Design and Build Spiv's Solar and Geothermal House

[AC_Hacker]

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

[Spiv]

Originally Posted by AC_Hacker

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!

[NiHaoMike]

Originally Posted by Spiv

Here it never freezes, but we need to heat the house 3~4 months a year

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?

[Spiv]

Originally Posted by NiHaoMike

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.

[DEnd]

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.

[Spiv]

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.

[DEnd]

Originally Posted by Spiv

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.

[NiHaoMike]

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.

[Spiv]

Originally Posted by NiHaoMike

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 , 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?

[mejunkhound]

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!