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Old 09-12-16, 04:00 AM   #11
DEnd
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The Double stud wall is the cheapest to build but I don't think it is the best wall. if you are ok with foam, you may be able to find used foam insulation for cheap enough that a double stud wall may not make sense, especially if you are the labor supply. There is also adding foam strips to the interior of the studs with a 1x on the interior side for a nailing strip. This can add a bit more cavity depth and also reduce thermal bridging.

As far as sub slab insulation is concerned my inclination is to say either that or perimeter insulation is a good idea. however I would hire Energy Vanguard or some other firm (Allison Bailes at energy vanguard can probably recommend someone if they can't do it) to do some energy modeling and cost optimization. Now is the time to start that conversation as they can help you avoid design issues that can cause large energy penalties.

As for GTHP, I'm meh on them. great concept, not so great execution. The other issue I see judging at least by the ingrams site is that they really don't have something small enough for your situation. I'm betting if you build your house well you will see an AC load of around 1 ton. Heck even finding conventional equipment that small can be a challenge. The majority of your heating and cooling hours will be at part load conditions, this is the area that mini-splits excel at, and where they beat GTHPs.

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I would highly recommend you go with non-wood SIPs (Structurally Insulated Panels). May cost more for the materials but time, ease, and insulation value is not beatable.
Not for a first time DIYer. If he can find a contractor with experience with them then they can be a viable option. The SIPs supplier may be able to recommend someone.

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Old 09-12-16, 07:52 AM   #12
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Steven those numbers are for sure nice, I'm still concerned with it being over sized, but at that price your right it is hard to beat. We are not stuck on the mono pitch yet. I think as long as we have vaulted ceiling in the great room/kitchen area we would be happy. I still hate the idea of having my duct work in the attic unless of course I can have the rather a insulated, but then I hate the idea of heating and cooling my attic. So many options, so much more research. I wish more people had these type systems/houses in my area.

DEnd, I am really liking the idea for sips they seem quick and a good product, I'm going to do some calling around to see if anyone in the area builds with them. I have a lot of connections around here. I can make more money at my job than I can save doing the time consuming labour parts of the house. I'm the general contractor for sure though.

Thanks for all the input guys.
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Old 09-12-16, 07:59 AM   #13
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If you are concerned with oversize at 3 tons, then put in a two ton unit. The key is the two speed compressor. Most of the time the GTHP will run on stage 1 (lower compressor setting). This maximizes water extraction and maximizes efficiency.

Remember that minimal human activity, electronics, appliances and cooking can easily add one ton of cooling. And cooling is your 80% issue - not heating. This is on top of the manual J load. So if the house, by manual J, is one ton, then you really need two tons for the most basic cooling issues. Cooking is a major contributor. Second is electronics and appliances in terms of providing vampire heat load. People are significant and significant heat, but a LOT of moisture. Remember that cooling load is just not heat, but also indoor latent humidity in addition to that which is outdoors (and leaks in).

I am just not seeing the longevity with minisplits as compared to GTHPs.

I also REALLY like SIPS for speed of building, envelope tightness and strength


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Old 09-12-16, 08:38 AM   #14
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Mono roof pitch is easy to build, easy to put metal roofing panels on, and provides roof at the minimal sq foot area, but can be a problem in providing shade. A reasonable pitch (3/12) means that a significant southern overhand is wide. And this means that your southern roof line at the eve must be high. Otherwise, you hit your head on it.

Make no mistake, I really like a flat pitched roof - especially if it is a SIP roof. It provides great interior height. But it also means a very high northern wall at the roof high end. I am assuming that the roof will pitch to the ~ south. That means the north aspect of your home will be your high side.

Because SIPS can span a large distance, it is not hard to do a standard gable roof with just SIPS and not needing trusses. A bit more roof surface area (compared to a mono pitch) to cover a given house footprint.

A mono pitch roof is great, but you need to build one VERY tall wall. And that is more expensive than a few more sq feet of roof area.

Assume your low wall is at 10 feet and your home is 24 feet wide. This means the high wall must be 16 feet high. This is based on a standard 3/12 pitch.

Lots of trade offs . . . .


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Old 09-12-16, 09:28 AM   #15
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OK so now I'm 50/50 on Geo vs mini splits. So monopitch is out now. We will have attic space for ducts if needed.
What type well pump do you use for your open loop Geo systems?
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Old 09-12-16, 10:30 AM   #16
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I have a 1.5 HP 220 V single phase deep well pump - but I am also watering livestock and my water table is down almost 70 feet. If I recall, your water table is much higher.

My well pump is supplied by my solar panels.

Why not just put PVC supply tubes for HVAC under slab? That way, you don't have to use hot attic for supply ducts.

You have time to decide on MS vs GTHP.



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Old 09-12-16, 11:10 AM   #17
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Would the PVC ducts in the floor need to be insulated? Would the slab then need to be insulated? I like the idea just don't want to add tons of cost. Is doing a well pump going to off out the geothermal savings? I just am having a hard time seeing a pump run for that long without drawing a lot of power. The discharge/pond idea is great though. I can solar power mine as well, and one day plan to, but that is a huge extra cost. Thanks for all your advice its going to help me make the best choice.
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Old 09-12-16, 12:32 PM   #18
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I did not insulate my sub-slab PVC ducts and my ground temp in Oklahoma is about 60 F. You are a few degrees warmer. I did look into PVC duct insulation and the cost was way too expensive. I did not insulate my slab. Absolutely necessary up in the cold north.

Of course you will need amps to run a deep well pump, but you don't need pressure and you can run a GTHP on 10 psi. Then have a separate "booster" surface pump to do 60 psi for home use.

The alternative to an open loop (aka "pump and dump") is to put in expensive vertical wells or did like crazy and put in a huge loop field. Lots of time and or $.

Solar, to run a pump with a grid tie, is NOT expensive. If fact, it is so cheap that you can't afford not to do it. Your 20 year lifetime kWhr cost will be a fraction of the current retail kWhr cost.

But you did confirm, "as efficient as money will allow" . . . . .

I would do open loop geothermal, a 10 kW solar system and a SIP home. You are FAR better to do solar PV and efficient heating/cooling now. If you install yourself (not hard) the cost is about $1.1 a watt. Then the 30% tax credit - so the real cost is about $0.75 a watt.

This means about $7,500 to put in a 10 kW PV system, let's say $4K for a GTHP (including ducting). That total is under $12K. Pay someone to do this and add another $20K. Typical charges to put in a grid tied PV system are $3+/watt.

Start by setting yourself up for savings and then put other important stuff around it - like LED bulbs, SIPS, tight house, ERVs, etc.

Think strategically - not tactically . . . . it is all about saving money down the road.

Lastly, what you pay for electricity is AFTER tax money. Lets assume you are in the 20% IRS bracket (being conservative). To make $100 in take home, you have to make $120. But you pay for all stuff AFTER taxes. That is why money saved is such a boost.


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Old 09-12-16, 03:03 PM   #19
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Quote:
Originally Posted by MEMPHIS91 View Post
Steven those numbers are for sure nice, I'm still concerned with it being over sized, but at that price your right it is hard to beat. We are not stuck on the mono pitch yet. I think as long as we have vaulted ceiling in the great room/kitchen area we would be happy. I still hate the idea of having my duct work in the attic unless of course I can have the rather a insulated, but then I hate the idea of heating and cooling my attic. So many options, so much more research. I wish more people had these type systems/houses in my area.

DEnd, I am really liking the idea for sips they seem quick and a good product, I'm going to do some calling around to see if anyone in the area builds with them. I have a lot of connections around here. I can make more money at my job than I can save doing the time consuming labour parts of the house. I'm the general contractor for sure though.

Thanks for all the input guys.
Why do you hate the duct work in the attic? If it is insulated you are conditioning the space regardless, and you get conditioned storage space. If it is un-insulated then a well sealed duct system buried in the insulation is a fairly decent system, though you would not want to put any mechanical equipment in there. I agree that it is not the best solution (due to low fault tolerance), but it can be a workable one.

I don't really have anything against SIPs, but their details are not common knowledge. Yes they are fairly simple, but finding people who know how to move the Sips efficiently and safely as well as detail any penetrations they have, and know the tricks of wiring etc... is a lot harder than finding people who are familiar with the details of stick construction.

I would say you need some form of slab insulation regardless. At minimum you need to address the thermal bridge at the outside of the slab. BSC has a few ways to do this: https://buildingscience.com/document...059-slab-happy
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Old 09-12-16, 03:45 PM   #20
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I would like to throw out a few design ideas at you. One of my favorites is Away space. The basic idea is that you provide a lounge/work space for each member of the family. Say you have two kids, that is an easy one, you provide enough space in the bedroom for a chair and desk, then for each of the parents you provide a space in the master for a chair or two and then you have the living room. But what if you have three kids? well you could do a fourth bedroom, but a den/home office might be worthwhile instead. Even with just two kids a den/home office is a pretty good Idea. Because, lets face it what parent wants to be subjected to Spongebob when they are trying to get the bills paid?

Does someone work from home? If so (or if it is a possibility) then the placement of the home office is critical. This space should be somewhat private away from the noise and distractions of the rest of the house. I tend to like the front rooms of a house for this. It can be placed in a way that the kitchen is basically concealed from view for any clients that may come by. Also having a formal dining room at the front is fairly popular now as well, this allows that space to also be used as a small conference room.

I like the idea of having a kitchen in a separate space from the rest of the living areas as well. It can still be open to those spaces but make sure it is out of the traffic flow.

I also would recommend having a full bath available on the first floor, preferably one that is laid out with wheelchair accessibility in mind. Along with this have a space that can be converted into a bedroom.

Speaking of kitchens and baths, they are the most expensive square footage in a house, limiting their size and numbers is a great way to save money. That said layouts that work well even if a bit larger are worth the money.

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