I have a question about SIPS and HVAC. *6 inch SIP walls, 8inch SIP roof *SIP structure of two stories about 750 square feet on each floor. *!~400square foot attic/loft The bottom floor is one big living room with a kitchen in the corner The second floor has two bedrooms and a bath in between. I'm thinking of using a ductless HVAC system. I'm guessing 24,000 BTU Unit will be sufficient for Oklahoma weather and less than 2,000 square feet of space. I was thinking of a split system with only two zones, one downstairs and another upstairs on the second floor. The idea I had was that since the SIPS are low infiltration and well insulated each room would not need its own unit. One 12,000 BTU unit on each of the floors would be sufficient. If one of the units was in a single bedroom the other bedrooms temperature would even out The loft space is small and would not need its own unit as it would even out to the temperature of the rest of the house. While this is probably not an ideal scenario, for low cost and easy installation what do you guys think? Constructive criticism is appreciated. Thanks.

Some thoughts about ductless HVAC systems:
I would think that control of the temperature of each area would improve with its own evaporative coil (fan coil) and thermostat.
Additional fan coils will add to the initial cost but may help to reduce the energy bill if certain areas do not need to be conditioned as much.
Wall and some ceiling mounted evaporative coils will not need a condensate pump.
Some ceiling mounted fan coils can be ducted to adjoining rooms. This would reduce the number of fan coils installed and thus costs.
Some brands of ductless systems can support from 4 to 8 evaporative coils.
Compressors that support 8 fan coils are more complicated and expensive than compressors that support up to 4.
Fujitsu sells a system and also makes parts for some of the other companies.  Price it along with LG, Daikin, Mitsubishi, etc.

Keep us posted on your progress.

Indoor units are cheap enough that you will want to have one in each bedroom just for the control over temperature prefs. Just restating what Alton said. :-)

Of course, you will do a heat loss calculation using your selected windows and doors for the design temperatures in Norman, right? And, even though SIPS make a tight build, don't forget infiltration.

And, before you size that heating system, pay particular attention to the actual heating and cooling capacities from a "24,000 BTU unit" at some of your local low temperatures, and, for that matter, the high temps, too.

heat loss calc - got links to some help with that calculation?

Thanks

You can Google the following phrase combo; "heat loss" calculator

and come up with some stuff to keep you busy for a while.

You really don't want to make a mistake here; you might be walking the line with your 24,000 BTU ductless plan, so spend some time until you feel you are sure about your heating needs. You may need a 30K - 36K unit.

You need to figure out what's happening with your floor and windows and doors in terms of area and heat loss.

If you are planning a tight house, you need to decide what you are doing for ventilation and how that will affect heat loss.

Some ways you could build a little buffer in for protection against those low temp spells is by adding a wall heater to the bathrooms or a gas or electric fireplace for ambiance and, of course, backup heat.

Even the home siting might make a difference in this case - out in the open and exposed, or in town and more protected.

You can use a trial version of energy gauge http://www.energygauge.com/usares/trial.htm set up zones and do a detailed analysis. Be aware the program is very detailed (and the old adage of "garbage in - garbage out"). It will take some time to get all your inputs. I think the minisplits are a great way to go. I'll be using Mitsubishi (3) 9000 btu indoor units. I'm doing mine in vertical zones. Units will be installed in the attic (conditioned space) and controllable through floor vents providing a path down to the next floor (or two floors). By using the variable rates (inverter technology) you can somewhat oversize the units and have them still capable of providing sufficient run times.

It pays to have a professional do a manual J, for $150. so that there are no errors

Certainly from a cost-time perspective paying for a manual J is faster/cheaper. I used the modeling as a planning tool. I'm somewhat suspicious of a Manual J because I remember seeing a number of them coming out to 1 ton per 500 square feet regardless of construction method, orientation etc. I like knowing my numbers are based on specific overhangs, glass type, seasonal variations, tightness, orientation etc. By the way there is a whole industry around professionals and errors - It's called E&O Insurance. But in all seriousness your advice is probably better in most cases.

Torben; I know many engineers that "over engineer" instead of carrying E&O insurance, that way the builder/consumer pays the premium

It pays to have a professional do a manual J, for $150. so that there are no errors

I can't help but wonder what kind of product you are going to get for $150. I've seen a number of "professionally" done Manual J's and I'd say about half of them didn't even get the input right, much less the output, and they all wanted to get like $300-$450.

Seriously, how does Joe Homeowner just go out and find someone do a Manual J that he can count on?

Posted By ICFHybrid on 20 Dec 2011 12:10 AM

It pays to have a professional do a manual J, for $150. so that there are no errors

I can't help but wonder what kind of product you are going to get for $150. I've seen a number of "professionally" done Manual J's and I'd say about half of them didn't even get the input right, much less the output, and they all wanted to get like $300-$450.

Seriously, how does Joe Homeowner just go out and find someone do a Manual J that he can count on?

It is the price we pay to get our calcs done, the difference between a professional builder and "joe homeowner" is we have experience on our side, we have already gone thru the learning curve that the DIY'er will do for the first time and if not careful it will cost them money - risk vs. reward.

There is no guarantee that they will pick the right company, unfortunately it is the price pay sometimes by doing it themselves.

I can only advise that the HVAC system is the most critical part of an energy efficient home and they had better do their due dilligence in this area

Well, I couldn't agree with you more, but that still leaves the average homeowner high and dry when it comes to getting residential energy consulting that can be trusted. Is there somewhere that one can go to get energy answers without someone else trying to sell him insulation or over priced equipment or who isn't trying to turn their house into a thermos bottle, etc?

Posted By ICFHybrid on 21 Dec 2011 08:07 AM
Well, I couldn't agree with you more, but that still leaves the average homeowner high and dry when it comes to getting residential energy consulting that can be trusted. Is there somewhere that one can go to get energy answers without someone else trying to sell him insulation or over priced equipment or who isn't trying to turn their house into a thermos bottle, etc?

Yes it does, as I said due diligence. There are resources such as USGBC, FSEC and ResNet that will assist in finding a qualified professional that are capable of a proper design. If Joe homeowner wants to venture out on their own to save pennies, there is a good chance of failure, the GBT forum is flooded with such stories. It is why you enlist professionals.

What kind of SIPs are you using? I am assuming eps? If so, 8" is not thick enough for a roof in Omaha. I would think you want 10" min, 12" would be better. Infact I would ue 8" EPS on the walls as well. Using these thicknesses, I would think you can get your heat load close to using 2 Hi2 units totaly, 1 12k on each floor. However you will still probably want to throw a couple electric baseboard heaters on each floor to cover the peak heating loads and provide backups when the temp drops below the output of the mini split. Also in a tight house the temps should regulate, however I would put the heads in a place such as a hall instead of one of the rooms. I would think it would over heat the room it was located in. Transfer grills can also help spread the heat around evenly.

Posted By lzerarc on 21 Dec 2011 11:28 PM
What kind of SIPs are you using? I am assuming eps? If so, 8" is not thick enough for a roof in Omaha. I would think you want 10" min, 12" would be better. Infact I would ue 8" EPS on the walls as well. Using these thicknesses, I would think you can get your heat load close to using 2 Hi2 units totaly, 1 12k on each floor. However you will still probably want to throw a couple electric baseboard heaters on each floor to cover the peak heating loads and provide backups when the temp drops below the output of the mini split. Also in a tight house the temps should regulate, however I would put the heads in a place such as a hall instead of one of the rooms. I would think it would over heat the room it was located in. Transfer grills can also help spread the heat around evenly.

This is a prime example of the fly by the seat of your pants advice that gets people in trouble.

explain how so...Omaha is zone 5, just a few hours from me, those numbers for sips do not even meet code. Plugging the new numbers into Revit MEP with the house size, loads should be <20k btu obviously depending on windows, etc. I am not disagreeing about someone doing a load calc. But his shell numbers arent there to begin with to achieve what he is even after.
Obviously if any homeowner (non-pro) takes advice from anyone on this or any forum and uses is without consulting a professional designing their specific project, they are already in trouble.

Omaha is about 500 miles to the north of Norman Oklahoma (I'm guessing the city, but I at least got the state right). That is climate Zone 3 (not 5). An 8-inch roof panel would be about R-32 (above the IECC recommended R-30). Look at this link http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/ba_climateguide_7_1.pdf. You should be careful about giving advice that is so erroneous. I am an owner-builder and I have done my own energy calculations. It took me a great amount of time but the data is much more useful and accurate than an outside professional would have provided. Orientation, shading and air sealing are huge impacts on performance. To dismiss them indicates a real lack of understanding.

I appologize. I read his post quickly as Omaha (as in Nebraska), not Oklahoma. Reading error. given that, my info was still accurate. Omaha is zone 5. However....not accurate to his question.....sorry. I also never mentioned anything about dismissing orientation, shading, and air sealing.

From the standpoint of paying my energy bill I would much rather not meet code (level of insulation) than have a leaky building envelope. I have run the numbers a variety of ways and leaks have a tremendously greater impact on energy efficiency than any other item (when you consider percent change in infiltration or R-value versus energy use).

and no one is claiming otherwise. It was assumed (at least by me) the SIPs shell could achieve <1.5 air changes, far surpassing typical 2x6 construction. That number is also what I used in my program. If it were me, however, I would much rather exceed IECC as well as test out below 1 a/hr @ 50 pc.... (which I have with 2 projects now....).
The goal on my next project is PH levels, trying to hit around .6. I think most poeple on this forum understand the importance of tight construction.