Hydronic Radiant Heating in a Bus

[texasrednek]

I have seen radiant heat supplyed to green houses through 1 inch pex and being heated by a manure/compost pile wich puts off quite a bit of heat sure but nothing like a hot water heater.....just speculating not trying to be argumentitive its hard to convey tone in type.

[nat_ster]

Originally Posted by texasrednek

I have seen radiant heat supplyed to green houses through 1 inch pex and being heated by a manure/compost pile wich puts off quite a bit of heat sure but nothing like a hot water heater.....just speculating not trying to be argumentative its hard to convey tone in type.

Quite to opposite. I encourage others to think along, present challenges, and bring forth other idea's and solutions.

They way the pipes were looped, without the conventional bottle necks in the manifolds, may have played a big role in that greenhouse system being successful.

Nat

[texasrednek]

I was also thinking more about that green house. I realized a fairly large variable difference in application, the temps out side were in the 40's and 50's f. And only raised temps in the green house by a few degrees in early spring I wasn't thinking its going to be used to heat a living space to a comfortable level when its in the single digits. But hey I'm from Texas if I needed to heat my bus in the grips of winter I would light a candle!

[nat_ster]

Originally Posted by That Guy in Maine

Hey guys,

I got some good answers in my thread about propane storage but I'm trying to figure out a bit more information on the typical usage for LP on board a bus. It's looking like I might get a coach right now and so there's plenty of under-bus storage for utilities like water tanks (especially since I won't have a black water tank), batteries, and propane tanks...but I need to budget space for a heating system which can be a bit more complicated.

I've tossed around the idea of using a few different systems and compiled some pros/cons of each...

Between wood heat, RV furnaces, electric heaters, and radiant heat I think that radiant is the best option. There are a few reasons, first of all it's quiet and works completely in the background, very little input is necessary from the inhabitant. The systems are generally regarded as being energy efficient, and the cost isn't too extreme from what I've found so far. On top of that it means that the floor will always be warm and I'll be able to walk around in the dead of winter in my bare feet. When we put an addition into our current home the master bathroom got radiant floor heat and it's so nice in the winter to not have to put socks/slippers on to go to the bathroom.

Anyway, for now I want to plan for radiant heating. If anybody has experience with this type of system in a conversion I'd love to hear it!

I have chosen to run a closed loop system, this means one hot water heater for the floor and one for domestic use. Because I'm doing a closed loop I can also use the radiant heat to heat the diesel engine in the winter which will be of great benefit on ski trips that take me into the mountains in the dead of winter.

Finding a properly sized water heater is proving to be difficult. First of all I am not really sure how to calculate the BTUs required for the space. I've googled "BTU calculator" and plugged the same information into a few calculators and gotten different numbers ranging from ~8,000 BTU all the way up to ~75,000 BTU and some in the middle.

So assuming the high end of that BTU rating is the accurate one, do I just look for a water heater with a 75,000 BTU output rating? Would that mean it's on all the time? Should I be looking for a 150,000 BTU rating heater? I'm not really familiar with all this heating stuff.

The plan is to use rigid foam underneath the floor that the radiant is in, and blown in insulation in the sides and ceiling of the bus. I also plan to insulate the accessory bays under the bus that house the water tanks so they don't freeze in the winter.

Then my other question is about gas consumption, how much should I be expecting to consume with a hot water heater tasked with heating via radiant heat?

Sorry for so many questions but heating is one place I'm a bit overwhelmed...the bus will surely be used on days where it gets to -15F or colder at night and barely above 0F some days. Last night it was below -20F here but that's probably the coldest night of the year so far.

Any help would be appreciated!

With the insulating method you mentioned, A 30 to 40,000 BTU low efficiency propane hot water heater is all you need.

The cabin I built uses this system, and has worked great for the last three winters.
Cabin build for Old Timer - Pirate4x4.Com : 4x4 and Off-Road Forum

Nat

[somewhereinusa]

The boiler I use is rated at 10,000 btu, runs on diesel fuel out of the fuel tank. I did the floor basically like you described. It was -5 the other day and got so warm I had to start turning things down ( I haven't got all of the thermostats in yet). Once it's warm it just kinda idles keeping things warm.
There are pictures on my build thread and at SomewhereinUSA

Dick

[That Guy in Maine]

OK, so I'm trying to figure out what I'll need to construct a full system. I'm planning to build a system similar to what somewhereinusa uses in his bus. Here's his schematic: http://www.somewhereinusa.x10.mx/hydronic%20heat.pdf

The plan is to have four (possibly five in the future) zones.

Zone 1: Driver area, probably won't have any PEX heating but will have the original blowers and an aftermarket kickspace heater like this: UC101B - Cadet UC101B - Perfectoe Black Under-Cabinet Heater, 1000 Watt (120V) mounted behind the driver seat facing forward.
Zone 2: Lounge/work area, PEX tubing throughout with one kickspace heater under the desk.
Zone 3: Bathroom, no kickspace heater, just PEX tubing.
Zone 4. Bedroom, one kickspace and PEX tubing throughout.

The possible 5th zone would be in the enclosed trailer behind the bus, probably using a one or two kickspace heaters and would only be turned on to do stuff like ski tuning in the winter.

The hot water heater will also be able to feed the domestic hot water and engine coolant via two heat exchanges, I could use some help selecting which exchanges to use though, would something like this be enough for both uses? BP400-10LP - Bell & Gossett BP400-10LP - 60,000 BTU/Hr Low Pressure BPX Brazed Plate Heat Exchanger

So for each zone I would need a valve and thermostat, correct? I also need a control board to manage the entire system. I also need an expansion tank.

Am I missing anything? Any product suggestions?

[somewhereinusa]

Originally Posted by That Guy in Maine

OK, so I'm trying to figure out what I'll need to construct a full system. I'm planning to build a system similar to what somewhereinusa uses in his bus. Here's his schematic: http://www.somewhereinusa.x10.mx/hydronic%20heat.pdf

The plan is to have four (possibly five in the future) zones.

Zone 1: Driver area, probably won't have any PEX heating but will have the original blowers and an aftermarket kickspace heater like this: UC101B - Cadet UC101B - Perfectoe Black Under-Cabinet Heater, 1000 Watt (120V) mounted behind the driver seat facing forward.
You can build your own much cheaper using an automotive heater core and muffin fans.I'll take some pictures of the one I built.The rest of mine are commercial that I got a good deal on. The one I built puts out more heat.
Zone 2: Lounge/work area, PEX tubing throughout with one kickspace heater under the desk.
Zone 3: Bathroom, no kickspace heater, just PEX tubing.
Zone 4. Bedroom, one kickspace and PEX tubing throughout.
As it turns out, I probably don't need all of the kickspace heaters. They do make it nice though for quicker initial heat up. I might not have enough in the front, the flat nose buses tend to be a bit cold while driving.

The possible 5th zone would be in the enclosed trailer behind the bus, probably using a one or two kickspace heaters and would only be turned on to do stuff like ski tuning in the winter.
I think this would be a problem area. You would need to make some provision for unhooking which wouldn't be a big deal but, it would introduce air which IS a big deal. It takes a lot of bleeding to get rid of the air and it is VERY inefficient when there is air. You would also need to insulate the tubing so you don't loose heat between bus and trailer. I would think some sort of space heater (electric,kerosene?) would be better.

The hot water heater will also be able to feed the domestic hot water and engine coolant via two heat exchanges, I could use some help selecting which exchanges to use though, would something like this be enough for both uses? BP400-10LP - Bell & Gossett BP400-10LP - 60,000 BTU/Hr Low Pressure BPX Brazed Plate Heat Exchanger
That looks like the one I used except it is a 40 plate,146,000 BTU,I got it much cheaper on ebay. If you use a marine water heater similar to this Seaward S600 Marine Electric Water Heater with Rear Heat Exchanger it has a heat exchanger built in.

So for each zone I would need a valve and thermostat, correct? I also need a control board to manage the entire system. See my comments below.
I also need an expansion tank.
I didn't do it that way. My boiler has a pump in it. I control the zones with a pump on each loop. I used four of these Webasto Espar Hella Water Coolant Pump Heater or Hydronic DC Boat RV | eBay connected to the thermostat using a relay. These pumps are the same as built into the boiler. The fans for the kick space heaters just have a toggle switch. I used a temp switch (102°F) mounted to the incoming water line to the heater. When the t-stat turns off the water pump the water cools enough to turn off the fan. It also keeps from blowing cold air until the water is warm enough.

Am I missing anything? Any product suggestions?

I miss remembered, my boiler is a Hydronic 10,putting out 32,400 BTU/hr on high. Link to manual http://www.esparofmichigan.com/cmsAd...Hydronic10.pdf

This is just my opinion. I think that some sort of system made to be used as a heat source for the water would be better. I can't say for sure but I would think even more economical to run. The one I have has a control module complete with 7 day timer if needed. And while it is on all of the time when it is on, it cycles between high and low to keep the water at an even temp. Even in below 0 temps it stays on low much of the time. I'm also not a big fan of propane, not particularly because I think it more dangerous, I just think it a pain in the A**.


Hope this helps
Dick

[nat_ster]

We need to know where you live to really have a grasp on your needs.

Like somewhereinusa I use a pump with a thermostat wired into each loop. When the thermostat calls for heat, it simply turns the pump on, starting the flow of hot water under the floor.

What you use for a boiler / water heater will depend on your budget.

At the lowest end of the scale is the 40 ga 30,000 to 40,000 BTU propane water heaters. Cost around $250 to $400.

Next would be a boiler with the settings that somewhereinusa mentioned. Cost starting around $2500, and hard to get one with a small enough heat output to keep it from short cycling.

Or last would be a high efficiency 40 gal, 75,000 BTU water heater that is made to use as a space heater / potable water heater. They have two sets of ports, some come with a back up electric element.
Cost Starting at $3000

One more thing I want to mention is this.
In cold climates, Hot water lines should be run under your entire interior floor space. This means under cabinets, closets, ect. This prevents cold from creeping in from the sides, and keeps the entire interior a even temp.

This really makes it more simple to install. My bus will have 7 runs of half inch line from the front, all the way to the back. This means I will have 14 lines under my feet, one every 4 inches. All lines will have their connections at the back of the bus, where they tie into the manifold that connects them to the 1 inch main feed line coming from the boiler.

I want to emphasize the need to keep the system restrictions to a minimum.
For instance, I could run all my loops as one long line. 7 x 60 feet = That's 420 feet. Max run for half inch line is 200 to 300 feet depending. We could use a bigger pump, but that is a bad idea. By manifolding the loops, we can use a pump one tenth of the size without loosing flow. Smaller pump = cheaper and more efficient to run.

I'm still thinking of custom making my boiler out of stainless, low profile to fit under a bus, with two built in heat exchangers, and 6, one inch ports for electric heating elements. Sadly there is nothing on the market like this for under $3500, and all commercially available units are to tall to fit under a bus.
This would seriously simplify installing the hydronic heating in a bus.

If I do make my own boiler, I may make a few more to sell to fellow skoolies. There would be no profit for me, just helping out fellow members.

Originally Posted by somewhereinusa

The one I have has a control module complete with 7 day timer if needed. And while it is on all of the time when it is on, it cycles between high and low to keep the water at an even temp. Even in below 0 temps it stays on low much of the time. I'm also not a big fan of propane, not particularly because I think it more dangerous, I just think it a pain in the A**.

The $400 propane hot water heater that heats the 16 x 24 cabin only cycles 25% of the time when it's -25C or lower. We keep the tank temp setting low, and increase it as the temp get's colder outside. This keeps our efficiency up, as the hotter you try to heat the water, the less efficient a propane / gas boiler gets.

The water heater is installed in a sealed closet made specifically for the water heater. The closet was built with minimum clearances to combustibles and vented to the outside.

Nat

[somewhereinusa]

Here's a couple pictures of the heater I built.





Basically sandwiched the core then built a box. I mounted the fans so they would suck through the core. They seem to move more air that way. Mounting would depend on how your core is built. This was a nice copper one that someone gave me.

[That Guy in Maine]

Originally Posted by somewhereinusa

-snip-
Hope this helps
Dick

Very good information there, thank you.

Originally Posted by nat_ster

We need to know where you live to really have a grasp on your needs.

One more thing I want to mention is this.
In cold climates, Hot water lines should be run under your entire interior floor space. This means under cabinets, closets, ect. This prevents cold from creeping in from the sides, and keeps the entire interior a even temp.

The $400 propane hot water heater that heats the 16 x 24 cabin only cycles 25% of the time when it's -25C or lower. We keep the tank temp setting low, and increase it as the temp get's colder outside. This keeps our efficiency up, as the hotter you try to heat the water, the less efficient a propane / gas boiler gets.

The water heater is installed in a sealed closet made specifically for the water heater. The closet was built with minimum clearances to combustibles and vented to the outside.

Nat

I live in the White Mountains of NH, this is how a typical February goes here (this is this years):

Most days get above 10 degrees, some nights get as cold as -20F.

I plan to run the radiant through the entire floor, but I've heard that it would be smart to not loop under your refrigerator which makes sense to me so I'll probably pre-plan for that.

As for water heaters, I think a tankless unit makes the most sense for me. I'm not too worried about spending $25 or $50 a month more than if I had a boiler or something more efficient. I just want something that will work and not take up a lot of space.

This may be a stupid question but if I get a hot water heater rated for 150,000 BTU is it going to work for such a small application? Or what is a good way to find a smaller sized water heater? I want something that's powered off of propane preferably.

Thanks again guys, this is a huge help!

[nat_ster]

A tankless water heater WILL NOT WORK. That is what prompted me to start this thread.

I have to run to work. I will tell you why tonight.

Nat

[That Guy in Maine]

Originally Posted by nat_ster

A tankless water heater WILL NOT WORK. That is what prompted me to start this thread.

I have to run to work. I will tell you why tonight.

Nat

Good thing I asked!

I appreciate all your help, I'll look forward to your reasoning!

[taskswap]

We're coming out of a home where I did a DIY hydronic wood boiler and DHW setup, with a custom Raspberry-Pi controller running the thing. That means I'm super comfortable with hydronic itself and the electrical and plumbing involved, so I plan to take advantage of that in our conversion.

After toying with the thought of a wood stove (no power required, romantic look and feel) we decided to go the boiler route too. In our case I was seriously looking at the diesel "coolant heater" options that Espar and Webasto make. These are pretty cheap on eBay, they're small enough to fit in the "basement" (big advantage IMO) and it makes a lot of sense to me to use a fuel that I already have a 100-gal tank for as part of the bus.

As for heat output, I'm not worried about this. We heat our very poorly insulated 2400 sq. ft. house in CT winters (it's 9F outside right now, and the wind is blowing) full time with an ancient 100kBTU Energy-Mate wood boiler. We have to run the thing flat out to do it, but in a well-insulated 300 sq. ft. space these coolant heaters may be a good option.

For the electric backup, one thing I am NOT is a good welder. I don't trust myself to make a pressure vessel out of stainless like nat_ster, so I'm going to keep the boiler itself pretty much as-is. What I'll do is install a 20- to 30-gal domestic hot water heater in a cabinet under the master bedroom closet. I'll configure the plumbing such that the diesel boiler can heat this tank, or the electric element can be activated instead. That storage tank is an important part of a hydronic system. Properly configured, a storage tank can greatly increase a hydronic system's efficiency and reduce the cycling on your boiler, especially in the "shoulder season".

With this setup, if I have "shore power" I can heat using that, and get both DHW and cabin heating the other times. You have to be careful to pick the right unit if you do this because a lot of these units expect a beefy 240V feed, but there are plenty of low-power 120V options available. They don't have enough "oomph" to heat a whole house, but they're fine for a camper with a low-flow shower head and no water-hungry appliances like dishwasher/washing machine.

I don't plan to install one right away, but I'll plumb to add solar hot water later. I'm a fan of both electric and hot water and will probably add both eventually, we're just on a budget getting started and I want to be realistic. Solar hot water is really efficient and very easy to do. In areas where it's hot out I expect to be able to supply most/all of our DHW needs just from this source. That'll let us do a lot more boondocking in the summer.

I don't plan to run glycol in any of these lines, which eliminates some components (and concerns). We're going to be full-time and I wouldn't let these pipes freeze any more than I'd let them freeze in my house. There's an additional advantage here - pure water has WAY more thermal capacity than glycol - it's always the best choice, when you HAVE a choice. If we add solar I'll have to make a decision about that. I may do a drain-back setup in that case, which also eliminates the risk of overheating in the solar panels themselves. These systems are so small that you don't need a big tank for that. A length of 2" pipe in a wall has enough volumetric capacity to be the "tank".

Note: for you waste-oil (WMO/WVO) lovers, these coolant heaters won't work well with that fuel. They're blower-driven burners like a typical house boiler, not compression-fired diesels, so they're less tolerant of thicker fuels and I don't plan to modify mine just to support that. I figure if I'm going to mix fuels or use WMO/WVO, I'll do it with a separate tank and just for the bus engine itself. That's in the "we'll see" category in our plan.

[nat_ster]

Sorry for the delay, that was a good 4 days of work I just finished. Roofing with metal in the -20 C with blowing snow and 60 kmh winds is no fun.

My next project starting tomorrow is hanging drywall in a warehouse. Four more days of good $$.

Originally Posted by That Guy in Maine

Good thing I asked!

I appreciate all your help, I'll look forward to your reasoning!

Originally Posted by taskswap

Properly configured, a storage tank can greatly increase a hydronic system's efficiency and reduce the cycling on your boiler, especially in the "shoulder season".

Other reasons are:

High install Cost.

Hard to find model specific parts.

Not nearly efficient as claimed.

Low duty cycle. Unit will burn out under continues use.

Highly restrictive flow. Tankless units restrict the flow to insure the water is fully heated. This would cause you to need a massive high cost circulating pump.

And many many other reasons I can't think of right now.

In my opinion, a water heating system is no good without the heat storage reservoir. This is the single biggest mistake in most hot water heating systems.

Originally Posted by taskswap

With this setup, if I have "shore power" I can heat using that, and get both DHW and cabin heating the other times. You have to be careful to pick the right unit if you do this because a lot of these units expect a beefy 240V feed, but there are plenty of low-power 120V options available. They don't have enough "oomph" to heat a whole house, but they're fine for a camper with a low-flow shower head and no water-hungry appliances like dishwasher/washing machine.

I agree.

Many many sources of 15 amp 120 volt power. Even big road signs in parking lots have a 15 amp connection at the bottom for Christmas lights ect.

This is why I'm making that stainless steel tank with 6 one inch ports for heating elements.

I can have 2 running 240 volt. one at 5500 watts, and one at 3500 watts for versatility.

Two more running 120 volt. One at 750 watts and one at 1500 watts. This will give the ability to use half a 15 amp feed for heating, or use the full 15 amps.

And last the two low voltage heating elements for use of renewable electricity. Depending on my solar / wind generating system, the elements will be used as dump systems for when my storage battery's are full. This way my wind turbines will always have a restrictive load on them to prevent over speeding.

If I can build enough wind turbines and set up enough solar, I should be able to heat with only electricity in the spring / fall shoulder season.

Nat

[That Guy in Maine]

Nat,

I know you mentioned using the Polaris unit in your bus. I looked at that unit and while it's high priced it's worth it from what I conclude. My biggest worry is that it's specifically mentioned in the manual as being not fit for use in an RV.

As for a storage tank...do you mean plumbing your system something like this?



I might have made some mistakes here, but the basic idea is that the small black boxes are valves that would be controlled by DHW needs, a switch to pre-heat the engine, and the thermostats opening loops for different zones in the bus for heat.

There are two heat exchanges, one for the engine loop and the other for DHW loop. Then there is another valve that would basically allow hot/warm water to bypass the heater and get pumped back into the storage tank and then if it's needed it would be pumped into the loops. If the storage tank gets below a certain temperature then the water heater would turn on and circulate water as needed to get the storage tank up to temp again.

Am I designing that right?

[somewhereinusa]

My biggest worry is that it's specifically mentioned in the manual as being not fit for use in an RV.

It's probably a liability thing. This covers them if you do it and something goes wrong and you try to sue them. Also, might be hard to keep fire lit while moving, but I don't think you are going to try that anyway since you are tying into engine heat.

I've been told you need a pressure relief valve in the domestic hot water, since you are getting heat from the engine. Mine is built into the water heater. I also have what amounts to a pressure relief valve in the heating loop, I built it using an automotive radiator cap with a catch can.

[taskswap]

Usually with a radiant system you do this with a mixing valve. It stops you from short-cycling your boiler, increasing its life (and lowering its overall duty cycle), increases the return water temperature to the boiler (which is important if your boiler isn't stainless), and greatly increases the temperature stability of the system. Here are two options - the 3-way is passive and the 4-way is motorized (takes power... but then so does the circulator, so...)





The reason for this, plus storage, has everything to do with the reason we use water in these systems in the first place. The literal definition of a BTU is the "heat" stored in a pound of water raised 1degF. If you have a hydronic system that is meant to heat well from 110F-130F, that's a 20 degree difference. Now, say you have 200' of 1/2" PEX. Per this chart here:

Radiant PEX Tubing. Radiant Heat Systems. PEX Pipe Tube Underfloor Heat

that gives you about .92 gallons, or 7.67lbs of water. (Water weighs 8.34 lbs/gal.)

Now stay with me. If you heat that water from 110F to 130F with your boiler, you have stored 153 BTU in it. That's some heat... but not a lot. A 34kBTU/hr (10kW Webasto) boiler is going to cycle on and off a lot doing that.

Now suppose you add a 20-gal domestic hot water heater, just an off-the-shelf unit from Home Depot. (And no, I don't buy that entry-temperature argument I've seen elsewhere - these things are designed to HOLD water up to 180F or higher - having water enter at some number lower than that be a damaging factor makes no sense.)

Now you have 21 gallons of water in your system - 20, plus the 1 gallon in the pipes. (Again, not counting whatever's in the boiler.) Again you heat it 20F, but now you have 175lbs of water, so you store 3500 BTU in it. That's going to last a lot longer!

Not done yet, tho. Now you add a mixing valve and you run that hot water heater up to 180F or whatever it's rated for (I live on the edge and do mine to 190F - gasp). Now you're looking at a 70F temperature rise on that same water, so you're storing 12,500 BTU in it!

Doing this increases the system's overall efficiency although there are negative impacts too because even the best insulation in the world is going to leak some heat from that tank - but what the heck, it's leaking into your living space. Usually with a system like this where you want some extra efficiency you add what's called an "outdoor reset", which is a temperature sensor added to your aquastat. When it's warm out and it knows you're only heating shower water, it lowers the temperature it runs the system at to like 130F or so.

This kind of system takes a little extra work to set up but has some other benefits that make it worth it IMO. The solar is the big plus - it's super easy to add to this kind of system and "store" heat in that hot water tank. Solar is kind of useless without some form of storage, IMO, and this kills two birds with one stone. And with an electric element (or whatever nat_ster is doing - six or something???? <grin>) you can get your hot water that way when electricity can be had. Three heat sources (diesel, electric, solar), one storage tank, a mixing valve, and your radiant, and you're done!

[nat_ster]

Originally Posted by That Guy in Maine

Nat,

Am I designing that right?

That's close to what I have in mind. If possible, combine the heating tank with the storage tank. My heating tank will be my storage tank.

I don't use or like zone valves. I feel it is too hard to balance a system that way.

Try to use as few zones and as few circulating pumps as you can.
Pumps are expensive, and use electricity.
A bus is small so only a few zones are really needed.

Mine will be 1 zone for the entire floor.
Then a zone for keeping the tanks in the basement of the bus from freezing.
One more zone will be wrapped around the bathtub so I can sit in the tub for hours without it cooling off.
Last zone will be a future connection for heating the stacker trailer I will pull with my bus.

Originally Posted by somewhereinusa

It's probably a liability thing. This covers them if you do it and something goes wrong and you try to sue them. Also, might be hard to keep fire lit while moving, but I don't think you are going to try that anyway since you are tying into engine heat.

I've been told you need a pressure relief valve in the domestic hot water, since you are getting heat from the engine. Mine is built into the water heater. I also have what amounts to a pressure relief valve in the heating loop, I built it using an automotive radiator cap with a catch can.

I would agree. They also may fear what the vibration will do to the unit.

[opus]

I've not read this whole post but why dont you skip to the chase and use a Webasto dbw2010?

[nat_ster]

Tankswap

Heating the heat storage water to hot can have disadvantages depending on what system is used for heating.

In a closed loop electric heated system, you can heat the water to just under the boiling point with no loss in efficiency.

With a $400 propane hot water tank, you want to heat the water to the lowest heat that can still effectively heat the space. The hotter you have it set, the lower the efficiency.

I don't use mixing valves because I don't heat the tanks that hot.

Originally Posted by opus

I've not read this whole post but why dont you skip to the chase and use a Webasto dbw2010?

I will have one for back up and versatility. However many of us need more than it offers at a much lower operating cost than it has to offer.

Nat