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Old 07-03-16, 04:55 PM   #11
NiHaoMike
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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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Old 07-03-16, 07:03 PM   #12
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Thank you DEnd,
I will look into Passivhaus.

Still, we do need to heat our houses for 3~4 months and I cannot think of a nicer feeling than to walk barefoot on warm floors.....

Natural gas is very cheap in WA, perhaps hydronics and gas heating is the cheapest answer.
The issue with hydronic floors is that for a tight house insulated well the needed floor temps are not actually toasty. To get the floors toasty warm you end up overheating the house. At the needed floor temps you can get very similar temperatures just by providing air space under the floor.

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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Old 07-04-16, 03:02 AM   #13
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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.
I am a Land and Quantity Surveyor, built several 2 storey houses, two composite 40' catamarans, love woodwork, can weld, braze, do electrical work (but do not tell electricians....),used to fix my cars (when I was younger), I am an ex sat diver, sailor and a few other bits and pieces.
So, given the right advice, I am sure that I will have fun building one.
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Old 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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Old 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.

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Old 07-05-16, 03:15 PM   #16
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Quote:
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Since you have much higher cooling demands than heating, a ground or air source heating/cooling system should be sized for your cooling demands.
Yes, in Western Australia we have higher cooling demands, but as I mentioned, close to the coast where I am building, we most times just open the windows and let the sea breeze in.

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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.
The area has been graded with big dozers by the developer, all hard capstone has gone and the underground limestone is normally managed by a backhoe or a small excavator. I'd expect half a day's work is all I'd need and I have contractors ready to do it.

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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.
Could not find much about desuperheaters.....
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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Old 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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Old 07-06-16, 10:01 PM   #18
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Originally Posted by Spiv View Post
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??
Proper Insulation and air sealing are the most important yes. Since you have a mild climate you won't likely need massive levels of insulation. But that all depends on what your energy use goals are. A passivhaus consultant and/or a mechanical engineering (HVAC) firm can likely do some energy modeling and give you an Idea on what your energy expenditures are likely to be. Energy Modeling is far from precise but it is the best tool available.

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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Old 07-07-16, 07:07 PM   #19
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Solar thermal doesn't make a lot of financial sense in many cases. Solar Thermal Is Really, Really Dead | GreenBuildingAdvisor.com
Perhaps in the USA, here there are hundred of thousands installed and you can get a 300Lt for around AUD3,000.

On the other hand, a 340Lt air to water heat pump might make more sense.
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Old 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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