Effective cooling in enclosed areas

[gizmag1]

I've got numerous clients in the catering/ leisure industries. They all have purchased large invertor/generators of 6.5 kva and wish to have them installed in their motorhomes or coffee vans etc. The problem being that the previous model is liquid cooled while this invertor model is air cooled. Installation of these units all have the same requirements. While they only produce 52db @ idle, they still want them silenced further, also access for servicing ( on 5 of the 6 faces)
I've been in touch with the Australian Division of this engine manufacturer. But they don't have any info regarding air through-put, etc. The only info I've managed to get is that the intake air temp. can't exceed 40 degrees, ( we've managed these sorts of temps. @ 25 degrees ambient... But outback temps. of 38+ degrees not uncommon )and that any exhaust mods must still maintain an exhaust back pressure of 1120m.m. / 40" of water.
Also of concern, is the explosive mixture of fuel vapour from the fuel tank cap which vents through itself.
My suggestion to the first installer was to replace all his checker plate floor for stretch mesh - for the engine intake, and spin the unit throgh 90 degrees to have the exhaust facing the drawbar of the trailer, and have that face also constructed of stretch mesh. This, I feel would allow enough ventalation and still allow him the two side facing panels to be solid for advertising.
Any further suggestions or formulas would be greatly appreciated.

 

[dcasto]

Sounds bad, but maybe a fan running on the electrical side with an on/off based on temperature like most cars have today. If you think about it, the water cooled units had fans and pumps that took power from the engine.

 

[gizmag1]

The thought had crossed my mind but was uncertain as to the cfm rating the fan would need to be? Based on a thirteen horsepower engine, sitting between 1250 and 3600 r.p.m., and if you thought it would increase the noise levels considerably?

 

[IceStationZebra]

I assume that the engine already has a cooling fan. You will probably some a marked improvement by making sure this gets fresh outside air and not recirculated air from inside the enclosure.

If the engines have pressurized lube you could add an oil cooler. (I doubt a 13hp engine does but worth a shot.) Many manufacturers of air cooled engines do this.

If you do decide to add an additional cooling fan, or replace the current one with a larger one, remember that a ducted fan is more efficient than an unducted one. As a side benefit the ducting might help reduce the sound transmitted to the interior of the trailer (depending on where the exhaust is pointed). BUT messing with the original package in any way may end up increasing the sound levels at certain frequencies. OEM's often size/tune components so they act as notch filters to take out pesky irritating sounds.

And lastly, the exhaust back pressure you gave is almost certainly the maximum not a requirement. If you extend the piping this would be easy to check with a simple water manometer connected to a nipple welded in the pipe just after the head. You can even make one yourself with a ruler and some clear tubing.

I suggest that the quickest/cheapest route may be to build a box that simulates the installation to try your ideas out first.

ISZ

 

[MikeHalloran]

For exhaust backpressure, 40"wc is actually quite a lot. Most eyeball- engineered systems will come out well under that, even with restrictive mufflers.

It is almost certainly a maximum. Only a few marine turbo Diesels specify a minimum backpressure value, and frankly I think it's because their design engineers at the home office mis-read some turbo mfgr. documents, but nobody argues with the home office.

If you do decide to measure the backpressure, and there isn't a handy plug you can remove (there usually is), weld a steel coupling into the most upstream bit of steel pipe, and insert a brass nipple at least 6" long into it. The usual size for such a tap is 1/4" NPT, but 1/8" might be a better choice for such a small engine. The purpose of the brass nipple is to partially isolate the hose to the manometer from the exhaust heat. Connecting a flex hose directly to a manifold will burn the hose very quickly.



Mike Halloran
Pembroke Pines, FL, USA

 

[gizmag1]

Ice station zebra, Thanks for your reply. To my Knowledge,The only cooling fan is the flywheel, which is engine speed dependent. Naturally the manufacturer has included nicely formed shrouds to duct the cooling air across the cooling fins and the inverter. The Problem is that the manufacturer recommends that the unit only be run out in the open. So I guess I should really be asking, How many external panels, of it's custom made enclosure, can be used before its classed as enclosed. And, if it is put in a sealed box, with the exception of the floor and the exhaust side, would an automotive (say 12" ) electric thermo fan be sizable enough to simulate "open air running" - with the exhaust mods through the floor. Would it shift enough cfm's air per minute to keep up with btu output?

 

[MikeHalloran]

Open air is open air. Forget any warranty when you put it in a box, even a screen box.

The problem with an air-cooled engine is that every bit of it radiates noise, and you can't put acoustic insulation there without overheating the engine, so you have to stop the noise between the engine and the outdoors.

A really big oil cooler might help the engines live, but that won't help the alternator.

The best you can do is try to get a free flow of air to the flywheel/fan that's already there, and away from wherever the hot air comes out, and discourage recirculation.

For noise control, cover any air baffles or ducts with sound absorbent material, and put bends in the ducts so you can't see the actual genset.



Mike Halloran
Pembroke Pines, FL, USA

 

[dcasto]

thread384-192333

Here are some ideas on design in the above thread, you may want to post further questions in the area.