Webasto Heating System

[Lee Bradley]

Model T Fords used it. No water pump but I think that was the last time.

[Jcparmley]

I know it has been a while but I am still tweaking my proposed heating system.  Richard, is this similar to your old setup?  I know I added a Flat Plate Exchanger because I wanted to keep the engine coolant separate from the house system just in case I have a failure I don't want both systems down.  Let me know if you think this will work? 

I also eliminated the extra pumps as it sounds like the engine pump and the Webasto pumps are large enough to circulate the coolant.  However, if I do need to add a pump I would do it probably before the distribution manifold.  Let me know what you all think.

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.

[richard5933]

I know it has been a while but I am still tweaking my proposed heating system.  Richard, is this similar to your old setup?  I know I added a Flat Plate Exchanger because I wanted to keep the engine coolant separate from the house system just in case I have a failure I don't want both systems down.  Let me know if you think this will work? 

I also eliminated the extra pumps as it sounds like the engine pump and the Webasto pumps are large enough to circulate the coolant.  However, if I do need to add a pump I would do it probably before the distribution manifold.  Let me know what you all think.

Couple of thoughts...

The pump on the engine loop will be necessary if you every want to use the Webasto to pre-heat the engine. And you probably will want to do this at some point.

Not sure about the house side loop. Hard to tell what's going where as your arrows seems to push against each other in a few places. Also not sure what the two connection points between the hot/cold side of the manifold are for.

Could you run the engine plate exchanger as another point in the manifold? Not sure if you are going to use electric solenoids to open/close the various loops in the manifold, but it seems like having the plate exchange unit work off the same manifold will make it really easy to turn that on or off as needed and will eliminate the need for the check valves.

[Jcparmley]

So I changed it up a little.  Here's how I have it drawn up:

1:  When the engine is running the engine water pump will heat the engine loop as well as the plate heat exchanger on the house manifold heating the house loop.  (Is the engine pump strong enough to do this, or do I need to add a pump?)

2:  When the engine is off and cold I will pre-heat the engine by turning on the Webasto with a switch, which will heat the plate exchanger and push coolant through the engine loop. (Is the Webasto pump strong enough to do this or do I need to add a pump)

3:  When the house loop needs heat the thermostat will turn on the Webasto and heat the house loop.  I will need to use a solenoid or some kind of valve that will close off the plate heat exchanger so the cold engine doesn't pull out all the heat in the house loop.

4:  When the bus is on the road and the Series 60 engine calls for more heat the OEM controller will turn on the Webasto, which will heat the plate exchanger and thus the engine will be brought up to temp. (How will the OEM controller know that the coolant is below 160 Degrees?)

5: The house loop system will have a reservoir tank at the highest point for fill and air bleeding.

Does that all make sense.  I still need to wrap my head around how the OEM Webasto controller will know when the Series 60 needs heat if the Webasto is not plumbed inline with the engine. 

Couple of thoughts...

The pump on the engine loop will be necessary if you every want to use the Webasto to pre-heat the engine. And you probably will want to do this at some point.

Not sure about the house side loop. Hard to tell what's going where as your arrows seems to push against each other in a few places. Also not sure what the two connection points between the hot/cold side of the manifold are for.

Could you run the engine plate exchanger as another point in the manifold? Not sure if you are going to use electric solenoids to open/close the various loops in the manifold, but it seems like having the plate exchange unit work off the same manifold will make it really easy to turn that on or off as needed and will eliminate the need for the check valves.

[richard5933]

You're out of my league with the OEM engine Webasto questions.

My thoughts on the engine loop is that you'll need the extra pump. There's a reason you see them in system. Even a stock bus will oftentimes have an extra pump to bring the coolant up front to heat the heater core, so I wouldn't put much confidence in the engine pump to do the work, especially at idle speed.

[Jcparmley]

Ok, here is the most recent version of my layout.  Perhaps Jim or Buswarrier could chime in and advise on some of the other questions.

[richard5933]

That one makes sense to me. Now if you can get the 160 degree question answered it sounds like you're set.

[Jim Blackwood]

JC, I really hate to say this after you have put in so much effort on this system, but it strikes me as needlessly complex. My bus is also a '96 DL with the aux heater and I have to think we must have similar goals here which would be:

Maintaining adequate engine heat and cabin heat OTR
Providing cabin heat only  when parked
Preheating the engine for starting

I'm not sure anything else is required aside from defrost.
I will attempt to do this while keeping most of the OTR system intact where you are adding a supplemental system. I do understand that you feel it is best to keep the systems separate but there has to be some inefficiency involved in transferring heat across a heat exchanger. Even under the very best conditions it cannot avoid at least slowing things down some. I think you will discover this as additional delay in getting heat out of the registers. That may not bother you, but you might want to trigger your fans with a temp sensor at the radiator to avoid blowing cold air when the webasto kicks on.

Will you need more pumps? Maybe. Take a good look at the existing plumbing. Are your lines going to be the same size and go the same distance? Probably not. Your dash heat lines may be the same. Your pumps are rated for a specific flow rate AT a specific pressure (or "head") Changing the lines will change either the pressure or the flow. You can get by with some of that, and some you can't. Think of it as delivering coal. You have a specific volume of heat that you are trying to deliver to the radiator. The flow affects that but so does the temperature. You want the flow to be slow enough to pick up a lot of heat but not so slow that the boiler overheats. Then the quicker that gets to the radiator, the more of the heat can go where you want it. So you want the lines small enough for high velocity flow but big enough to allow adequate flow through the boiler, and a well designed system will do this seamlessly.

So Ideally you would take pressure and temperature readings at all key points in a properly operating OEM system before changing anything, and endeavor to match those readings in your new design. (Those heat exchangers could make that interesting.) Pay particular attention to the cross sectional area of your piping as well as the length of the runs. The area will affect flow quite a lot more than the length but the length should not be ignored. The pumps in the OEM system were perfectly sized for the job they were asked to do. If you can ask them to do a similar enough job you will be happy with them. If not, you may want to make changes.

Jim

[Jcparmley]

Jim, thanks for your insight.  I was planing on using 3/4 pex to the manifold and 1/2 pex for the runs.  I guess I never thought of it in terms of pressure and flow.  So if I remove the plate exchanger out of the system it would simplify the design.  However, if I have a failure then both engine and house loop will be down.  Perhaps that's not that important.

I have also considered not having hydronic heat at all.  I have a large generator that is more than enough power to have some electric heaters.  I also have a propane heater for those occasions where I need that.  I'm not going to be full time in the bus so for what it's worth it may not even be necessary.

[RJ]

I have also considered not having hydronic heat at all.  I have a large generator that is more than enough power to have some electric heaters.  I also have a propane heater for those occasions where I need that.  I'm not going to be full time in the bus so for what it's worth it may not even be necessary.

JC -

My coach has hydronic heat available from the cantankerous AquaHot unit, plus Cadet "Perfectoe" 1000w 120vac undercounter ("toe-kick") electric heaters. Each system has four registers scattered thru out the coach: bedroom, bath, galley and front salon. There are also hydronic registers and small electric heaters in three of the four bays (none in the generator compartment.) There is no propane on board - didn't want a coach with that fuel source.

Just the four Cadets kept the coach at 68º inside when it was 10º outside a couple weeks ago, so they work, each cycling on and off as their individual thermostats controlled them.  I did not fire up the AH unit because I didn't want the exhaust blowing into the rig of the neighbor parked behind me.

I do not know if there's a supplemental water pump on the engine's defroster core loop (no OEM HVAC on this coach), but then again, I haven't gone searching for one, either.  There is a small pump in the AH unit for the engine coolant loop, in addition to one for the cabin heating loop, but that only runs when the AH is on for pre-heating the engine.

Anyway, that's the way Vantarè did it on my conversion, perhaps that will help you with your design.

FWIW & HTH. . .

[Jcparmley]

Thanks RJ, that is helpful.  Do you plug into the pole or use your generator mostly? 

JC -

My coach has hydronic heat available from the cantankerous AquaHot unit, plus Cadet "Perfectoe" 1000w 120vac undercounter ("toe-kick") electric heaters. Each system has four registers scattered thru out the coach: bedroom, bath, galley and front salon. There are also hydronic registers and small electric heaters in three of the four bays (none in the generator compartment.) There is no propane on board - didn't want a coach with that fuel source.

Just the four Cadets kept the coach at 68º inside when it was 10º outside a couple weeks ago, so they work, each cycling on and off as their individual thermostats controlled them.  I did not fire up the AH unit because I didn't want the exhaust blowing into the rig of the neighbor parked behind me.

I do not know if there's a supplemental water pump on the engine's defroster core loop (no OEM HVAC on this coach), but then again, I haven't gone searching for one, either.  There is a small pump in the AH unit for the engine coolant loop, in addition to one for the cabin heating loop, but that only runs when the AH is on for pre-heating the engine.

Anyway, that's the way Vantarè did it on my conversion, perhaps that will help you with your design.

FWIW & HTH. . .

[luvrbus]

Careful with the pump volume to much flow the system will not transfer the heat not enough flow the Webasto will over heat and shut down ,check the temperature rating on the Pex if tied to the engine some PEX don't like anything over 140*,if using the toe kick heaters clean those puppies a lot of Prevost and other brands have had fires because of the lint build up associated  with those 

[Jim Blackwood]

I'd definitely use the aux heater. I will in fact be using it on mine which will require me to drain down the system and add at least one solenoid valve.

Now something to consider is that the engine driven system without the aux loop is quite capable of running fine with the cabin heat either on or off. But I'd have to go back and look to check the conditions. Some relevant questions need to be answered.

Does the coolant still flow through the cabin loop when the AC runs? (Not sure about this one but I suspect not, or perhaps throttled back by the main solenoid valve on that line.)

Is the dash heat an extension of the main line to the cabin heat? (I think it is, easily checked.)

I'm pretty sure the dash heat has a manual control valve. Should be a T handle on the left.

The point is, you can shut off cabin heat by turning off coolant flow I'm pretty sure. That means effectively restricting the flow from the water pump when the heat is turned off, which does several things, but mainly it causes a small increase in pressure on the outflow side to the radiator, and should increase that flow somewhat. But since that side is a good bit larger the proportional increase won't be that great. Conversely flow through the engine block will decrease somewhat as the outflow is restricted by removing the cabin path. So flow through the block (and pump) goes down while flow through the radiator goes up, which could but not necessarily will cause an increase in engine temp. A completely different effect from removing the heater cores as radiators.

But what about the aux heater then? That really depends on how it is plumbed and controlled. As is, we understand the engine preheat function and we get some cabin heat while doing that but the flow may give preference to the engine and probably does. This was probably the primary function engineering-wise and it seems likely it was optimized for that mode. So it can circulate coolant to the cabin, but may not do it particularly well.

OTR it is designed to supplement engine heat when needed. Again that means it only needs to add heat to the engine loop and the pump is sized to prevent overheating the boiler. This is a more demanding application due to the engine's heat output so pump size would be determined here.

But what happens if you take the engine out of the loop? That is the question we need to ask and answer. Is the flow through the main cabin loop then sufficient to prevent boiler overtemp? (We can disregard the dash loop since it will not always be used.)

Seems to me those lines are at least 1" and maybe 1-1/4" diameter, which I think is the same as the lines to the webasto pump. So ideally your coolant lines to the cabin radiators would add up to the same area. Keep in mind that doubling the diameter quadruples the flow, so it takes four 1/2" lines to equal a single 1" line.

Jim

[freds]

You're out of my league with the OEM engine Webasto questions.

My thoughts on the engine loop is that you'll need the extra pump. There's a reason you see them in system. Even a stock bus will oftentimes have an extra pump to bring the coolant up front to heat the heater core, so I wouldn't put much confidence in the engine pump to do the work, especially at idle speed.

If the bus has the extra pump for the front heater core; I would simply add a relay to turn it on for engine preheating. My bus has such a pump and it is of a fairly hefty size. Going to remove the extra pump I added for my system and go with this approach.

[RJ]

Thanks RJ, that is helpful.  Do you plug into the pole or use your generator mostly?

JC-

Both. On the pole for extended stays, genset when on the road or boondocking. If/when solar gets installed, there will be less genset usage while boondocking. But that's currently a low-priority project at this point.

Clifford -

Thanks for the reminder tip to clean the toe-kicks! I will move that to the top of my "to do" list!