07-03-16, 04:55 PM | #11 |
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How are your DIY skills? Geothermal is one of the areas where it's relatively easy to DIY a unit that is cheaper than buying one.
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07-03-16, 07:03 PM | #12 | |
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The least cost option is likely using a point source of heat/cooling. This becomes possible with high insulation levels, and high levels of air sealing. Point source options (like ductless mini-split heads) can however have distribution issues. There is a Net Zero builder up in Maine that uses a single ductless mini-split head on each floor of his houses. (http://transformations-inc.com/press...ards-Issue.pdf) One issue is that to keep interior temperatures consistent across rooms doors need to remain open. Another issue with a point source is that you don't tend to have very good air mixing, which can lead to pollutant build up in one area. Energy use wise a heat pump has to get a Coefficient Of Performance above 3 to use less energy than natural gas. Even mini-splits typically only get this COP in mild temperatures. Of course if you get a really tight house insulated well then you may not even be able to find a Furnace with a low enough output. Also quite a large percent of a mini-splits energy can easily be offset with photovoltaic panels. With on site production and storage a mini-split only needs to get its COP slightly below 1 to use less energy than natural gas. Grid Tied PV offsetting mini-split energy useage raises the needed COP to about 1.5 - 2 or so. If you take a look at environmental sustainability a heat pump wins in most cases. A furnace will never see CO2 and other emissions reductions, a heat pump, for most parts of the world, will always see a reduction in its emissions over its lifetime. This is because the electric grid is being pushed by market forces to be more efficient. Also you can easily add emissions reductions by adding PV to the system. |
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07-04-16, 03:02 AM | #13 | |
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So, given the right advice, I am sure that I will have fun building one.
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07-04-16, 06:24 AM | #14 |
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DEnd,
that's an interesting article. Great results at a competitive price /sqm (or sqf). So, proper insulation if the most important factor. I will research how to obtain the best possible without changing construction methods used here as that would bring costs up. Also he costs ground source heatpumps at USD22,000, I'd expect a DIY system to be much cheaper. On another note, we use a lot of solar hot water heating here, perhaps i could look at using that as a source of heat rather than geothermal??
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07-05-16, 09:14 AM | #15 |
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Ok, here's my take on your build:
Since you have much higher cooling demands than heating, a ground or air source heating/cooling system should be sized for your cooling demands. Since it rarely dips to freezing temperature outdoors, an efficient air-source unit would have no problems heating during the chilly weather. No defrosting equals no wasted energy, so a variable speed outdoor unit (or a few single-zone minisplit systems) would be the most cost-effective to install. During those sweltering summer days, a ground loop would be more effective, but at a very high upfront cost. With limestone, you can't just grab a dozer or backhoe and dig a trench; dynamite, drills, jackhammers, etc. are necessary and push up both the material and labor tremendously. A few boreholes might be cheaper than a slinky field of equal capacity. As for heating water, your space heating method would dictate how to approach the solution. Using a phase change heating/cooling system, a desuperheater would provide hot water whenever the outdoor unit operated. This approach ties in with a dedicated heat pump water heater or solar pv panels. Many ecorenovators have published their experiments, trials, installs, and real-world, real-time results with these combined systems, many preferring to spend extra upfront on solar pv panels over thermal collection strategies. Main advantages are things not needed: regular frequent periodic maintenance, freeze protection, thermal store, extra pumps and plumbing, etc. With natural gas being very economical in your area, it would be stupid not to use it for at least a backup energy source. Besides heating, it may make sense for backup power generation as well. I don't know how often you have power outages, but where I am they happen a few times a year. An automatic backup generator does a better job than solar pv unless you have a really large collection array. Cheap insurance against mother nature. This says nothing about your construction and insulation, others before me have covered that subject well. Main idea is anything worth building is best done correctlythe first time, and anything worth insulating is worth superinsulating. Spend a little extra once, save forever after. Last edited by jeff5may; 07-05-16 at 09:46 AM.. Reason: Grammar |
07-05-16, 03:15 PM | #16 | |||
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We do not use PV for heating water, just solar heat collectors. PV is also used to generate electricity, the government used to provide incentives and rebates, but lately cut them. The power companies at first used to buy power back at the same price, but now they give you 1/3 of what they charge you, so PV is going out of fashion. However, we might get a new government (ASA we find out who is the winner...), so we might get back into the subsidies.
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07-05-16, 11:20 PM | #17 |
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Read this:
What is a Desuperheater or Hot Water Generator? Whether to run thermal or pv solar collectors or arrays (or both) is a big decision that you want to make early, as it will steer your system design plans. Both types of systems have advantages and liabilities. In the last decade, prices have come down on pv panels, and modular, scaleable, reliable controls are readily available. There are quite a few members with working systems operating as we speak. Those with electric vehicles are especially pleased with the choices they made, and most plan on further upgrades in one way or another. It's one of those things that helps you down the path to netzero or uber-efficiency in your energy budget. Once they have something running and laying waste to the utility bills, most people feel an urge to increase their savings. Once again, I'm just tossing around ideas. Im not a salesman trying to steer you towards a certain product. Just shining some light on these modern building trendsetters. |
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07-06-16, 10:01 PM | #18 | |
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I'm pretty skeptical on GSHPs. I want to love the idea, but the install cost drive me batty, especially when you can get similar operating cost from air source units in a lot of climates. Solar thermal doesn't make a lot of financial sense in many cases. http://www.greenbuildingadvisor.com/...ly-really-dead |
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07-07-16, 07:07 PM | #19 | |
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On the other hand, a 340Lt air to water heat pump might make more sense.
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07-07-16, 10:47 PM | #20 |
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If you are looking at installing a solar thermal collector array, take a good hard look at "steam back" system design. They combine the strengths of other types of systems, and are safe and durable over the long term. The steamback can be over built, containing more collection area than other types of systems. This gives you more productive operation when the sun is out, covering demands overall throughout the years. On especially sunny days with low demand, the panels simply stagnate and the liquid boils out if it can. No harm, no foul, no problems. Slick and simple operation.
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