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Feasible to hook coach up to hydronic heating?
My 1000sf race shop was planned before we owned a Prevost and started just after we bought the bus in May of 2014. Now that I understand the coach much better having owned one for a year and half and dealing with it in the winter time, I’ve come up with an idea to keep the coach warm in our cold winters. This came to me after Steve the Tinman suggested I run the Webasto to keep the bus warm. Good idea, fall back tactic when it really gets cold, or something unexpected happens. But I preceive the Webasto as kinda inefficient, uses lots of diesel, and creates an odor the neighbors might object to. Steve’s suggestion got me thinking and then I realized I have a really, really efficient boilder just 40 feet away!
I don’t have the option for a bus barn (1000sf max on accessory buildings and I have one already that’s full), I don’t want to park the coach somewhere else that “might be heated”, I’m not yet in a position to move to warmer climes in the winter like George is going to suggest, and winterizing and unwinterizing ever time we want to use the coach in the winter is of course a pain.
The race shop has hydronic heating in the floor with a fancy condensing boiler that is located on the opposite end of the building from where the coach is located. Hind sight being 20/20, I could have run a supply (hot) line and a return (cold) line dedicated to the coach from the boiler through the floor (with the rest of the pex lines) that would terminate along the wall that the coach sits against.
Then in the coach, install a water to water heat exchanger in the plumbing for the Webasto system that would allow the hot water from the natural gas shop boiler to heat the coolant in the Webasto system. I’d envision using two quick-disconnect lines to connect the coach to the lines in the shop that would be insulated.
Turn on a pump at the boiler for the dedicated coach line and I have an endless supply of hot water. Turn on the Webasto pump, close off the circuit to the bus engine (unless I want to preheat the bus engine with shop heat), and the Webasto pump would circulate the bus coolant through the heat exchangers in the coach as well as the water heater which would warm the water bay.
Then the coach would be kept warm and safe from freezing using the very efficient natural gas boiler in the shop. I might need fans in the coach to blow the air around circulating it under the sinks, through the toilet room, and near the washer. But just the fans will draw considerably less amps than the heaters.
Right now I’m keeping the coach warm and safe from freezing using electric resistance heat, which is inefficient, kinda expensive, a potential source of fire if a heater malfunctions, and suspectible to tripping a breaker and not providing enough heat to keep the coach safe.
Unless I’ve missed something, this is what’s needed:
1. Water to water heat exchanger plumbed into the Webasto plumbing in a location that will allow circulation through the Webasto pump, heat exchangers in the coach, through the copper lines in the water bay, and the water heater.
2. Valve to isolate the Webasto plumbing from the bus engine; if it already doesn’t exist.
3. Two lines plumbed from the new water to water heat exchanger to the side of the coach with quick-disconnects.
4. New Grundfos pump at the shop boiler for the dedicated line to the coach.
5. Supply and return lines plumbed from the shop boiler to the shop wall next to the coach with quick disconnects.
6. A way to turn the Webasto pump on without having the Webasto boiler go on (I don’t think I can do that today). I already have two Webasto thermostats in the coach (one in kitchen and one in bedroom) that should take care of those areas if they control the Webasto pump. I will probably put a third in the water bay.
7. Would need someway to tell the new Grunfos pump at the shop boiler to turn on based on when the Webasto pump gets turned on which is when one of the three thermostats in the coach is calling for heat. That would likely be a low voltage line from the Webasto pump to a receptable on the side of the coach, then a short pig tail from the coach to the side of the shop, and then from there to boiler.
The boiler heats the water (coolant) based on outside air temp which appears to give it a “target” for the outgoing water. If the target isn’t being met I’m told the flame gets bigger and puts more BTUs into the coolant to maintain the proper outgoing temp. This is also tied into the thermostat on the wall of the shop. If the shop temp is below the set point, the boiler bumps the outgoing temp up. During the recent cold snap, the outgoing water was as high as 118 degrees. I’ll have to asked the plumber how adding the coach would impact this setup.
So … does my idea make sense? Can it be done that easily? Or is this over engineered to solve the problem?
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12 Replies
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It will work, but that is a whole lot of work and dollars and it is literally no more reliable than 2 or three small electric heaters in the house and one in the water bay.
If the electric fails, no matter what you are using the heat stops working.
There is nothihg better (as a starting point) than getting your coach inside and protected from the heat, cold, sun and winds. If you want to spend as much money as your plan will cost, use the money for closing and moving expenses for a different house with a bus garage. Your tires, paint, roof and Vitricor will all thank you.
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Dick,
I’m with John,
Everything you say about hooking up to your condensing boiler is workable. Your plummer can hook you up with a plate heatexhcnger (water to water) to seperate the coach which has antifreeze in it from the Boiler water which may or may not have antifreeze of some kind and your pumps and inline thermostats. Sounds like quite a big deal.
As far as neighbors smelling your wabasto, it won’t stink any more than a fuel oil furnace. I have never had the nozzel out of my burner so I don’t know what the fuel usage really is. I wouldn’t think it would be more than a .5 gallons per hour. That still is still expensive but not as expensive as the damage sitting outside could cause you in the end…Steve
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All good ideas and good points.
The hydronic system has some kind of boiler antifreeze in it. I’ll keep you posted.
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The webasto will use a lot less fuel than .5 gal/hr…even the genny doesn’t use that much….you’re only heating 300 some sq ft and not maintaining the same temps you would in your house. Geo.
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Maybe Rudy can enlighten us as to how much fuel a Webasto uses.
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My guess is less than 1/2 gallon per hour a number I just pulled out of thin air, and is dependent upon if you are heating the engine or not.
I know when Liberty first installed a Webasto that tests were run on fuel consumption and if my memory is any where near accurate a full tank of fuel lasted a month. I just cannot remember the details.
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Jon,
Would that month be at 0deg or at 32deg?
Steve
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The problem is my brain has failed me in knowing if what I posted above is even accurate, much less under what ambient temps the testing was done. Frank Jr. did the test. Perhaps someone in Stuart could find the details and post.
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I was told that the Webasto 80,000 btu units burn about .8 of a gallon an hour when it is burning but we all know it only burns for a portion of any hour even during the first hour when starting from a cold start.In 15-20 degree weather that I was in a couple of years ago I would estimate about 30-40% burn time to maintain a toasty coach.
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The 50k btu Webasto burner burns .5 gal per hour while firing. In the Aqua Hot situation, the heater uses 2 to 3 gallons of diesel in cold conditions and 3 to 4 gallons in frigid contitions per day.
Webasto heat exchanger situations have a run time I am not familiar with so I can not state an estimate of fuel used per day. I do not know the fuel burn of a 80k btu burner.
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If the 50K burns .5 GPH then it would make sense for the 80K to burn .8 GPH.
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Theoretically energy is energy so once a coach is at a given temp, the energy used to maintain the temp should not vary.
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