ACC Induced Draft vs. Forced Draft

[Rvanderwood]

Any experience – good/bad with induced draft [fans on top] ACCs?

I am starting to see induced draft configuration ACCs as first offer from suppliers. From a system perspective, seems like they work without much system risk. They are newer to the ACC landscape so that is a hurdle to get over.

[gmirsky@galebreaker.com]

I have a few years in the cooling equipment industry,45, cooling towers and ACC. I have thought about this change in concept. In a way, it seems similar to the difference of a counterflow tower vs. a crossflow tower. My feeling is that specifiers must be more aware of the difference in recirculation. CFD analysis would be a good way to compare if there is an appreciable difference.

The next concern might be concerns for wind ward freezing in the winter in the fin tubes.

The last concern is the gear reducer and motor are sitting in the hot air stream as opposed to sitting in the cold air stream. Cooling gear reducer oil needs to be addressed. Most motor insulation is rated at 40 degree C ambient. So, a higher level of insulation for the motors needs to be addressed. Removing the mechanical equipment also seems to be more of a challenge.

[CJ Meyer]

From my more academic perspective the introduction of induced draft systems are indeed interesting. We have done extensive CFD on forced draft systems so there are exciting times ahead as we are looking forward to do the same for these new systems. 🙂

Another aspect to consider is that the fans will now be ingesting air at a higher temperature and hence a lower density which of course means a lower mass flow rate for the same volume flow rate. So generally fans will be working harder and hotter to obtain the mass flow rates required for adequate heat transfer.

Of course the more interesting question is what will the effect of wind be on the induced draft systems. Apart from the hazard of freezing, many systems are located in much drier, arid regions with occasional high winds. We might see quite strange forms of hot air re-circulation or rather short-circuiting for instance. If it is indeed present, the CFD will pick it up, so this will be the way to go.

[Jason Newquist]

Rvanderwood, ENEXIO has been offering the InAIR® inducted draft ACC since 2014 with 8 installations in operation. We have done extensive R&D and now field testing to validate the performance and benefits in the areas of thermal performance, fan loading, vibration and recirculation. Please contact ENEXIO directly at americas@enexio.com and we would be happy to discuss the technology with you further.

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