Recirculating kitchen hood--baffles or mesh filters better? Model reco

3 years ago

I know that a ducted system is best. We can't do this due to our condo townhouse association and the fact this is a first floor, interior wall that is common property. So I have to go recirculating/ductless.

I have read that when one inserts the charcoal filter a recirculating system requires it effectively cuts the air flow in half so I will need to buy a hood with a higher CFM to compensate for that loss of flow. I also know that with a ducted system baffles are considered better than mesh filters. Does this also hold true for non-ducted systems?

The kitchen itself is completely interior and quite small--9 x 13-- but it has large openings into other areas of our 900-100 sq ft first floor; there is a ceiling fan in the kitchen. In our remodel we will be installing a 30" induction range. The current electric range has the standard absolutely useless as far as venting OTR microwave. We definitely cook but don't do lots of high-BTU-required Asian cooking, and we don't do any deep frying. This home is used for only half the year.

I am still in the design phase and debating between a chimney hood and an under cabinet type hood, leaning pretty strongly towards the under cabinet pull out type primarily because the space is small and this would be less intrusive.

l know there are recommendations for Vent a Hood for a good ductless system, but I don't want to spend the 3K that VAH will cost (I priced it out). When I look at search parameters, should I attempt to find a baffled recirculating hood? Or, with ductless is the difference between mesh and baffles rather negligible? Any other tips?

Also, if anyone has an efficient and quiet ductless hood they can recommend, I'd appreciate the info. Thanks.

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Comments (5)

kaseki
3 years ago
I haven't searched for one, but it is possible that Broan/Best has a recirculating system with both grease filtering and charcoal-based odor filtering.

To the question: Generally baffle filters are superior in grease extraction efficiency. This is why commercial hoods use baffles. Specifically, the baffles remove the larger end of the particle size spectrum while retaining their performance no matter how much grease is collected. The smaller end of the spectrum is expected to (hoped to) exit the system on the roof. The pressure loss of the baffles remains the same, greasy or not, and this allows the overall air flow to remain constant.

However, baffles work by centrifugal extraction due to the air making two reversal in the baffle space. This requires some minimal velocity that likely depends on the details of the baffle design. For modest cooking where low blower speeds are adequate, there is a point where mesh filters -- if kept clean -- may become superior grease collectors. Mesh filters work by impingement.

A hybrid baffle system seems to be intended to filter by mesh while providing the appearance of a baffle system.

In some commercial applications, the stringent filtering requirements lead to stacked filters, the first usually being baffles, followed by mesh, ball bearing, and other schemes that address different parts of the particle spectrum. UV disassociation of grease and odor molecules is also popular.
julieste
Original Author
3 years ago
Thank you Kaseki--

I think you are saying that for my purposes perhaps either mesh or baffle might be okay. Or, did I get this wrong?

Best/Broan is a good/recommended manufacturer and the place I should start my search?
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I can only guess on this one because a true comparison would require both to be the same size and have the same achieved air flow rate. I would not expect anyone to have such a setup that could be compared. The baffle noise will be due to turbulence from air passing over the sharp edges of the baffle sheet metal. The mesh noise will be due to turbulence from air passing over the edges of the mesh holes. Although baffles have more metal surface than meshes filling the same area, I would argue that baffles have less edge length. This suggests that the mesh filters would generate more turbulence and thus be noisier. However, the size of the turbulence cells could be different in each case, and the sound frequency spectrum for one might be different than the other, leading to different perceptions of the noise relative to the actual achieved acoustic power. So, we are faced with a lot of qualitative fluid dynamics phenomena that don't lead to an obvious conclusion, so intuition prevails. In my estimation baffles will be no more noisy than meshes for the same air flow rate. I would also estimate that at moderate flow rates where the mesh induced noise isn't partly ultrasonic, the mesh noise will be louder. Also, relative to the italics above, equal fans do not yield equal flow rates, even with perfect MUA control. The losses in ducts of different diameter are not equal, and meshes will cause greater pressure loss, even when clean, than baffles for the same actual aperture area. (And most mesh filters do not cover as much area under their hood's boundaries as baffles usually do for the same hood boundaries.) So the flow rate achieved with meshes may be lower, but at the same time the air velocity at the mesh may be higher, and hence more noise is generated per unit area for less area. This is a non-trivial condition for which to have to estimate relative noise. kas
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There is no single filter type that collects aerosol grease particles of all sizes within the particle spectrum generated by cooking (possibly excluding intense UV conversion of grease to gases.) One can tour on-line advertisements for commercial filters and see what part of the particle spectrum they are designed for and how well they work over part of the spectrum. What you hope for in a residential hood is that you collect the larger particles in the filter and the smaller particles exit the ducting before they can condense on the ducting. The result will always be imperfect relative to the goal. Deposition depends on what sizes pass the filter (baffles or mesh, usually) and the velocity of the air in the ducting, and the temperature of the ducting. Note that Magic Lung centrifugal grease slinging is not that different from how baffles work to collect grease. Like baffles, the Magic Lung squirrel cage fan can only impinge the larger particles against the assembly wall. The fine ones stay as an aerosol in the air flow and are passed up the duct. kas
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Thanks, RChicago! I've narrowed my choices to either a VAH or a Modern-Aire hood. They offer 600 cfm and smaller hoods that I can vent directly out the back wall. It's too costly and way too complicated to vent the hood vertically (there's a large bedroom window in the way). I had to rule out a number of others because they either were ridiculously overpowered for my needs - no way could I avoid MUA costs - only vented vertically or required at least 24" of vent pipe to vent to the rear (couldn't accommodate), or were too expensive. I've read through dozens of old threads about ventilation, plus I've consulted several experts (ventilation reps and CMKBDs) and I've concluded that 400 cfm will fulfill my needs. I know that's going against GW wisdom that bigger is always better but oh, well. :) Our 20 yr old pop-up downdraft is rated at 500 cfm for our standard gas cook top (rarely used it on high, too danged noisy and it sucked the flames sideways). And yet I'm quite sure that a 400 cfm hood will easily beat the ventilation pants off that old pop-up downdraft. I'm leaning towards the Modern Aire. I like its appearance plus, at 24" deep, it has a better capture area than the 300 cfm VAH (only 21" deep). In case anyone else is on this same quest, here's the list of possibilities I compiled, in no particular order: Imperial Prestige DCS Wolf Modern Aire Viking VAH Kobe ZLine A few brands never made the list because they were poor qual1ty. I looked briefly at Best but their baffles were backed with mesh (what they apparently call their hi-low filter system), which is not what I wanted. This post was edited by lisa_a on Fri, Sep 26, 14 at 11:31
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"That flipping can result in a plume of perhaps 4000 CFM which massively overloads even a 1400 CFM hood. It's containing these very brief but quite huge bursts until they can be exhausted that containment volume is needed." 4000 CFM is 67 cubic feet in one second. There is nothing I have ever cooked, or viewed being cooked that, for a one-second transient, had any hope of generating 67 cubic feet of effluent (a cube four feet on a side) over the pan. The space above a 2 ft. wok to a 4 ft high baffle array is only around 15 cu. ft with some plume widening included. I agree that if this transient is not captured, entrained, and immediately contained, it will surely expand to a much larger volume. And this happens in the commercial hood, but the velocity is degraded by the expansion, and the CFM required for baffle effectiveness is less than for the high velocity plume hitting the low baffles of a typical residential hood. In any case, @opaone, the requirements we should strive to suggest depend on whether a commercial hood, reasonably functional residential hood, or a non-functional residential non-hood is being considered. I love your enthusiasm for commercial hoods everywhere, but that is not going to happen until kitchen designs become much different than most have or will have. For myself, my goal is to merely try to orient visitors here away from predictably poor performance ventilation systems.
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kaseki
3 years ago
I think Broan/Best/Nutone are competent, but supply something for everyone, including owners of poser kitchens, and owners of salesman defined ventilation systems, so it is possible to have a decently designed device that is insufficient for the purpose one has in mind.

I also think that the demand for effective recirculating hoods is modest, so if one doesn't want to pay for the VaH ARS, and the only effective (one hopes) lower price model has mesh filters and modest flow rate, than one has little choice but to accept the lower priced model's limitations. A mesh filter kept clean (be sure any mesh filters can handle being cleaned in a dishwasher) can be effective at low flow rates. (I'm not sure exactly where in the ft/min velocity range a given manufacturer's mesh filters should be considered effective since I haven't had a need to investigate that.) But the overall flow rate, or the specific flow rate (CFM/sq. ft. of hood aperture = air velocity) has to be adequate for the velocity of the plumes resulting from the temperature of the cooking to be filtered. An ineffective hood is worse than no hood, in my view.
julieste
Original Author
3 years ago
Thanks so much for all of your help! This is a thorny dilemma because I know we can't use what is truly effective (a vented situation) and will have to settle.
User
3 years ago
great question. the demand for recirculating is more than people think. when looking at apartments in manhattan, none of the 7-8 i looked closely at had vented hoods.

would love to know what brand and model you went with!

Recirculating kitchen hood--baffles or mesh filters better? Model reco

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Recirculating kitchen hood--baffles or mesh filters better? Model reco

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