Design and Build Spiv's Solar and Geothermal House
 

This thread is started with the intent to help Spiv design his solar and geothermal house in South Western Australia.

(This thread is re-directed from THIS_POST.)

Here is some information that could be useful in this project:

A Google map of the area where this house is to be built:

LOCATION_MAP

SITE_MAP
(house is to be built on empty lot above arrow)

DESIGN_DRAWING_A

DESIGN_DRAWING_B

CURRENT_HEATING_DEGREE_DAYS (for each of the last 365 days)

Let's show Spiv what EcoRenovating is all about!

Sincerely,

-AC_Hacker

Just to recap from my posts on the other thread:

My interest is in a new home I will be building in 4~5 months, hopefully the last home I have to build:

• The ground floor is 196mq - garage= 150mq and the first floor is 122mq.
• The floors will be solid concrete on sand and limestone ground.
• All windows double glazed,
• All walls and roofs will be properly insulated,
• Flat metal roofs.
• Here it never freezes, but we need to heat the house 3~4 months a year
• 8~9 months we open the windows and let the sea breeze in the afternoon and the land breeze at night, but some days it goes over 40c (100F), so cooling ability will help.

I am exploring the ideas of:

1. Geothermal floor heating using a heat pump with solar as well.
2. Perhaps cooling with cool air exchange??
3. I am thinking to place the slinkies below the house in trenches, before I build the concrete floor slab, is that a good idea or should they go under the driveway?

Any help to get on the right track deeply appreciated!

That's a rather unusual combination. What's the average temperature for the months of the year? What about the underground temperature? Those factors will tell if it's worth going with geothermal as opposed to a conventional heat pump.

Do you expect to need any dehumidification?

Hello NiHaoMike,

I remember reading a survey from Singapore Airlines on which was considered the city with the best climate in the world and Perth came first, pari with San Diego (where, I see, you live).
We are at 32 degree South and the lot is on a small hill close to the Ocean, the microclimate here is different from even 2km further inland. The sea breeze and land breeze blow nearly every day mitigating the temperature. You can see here some statistics. Not sure how accurate they are, but the long term minimum average is 6.7° which seem correct.
I lived here 36y and rarely suffered from high humidity.
People used to have fireplaces or slow combustion stoves to warm the house in winter, but nowadays most use reverse cycle air conditioners, is that what you call a conventional heat pump?

The reason I am researching this system is my desire to use less grid-supplied electricity.
In the last 20y I built 6 two storey houses here, so I know how most things get done.
However, I am not stubborn and can change my mind easily if I am shown a better way.

Spiv,

It sounds to me like you have a fairly low heating load. In that case for choosing equipment I would go for a heat pump over geothermal. I would also forgo hydronic in floor heat, simply because you seem to be in a mild climate. If you are indeed in a mild climate, I encourage you to look closely at the Passivhaus concept. If I remember correctly you already have plans drawn up? If so I doubt you can really go whole hog on a passivhaus but it's concepts are hugely helpful in reducing your energy bills.

The biggest concepts are air sealing with testing, and mechanical ventilation. All the other sexy stuff like tiny mechanical equipment, Earth tubes, HRV/ERVs, massive insulation levels, etc... only become effective when air sealing with testing and mechanical ventilation are taken care of first.

What I would do: Insist your architect shows how the air sealing is to be done, especially around windows, doors, and any place the air barrier changes material, direction or planes. These drawings need to be included in the plans. Insist your contractor follows those drawings. Insist on having the house tested for air tightness with a blower door test (pressurizing and depressurizing the house). Typically this should be done three times during construction, once upon initial completion of the air barrier, again when all known holes through the air barrier are done (windows, doors, electrical, HVAC, water, etc...) and once again at completion. At completion a house done very well will have passivhaus levels of air tightness which is 0.6 Air Changes per Hour at 50 Pascals of pressure (ACH50), Well built houses will be about 1 ACH50. I would highly prefer all HVAC equipment to be inside of the air barrier (conditioned envelope really). Insist that a Manual J calculation be performed by a competent engineer. I would also insist that the HVAC equipment be tested with a duct blaster (unless you go with ductless minisplits). I would also insist that the system be commissioned so that the air flows from the registers match what is called for on the manual J calculations.

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.

Don't forget to check the service charge for natural gas. In some cases, it can be significant enough to more than offset any savings. The latest (conventional) heat pumps are getting so efficient that they're competitive with natural gas in many areas.

How much does it cost to install the ground loop (just the loop itself, no equipment) from the start? It's probably worth installing just in case you decide to get geothermal later on.

Gas will be installed in all cases, most houses in Perth get tied to the grid. We have gianormous gas fields and export million of CuM of gas. Industries have got deals with the state to get pilelines down from the gas fields to Perth and our gas is cheap
This is from one of our providers:

Standard Gas Prices

Our standard gas prices are based on the regulated tariff caps approved by the Minister for Energy.

Residential Customers:
Supply charge 20.58 cents per day
Usage charge – for the first 12 units used on average per day 14.20 cents per unit
Usage charge – for each additional unit used on average per day 12.81 cents per unit

Don;t ask me what a "Unit" is as I could not figure it out :o, however, Here is a cost comparison.

When you guys on this forum refer to "Conventional Heat Pumps" what do you refer to?
Something like this?

Those Daikins are just one example of a conventional (air source) heat pump.

So that's just over $6 per month service charge, not too bad. But the page says that for a water heater, going with gas (as opposed to conventional electric) is only a 40% savings. Contrast that to a heat pump water heater where a well designed unit easily uses less than half the energy, a really good one less than a third.

I'm going to guess that gas isn't actually cheap in your area, but they use obscure units to make it look like it is.

You'r probably right about costs.

So, that's why I am exploring the possibility of using the nice warm ground on a water to water and or air heat pump.
Also I want to be more self reliant and have less footprint.

Do they exist?
How much do they cost?

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.

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.

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.

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??

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.

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.

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.

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...:D), so we might get back into the subsidies.

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.

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

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.

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.

We don't seem to have any problems with the systems available in Oz, in previous houses, we often went on holidays and left the house empty in the middle of OUR summer and the solar panels didn't boil or were otherwise affected by excessive heat.

Had to look up what a WA AUS unit was for gas, elec unit is the kw-hr.

Gas unit is 3.6 megajoules = 1 kw-hr (0.034 therms) 1$ US = 1.3 $ AUS

3.6 megajoule number comes from,
.278*3.6 MJ = 1kw-hr




Rates are gargantuan compared to USA WA state: About 3X higher!

Elec power runs about 30 cents kw-hr including supply charge (AUS$) < 10 cents in WA state USA
Gas is $3.50 a therm ($1.50 or less in USA depending on area)

SPIV: IT IS TIME FOR GSHP! with your high rates.

Really surprised you nat gas rates are so high - of course, prior to fracking, many USA gas prices were over $2 a therm (7 cents a 'unit')

My DIY GSHP (60,000 BTU, 5 ton) cost under $600 and has a COP of 5.7 with 52 deg ground temp below water table.

With the WA high rates, solar is a definite option to consider!

And I thought our gas was cheap!!! :mad:
That sounds good, pity I don't understand it.....:o.
Can you help me out with those figures and tell me where to find info on DIY GSPH?

......help me out with those figures and tell me where to find info on DIY GSPH

If you have not already done so, read ALL 1,910 discussion in AC_Hacker's 'heat pump manifesto' thread !

99% of your technical questions will be answered there.

For the solar questions, look at those threads.
You really should look at solar first given you high energy rates in Perth area.
To assess your solar potential, research 'solar insolation' NOT installation or insulation, inSOLation - e.g.
Australian Climate Averages - Solar exposure

Just for curiosity I looked at the link on the prev post.

You are pretty much under clouds in July there, eh? Only about 3 kW-hr per day available for a 2 by 3 meter array of solar cells, $1 at your rates, right when you need heat!

so maybe solar is not a good deal in Perth due to overcast skies when you need the power for gshp ?

In January, you will get about $5 worth of power a day from a 2x3 meter array.

Yearly average solar power of maybe close to $1000 though.
A 2x3 meter array PEAK power rating would be about 1.2 kW, Maybe $1500 DIY installed - pretty good payback due to high rates there!

Kinda like parts of Germany, where power rates are close to 40 cent kw-hr, and nearly everybody has some solar or wind.

Does AU have solar subsidies or tax credits? Look into it !

COP: coefficient of performance. A measurement of heat moved divided by power consumed. Watts / watts. Higher is better. Most manufacturers use weighed (seasonally adjusted) measurements for performance figures. All refrigeration units are more effective and efficient when the outdoor air or ground water is close to the target indoor temperature. As the difference widens, it takes more energy to move the same amount of heat. The weighted figures make it easier for the common buyer to choose between units.

So,

from the advice received and what I learned from it, it seems that the most appropriate course of action is:

1. Insulate as much as economically viable.
2. Ensure good airtightness of the house
3. Use mini splits
4. Use Solar PV to assist minisplits in summer
5. Use gas to to assist minisplits in winter.

Did I get it right?

Minisplits are definitely the easier and cheaper option up front.
I had them installed in previous houses and it only takes an afternoon to get them retrofit, in a new install it might even be easier as the electrical and plumbing can be worked out in advance.

What I have against them in the noise they make and the seem to waste a lot of energy (a lot of heat is produced by the external unit).

I was sort of sold to the idea of hydronic floor heating as a sort of quite and ecological way to get warm in winter, but I might have to give up that idea.....:mad:

The more you are able to slow heat loss, through rigorous control of infiltration (will require a very high efficiency HRV), and heat loss through walls (insulate > 2X the required insulation in you area)...

...And also use construction that will prevent thermal bridging (which will eat away 18% of your insulation value), the less you will need to heat and cool your house.

Just imagine, silent comfort with no moving parts, due to proper design of your structure.

-AC