Bus Interior Heating Plan

[Stormcloud]

I have a ProHeat to install in the bus for hydronic heat and domestic hot water.

Attached is a (very) rough sketch of 'the plan'.

The thermostats will control the pumps, and also the fans behind each of the heaters.
The 5 or 6  gallon reservoir will be install in the freshwater bay, to utilize the resulting heat loss of the reservoir. I will plumb in ball valves on each circuit at the manifold to isolate should it be necessary.
I'll also plumb in 2 ball valves at the manifolds for future engine pre-heating.

Will I need individual pumps in this scheme, or can I use just one pump and solenoid operated valves?

Am I on the right track? Any suggestions? Thanks!

Mark

[bobofthenorth]

I think for simplicity I would go with 2 pumps at a minimum (one for the water heater loop and one for the house) but probably 3 pumps.  You could likely engineer a system with restrictors such that the resistance in each loop was adequate to ensure equal coolant flow to all the loops.  But sometimes things can get over-engineered and it is better to go the simple route.
 

[Brian Diehl]

Mark,

I have a single pump in my system.  My system used 3/4" pex to distribute to the manifold.  The manifold then disperses to 4 different zones.  Each zone uses 1/2" pex to feed each radiator.  I have had no problems with the single pump.  I used a March Magenetic pump:  http://www.marchpump.com/documents/809-HS.asp

This pump works perfectly with the Webasto I have.  I personally would not put a pump in each zone as it is a bit of overkill.  However, you certainly won't need to worry about loosing a pump like I would.  Of course, I'd just pull the pump motor of the engine loop and put it on the interior heating loop pump body.  That is the beauty of the March pumps.  I also liike the 24v pumps as I've tried to keep as much of my system 24v as possible.

Another thing to consider ... I did not use a heating resevior like you are planning.  I have about 2.5 gallons of liquid in my system.  This is just barely enough coolant to meet the minimum requirements of the Webasto.  However, the benefit is I get heat IMEDIATELY as soon as the webasto kicks on.  I use diesel only as long as I need heat.  I don't spend any extra time heating water in a resevoir that I won't need to heat the bus.  I really like the instant heat available by doing it this way.  I've been running this system for 4 years now and have had no issues.

[bruceknee]

1 pump will take care of your needs for heating and domestic hot water. If you also plumb in a flat plate heat exchanger, you will have almost instant, endless hot water. Solinoid sp? valves will work the heat loops by thermostat and the water heater loop will always be on. When it is cold outside, the proheat will cycle 3 min. every 18 mins. We use 24 vac. Taco valves available at Lowes with a transformer.  We have installed 8 systems and everyone is happy and warm. If you would like more info, bruce   -  knee at att.net. Take the dash out.

[TomC]

Something to consider- The first thing installed in my bus was the bathroom.  So my 2-10gal electric water heaters (straight from Home Depot) have been in use since 1995 (one feeding into the next with the final one powered through the inverter for hot water going down the road).  Then in 1999, installed the propane furnace (single 35,000btu).  In the time since, I haven't done anything (except drain the water heater a couple of times & clean the furnace) to either the water heaters or furnace as to repair.  The grand total cost for both-$1,100.00.  Compare that to the cost of a hydronic system, the upkeep, the pumps, the plumbing, etc.  If I needed a block heater, I'd just install an electric one.  Granted hydronic heating and water heating is a very powerful way to go, but it is expensive with maintenance involved.  Good Luck, TomC

[Sean]

... Am I on the right track? Any suggestions? Thanks!

Mark,

While I see no real "problems" with your plan, I have to say that it is an unnecessary level of complexity in a bus.  I think you'll be perfectly happy with the results if you just put everything, including an engine heat exchanger, on one big loop.  You'll get better boiler performance as well.  Then there are no valves, manifolds, or extra pumps to maintain or worry about.  A two-way valve can be used to bypass the fan heaters for "summer" mode (so you can get hot water without heating the bus).  The individual zone thermostats then merely switch the fans in the fan heaters on and off.

Our system is plumbed this way and we are very happy with it.

...
Another thing to consider ... I did not use a heating resevior like you are planning.  I have about 2.5 gallons of liquid in my system.  This is just barely enough coolant to meet the minimum requirements of the Webasto.  However, the benefit is I get heat IMEDIATELY as soon as the webasto kicks on.  I use diesel only as long as I need heat.
...

Well, actually, you are not really using any less diesel this way (more on this in a moment), and it has other downsides.  For one, the boiler will cycle more frequently, possibly in cycles shorter than the boiler manufacturer recommends (this is the reason for Webasto's minimum requirement).  But, more importantly, if you are using an engine heat exchanger to pull free waste heat from the engine while under way, you won't have any real thermal mass to capture that heat to make maximum use of it.

When we stop at the end of the day, we get another hour or so of free heat and hot water from the system before having to switch the boiler on.  On most travel days, we never have to turn the boiler on in the evening, just when we get up in the morning.  As far as conserving diesel, when we are done with the heating system we switch the boiler off 45 minutes or so ahead of time, but leave the circulating pump on.  This lets us extract the heat that is contained in the thermal mass of the reservoir, so the "extra" diesel we used to heat that mass up, if any, is not wasted.

You are right, though, that your fan heaters will be at temp much sooner with less thermal mass to heat.  From a cold start, where the outside temps are, say, in the 40s and the fluid is down at ambient, it takes perhaps 20 minutes for us to get heat.  That's why we installed the system switch in arm's reach of the bed -- Louise just reaches over and flips it on half an hour before we get up in the morning.  But this could also be easily controlled by one of those electronic thermostats with a built-in time "program" as well.

If you do choose to omit a thermal reservoir, though, do remember that any hydronic system still needs an expansion tank of some sort.  If you've included one of the radiators in your loop (also not my recommendation -- I suggest heat exchangers to couple engine and house systems), then its existing expansion tank has you covered.  But, if not, you will need to have at least a small tank, with a proper safety relief cap, at the high point of your hydronic loop.  (On our system, a single tank serves as both expansion tank and thermal reservoir.)

-Sean
http://OurOdyssey.BlogSpot.com

[belfert]

My only comment is why three heaters in the lounge area?  It seems like more than necessary to me.

[bobofthenorth]

As I'm sure Mark is aware, he is getting a lot of advice from people who never have to deal with any serious amount of cold.  I stand by my advice that 3 separate controllable loops is the ideal way to approach this or at a minimum 2 loops.  A bus can shed a lot of heat when its -20 outside and its fine to say "Oh well nobody would ever try to use it in those conditions" but those of us who live in the cold climate at a minimum have to stay warm while we get the H out of Dodge.  Some of us are even foolish enough to try to live in those conditions.  When you do that you pretty quickly find out where the weak points in a system are.  Trying to run multiple loops off one pump gives no redundancy and guarantees cold spots.  Sean is right - if you are going to go with one pump then one continuous (series) loop is the least worst alternative but it will have cold spots.

[Sean]

My only comment is why three heaters in the lounge area?  It seems like more than necessary to me.

We have five fan heaters (and one non-fan radiator) and that is just barely adequate in sub-zero weather.  Two of those are in the salon, and a third is in the "cockpit" area.  So I don't think three in this picture is off-base.

I agree with Bob about designing for colder temps, and I have to bow to his experience with separate loops in those conditions.  Although I will point out that the total heat delivered is the same irrespective of number of loops, and is limited by the capacity of the boiler.  Ours is 45,000 BTU/hr, which may be insufficient for coaches which spend significant time in sub-zero conditions.  For us, the next size (80,000 BTU/hr) was overkill.

BTW, if you are going to run in those conditions, don't forget to have some of the heat go into the bays where water tanks, batteries, and other sensitive items live.  In our case, we ran all the hoses through the bays, which provides enough heat down there to keep things from freezing.

-Sean
http://OurOdyssey.BlogSpot.com

[busshawg]

Hey Mark, Looks like you've been doing some thinking, looks good. Just wondering what type of tank you are planning to use. Will it have something like a rad cap on the top? What will you do to fill the system or to keep it topped off as your tank will be in the back bay. The pumps will be 12v? If your not running the pro heat through your bus engine I wonder if you will need all 3 pumps.  Those are good units and the engine looses alot of heat out there in the cold while the unit actually heats it up relatively quick. Might help conserve on your 12v if you don't need it. Looks good.

[bobofthenorth]

I agree with Bob about designing for colder temps, and I have to bow to his experience with separate loops in those conditions.  Although I will point out that the total heat delivered is the same irrespective of number of loops, and is limited by the capacity of the boiler.  Ours is 45,000 BTU/hr, which may be insufficient for coaches which spend significant time in sub-zero conditions.  For us, the next size (80,000 BTU/hr) was overkill.

BTW, if you are going to run in those conditions, don't forget to have some of the heat go into the bays where water tanks, batteries, and other sensitive items live.  In our case, we ran all the hoses through the bays, which provides enough heat down there to keep things from freezing.

In this case its not the total heat output that is an issue but rather its distribution throughout that 40' long metal tube we call a house.  In our case the PO designed a parallel loop system and that just flat doesn't work because the coolant takes the path of least resistance.  A parallel loop might work if you had extreme overkill on the pump size.  A series loop means that the rads at the "end" of the loop are going to receive considerable colder liquid.  In theory you could probably design around that but in practice it means you are going to have cold spots in the coach.  We have a 45k ProHeat and that was more than adequate down to -25C but we have cold spots because of the crappy design.

Mark has already been thinking about the bay heat and has some good ideas to deal with it.  I was surprised by the lack of heat required down there.  Our tanks sit flat on the floor with no protection under them and we have no dedicated rads to heat the bays.  I bought one thinking we would need it but never got around to installing it and have no immediate plans to do so based on our experience in Dec.  There is actually an incredible amount of heat shed off the ProHeat.  Maybe the newer ones are better insulated but mine wastes enough heat to keep the compartment it is in toasty warm.  The water tanks are in the next bay with their fittings next to the "warm" bay and that seems to be more than adequate for them as well.

[Lee Bradley]

Mark,
Looks pretty good. I would go with a single heating loop with the room that you like coolest at the end (bedroom for me) and thermostats, to control the fans, in each room. Have you consistered an electric hot water tank for the reservoir? Electricity when available is cheaper than diesel and quieter than the boiler. I don't know if you are going to have propane but if you do you might look at the electric/propane/hot water RV units. Do you still have the driver's heater? Will you make that part of the house system or keep it on the engine only? If you put it in a loop with the reservoir and engine, you will have heat/defroster before you start the engine. If you loop it separately, you can use it as a supplement to the house heaters without heating the engine. I plan on using the engine coolant expansion tank as the expansion tank for the house heat; single line from the high point of the house system to the tank and shut-off valve between the tank and engine so engine work can be preformed without draining that tank. More questions than answers but what do you expect it these prices?

[Brian Diehl]

I use a parallel loop system with shut off valves on each loop.  I just balance the heat by partially closing the shorter loop valves.  Simple, easy to manage, and extensible with each radiator getting the same temperature coolant.  I have used this system in below 0 temperatures (about -10) and have no issues with the design.  45k btu is more than enough even at 10 below.

[Stormcloud]

Thanks for the comments and advice. Keep it coming!!!!!

Bob (of the north) and I have discussed the heating system a few times. Since we live (sometimes  ) in similar climates, he knows what will work and what will excel, based on his personal experience.

I've made a couple of alterations to the plan, namely the engine preheat will be included with the bedroom/bath loop and controlled by a few valves. I dont expect to use the engine preheat, since I have a block heater, but redundancy is not a bad thing and having the valves in the last bay under the bedroom near the engine seems to be a good spot.

The front bay (electrical) will have the ProHeat in it; close to the diesel tank and power.

The middle bay (freshwater) will hold the 5 gal reservoir, manifolds and pumps; residual heat loss should prevent the freshwater from freezing. Likely the marine hotwater tank will be here also.

The last bay presently holds a grey and a black tank. These are to be replaced by a single tank. This tank will sit on a piece of 1.5 inch styroam insulation in which a groove has been routered to accept the Pex pipe on the return from the bedroom/bath loop. This should keep that tank from freezing.

I'll run all the lines on the bottom side of the floor, and only pass through the floor for the heater connections.

The pumps I have are 1/25 Hp Grundfos pumps (120 volt though). This isnt a problem as we always have the inverter on, and also carry an backup inverter...

I'm a bit on the fence about the marine water heater, though.

Tell me more about the flat plate heat exchanger and how well they work; especially if you have had both, which do you prefer? The plan may change again.

Mark

PS: Grant...I didnt show it in the plan, but I will have a fill point and expansion tank in the bathroom, directly above the reservoir. Still got coffee on if you're in the area.

Lee...I considered using a hot water tank as the reservoir, but the element size is a concern. If I installed a 1500watt element, that can make quite a diffence in available power if Im plugged into a 30amp service. I think I would likely have the tank custom made (to fit the available space), and I'll foam insulate it when its completed/installed and no leaks. Thanks for the suggestion!

[Brian Diehl]

Mark,
You might consider putting the proheat in the water bay.  The proheat puts out a pretty good amount of heat when running.  Also, I highly recommend you put a heat exchanger in the water bay no what you do with the proheat.  I know my system with a heat register in the wet bay cycles on and off even with the webasto in the same bay.  You will also really enjoy the register there when trying to bring the bus up to temp for use in cold weather.  A thermostat in the bay is perfect to be sure your bay stays above freezing.  When we are going down the road I turn the burner off and use engine heat to keep the bay warm.  By having the bay on a thermostat I have an easy way to combat heat loss from going 60+ mph down the interstate.  I just don't see how radiant heat loss from your resevoir is enough to keep the entire bay warm in really cold weather.

-Brian