Heat Exchanger (coolant) for Hot Water/Shower?

alexk243

alexk243

KulAdventure
Has anyone ever done a DIY install of a heat exchanger to heat their hot water? I remember working on a VW Rialta that had a heat exchanger built into the electric hot water heater (coolant to hot water tank), but I didnt like the idea of running coolant all the way back to the hot water tank, so was thinking about running water into the engine bay, however due to freezing risks may do it in reverse.

Was thinking about using a Heat Exchanger like these (or a different style like this).

Has anyone done this before? Would you have to run a separate electric water pump to circulate the water?
 
M

Midwestdrifter

Engineer In Residence
Yep, done it on other vehicles. Just put a plate exchanger in series with the cabin heater core. You can use the auxiliary electric pump powered by a secondary relay. Quick and simple, also cheap. You must use a thermostatic mixing valve to prevent scalding. With the engine running no extra pump is needed.
 
alexk243

alexk243

KulAdventure
Midwestdrifter said:
Yep, done it on other vehicles. Just put a plate exchanger in series with the cabin heater core. You can use the auxiliary electric pump powered by a secondary relay. Quick and simple, also cheap. You must use a thermostatic mixing valve to prevent scalding. With the engine running no extra pump is needed.
Click to expand...
If you put it inline with the heater core then don't you have to have the heat on to have the coolant flow through your exchange? or does coolant always flow through the cabin heater core?

With the engine running the coolant would cycle, but wouldn't you still want the hot water to cycle through the exchange back into its tank?
 
M

Midwestdrifter

Engineer In Residence
It depends if you want on demand only, or storage.

If you plumb it on the return from the heater control valve it will always have flow.
 
alexk243

alexk243

KulAdventure
Midwestdrifter said:
It depends if you want on demand only, or storage.

If you plumb it on the return from the heater control valve it will always have flow.
Click to expand...
Ah, yeah that makes sense.

Are these exchanges good enough to do it on demand? I assumed they would only heat the water slowly and therefore need tank to heat up.
 
M

Midwestdrifter

Engineer In Residence
Yeah, a 20 plate, or possibly 10 plate would do 2rpm on demand heating with good coolant flow. Engine must be warm. After a drive you have several hours before block cools, when you can take a "free" shower
 
owner

owner

Oz '03 316CDI LWB ex-Ambo Patient Transport
I have a 60 plate in mine in the location you have been discussing. For on demand I have to have it on high idle to keep good temp for a shower (Or I have have the Espar on if not running the engine).

I have the fresh hot water going into a 10l reservoir under the sink. Then a TMV to the shower. The sink I have at full temp and you need to be careful not to scald yourself. I have been meaning to rig up a one way valve circuit and pump so that I can recycle the 10l reservoir back into the HE continuously. That would give me 10l of piping hot water every time I stop the van.

At the moment I have an auxiliary tap which flows back into the main fresh water tank. So I can siphon off the 10l of cold water in the reservoir and replace it with hot water from the HE, but there is some mixing so its not as hot and I often forget to do it before we stop..
 
G

Graphite Dave

Dave Orton
Using the engine hot water works but I think heating electrically has some advantages.

1. The alternator produces power to heat immediately with engine start. Water has time delay.

2. Installation of power cord is easier than water hose plumbing. Small diameter flexible electrical cords easier to route compared to water hoses/piping.

3. The electrical cords can not leak water inside the van.

4. A thermostat can turn off the electric heating at the shower temperature you prefer. Engine water too hot to shower so hot/cold water mixing is required.

5. No plumbing required for electrical. Just use a submersible 12 volt DC pump that pumps into a garden hose and nozzle with on/off switch.

6. Electrical cords do not freeze.

7. Electrical heating can use shore power when available if 120 volt AC heating element.

Heating element can be either 12 volt DC or 120 volt AC. 12 volt eliminates the use of shore power but is more efficient and eliminates the need for a inverter. 120 volt AC heating element requires an inverter so part of energy is wasted due to inverter efficiency.

In my case I have a 120 volt AC heating element and an existing vehicle powered inverter. Can use shore power, "shore power" from the vehicle powered inverter or if weather conditions permit I can use 120 volt power from the house inverter/battery. Heating element has a cord that can be plugged into shore or house inverter/battery power.

Using the house inverter/battery uses 9% of the 255 amp-hr battery capacity to heat 70 degree water to 93 degrees in 45 minutes with a 625 watt heating element. Obviously the run time required depends on the water beginning temperature and the desired shower water temperature.
 
Last edited:
alexk243

alexk243

KulAdventure
Graphite Dave said:
Using the engine hot water works but I think heating electrically has some advantages.

1. The alternator produces power to heat immediately with engine start. Water has time delay.

2. Installation of power cord is easier than water hose plumbing. Small diameter flexible electrical cords easier to route compared to water hoses/piping.

3. The electrical cords can not leak water inside the van.

4. A thermostat can turn off the electric heating at the shower temperature you prefer. Engine water too hot to shower so hot/cold water mixing is required.

5. No plumbing required for electrical. Just use a submersible 12 volt DC pump that pumps into a garden hose and nozzle with on/off switch.

6. Electrical cords do not freeze.

7. Electrical heating can use shore power when available if 120 volt AC heating element.

Heating element can be either 12 volt DC or 120 volt AC. 12 volt eliminates the use of shore power but is more efficient and eliminates the need for a inverter. 120 volt AC heating element requires an inverter so part of energy is wasted due to inverter efficiency.

In my case I have a 120 volt AC heating element and an existing vehicle powered inverter. Can use shore power, "shore power" from the vehicle powered inverter or if weather conditions permit I can use 120 volt power from the house inverter/battery. Heating element has a cord that can be plugged into shore or house inverter/battery power.

Using the house inverter/battery uses 9% of the 255 amp-hr battery capacity to heat 70 degree water to 93 degrees in 45 minutes with a 625 watt heating element. Obviously the run time required depends on the water beginning temperature and the desired shower water temperature.
Click to expand...
I do like this idea better and agree with you that electrical is easier to run than plumbing and since I am running solar the "free" aspect of the energy is similar.

My concern however is how to install a 12v heating element into a tank. Right now I have a 20 gallon fresh water tank, I would like it to be heated to 90 degrees or so and keep it there so I don't have to mix it, I have not figured out a way to make that work safely. I worry about putting a heating element into a tank like this 20 gallon fresh tank that I am using.

Do you have a write up/information on what element you used and how you temperature controlled the heating element? I would have to stick with DC power as I have decided to avoid an expensive inverter, but do have the solar and battery capacity to support a DC heating element.
 
J

john61ct

Active member
Heating water from solar PV is usually impractical, most all heat production, very inefficient.

Maybe to take advantage of "free excess" power one the batteries are nearing Fully charged.

Alternator output is much higher current.

But actually heating the water takes a fair bit of time regardless.

For solar, better to just use a black shower bag or PVC pipe to get the sun to heat the water directly.
 
avanti

avanti

2022 Ford Transit 3500
john61ct said:
For solar, better to just use a black shower bag or PVC pipe to get the sun to heat the water directly.
Click to expand...
There exist many solar water heating panels. Popular in the Southwest for heating DHW and pools. No reason you couldn't put one on your van.
 
G

Graphite Dave

Dave Orton
alexk243 said:
I do like this idea better and agree with you that electrical is easier to run than plumbing and since I am running solar the "free" aspect of the energy is similar.

My concern however is how to install a 12v heating element into a tank. Right now I have a 20 gallon fresh water tank, I would like it to be heated to 90 degrees or so and keep it there so I don't have to mix it, I have not figured out a way to make that work safely. I worry about putting a heating element into a tank like this 20 gallon fresh tank that I am using.

Do you have a write up/information on what element you used and how you temperature controlled the heating element? I would have to stick with DC power as I have decided to avoid an expensive inverter, but do have the solar and battery capacity to support a DC heating element.
Click to expand...
Info on my shower water heater:

https://sprinter-source.com/forum/showpost.php?p=654456&postcount=150

More info:

https://sprinter-source.com/forum/showpost.php?p=662130&postcount=1

120 volt AC heating element I used:

https://www.pplmotorhomes.com/parts...ter-repair-parts/lightning-rod-10-gal_49-1756

Had SS tank fabricated for the shower water tank. Tank is also the support pedestal for the portapotti to use that wasted space. I have a 1000 watt vehicle powered inverter that is used for shore power charging or shower water heating or air heating with a baseboard heater in back.

Do know 12 volt heating elements are available.
 
alexk243

alexk243

KulAdventure
Oh yeah, I've read your post before. Good write up. My concern was that I am not using a SS tank and wasn't sure it was possible without creating a sperate tank specifically for hot water. Not sure the plastic tanks can withstand a heater element in them...

Sent from my Nexus 5 using Tapatalk
 
G

Graphite Dave

Dave Orton
john61ct said:
Heating water from solar PV is usually impractical, most all heat production, very inefficient.

Maybe to take advantage of "free excess" power one the batteries are nearing Fully charged.

Alternator output is much higher current.

But actually heating the water takes a fair bit of time regardless.

For solar, better to just use a black shower bag or PVC pipe to get the sun to heat the water directly.
Click to expand...
My recent tests with my system show that heating shower water with excess power available from my 300 watt panel on full sun days works. Use house inverter/battery. The water heating uses about 9% of the 255 amp-hr house battery capacity. Heated the 5 gallons of 70 degree water to 93 degrees in about 45 minutes. If heating done in morning I was back to 100% SOC in the afternoon.

As a backup when weather conditions force its use, I can run the engine to power my vehicle powered inverter to provide the power to heat the water. I can also use shore power if it is available.
 
G

Graphite Dave

Dave Orton
alexk243 said:
My concern was that I am not using a SS tank and wasn't sure it was possible without creating a sperate tank specifically for hot water. Not sure the plastic tanks can withstand a heater element in them...
Click to expand...
I had thought about heating my fresh water tank to warm the interior of the sold Sprinter. Decided that might create a nice environment for mold production so did not pursue that idea.

A separate tank for heating shower water makes sense. Do not know if a plastic tank would work. In sold Sprinter I used a 5 gallon SS beer keg. It actually heated water faster than my custom SS tank in the Transit. Think the tall form factor and the heating element location made it heat faster. My uninsulated Transit tank also has some contact with the 80/20 structure which dissipates some of the heat. New tank has 625 watt heating element and Sprinter had a 450 watt heating element. Both take about 45 minutes to heat the water. I did gain space in Transit by utilizing the wasted space under the portapotti.
 
alexk243

alexk243

KulAdventure
In case anyone else is researching this the method I went with (for now), is a 12v heater coil. Its much slower than a 120v heater coil, but can run off my batteries and use excess solar. I temperature controlled it to 90 degrees also. The write up for the install and setup with pictures is here.

I had a test run with it last weekend and it worked great, but did take a considerable time to heat up the water (3-5 hours), so really only works if you are plugged in or driving (which works for me).


 
G

Graphite Dave

Dave Orton
alexk243 said:
In case anyone else is researching this the method I went with (for now), is a 12v heater coil. Its much slower than a 120v heater coil, but can run off my batteries and use excess solar. I temperature controlled it to 90 degrees also.
Click to expand...
Are you concerned about mold in a fresh water tank that is kept warm? I had couplings installed in my sold Sprinter fresh water tank but chickened out using them to heat the water.

Maybe someone on this site has some experience with a heated fresh water tank.
 
alexk243

alexk243

KulAdventure
Graphite Dave said:
Are you concerned about mold in a fresh water tank that is kept warm? I had couplings installed in my sold Sprinter fresh water tank but chickened out using them to heat the water.

Maybe someone on this site has some experience with a heated fresh water tank.
Click to expand...
I am, absolutely. I discussed filtering the water in another thread and that brought up the idea of keeping a mix of clorine bleach in the tank and filtered out with a charcoal filter. I would hope that the bleach would keep the mold at bay.
 
M

Midwestdrifter

Engineer In Residence
Yep, chlorine/bleach at low levels wills stop microbial growth (it does in domestic water systems). You can shock the system occasionally if needed. The reality is that without organic chemicals for food, you won't see much growth.

Another option is to periodically heat the tank to 161F for 30 seconds, or 145F for 30 minutes. This will kill any microbes in the tank.

My vans hot water tank is hot 75% of the time. I occasionally let it get to 170F+, which has prevented any issues. In addition I often use city water, which has residual chlorine (1-3ppm usually), which makes a difference as well.
 
alexk243

alexk243

KulAdventure
Midwestdrifter said:
Yep, chlorine/bleach at low levels wills stop microbial growth (it does in domestic water systems). You can shock the system occasionally if needed. The reality is that without organic chemicals for food, you won't see much growth.

Another option is to periodically heat the tank to 161F for 30 seconds, or 145F for 30 minutes. This will kill any microbes in the tank.

My vans hot water tank is hot 75% of the time. I occasionally let it get to 170F+, which has prevented any issues. In addition I often use city water, which has residual chlorine (1-3ppm usually), which makes a difference as well.
Click to expand...
It would take me 5 hours to get to 161/170 and I'm not sure I trust the tank and fittings at that temperature. I typically use city water also, but I plan to add more bleach to the tank while traveling.
 
You must log in or register to reply here.

Top Bottom