Good results from an 8 Star house on a nice hot day

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Good results from an 8 Star house on a nice hot day

Postby PeterReefman » Mon Jan 02, 2012 6:35 pm

Hi all

Just a quick post with results from my 8 Star house for today which maxed out at 41.4c today. This was the hottest day here (Portland, Victoria) since moving into the house in 2009.

Without any air-con, the house stayed about 25c for most of the day but towards the end (about 5pm) it got up to 26.5c.

Right now it's 26 inside and 25 outside (yes the cool change has hit and dropping the temp quickly)

Full stats - http://www.energised.com.au/8Aquarius_temps.asp

Meanwhile - with 2011 now behind us, there was 4 nights during winter that needed artificial heating (using a heat pump). Total energy for the year to heat & cool the house to comfortable levels was 10.6kWh, or about $2.60

And running beside that, the house's 3.4kW solar system generates about twice the energy than the house consumes, making it operationally carbon zero.

Cheers,
Peter
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Re: Good results from an 8 Star house on a nice hot day

Postby Tracker » Tue Jan 03, 2012 3:29 pm

PeterReefman wrote:And running beside that, the house's 3.4kW solar system generates about twice the energy than the house consumes, making it operationally carbon zero.

So, is this saying that basically, you are only IMPORTing a bit more than you are EXPORTing.
PeterReefman wrote:Total energy for the year to heat & cool the house to comfortable levels was 10.6kWh, or about $2.60

So , this is not really an accurate statement.. It should have said "Total energy paid for, was 10.6KwH" ;)
I can't believe that ANY house could consume ONLY 10.6KwH in a year.. :roll:
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Re: Good results from an 8 Star house on a nice hot day

Postby Smurf1976 » Tue Jan 03, 2012 5:51 pm

Tracker wrote:I can't believe that ANY house could consume ONLY 10.6KwH in a year..

I took it to mean that this was the amount used for heating.

It's a long way short of the generally accepted 12,000 kWh (that figure is for Tassie however) but if you had the passive solar all worked out nicely and weren't too fussy about the actual temperature inside then I'd think you might be able to get away with a figure that low.
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Re: Good results from an 8 Star house on a nice hot day

Postby PeterReefman » Tue Jan 03, 2012 11:27 pm

Sorry Tracker you did read it wrong. The house really did only used 10.6kWh for heating and cooling for 2011. This is because the heater was only switched on for four nights during winter, and each of those nights used about 2.5kWh.

Actually the figure would have been lower but I forgot to turn off the hard-wired power meter to the heater, and the 0.1kWh phantom load per day from the meter running for a month or so kicked it up a few extra kWh.

The house has a single heated room which is the main living area. This room has an 8 Star (in the old scale) 2.5kW reverse cycle air-con which provides the heating (it's never been used for cooling). When this room goes below 20c the heater goes on - no ifs or buts. My wife sees to that. The coldest this room has been (while we were out) was about 17c. The reason this room is the only heated is because it's where the TV is, which is of course the coldest habitable activity people do in houses.

The rest of the house can have temps below 20c which is fine without needing heating, because those rooms (bathrooms, bedrooms, etc) have uses that are naturally warmer for us than the ultra-passive activity of watching TV.

So while there is an element of behavior (as there should be), the bottom line is no one ever puts up with uncomfortable temps anywhere in the house - the natural efficiency of the house means the minor rooms have a usual winter night time temp of 18-22; and a usual summer daytime temp of 22-26.

I regards to TOTAL consumption, we as a family of four consume about 8kWh per day for everything (no gas, wood, etc) for about 2,900kWh per year; and the 3.4kW PV system produces about 4,700kWh per year, so the net result is actually a true surplus of about 1,800kWh - but of course getting net consumption below 0kWh is really just a matter of matching consumption with a large enough PV system. Not that difficult.

It's the thermal efficiency that is really standing out. I think - and Monday's very hot conditions were really quite a satisfying test. I'm pretty rapt to see it working well.

Cheers,
Peter

p.s. I did notice that I got one figure wrong in the first post. I said "the house's 3.4kW solar system generates about twice the energy than the house consumes"; when it should have been "the house's 3.4kW solar system generates about 60% more energy than the house consumes". Sorry about that.
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Re: Good results from an 8 Star house on a nice hot day

Postby Tracker » Wed Jan 04, 2012 9:55 am

PeterReefman wrote:Sorry Tracker you did read it wrong. The house really did only used 10.6kWh for heating and cooling for 2011.


Thanks for the clarification.. A most impressive energy efficiency !

What would you say is the yearly average consumption per day - ie.. total power
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Re: Good results from an 8 Star house on a nice hot day

Postby PeterReefman » Wed Jan 04, 2012 1:07 pm

Hi Tracker - No worries and thanks for that.

The total energy consumption last year was pretty much exactly 8kWh per day.

Basically during the warmer 6-8 months of the year it's approximately 6-7kWh, and during cooler months the solar hot water system's electric booster makes an average "cool day" consumption more like 9-11kWh.

I'm keen to upgrade the house's energy monitoring equipment (currently a single channel ENVI-r) to be able to have itemised real-time and historical consumption data
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Re: Good results from an 8 Star house on a nice hot day

Postby Tracker » Wed Jan 04, 2012 2:15 pm

PeterReefman wrote:I'm keen to upgrade the house's energy monitoring equipment (currently a single channel ENVI-r) to be able to have itemised real-time and historical consumption data

and, don't we all.!

My only gripe is that it can cost so much to get all the data, and it does not really make that much difference in the end... You are either using as little as you can or your are not trying hard enough.. :!: .... :lol:

I could only dream of ever seeing Under 10 !

A dumb question to anyone deep into thermodynamics - what would be the most "Efficient"..
If you have three or ten Fridge/Freezers, do you keep them centralised in an Air-Conditioned area, or get them away to open areas (HOT).. The opposite extreem is placing them in the blazing sun
My faulty thinking - the biggest issue with refrigerators is the heat transfer thru the cabinet.... the temperature differential !!!
If they are in an conditioned "Living" area, then they will not run as long (to maintain their cool), and hence not generate as much heat.. but will the advantages of the lower thermal difference be swamped by the power to cool that living space.. ie (say) five motors running less, to make one run a bit more :?: ... :roll:
and meanwhile, the heat that IS seeping throught the walls, is cooling the local environment..anyway..
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Re: Good results from an 8 Star house on a nice hot day

Postby Gordon-Loomberah » Wed Jan 04, 2012 4:24 pm

Tracker wrote:If you have three or ten Fridge/Freezers, do you keep them centralised in an Air-Conditioned area, or get them away to open areas (HOT)..


Keep in mind that if they are operating at say a COP of 3 ( I have no idea what fridges/freezers actually run at), and they have 200W motors, then each one will effectively be putting 600W of heat into the room. 10 of them makes 6kW you have to remove, so an AC with a COP of 4 will need to be consuming 1500W to keep the room temp down... although the heat gained through the walls is also cooling the room a little.

It would be much better to add more insulation to them! Or better still, combine them into one large fridge/freezer ( and add some insulation for good measure), to reduce the surface area/volume ratio, and hence the heat gain from the environment.
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Re: Good results from an 8 Star house on a nice hot day

Postby Tracker » Wed Jan 04, 2012 4:42 pm

Gordon-Loomberah wrote:Or better still, combine them into one large fridge/freezer ( and add some insulation for good measure),.

I think that is the the REAL answer.. Some SERIOUS insulation... An oversized freezer and Produce Room, all based on the same principle of controlled-stealing cold air from the freezer to cool the Produce Area.. and a remote compressor..

I know that it boils down to the maths of COP and all that, but I just had this feeling that there was a break even point and anpther one of advantage.. Just another dream of a perpetual-motion machine.. :lol:
Well , not quite !
How I would love to be 30 years younger and planning a new home..

PS - I have never seen a suggested figure of COP for a domestic refrigerator, but it could be better than a RAC, as it would not have the wild fans distributing the Hot/Cold air.
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Re: Good results from an 8 Star house on a nice hot day

Postby Smurf1976 » Wed Jan 04, 2012 6:00 pm

I don't know this for a fact, but I'd expect that the COP for a domestic freezer is actually quite low. The heating efficiency of a RAC drops dramatically at very low temperatures, and a freezer is running at somewhere around -18 degrees, with heat discharged into a roughly 22 degree room on the outside, which makes me think it wouldn't be anywhere near as efficient as an air-conditioner cooling a room to 22 degrees when it's, say, 35 degrees outside. The temperature differential with the freezer is pretty large...

I could be wrong, that's just my thoughts on it. Cooling to -18 seems like a much harder task than cooling to 20 or 25 degrees like a RAC does, or even extracting heat from a 0 degree outdoor environment in reverse cycle mode.
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