My understanding is that HRVs are intended to provide a modest change in interior air while capturing back some of the heat that would otherwise be lost through air exchange. Typically, they are not scaled for 600 - 1600 cfm flow rates, but I don't know what yours is designed to do. If your house were perfectly sealed, the flow up the kitchen vent would equal the flow in through the HRV. This might be only 200 cfm even though your kitchen vent blower was rated for 1200 cfm. In other words, the HRV may be too restrictive for the flow rate you want. This leads to requiring a larger duct that opens only when there is significant vent flow. (This part is easy.) But still, the house pressure may drop too low. Problem 1: For safety with any combustion appliances in the house that are not separately supplied with air, or fireplaces that are almost always connected to the kitchen pressure, the house pressure cannot be allowed to become more than slightly negative. This may force the MUA system to be an active system with a blower. Problem 2: When you need to heat and/or filter the MUA, then there is yet more restriction and it may again be necessary to provide a blower in the MUA duct. Problem 3: Controlling this blower so that it works correctly for any cooktop vent flow rate, bathroom fan flow rate, window condition, fireplace operation, etc. leads to a complex design. The least complex design I can imagine for a high flow rate kitchen hood has these characteristics. a) All combustion appliances have their own MUA (and no chimneys leak). b) No fireplaces are used when the kitchen vent is on. c) A large duct (at least equal to the one above the vent hood) with damper is used to bring in MUA, and the damper is controlled by a hood duct flow switch d) If heating is needed, an electrical resistance grid that causes minimal pressure loss is used in the MUA duct, controlled by a thermostat. (The power requirement may be significant, at least for the period of high ventilation cooking.) e) If it is hot in the summer you have to lump it. All other approaches of which I am aware will have additional complexities and costs. MUA induced into the hood will not work well and doesn't in most commercial settings. Use of water-to-air heat exchangers, or refrigeration-to-air heat exchangers (heating or cooling) in the MUA duct will cause enough restriction that the house pressure will become too low or little MUA will flow, mandating an in-line blower and its control system. Fin type heat exchangers will also require quality air filtering for further pressure loss and bigger compensating blower. kas

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

Posted by canarybird (My Page) on Tue, Aug 25, 09 at 18:11 Depth of Field Hi again everyone. I'm back with another entry on how to use your digital camera for taking tabletop photos. Today I want to talk about Depth of Field. Depth of field is the area of your picture, from foreground to background, that is IN FOCUS. Here, in the first picture (left) you see the two pieces of fruit clearly because they are in focus. The background is out of focus, or blurred. This is a technique used to emphasize a subject and make it stand out from the background. Here again is another example in this sports photo (right), where the player in the foreground is in sharp focus against a blurred background. (Sport photo credit at right to Allen Eyestone/The Palm Beach Post) You will also see depth of field referred to as DOF in photography texts. In these next examples, the first mug (left pic) is the only one in focus and the rest are progressively more blurred. We can say that in this photo there is a SHALLOW DEPTH OF FIELD because the area that is sharp extends only to the first mug, in the immediate foreground. In the photo above right, there is a DEEPER DEPTH OF FIELD where most of the mugs are in focus. Sometimes you will want to have the whole of your photo sharply in focus (eg. landscapes, holiday pics or full dining table), and other times, such as in some food photos, you may want to have your subject stand sharply against what is only a suggested background, misty or shadowed to give an impression of what's there without detracting from your subject. Although creating a very shallow depth of field can be done beautifully with DSLR (digital single lens reflex) cameras, due to the lenses available for them, (you change the lens according to the type of photography you want to do), it's possible to get an attractive blurred effect with a simple point and shoot, such as the left picture of the mugs above. (I think in future I will call them P & S cameras, as it sounds better and is easier to write). Just to digress and show you what I mean about the possibilities of the DSLR, here below is the same subject taken by a DSLR at left and with a P & S right. You will have seen such extreme shallow depth of field on many food blogs on the web. In this case you see both the foreground and background out of focus, while the second row of the left egg and the right ceramic chicken are relatively in focus. To the right, the P & S version shows nearly all in focus except the chicken in the rear. I deliberately used a very shallow depth of field on the DSLR to demonstrate that a middle plane can be also chosen as the in-focus area. (50 mm Canon lens at f/1.4). So how do you get your foreground sharply in focus and the background out of focus? Here is one way to do it. Let's make a test run during daylight. Find your best window light with a table or shelf underneath and get some fruit, eggs, muffins on a plate or whatever you want to use as a subject, preferrably an object with a little height. Even a couple of coffee mugs will do. Take some other larger objects which could be pots and pans, a plate of fruit, a vase of bushy greenery or even a stack of books. Set your table so the pots, books or whatever are about 20 inches (50 cms) away from your subject (fruit, muffins etc.). Here's my setup for the first photo on this page...the prickly pear and kiwi pic at top left. I sat on the low stool and rested my forearms on the edge of the table, holding the camera. See if you can somehow duplicate this setup and sit low down enough to be able to have the camera just above table level and close to the subject. Set your SCENE or MODE dial to PORTRAIT. Why do I use portrait mode so much on these examples? The reason is that portrait mode is a medium closeup setting, meant for taking photos of someone about 6 feet away in front of you, rather than of a distant landscape. Therefore the aperture (lens opening) is wider than it is for distant shots. (Explanation about aperture later.) When the camera lens is wide open, the depth of field is shallow, which will make foreground objects sharp and background objects unsharp. So that a person in a portrait will stand out more against an out of focus background. (Are you still with me ? :-)) So this is probably the best setting for closeups of food. Many digital cameras have a "cuisine" setting which also adds extra red to give warmth to the picture. Do try it out if you have that option, because it will be designed for a tabletop setting. You may or may not like it but don't ignore it before giving it several tryouts on different foods. So back to the test. You have your SCENE set to PORTRAIT. Add MACRO (the tulip icon) as well to your portrait setting. Point to the subject and add some optical zoom until the subject fills the viewfinder and you are happy with the composition. Press the shutter halfway and check that your focus light doesn't blink. If it blinks, then unzoom a little or move the camera a bit further away from the subject. Press the shutter halfway again.....does the focus light still blink? If so, move back a little again. Press the shutter halfway again and once the focus light stays steady, press the shutter the rest of the way. Now take another 10 pictures in the same manner. Go and check them on your computer. Not happy? Do it all over again :-). The key to good photos is practice, practice, and practice again. You will find that you do get better as you learn and it's a great feeling! The way to get blurred backgrounds in tabletop closeups with a P&S is to get close to your subject and have your background items at least 20 inches away as explained above. The closer you are to the subject and using MACRO, the more out of focus your background will appear. To get a nice background blur outdoors is to have a subject ...such as this dish of fruit below (photo left)....resting on a table about 10 feet in front of a tree and hanging basket. I sat in a chair next to the table where the dish was resting and using PORTRAIT, MACRO and optical zoom on the bowl, took this closeup showing a background that was nicely out of focus. You can have some good effects when you get close to and zoom in on a subject which is a good distance from a dappled shrubbery background where you see pinpoints of light (photo right). You need to experiment constantly. Bokeh You may hear this word used by photography buffs at one time or another. Bokeh is the Japanese term for "blur" and refers to the beautiful creamy out of focus backgrounds behind a sharply in focus foreground subject. I haven't found out why we use a Japanese word but it does sound a little more exotic than just saying "blur". And here again I have to say that the best bokeh comes from the SLR (single lens reflex) cameras, both film and digital, just because one can use lenses with very wide apertures, wider than are seen on a P & S. There are other difference between the two types of cameras but I won't go further here. Point and shoot cameras are designed to take faultless, sharp travel and holiday photos of beaches, landscapes and family events with the least possible intervention of the photographer. They're made to be easy to use although they do have some creative possibilities if one so desires, in both the manual and semi automatic settings. Here are a couple of pics I took with my Canon EOS 30D DSLR where you see examples of background shrubbery totally out of focus so the subject stands alone. And here are a couple taken with the P & S, outdoors with a brass vase on a table about 20 feet away from bright shrubbery . I sat at the table, about 2 feet from the vase, used PORTRAIT, MACRO, and optical zoom to bring the vase closer. I moved my position slightly to the right to get two different shrub backgrounds. Do try to see what you can get using a similar setup in daylight. Best results are when the background has a dappled sunlight with light and dark areas and it fills the screen behind your subject. Use your MACRO and optical zoom or get close to your subject, aiming so both the subject and background are within the viewfinder (or LCD screen.) I think this is enough for one day. I did want to go into some visual diagrams to better explain how depth of field is altered by the aperture or opening of the lens. A wide lens opening gives a shallow depth of field and a small lens opening gives a deeper depth of field (all is in focus from near to far). Well there's always next week isn't there. Coming up will again be more about aperture shutter speed, and the meaning of f/ stops, but I'll go softly and keep explanations simple. It may also be handy to have a quick guide on how to open and set up your tripod. It's sometimes a very frustrating experience the first times you do it. I hope you are understanding it all and if you have questions please ask here or PM me. So thanks for joining me. I'll be uploading the next installment soon. And please feel free to save the pages on your computer. Sharon (Canarybird) :-) (All text and photos copyrighted) Free for personal, non-commercial use Follow-Up Postings: o RE: Food Photo Tips: Part 8 - Depth of Field clip this post email this post what is this? see most clipped and recent clippings * Posted by publickman (My Page) on Mon, Nov 2, 09 at 2:34 I did a lot more with depth of field when I used a film camera than I did with digital, and I'm still learning how to use my new digital camera. It was much easier for me with film. Lars o RE: Food Photo Tips: Part 8 - Depth of Field clip this post email this post what is this? see most clipped and recent clippings * Posted by canarybird (My Page) on Mon, Nov 2, 09 at 4:58 Lars depth of field is a cinch to handle with a DSLR, and lenses where you can adjust the aperture ...(f/1.4 to f/22). It's not so easy using a non-reflex digital camera. o RE: Food Photo Tips: Part 8 - Depth of Field clip this post email this post what is this? see most clipped and recent clippings * Posted by publickman (My Page) on Wed, Nov 4, 09 at 2:40 Unfortunately, I don't have that range of aperture on my camera - the maximum aperture is 2.8, which is not bad, but not as good as 1.4. The ISO range will go to 1000, which I find helpful, since I photograph in ambient lighting, aka fluorescent, in my office most often. I have been lazy and set the camera to be completely automatic for most of the photos I take of my cardboard furniture models, since I have to fix them in Photoshop anyway. I often cut out the background altogether. I also Photoshop out the reflections made from the tape I use to make the models. Lars o RE: Food Photo Tips: Part 8 - Depth of Field clip this post email this post what is this? see most clipped and recent clippings * Posted by canarybird (My Page) on Fri, Nov 6, 09 at 11:27 Lars is you can get what you want with fully automatic settings then that's great and it's true you can usually make adjustments in Photoshop or other programs. I had some disappointing results the other day with my DSLR in the Botanical garden where there are extremes of dark shade and bright sunlight. I'm going back there again and will use only automatic to see what settings the same camera chooses and how the pics turn out. Then I can go back again and hopefully fine tune my settings for some better pictures. It's all trial and error sometimes in difficult lighting situations. Luckily the entrance fee is just a couple of Euros. :-) SharonCb

The fundamental issue is that fan/blower flow rates are measured in open air. The result is the zero static pressure flow rate. In a hood with filter, shape transitions, duct losses, and make-up air pressure losses, the actual flow rate is likely to be in the 200 - 300 CFM region. An 18-inch x 30-inch hood has an entry area of 3.75 square feet. At 90 CFM/sq.ft., the actual flow rate called for is ~ 340 CFM, requiring a motor rated at 500 CFM or higher, depending on myriad factors. And even if this is achieved, if the cooking plume is not entirely captured due to a smaller than needed hood aperture, there will still be grease, moisture, and odor escaping into the room.