants to run his for just the bay heating and engine heating. 

My intention is to have interior heat while driving (OTR) and a back up system while parked.  My primary heat will be mini split heat pumps when on the pole or when it's not super cold, and a 42K BTU Propane Furnace when boondocking or when it's really cold. 

My drawings are very basic rough draft so I can visualize the major components and get my head around the system.  I hope that makes sense now and clears up some of the confusion. 

What I need to figure out is do I plum such a system in series or parallel?  Do I separate engine coolant loop from the interior loop?  If so how do I keep the engine from overheating when the interior is calling for heat?  All your points are very much appreciated.  Keep them coming.

Sorry, but it appears differently in his recent posts and in the drawings being posted. Your point was valid on the earlier thread, but now it appears that the system will also be used to warm the interior, at least some of the time. The heat exchange units labeled as 'kitchen', 'bathroom', and 'bunkhouse' are certainly part of the interior.

Here's how this thread began...

[richard5933]

I liked the version with all the heat exchange units parallel and run through the manifold. You will then be able to micro manage how much heat each produces by opening/limiting flow. Probably will need a safety to be sure that all of them are not able to be closed at the same time though, or your pump will be really unhappy.

If your interior heat loop and your engine loop are the same you'll lose a considerable amount of heat through the engine. That's a lot of cast iron hanging out there in the cold, and it will suck all the heat from your system and make the Webasto work really hard to keep up if it's always getting flow from the Webasto.

The Webasto on our 4106 had a loop for the interior heat. There was also the OEM loop from the engine to the defroster core and back again (chassis loop). They were usually separate, so we could easily heat the interior using the Webasto without losing heat to the engine.

When we wanted to preheat the engine, there was a third 'loop' which connected the chassis loop to the interior loop. It was really just a feed and return line between the two loops. The feed line had a 12v Bosch pump which took hot water from the Webasto system and pushed it into the chassis loop. When we flipped the switch on the control panel to 'engine heat' the Bosch pump came on and diverted the heated coolant into the chassis loop. Ours used the existing OEM coolant boost pump to circulate the heated coolant, but you could also add another Bosch coolant pump to the chassis loop to be sure that it made it to the engine.

Hope this makes sense. I tried to sketch it out but didn't have much luck doing that on the laptop. If you need, I'll break out the markers and do a paper sketch later on.

[Jcparmley]

Thanks Richard.  My bus came from the factory with a webasto for keeping the engine up to temp.  It's all disconnected now because the webasto needs to be rebuilt.  I would need to keep that feature.  I like the parallel system as well.  If you don't mind could you draw out how you system worked?  I know it's a lot to ask but I am a visual learner.  Was your loops separated from each other with a flat plate exchanger or something similar?

[richard5933]

Thanks Richard.  My bus came from the factory with a webasto for keeping the engine up to temp.  It's all disconnected now because the webasto needs to be rebuilt.  I would need to keep that feature.  I like the parallel system as well.  If you don't mind could you draw out how you system worked?  I know it's a lot to ask but I am a visual learner.  Was your loops separated from each other with a flat plate exchanger or something similar?

I'll try and sketch out something this weekend. They were separate loops, but were also connected. It'll make more sense when I get it on paper.

[Jcparmley]

Ok, thanks Richard

I'll try and sketch out something this weekend. They were separate loops, but were also connected. It'll make more sense when I get it on paper.

[Jim Blackwood]

JC, some of the features of the original system were very good but it was designed with warmup and OTR use in mind so it needs a few mods to work well as an RV. Basically you just need to be able to restrict flow to the house loop and webasto loop only. Although you have disabled that system there are still parts and features of it that you could use.

Originally the house loop was an auxiliary loop that paralleled the engine loop and could be shut off at both ends. This allowed warmup and engine heat, or warmup, engine heat, and coach heat. There was no way to take the engine loop out of the system. Normally the manual valve on the coach loop was left open and the solenoid valve controlled the level of coach heat.

This system could be reconfigured to allow house heat exclusive of engine heat. That requires a minimum of one additional bypass line and one additional valve, either manual or solenoid type.

The best way to think of this system is as a set of interlocking loops. Always the primary loop contains the engine and the radiators, including of course the engine driven coolant pump and surge tank. The next loop contains the webasto and the circulation pump. The final loop contains the house radiators. This is the only passive loop as it needs no pump. It can be series or parallel regarding the radiators, or in fact both. The biggest problem with your serial radiators is line size and flow capacity. Usually such a system uses one or two very large radiators. A parallel system is much less expensive to build but has more complex plumbing. The original system can be thought of as a hybrid series/parallel even though the series (main) circuit only has one radiator. Flow is controlled by valves and line sizes. It's not particularly hard to understand if you have a reasonable grasp of plumbing in general.

Anyway the three loops are interconnected by no less than two points for each loop pair, one on the supply side and one on the return side. Look to the pump to see which is which. If you want to supply webasto heat, connect the webasto loop to the loop you want the heat to go to, such as the house loop. Because the  circulation pump is part of the webasto loop it controls coolant flow. Similar for heat both to and from the engine, though in the first case you connect the webasto loop to the engine loop and in the second connect the engine loop to the house loop.

That's really about all there is to the theory, the rest is just details.

Jim

[richard5933]

Here's a really basic layout of what we had in the 4106. The two basic loops are the engine/defroster loop (black in the diagram) and the interior heating loop (purple in the diagram). There is an surge tank on the interior heating loop which increases the volume of coolant in the system and allow for expansion.

The two main loops are interconnected with the two lines running between them (red in the diagram). There are two auxiliary pumps used when the system is on pre-heat: one to circulate the coolant in the engine/defroster loop, and another to exchange coolant between the interior loop and the engine/defroster loop.

When the pumps are turned on, heated coolant from the interior Webasto loop is exchanged with the engine loop. Can't remember if there was a solenoid to shut off the return between the two loops, but I don't think there was. Any exchange between the two systems when the pumps are off would be minimal.

The distance between the feed line and return line between the two loops will effect how much exchange there is between the loops.

Curiously, this is very similar to how the boiler was connected to the radiator loop at my old wood shop. There was a loop throughout the building which circulated water to all the radiators, and another very small loop between the boiler and the surge tank. There was a feed line and a return line between the two, and when the system called for heat a small pump turned on to exchange water between the two loop. That 5000 sq. ft building was heated nicely, and there was only about 6" of space between the feed line and the return line for the exchange to take place.

[Jim Blackwood]

you can also think of it in terms of source and sink. Your sources are the webasto and the engine and your sinks are the radiators, defroster, and engine but conceptually that's a little harder to keep straight. You can make it as simple or as complex as you like. MCI went for simple I think and I like that approach but complex can work too and has some theoretical advantages. However a simple system that is well designed can be essentially invisible to the occupants and this is also an advantage. You will have to decide what you like.

But think in terms of pumps transferring heat. The circulation pump runs on demand, the engine pump runs with the engine. You can add more pumps if you like but don't have to, and every additional pump is another source of potential failure. Usually not if but when.

I would seriously question the logic behind adding additional heat exchangers. Even if potable water is part of the system. Do you drink water from the hot water heater? Few people do because of concerns about lead leaching and aluminum anions affecting long term brain health but it's an individual choice. I can't think of another justification. Also using the water heater as a heat source is perhaps not the best idea, as it doesn't put out enough heat to do much and will shorten the life of the heating element. Losses through the exchanger will diminish even that, and the exchanger adds a restriction that will reduce the efficiency of the entire system.

Jim