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Old 09-12-16, 04:52 PM   #21
MEMPHIS91
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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. Ok so I would need to plan on a small room in the centerish of the house because the unit is not to like pushing the air 50 feet through a 8" pipe.

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. Gotcha, that sounds like it makes sense but without a diagram or picture I will need to look it up more lol

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 $. I have a digging machine capable of digging to 27' in one scoop, so going deep in a loop field would not be that hard. Just another idea.

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. I will plan on adding this to the solar system design

But you did confirm, "as efficient as money will allow" . . . . . Maybe I should say as much money as well be helpful, I don't want to pay 40k for a 2% increase in performance.

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. I will post a floor plan soon so that recommendations can be made on the how and where for sip/conventional building

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. $7,500 plus an inverter plus racking plus wiring and that is if TVA will pay me for the solar I make, unless I go off grid, in which case batteries will cost more than the house. Don't get me wrong I'm going to have solar, but $7,500 is shy of the real cost.

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. I like saving money


Steve
I don't think open loop would save that much money. Those pumps still use lots of power, and they don't give me usable water, and you have to worry about freezing your loop field. Submersible Pump 4" Deep Well 1 HP 220V 33 GPM 207 ft Max Long Life | eBay

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Old 09-12-16, 05:02 PM   #22
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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 have duct in the attic now. It is a pain to check on and work around in the attic, plus mine wasn't done right so I am biased.

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 did some calling around today there are only a few homes that were built with sips in the Oxford area. And those don't look like they were done right. I will either hire a crew or just do them myself.

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
Yes thermal bridging at the outside edge is on the list, I got about 4 sites all saying the same info, which is a good thing
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Old 09-12-16, 05:04 PM   #23
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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? No kids, BUT those are good idea, other than we will have no cable/sat tv in our house. lol

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. Good idea!

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.
Again thanks so much for your input
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Old 09-12-16, 05:35 PM   #24
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Memphis - the price I quoted you on PV solar is a complete system (panels, inverters, racking, wiring, etc) - just no install labor. Right now, after tax credit - about $0.75 a watt.

A lot of people simply can't believe this - but I am quoting you actual numbers.

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Old 09-12-16, 06:51 PM   #25
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You got a examples? I can barely find 10k of panels for $7,500 (with 30% tax credit). That is awesome news!!! Sounds like open loop/pump and dump system will be making its way to the 60% likely now.
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Old 09-12-16, 07:03 PM   #26
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I am quoting prices that are on the Renvu site right now - not specials, but regular prices. I forgot, shipping is extra - add another $500.

I see 260 watt panels at $0.64/watt and microinverters (Enphase M215) at $98 each. Roof racking is about $28 per panel. Trunk cable at $17/panel. Add it up . . .

This weeks RENVU special is the M215 at $86 and also cheaper panels.

renvu.com | Search By


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Old 09-12-16, 10:29 PM   #27
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-all led lighting wired 12v

Keep in mind, lower voltage means heavier gauge wire to combat the voltage drop and handle higher amperage.

I haven't done any research on it, but if I was to take a wild guess at it, I would probably go with a minimum of 36v DC circuits. You can get 36v LED COBs on Ebay for cheap, you just have to attach them to a heat sink.
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Old 09-13-16, 10:10 AM   #28
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Steven, your right, I guess I was looking at over priced sites, that is not a bad deal at all. Do they make inverters that can charge batteries just in case I want to have back up power?

Nathan, thanks I'll look into that
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Old 09-13-16, 11:36 AM   #29
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Just found this https://enphase.com/en-us/products-and-services/storage
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Old 09-13-16, 12:36 PM   #30
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Memphis - to get an idea of the amount of perimeter BTU leakage, first get the peripheral area that is exposed. This might be one foot high all around the house. Assume 300 sq feet.

Then multiply that by the temperature difference between inside and outside. Lets call the interior slab 70F and the outside 50 F. That is a 20 F difference. The concrete stem wall already has an R value of 2-3.

Now go look this up in the manual J calculator and you will see that it is a very few BTU/hr. However, in the summer, you "bleed" BTUs into the soil (soil cooler than slab) and a non-insulated slap helps keep the house cool. You are in a dominant hot area and your winter load is very low. I figured that my noninsuated slab basement was about 12-15 KBTU/hr in terms of cooling. Yes, the floors were just a bit cool in winter, but we had throw rugs down there.

If I had all the money in the world, I might insulate everything - but time is also an issue and you want to build this before you die . . .

Again, you will do what "allows you to sleep at night". For some, in a moderate climate, this is R100 - for others it is R40 (just picking an example for attic insulation).

AC has some very nice tables that have cost/benefit intersecting lines on it. Study this concept.

Now look up the cost to insulate the entire periphery and see how much you lower your BTU loss in winter. Will not be much.

The entire issue is to do perimeter insulation in climates where it is a MAJOR cold area. You just are not that cold and your "frost" depth is on the order of inches.

You can do the same with sub-slab duct insulation. But remember that if using a GTHP, that the supply temp is only 100-110 F. A standard gas fired heater has very high hot air. So in the case of sub-slab, the delta T is 105-65 = 40 degrees F. If the dirt under your slab is kept dry (which is typical), then there is "insulation" around the PVC duct Now look up the cost of closed cell duct insulation and gasp. I found it was not worth it IN THE SOUTH.

The reason I am doing this in caps is that we have people from tropical areas all the way almost to the poles on this site and insulation is highly regional.

One size (or advice) does not fit all.


Steve

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