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| We're looking for some on-the-gound wisdom about super insulated homes (heating, cooling, etc.) as we move toward building a 2,000 sq ft house in zone 4b with r-40 walls and r-60 in the roof. South, Southwest orientation. We have looked at geothermal with radiant and are now exploring ductless mini-splits which seem to get good reviews. |
Follow-Up Postings:
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- Posted by Brian_Knight (My Page) on Tue, Feb 19, 13 at 11:05
| Thats great Mulchie. Youre way ahead of the majority when it comes to building a home with very low energy and environmental costs. Your concentration on high insulation values is a great first step and perhaps more important than that is how airtight you can get the super insulated structure. One of the best aspects of building new is that its much easier to create an airtight, continuously insulated building envelope. This is usually much more cost-effective than most renewable energy technology especially considering there is no maintenance. Passive solar is an easy, low cost way to dramatically reduce heating costs and increase passive survive ability if you have the right site. As the envelope gets more efficient, renewable and HVAC systems can be downsized which makes them more affordable. Geothermal is great, but paybacks can be a long time and a lot of the listed COP numbers dont include the circulating pump's energy demands. Radiant can be more troublesome with high performance homes as there is a long lag time between thermostat adjustments. If you are in a humid climate, keep in mind that radiant will not contribute to cooling and is a very large upgrade for a highly insulated passive solar home in a zone 4 climate. Lots of high performance homes are going with Mini-splits these days and there's a decent thread going in the Building a Home forum. Getting the building envelope right will take some up-front planning and I would suggest getting a competent energy rater and builder involved early in the process. |
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| Hi, Brian- Thanks for your reply. I've been doing a great deal of research and everything you say rings true. We were looking at geothermal and radiant and have completely backed away from that approach in favor of... mini splits with a Zender air exchange system. It has been a journey and we haven't yet broken ground. But you're quite right, building new allows you to really control all these decisions and design a tight envelope. We have a south-facing lot, so that maximizes our ability to use passive solar. ... I'm not sure I'd enjoy the process as much if there weren't all these variables. It's fascinating and the potential is terrific. Unfortunately, still expensive compared to conventional builds We've got a good energy rater on board. Where are you? You sound as though you are very experienced. cheers |
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- Posted by Brian_Knight (My Page) on Sat, Feb 23, 13 at 21:08
| Thats great! Thanks, Iam in Western North Carolina. I dont think its necessarily more expensive to build high performance but as you know, the details and variables are immense. Luckily, it can all be broken down and I think most of the hard work is behind you. If you build to the minimum energy codes (IECC 2012), then you are in a way, building as cheap as the law would allow. This reasoning ignores that local jurisdictions dont adopt the broader codes but in a way, shame on them. I feel building to this level as a minimum is a very cost-effective approach. It will make for a comfortable, energy efficient home with healthy indoor air quality. Its tough to put a price on the health benefits. |
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| Mulchie, while I am in central NH, CZ 6 (7500 heating degree days), a lot colder in general than where you are, I have a superinsulated house, and I applaud your interest in building one. In general terms, it has R40 whole wall exterior walls, double frames and 12" cavity; attic is R60, slab and foundation walls are R20, and windows are triple pane. Heating is via ground source heat pump (aka "geothermal"); that was a good choice for us, as we were putting in a new well for water anyway, and no extra drilling was needed to support the heat pump. However, a superinsulated house loses or gains heat so slowly that almost any heating system can be used, and its operating cost will be low. In my case, size is close to 4000 sqft, and the heat pump is just a two-stage, two-ton, and slightly oversized at that for winter operation, as it keeps the house at temp easily without going to second stage. For summer A/C, it's oversized by a factor of at least two. Heating season cost is around $600, for a normal winter. In your CZ 4B, a minisplit likely would be a good choice, with good year round average COP 3 or better. I am completely happy with the performance of the house. It is very comfortable, has no drafts, and is very quiet. For a new house, going the superinsulated, or at least very highly insulated route doesn't cost all that much more. The usual number I see is about 5% more over "conventional" construction. I see it as a good long-term investment, in terms of both operating cost and comfort. |
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| Thanks for sharing your experience. I'm very encouraged by how much you enjoy your new house. Could I ask what window manufacturer you settled with and why? That's a difficult part of the process, for sure. We believe we'll be fine with a single mini split, but we are building in the capacity for a second in case this seems insufficient. We've done all kinds of projections and moved away from geothermal as a case of classic overbuilding. It's daunting how many details interrelate! But it's great to hear you are so happy with the outcome. Thanks for your reflection. |
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| I used Thermotech Fiberglass (Canadian). They are a mix of mostly casements and a few fixed glass. They certainly are well made, but maybe the most expensive. Since I selected them three years ago, some other decent ones have appeared in discussions on greenbuildigadvisor.com and the building science forum of jlconline.com. I don't recall the names of the newer ones that seem to be liked. One builder of double wall houses in Maine spoke of problems with after sale service from Thermotech Fiberglass. |
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