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Old 04-06-2022, 11:32 PM   #1
Bus Nut
 
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Join Date: Oct 2021
Location: Jacksonville, FL
Posts: 709
Year: 2003
Coachwork: BlueBird
Chassis: TC2000 28ft
Engine: Cummins ISB 5.9 24v, MD3060
Rated Cap: 14
Marine Water Heater and Webasto Diesel Heater

I'm working on my install plan for my new 16KW diesel heater. I originally bought it for heat while parked as well as preheating the engine coolant for warm starts. I still haven't figured out my hot water heater.


Originally, i was going to use a hybrid propane/120v water heater like the below.

https://pantherrvproducts.com/94022/


I don't plan to have propane heat fridge or stove. I plan to have 10KWH of battery storage as well as 2-4k watts of solar on the roof. I hope to run water heat on solar/120v as much as possible. I do want a backup source as well and don't want to carry propane (might do 1lb bottles for grill).



So back to my coolant heater. Its a monster and i honestly don't plan many cold trips to even use it.. I was maybe going to repurpose it into using water and additional hot water tanks for showers. Just blew my mind finding 120v marine water heaters with 5/8 coolant ports for heat exchanging. I can easily plumb it into my coolant loop.
So they have a 6,11, and 20 gallon. What i wonder is which size might be best.
They all have 1500w burners, so each one should theorically take twice as long to heat at 120v as the smaller one. Also, i can utilize my 180ish engine heat to circulate and preheat the water. This is makes much more sense in a boat except maybe the few cases where my family would shower right after stopping (in which case the 20 gallon heated for free would make sense).


Which size might be optimal to be matched with the 55k BTU diesel heater, so that i can flick it on before showers in order to have "unlimited" hot water powered by my diesel fuel.


Based on my initial calculations, the 11 gallon one would take 56minutes to heat from ambient to 120F with the 1500watt element. On the other hand, assuming the 16kw diesel heater has 50% efficiency 8000watts of energy through the heat exchangers would take 11minutes. This would give me "unlimited" hot water from my diesel. So all the sizes will pretty much give this, but the 11 gallon gives me enough reserve for sinks and things without having to carry more hot water than i need and keep it warm using the 1500w element.


I haven't seen anyone do this with a Diesel coolant heater (other than a few very fancy hydronic heat systems which I'm not interested in). Anyone have any input before i forage down this rabbithole? Ill have to navigate the sailboat forums for some tips and they might be a stranger crowd than schoolbus folks!

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Old 04-07-2022, 09:01 AM   #2
Bus Crazy
 
Join Date: May 2018
Location: topeka kansas
Posts: 1,771
Year: 1954
Coachwork: wayne
Chassis: old f500- new 2005 f-450
Engine: cummins 12 valve
Rated Cap: 20? five rows of 4?
webasto

Webasto makes a heat exchanger for hot water. I do not have this on my bus -yet - but think about this.... a really hot hot tub might be 107 I do not see the point in making 120 degree water.... I have some friends that set up their shower with only hot water. the thermostat is set at 100 degrees. Is it super hot? nope. but it is not cold or even cool. no mixing valves, only one waterline, and one 90 degree ball valve. very simple set up KISS keep it simple stupid.

I think, instead of a 20 gallon tank think about no tank. put the heat exchanger right next to the diesel heating unit flow the water for the shower right there... keep plumbing as short as you can and be very careful that the first water out does not burn you. webasto on first. there should be water in the exchanger already, then shower water on... a little time spent watching temperautres and you will have an idea of how long stuff is on and working and what kind of temps you have at the shower. do a navy shower and I bet you can use three gallons. with use of control valve on the webasto circuit you dont heat the entire system... or you can have a heater tank and "bank 20 gallons and have luxury showers......sky is the limit.. or space or money or time.

you get the idea

william
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Old 04-07-2022, 10:03 AM   #3
Bus Nut
 
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Join Date: Oct 2021
Location: Jacksonville, FL
Posts: 709
Year: 2003
Coachwork: BlueBird
Chassis: TC2000 28ft
Engine: Cummins ISB 5.9 24v, MD3060
Rated Cap: 14
Awesome points William. I had thought about a pull chain shower for the family. I was in the army and can be out in 2 minutes. My sister has lived with us for about 5 years and showers no less than 1hr. I should maybe pull chain her current shower...


I would like to avoid having mixing valves in the shower, so maybe one mixing valve for everything and then everyone gets 102degree water or something. This would work for the sink, the indoor shower and the outdoor shower. This would also shrink my pex runs. I think I'd still like a small tank for hand washing where the 1500watt element just keeps it going. If I can avoid propane, then I may want to go ahead and add a second diesel tank for my webasto pickup with an aux pump to fill the main.
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Old 04-08-2022, 12:15 AM   #4
Bus Nut
 
Join Date: Feb 2022
Location: Midwest
Posts: 267
If you guys are doing hot water tanks and storing water in the 100 degree range, then you need to read up on Legionaire's disease. I bring this up because 80-110 degree water is like a Legionaire's bacteria vacation resort.
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Old 04-08-2022, 07:12 AM   #5
Bus Nut
 
Join Date: Sep 2020
Location: Central PA
Posts: 350
Year: 2002
Coachwork: AmTran
Chassis: International/IC Bus
Engine: T444E
Rated Cap: 78
I'm working on a system exactly like this. I'm planning to attempt to run the domestic hot water in an "on-demand" fashion to avoid the marine water heater. My heater is an ITR Hurricane, but I'm basically in the process of building the exact system you are.

I will be utilizing the factory bus heaters on their own loop. The engine preheat loop will be separate and heated through a 20 plate liquid-liquid heat exchanger. The hot water loop will also have its own heat exchanger as well (pic below). I'm still working out the details as far as temperature control goes. It will likely involve a few aquastats and a mixing valve.



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Old 07-21-2022, 10:46 AM   #6
Bus Nut
 
Join Date: Apr 2018
Location: League City, TX
Posts: 321
Year: 1994
Coachwork: Thomas
Chassis: International 3800
Engine: DT408 6.7L L6
Rated Cap: 14
Here's my take. I'm slow, so don't hold your breath.

https://www.skoolie.net/forums/f11/1994-international-thomas-7-window-w-c-22847-post458163.html
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