Alternative Technology Assn Forums

1. 

   Benny
   Member

   As usual the web site doesn't explain clearly what this is. I think its a re-hash of a previous version - a heat exchanger that sits in the roof space and pumps the filtered air in to the house through the existing ducting. Makes some pretty wild claims though. "save $7500 over 6 years on heating costs" ie $1250 per year. Maybe some of you guys in Canberra spend this much on heating - but here in Perth - where it comes from - I don't see anyone spending that much let alone saving that much. Usually only a few hundred per year.

   clamair.net

   Posted Saturday 11 Apr 2015 @ 10:18:27 am from IP #
2. 

   Morbo
   Member

   check how much sun you get in winter. Spring and fall opening windows at daytime does the same for nothing.
   Keep in mind, the roof space is way smaller than your living space, so I cannot imagine, within 8 or so daylight hr it gets enough heat to warm up your house. In Melbourne is not much sun in winter, I measured a black roof for several years, just pointless. Here these things warm people because they believe 1000s worth of stuff really works.
   $7500 in 6 years are my electricity and gas bills combined. Tis includes $800 utility fees per year.

   Posted Saturday 11 Apr 2015 @ 9:36:33 pm from IP #
3. 

   ghostgum
   Member

   Morbo said:
   Keep in mind, the roof space is way smaller than your living space, so I cannot imagine, within 8 or so daylight hr it gets enough heat to warm up your house. In Melbourne is not much sun in winter...

   In Melbourne the solar radiation figures are 7.1MJ per m2 in June.
   A five star house in Melbourne is 150MJ per m2 per year, so with 150 days of heating that is 1MJ per m2 per day. So it is possible to heat with a solar air heater given that you can collect about 1/4 of the global solar radiation. A better predictor of output from a solar air heater r is the hours of strong sunlight, and as you say in Melbourne there are many overcast days, during which a solar air heaterr doesn't help much. I should do the calculations comparing the heating cost savings of increased insulation vs solar air heater.

   I do have two solar air heating systems on my house. I do like them and the heat they dump into the south of the house, but the payback time is somewhat longer than is usually advertised. For my house they provide 10-20% of the heating.

   Posted Saturday 11 Apr 2015 @ 10:22:10 pm from IP #
4. 

   ghostgum
   Member

   I have enough solar air heating that on a sunny winter day there is no other heating required for daytime and evening. In autumn and spring it can overheat the house during the day. To increase solar air heating any further than I have already done would require heat storage to last 2-3 days, which is expensive. It would be better to use a solar water heater and lots of water storage instead of a solar air heater for multiday storage.

   Posted Saturday 11 Apr 2015 @ 10:57:08 pm from IP #
5. 

   Bushwalker
   Member

   ghostgum said:
   It would be better to use a solar water heater and lots of water storage instead of a solar air heater for multiday storage.

   I've thought about that and I keep coming to the conclusion it would be better to use PV to run a heatpump to heat the water. Still doesn't help much on overcast days, but I think the PV works better on lightly overcast days than solar HWS...

   Posted Saturday 11 Apr 2015 @ 11:14:53 pm from IP #
6. 

   Morbo
   Member

   April 7 1.5kWh harvested over an entire day. Lets see what the PV gets this winter. Am really not convinced with the solar hot water option, because 6 months a year you would produce way more than you need, just a waste of money. PV you can control and even get amazing 6ct per kWh feed in.
   My data logged for winter, the roof is barely over ambient most days, I really doubt it helps.

   Posted Saturday 11 Apr 2015 @ 11:50:24 pm from IP #
7. 

   ghostgum
   Member

   Morbo, my roof would be a lousy collector given that it is light in colour and has RFL underneath. I've got 9 square metres collection area of glazed solar air heater. That works much better than a roof.

   Bushwalker, yes the PV works better than the solar air heater on cloudy days. Given that we have a gas heater, I'll keep using that until it fails. At that stage I'll consider a heat pump running during the day from PV and overnight heat storage. It all depends on the energy costs in 10 years...

   Posted Sunday 12 Apr 2015 @ 1:07:37 am from IP #
8. 

   Morbo
   Member

   so does mine. In Perth its more cooling days than heating days I suppose, so it would be wiser to keep the summer heat out than getting some winter warmth in. My roof now on a 40 deg full sun day reaches 40 degrees a with a few hrs delay to the ambient. Last Melbourne summer was not really hot by am quite sure the roof space being 10deg cooler now helped.

   Posted Sunday 12 Apr 2015 @ 6:30:47 am from IP #
9. 

   Morbo
   Member

   

   

   thats why I am not convinced. Would only work for me when its same as easy if I was just to open the windows.

   Posted Friday 15 May 2015 @ 12:01:01 pm from IP #

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