Webasto Heating System

[Jim Blackwood]

All I have to go by is the '96 102DL3 and some not-the-best schematics which I haven't studied for a few months but I'll do my best. Those drawings are the ones I'm going by, the ones that can be downloaded from MCI.

Anyway based on the above, yes either pump is more than adequate for circulation through the entire system. The aux heater, in this case an Eiberspacher of over 80Kbtu is well able to heat the engine and the coach interior. Being able to remove the engine from the system would only make it heat the coach faster, a mod I will make when I have reason to get into the coolant system. Until then I will accept the reduced efficiency and performance of also heating the engine, with the entire original configuration intact and pay the surcharge of increased fuel consumption.

The aux heater did not work when I got the bus, but after removal and inspection I found the issue to be with the timer type controller. I connected a thermostat instead and plan to add to that later. My plan is to route the warm/cold air from the original HVAC ductwork into the rear of the cabinetry for distribution. For the time being at least I am retaining the original baseboard ducting which I expect to modify/remove as needed.

If I understand you correctly you still have the OEM webasto unit, but it is in questionable condition. If that is true, then despite what BW said about hydronic systems (and he is right) it is still possible that the cheapest, quickest, easiest route to abundant heat is to restore the original webasto to proper operation if that is still an option. I fully agree with the thought that the Admiral's comfort is paramount and to that end there aren't many better ways to warm the coach up quickly than the OEM webasto. It does make a little noise but it's not really objectionable, not like a generator anyway.

Just as a hypothetical, say you did restore that end of the system and put in the engine shutoff and return bypass. If I remember right, the return line from the coach has a manual shutoff valve where it exits the bodywork. From there it connects to the engine. I do not recall at the moment if there is any other connection to that line but that is the line you have to modify. Basically it means putting in a "T" on the coach side of the valve so that you can shut that valve and divert the flow back to the webasto pump inlet. However a solenoid valve would be much more convenient but costly, while a ball valve brings the option of running a shaft through the wall to a control handle in the bedroom. The important thing here is that you complete the loop from the webasto to the heaters and back, while shutting off the lines to the engine. As far as a surge/recovery tank goes, the OEM one should do the job and if it does not, a small bypass leak created at the shutoff point(s) should do the trick.

Jim

[buswarrior]

I am reminded of another design issue, capacity to warm up, vs keep warm.

If a busnut is out using the coach in cooler weather, the goal is continuous, keeping the coach warm. That is a very different capacity than warming up a cold coach.

For those used to air conditioning, you know the same issue from the other side, it is easier to keep the coach cold, than to cool down a hot one.

The difference between warm up and keep warm is wide enough, that aiming at one, will compromise the other.

The challenge is how to throttle a heat source that makes xxxxx BTU, when the interior only needs 5-10k to keep an evening chill off, but needs to be able to put the whole xxxxx BTU into the interior on returning to the coach in cold weather when away at some event, where leaving the coach heat on was not allowed or desired, or when Old Man Winter follows the snowbirds south.

A hint: "wasting heat" to the engine block may be VERY desirable, to tame a big coolant boiler under warmer weather conditions. Sure, open a window, make a draft, make the Admiral miserable again...

Also, on those cool evening chill type scenarios, after a day's drive, along with the whole coach already being "at temperature" there's over 2000 lbs of cast iron down the back that isn't going to be cooling off for a long time that can be tapped without burning any more fuel.

The first evening, the bedroom is lovely, the second evening, the engine has gone cold, and now the bedroom isn't lovely...

Keeping the inside temperature from varying wildly, under all these different conditions is really tricky, and as usual, the forums are skinny on reports of failures, only reports of successes...

The electrical power consumption of the heat distribution system often makes trouble. Fans, pumps, burners all consume battery power, at a time when most battery bank capacities are also challenged by colder temperatures.

Just as an example, running the stock coach HVAC fans in an MC8 via a bypass switch, a DBW300 firing and circulation pump running, and water valve cycling, draws about 11 amps of 120 VAC via a shore cord feeding a Trace 4024 inverter, supplying the 24 volts to a set of topped-up house batteries. That's somewhere around 1320 watts burning a hole in the coach's electric budget.

What is the consumption of available fan units?

Check the newer low floor transit coaches, they are running radiant heat the length of the sidewalls where the duct work used to be... That copper pipe and aluminum fin radiator has a rating per foot, at a certain water temperature... if I could find it again...

So much fun playing with the variables.

happy coaching!
buswarrior

[buswarrior]

And there's no reason for a generator to be noisy, except for a busnut to choose to have a noisy generator.

There are good reasons for a busnut to make that choice, but for those who want silence, it is achievable.

Generator noise is one of the easiest ways to attract attention and get asked to leave when "urban camping"

happy coaching!
buswarrior

[Jcparmley]

"Check the newer low floor transit coaches, they are running radiant heat the length of the sidewalls where the duct work used to be... That copper pipe and aluminum fin radiator has a rating per foot, at a certain water temperature... if I could find it again..."

Buswarrier has a good point.  Would it be a better system to use radiant basboard heat instead of forced air exchangers?  I could install a couple exchangers for quick heat and use radiant for keeping a already warmed coach warm.  Thoughts?

[Jim Blackwood]

The thing about radiant is that it's generally designed to be on all the time or most of the time. That's fine if traveling, but brings additional challenges when parked. If you size your webasto for efficient operation full time it won't have the reserve for rapid warmup. But, this is where your water heaters could be handy.

Note, careful design can allow standard heater cores to act as passive radiators with the fan off, and it is also possible to run a passive thermosiphon loop for the coolant. That won't do with the webasto burning but with the water heaters it might be made to work. However, don't count on the coolant loop of standard water heaters, you will want the entire output, so dedicated units would be the better approach.

Jim

[Jim Blackwood]

What I'm saying is, use a water heater to power the thermosiphon loop and run the coolant through where the water usually is. Use a dual power unit so it can be run on shore or LP. Then that's your low level "keep warm" heater and you can fire up the webasto for on-demand use. With the water heater in a storage bay and the heater cores at floor level you have enough height to do thermosiphon so the only energy cost is the burner or heating element. 6Kbtu is about the most you can expect from a water tank heating element at 220V.

Jim

[Jim Blackwood]

Also, the thermosiphon loop does not have to be separate from the rest of the system. It can use the same radiators as the webasto.

Jim

[buswarrior]

How many ways are there to control temperature inside the coach?

On and off works, but is a bit of thuggery...

Coolant temperature doesn't need to be 160 to take a chill off...

Fans don't need to run all the time...

All the heat distributing devices don't have to be fed warm coolant all the time...

If the coach can't keep a chill off while boondocking, using only a modest battery consumption...

If the only person who can make it work is the owner...

And the Admiral rolls her eyes when someone asks if her coach stays warm...

we've not done a good job?

Aim for invisible, simple to control, repairable, serviceable, and easy to explain the operation to the next person.

And with dementia/Alzheimers running rampant, it might be yourself that will need help!!

Design engineering is great fun!

Happy coaching!
Buswarrior

[richard5933]

Temp regulation on our 4106 was a simple as setting the temp on the thermostat and letting the system do its thing. When the system called for heat, the coolant circulated. If it wasn't warm enough, the burner kicked in. When the room came to temp, things shut down. Worked just the same as our furnace does at home.

Both circulating pumps ran off 12v. The air blower(s) were 12v as well. The Webasto was of course 12v. We could easily go through the night with outside temps in the 20s without having to worry about batteries, running the old Norcold swing motor fridge at the same time.

Read the old literature on the Webasto setups. Doesn't need to be complicated.

[Jcparmley]

Jim, I had to look up what a thermosiphon was.  It's very interesting.  I am wondering if a small on demand propane hot water heater would work in such a system? 

What I'm saying is, use a water heater to power the thermosiphon loop and run the coolant through where the water usually is. Use a dual power unit so it can be run on shore or LP. Then that's your low level "keep warm" heater and you can fire up the webasto for on-demand use. With the water heater in a storage bay and the heater cores at floor level you have enough height to do thermosiphon so the only energy cost is the burner or heating element. 6Kbtu is about the most you can expect from a water tank heating element at 220V.

Jim

[Jim Blackwood]

I'm thinking that for make-up heat it could work. Depends on how much you need and how much you have naturally. Line sizing would be important and insulation on the hot line helpful. As there is no pump the flow is more sluggish and larger lines are helpful, up to a point where the line cools before reaching the top. So to at least some extent the larger lines used for the on-demand heat with pump flow would be sized well for convection flow. The main thing is to be sure there is still heat in the line when it gets to the radiators, but that there is also enough volume in the flow to carry all the available heat away from the boiler (hot water heater). Ideally you will retain all heat all the way to the top of the system.

At the radiator you want the hot line to go to the top and the return to come out the bottom. Avoid dips and traps in the lines of course and put an air bleed at a handy location at the very top of the loop. Any air in the line will defeat the effect. Often thermosiphon systems place a reservoir at the high point for that reason and that's not a bad idea, however just a large tube section with a bleed valve can suffice. The size of this chamber will determine how often bleeding is necessary. A small bleed line back to the main reservoir up by the engine radiator can eliminate this need.

The passive radiators need enough area to dissipate all the heat without a fan so they need to have an unobstructed airflow that will allow the heat to carry the air up and away from the radiator. If they have enough area for the on-demand heat they should be plenty big enough for passive.

The fluid can be interconnected to the on-demand system. More fluid mass can degrade performance but the real question is how much and in what ways? Operation may still be quite acceptable. As long as connection to the main coach distribution lines does not create any air traps or use up your heat before it gets to the top it should still work. However, because the coach loop already has one solenoid valve on the supply side for heat control and you need a valve on the return side to isolate the engine, you could consider an additional solenoid valve to isolate the passive system that opens when the webasto lights off. These valves are expensive however, average cost is probably about $350 from what I've seen, though you might find one for less if you look. A passive check valve here could work as well but does create a restriction. The thermosiphon flow would never create enough force to open it so it would remain closed during passive heating and block off the rest of the system. That would work on both sides, be much less expensive than solenoid valves and function automatically. Perhaps a flapper type check valve with the spring removed to work by gravity alone would do.

You'd have to check the btu rating of the water heater on both gas and electric. Just knowing it gets hot isn't enough. If the element only puts out 3000 watts that's the equivalent of two small ceramic plug in heaters. Is that going to keep your house warm? Better to err on the side of excess here.

Jim

[richard5933]

This is one of those times when you've got to look around and see what's being commonly installed, both in bus conversions and in commercial motor homes, and ask if maybe they're on to something.

I'm not knocking the thermosiphon idea in principle, just in application. I enjoy doing something just to see if it works as much as the next guy, but in this situation there already will be in place a few redundant systems - heat generated by the engine, the Webasto, electric heat pumps, and an LP furnace. Is there need for yet another? is there enough advantage to thermosiphon to add yet another?

[freds]

Suggestion:

For those wanting a cheap diesel heater look on ebay for Nissan Leaf auxiliary heater as they generally don't know what they are selling and price it lower than if it was sold as a truck version. The seller is more in likely looking to make their salvage nut on selling batteries out of the battery pack.

Note this is not a high power heater!!! However for the price you might want to buy two or three for added capacity and fault tolerance.

I think this is actually an Espar 5KW/13500 BTU unit.

[freds]

This thread and others like it kind of ricochet back and forth between a lot of sub subjects, when what we really want in the long run is a DIY Hydronic system that we do not want to spend thousands of dollars for.

As Busnuts we are basically frugal (OK cheap) in that we will trade labor/skull sweat for verses spending lots of money on a prepackaged system.

To quote our hero member BusWarrior; our basic mission statement is:

"The Admiral (significant other) is MIGHTILLY PISSED OFF that the (profanity deleted) coach still won't work like home, further eroding her desire to spend time with the coach, or you..."

How about we divide this complex subject up into separate subject area's starting with the Subject Tag "DIY Hydronic"? That way we can pool our collective knowledge.

As an example:

DIY Hydronic boilers
DIY Hydronic Additional heat sources
DIY Hydronic Storage
DIY Hydronic Engine/Generator preheating
DIY Hydronic pumps, valves, heat exchangers
DIY Hydronic plumbing and heat distribution
DIY Hydronic Automation or Manual controls
DIY Hydronic Weather protection of house systems

Your thoughts?

[Jim Blackwood]

This is one of those times when you've got to look around and see what's being commonly installed, both in bus conversions and in commercial motor homes, and ask if maybe they're on to something.

I'm not knocking the thermosiphon idea in principle, just in application. I enjoy doing something just to see if it works as much as the next guy, but in this situation there already will be in place a few redundant systems - heat generated by the engine, the Webasto, electric heat pumps, and an LP furnace. Is there need for yet another? is there enough advantage to thermosiphon to add yet another?

You know, somebody has to ask that kind of question. Otherwise we might be into all sorts of messes. In this particular case it may or may not be a good idea. Are all of those other systems already installed and working? Because I thought what we have been discussing was installation.

Convection heating has been proven to work. To find if it will work here really isn't so hard during the installation stage of the game. Plumb a water heater to a heater core about 2-3ft above it, burp out all the air, fire it up and see if you get heat. The results would tell us a lot and might determine if the method has any future here.

Jim