Replies

1. 
   Norman_Williams | Feb 21, 2000 01:23am | #1

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   After reading the vent or no vent postings, I believe that the proper terminolgy for what I,m looking for is air to air heat exchangers. Gene, please fill me in on your book and where it can be purchased. Thank You

1. 
   Mike_Smith | Feb 21, 2000 02:09am | #2

   *.......yes GeneL....after borrowing your's from the library, I decided I would like the latest edition. (the one they had was the Audell bookshelf edition)..which edition should I be looking for, the publisher , etc,,,, and can I buy it at Amazon.com ???Mike

1. 
   Gene_Leger_ | Feb 22, 2000 06:28pm | #3

   *Gentlemen. The title of my book is Complete Building Construction, 4th Edition, publiched by Macmillan. You can get it at Barnes and Noble or Amazon.com. Note: I wanted to do a 100% revision of this book but was not allowed to do so. Thanks for your interest.

1. 
   Aaron_J._Harvey | Feb 29, 2000 02:48am | #4

   *Norman,I just finished installing to Venmar ERV's in an 8000+ sq. ft. house. I highly recommend the Venmar line. The units are well laid out, extremely quiet, and easy to balance once you acquire a magnehelic gauge (about $70). Because of the size of the house and the extant duct work for two FA furnaces, we chose to exhaust and supply into and out of the furnace supply and returns. As per Venmar's instructions, the only thing to watch is that the ERV's fresh air (plumbed to furnace supply) has a 90 elbow into the furnace air stream so that the ERV air can "merge" with the higher CFM furnace supply air. Works great, we could smell the fresh air in the house the first day. I'm starting an ICF house in about 30 days and plan to use the same Venmar ERV. I'm curious about using it in place of a bath exhaust by kicking it into high speed exchange for 20 minutes with a timed switch. Venmar claims this is possible. Breath deeply.

1. 
   PE_Jim_Nation | Mar 06, 2000 04:44am | #5

   *One thing you want to watch with exhaust air heat recovery is possibilities for freezing on the exhaust side, particularly if it is used to exhaust a high humidity area such as bathrooms and laundry areas.Some manufactures offer automatic defrost by reversing flow thru the heat exchanger, others recirculate house air thru the exhaust side to defrost. Just be sure your supplier has provided for the problem.

2. 
   Rob_Susz_ | Mar 07, 2000 07:03am | #6

   *Surprised Gene didn't mention it again, but this discussion of AAHE's came up last winter. The studies he quoted said that the life cycle costs of these devices is solidly negative. They never pay back.-Rob

3. 
   David_Thomas | Mar 13, 2000 07:35am | #7

   *That's easy to imagine: $2,000 for HRV and ductwork, not to mention the additional floor space you need to set aside. Put that money in the bank and crack a window open and use the interest to buy a little more natural gas.I had to put one in for code/energy rating reasons and it does eliminate brutally cold breezes through an open window left open for ventilation. But then it regularly gets to -20F each winter (that's -30C in Canadian) and last winter stayed at -40F (or C) for a week.Back on thread: The question was about wheel-based systems and everyone responded about the cross-flow heat exchanger types ( in which the HX core looks like corrugated cardboard, but in plastic, with each layer stack at 90 degrees. It's an easy clever way to make a HX but not nearly as efficient as it could be. The heat exchange wheel (which use the heat capacity of the wheel to move heat between one air stream and the other) can be much more efficient. I've used much larger versions that did better than 90% heat recovery.My only concern about them for HRV use is in the summer. If you get condensing conditions when you are recovering cold instead of heat (high humidity outside and cold air inside due to A/C use) That wheel will get wet and stay wet. Things that stay warm and wet can harbor Legionaire's disease as well as the more common molds and mildew. If you plan to use it in the summer, check what provisions are made to disinfect (coated with a biocide like copper or silver) or to periodically dry it out and kill the beasties. -David

4. 
   Scott_Mazur | Mar 13, 2000 07:17pm | #8

   *Just found another blurb on Heat Recovery wheels recently. Can't quote it word for word, but the description mentions something about the use of a disecant (spelling?) material on the wheel. The disecant absorbs and releases moisture out/in to the air. In theory, cold dry winter air is pre-heated AND pre-moisturized with the moisture and heat absorbed from the warm humid waste air. Part of the greater efficiency is the added gains from the condensing and evaporating the moisture. Plus, you not only get temperature conditioned air, but moisture conditioned as well without having to deal with plumbing the condensation somewhere. I believe this works equally well and in the opposite direction in summer. Warm, humid fresh air has the heat and moisture stripped out of it by the cool dry exhaust air. Never found any notes regarding wet mold hazards. In any case I assume you would want to carefully prefilter the incoming air and exhaust air to keep dust and crud out of the wheel anyway. Same for a plate type exchanger (which suffers from the same warm wet conditions in summer).

5. 
   Gene_Leger_ | Mar 13, 2000 09:59pm | #9

   *Gentlemen. within the last six months of last year, I reposted my discusion of the cost of ventilation with AAHE. My book, Complete buidling Construction still has the name AUDEL in black letters at the top of the cover. Be sure you get the 4th EDITION. Unfortunately, because I was not allowed to do a 100% revision much is left out. So you won't find anything on AAHE/HRV/EHR. do search the archives for my coverage of these devices. Thanks for your interest. GeneL.

6. 
   Scott_Mazur | Mar 14, 2000 12:12am | #10

   *Gene, I've been searching the archives for your coverage. Maybe I'm just not using the right keywords, but the best I can find is an equation to calculate the energy costs based on DD. With it you clearly state that where you live the cost isn't worth it, where as in a place like "Saskatchewan" (pick me! pick me!) the cost savings are significant. Unfortunately, nothing I've found actually tells me a thing about what they do, how they work or whether any one design has advantages over another.So put your touque on, carve some back bacon off the pig over by the fire and share your views on just how I can keep my igloo happily ventilated without burning all the seal oil pre-heating the replacement air.

7. 
   Patrick_M. | Mar 16, 2000 02:13am | #11

   *ScottHere's a copy of one of Gene's posts b <> which should answer your questions if you plug in your own numbers. Given Gene's patience here with all of us, I'm sure he won't mind my posting it to save him yet another time consuming effort!"The need for an AAHE/HRV depends on 1) the energy cost of ventilation ; 2) costssavings from heat recovery; 3) the cost of an HRV. The costs of ventilationdepends on a) the rate of ventilation; b) the coldness and duration of thewinter; c) fuel costs; d) furnace efficiency. The energy costs of ventilationover a heating season can be calculated from the formula: Q= 0.18xACHxVx24xDD,where Q is the required energy in BTUs, 0,018 is the heat capacity of air, ACHis ventilation rate in air changes per hour, V is the house's volume and,DD is the number of degree days.Given a 2500 ft² house with a volume of 17,000ft³ located in a 7000DD year,heated with propane costing $0.99 cents per gallon, and an air change rate of0.5 ACH, what is the annual energy consumption? Q= 0.018x 0.5x17,400x24 hours x 7000 = 26,308,800 Btu per year.The cost of this energy is found from the equation: C=[q/(Uxe)]xP where C isthe yearly cost in dollars, U is the number of Btus per unit of purchasedenergy,e is the efficiency of the furnace, and P is the cost of purchased energy.C=[26,308,800/(95,000x75)]x0.98=$365.55 per year.The ventilation costs of this house are high and an HRV might make sense. Ifthe ACH were 0.25 the cost would be reduced to $182.78. If natural gas wereavailable, and a 95% efficient gas furnace was used the cost would reduce to$92.77. The cost of operating the fan is not included in these calculations.Because ventilation costs are low, heat recovery is less feasible. Clearly then, a number of factors must be considered before installing anAAHE/HRV: ventilation rate, climate, energy costs, furnace efficiency, and theelectrical cost of defrosting the HRV in cold climates. In Saskatchewan with 12,000-degree days an HRV provides substantial savings. In milder climates,savings are marginal. The 1200 ft² Leger House (8700 ft ³ f volume) locatedin a 7000 DD, uses natural gas, and has an ACH of 0.25. The annual cost ofventilationwas a mere $25.88. Although the HTV reduced the high RH, the very low costof ventilation shows that the HRV is an extremely expensive and unnecessarymethod of ventilating this house.The Saskatchewan Conservation House and the Leger House are so-called superinsulated houses. Because of this, the actual savings from heat recovery, andventilation costs would be 10 to 50% less than the calculated costs in theseand similar houses." - Gene L.

8. 
   Scott_Mazur | Mar 17, 2000 04:04am | #12

   *Thanks Patrick, I've already seen and read this... a number of times. It didn't need to be reposted. Read it the first time it was posted, and re-read it searching the archives. In fact I even saved a printed copy to refer to when number crunching is required.The point of the questions is not the cost benefit to which I'll re-quote "In Saskatchewan with 12,000-degree days an HRV provides substantial savings" (maybe should have highlighted that point in another color). The point of the question is heat recovery, what works what doesn't, what's better or worse. And in consideration of Gene's patience (I've been learnin lots from him already and find his advice invaluable) I think the patience of those asking questions about HRVs has to be commended as well because all I'm seeing from Gene on this topic is "It doesn't pay" - unless you happen to live where I do and "Check out my book" - which unfortunately doesn't contain any of the HRV revisions (Gene why do you bother to mention your book here if the HRV stuff never made it to revision? Now I'm going to have to order it just to see what everyone's been talking about! ;-)Let's say that slippery salesmen and high end installers are pushed out of the market by competition and the cost of HRVs is cut in half. Are we still arguing about cost benefits or will we now be arguing about whether a heat wheel design is better than cross flow design? Maybe for Gene and his clients it will still be cost benefit. For me it's already beyond that. Besides, code is just around the corner (if not already nipping at the heals) and then cost benefit really won't mean beans except in terms of which one costs less.Sorry if I've been poking ya with sticks Gene, didn't mean to get up in a huff, just trying to get through to the good dirt.

9. 
   Mike_Smith | Mar 17, 2000 02:55pm | #13

   *here's two HRV's listed in Grainger's:both Broan, both with all the bells and whistles:i list the 120 CFM only , there is also a 180 CFM..HRV100H...$883ERV100HC.....$1206both have same performance specs, the higher priced one has better control capabilities...?pg.3498

2. 
   Norman_Williams | Mar 17, 2000 02:55pm | #14

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   Do any of you mechanical types have any experience with heat recovery wheels used to introduce fresh air into the structure. We build ICF homes with polyurethane insulation in the attics. Daily air exchanges are a must. Someone mentioned these to me and I would like to hear about them from people in the industry. Thanks in advance. Norman