Heating Water with an Inverter

[Stormer]

I have an old Yanmar 2QM15 raw water cooled engine with a high out Balmar alternator (100 AMP dialed down to 85 AMPS). My battery bank is 440 AH capacity (4 group 31 AGMs).

The low running temperature of the engine seems to make it impractical to heat water (12 gallon Raritan water heater - why they originally ran engine output water though it I have no idea!).

Can I heat the water using the electric option, running off the inverter with the engine running? From what I can tell, the hot water heater draws about 20 amps on the AC circut. So - If Im inverting DC power from the battery banks - running the engine and charging at a rate greater than 20 amps - it should power the water heater, right?

Does this make sense? Can I do it? Should I do it (will it mess up my electrical system somehow?

Thx.

Matt

[Valiente]

Why is the engine running temperature so low? Mine is 160 F, and that is plenty to heat hot water for sinks/showers (I keep it at 145 F at home, for instance).

I only point this out because the engine-heated water is free, from a systems point of view, whereas the "kettle" approach in the hot water heater is electrically intensive and more apropos to dock power.

Have you considered converting your diesel to fresh water cooling with a heat exchanger? That way, the heat from the engine raises the temperature of the coolant to 160F-190F, and the raw water is moderated via the thermostat to cool that coolant in the closed circuit. You can plumb the heat exchanger coolant circuit into the hot water tank, and the engine heat is thus transferred to the tank, which gets 12 gallons of hot water in it in a matter of minutes.

My grasp of thermodynamics is not Newtonian, but that seems more feasible than the kind of inverter and battery capacity you'd need to put 12 gallons of water on the boil using a 12 VDC-120 VAC conversion.

[sailingdog]

Bad idea. The running temperature of a diesel engine is about 180˚, the temperature for a domestic hot water heater is usually no more than 140˚. Given the efficiency of heat exchangers, why wouldn't you use a engine-coolant based heat exchanger to heat water??

The elctrical heater route is more complicated and requires a very large inverter... and I doubt that your alternator can handle that kind of load by itself, so it would put a relatively large load on the batteries as well. 20 Amps @ 120 Volts is about equal to 200 Amps @ 12 Volts... and that isn't accounting for the conversion losses in the inverter circuitry. The inverter gets pretty warm...that's the conversion losses showing up as heat.

[Stormer]

Valiente - what type of engine to you have? is it freshwater or raw-water cooled? The raw water cooled engines run at lower temps. My thermostat is full open at about 50 C / 120 F.

Assuming you have a raw water cooled engine - did you change the operating temp by changing the thermostat?

[sailaway21]

Valiente is on the track to another point as well. You do not wish to run your engine "cold". 180 degrees is generally thought to be about ideal. As Val intimates, this is easily accomplished with a heat exchanger and the proper thermostat. "Cold" running engines produce excessive moisture in the crankcase and corrode throughout. At about 180 degrees the moisture is vaporized and exhausted. Hot water, with the system you already own, is a bonus.

[sailaway21]

Stormer,
I'd probably go up to a 160F thermostat. That would probably give you an oil temperature of around 180F as desired. 120F is way too cold.

[sailingdog]

BTW, raw water cooled engines should have the thermostat set at 140˚, but this is still plenty of heat for a hot water heater via a heat exchanger. The reason raw water cooled engines require a lower temperature is the salt will precipitate out at about 148˚ and clog the cooling passages. If the thermostat is set at 120˚, it will probably not run as efficiently as it should.

[Stormer]

Thanks guys. I'm going to investigate upping the thermostat. Thx!

[Sailormann]

FWIW I don't get very hot water out of my heat exchanger. It's warm, probably warm enough to shower with if I didn't mix any cold in, but nowhere near as hot as when we're plugged in to A/C. Have no idea what the thermostat is set to, and as the engine runs like a charm right now, I'm not going to change anything. (That would just be waving a red flag in front of the Diesel God's nose...) Engine is raw water cooled Volvo about 19 years old - water heater looks fairly new - Atlantic 6 gallon...

I'm thinking that the effect of the heat exchanger would probably be inverse to the capacity of the water heater... So the best thing to do might be to grab a Solar Stik thingy and put up a passive solar water heater...

[sailingdog]

Sailormann-

I am willing to bet that your themostat is set to open at 120˚, and that is why your hot water is so cold.