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Old 09-24-2015, 05:19 PM   #1
Inertiaman
 
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Default Proposal for shower/hot-water reservoir heated by Espar D2

In another thread about Webasto products, GeorgeRa introduced the idea of using the D2 hot air outlet + a heat exchanger to function as a hot water heater. That tangent began w/ post #16 on this thread:
http://www.sprinter-source.com/forum...t=42263&page=2

I think the idea has sufficient merit to create a new thread specifically for this idea. The back story is in posts 16 - 23 of the thread above, but here is the basic concept:

Direct D2 output flow across a small heat exchanger. Flow water from a small reservoir through the exchanger to warm it for showers, etc. There would be no "coolant" loop; the goal is direct heating of water for personal use.

Two examples of small heat exchangers (credit to GeorgeRa):
HydroInnovation
DemonTweeks

With sufficient heat and airflow from the D2, water could be heated more than sufficiently for showers/etc. A variety of implementations would be possible, from permanently plumbed ones to portable ones. There are a couple flow diagram example from GeorgeRa in the other thread.

Here is a one approach I'd like some feedback on:

A modular water heater / warm water reservoir system heated by D2 output.

For a reservoir, use a 2.5 or 5 gallon military water can from Lexington which are very robust. The lids have multiple fittings and space to add more. You can also purchase extra lids (which we'll need for DIY mods). Use an inexpensive submersible pump, dropped into the water can, for water flow. On the lid, drill a hole and create a fitting which would have a flexible hose going to the submersible pump on the "inside" and a two way diverter valve on the outside. One valve output would go to the heat exchanger, through its matrix, and return to the water can through the lid (either the stock pour fitting which is threaded, or another DIY hole/fitting). The second valve output would go to a shower wand, or to a quick connect fitting that could snap to a sink, etc.

Note that all of the water can connections are at the lid, so that lid can be moved to other/identical water cans. So as you deplete one water can, you can rotate in a full one, and avoid any water transfer from one reservoir to another. Each water can still has its own original lid on a retainer, so there are never cans without lids.

To provide hot air to the heat exchanger, you would need to build a small enclosure and a means of attaching an inlet duct which can attach to the D2 outlet. Many approaches are feasible, but I'll focus on a common scenario: the D2 is already mounted under the seat, with the outlet at the rear of the seat pedestal. So your heat exhanger "box" would have a short flexible duct with an oversized grommet or flange on the end, it could attach to the D2 outlet by tension (silicone rubber?) or maybe magnets to the seat pedestal.

To operate, turn on your D2 and turn on the submersible pump, with the valve set to the heat exchanger side. System begins heating. Water constantly re-flows through the exchanger and gets warmer with time. Run the heater until the water is at your desired temp.

Based on some calculations from George, getting water from 68F to 104F requires about 2.5 min per gallon, but this is a parameter which could vary widely by flow rate, D2 settings, ambient temps, exchanger size, etc and needs some real world testing. Suffice to say that the heating rate is in the realm of useful.

In the winter, the air output of the heat exchanger could be fed directly into the cabin space. In summer, you'd want to direct the air flow out of the exchanger to the outside.

When you get your 2.5 gallon can to 100F, you turn off the D2 and the pump. Turn the valve on the lid from the heat exchanger direction to the shower wand direction. Turn the pump back on, and use the shower. Voila!

LOTS of options to improve/change the concept. One could permanently install much of the system, with a diverter on the D2 output to divert to the exchanger or normal flow to the cabin. You could install a semi-permanent water reservoir with insulation around it, which could easily maintain decent water temps for many hours. You could use siimple thermal sensors/switches to switch the D2 off at a given temp, or (very easy) provide an audible alarm at a target temp.


This isn't a direct substitute for genuine hot water systems like a D5 and an Isotemp, and it has limitations. The exchanger needs to be proximate to the D2, the efficiency likely isn't super high if you are "wasting" the exchanger air output (summer scenario), etc. It lends itself well to manual operation, though an automated permanent install would add considerable complexity. But there doesn't seem to be major obstacles or risks. Even running open loop without attention, I doubt the water would ever approach temps that would require concern (like boiling/pressure/etc).

For some of us, this could open up a world of possibilities to provide decently warm water, decently quick, without a big investment in cabin space, $$, large new components or complexity.

My personal use case suggests a "portable" scenario:

I would have the heat exchanger enclosure and associated duct on one small "chassis", independent of the reservoir. The water connections would quick-disconnect from the water can lid. When disconnected, connect the inlet/outlet hoses together so the exchanger chassis can retain the water in its system without leaking during storage. The pump would be permanently integrated with a lid, with a 12V cord to a common cig lighter plug.

In use, place the water can on the slider door step close to the D2 vent, connect the lid & exchanger, run the system to temp while doing other things, turn it off. Disconnect the exchanger from lid. Unplug the 12V, move the water can to the rear of the van, plug in 12V there, and shower. One could easily adapt a small lithium backup battery to run the pump, and be able to shower away from the van at campsites. Or use a battery powered submersible shower wand like THIS The heat exchanger and associated duct / tubing could store in a relatively small box/container and only be used when needed. The specific water can lid/pump could be stored in the same box.

Last edited by Inertiaman; 09-24-2015 at 05:27 PM.
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Old 09-24-2015, 05:43 PM   #2
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

D2 (or any Espar Airtronic) is sensitive to restricted air flow.


The slower combination blower/intake air will produce a richer fuel/air mix that will cause 1) the internal temp sensor to fault and shut the unit down and 2) carbon buildup fouling.



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Old 09-24-2015, 06:05 PM   #3
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

I'm all for exploring out of the box ideas, but in this case, I think an Espar D5 (hydronic) and a water-to-air heat exchanger makes a lot more sense. I'm no expert, but my intuition is that it is easier to heat air from water than it is to heat water from air.
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Old 09-24-2015, 06:53 PM   #4
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

Quote:
Originally Posted by OrioN View Post
D2 (or any Espar Airtronic) is sensitive to restricted air flow.

The slower combination blower/intake air will produce a richer fuel/air mix that will cause 1) the internal temp sensor to fault and shut the unit down and 2) carbon buildup fouling.
.
I understand the D2 has this sensitivity, and I think this is the crux issue re: the viability of the idea. Its not clear to me how much air resistance is created by these exchangers, and if it is sufficient to trip the D2. Is 6" of duct and a heat exchanger more resistance than 10' of ducting and two 90 deg elbows?

Also, some of the exchangers (the Demon one above is an example) include a fan which would provide additional airflow. Or one could include a fan in the enclosure for the Hydro Innovations exchanger. Will that trip the D2 for the opposite reason (too much airflow)? Not sure. Presumably there is a fan speed on an exchanger which, combined with the resistance of the exchanger, would appear neutral to the D2. If you delay attachment of the exchanger ducting until the D2 is up and running hot and fan on high, and the exchanger fan is already running, it could minimize apparent changes to the D2.

I'm not saying it will work, or that getting it to work won't reach a level of complexity that makes it not worthwhile. But I'm not (yet) convinced it isn't worth exploring.
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Old 09-24-2015, 07:03 PM   #5
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

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Originally Posted by Inertiaman View Post
I understand the D2 has this sensitivity, and I think this is the crux issue re: the viability of the idea. Its not clear to me how much air resistance is created by these exchangers, and if it is sufficient to trip the D2. Is 6" of duct and a heat exchanger more resistance than 10' of ducting and two 90 deg elbows?

Also, some of the exchangers (the Demon one above is an example) include a fan which would provide additional airflow. Or one could include a fan in the enclosure for the Hydro Innovations exchanger. Will that trip the D2 for the opposite reason (too much airflow)? Not sure. Presumably there is a fan speed on an exchanger which, combined with the resistance of the exchanger, would appear neutral to the D2. If you delay attachment of the exchanger ducting until the D2 is up and running hot and fan on high, and the exchanger fan is already running, it could minimize apparent changes to the D2.

I'm not saying it will work, or that getting it to work won't reach a level of complexity that makes it not worthwhile. But I'm not (yet) convinced it isn't worth exploring.
Espar has a 'workbook' with coefficients for fitting and duct sizes to use to keep the system in balance. The units/components you want to use would need to be tested for coefficients.

The exchanger with the fan will slow down the absorption of heat at a minimum. BUT most certainly will suck more air into the unit and speed up the Espars blower/combustion fans and that should result in mixture and/or electrical/induction issues.




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Old 09-24-2015, 07:05 PM   #6
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

Quote:
Originally Posted by avanti View Post
I'm all for exploring out of the box ideas, but in this case, I think an Espar D5 (hydronic) and a water-to-air heat exchanger makes a lot more sense. I'm no expert, but my intuition is that it is easier to heat air from water than it is to heat water from air.
This is by no means a D5 class solution. But that's comparing a $2000+ system to a $200 solution, among other differences. If it can work, it could be very useful to some demographics of van owners.

As to water vs air, its all heat transfer. Air is used to cool water in the engine. Using air to heat water isn't fundamentally different or less viable. As long as there is temperature delta, exchange surface area, and flow rate, it "works". How well it works as proposed is tbd. If it can heat 2 gallons of water from 60F to 100F in less than 30 minutes, I personally think its useful. GeorgeRa's calculation (admittedly simple and rife with assumptions) suggests the rate of transfer is much higher than that, so there is room for "worse but still sufficient."
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Old 09-24-2015, 07:08 PM   #7
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

I see. I didn't read much of the other thread. If this can be done for $200, then I agree it is interesting. Thanks.
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Old 09-24-2015, 07:14 PM   #8
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

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Originally Posted by OrioN View Post
Espar has a 'workbook' with coefficients for fitting and duct sizes to use to keep the system in balance. The units/components you want to use would need to be tested for coefficients.
Nice! Can you possibly point to this Espar material online? Perhaps there are coefficients available in specs for some exchangers that could be compared.

Surely the Espar has fan speed or other adaptations that help it work across a range, even if a narrow range. The coefficients you mention are probably the closest we'll get to a quantified definition of that range.

Would a Webasto present fewer challenges or more solutions (I'm thinking their manual reduction in fuel rate for high altitude)?
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Old 09-24-2015, 07:35 PM   #9
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

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Originally Posted by Inertiaman View Post
Nice! Can you possibly point to this Espar material online? Perhaps there are coefficients available in specs for some exchangers that could be compared.

Surely the Espar has fan speed or other adaptations that help it work across a range, even if a narrow range. The coefficients you mention are probably the closest we'll get to a quantified definition of that range.

Would a Webasto present fewer challenges or more solutions (I'm thinking their manual reduction in fuel rate for high altitude)?
Espar has locked down their site the last 2 years or so, so go here for the 'Parts List':

http://www.rixens.com/wp-content/upl...ts-Catalog.pdf

The last dozen or so pages has the info you need.


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Old 09-24-2015, 07:57 PM   #10
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Default Re: Proposal for shower/hot-water reservoir heated by Espar D2

Might be easier to just put an electric heating element in a container. All the energy would then be converted to heat instead of some used to run blower. Container could be insulated. There would also be less energy transferred to the surrounding area from the heat exchanger and duct work that could have gone into the water.

It would also be quieter.

The heating elements are available as a kit that includes a thermostat. The AC kits are designed to add electric heating capability to an RV Atwood or Suburban water heater. The RV can then use RV park power instead of the on board propane. One brand is "Lightning Rod" and is available as a 6 or 10 gallon kit. I paid $91.62 for the 10 gallon kit. 120 volt AC is required and the package says 6 gallon requires 4 amps and the 10 gallon requires 6 amps. I used the 6 gallon one on my sold Sprinter conversion and it took about 45 minutes to heat 5 gallons of water to 90 degrees. Did not measure the initial water temperature but it was probably between 60 and 70 degrees. The Sprinter had a 600 watt inverter powered by the Sprinter 12 volt system. The new Transit conversion will have a 1000 watt inverter to power the 10 gallon heating element so expect to cut time down to 30 minutes. With Transit I will not have to drive to get hot shower water because I can idle the gas engine.

While your proposed design would probably eventually work, the problem would be the time required to heat the water. As the water temperature rose the heat transfer would decrease. Any heat in the air left after you go through the heat exchanger would be lost. Suspect the water heating time will be substantially longer than direct heating. Your system would be more efficient in the winter because any left over heat after passing through the heat exchanger could be directed inside the van for air heating. In summer all the energy in the heat exchanger exhaust would be wasted.

Heating element does not have to be 120 volts AC. Could be 12 volts DC which would be more efficient than using an inverter due to the 15% inverter losses. In my case I already have the 120 volt AC available with engine running. I use the 120 volt AC for water heating or house battery charging or a rear mounted 750 watt baseboard air heater.
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Last edited by Graphite Dave; 09-24-2015 at 08:03 PM.
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