What to do about my energy hungry airconditioner?

The greenest watt is the one you don't have to create. Energy efficiency is the low hanging fruit of greening our homes. Ask your questions or post your energy efficiency tips in here!

What to do about my energy hungry airconditioner?

Postby DoctorI » Sun Dec 27, 2009 8:16 am

G'Day All

I have an evaporative air-conditioner ducted throughout my home in Alice Springs. Over the last week I have kept a daily record of my power usage (and generation) and it would appear that the Air-con is using up to 20 kWh in a 24 hour period. This is an extreme climate so I have been running it constantly to keep the house at about 25 degrees compared to an outside temp of 40 degrees for much of the day and overnight lows of 25 to 28 degrees.
Is this reasonable usage or can I do something to reduce the energy usage without letting the house become unbearable?

And before you ask: Yes the house is insulated, we had that done two years ago and it made a huge difference. Installing roller shutters on the north and west facing windows has also made a large difference.
The Motor in the air con unit is labelled as 1100 watts.
The roof is already painted white.

I have considered replacing the motor with a smaller one and accepting a lower air flow (I already only run it on its low speed).
I have also thought about venting the air out through holes in the ceiling and then through the ceiling space and out the 'whirlybirds' on the roof.
I have also considered building a shade structure over the ground mounted aircon unit.
Can any of you suggest which of these three options will provide the most benefit?
OR do you have any other suggestions to help me reduce how much energy this unit is using?
1.5 kW PV and solar hot water installed Nov 2011.
DoctorI
Solar Fanatic
Solar Fanatic
 
Posts: 32
Joined: Mon Nov 30, 2009 9:48 pm
Location: Perth (Roleystone)

Re: What to do about my energy hungry airconditioner?

Postby Bthree » Sun Dec 27, 2009 9:07 am

The 20 Kwh per day would be right using a 1100watt motor on low,
calculations show the motor on low is consuming 840watts and that is correct
The unit you have would be large but is required to do what you want, evap a/c rely on a change of moist air in the home to remove heat, if you reduced the fan speed any further the heat extraction method would be comparised.
Have you insulated the ducting from swampy to the outlets, helped me in my last home, especially if they are running through the roof
I like your idea of venting the waste air through the roof cavity but would need a lot of 'whirlybirds' to take out the used air, possibly there are enough natural extraction points in the roof already to do the job.
Shade over the unit is worth a try but suspect not worth the effort, just a top hat, but don't restrict the air flow.

Consider this... i have a 160m2 home with reverse cycle AC which would use your 20kwh in 4 hours of run time and it runs 12 hours plus on a 40deg day
Network = Powercor .. Retailer = Origin .. Installed Christmas 2008
Latronics PV-1200 feed by 8xTrina TSM DC-01 .. 170watt = 1360watts DC in .. 1096watts AC out .. 5+years later 990watts ac out
Bthree
Solar Crusader
Solar Crusader
 
Posts: 429
Joined: Thu Sep 24, 2009 10:14 pm
Location: NorthWest Victoria

Re: What to do about my energy hungry airconditioner?

Postby DoctorI » Sun Dec 27, 2009 11:14 am

thanks Bthree

yes my evap unit is big.
I will have to use your reverse cycle power figures to convince my wife we do not want reverse cycle fitted. The evap works so well here because our air is so dry [I have even seen the official relative humidity figure go down to zero]
1.5 kW PV and solar hot water installed Nov 2011.
DoctorI
Solar Fanatic
Solar Fanatic
 
Posts: 32
Joined: Mon Nov 30, 2009 9:48 pm
Location: Perth (Roleystone)

Re: What to do about my energy hungry airconditioner?

Postby Gordon-Loomberah » Sun Dec 27, 2009 2:47 pm

Are you out of town or in town with a large area of available ground area, or have a large water tank or dam nearby? The annual average temp at Alice Springs is close to 21C (data from PO), so 2m underground.the temperature will be close to that.
From experiments I've done, you can get down to about 20C by evaporating water into air, so its a similar temperature to underground.

You could run an array of pipes 2m deep outside your house,

=========================== > air to house
|| || || || ||
|| || || || ||
|| || || || ||
===========================< from house + some fresh air

( I hope everyone sees the same font on here, otherwise the above may look silly)

With a couple of hundred metres of 100mm pipe you would have a good supply of cool *DRY* air, not sticky humid like with a swamp cooler.
You dont want to try to force all the air through 1 long pipe- too much frictional resistance meaning too large a motor would be needed, but you do want lots of surface area to have sufficient capacity to absorb the heat from the extraced house air, and sufficient surface area for the heat exchange to occur. Also sufficient volume of the thermal mass nar the pipes to it doesnt get too hot in summer.

I've been thinking about something like this here for quite a few years, but I don't like the idea of breathing PVC fumes if stormwater/sewer pies etc are used. Poly pipe might be better, but is more expensive, the company I emailed about earthenware pipes never responded, I guess they only deal with big corporations, councils etc. So I sort of ran into a dead end for a suitable pipe material.
Searching the net I found others are doing this, but using PVC. 2 or 3 years ago I even found someone who had just installed a similar system in a new house, and it did keep the area at a very pleasant temperature, but he had nowhere near enough length of pipe for the huge house he had built,(internal floor area something like 450m^2) so it just kept part of it cool. He was drawing outside air in, with zero recirculation. I measured 34C air at the intake and 25C in the room it was cooling (from memory).

If you had access to a large body of cool water, that would be an even better source of cooling, you could use one lenth of pipe for water circulation with no array needed, and blow air through a heat exchanger in/under the house. Cool air with no added humidity.
Other thoughts I've had about this idea are to have heat exchangers with water circulating to make use of cooler night time air/rainy days to cool your source of cool water or earth. If you have sufficient volumes of "cool storage" you can even do this year round- using cold/frosty nights to take heat out of your storage mass. A simple comparative thermostat could turn a circulation pump on whenever the air temperature is lower than your storage mass.

Of course you may be in a climate that requires heating in winter and cooling in summer- that 20C air from underground that feels so cool in summer, seems pleasantly warm in winter ;)

Digging deep trenches is probably fairly expensive, and may or may not be possible depending on your soil type/rock etc. Pipe also is expensive, but it's also a once off capital expense, then you are just left with the cost of blowers and or pumps, but they would not need to be as large as 1100W for an average sized house.

Gordon
Last edited by Gordon-Loomberah on Sun Dec 27, 2009 3:36 pm, edited 1 time in total.
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
User avatar
Gordon-Loomberah
Community Moderator
 
Posts: 5748
Joined: Thu Sep 24, 2009 9:41 pm
Location: Loomberah NSW Australia

Re: What to do about my energy hungry airconditioner?

Postby DoctorI » Sun Dec 27, 2009 3:19 pm

Hi Gordon
Thanks for the response. Unfortunately I am unable to implement the underground cooling pipes option for several reasons. The house is on an 800 square metre suburban block. The house has a solid concrete floor and 1 metre wide (minimum) concrete paths around it.
As for a dam, there is one about 500 m away but it is only for flood mitigation.
On the other hand, humidifying the air here is necessary since it is so dry to start with. Currently 10% RH (dewpoint -0.5 deg C)
1.5 kW PV and solar hot water installed Nov 2011.
DoctorI
Solar Fanatic
Solar Fanatic
 
Posts: 32
Joined: Mon Nov 30, 2009 9:48 pm
Location: Perth (Roleystone)

Re: What to do about my energy hungry airconditioner?

Postby Tracker » Mon Dec 28, 2009 8:12 pm

I would have to wonder about the use of a straight Refrigerated Air Con.

I presume that the high power motor is needed to give the Air-Flow and the resultant evaporation/cooling.

One would think that you could actually run a refrigerated system for that power, and run a sealed house, rather than having to vent and maintain flow/cooling.

Do you have any neighbors who have Refrigerated Air-Cond, to compare with?

I like the idea of a 2Mtr deep pipe array, but would wonder what the cost would be to undertake it.
2mtrs down, WOW, I suppose there are trenchers who can do it.
(You have no such chance because of your location)
Retired Engineer and keen PV experimenter - Always ready to learn and share.
2 x CMS2000 (fan cooled) GCI and SE 170W panels
1.7kW First Solar/Outback Island circuit - Peak Replacement Power
Governments won't save the world :-) They will just TAX it :-(
Tracker
Solar Crusader
Solar Crusader
 
Posts: 5108
Joined: Wed Sep 23, 2009 5:54 am
Location: SYDNEY --- EA - Network, Retailer - EA

Re: What to do about my energy hungry airconditioner?

Postby Gordon-Loomberah » Mon Dec 28, 2009 8:25 pm

Tracker wrote:...2mtrs down, WOW, I suppose there are trenchers who can do it.


No problems, the house I looked at had their pipes 4m down!

Gordon
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
User avatar
Gordon-Loomberah
Community Moderator
 
Posts: 5748
Joined: Thu Sep 24, 2009 9:41 pm
Location: Loomberah NSW Australia

Re: What to do about my energy hungry airconditioner?

Postby Helipos » Mon Dec 28, 2009 9:29 pm

Whats the house constructed from ?
Ie double brick or what ever.

Cam
User avatar
Helipos
Solar Crusader
Solar Crusader
 
Posts: 360
Joined: Tue Oct 06, 2009 9:18 pm

Re: What to do about my energy hungry airconditioner?

Postby terryw » Mon Jan 04, 2010 4:43 pm

Hi Doctor1

I don't want to seem critical....but do you really need aircon in Alice? I lived there a few decades back and we survived easily without aircon. Try getting used to being hot. It's not so bad.

Otherwise...plant trees, trees and more trees.

Good luck
terryw
Solar Supporter
Solar Supporter
 
Posts: 8
Joined: Wed Dec 09, 2009 10:47 am

Re: What to do about my energy hungry airconditioner?

Postby DoctorI » Tue Jan 05, 2010 5:12 pm

Yes we do need airconditioning this summer, it is needed for cooling and humidifying the air within our house. Last summer wasn't so bad and we got by using it a lot less. So maybe the summer you were here was a cooler one.
1.5 kW PV and solar hot water installed Nov 2011.
DoctorI
Solar Fanatic
Solar Fanatic
 
Posts: 32
Joined: Mon Nov 30, 2009 9:48 pm
Location: Perth (Roleystone)

Next

Return to Energy Efficiency

Who is online

Users browsing this forum: No registered users and 1 guest

new solar power specials
cron