Yanmar 2TNV70 heat output & loading question

[diesel]

Hi all,

First time post. Thanks for the great information provided in these forums.

I'm setting up an off-grid power system for my brother in Australia (Victoria). As he is completely off grid and LPG is expensive I am considering using a water-cooled diesel generator as both heat and electricity source. They are surrounded by trees so solar isn't an option. At this stage I've purchased a Trace SW4548E (4.5kW, 48V) inverter/charger, and will shortly be purchasing a battery bank (around 300Ah). This part of the installation is pretty much set in stone. Power requirements are pretty small at approx 5-6kWh per day (accounting for efficiencies in the charge / discharge cycle).

Hot water heat input requirement is around 10kWh per day (120L raised 60degK + allowance for losses in the heat exchanger & tank).

The trace will be capable of pulling 3.5kW during bulk charging. Given alternator & drive efficiencies and auxiliary losses in the generator (assumed loss of 30%) this requires a 5kWm input.

I can obtain a Yanmar 2TNV70-PGA for a good price brand new. This is rated continuous at 9.76kWm @ 3600RPM / 8.16kWm @ 3000RPM. I could belt this engine down where it would run efficiently (ie. 2000RPM, continuous output of 5.4kWm). I could also belt it to the peak of it's torque curve at around 2800RPM (continuous output of 7.7kWm).

Questions
1. Has anyone got experience with similar size engines (~13HP) running at lower load? Will it glaze / gum up at 50% maximum load?
2. Will the heat output from the cooling water drop off too much to be usable?

Any pointers or information would be greatly appreciated.

Another option is to add a 1.2kW water heating element, pushing the engine loading up to about 6.5kWm. This would also push 2.4kWh into the hot water system over the gen's 2 hour run time.

Thanks for looking 

[Ronmar]

Ideally diesels should be kept at or above 75% load.

Rule of thirds is a fair estimate for output.  IE: if you burn 24KW worth of fuel, 8 goes into the cooling system, 8 goes into mechanical output and 8 goes into the exhaust.   If you are getting 5-7KW of electric power, that is probably close to 6.5-8KW of mechanical energy out of the generator set at around 85% generator efficiency.  You should be able to recover about that same 6.5-8KW of heat energy out of the cooling system...  An exhaust heatexchanger will up your heat recovery considerably, but they can be problematic on a diesel engine requiring frequent cleaning/maintenance to maintain efficiency and not cause damage to the engine/lower engine efficiency.

Electric heating elements that switch on as charging load tapers off, to heat water and maintain peak engine load is an excellent idea IMO.  Controlling it may be a little bit of a tech challenge, but definitely doable...

Good luck