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HVAC, windows, insulation and ventilation for ICF
Last Post 15 Aug 2009 08:38 AM by rykertest. 48 Replies.
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OhioICF
New Member
Posts:13
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29 Mar 2009 12:43 PM |
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I've found this site immensly helpful in designing my house, and thought I'd share my experiences. This might help you, and it might still help me... so in advance, thanks for reading. I'm building a ranch ICF house with a walkout basement. Each floor is 1800 sqft, with 9' ceilings. It has approximately 450 sqft of glass, most of it facing north (on the walkout side), and will use an air-to-air heat pump as the primary heat source (w/ propane fireplace and woodburning stove backups). We'll be using raised-heel trusses to permit R-49 formaldahyde-free blown fiberglass insulation to extend to the outer edge of the 6" ICF forms. We've been told to assess the walls at an R-40 for HVAC purposes (if you add up the materials it comes out to be R-25 or so, but they don't permit air infiltration, which is the real killer in houses -- this is the primary reason for building with ICFs in the first place). We're also placing R-7.5 rigid foam underneath our basement slab. I have no idea what effect this will have, but if it keeps our toes a little warmer, it's money well spent. Our initial heat loss calculations were done using this free tool (note that it sizes heating, not cooling): http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htmIt allowed us to make tradeoffs between differing options to get a sense of where our money was best spent. Additionally, it's numbers seemed to be close to that of other tools I found along the way. Kudos to the tool's designer: Gary Reysa. Some interesting things that we found were that Serious Materials vinyl windows came in at around $13,000 with an R-5 (whole window) and lifetime warranty, whereas Pella were about $9,000, with an R-3 (whole window) and 20 year warranty. We also looked at Anderson, Milgard and Kolbe; all have very good products. Unfortunately, I can't endorse product here... but check out these websites: http://www.seriouswindows.com/html/vinyl.html http://www.seriousmaterials.com/SeriousWindows_Bro.pdf
Double-hungs tend to be cheaper windows, but casements/picture windows let more light in (because there is no hardware right in the middle) and have better R values. We also learned alot about HRVs and ERVs. Because our house will be so well insulated... it turns out that a 1.5 ton heat pump (smallest you can get without going into mini-splits) might be oversized. This may result in the AC not running long enough to pull much humidity out of the air. We are solving this problem by using an ERV. (ERV's pull humidity out, HRV's don't... and we have to use something because of our airtight walls.) Because our house will have low humidity as a result of the ERV, we can keep the thermostat higher in the summer, and that should offset it's operating expense. The Ultimateair 200DX ERV has an efficiency of 95%... combined with airtight, well-insulated walls/windows, and ample (well-placed) attic inulation, this means very little energy loss. |
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James Eggert
Basic Member
Posts:411
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29 Mar 2009 04:25 PM |
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A free tool to size heating is a good start.
try www.hvac-calc.com which is the software I have used for years. It has an ICF setting so the thermal mass effect is considered, as well as the lower air infiltration factor.
I believe the single use for a project is $50 so you don't have to buy the program for $400. |
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Take Care<br>Jim<br><br>Design/Build/Consulting<br>"Not So Big" Design Proponent |
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robinnc
Advanced Member
Posts:586
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29 Mar 2009 06:50 PM |
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Ohio.....Wow!! You 'only' need 1 1/2 tons for 3600sf??
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BlackHatch
New Member
Posts:50
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29 Mar 2009 07:30 PM |
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There are more efficient windows than the Quantum offering.
You can get a casement in a U-Factor of sub 0.16 quite easily (R-6+) |
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heatoftheearth
Basic Member
Posts:113
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29 Mar 2009 08:18 PM |
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We've been told to assess the walls at an R-40 for HVAC purposes (if you add up the materials it comes out to be R-25 or so, but they don't permit air infiltration,
who ever told you this is wrong, Free heat calcs are great for experimenting . To size your heating ,ventilating equipment Manual j 8th ed is what you need It will certainly take into account your building materials heat loss/gain through conduction and convection(aka air infiltration) |
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OhioICF
New Member
Posts:13
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29 Mar 2009 09:20 PM |
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Thanks for the replies everyone...
I guess the first thing I'll throw out is that I'm not an expert, but am happy to share what I've learned.
As far as I can tell, the "thermal mass effect" is a benefit, but not the biggest one. Here's a good paper on the theoretical mass effect (by itself):
http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/index.html
The left side of the page lets you navigate the article, and the embedded figure links let you see the graphs... The ICF thermal mass effect (by itself) will give you about a 7% energy gain over a similarly insulated stick construction. This is a good benefit... and I believe that ICF construction may be more cost effective than the other two wall configurations the authors suggest.
The solid 6" concrete wall going from footer to truss isn't going to let much air through... by using airtight can lights and a whole bunch of spray foam around every conceiveable penetration... it should be about as airtight as a house can get. In fact it's dangerous to not use and ERV/HRV in an ICF house. Of course, the dryer vent and bathroom fan vents (energy star rated) will be holes... these are unavoidable. But because wind on the side of house will have basically no effect, there is no way for the pressure to fluctuate on the inside of the house. The inside air should stay inside.
BlackHatch is right that more efficient windows can be found; I've actually found one that was R-20 (whole frame). ... but $$$ becomes a problem. For the money, I think we found a good balance of R-value and performance. If anyone has found double glazed windows w/ U values below .20, please let me know. (triple-glazed is out of our price range).
Here's a link that suggests an R-value for ICF:
http://www.nudura.com/en/NuduraICFFAQ.aspx
...but to be honest, through expermenting with free software mentioned above, the R-value of the wall could change between R-25 and R-50, and the difference is only 1/2 ton of heating capacity. Walls just don't matter much in my climate beyond R-20. The big drivers are windows (nearly a ton differnece between R-3 and R-5), attic insulation, and air infiltration (as in any climate). By controlling those three things, the difference can be astounding.
Here are the inputs I used for the build it solar tool:
-10 design temp 5800 degree days F celing area: 1800 at R49 walls: 2400 sqft at R40 windows: 450 sqft at R5 floor: 0 at R20 slab: 100 ft at R40 infiltration: .005 (remember I am using a 95% ERV in an airtight house) volume: 35,000 occupants: 3
The tool also has some disclaimers (it does not factor in solar gain or thermal mass, so the estimate of BTUs/hr should be high). I found it fascinating how much difference occurs by changing attic insulation from R-20 to R-50 (and this is a cheap addition to the house), by changing windows from R3 to R5, and most especially by assuming that it was stick construction without an ERV (by setting the infiltration to .33).
I did have a couple HVAC people come back and quote me at 2-2.5 tons... but both failed to account for air infiltration or an insulated slab perimeter... and both assumed an attic of R-20. The reason for this is partially because houses are typically sized for AC -- not heat (for humidity control reasons).
This really means that my 1.5 ton estimate is way too big... perhaps a 1-ton unit would be better... but good luck trying to find one of those... and the ERV should help with humidity anyway.
Thanks guys.... but again, I am not an expert, and am only sharing what I have learned in the past six months working with my builder trying to build a good green house. |
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OhioICF
New Member
Posts:13
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29 Mar 2009 09:39 PM |
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...oops... I should have also mentioned the HVAC contractors were told R-3 windows when they were developing their quotes. By changing them to R-5, we dropped about a ton in HVAC heating capacity. |
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dmaceld
Veteran Member
Posts:1465
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30 Mar 2009 12:35 AM |
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One aspect of a well insulated air tight house that I haven't seen much discussion of, and is causing me to have some questions, is the heat generated by bodies and normal living activity. I'm about same as finished with my 2000 sf ICF house. I used 6" Buildblock forms, have an insulated crawl space including XPS under the rat slab, have about R 35 to 40 spray foam on the underside of the roof, and Andersen 400 casement windows. My heat load calculated at about 20,000 Btuh at 20° outside, and 36,000 at 9° outside. I installed a 3 ton Daikin heat pump.
Here's my problem, or potential problem. We're not living in the house yet, but have been working in it all winter. What I have noticed is when the outdoor temp is about 40°+ the body heat from 4 workers, and the power tools and lights we used, along with solar through the front windows, would raise the indoor temp from about 70° to 73° during the day with the heating system not kicking in at all. The windows still have the factory plastic film on them so they aren't totally clear.
What I'm beginning to wonder is if I may have traded a reduced heating bill for an increased air conditioning bill. I may have to run the a/c at a lot lower outdoor temp than one would normally expect to have to to get rid of the normal heat generated by life activities. I haven't made much use yet of the Econo Cool mode of the Ultimate Air ERV so I don't know yet how effective that will be in cooling the house.
Be aware that as you super insulate your house, and get the required heating system size down to a very minimum, you may be holding naturally created heat inside to such a great extent that you will need cooling from March to November!!!
Like I said, there hasn't been much discussion about this, that I've read anyway, and I don't have a long enough history yet to define the issue better, but I really think it's a subject we need to keep in mind. The real kicker is that heat generated by breathing, walking, talking, cooking, watching TV, surfing the 'net, etc., is such a variable it will be hard to place a reliable number on it.
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Even a retired engineer can build a house successfully w/ GBT help! |
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dmaceld
Veteran Member
Posts:1465
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30 Mar 2009 12:41 AM |
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Posted By OhioICF on 03/29/2009 12:43 PM (ERV's pull humidity out, HRV's don't... and we have to use something because of our airtight walls.) You will want to verify this. My ERV, the same one you're planning on using, does not have a condensate drain. My HVAC installers said the HRVs they usually install do. An ERV moves the humidity from one air stream to the other, the HRV extracts it and dumps it down the drain.
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Even a retired engineer can build a house successfully w/ GBT help! |
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OhioICF
New Member
Posts:13
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30 Mar 2009 06:54 AM |
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dmaceld, check out:
http://www.airgenerate.com/products/airtap.html
I've often wondered the same thing. That builditsolar website I keep mentioning suggests that between 1800-2500 BTU/hr are from people. That could certainly add up over the course of an 8 hour workday. You would certainly have to use AC over a larger time range to compensate... but in the peak of summer if your house wasn't airtight, you'd be losing your conditioned air to the outside as well. So although the range might be larger (mar-nov), but it won't have to run as long on any given day. You also will be retaining heat in the winter, so your heating bills should be less.
Now, that link I gave you above is quite interesting in my opinion. It allows you to use a heat pump to heat your water using the heat in your house's air. It's like having a very small AC unit on all the time. Of course, body heat and your larger heating system will have to compensate for this in the winter by pulling heat out of the outside air. The basic idea is that the heat pumps are pulling heat from elsewhere (even cold air), not creating it directly, and thus can be more efficient than resistance heat. So if you find your house having an oversized heating system, this might be a good way to compensate. It will also minimize the time that your AC spends running in the summer months.
It looks like your 3 ton unit should be able to handle this quite easily. (again, not an expert)
I've also given quite a bit of thought about how to install these... and because they heat water slowly, it might be good to use two large tanks (each 80 gallons or more). The first tank would be good to use with the Airtap as a preheater, the second should only kick on if the water temperature is too low coming in. That way you will never run out of hot water, and the use of resistance or gas should be minimized.
Good call on the 200DX not having a drain... I didn't realize that. I checked the site, and it says it strips about 50% of incoming humidity. It must do this through the filter media (?).
http://www.ultimateair.com/Ultimate_Air/support/faq.aspx#14
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dmaceld
Veteran Member
Posts:1465
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30 Mar 2009 08:21 AM |
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I have an Air Tap. Sorry I don't have time to find the thread right now, but you can find it by searching for Air Tap and my posts. I discuss some of the pluses and minuses I've learned about using it.
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Even a retired engineer can build a house successfully w/ GBT help! |
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mac31313
New Member
Posts:20
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31 Mar 2009 09:00 PM |
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have you done a blower door test to confirm your air exchange?
it is true icf's are "tight", but the other systems (insulation,doors,windows) may not be. spray foam is very air tight and will maintain indoor air temp well if installed properly.
have you accounted for the "latent heat" created by cooking, fridge, laundry, shower, ect?
location of windows and shading (overhang, e--lass, ect)is very important when using a program to calculate loads, if you desire accurate results.
mac
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OhioICF
New Member
Posts:13
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01 Apr 2009 07:11 AM |
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Actually, this week we are signing our specs/contract. Hopefully, we will be breaking ground in a couple months.
I'm assuming latent heat to be around 2000 Btu/hr... I'm not sure what our HVAC sub's software assumes.
We've actually had a few things change over the past week; we decided to switch our insulation to R-49 cellulose (instead of blown fiberglass). The cost is about the same (under $2000), and the cellulose has much less air infiltration, and does provide some thermal mass.
http://www.houleinsulation.com/cellulose_vs_fiberglass.html
To prevent drywall sagging issues we are going to have to change the 1/2 drywall ceiling to 1/2 high-abuse board (drywall with glass fibers). Of course, all the penetrations will have to be caulked/foamed to alleviate dust issues.
I talked briefly to our HVAC sub the other day; his MJ8 software says we need 2 1/2 tons of cooling. ...but he said the software is somewhat limited on what can be modeled such as air infiltration, slab insulation, thermal mass, etc. He's agreed to drop us down to a 2 ton condenser with a 2 1/2 ton blower. Right now I'm planning to trust his expertise on this... If we are oversized a bit, my hope is that the ERV can manage humidity.
Has anyone had blower door tests done on ICF houses with sealed attic/wall penetrations? I'm curious what they'd achieve...
dmaceld-- I did look through your posts about the Airtap, and you mention using it in your garage, but I didn't see the pros/cons. Have you had issues with it?
best, OhioICF |
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dmaceld
Veteran Member
Posts:1465
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01 Apr 2009 08:41 AM |
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Posted By OhioICF on 04/01/2009 7:11 AM He's agreed to drop us down to a 2 ton condenser with a 2 1/2 ton blower. Right now I'm planning to trust his expertise on this... If we are oversized a bit, my hope is that the ERV can manage humidity.
dmaceld-- I did look through your posts about the Airtap, and you mention using it in your garage, but I didn't see the pros/cons. Have you had issues with it?
If humidity removal is a concern you will want to reverse your sizes, 2 1/2 ton condenser and 2 ton coil. You're also better to be undersized for a/c than oversized. For a lot of discussion about this go to www.centralair.com, I think. It's the web site of a Houston a/c guru. I'll write about some Air Tap issues later when I have more time, maybe this evening.
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Even a retired engineer can build a house successfully w/ GBT help! |
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RichColorado
New Member
Posts:25
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01 Apr 2009 11:36 AM |
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OhioICF,
Thanks for sharing all the great info.
Also using Serious Materials windows, made here in Boulder.
Try 5/8 Drywall for ceilings. Solves sag problem cheaper than 1/2 with fiberglass and adds thermal mass.
We are using 2 layers 5/8" thru out the house both for thermal mass and sound proofing. Also 2 layers feels much more substantial.
We are salvaging any usable scraps from other jobs and using as base layer. On SIPS any piece that is 4'x 1'+ is useable. Will use full sheets on outer layer. It is amazing how much drywall is tossed on any job. Another builder puts drywall scraps between the studs of interior bath walls. Soundproofing, thermal mass and savings on dump fees.
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OhioICF
New Member
Posts:13
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01 Apr 2009 06:07 PM |
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dmaceld -- that's an interesting idea about reversing the sizes... and makes sense. A colder coil removes more humidity; there would just be less air flowing over it. I'll have to look into this more.
RichColorado -- Today I learned that there is a ICB product "Interior Ceiling Board" that is a 1/2 inch drywall with the strength of 5/8". The price difference to hang the ICB instead of regular 1/2" for 1800 sqft is about $75. I really like the idea of putting scraps in walls; I'm adding that to my spec sheet. Thanks!
I'm getting a copy of some ICF-specific HVAC software from my Nurdura block suppliers. I'll let you all know how that compares with the builditsolar software. |
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markross
New Member
Posts:38
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01 Apr 2009 07:45 PM |
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Posted By dmaceld on 03/30/2009 12:35 AM One aspect of a well insulated air tight house that I haven't seen much discussion of, and is causing me to have some questions, is the heat generated by bodies and normal living activity. I'm about same as finished with my 2000 sf ICF house. I used 6" Buildblock forms, have an insulated crawl space including XPS under the rat slab, have about R 35 to 40 spray foam on the underside of the roof, and Andersen 400 casement windows. My heat load calculated at about 20,000 Btuh at 20° outside, and 36,000 at 9° outside. I installed a 3 ton Daikin heat pump.
Here's my problem, or potential problem. We're not living in the house yet, but have been working in it all winter. What I have noticed is when the outdoor temp is about 40°+ the body heat from 4 workers, and the power tools and lights we used, along with solar through the front windows, would raise the indoor temp from about 70° to 73° during the day with the heating system not kicking in at all. The windows still have the factory plastic film on them so they aren't totally clear.
What I'm beginning to wonder is if I may have traded a reduced heating bill for an increased air conditioning bill. I may have to run the a/c at a lot lower outdoor temp than one would normally expect to have to to get rid of the normal heat generated by life activities. I haven't made much use yet of the Econo Cool mode of the Ultimate Air ERV so I don't know yet how effective that will be in cooling the house.
Be aware that as you super insulate your house, and get the required heating system size down to a very minimum, you may be holding naturally created heat inside to such a great extent that you will need cooling from March to November!!!
Like I said, there hasn't been much discussion about this, that I've read anyway, and I don't have a long enough history yet to define the issue better, but I really think it's a subject we need to keep in mind. The real kicker is that heat generated by breathing, walking, talking, cooking, watching TV, surfing the 'net, etc., is such a variable it will be hard to place a reliable number on it.
Done right, and this is a real problem, however dont forget the heat of curing is also still adding to your load. I am so glad some one finally noticed what can be achieved with this type of building, and yes, we have larger cooling systems than heating systems even in Michigan (existing building operating for 7 years now), the issue is that these buildings will simply keep the climate inside closer to sum of all interior heat, less loss, so ensure you put protection on your outside compressors for cold AC operation, otherwise you could, potentially, damage your equipment Mark Ross
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Mark Ross<br><br>"Le Canuck" |
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dmaceld
Veteran Member
Posts:1465
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01 Apr 2009 09:49 PM |
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Posted By OhioICF on 04/01/2009 6:07 PM dmaceld -- that's an interesting idea about reversing the sizes... and makes sense. A colder coil removes more humidity; there would just be less air flowing over it. I'll have to look into this more.
RichColorado -- Today I learned that there is a ICB product "Interior Ceiling Board" that is a 1/2 inch drywall with the strength of 5/8". That's what I did when I replaced the a/c unit in the house we had in Louisiana, 2 1/2 ton condenser, 2 ton evaporator. Did a great job removing humidity. I didn't know about ceiling rock until I got bids for my house. One caution, it's a lot harder than wall rock. You know those plastic corkscrew wall anchors? They go into wall rock quite nicely. The other day I broke three of them one after the other trying to get one into ceiling rock. Gave up and just drove the screw directly into the rock!
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Even a retired engineer can build a house successfully w/ GBT help! |
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dmaceld
Veteran Member
Posts:1465
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01 Apr 2009 10:22 PM |
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Air Tap issues.
First one I encountered is the thermostat. The unit comes with a bulb sensor that is part of the coil that goes into the tank. The problem is it only goes down into the tank about 18". Letting it control the Air Tap means that only the water at the top 18 to 24" inches of the tank gets heated to full temperature. When I complained about this to Airgenerate they sent me instructions how to bypass the built-in thermostat and use the water heater thermostat to control the unit. I connected it to the bottom thermostat and the entire 80 gallons gets brought up to set temp, which in my case is 130°. The water heater is not connected to 220 volt power. A person could rearrange the wiring such that the bottom thermostat controls the air tap and the top thermostat switches 220v power to the top element.
In new construction the Uniform Plumbing Code requires a water heater to have a minimum "First Hour Recovery" rating, depending on how many bedrooms are in the house. The Air Tap won't meet that requirement. Neither will any "smart" water heater I have looked at. Therefore I have a second 60 gal water heater in series after the 80 gal heater. Originally I planned to preheat to something like 100 to 120° with the Air Tap and top off to 140° with the second heater. However, the Air Tap will bring the temp up to 130° reasonably well so now the second heater is basically a temperature maintainer and backup. It's also set at 130°.
Heat source for the Air Tap can be an issue. For it to run efficiently the air it extracts heat from should be 50°+. That's no problem in summer. If the unit is in the garage it can help cool the garage, or just suck heat from the hot garage air. If it's in the house it will help cool the house. Winter is another story. You need to supply heat to the Air Tap air somehow, or not use the Air Tap. I planned on my garage wall unit of the Daikin heat pump to bring in that heat at a COP of 3. It turns out the operating efficiency of the heat pump, when only the wall unit is running, is only about 1, same as straight electric resistance heating. For winter I'm considering modifying the Air Tap to bring air from the house space and return the cooled air to the house. The air in the house is heated with the heat pump running at a COP around 3+. In the summer I would have it circulate garage air to help cool the garage. My garage is ICF with insulated roof. This isn't an easy option to execute because codes, and common sense, prohibit any likelihood of garage air from entering the house.
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Even a retired engineer can build a house successfully w/ GBT help! |
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dmaceld
Veteran Member
Posts:1465
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01 Apr 2009 10:28 PM |
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Posted By markross on 04/01/2009 7:45 PM Done right, and this is a real problem, however dont forget the heat of curing is also still adding to your load.
[/quote]
Yeah, I did forget about it, even though it had been mentioned in a thread some months ago!
Any handle on how long the half life of the curing heat is? By January the concrete had been in place about 5 months.
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