We live in Canberra & about 4yrs ago bought a fairly large house that is now about 15yrs old. It is on a slab with off-peak inslab heating. The house was architect designed with large north facing windows. After being here 1mth in winter we got a $700 electricity bill (that's right, 1 month) & when we queried it we were advised to turn the inslab down from 20 degrees, which is what we used to have the old place set to on ducted gas. The house had wall & ceiling insulation, heavy curtains, & I'd put up kit pelmets. Basically we couldn't afford to heat the house so last year in winter we invested in a HRV (2 units, 1 slaved to the other due to the large house) with 2 solamate panels. It was installed on our light reddish/cream coloured concrete tiles with no sarking underneath, on the north facing roof that is partially shaded by a gum.
The next quarter our bill was approx $250 lower & the off-peak usage was down 25%. It will take a long time to pay the system off at that rate but we are a lot more comfortable, & use small panel heaters to temporarily heat bathrooms etc. It is certainly most effective in autumn & spring, being able to get the house from 17 in the morning (our new set temp for the inslab) to 23-24 degrees by late afternoon with the curtains & windows closed while we're out. In mid winter it raises the temp to about 18-20 on most days, which I class as adding about 3-4 degrees because instead of losing heat during the day as the slab cooled (when it is 10-12 outside max) we actually gained heat. I have seen the roof get to 25 degrees on days when it is 8 degrees & sunny outside, & it gets to 63 degrees in full summer (so the whirly gigs go incredibly fast).
In summer we are all sleeping a lot better with the HRV moving cool air in on those still nights, & when Summernats is on we can close the windows to keep the stink & noise to a minimum & get fresh air pumped in at night.
Overall we are extremely happy with the investment as there was little else we could think to do, having done the easy stuff like window coverings, shading (summer) & sun access (winter). I suppose it all depends on what you expect for what you pay, our aim was to take the load off the inslab heating & make it more comfortable in the day (the house gradually heating instead of gradually cooling)
Posted Monday 16 Aug 2010 @ 7:12:42 am from IP
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