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HELP! On Custom Vent Hood

Posted by davidahn (My Page) on
Mon, Nov 7, 11 at 4:27

Hi guys. A call for help from ventilation experts, please. I've been told to specifically ask for Kaseki, but anyone else with wisdom to share, please do so! I have searched the equipment forum a bit, but haven't found anything specific to my situation.

I've settled on a 60' Capital Culinarian cooktop, 23000BTU x 6 + 30000BTU 24' griddle top. The ventilation is the challenge. I'd like either an in-line or roof ventilation fan.

1. CFMs. The most common rules of thumb (1% of BTUs) suggests 1700 CFMs (23000 BTU x 6 + 30000 BTU = 168,000). Fantech says 100 CFM per lineal foot = 500 CFM, a HUGE difference from 1700. So how much do I need? I'm looking to make it 72W x 27D at 30' from the countertop, 28' from the burner grates. We do do a lot of wok cooking in case that makes a difference. Rooftop would be great, but if we need serious CFMs I think we'll need in-line.

2. Inserts vs. fully custom. I'm tempted to go fully custom to get the full 27' depth and to have one set of controls rather than two sets of controls with dual 36's. I'm very interested in a very slim, 'under-cabinet' style look. I like the look of the Miele, but it's only 16' deep! I've got a custom metal fabricator who has done restaurants, but he needs specific drawings. Here's my draft design so far:

3. MUA. I read about someone here who's piping in MUA into the front of the hood, so I'm leaning in that direction. The home is in San Diego, so most of the year, outside air should be fine, but for those days when outside temps go over 80 degrees, it would be nice to have conditioned air. I don't know if anyone uses a split A/C for these purposes?

4. I've found these stainless steel baffles, but I'm not sure about the quality:
http://www.cpapc.com/20-x-16-x-1-12-Stainless-Steel-Grease-Filter-P4810C278.aspx

5. Also looking for suggestions on where to put (and where to source) the warming lights, as I plan on a 9' deep warming shelf about 12' down from the hood.

Any help would be greatly appreciated! Thanks.

Here is a link that might be useful: Draft Hood Design


Follow-Up Postings:

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RE: HELP! On Custom Vent Hood

First, let me note that I'm only an authority on what I've read to the extent that what I've read is valid; but I did research ventilation quite a bit before starting my renovation.

I am not going to recommend specific products because I haven't used almost all of those that exist.

There are several rules of thumb for specifying the required cfm, that is, the cfm you actually get, not the blower's rated zero static pressure cfm. Some are very simple, while others have been established in commercial settings and vary with the type of cooking surface. See for example technical articles at greenheck.com.

(Note that rules of thumb for the required cfm per foot of hood may require one to include the hood ends or entire circumference for island hoods.)

The real issue is keeping the effluent flowing where it meets hood surfaces and/or filters/baffles.

Here is my probably-good-enough rule of thumb (in English unit of measure), but it requires some computation and guesstimation.

Assume that the upwelling effluent velocity is 3 feet per second. Ideally, all of this is captured by a large enough hood, but if it isn't, at least the part that enters the hood needs to be contained and not allowed to spill back out.

Calculate the hood aperture area in square feet. Multiply by the velocity to find cubic feet per second of air that should flow at the aperture, worst case. Multiply by 60 to obtain cfm.

Worst case might be a mesh filter located at the aperture. For hoods more commercial in appearance, with some depth, sloping sides, and internal filtration, the rising effluent is concentrated somewhat and its upward velocity is mostly retained when it reaches the baffles or whatever. The area of the baffle opening may be smaller than that of the aperture, and this may provide some benefit in the required cfm. So, one might picture a given configuration and ESTIMATE that the effective aperture area is, say, 60% of the entrance aperture, and hence the cfm required is only 60 percent of the number calculated above.

Let's do an example. The hood inside aperture is 6 feet by 2 ft = 12 square feet. This calls for 12 x 3 = 36 cubic feet per second or 36 x 60 = 2160 cfm. A hood such as Wolf sells will have an internal baffle area that will have complex flow at the baffles. I will guess that aerodynamic effects allow one to reduce the required cfm to 50% of that calculated above, or about 1100 cfm.

Do we get this with an 1100 cfm rated blower. No. The blower will need to be rated ca. 1500 cfm to be able to flow 1100 cfm with the system's pressure losses.

What are these pressure losses? Examples are:

Transition turbulence at the hood entrance, baffles, and duct transition
Momentum changes at the baffles
Duct friction & turbulence losses
Duct bend momentum loss
Dirty filters in the case of meshes
Pressure loss in providing make-up air (passive systems will have a higher loss than active systems)

I won't get into fan curves and why 1500 is a plausible number, but the above is the rough rationale hinting that one has to move a way up the fan curve to find the likely actual cfm.

Generally, all the numbers required for a proper calculation won't be available.

MUA introduced elsewhere in the house, or from a wall diffuser panel, or from under the range should minimally disturb the rising effluent. MUA introduced at the hood has to be done correctly so that it doesn't compete with capturing and containing the effluent.

If there are other combustion appliances in the house not separately supplied with air, the house pressure should not be allowed to fall below 0.02 inches of water column. Passive MUA may not be able to achieve this.

The desirable hood size is a topic for another time.

kas


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RE: HELP! On Custom Vent Hood

kas,

Wow. I had to read your post at least 2 more times to get most of what you said! Thank you so much for taking the time. You are awesome.

To do some calculations per your suggestions, I was going to use a 27" x 6' capture area, so 2430 CFM (a little extra compared to your numbers due to the extra 3"). If I also use those side wings that were just going to be for looks, that would be 27" x 9', so 3645 CFM. Assuming a 50% reduction from baffle aerodynamics, plus a 40% increase due to pressure losses, I'm looking at either 1700 @ 6' x 27" or 2550 @ 9' x 27" capture areas.

I would guess the baffles would REDUCE airflow, but you're the expert! I just hope these restaurant baffles I found would have similar benefits?

As for the makeup air supply, I'm leaning now toward a split A/C unit tied to the fan controls somehow. This will give positive pressure air flow rather than relying on passive replenishment, and also add additional cooling to the kitchen which will definitely be a bonus when cooking for large groups during the summer. Thanks for pointing out that the MUA in the hood would push some of the effluent into the kitchen, which I definitely don't want!

So would you recommend 1700 or 2550 CFM... should I count the passive under-cabinet area, or just the active cooking area?

I linked to my updated draft design (I couldn't figure out how to do it inline). Thanks so much for your help!

Here is a link that might be useful: Hood Design Rev 2


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RE: HELP! On Custom Vent Hood

To clarify, the baffles do reduce flow by inducing a pressure drop across their boundary. This pressure loss forces the blower to flow less cfm. However, the guess factor relates to the area that has to provide the 3 feet per second air velocity, which is less than the full aperture in many configurations.

Essentially, one wants to have enough velocity around the baffles that when the rising effluent hits the baffles at their blockage part and tries to "reflect" away from the baffles with a similar velocity to the effluent's initial velocity, (recall angle of reflection equals angle of incidence re the normal) the blower flow velocity provides a net rising velocity that keeps the reflected part in the hood.

Or to look at it another way, in images of Schlieren photography the effluent rises and curls around and spills out of the hood if the flow is insufficient for the rising effluent.

That's how I look at it, anyway.

Ideally, hood manufacturers would provide pressure loss vs. flow graphs. I have only seen one datum on this for a commercial baffle type hood where the loss was (as I recall) 0.1 inches at some flow rate that was the design point for that hood.

When side wings etc. are in use, but there is no rising effluent below them, then I don't think their area has to be included. One can get pretty involved in estimating what part of the hood is actually in play at any time and how much flow is needed to capture and contain the effluent.

You may imagine that if only one burner were working, the effluent would rise and spread out in the hood. However, you don't generally have any way to adjust the flow to match the effluent velocity distribution over the hood guts.

There are some published papers on what the upwelling cfm is for various cooking activities and surface types. One could calculate the total up cfm that was generated by some worst case cooking activity and then specify the actual cfm needed accordingly. Then scale up for pressure loss.

Or you could scale by the recommended (deemed adequate, I suppose) fan cfm values in Wolf's Design Guide for various cooking cases and hood sizes.

I went through a lot of different approaches to conclude that for my island hood (internal aperture 27 x 61) over a 36-inch induction cooktop and 3500W induction wok, that a 1500 cfm blower would be adequate (zero static pressure rating, probably 900 cfm actual at minimum negative house pressure and system pressure loss). It seems to be adequate so far.

Your drawings are a bit unclear to me; perhaps I need to look at them longer to be sure how the hood and cooktop are related.

kas


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RE: HELP! On Custom Vent Hood

Thanks for the explanation. I'm not a physicist by any means (I was briefly a physics major until I realized how much math I'd have to take). Fluid dynamics are not my thing (I believe gases follow the same principles). But I don't have to understand the math of it if in the real world it works out to great ventilation with little effluent leakage! If your setup works well, that's the kind of real-world guidance that matters most to me!

There's a lot going on in my diagram, and it's kinda small, so I've blown it up for you and included the location of the range top:
http://www.flickr.com/photos/8160682@N08/6323636209/

I also included elevation view; I hope that helps to clear it up some.
http://www.flickr.com/photos/8160682@N08/6324185974/

Thanks!


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RE: HELP! On Custom Vent Hood

Yes, the original drawings' labels wouldn't render well and zooming up didn't help. Unfortunately, this is also true of the new drawings. In the new plan, where is the MUA being injected, above the cook's head, behind the hood along the wall, or somewhere else?

Are the spaces to the right and left of the Culinarian cooking surfaces? Locations for future specialty cooking devices? Well ventilated shelf spaces?

kas


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RE: HELP! On Custom Vent Hood

Reviewing all I can find on MUA and this is a great help. Thanks kas.


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RE: HELP! On Custom Vent Hood

The paper at this link provided by another member in a different thread may be a helpful summary.

kas

Here is a link that might be useful: CA energy board paper


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RE: HELP! On Custom Vent Hood

Hi Kas, sorry you haven't heard from me. I got delayed by our EXTREMELY long and demanding escrow process (almost 3 months) due to our unconventional renovation loan (no kitchen in the repo house). But we finally closed escrow the day before Thanksgiving, and here I am again, back to try to figure out the vent hood!

The current version of the kitchen has a 60" range top with two 15" induction wok burners. I tried to get off the shelf hoods, but I can't find any line that makes a sleek wall hood in both 24" and 60" widths. Plus, I'd really like to have a quiet, powerful inline blower. So I've attached a new drawing and enlarged the type, hopefully it's clearer:

1. Front Elevation: http://www.flickr.com/photos/8160682@N08/6646663981/
2. Plan & Side Views: http://www.flickr.com/photos/8160682@N08/6646663925/

Thanks a lot for the article, it was very helpful! I'm encouraged that some of my strategies will help: side "panels" (27" deep cabinets) and deeper hood (27" vs 24"). I'm leaning toward an inline Fantech FKD12XL for a max of 2016 CFM. I'm also considering buying 3 sets of Broan's 33" baffle filters (RBFIP33) and have my fabricator build my custom vent hood around them.

I'm tempted to buy a $199 36" hoods from eBay just for the electronics; what do you think? For my custom job all I could find was these ugly controls: http://www.amazon.com/gp/product/B003AUE32S/ref=s9_simh_gw_p60_d0_g86_i3?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-3&pf_rd_r=1YM9KJAM9V4GXC49QN6Q&pf_rd_t=101&pf_rd_p=470938811&pf_rd_i=507846 and http://www.amazon.com/gp/product/B000HQAVNI/ref=s9_bbs_gw_d0_g60_ir01?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1YM9KJAM9V4GXC49QN6Q&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846

As for MUA, I was leaning toward a split A/C unit like this one: AIR-CON A13CH/EM4H4G24 24,000 BTU Ductless Mini-split Air Conditioner w/Heat. It blows 1330 m3/h, which is 782.8 CFM. If we turn the vent hood to max, we will need to also open a window or turn on the central A/C fan. I'd like it to blow under the range top base cabinets, but the blower unit is pretty bulky, so placement would be a real problem/eyesore. So now I'm wondering if I could just put a couple 8" Broan Model SMD8 dampers at floor level under the range cabinets. I do live in San Diego, so it'll usually be unnecessary to condition the air, but on the few near-90 degree days it may get a bit warm in the kitchen. Of course, if the A/C is on, it should suck in very little from the outside, right?

Tell me what you think, and again, any help would be greatly appreciated. Thank you so much in advance!

David


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RE: HELP! On Custom Vent Hood

I'll leave it to kas regarding the performance issues. What I want to do is to strongly recommend that you look at dedicated custom hood fabricators before you get some sheet metal guy pretending to know what he's doing building yours. This is a major league ventilation project and hate to see you end up with a kludgy home brew solution when better ones exist.

I am a broken record on this recommendation, but it's the only one I can make based on personal hands-on experience. We had our custom hood liner built by Modern-Aire:
Modern-Aire
Ours is a 64'' wide unit with their high quality baffles running across the liner. They can fab the size and configuration any way you want: we have fully dimmable halogen lights running to a wall dimmer, along with the Fantech blower controlled by an adjacent infinitely variable speed control adjacent to the light switch. They can configure it for 12'' ducting, which you'd need with the FKD 12XL (and I'm impressed that you can find space to run 12'' ductwork!). I can virtually guarantee that the quality will exceed what an inexperienced fabricator can do, and at a price that will be competitive. There are other companies that can do an equally good job and I am sure others can post of their experiences with those.

One more question: I'm confused by the concept of using an air conditioning unit for MUA. I worry you are missing the basic concept of MUA. MUA is all about high volumes of outside air flowing unencumbered into your kitchen. Correct me if I'm wrong, but split systems are designed to recirculate 100% of the cooled air--the ones we use at our office to cool our lab and server closet have absolutely no outside air source. Therefore, they would provide zero cfm of MUA, right? The only way I know to do what you're asking (to bring in cooled MUA) would be to use a heat exchanger, something usually reserved for commercial applications. But then again, if you're pulling that much air out the hood, maybe that's what you need. Your suggestion of dampers in the cabinets might be closer to the mark, assuming you can get large enough ducts under your cabs to allow 1500 cfm of MUA to flow. If you had the room, you could then run those ducts through the heat exchanger to give you at least partial cooling of the outside air before it hits your kitchen.


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RE: HELP! On Custom Vent Hood

Clin(?), thanks for your advice. I am also looking into Modern-Aire and Rangecraft, waiting to hear back from them or their dealers. I really started this in earnest yesterday. :) I am looking for something like the PS-16 but the website states up to 96" wide, I need 108". They have contacted me but only to redirect me to a dealer, did not address my size needs.

I have used my fabricator before to fab large curved pieces, and he did a beautiful job. There were two basins for waterfalls, 11'6"W x 12"D x 12"H with complex bends and an 8' gently curved section. He fabricates custom vent hoods for restaurants, too, which I've seen in his shop. But I see your point, all Modern-Aire does is range hoods, so no trial and error in the design.

Can I ask how much ballpark your 64" Modern-Aire was?

You're right on the split A/C, unless I can hook up its intake to an external damper rather than having it recirculate indoor air.

Thanks again for your advice.


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RE: HELP! On Custom Vent Hood

Modern-Aire can build any hood pretty much any size so 108" is not a problem in the PS16

This one is slightly smaller than 108" but can be extended

Photobucket


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RE: HELP! On Custom Vent Hood

David: sent you an email with some additional info.


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RE: HELP! On Custom Vent Hood

Answered in parts, not necessarily at the same time.

The first URL(Speed Control for Fantech Fans) is for a typical motor control wall unit. You need not mount it with that particular cover plate, any switch plate will work. You just have to remember (if the installation turns out to be silent :) which way is off. The only issue is whether that control is sufficient for the fan motor you want to use. Fantech can answer that.

kas


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RE: HELP! On Custom Vent Hood

I don't recall such an email... Sorry


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Hood fabrication.

I agree with clin' and trevor that having a fabricator familiar with the subject of hood and baffle design who can build a complete hood is usually a better approach. I also notice that Wolf makes a 27 x 66 wall hood. (See the Wolf Design Guide page 106.)

kas


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RE: HELP! On Custom Vent Hood

Trevor, thanks for the pic, it looks awesome. I'm looking for a wall mount with a very minimalistic esthetic like the PS16.

Clinresga, got your e-mail. Thanks!

Kas, thanks. Fantech actually pointed me to a nicer Decora-style 7-speed "switch" (looks like a dimmer): the SCD 7. But now Clinresga has me leaning heavily toward Modernaire... just need to get a price to see if they're in the ballpark!


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On MUA

The first principle of MUA is that what goes out of the kitchen through the hood must come into the kitchen from somewhere, and its converse, what isn't allowed to come in won't go out. (A positive displacement vacuum pump would be an exception.)

The second principle is that as the restored MUA is restricted such that the house pressure falls, the outflow will be less because the ventilation fan is spec'd at its rated cfm at zero static pressure. (Fantech provides fan curves or tables that specify the flow rate at various pressure differentials.)

The third principle is that there will be pressure drop in the outgoing hood and ducting, and that there will be pressure drop in a passive MUA system. Some of this can be overcome by an active MUA with a fan. Nominally, you would need a fan commensurate with the ventilation fan (FKD12XL), or larger if there are additional house exhaust fans.

With a passive and unrestricted MUA, the ducting should have at least the sectional area of your exhaust 12-inch ducting. Multiple smaller ducts meeting this relationship can work, but need to exceed it a bit due to increased wall friction.

The first question to ask, is do you want to screen the MUA intake? From eagles? Mice? Mosquitoes? Dirt and dust? The finer the mesh, the more pressure drop. This can be _partly_ compensated by using large screens and/or filters with a duct transition to the desired duct size.

Are there any combustion appliances in the house that have air intakes that are not isolated from the kitchen air. In that case you may have to use active MUA because the pressure drop through a filtered passive MUA will exceed that which causes back-drafting in many cases.

If you can insert the MUA somewhat close to the range, then heating and cooling requirements may be less or non-existant (in the case of San Diego and probably most of Hawai'i). Otherwise, a means of heating and/or cooling is required. This is a lot of air to heat or cool per unit time. Significant BTUs per hour will result from a simple calculation of mass of air flow per hour times the specific heat of air. (All that you need to know is on the web somewhere.) Conditioning the air is out of the scope of this message.

kas


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RE: HELP! On Custom Vent Hood

Kas,

Thank you. Great points I need to consider.

I don't know how much of the article on improving commercial kitchen ventilation applies to residential kitchens, but it talked about transfer air from the dining room, diffusers in wall/floor/ceiling, and most of the integrated hood plenum options seem less than ideal in a residential kitchen due to esthetic concerns. I just don't know how much central air can alleviate some need for MUA like they seem to suggest.

Since I feel 2016 CFM is oversize for my needs (I don't know for sure), it should probably compensate for the passive MUA, especially if the dampers are close enough to the range hood and adequately sized. I would like a screen but not a filter as that would restrict flow too much. The 12" duct has an opening area of 113 in2, dual 8" dampers 100 in2.

Come to think of it, I may need to have the dampers in the roof, as I don't want the things sticking out both sides of the wall!

As for combustion appliances, we have 3 gas fireplaces, but they're about 35, 60, and 90 feet away. That would be a good reason to consider active MUA, though with free flow MUA within 10 feet of the hood should greatly reduce the risk of negative pressure 40-90 feet away.

I think 350-360 days a year, we should not need conditioned MUA, and the other 5-15 days we can crank up the A/C. If we're still hot in the kitchen, I can always add a split A/C unit for cooling purposes. I'll get a heat pump model just in case, but if we're creating so much exhaust we need 2000 CFM of MUA, we're probably making a great deal of heat (though most of it will be exhausted out!).

Kas, thanks again for your in-depth analysis. I hope to have an update for everyone soon as to whether we will be going with ModernAire or Rangecraft or fully custom.


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hrv/erv + dampers = mua heaven?

I have almost decided on a 27D x 108W custom box-style hood from Rangecraft. Now back to the MUA issue:

Why can't we tie range hoods into HRV/ERVs (heat/energy recovery ventilation)? Seems like it would be the perfect solution: a range hood needs an exhaust fan and ideally, an intake (MUA) fan and a way to condition the fresh air. Rather than purchasing 1) a blower for exhaust, 2) a blower for MUA, 3) a conditioning solution (and dampers and such), and 4) a separate HRV/ERV for your airtight home, why not tie the range hood to the HRV/ERV?

The HRV/ERV has both exhaust and intake fans as well as conditioned air: seems like a match made in heaven. Add dampers that switch between range hood duty and whole house duty, and this seems to me to be the ideal solution. This assumes, of course, complete grease removal from the range hood exhaust to reduce fire risk.

Am I missing something here? Please educate me! Thanks in advance for your expertise. I'm looking at the Fantech SHR-14104, a 1410 CFM HRV (4 blowers, I'm guessing 2 for exhaust and 2 for intake?).

David


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RE: HELP! On Custom Vent Hood

What you won't be missing after a while is the grease that will accumulate in the device that takes heat or cold (physicists need not point out the sloppiness of that phrasing) from the outgoing air and puts it back into the incoming air. Any effective and practical heat transfer device that I can think of will collect grease and dust in this application. I don't know how easy it would be to clean such a unit, but my guess is that they are not designed for this.

Essentially, all kitchen ventilation puts effluent into the environment. This is nearly inevitable. The only question is what kind. Residential units and most commercial units pull grease, smoke, and water vapor from the kitchen and put it directly into the environment.

The probably rare UV systems convert the effluent to simple molecules, but then the ozone they generate has to be vented, or somehow filtered out, perhaps by charcoal, generation of which has its own issues. So the only thing green about a kitchen is the paint, and the goal is to minimally risk fire while getting rid of the effluent.

However, my view on this is somewhat speculative. A commercial HVAC company that deals in large HRV might have something that would be practical. Perhaps some need for commercial heat recovery has spawned a practical kitchen venting HRV.

The Fantech has a washable filter. How long would it take for cooking grease to gag it? What of potential grease fires. And the specified cfm has to be reduced by all the other pressure losses, so you would likely need a larger unit anyway.

kas


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RE: HELP! On Custom Vent Hood

Thanks, kas.

I was hoping there was a way to remove ALL the grease to avoid gumming up the HRV's works. If not, this idea is a non-starter and I'm right back to separate exhaust and MUA systems. I do have an e-mail out to an HVAC engineer in my area; I hope they can think of something!

You're right, kitchens are NOT green. The people on the greenbuildingadvisor.com forum HATE big kitchens. It seems to me that induction is currently the best technology to minimize waste heat and effluent, but the gas cooking fans are rather resistant to it (including my wife).

As for the UV system, I'm definitely NOT OK with creating ozone pollution (ozone is a free radical and promotes DNA mutations in living tissues). San Diego has enough ozone without me adding to it (thanks to Tijuana?).

David


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RE: HELP! On Custom Vent Hood

Another thought about the un-"green"-ness of kitchens, specifically with regard to the browbeating often aimed at those with large, commercial-size kitchens:

1) trophy kitchens aren't creating an environmental impact as long as they aren't used, and most who can afford one rarely cook
2) those who do use these kitchens to full capacity by cooking for large groups (like us) are "range pooling": we use a lot of energy in our kitchen, but 20-40 people AREN'T doing so in their kitchens or in restaurants for that meal
3) some have suggested outdoor kitchens as a greener alternative, but the waste heat still affects the environment, just not the house's thermal envelope

David


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RE: HELP! On Custom Vent Hood

If one could filter out all the grease, then one might as well push the exhausted air right back into the house without any HRV being needed. With gas cooking, there is some BTU level for which combustion product absorption would be needed before recycling the air.

A few odor filters after the perfect grease filters would be a good idea.

kas


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RE: HELP! On Custom Vent Hood

True, if it were possible to remove the grease completely, returning the air into the house is more feasible. But the HRV would offer the benefit of fresh air vs. whatever lingering odors there might be, and especially in the summer, the ability to exhaust the heat, though the hot effluent air through the HRV will probably heat the incoming air (we're in San Diego) and be counterproductive, though in the winter it'll be great. It'll also be fine for changing out air conditioned air in the summer.


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On second thought ....

I should clarify that I find the Fantech unit rather impressive in flow vs. pressure loss. It might be worth their time, given the likely cost of the unit, to provide some advice to you on its utility (or UL approval) for kitchen venting and what type of filter pack they might deem to be adequate, if any. One could do a lot of filtering for 0.4 inches w.c. (as long as the duct was transitioned up to four square feet or so for the filters and then back down to the interface size).

I'm guessing that a metal mesh filter on each side of a deep particulate filter would provide some predictable fire resistance, as meshes are used in many residential hoods. Particulate filter caddies are available that would make replacement easy, albeit expensive if the filter loaded up quickly. The mesh filters would have to be regularly de-greased and de-linted also.

Ultimately, the heat transfer efficiency of the HRV would fall due to surface heat transfer coefficient loss with grease build up; but this might be slow, and Fantech may have made cleaning practical.

Please let us know what you find out.

kas

P.S. In order for the house pressure to remain near zero differential with the outside air, the flow in has to equal the flow out. Because the fan curves are not vertical, some balancing of the pressure loss in each path would be needed.


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RE: HELP! On Custom Vent Hood

Thanks for the suggestions, kas, I've e-mailed my contact at Fantech based on your suggestions.

As for balancing the incoming and outgoing air through the HRV, you would think that would be part of its design, no?

I'll keep you posted!

David


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RE: HELP! On Custom Vent Hood

On the intake path, there is the exterior (filtered) air intake, likely at a different distance from the HRV than the exterior vent on the exhaust path. (These need to be separated by 10 - 12 feet depending on code. Put the intake upwind.)

On the kitchen side of the intake may be a filter and a diffuser. On the kitchen side of the exhaust will be the hood with its baffles, as well as the gorilla filter you need to keep grease out of the HRV. Ducts and transitions will differ.

Hence, the pressure drop exclusive of the HRV in the intake path will be different from that for the exhaust path. Somewhere an adjustable damper may be needed. This is where primitive sophistication has a role. A pressure activated damper control can be used to provide dynamic balance so the unbalance effects of turning on a bathroom fan are compensated. No electronic servo controls should be required.

Commercial building HVAC companies should know a lot about how to best set up this kind of system.

kas


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RE: HELP! On Custom Vent Hood

Kas, you said: "The Fantech has a washable filter. How long would it take for cooking grease to gag it? What of potential grease fires. "

.... aak, I never thought of this. So I need to worry that my inline upstream fantech blower might be getting clogged with residual grease-gunk? I should be thinking about cleaning this thing out?

David: LOL ~ "...trophy kitchens aren't creating an environmental impact as long as they aren't used, and most who can afford one rarely cook".

...probably this isn't so relevent among GW'ers, but who knows?


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RE: HELP! On Custom Vent Hood

The upstream Fantech blower will condense some grease, just as the ducts will condense some grease. Judging from some ducts I ripped out for my kitchen reno, the build-up per year is modest. The NuTone fan that I had been using for 20 years as a range vent exhaust was fine for re-use as a venting blower for over the wall ovens. However, I wasn't trapping the grease in a filter, and I wasn't doing much wok cooking, or griddle cooking. A film of grease on fan blades will have less effect on the fan than a film of grease on a heat exchanger will have on an HRV's thermal efficiency.

kas


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