Rob, A project I did for a Government contract (Army National Training Center where the Army practiced for Desert Storm etc.) involved a few Onan 12.5 KW AIR COOLED DIESEL GENERATORS. One of the objections I raised about an installation that was to supply power to coaxial amplifiers to boost and reboost base band video on a long overhead run (mountain top to desert floor) was that the design of the installation was NOT GOOD.
I pointed out that the generator got its cooling air flow from inside the bld (about 20x25 metal bld) and the effluent airflow (heated air) was dumped inside the building. There was a couple low mounted good sized rectangular louver vents for fresh air. Here is the problem: when commercial power went down and the generator fired up to maintain the battery voltage on a huge bank of NiCd cells, the hot air off the engine mixed with the room air and this mixture was drawn back through the engine to cool it. A 20 min run was no big deal even with the desert temp was 100+ but over time the room temp went up to unsatisfactory levels for the installed equipment and in a prolonged run of several hours the engines cooling capabilitiy was compromised (electronic equipment and battery chargers with solid state electronic circuitry were abused.) If any air moved through the louvered vents, they removed a little of the moixture not pure hot air from the engine so they were very inneffective.
I suggested an economical fix but since the SUITS didn't understand they had me make test runs with some thermometers to prove my point which I easily did.
Onan makes sheet metal shrouds for their aircooled generators so that you can send all the "used" heated air from the engine into a duct and send it out of the bld. Then the cooling system on the engine will suck a small partial vacuum on the bld which will draw in fresh outside air. By exhausting "PURE" hot air instead of the mixture the air temp waas lowered significantly in the bld which gave the batteries, chargers, etc a break and a chance for a long useful life.
With a water cooled engine the same thing happens if you don't make a provision to exhaust the heated air from the bld. Passive vents help but are usually not enough. You need to direct the hot air coming off the engine out of the bld so as to exhaust the "pure hot" air and not mixture.
This is an exponential dilution problem that can be modeled by a table spoon of milk in the bottom of a glass. Run water at a moderate rate into the glass and note how long it takes to get rid of the milky color. It takes many many table spoons of water down the drain to get the water in the glass to look really clear. You are removing mixture, not milk and it is not an efficient way to get rid of the milk. Dumping the "pure milk" does it much quicker.
One of the Onan installations was in an aluminum "BOX" called a Helicopt Hut. It fit in the bed of a deuce and a half and had lifting eyes so you could transport it by chopper. There is aboiut 6 ft headroom (I had to stoop.) I subdivided one of these boxes into two equal rooms with a connecting door. On one side I put an Onan 12.5 Kw air cooled diesel generator sitting on a custom anti vibration mount, surrounded by lead loaded acoustic foam and some storage bins and a work bench. In the other half of the box I put several racks of electronic equipment and a computer. Two operators occupied the room. (close quarters) The generator had to run when the unit was in use as it was THE source of power in the field. I put extra insulation on the roof and a Coleman A/C unit for the operators. This was used in the deseert between Death Valley and Barstow CA (Ft. Irwin, NTC)
Rob, Have you any reason to suspect the thermal design of the generator installation is better than the advance site work that insured the trees were not in the way of the panels on the trackers?
Pat
