Attwood Electric Hot water heater w/built in heat exchanger questions

[Tenor]

Just realized that this came with many other parts for my conversion.  It is brand new and uses engine coolant to heat the water and an electric 110 heating element.  So, what's the best way to use this for my needs?

I had planned on using my propane water heater to allow boondocking easily.  Based on that, this is a 1500 watt unit for the 110 side.  Would I be smarter to install this into my generator coolant lines and be able to heat my water electrically and mechanically while using my genset?   My genset is a Kohler gas 4 cylinder water cooled 7.5kw unit.  It may be an old marine unit since the exhaust manifold is liquid cooled.  This also would help heat the water using waste heat.  Or - Just tie this into my bus coolant system, or is there any point into tying it all together?  Excitement and curiosity abounds!

[tekebird]

hooking to your APU coolant defeats the purpose

hook to your engine coolant and you will have enough hot water after every running period to take two navy showers, even several hours after shutting down

[Chaz]

I'm no authority, but couldn't it be hooked to both? I can see the motor giving you a tank full of hot water while you were driving, but if you were boondocking and fired your gen up in the evening to charge your batteries, you could again get a tank of hot water............not?

  Just a thought.
    Chaz

[tekebird]

if your APU is on why not use the elctric it provides?  APU's prefer to be loaded......I would suspect that if you are running the APU long enough to make hot water via heat exchange....it will heat via 120v near as fast.

[Tenor]

Tekebird,
I would plan to use the generator to power the 110 to heat the water, but my curiosity is how long would I need to run the genset just to heat the water using 110, vs using the additional heat from the genset's friction heat put into the coolant and the exhaust heat also put into the coolant?  Does that make the question clearer?

[TomC]

I have two 10 gal 120v water heaters from Home Depot (one feeds into the other with the final one powered through the inverter for hot water going down the road).  In the morning while cooking and making breakfast, it takes about 45 minutes to heat the water.  Good Luck, TomC

[tekebird]

I understand but I would say that if you are running the genset to charge the batteries you will be running it long enough to heat the water electrically 45 minutes or so

IIRC my 20 gallon would heat up electrically in 30 minutes or so.

[Hartley]

The actual amount of contact region for the coolant line feedthrough on the water heater is very small. Like about 2 inches of tubing length. It takes a lot of 180 degree coolant a long time to transfer the heat into the metal of the aluminum tank.

The reason is because water heated to anywhere near the same temperature of the engine cooling system would render the skin off your bones and cook you. The Manufacturer
purposely limits how much heat is transferred based probably on an 8 hour calculated scale.

And still in the documentation will warn you of the risk of very hot water and potential for injury or burns.

In order for a safe system you would be advised to have a temperature controlled valve that closes off the coolant when the tank temperature reaches 120 degrees or so.

I originally had my electric water heater set for 150 degrees... Too HOT.. nearly scalded myself a couple of times. Now at 120 and still hot but easier on the skin. The cooler the water the lighter the electrical load is to heat a specific amount of water. Mine is a 2,000 watt 12 gallon and works fine.

Commercial restaurant systems run at 180 degrees mainly to kill germs when washing dishes.
( They will scald you seriously )....

LP Gas heaters recover very fast when on gas at the 9,000 to 12,000 btu rates.
on electric at 1,500 watts the recovery would be several times as long depending on tank capacity and desired temperature.

And.. If you pipe coolant to the water heater, You lose heat out those hoses when the water heater is warmer than the auxillary coolant lines so when on electric you fall behind slowly.

In a quick answer. Cool.. But I wouldn't hook it up. It just complicates your cooling system and makes for more potential leaks later. ( the water heater is aluminum and so is the coolant tubing ) and prone to corrosion.

[tekebird]

you would be supprised how efficient the heat transfer from a purpose built heat exchanger is.

true the water produced through heat transfer will be very hot......definitley mix with cold water unless it has been in storage with engine off for a bit

[captain ron]

Glen, I would hook it to every available source of energy. You can use zone valves to shut off sources when you don't need/want them or if you have issues. I can attest to the fact the exchanger on the water heater is not the greatest. Also invest in a flat plate heat exchanger for nice and quick hot water.

[tekebird]

charley, what kind of water heater did you have.

ours work great

[TomC]

Granted you can get more hot water with higher temperatures, but I believe it also can cause more calcification inside the tank.  I always believe in setting things or designing mechanical items to be run in the medium speed range for longer life.  Just as a lower temp setting will let the water heater last longer.  Good Luck, TomC

[tekebird]

the 04 had the water heater rplaced once in 30 years...mainly using very hard water from Central PA well.  No noticable mineral deposits when I removed it...in fact it is a backup now in case the one in one of the rental offices fails

[Tenor]

I think I'll go ahead and install it and plumb it for use with both engines using some valves for engine 1, engine 2 and shutoff in case of any problem/maintenance needs.  I do have a new propane model that I could install in the old AC bay with the propane tank or is it a bad idea to have them both in the same space?  Thank you to everyone for their input!