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Dana1
Senior Member
Posts:6991
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| 08 Jan 2013 11:22 AM |
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Most of the time its garbage-in-garbage out issues. Amongst the less-informed practitioners there is a bias toward understating the actual R-values, and not including all load-reducing factors like plug loads, window shades, warm-blooded occupants, etc. leading to accumulating higher-than-reality U-factors and discounted offsets from passive heat sources. Then there's the overstated interior and outside design temp issues (I know gramma likes it to be 78F inside, and it got down to -35F here once back in the 1980s, so...) As Hank Rutkowski states clearly:
"First, the contractor should perform an aggressive Manual J calculation-taking credit for every load-reducing feature or detail he can, including drapes and blinds."
(see: http://www.greenbuildingtalk.com/buildcentral/sip/article_hvac_sizing.aspx )
Many ignore all other factors, factoring in only the raw unoccupied shell, yet a family of four with a dog puts out over 1000BTU/hr even while sleeping, and the background load of the refrigerator counts for something, eh? (A Tivo is worth ~400 BTU/hr or more.)
If you're really aggressive and careful about getting the right U-factors, the biggest error is likely to be in the natural ventilation/infiltration rates. But it's possible to get within 10% of measured reality using Manual-J if you're "aggressive" in the right direction.
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BadgerBoilerMN
Veteran Member
Posts:2010
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| 08 Jan 2013 05:49 PM |
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You I can't find background loads on any of those free on-line Manual 'J' programs. Where do you plug in the dog btu's?
Aggressive in my neck the woods is called drive-by sizing...drive by, put up a thumb and if it covers the house you gunna need bout 100 towzen, but if it takes two tums - watch yer driven der Sven - din ya gonna need 2 hunderd towzen... you bet cha...
If you can get anyone to do any heat load for residential boilers or furnace...ever. You are making progress.
Seriously. Whether you have a tobacco shed or a Passivhaus, the right software in the hands of a skilled designer is the answer and takes much guesswork out of the equation.
It is not a convincing argument that some charge too much and other are incompetent so there is nothing to be done.
We have designed and installed nearly every kind of residential heating system in nearly every kind of structure including ICF and SIP, which are not particularly challenging by the way. |
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| MA<br>www.badgerboilerservice.com |
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Lbear
Veteran Member
Posts:2740
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| 09 Jan 2013 08:40 PM |
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After some brainstorming, I am going with all ductless mini splits for my 1st floor (Dana1 will be happy)  Since I have a conditioned attic space on the 2nd floor, I will go with a heat pump, ducts & air handler for the 2nd floor as that will be an easy install and duct run. (2 ton unit). In a tight high R-value home, if a mini split is on the far corner of a room that is 400 sqft, could that single mini split condition an adjacent room (also 400 sqft) that is completely open to that room all under a vaulted ceiling area? There will be air movement in that area via a ceiling fan and ERV. |
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cmkavala
Veteran Member
Posts:4327
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| 10 Jan 2013 06:50 AM |
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Posted By Lbear on 09 Jan 2013 08:40 PM
After some brainstorming, I am going with all ductless mini splits for my 1st floor (Dana1 will be happy) Since I have a conditioned attic space on the 2nd floor, I will go with a heat pump, ducts & air handler for the 2nd floor as that will be an easy install and duct run. (2 ton unit).
In a tight high R-value home, if a mini split is on the far corner of a room that is 400 sqft, could that single mini split condition an adjacent room (also 400 sqft) that is completely open to that room all under a vaulted ceiling area? There will be air movement in that area via a ceiling fan and ERV.
It will condition the adjacent space , but not adequatey I think using mini-splits for new construction when a conventional split system is possible is a mistake, mini-splits are great for additions, where spot conditioning is problematic I also think it would affect resale negatively |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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ICFHybrid
Veteran Member
Posts:3039
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| 10 Jan 2013 07:47 AM |
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Aren't two 400 sf rooms that are completely open to each other under a vaulted ceiling really one 800 sf room? |
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cmkavala
Veteran Member
Posts:4327
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| 10 Jan 2013 08:00 AM |
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Posted By ICFHybrid on 10 Jan 2013 07:47 AM
Aren't two 400 sf rooms that are completely open to each other under a vaulted ceiling really one 800 sf room?
yes the size of a small house, a mini-split will not be effective |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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toddm
Veteran Member
Posts:1152
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| 10 Jan 2013 09:11 AM |
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I have a 2-ton mini on one end of an 800sf room with den and bath appended to the far end, 1k sf all told. Cooling is near perfect in the three rooms, most likely because they share a concrete slab and porcelain tile floor. Heating is less effective. The two rooms run about 8 degrees colder with the doors closed.
I paid $1500 for the mini, so I am not particularly worried about getting my money back at resale. Nor am I worried about the house's appeal. |
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Lbear
Veteran Member
Posts:2740
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| 10 Jan 2013 12:34 PM |
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Posted By cmkavala on 10 Jan 2013 06:50 AM
It will condition the adjacent space , but not adequatey
I think using mini-splits for new construction when a conventional split system is possible is a mistake,
mini-splits are great for additions, where spot conditioning is problematic
I also think it would affect resale negatively
It will still have a conventional ducted system for the 2nd floor area and we will be able to run one of those duct runs down to do a room (1 of 3 rooms) on the 1st floor. The reasoning behind the mini splits on the 1st floor is that duct runs are not possible for the other 2 rooms. |
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ICFHybrid
Veteran Member
Posts:3039
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| 10 Jan 2013 01:04 PM |
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I have 2 X 9K BTU minisplit heads heating 6000 sf right now. Outside temperatures were 34F last night. It can work. |
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Lbear
Veteran Member
Posts:2740
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| 10 Jan 2013 05:23 PM |
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Posted By ICFHybrid on 10 Jan 2013 01:04 PM
I have 2 X 9K BTU minisplit heads heating 6000 sf right now. Outside temperatures were 34F last night. It can work.
Will the mini splits be your only source of heat for the home? What are your indoor temps? What brand did you go with? |
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cmkavala
Veteran Member
Posts:4327
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| 10 Jan 2013 05:51 PM |
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Posted By Lbear on 10 Jan 2013 12:34 PM
Posted By cmkavala on 10 Jan 2013 06:50 AM
It will condition the adjacent space , but not adequatey
I think using mini-splits for new construction when a conventional split system is possible is a mistake,
mini-splits are great for additions, where spot conditioning is problematic
I also think it would affect resale negatively
It will still have a conventional ducted system for the 2nd floor area and we will be able to run one of those duct runs down to do a room (1 of 3 rooms) on the 1st floor. The reasoning behind the mini splits on the 1st floor is that duct runs are not possible for the other 2 rooms.
Lbear; Have not yet seen one yet that could not be ducted, they do not need to be in ceiling, side wall vents work well too |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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Lbear
Veteran Member
Posts:2740
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| 10 Jan 2013 06:35 PM |
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Posted By cmkavala on 10 Jan 2013 05:51 PM
Lbear;
Have not yet seen one yet that could not be ducted, they do not need to be in ceiling, side wall vents work well too
Being the walls are ICF and the vaulted ceiling is Steel SIPs, the
vaulted ceiling areas of the open spaced Living Room and Kitchen cannot get ductwork
in there without creating some exposed industrial looking HVAC ducts. I've had three HVAC guys look it over and
my architect and both conclude it is not feasible and there is no aesthetic
room for soffits in those areas.
We are on a slab-on-grade so there is no basement and running ducts under the slab is
something I don't want to deal with (noise, bugs, humidity, etc). That was the only option they gave (under slab ducting), besides the industrial looking exposed ceiling ducts (which we don't want).
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ICFHybrid
Veteran Member
Posts:3039
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| 10 Jan 2013 09:10 PM |
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No, they are just what operates right now. The main source of heat will be radiant. The ductless minis were afterthoughts to solve local issues. I am running one in the 1300 sf basement and one in a 200 sf room next to the main open area which is 3000 SF. The units are set at 72F and they cycle on and off. Basement is too warm, but we want to keep the moisture from settling there during construction. Temps in the main area run from 68F - 65F. I have some large window arrays at the far flung corners (more than 60'-70' from the indoor units) and temps in their vicinity get down to 64F or so. All this is with no circulation running and a 10" diameter hole in the kitchen ceiling which I am too lazy to get up and plug.
They are Daikins. |
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