Use of a Water-Cooled Diesel Generator as an Off-Grid CHP System

[Francophile]

TL;DR Summary

Would it be feasible and cost effective to use a diesel powered generator as a CHP system to provide rapid hot water heating and electricity for a building containing a swimming pool.

I am looking at options I have available for providing Power Heat and Light to a collection of houses and barns I am planning to convert into a small holiday complex in rural France.

I plan to run this complex as an agricultural small holding with holiday let's in 4 x renovated French farm cottages. The cottages are located around a central barn in which I would like to install an indoor swimming pool / gym / sauna etc.

I would hope to operate Spring, Summer and Autumn seasons using mostly solar heat recovery with supplementary heat from ground source heat recovery. But I feel that if I am to make this a commercial venture I may need to consider an oil-fired back-up system for rapid warm up and Winter climate conditions.

I plan to have a ready supply of red diesel from the agricultural side of things and I'm wondering if a Water-Cooled Diesel Generator could be used just as efficiently as an oil fired boiler. I would use it to heat water both electrically and directly from the engine cooling system. I would plan to house the generator within the building insulation envelope and take measures to recover heat from the exhaust system.

The additional benefit from this system would be an available source of 3 phase electricity.

I already have a similar arrangement on a canal boat where 15 - 30 Minutes of Diesel Engine Running to charge leisure batteries produces a full tank of hot water that can be used for domestic purposes or circulated around heating radiators via a heat exchanger.

From the point of recovering the available energy from the fuel used is this a viable proposition.

 

[anorlunda]

I presume you mean a heat exchange between the engine's coolant and the water for heating. Yes that could work. You might also gain more heat from the engine's exhaust gasses.

But I would be surprised if you have to invent it yourself. There should be commercial heat exchangers designed for just that purpose. Do a little google searching. You might even find an integrated package with diesel, generator, and heat recovery exchangers all in one package.

Pleasure boats with diesel engines frequently heat a hot water tank. Small diesel engines are around 40% efficient, leaving 60% to be recovered as heat.

 

[Rive]

CHP - is it okay for you to sell electricity for the grid? Not necessarily an easy adventure. You better check on the local regulations and customs.
Otherwise, you can try to use some mechanically connected diesel-heat pump solution. With some tinkering (hopefully done by a professional) you can get ~ 70% of the heat from the diesel and the rest is multiplied by the COP of your system.
'tkt-380pb' seems to be a good start for a search
But I'm sure once you have the right words to search for you will get plenty of interesting hits.

 

[essenmein]

Heh, I've often thought about this exact thing. We heat with oil and in the winter months my mind wonders and the idea of using a diesel to both generate electricity and use the waste heat for the house/hotwater crossed my mind more than once.

The only thing I can think of as a negative, assuming you can deal with the noise and vibration, is much higher maintenance cost. I think efficiency wise, if you recover much of the exhaust heat to use as low grade heat (eg pool), you should be about to get the same as a furnace (80-90%).

Just as an example the small diesel I have here as a generator (unfortunately air cooled...), wants new engine oil every 50hrs of running, fine for back up and intermittent use, but new oil every two days would get tiresome for full time use. Basically a diesel is far more complicated than an oil burner and that will reflect in the maintenance cost and effort, depending on how reliable the power has to be, you may need two units to allow one to be down for maintenance while the other is running.