My engine coolant tankless hot water system

[Vannautical engineer]

Figured I would start a separate thread on this from the rest of my build since it is by far the most mechanically complex feature on my van. I was not sure how well it would work, but now that it's all put together, I can confirm that it is very possible to build a tankless hot water system that uses a plate heat exchanger to heat water off of the engine coolant whenever the engine is warmed up. I am still fine tuning the control system that allows me to dial in the water temperature. Right now the water temperature swings up and down pretty significantly, but overall it works.

I would estimate I put about $400 into the components of the system, but the real killer was the labor. Between running coolant lines the whole length of the van, mounting the heat exchanger underneath the van, and wiring all of the electronic controls for the system, I probably have at least 100 hours of work into the system.

The basic premise is that you run hot engine coolant through one side of a heat exchanger, fresh water through the other, and you get hot water. If anyone is seriously interested in trying to replicate what I've done, I could do a very in-depth write up on it. But, it would take some time and effort to put a really good write up together. And as far as van project difficulty, this is right up there. So if nobody else has a real interest in investing the time and money to put something like this together in their vehicle, I won't bother. Let me know if there is some interest, thanks.

 

[PlethoraOfGuns]

You should do a detailed writeup with pictures and stuff. I don't think many on here have running water in their rigs. My last rig I ran the engine coolant through heat exchanger to get hot water for a shower. No electronics besides an rv water pump. Temperature was controlled via a simple thermostatic mixing valve. Only downside was that I'd have to have the engine running to get the hot water, but it was very hot and worked great! Curious how you have the setup with electronic controls.

 

[eDJ_]

I think you'll find a few kindred spirits here who enjoy creating concept projects that could make Van/RV life more stable & enjoyable.  Perhaps offering safer, simpler, more dependable, amenities that would be less  expensive than current RV solutions would be worthwhile & welcome.   Maybe offering items an individual builder could fabricate could be a start. (with basic tools of course)

Or they could purchase part of the system prefabricated and custom craft the rest of the project on their own. There is much to be said for re-purposing existing items where those components may be available thru sources such as Amazon or ebay. 

My background was in Industrial Design.

 

[Vannautical engineer]

Ok, well I'm still not sure anyone else will actually want to put forth the effort to do this, but for now I'll start with a list of parts in no particular order. The little 1x or 2x before each link is the quantity of each part you need.

[font=Tahoma, Verdana, Arial, sans-serif]1x https://www.ebay.com/itm/392734298081[/font][/SIZE]

30 plate heat exchanger with 3/4" MNPT connections. If I had to do this again, I would get one with female connections instead of male, because it would save me one set of coupling fittings. I do not have enough knowledge to actually calculate how big of a heat exchanger I actually need, but this one seemed about right. And it does seem like it works. Important note on this one is you want to get one that is designed to be used for food applications since all of your water will be going through it. You can buy much more expensive versions of these that are made in the US. I have no idea if they are that much better. Even this Chinese one seems like a pretty solid chunk of metal to me. And its rated pressure of 435psi is WAY higher than anything it will ever see in this application.

2x https://www.supplyhouse.com/sh/control/product/~product_id=SSPEX-FA0507

1/2" pex to 3/4" FNPT fitting in stainless steel. It's important to buy this one in stainless rather than brass to avoid galvanic corrosion between this fitting and the heat exchanger. (Also this assumes your water system is using 1/2" PEX like I did.)

2x https://www.hydraulichoses.com/5000-SAE-140138-NPT-fittings-p/5000.htm

This is a link to a list of fittings, but you will want to buy the [font=Montserrat, sans-serif]5000-12-12 - 3/4" NPTF Female x 3/4" NPTF Female hydraulic fittings. You can also get these in stainless, but galvanized steel should be ok since one of the fittings you will connect to them will be galvanized too. You can skip these if you get a heat exchanger with FNPT fittings. But you would also need to buy the above mentioned stainless PEX fittings in male NPT instead of female.[/font]

[font=Montserrat, sans-serif]2x https://www.napaonline.com/en/p/BK_6601475[/SIZE][/font]

[font=Montserrat, sans-serif]3/4" male NPT to 3/4" heater hose barb fitting. This was about the only fitting I could find that goes from 3/4" NPT to a heater hose barb. You can get a similar fitting much more easily in brass, but don't, because it is probably not actually the right kind of barb to use with a heater hose, and you risk galvanic corrosion with a brass fitting again.[/font]

[font=Montserrat, sans-serif][size=small][font=Montserrat, sans-serif]2x [/font]https://www.ebay.com/itm/223774957452[/size][/font]

[font=Montserrat, sans-serif]3/4" cast aluminum heater hose tee fitting. You will use these to tee into your cooling system. You may need a different fitting if the lines going to your heater core are not 3/4" inner diameter. You can find similar fittings to these at any auto parts store in plastic, but I really wanted these in cast aluminum since these are in a very hard to change spot in my build, and they are near the exhaust, so I don't trust plastic to hold up in the long term.[/font]

[font=Montserrat, sans-serif]1x https://www.amazon.com/gp/product/B0016IDG6A/[/SIZE][/font]

[font=Montserrat, sans-serif]ACDelco auxiliary electric coolant pump. My build has very long runs of coolant hose from where it tees into the rest of the system to the heat exchanger, so I wanted a helper pump to ensure I would get good flow through the heat exchanger. Having this in the system also means that your engine does not have to be running, it just needs to be hot, for you to get hot water, since this pump can circulate coolant through the exchanger even with the engine off.[/font]

[font=Montserrat, sans-serif]1x http://amazon.com/gp/product/B000C9VW9M/

Plug to fit the coolant pump. A little pricey just for one connector, and you could probably get by without this if you solder wires directly to the pins on the pump.[/font]

[font=Montserrat, sans-serif]1x https://www.amazon.com/gp/product/B06W9JXLV7/[/SIZE][/font]

[font=Montserrat, sans-serif]Electric coolant shutoff valve. This will allow you to shut off coolant flow through the heat exchanger when you are not using the hot water system. Be aware that I ordered one of these off of ebay and it was bad right out of the box. So be careful. When 12V is applied to this, it should shut off ALL flow through it. You can check this by blowing through the valve. With 12V applied, you should not be able to blow through this at all. The bad one I got still allowed flow. I think the solenoid was stuck.[/font]

[font=Montserrat, sans-serif]1x https://www.amazon.com/gp/product/B071RRGD66/[/SIZE][/font]

[font=Montserrat, sans-serif]Plug to fit the shutoff valve. Again probably not 100% needed, but nice to have to make life easier.[/font]

[font=Montserrat, sans-serif]1x https://www.ebay.com/itm/294209467155[/SIZE][/font]

[font=Montserrat, sans-serif]50ft of Gates 28442 Green Stripe heater hose. This is some pretty pricey heater hose, and you could get by with cheaper stuff, and you might need less of it depending on your build. But since I'm running hoses the whole length of my vehicle, and under the vehicle where they are especially vulnerable, I wanted to use good heater hose.[/font]

[font=Montserrat, sans-serif]1x https://www.amazon.com/gp/product/B00OA3XJOW/[/SIZE][/font]

[font=Montserrat, sans-serif]Maybe not 100% needed, but this is nice tough hose protection sheathing that will fit around the Gates heater hose to protect it from abrasion in certain spots where it might be prone to it. You might need a different diameter of this if you go with another heater hose that is not as heavy duty as the Gates Green Stripe.[/font]

[font=Montserrat, sans-serif]Ok, that's most of the mechanical parts aside from some odds and ends like hose clamps. I'm tired, I'll cover the electrical control side of it later.[/font]

 

[eDJ_]

Interesting.  The things you can do when you know of materials to work with. 

I had posted a baseboard hydronic heating system that used a small tankless propane heater for the heating source.  This was a few years back.   I was using an early Toyota Prius electric water pump similar to what you cited to circulate the water/RV non toxic antifreeze solution thru it.  The pump would create enough flow to trigger the ignition of the heater.  The control would be a mechanical thermostat and a main power toggle switch. I used a  Bosch type relay in the control system with the thermotat's signal.  There was also a small expansion tank built into the system too. 

Years ago I had considered this system with an electric water pump that was being marketed to have heat from the coolant in the engine but I haven't been able to find that pump since.  It was a linear action piston connected at one end to a diaphragm in a housing with check valves to circulate in one direction. It would rely on the residual heat of the cast iron motor block to deliver the engine's heated coolant to the heater core for a longer duration while the motor was not running.  Then the driver would have to start the motor (which would cut the electric  pump out of the circuit) and the motor's mechanical pump would resume with the pumping.  In theory the motor would only have to start and run a few minutes two or three times an hour. 

I had not considered heating potable water with the design.  But with the addition of the "Plate" exchanger that could be a aggregated into the system.  In warmer weather the baseboard hydronic system zone could be closed off allowing the plate exchanger to heat potable water via the tankless heater. (which would be heating a solution of RV antifreeze mixed with distilled water.

Just a thought.

In this system I would have Co2 detectors used with fresh air venting into rig.  I had initially thought of
the system using the linear pump with controls to start and stop the motor thru the night to provide heat
to provide a 60 Degree F sleeping environment and 68 to 70+ for the day time.

 

[eDJ_]

This is an early sketch layout of the heating system I described above.  Whether it be a warm floor zone like shown or using a baseboard system along the left side of the Van. 

[img=330x210]http://djsaan.homestead.com/Van_Floor_Heating.jpg[/img]

The underside of the floor would have to be insulated in this design where with the baseboard hydronic (double over/under row would not require that.  But still the floor would need some kind of cover to be comfortable for bare feet.

This is only one half of the problem.  The other half is finding a way to Air Condition a rig by using Solar.

 

[Weight]

Never use plastic fittings on automotive cooling system. I found out the hard way. Remember the coolant temperature is in the 220F range and under pressure.

 

[JT646]

Some good information here (VE, eDJ and Weight). If this could be used for hydronic (floor) heating it opens up a possible option to heat a van--or at least a secondary/backup option. Heating up an insulated mass (van floor and anything attached to it) would be a smart way to go--no gases to vent...and the heat would not be quickly lost--as it is in a 'heated air'/ventilation type system. Not for everyone, but I would consider it if someone comes up with a good plan & parts list.

 

[Vannautical engineer]

Never use plastic fittings on automotive cooling system. I found out the hard way. Remember the coolant temperature is in the 220F range and under pressure.

Well, I found at least one plastic fitting from the factory when I was tearing into my cooling system to re-route the flow. Would it have been better to use aluminum? Sure. But there are definitely plastics that can handle the heat and pressure of a cooling system. Very many parts of any factory cooling system are plastic. They might not have the longevity of aluminum over years and years, but they will work.



Anyway, sorry I have not updated this with more parts and explanations. It's summer, the weather is nice, and I'm focused on other things.

As a quick summary, The way I control this system is I have a temperature sensor on the fresh water flow coming out of the heat exchanger. This sensor input is fed into an Arduino which can control relays that turn the coolant circulation pump and the coolant shutoff valve on and off. I also wired a potentiometer into the Arduino so I can adjust the desired temperature of my fresh water. Essentially, whenever the temp of the fresh water coming out of the heat exchanger meets my desired set point, the Arduino shuts off the coolant circulation pump and closes the shutoff valve. Whenever the fresh water temp drops below the set point, it opens the shutoff valve and turns on the pump, thereby circulating coolant and adding more heat into the water.

My biggest challenge right now is the system tends to see-saw back and forth between too hot and too cold. I have my temperature sensor for the fresh water coming out of the heat exchanger as close to the outlet of it as I can reasonably have it, but it's still several inches away. So the Arduino that controls it gets a little bit of a delayed feedback as to what the water temp actually is. So it's always kind of chasing its tail trying to keep the water at the proper temp. I need to figure out some logic I can program into the Arduino to help this. Instead of looking at the absolute temp of the water at any given moment, I need to program in some logic that will look at whether the water temp is rising or falling so it can better anticipate if the coolant needs to be circulating or not.

 

[Firebat45]

My biggest challenge right now is the system tends to see-saw back and forth between too hot and too cold. I have my temperature sensor for the fresh water coming out of the heat exchanger as close to the outlet of it as I can reasonably have it, but it's still several inches away. So the Arduino that controls it gets a little bit of a delayed feedback as to what the water temp actually is. So it's always kind of chasing its tail trying to keep the water at the proper temp. I need to figure out some logic I can program into the Arduino to help this. Instead of looking at the absolute temp of the water at any given moment, I need to program in some logic that will look at whether the water temp is rising or falling so it can better anticipate if the coolant needs to be circulating or not.

It sounds like you could benefit from using the PID library instead of just "bang-bang" control.  By tweaking the individual values you should be able to minimize oscillating.

Yeah, there is tons of plastic in automotive cooling.  Almost every modern radiator uses plastic end tanks and inlets.  You just need to make sure the plastic you use is rated for the heat.

I am very interested in seeing more of this project, I am planning an integrated hot water/hydronic system for my next build.

 

[Weight]

One edit and Some things to caution. Be sure the plastic fittings are compatible with the temperature of your engine coolant. Don't use the clean hot water for cooking or drinking if you are not sure all the components are lead free. That includes brass, solder and braising, or galvanized fittings. Be sure you can valve off the engine coolant in an emergency.

 

[Vannautical engineer]

It sounds like you could benefit from using the PID library instead of just "bang-bang" control.  By tweaking the individual values you should be able to minimize oscillating.

Yeah, there is tons of plastic in automotive cooling.  Almost every modern radiator uses plastic end tanks and inlets.  You just need to make sure the plastic you use is rated for the heat.

I am very interested in seeing more of this project, I am planning an integrated hot water/hydronic system for my next build.

I had no idea the PID library for Arduino existed. I might have to play around with that. I'm not sure if it will work for me or not. My output to control the temperature is just on/off (the coolant circulation pump, and it can't be run at variable speeds.) I'm not sure if the PID library needs to have a variable output to function or not.

However, after using this system in the real world, I'm not sure this is actually that much of a problem after all. When I was testing the system, I was just running the water at full bore with the faucet wide open for many seconds if not minutes at a time. And true in that circumstance the temperature see-sawed. But, when I actually used the system in real life, conserving water when taking a shower, I was not flowing enough water to have this problem with see-sawing.

So, fixing this issue is not really a high priority any more because it only really becomes a problem when using a lot of water at once, which doesn't really happen when you are actually living in a van and conserving the limited water you have.

Very little of my water system is plastic aside from the pex tubing, which I have found online can take pretty high temperatures, especially if you're not running a very high pressure. My water storage tank is plastic, but that is not really coming in contact with water after it's been heated, except when I recirculate water back into it while I'm waiting for my water flow to warm up. And even then it is mixing back with a lot of room temp water in the tank.

I have not forgotten this thread and I will update it with more info later, I've just been busy lately.  :thumbsup:

 

[Vannautical engineer]

Ok I have slacked off long enough on this. I will start trying to flesh this out with more info. I just made a (very bad) drawing of the basic flow through the system. I have tapped into my coolant lines going to and from my engine heater core. You want the heat exchanger to be in parallel to your heater core. You will need to consult a service manual to figure out how your coolant flows through your heater core. The reason for this is that the heater core is the first thing to get hot coolant flowing through it, even before the engine thermostat opens up, so it's the ideal place to tap into.

The flow through the heat exchanger is regulated by two things, the electric coolant pump to pump coolant through the heat exchanger when needed, and a shutoff valve to clamp off flow through the heat exchanger when not needed. Unfortunately most electric coolant pumps seem to not stop flow when they aren't running, so you need a shutoff valve to totally clamp off the flow when you aren't using the system. Otherwise your engine's own water pump will push some coolant flow through the heat exchanger when the engine is running, which isn't really ideal because your heat exchanger will get hot even when you don't want hot water.

The temperature of the hot water is controlled by allowing coolant to flow through the heat exchanger as needed by opening the shutoff valve and/or running the electric cooling pump as needed. There is a temp sensor close to the fresh water outlet from the heat exchanger. An arduino is used to monitor the water temp coming out of the heat exchanger and based on that, trigger the electric coolant pump and shutoff valve to operate as needed to maintain the desired water temp. I'll go into that more later.

I also added a recirculation line back to my water tank that's on a switchable valve. By using this, you can recirculate water back into your tank while you wait for the hot water to reach your faucet or shower head, instead of just wasting that water by running it out of your faucet. Nice to have, but not 100% needed.

Edit: I just noticed that in this very crude diagram I drew up, the flow of fresh water through the heat exchanger is backwards from how it ideally should be. You don't want cold water from the water tank to enter into the same side of the heat exchanger as the hottest coolant from the engine. It reduces thermal stress on the heat exchanger if the cold water from the tank enters the heat exchanger on the side where the somewhat cooler coolant exits the heat exchanger on its way back to the engine.

 

[Weight]

You need two shutoff valves at the engine end of both coolant lines. You could have the one valve in the cab to adjust the hot flow. You need a circulation water pump on the potable water side. If you tap into the proper location on the engine you don't need a pump on the coolant side. Think about how the water circulates through the heater core. That will continue through your system with the pump off or on.
I had an extreme hot water source. I used a standard plumbing supply mix valve that blended the potable hot water with cold water to automatically serve comfortable water at the faucet.

 

[Vannautical engineer]

[font=Tahoma, Verdana, Arial, sans-serif]"[size=small]You need two shutoff valves at the engine end of both coolant lines."[/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif]No, I don't need two shutoff valves. I have been happily using this system for months now. Just having one shutoff valve prevents flow through the heat exchanger to the point that it stays cool when I don't want hot water, even when the engine is running. While it's true that if you had two shutoff valves, you could completely close off coolant flow through the heat exchanger loop in the event that it leaked, I decided not to do this, mainly because where the heat exchanger loop taps back into the cooling system is in a very hard to reach place. In addition, since the shutoff valve I'm using is electric, you need to keep it energized at all times to clamp off flow. If you had two of them, and wanted to keep your coolant from leaking out in the event of a leak in the heat exchanger loop, you would need to hold both shutoff valves energized continuously until you fixed the leak. Not very practical.[/font]

[font=Tahoma, Verdana, Arial, sans-serif]"[size=small]You could have the one valve in the cab to adjust the hot flow."[/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small]I did not want to bring hot pressurized coolant into the cab. That is a huge pain, and now if you have a leak, it's inside your vehicle. And yes the heater core is inside the cab in every car, but there's no way around this. And besides, the way this system operates, I'm not manually adjusting the flow of anything. I just set my desired water temp, switch the system on, and that's it. I'll go into the controls more later.[/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif]"[size=small]You need a circulation water pump on the potable water side."[/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small]I left a lot of the components out of that diagram I drew. Obviously I have a fresh water pump. No water is moving anywhere without that. That was not meant to be a diagram of my entire water system, just the parts relevant to how I heat water. I figure that if anyone is going to reference this and attempt a project this involved, they're already well aware that they need a fresh water pump.[/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small]"[size=small]If you tap into the proper location on the engine you don't need a pump on the coolant side. Think about how the water circulates through the heater core. That will continue through your system with the pump off or on."[/size][/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small][size=small]The system is intended to be able to function with the engine running or not. The idea is that to get hot water, the engine only needs to be hot, not necessarily running. That's why I use an electric coolant pump. There is a lot of heat energy still in the engine block and the coolant after the engine has been running for a while and shut off. Indeed there have been times where I have still gotten hot water from the system about an hour after I last ran the engine.[/size][/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small][size=small]"[size=small]I had an extreme hot water source. I used a standard plumbing supply mix valve that blended the potable hot water with cold water to automatically serve comfortable water at the faucet."[/size][/size][/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small][size=small][size=small]Yeah this would probably work too. I wasn't aware of these valves when I made the system. You could probably figure out a system that regulates the water temp with a valve like this instead of the way I did it. But the way I did it works too, so I'm happy with it.[/size][/size][/font][/size]

[font=Tahoma, Verdana, Arial, sans-serif][size=small][font=Tahoma, Verdana, Arial, sans-serif]While I appreciate your input, I'm not really seeking out any input because this system is already completed and in use, and it works well. I'm writing this for anyone who wants to attempt a similar system. [/font][/font][/size]

 

[Weight]

You can end very sorry if you do not have manual valves on both connections at the engine. Otherwise, do what you want. It is always better to over complicate a simple system. :|

 

[Vannautical engineer]

Ok now here is an explanation of how I run the control system for this. I decided that I don't think it's worth going to the effort of explaining each and every little connection. If someone wants to replicate this system, you should probably be familiar with basic electrical and electronics already. And if you aren't, and you really want to put together a system like this, I'm open to help, but I don't want to write a really exhaustive writeup unless someone will actually need it.

I am running an Arduino with a relay shield on it, which allows it to control the electric coolant pump and the shutoff valve based on the inputs it gets from the fresh water temperature sensor and a potentiometer that you can use to vary the desired temperature of the hot water. An Arduino works well for this because it's basic, cheap, easy to program, and happily runs on 12VDC.

Here is the basic layout of how the system works. I have the power to everything including the Arduino on a switch, so that whenever you are not using the hot water system, everything is completely off and does not draw any power out of your battery.

When the system turns on, the Arduino looks at the temperature of the water at the exit of the heat exchanger. If it's colder than the set point you want for your hot water, it opens the shutoff valve and runs the electric coolant pump. If it exceeds the set point, it shuts off the electric coolant pump and closes the shutoff valve. I can post the code I wrote to do this if anyone wants it.

It should be noted that the power going to the shutoff valve is switched power that is only energized when the key is on. The whole point of the shutoff valve is to not allow any flow through the heat exchanger when the engine is running. If the shutoff was not there, you would get a little flow through the heat exchanger any time the engine is running just from the force of the engine's water pump. Since there is no reason to operate the shutoff valve when the engine is not running, (there is no flow through the heat exchanger when the engine is off unless you create flow with the electric pump) it's ideal to just wire the shutoff valve to ignition switched power, so it only operates when it needs to.



Enclosure box which fits the Arduino with the relay shield on it

https://www.amazon.com/gp/product/B089K9ZSBC/

Relay shield. You can also skip this and wire your own relays to the Arduino, but at $30 I think it was worth it to avoid a ton more wiring.

https://www.amazon.com/gp/product/B010N8A5PI/

10K potentiometers

https://www.amazon.com/WGCD-Knurled-Linear-Rotary-Potentiometer/dp/B06WWQP12J/

Temperature sensors. It should be noted that these little guys are TINY but they work.

https://www.amazon.com/gp/product/B07XF13HKZ/

A thermowell fitting. This is a fancy name for a 1/2" plumbing fitting that just has a little dead end hole going through it. You can shove the temp sensor down in this hole and it will be right in the flow of your water, giving it a nice accurate temp reading.

https://www.amazon.com/gp/product/B00GD9EQFM/

 

[tx2sturgis]

I would estimate I put about $400 into the components of the system, but the real killer was the labor. Between running coolant lines the whole length of the van, mounting the heat exchanger underneath the van, and wiring all of the electronic controls for the system, I probably have at least 100 hours of work into the system.

I respect the DIY approach to this, but I think I would have just spent the $400 (plus a bit more) on a Suburban Motor-Aid water heater.

Here's one:

https://www.airxcel.com/rv/suburban/water-heaters/direct-spark-ignition/motor-aided-spark-ignition

 

[Weight]

If one of the coolant lines develop a leak, lets say a large leak, how do you stop the coolant from escaping the engine?

 

[Vannautical engineer]

I respect the DIY approach to this, but I think I would have just spent the $400 (plus a bit more) on a Suburban Motor-Aid water heater.

Here's one:

https://www.airxcel.com/rv/suburban/water-heaters/direct-spark-ignition/motor-aided-spark-ignition

I totally agree with you if you have the space to install one of these units. But being in a Transit Connect, I definitely did not. Even the smallest six gallon unit you linked to would have been one of the largest items I would have had to try to find a space for inside the van, not to mention carrying around propane if you want to use the gas heating functionality of those units. Just way too much stuff to try to fit into something as small as a Transit Connect. What I built takes up pretty much zero space in the interior. The heat exchanger is about the size of a brick, and is mounted underneath the van between the fuel tank and the spare tire.