Hydronic Heating System

[Sean]

... are we getting picky there, Sean?  The Scholastic Series uses a DBW 2010 plus it has a pump and enclosure.  ...

As I wrote in another thread, not trying to be picky or argumentative, just accurate.  Mostly for the sake of newbies who come back to these threads in the archives, sometimes years later.

Not only are these different part numbers, but there are other differences as well.  For example, the DBW-2010 is available in 24 volts, whereas the Scholastic only comes as a 12-volt model.  For many bus owners, this is an important distinction and could be a point of confusion if they were looking for a Scholastic model.

For the benefit of anyone following along the Scholastic is a package system marketed by Webasto specifically for the school bus market (as in actual school buses, not conversions).  It is intended to be more "plug and play" for school bus fleets, and thus includes a pump, some additional control wiring, an interconnecting hose from the pump to the boiler, and, as a nod to "school bus yellow", the boiler housing is finished in yellow as opposed to the silver of a stock DBW boiler.

The DBW-2010 and its sibling, the DBW-2020, are boiler-only models which include the control relay module, but nothing else.  You add a circulating pump to this mix, which Webasto is happy to sell you but is usually made by a third party, and optionally an enclosure.

FWIW, most DBW installations in converted coaches will use a higher-capacity pump than the one that comes integrated into the Scholastic series.

Again, not trying to step on anyone's toes, just trying to be more accurate or complete with the information.  Hydronic heat is a complex subject and can be daunting for a first-time converter, and having partial information or terms mixed up can add to the challenge.

-Sean
http://OurOdyssey.BlogSpot.com

[Geoff]

Sean, I would like to say you made a very nice response.  But I can't.

--Geoff

... are we getting picky there, Sean?  The Scholastic Series uses a DBW 2010 plus it has a pump and enclosure.  ...

As I wrote in another thread, not trying to be picky or argumentative, just accurate.  Mostly for the sake of newbies who come back to these threads in the archives, sometimes years later.

Not only are these different part numbers, but there are other differences as well.  For example, the DBW-2010 is available in 24 volts, whereas the Scholastic only comes as a 12-volt model.  For many bus owners, this is an important distinction and could be a point of confusion if they were looking for a Scholastic model.

For the benefit of anyone following along the Scholastic is a package system marketed by Webasto specifically for the school bus market (as in actual school buses, not conversions).  It is intended to be more "plug and play" for school bus fleets, and thus includes a pump, some additional control wiring, an interconnecting hose from the pump to the boiler, and, as a nod to "school bus yellow", the boiler housing is finished in yellow as opposed to the silver of a stock DBW boiler.

The DBW-2010 and its sibling, the DBW-2020, are boiler-only models which include the control relay module, but nothing else.  You add a circulating pump to this mix, which Webasto is happy to sell you but is usually made by a third party, and optionally an enclosure.

FWIW, most DBW installations in converted coaches will use a higher-capacity pump than the one that comes integrated into the Scholastic series.

Again, not trying to step on anyone's toes, just trying to be more accurate or complete with the information.  Hydronic heat is a complex subject and can be daunting for a first-time converter, and having partial information or terms mixed up can add to the challenge.

-Sean
http://OurOdyssey.BlogSpot.com

[Larry B]

 Hi Dave--- I am not sure what you want for a schematic but I dug this out at shop today.and took a couple of pictures for you. These are only my thoughts. You have to design the system to make it do what you want it to. If you are going to use the engine to heat, you cannot interfer withits normal ability to cool and regulate its own temp.I live in Canada EH it gets cold here and I wanted to be able to start my engine in cold weather thus PRO HEAT. I had two extra three way air operated control valves left over from my steamfitting days, so I used them. . Valves 1&2 are opened and valves 5&6 closed to heat engine with pro heat. Other than to heat engine this order is reversed and all other valves stay open and control is by air valves. The heaters are Princess Auto about 9000btu (I think) The heaters I hung upside down in bay and aimed them at something that I could make a false floor in and blow heat a couple directions, like a vanity, kitchen cupboards or a seat. I hung heaters in bay because if they spring a leak I prefer antifreeze in bay not upstairs.I used 110 volt ac base board thermostats to control heater fans, they can handle the fan amps. Water like electricity will follow path of least resistance thus you need a balancing valve at each heater or you will get hot and cold spots in coach. Hope  this is what you are looking for.
  Larry B  

[Larry B]

A couple more pictures. The one picture has nothing to do with heating ,it contols my leveling jacks and slide

[PSmith]

Sean, just curious,

What is the size of the pump (gal/h or ltr/h) of most DBW2010 installations in conversions ?


FWIW, most DBW installations in converted coaches will use a higher-capacity pump than the one that comes integrated into the Scholastic series.


The specs in the Webasto manual are little confusing -  Scholastic vs DBW2010

Shed any light ?

[Sean]

What is the size of the pump (gal/h or ltr/h) of most DBW2010 installations in conversions ?
...

They're all over the map, and depend greatly on who designed and installed the system.  Also, GPH is a relative figure, since it depends on the apparent head of the system.  My pump, for example, is rated at 25 GPM at a head of around 8', but that drops to just 5 GPM at a head of 25'.  "Head" is a measure of backpressure in the system based on an open-ended pipe of the listed height, but in a closed-loop system like a hydronic heat system, is is really a function of size of tubing, number and tightness of bends, orifice size of the devices, number of independent paths, etc., which goes to your second question,

The specs in the Webasto manual are little confusing -  Scholastic vs DBW2010 ...

and this is exactly why: Webasto makes and sells component parts, and relies on its independent dealers to do the system engineering.

Figuring the backpressure of the system in order to properly size the pump requires advanced engineering in a specialty known as fluid dynamics.  That's not my particular expertise, and so I know just enough to be dangerous here.  I can tell you that most service and supply shops don't have this expertise, either, and so they rely on engineering rules of thumb, sometimes garnered over decades of experience.  They just know that with so much tubing of such a size and with this many devices you need a pump of X capacity.  Usually they err on the side of caution and recommend a slightly larger pump than is required.

The Scholastic is Webasto's attempt to take the guesswork out of this one segment of the industry.  They looked at the engine and heating configuration of the most common school bus models and sized a complete system that would work, out of the box, with the majority of them in most conditions.  This is facilitated by the fact that there is not a lot of variation in design, layout, and capacity of school bus heating systems -- they are all pretty much alike.  Bus conversions, OTOH, are all over the map in terms of design, layout, fluid capacity, devices, and whether the engine loop is integrated or separated by a heat exchanger.

Figuring the correct pump for your installation is probably the single most difficult part of a home-brew hydronic heating installation.  This is one area where your hydronic parts supplier or Webasto dealer can probably help by making a recommendation based on experience with similar layouts.

Probably not the answer you were hoping for, but I hope it helps a little, at least.

BTW, FWIW, I have a single-loop system with a "summer" bypass valve, two heat exchangers (one for the engine and one for the hot tub), a marine water heater, five fan-coil units, one radiant heater, and an expansion tank.  My boiler is a DBW-2010.  The pump I use is a centrifugal type with a stainless impeller, made by MP.  I'm pretty sure it's an MP FRX75.  The pump cost more than the boiler, and I'm on my third one (they really, really, really do not like being run dry).

That said, lots of pumps will probably work for most applications, just with varying levels of efficiency and lifespan.  Our system probably sees more use than most, anywhere from 200-500 hours per year; for a coach that only gets occasional use a less heavy-duty model would probably suffice.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

...
I would love to see a drawing and details.
...

Dave, it took me a few days to dig into my documentation.  Unfortunately, I could not find a drawing other than some hand chicken-scratch we did when we installed it that would not translate well here.  That said, I can tell you the layout in a less graphical way.

My system is arranged in a single loop, with a Y-valve to bypass the house heaters for warm-weather use (allowing the system to still be used to make hot water).  Starting from the lowest point in the system and running to the highest, my loop runs, in order:

Pump -> Boiler -> HX(e) -> DHWH -> HX(h) -> Y -> FCU(x5) -> Radiant -> T -> Expansion Tank

Where:
Pump = MP centrifugal pump
Boiler = Webasto DBW-2010
HX(e) = engine heat exhanger (30,000 BTU/h)
DHWH = marine water heater with integral heat exchanger
Y = Y-valve. This short-cuts past the house heaters
HX(h) = hot tub heat exhanger (30,000 BTU/h)
FCU = Fan coil unit.  There are a series of five of these through the coach
Radiant = radiant baseboard heater
T = "Tee" in the line where the bypass from the Y-valve joins back in
Expansion Tank = ~3 gallon tank with pressure cap at the high point of the system.

Obviously, the expansion tank connects back to the pump input.

Sometimes the "other source" heats the coach, other times it pre-heats the engine, and other times the engine takes the full load.  Also, most systems heat domestic water or use an additional water heater.  Engine heat can pre-heat the water heater, etc.   How do you control all that?

In a heat-exchanger system, the short answer is that all you need to do to get heat from the engine while driving is to turn on the hydronic circulating pump, without also turning on the boiler.  To pre-heat the engine, you need to turn the boiler and the circulating pump on, but you also need another small electric pump to circulate the engine coolant as well, since the engine water pump is not running.  So the "pre-heat" function involves turning on this extra pump.

Overall thermostatic control of the system involves one or more house thermostats, a thermostat on the water heater, and a thermostat on the coolant loop itself connected to the fans on the FCUs.  Theses later two thermostats are often called aquastats because they measure water temperature rather than air temperature.  Many hydronic dealers, for example Sure Marine, will sell you the thermostats and required relays as an integrated control package.

The basic layout is to multiplex the house thermostats and water heater 'stat into a single "ON" signal to the boiler control.  The boiler supplies a control signal to the circulating pump.  Each house thermostat also signals "on' or "off" to the fans of the FCUs depending on zone.  A relay prevents the FCU fans from running until the coolant aquastat closes, indicating sufficient coolant temperature to provide heat (this just keeps the fans from blowing cold air).

Wiring all this together is straightforward, but the circuit diagram can get large and complex depending on number of zones.  I don't have one handy or I would post it, but I would be happy to provide any more details that you need to make a working system.  Also, I'm pretty sure Dave Galey has diagrams of both the fluid side and the electrical side of a basic hydronic system in his book on the subject.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[edroelle]

Dave,

I found 2 old schematics that I am sending you.   They need explanation from learnings after installation, so they are not ready for prime time posting.

Ed Roelle
Flint, MI

[Geoff]

For those us you have the Scholastic Series DBW 2010 and are entirely pleased with their hydronic system I would like to add that the provided coolant pump with the unit produces 15-20 GPM, which has always been adequate for a basic converted bus heating system.  Plus my RTS (like other buses) has a factory coolant pump that can be used in conjunction with the Scholastic pump for pre-warming up the engine faster.  I have mine set up so the Scholastic heater can just warm up the interior, or the engine and interior at the same time.  I feel using the basic layout of the Scholastic Series with a few extras is the simplest and adequate system-- I think the heat exchanger method that the Aqua-Hot system uses is much more complex than necessary and way too costly and bulky.


--Geoff
'82 RTS AZ

[Sean]

For those us you have the Scholastic Series DBW 2010 and are entirely pleased with their hydronic system I would like to add that the provided coolant pump with the unit produces 15-20 GPM, which has always been adequate for a basic converted bus heating system.

Just to clarify my earlier comments, the pump included with the Scholastic series is, indeed, adequate for many conversion installations.  It is better suited to a handful of larger heaters, though, than many smaller ones, and the additional restrictions imposed by marine water heaters and multiple heat exchangers can challenge it.

In short, the Scholastic series is a good solution (and can be very cost effective) if the included pump is adequate for your needs.  If the included pump is not adequate, then buying the components separately might be a better choice, so that a larger or more robust pump can be specified.

... I think the heat exchanger method that the Aqua-Hot system uses is much more complex than necessary and way too costly and bulky.
...

FWIW, this is my take on Aqua-Hot as well.  It's a great company, with wonderful customer service, and buying an Aqua-Hot product takes a lot of the engineering or guesswork out of a hydronic system, but you pay a premium for that.  Individual components are generally cheaper, especially if you shop around.

-Sean
http://OurOdyssey.BlogSpot.com

[rgwilliams]

Nobody's mentioned this company.

They have all the manuals on line.  Perhaps you can get ideas from them.


http://itrheat.com/products/oasis-heating-system/