New House with ICF, Geothermal and 10K Watt Solar Array
Last Post 18 Sep 2014 10:23 AM by Ozrick. 9 Replies.
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fun2driveUser is Offline
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21 Aug 2014 11:47 PM
I know this question spans all 3 areas of ICF, Geothermal and Solar but let me start with some information. I am building a house in the panhandle of Florida that is a two story ICF house with large 3+ attached garage and upper story of the garage a media/ game room. My architect designs ICF homes so he is very familiar with how to do this. My question concerns sizing the HVAC system in tons. It seems like for the previous homes I have owned that every HVAC contractor has oversized the cooling tonnage by a considerable amount. I have not seen their manual J calculations but every one I have owned short cycles and I wanted smaller tonnage for the system. For example both homes I owned (1800 sq ft wood construction townhome 4 levels and 2100 sq ft condo one floor Hebel construction R40 ceiling) have 3 1/2 ton units and both short cycle. I don't want this experience with the ICF house especially since I don't plan living there in Florida in the summer. I am hoping the GT contractor will be able to size correctly so that my efficiency is as good as it can get. Some details about the house, SW facing over a bay with large first floor (10 ft ceilings) and 2nd floor windows that will be impact resistant and have the best R value possible but still a lot of window area. House size is 5000 sq ft for the main house and another 900 sq ft for the media/ game room above the garage. 10K solar array sitting on top of the SW facing roof. I am an engineer but not a mechanical but systems engineer and I am seeking input from the experience base here. If you are not familiar with Hebel construction it is air entrenched concrete and has good insulating and thermal mass properties not as good as ICF but still very good. Your inputs are appreciated...
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22 Aug 2014 06:52 AM
I did my own calculations with a $50 program. As long as you are accurate and honest about all of the many details you plug in, you should get an accurate number. Like all of the other parts of my DIY ICF build, I was told to hire a pro. Well, I had one 'pro' tell me what size HVAC system I needed OVER THE PHONE! He knew nothing about the house; not even what it was built out of, yet he claimed he could size the system based on square footage. His number was almost 3X oversize. Since I've been on my build site for a couple years, I know the exact sun angles and which windows are prone to solar gain, so I have better info than anyone who just walks in and starts measuring.

Although you don't plan to use your house in the summer (good idea) you really should have enough capacity for year-round use. What if you sell the house to someone who wants to live there year-round? Things in life change, and that sounds like an expensive seasonal home.

Let me add- If you are more comfortable hiring a pro, make sure that they know what they are doing. They need to understand ICF, and pay attention to solar gains, esp. in your climate. There's a lot to it, and if they're going to do a 'curb quote', you need to find someone willing to do the job properly.
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22 Aug 2014 08:25 AM
fun2drive, from the numbers it looks like the HVAC contractors used the faulty old-school rule-of-thumb that calls for 1 ton per 500 square feet of living space in your previous homes. As you have already experienced, the rule-of-thumb approach doesn't work.
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22 Aug 2014 10:03 AM
Even a perfectly sized AC will short cycle when the weather is mild and the sun isn't coming in. Consider a multi-stage HP or a smaller geo HP with assist from a mini-split during peak loads. Plus a stand-alone dehumidifier.
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22 Aug 2014 01:51 PM
Take a look at the Daikin heat pump system, or similar. It uses a variable speed compressor and fans and slows down and speeds up according to the load. My system cycles only once per day, normally. On when heat or cool is needed and changes speed according to the load, and then turns off when heat or cool is no longer needed.

Look for a dealer who uses Wrightsoft to do heating/cooling calculations. If they say they don't use it, or don't need to use it, go elsewhere.

Even a retired engineer can build a house successfully w/ GBT help!
fun2driveUser is Offline
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12 Sep 2014 10:57 AM
Thanks or the input. My general contractor is experienced with building ICF and I had the luxury of my GC finishing an ICF home for a friend of mine that also used geothermal and did a fantastic job. My architect, GC both recommend an ICF contractor that has built a lot of structures so I am good there.
I have investigated some of the manual J software programs and for 50 bucks considering what this house will cost that seems like a good idea. I plan to be very involved in the HVAC contractor selection and expect them up front to calculate a manual J which I want to review. If they use some rule of thumb as mentioned I will either see if they want to use my numbers for heat load (I will get my work reviewed too) or find someone that understands the heating needs.
Variable speed fans and compressors seem to be the way to go and I cannot really see a lot of difference in performance of the big names out there. Assuming this is true I think finding the best installer that is careful with attention to detail will be my choice. The geo system is going to be pretty expensive and I want to size it right. Even in the summer hottest days of the year my current HVAC short cycles so I know it is over sized a good deal.

Windows are really important to trying to squeeze as much energy efficiency out of the home as possible. Expensive impact resistant windows and doors with good SHGC and U-factor as well as good impact performance I hope will help. I don't have my vertical window dimensions but the horizontal glass area is large but the design does use roof and patio overhangs to cut solar gain into the home during the summer.

Please keep the ideas coming. I hope in about one month to submit my plans for approval to the HOA and start building DEC.
I can't DIY this monster and would be foolish to try given I have no relation with subs as my GC does, yet alone the permits and inspections.
I do plan to participate building the home since it is all of 400 yards from my current home and I work at home part time now so that affords me hands on.
I hope to document the progress of the build of all 4 major components (ICF-Geothermal-Solar PV-windows/doors) using my GOPRO for some video some pictures.

I hope that will serve as a benefit to those that are planning to retrofit or build new. At least they can see how this structure was built good or bad...
fairhopeUser is Offline
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13 Sep 2014 07:42 PM
3600 sq ft icf home, 3 ton Waterfurnace series 5000 geothermal system with 85 gallon Marathon hot water heater with hot water heated by geothermal a/c. To get a definitive design on the a/c system, you CAN'T beat Richard Rue @ http://www.energywisestructures.com/. Our builder and the geothermal contractor recommended a 4 ton unit, Richard's calculation and design is a 3 ton system. Completely satisfied with the excellent design and build work by Richard and his team. We moved in to the house in June of 2013, I have the TED 5000, connected to Bidgely.com for disaggregation of the electrical useage. Cooling cost $53.00 last month, we keep the thermostat at 80 and it is awesomely comfortable.
fun2driveUser is Offline
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16 Sep 2014 09:57 PM
Thanks for the information. I am looking at manual J calculation sheets but whatever I come up with it is well worth it to have an expert calculate the manual J. Florida requires a manual J form filled out anyway so this is good to know.
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17 Sep 2014 02:53 PM
Manual-J often turns in to a "garbage-in-garbage-out" situation, so don't just let some random contractor run the numbers. If you're building with ICF or SCIP or other mass wall it's even more important that they give it the full treatment, with no thumbs on the scale. Common thumbs to look out for are using something other than the actual 1% & 99% design temperatures &/or unrealistically high/low interior design temps, inserting code-min numbers for windows rather than the actual windows being installed, etc., or with mass walls, ignoring the mass effects and using 1/R as the steady-state U-factor for walls.

FWIW: Bidgely is becoming a fairly serious massive-data company- they just won a huge contract to help figure out how to manage Hawaii's PV-rich grid development issues:

http://www.greentechmedia.com/articles/read/bidgely-to-disaggregate-the-demand-side-of-hawaiis-solar-rich-grid

The name "bidgely" literally means "electricity" in Hindi & Punjabi, and probably a few other Hindustani languages that I'm less familiar with. (Watch enough Bollywood flicks and you can pick up on all sorts of vocabulary...) That's an apt name for a California based power monitoring company founded by guys named Abhay Gupta & Vivek Garud, (and funded by Khosla Ventures' Vinod Khosla ). I guess the name choice was a "desi appreciation" thing- and it clearly wasn't going to run into trademark issues in the US. :-) I'm not sure Bidgely(tm) will ever become a widely known name, but people in the grid-integration biz seem know and respect them, despite the fact they are an upstart that has only been around a couple of years. They have offices in Bangalore too (the Bengali word for electricity isn't quite the same- it's "bidget" or something), but it's not clear if that is to take advantage of the software talent, or if they are also going after contracts with utilities in India (a country with a huge electricity-theft problem.)
OzrickUser is Offline
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18 Sep 2014 10:23 AM
I have close to near the same set up as you. 5k sq feet, with attached garage with media/game room above. Differences. I was a 20x30 house (two level) then I added another 40x60 (two level) Icf basement/garage, upper level was stick built 6" walls. added geo 2 ton infloor heat for the new 40x60, and added geo 4 ton heat/ac for the whole house. The 40x60 (4800sq ft) part is super effeceint on both levels-even with the garage as part of it. I have a hard time heating and cooling the old 20x30 (1200 sq ft). I know I would be overkill if it were an icf house only. I actually had to install dampners reducing the heat and ac on the new section while its full open to the old 20x30 (1200 sq ft). so end of story im glad the old house needs at least 2 tons of my 4 ton system (maybe more), but I live in northern MN :/ heating most of the time cooling only about 2 months of the year. don't know if that helps - thought id let you know. If I did it again with a pure icf house I don't even know if I would do geo it would be so efficient, but I love my geo under my circumstances.
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