Modern-aire hood with Wolf remote blower
ILoveRed
6 years ago
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ILoveRed
6 years agoRelated Discussions
hood question: does a remote blower make sense in my case?
Comments (47)When the effluent rises it has some velocity, and hence momentum. When it enters the hood it has a tendency to "reflect" and curl downward and potentially escape. If the hood is deep enough (top to bottom) and the hood fan flow is high enough (cfm) the curling effluent will remain captured and will be exhausted. The barrel design in the picture looks to me (without examining one) like it has adequate depth. W.r.t. ya think's question a few messages up: First I would say that the change from vertical to horizontal should be as large a radius curve as you can fit to minimize pressure loss (as well as noise). The effluent momentum (which is a vector) is being changed in direction. This is akin to stopping it and starting it up again. If it can slide along a curve, the momentum loss is significantly less. There is one commercial ducting source I came across once that uses 90-degree transitions, but embeds a curved shape within the duct to improve the flow. I find it hard to answer the question of what questions to ask. Usually, the answers aren't available. Ideally, one would want to know the fan curve (flow vs. static pressure) and try to estimate all the pressure losses (including the pressure one might pull the house down to with or without make-up air) to see what the real maximum flow rate will be. This can then be compared against estimates of effluent generation rate calculated from the reference below. The power used might be adjusted to represent your cooking style, as rarely would one have all burners on maximum and cooking at the highest pan temperature. One thing is certain, flow rate in the hood has to at least equal the flow rate from all the active burners and pans, and arguably should be higher due to imperfect effluent collection. Implied above is that the hood manufacturer can supply pressure loss of the filters vs. flow rate, as well as that of the hood transitions. Getting that data, even if it were ever measured, would be unlikely, me thinks. I suggest that various hoods be "audited" in showrooms to gain a feel for their noisiness versus their designs. The reference worth reading, even if one doesn't intend to use it for calculations, is "Thermal plumes of kitchen appliances: part 2 cooking mode," by Risto, Hannu, and Pekka. (I've found it on-line whenever I've looked for it. Part 1 is also interesting.) If you do use it for calculations, please note the following apparent errors in their Equation 1: The constant should be 0.05 not 5. The units of phi should be kW, not W. (these corrections make their tables consistent with the equation) You will need a scientific calculator or counterpart software to do the exponents (unless you are very old school and know how to do logarithms). You will also need to convert BTU to kW and cubic meters per second to cubic feet per minute. This is left as an exercise for the student. [insert sociopathic laugh here] kas...See MoreRemote blower range hood?
Comments (45)3ilovepie, you said your dinning and kitchen are in the same room. What does it mean? Do you refer to literally both in a room or just open concept? I had my VAH at full 900 CFM this evening, pan frying fish sounds louder than the hood. Have you actually listened to VAH's sound? In case of not, you can go to Caplan's to try it. They should have a live 2-blower model at the time I bought mine. 3-blower one sounds same or even slightly quieter than the 2-blower. IMO, cleaning is not really an issue. I don't even need a dishwasher to clean the dripping trays once a while....See MoreHelp! Range hood w/ remote blower for 8" duct over 36" Bluestar
Comments (5)All of the above may be true, but are not in themselves totally limiting. In general, there is always a blower that will move a desired air flow volumetric rate through a given duct, but one might not want to operate it, listen to it, or pay for it. But in this case we are on the margin, and feasibility is not prohibited using conventional devices. For example, I have a Wolf/Broan 1500 CFM rated roof-mounted blower operating with a 10-inch duct, and given various estimated pressure losses, expect that it moves 900 - 1000 CFM. A 1000 CFM rated typical hood blower, no matter how large the duct, at a minimum will be significantly restricted by the hood baffles, and at a maximum by any added MUA pressure losses, and would be unlikely to move more than 700 CFM in use with a hood. An 8-inch duct has a sectional area of 64% of that of a 10-inch duct, so the pressure losses operating at 67% through an 8-inch duct of the air flow rate through a 10-inch duct will be similar. In general, one wants to select a blower having a fan curve that supports the desired flow rate at the pressure loss that one estimates is present. Without my looking up the specified hood, let us assume that its entrance aperture is 42 x 27 inches or just under 8 sq. ft. This calls for 8 x 90 CFM/sq. ft. or 720 actual CFM. A typical 1000 CFM blower may achieve this with a 8-inch duct, and one certainly can check the assumptions against blower fan curves (where available) to either ensure adequacy, or at least force the MUA system to be active and not cause significant pressure loss. Note that this doesn't violate your appliance guy's opinion about duct flow rates, although I am sure that his view is based on typical in-hood blowers. If you have the room in some part of the duct path, then including a silencer will help reduce noise back at the hood for only a small added pressure loss. In any case, numerous commercial kitchen ventilation blowers can be found that will pull 720 CFM against any pressure loss likely from a well designed hood/MUA setup. It is quieter to move a given flow rate when the fan blades are large and moving slowly than small and moving quickly, as the latter generates more high frequency noise from turbulence. Induction motors can be controlled by rheostat adjusted phase circuits, and these can be put into hoods. My Wolf hood has such a control, and now the technology allows for it to be performed with better techniques at low cost. These comments are meant to touch on most of your questions, but feel free to delve deeper as needed. kas...See MoreRemote Range Hood Blowers: hood brand or generic?
Comments (7)54-inches (4.5 ft) x 2 ft = 9 sq. ft. Desired volumetric flow rate to achieve 90 ft/min across the hood aperture is 90 x 9 = 810 CFM. Blower rating needed to pull 810 CFM with decent MUA will be around 1200 CFM, as you noted. Fantech provides 'fan-curve' data in the form of tables, and also plots. A 1200 CFM unit (at zero static pressure) will show a value near 810 CFM at some pressure drop (about 1.2 inches, w.c., for the FKD10XL). Excluding MUA, most pressure drop will be from the hood baffles, unless one has several tens of feet of duct. It would be useful for you to obtain pressure loss vs. flow rate data from Bluestar. Fantech in-line blowers are, I think, axial blowers (like a turbo jet pressure section) rather than a flat plate with radial fins (like turbo chargers use). Broan blowers, including inline, appear to all be the plate type. There is nothing wrong with these, but they may have a different characteristic fan curve shape than Fantech's blowers. I've never plotted both together. (It is important for residential blowers operated at uncontrolled pressure losses and any speed from low to high that they have monotonic fan curves. Else they might 'hunt' at some setting. That would be annoying.) Plate type blowers are least conspicuous built into a roof cap. Commercial up-blast blowers use induction motors often tied to the fan assembly via a belt and sheaves. These can be tailored to provide the desired CFM at lower fan speeds, thereby reducing noise. They are, however, significantly more conspicuous on the roof. The primary advantage to using a hood manufacturer's specified blower is that it will directly adapt to whatever fan speed controls are built into the hood. Other blowers may require some type of adapter or control replacement. So a Blue Star hood's control nature might have to be determined. My Wolf hood adapts to my Wolf blower, made by Broan/NuTone, and likely would work with any other single wire pair induction motor blower up to some motor power limit. The Fantech FKD10XL data sheet show curves for a 5-step transformer control, and for no control. One would have to check with them for compatibility with whatever the Bluestar hood uses, such as phase control. If you use an in-line blower, you also have to find a suitable roof or wall cap. Fantech many sell these. You should have a damper at the hood and also at the roof cap. You need to plan out the entire hood duct path. Is there room for a silencer? Can the duct path rise over its entire length (desirable)? What elbows are needed? Fantech makes some duct couplings that may prove useful. Hanger strap material will be needed. Sound dampening material may or may not be needed depending on blower assembly vibration, which is mostly, I expect, due to blower fan assembly balance quality. Best to match MUA actual flow rate to hood actual flow rate (ex: 810 CFM). This avoids all (well most) pressure drop in the house, conferring safety with combustion appliances and keeping the wall dust in the walls. If active MUA is needed to do this (depends on combustion appliances and their MUA, if any) then a blower that can provide the required CFM at the MUA path pressure loss (usually any air filters, but could include the heating scheme if hydronic). As usual, the duct diameter in the hood exhaust should support a full speed flow rate of 1000 to 2000 ft/min. The otherwise clean MUA path is not grease deposition constrained, but larger will reduce pressure loss if there is room -- useful particularly with passive MUA. I'll skip MUA control in this message, but it needs to be addressed. Commercial rigs usually run at constant speed (exhaust and MUA), so tuning is easy. Residential variable flow rate, along with perhaps a need to deal with other exhaust fans and fireplaces, imposes more difficult conditions for blower control. You might need a Fantech MUA setup, or their 10V control type blowers run by a controller trying to keep house pressure relative to outside within some bound....See More
kaseki
6 years agoILoveRed
6 years agoILoveRed
6 years agocobalt21
6 years agokaseki
6 years agocobalt21
6 years ago
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