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Solar heating & cooling systems

(30 posts) (14 voices)

Started 12 years ago by pete0762
Latest reply from jimferguson

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pete0762
Member

I am currently considering the installation of either an HRV systems or Solar Venti system in our "weekender" but I find it difficult to decide which system is better suited the the place - a completely renovated (with wall, ceiling and underfloor insulation) 1940s wheatherboard house, with colorbond roof (including plenty of northfacting roof, which already has a solar hot water system mounted).
Whats the pros and cons, advantages and disatanvtages for eiher of these. Price is almost the same, so its not a concern and savings on energy costs will be not high due to not extensive use of property.
I know that HRV uses an mains powered electric fan and Solar Venti a solar fan, both can have advantages (also noting that I have a 1.5kW solar power system installed at the place).

Any thoughts and experience welcome.

Posted Thursday 22 Apr 2010 @ 1:19:33 pm from IP #
dymonite69
Member

I posted on this before, you might be able to extract at the most 3.6-5.1 kWh/day of heating with a SolarVenti during a Melbourne winter. I would expect that it would be closer to 2-3 kWhr/day once you account for transfer losses.

This is equivalent to leaving a small 1kW bar radiator on for 2-3 hours a day.

http://www.ata.org.au/forums/topic/solarventi

Posted Thursday 22 Apr 2010 @ 1:54:53 pm from IP #
ghostgum
Member

I've got a Solar Venti, my sister has an HRV.

What colour is your colorbond roof? Is it light or dark. Do you have RFL under it already? The HRV would require a dark roof, and would be useless with my light coloured colorbond roof. If you have RFL, then HRV would need to draw the air from between the RFL and the colorbond.

From memory, the HRV uses an average of 10-20W of power, but you would need to check this. You can't turn the HRV system off unless you add an extra switch yourself. If the roof temperature is closer to the target temperature than the house temperature, then the HRV fan will run.

Both are designed to primarily ventilate the house, with heating or cooling as a secondary benefit.

Posted Thursday 22 Apr 2010 @ 11:05:37 pm from IP #
pete0762
Member

The color of the roof is a medium green and is without RFL. Seems that I may need to do some temperature measurements in roof cavity in winter to get a feel what temperatures I may get.

But from other posts it does not appear that these systems would do a lot and would never pay off.

I actually have a Sun Lizard on our house in Melbourne (Dandenong Ranges), which produces only moderate heat flow. Sun Lizard is not available anymore so I was looking for alternatives i.e. Solar Venti and HRV for our other house in South Gippsland.

Any more experiences with HRV?

Posted Friday 23 Apr 2010 @ 12:57:18 pm from IP #
ghostgum
Member

Definitely do some measurements in the roof cavity. The heating savings claimed by the HRV salesperson who visited me were never going to eventuate. Our gas usage bill is about $500 per year, nearly all for house heating in winter (piped natural gas, not the more expensive bottled gas). A $5000 system couldn't pay itself off in the claimed 4 years, if the maximum it could do was half the house heating. My SolarVenti may never pay for itself in reduced heating. What it does do is make the south room cosy warm on a sunny winter day, but we could have done that with a cheaper heat shifting fan.

Unlike a SolarVenti, the HRV does have an advantage on summer nights. When the roof cavity temperature falls below the room temperature (and is above the summer set temperature), the fan will come on to bring cooler fresh air into the house. This will use much less electricity than an evaporative cooler on fresh air mode, but more than windows catching the prevailing breezer.

I have read comments from others about the HRV that it heats Ok in autumn and spring, but poorly in winter.

My solar venti was installed in late August last year, so I don't know its winter performance. I do have logging temperature sensors in my house, the solar venti duct, the roof space, and outside. From these I can see the temperature rise in the south room (12m2 with open door to the passage of 20m2) of 2-3 degrees due to the solarventi during autumn/spring. I'll be watching the data this winter.

Posted Friday 23 Apr 2010 @ 10:33:07 pm from IP #
dymonite69
Member

It would need a pretty good filter if it was drawing air from my roof cavity filled with fibreglass insulation.

Posted Friday 23 Apr 2010 @ 10:50:22 pm from IP #
ghostgum
Member

HRV has a filter that needs to be replaced every 1-2 years. The service call from HRV to replace the filter was another reason why the savings weren't likely eventuate.

Posted Friday 23 Apr 2010 @ 10:58:50 pm from IP #
ghostgum
Member

If you are into DIY, have a look at the solar air heater designs at
http://www.builditsolar.com/
You can make one for a lot less than the commercial systems.

Posted Friday 23 Apr 2010 @ 11:02:08 pm from IP #
susambas
Member

Hasc any one built a DIY like Solar Venti system? Where could one find plans/drawings/specifications? I could not find it on the http://www.builtitsolar.com. web page.
Could any one help?
Thanks

Posted Saturday 3 Jul 2010 @ 7:34:11 am from IP #
GaryGary
Member

Hi,
I'm the keeper of builditsolar.
It looks to me like the Solar Venti is just a thermosyphon air heating collector with the intake air coming from the outside instead of the inside.
I came to that conclusion reading this page on their site:
http://www.solarventi.co.uk/index.pl?section=27

I may be wrong? But, if this is what it is, then I don't see why you could not take any of the thermosyphon type collectors on the Space Heating page, and just rearrange them a bit so that the intake pulls in outside air rather than inside air. I think I would try to arrange it so that you can switch the intake to either inside or outside, as when you are in the cabin in cold weather, having the intake pull in room air will make it a more efficient solar space heater.

The first one in this section:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm
is the one I use on my barn/shop -- its very simple to build and costs next to nothing.
There are a couple other designs down the page a bit.

Gary

Gary

Posted Sunday 4 Jul 2010 @ 2:22:33 pm from IP #
Benny
Member

I built one - Perth WA. Here's a picture ...
http://picasaweb.google.com/BennsOfMaylands/TechStuff#5490254470718766850

Al extrusion 120mm wide to make a box. 8mm ply to make the base. 12mm polystyrene insulation on the bottom covered with black anodised Aluminium sheeting. The white bits on the black surface are where I cut small flaps in the Al sheeting and lifted them up to disturb the airflow and get better heat transfer to the passing air. Corrugated polycarbonate cover.
Hole in bottom right is air inlet, where ducting comes in direct from the ceiling in my office - driven by a cheap extractor fan.
Hole in top left is outlet which goes through insulated air con ducting, back down through the roof and then through more ducting all the way to the floor under my desk. Photo 5 shows this duct inside my office. There's another extractor fan at the top of the ceiling in the outlet duct - so I have "a blower and a sucker". One of the $40 thermostats from jaycar controls it, but had to put the sensor on the end of 10m of extension wire to get it inside the outlet duct up on the collector.
Collector is up on the roof, facing NE (to get morning sun) and inclined at a high angle - it usually starts running about 8:30am and goes until 3pm when sun is just at grazing incidence. Outlet air is running at 26C at the moment with outside air at 2C.
On a really cold day like today it doesn't give enough heat to warm my office but throughout autumn and spring its great.

Posted Monday 5 Jul 2010 @ 3:32:16 am from IP #
ghostgum
Member

Gary, the SolarVenti uses a 120mm muffin fan to move the air, powered by an amorphous solar panel inside the SolarVenti.

At least in Melbourne, which is a southern state near the coast, the outside air temperature is often not so low that you need to recirculate the room air through the solar heater. During the heating months, the average difference between inside and outside is only about 8 degrees (from Heating Degree Days figures). Using room air would be more efficient, but using outside air will freshen the room air.

I've got a SolarVenti, but I am considering building a larger solar air heater on the north wall of our house.

Posted Monday 12 Jul 2010 @ 1:36:16 am from IP #
GaryGary
Member

I missed the muffin fan and internal PV panel -- nice to have it all self contained.

Nice job Benny -- free heat is good!

Gary

Posted Monday 12 Jul 2010 @ 2:39:44 pm from IP #
tedthebug
Member

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 #
dymonite69
Member

In slab electric heating is one of the most expensive forms of heating. Firstly electricity is about 5 times more expensive than gas. Secondly heating a slab takes far more energy than heating air.

Posted Monday 16 Aug 2010 @ 7:23:39 am from IP #
tedthebug
Member

To true, but the cost for getting gas connected & fitting a system in the roof (we have extremely limited space around the house) was about the same as this. In the end we probably should have tried harder or had 2 smaller gas units put in but we were attracted to the solar aspect as well as the cooling in summer. As I said, it met our needs & who knows, in 10yrs there may be a bigger improvement that we can incorporate. What I'm looking for now is a hot water system that can make use of the air that is heated in the roof as well, but again I think space is going to kill the idea (plus it is a topic for another thread)

Posted Monday 16 Aug 2010 @ 7:32:43 am from IP #
gully
Member

tedthebug: Best way for a hot water system to take advantage of the heated air in the roof is to *put* the hot water tank in the roof. Much more insulated in there than out in the cold!

Posted Monday 16 Aug 2010 @ 12:32:59 pm from IP #
tedthebug
Member

That's what I was thinking of investigating but I don't know how I'll go getting it in as all the ones I've been able to find seem to stand upright whereas I'd need one that can be set horizontally to get it in.

Don't know how much more insulated the roof is compared to outside. For some reason every new home I've seen built in Canberra doesn't have anything under the tiles or colourbond, they just fix them straight onto the battens, & ours isn't any different.

The temps go incredibly high in summer & below 0 in winter really quickly, & the roof cavity fills with dust/dirt/leaves etc.

Posted Thursday 19 Aug 2010 @ 10:48:00 am from IP #
Jeffbloggs
Member

tedthebug
In regards to laying a HWS boiler horizontally: I rang up both dux and rheem, and their electric ones can be installed horizontally so long the heating element remains completely submerged, otherwise it will void the HE warranty. Plus they also need to be installed according to the local council regs..and these might vary.

HWS in the roof should reduce air convection around the HWS compared to sitting outside next to a wall that captures the wind. Plus the roof space should generally be a higher temp in comparison to the outside. BTW I read a report about increasing the eff. of HWS, apparently just using copper piping straight from the HWS will increase heat losses by 15%, just from the convection of the water in a 12mm copper pipe!...go pvc pipe or loop the hot end straight down on the install to stop this, plus insulate/lag everything after the install.

Posted Thursday 19 Aug 2010 @ 12:10:56 pm from IP #
tedthebug
Member

Thanks jeffbloggs, something to keep in mind. Have to admit tho that I'm worried about installing things in ways not recommended by the maker, my luck would mean that something would go wrong & I'd not be covered by warranty. Still, I'm not in a big rush yet, the old one is still going ok, so I will wait & see what is available when it finally carks it.

Posted Tuesday 7 Sep 2010 @ 6:26:52 am from IP #
Peterws
Member

(In slab electric heating is one of the most expensive forms of heating. Firstly electricity is about 5 times more expensive than gas. Secondly heating a slab takes far more energy than heating air. )

Not to mention 10-20% heat lost to the great big heat sink in the ground!!

in slab is over rated!!

Posted Tuesday 7 Sep 2010 @ 6:50:17 am from IP #
tedthebug
Member

Yes electric in-slab is expensive, even off peak, but having warm floors underfoot & a fairly even air temp is a benefit in canberra winters. If we had built this house (it was approx 11yrs old when we got it) I probably would have gone with ageothermal/hydronic system + other things I'd like to have in my dream house. Unfortunately we are stuck with what we have for heating & anything else we can do to maximise gain in winter/minimise gain in summer & minimise loss/maximise air flow in summer.

We have had the roof resealed & painted with a well known paint brand that says it minimises heat gain, I've added pelmets (they come in a kit from WA - you send them the sizes & they make & flat pack it to you) to all the windows, we have good quality curtains, insulated shutters on the largest room, a new pergola on the North side that will have a grape over it in a few years & will have removable shade cloth in the meantime, a shade structure over the west window with removable shade cloth so we get the winter sun & skylights. I've sealed all the doors & am working on the windows next & we are saving to have all the stupid, ineffective downlights replaced with normal light fittings (whoever thought that one recessed downlight in the middle of each room was enough light needs their head checked - can't see a thing).

When things improve a bit more & we win lotto I will investigate getting an air heat pump hooked into the solarmate & then maybe turn the inslab off for good (dream, dream, dream....)

Posted Tuesday 7 Sep 2010 @ 8:11:24 am from IP #
Peterws
Member

I wasn't thinking electric in-slab, as I wouldn't consider that under any circumstances, gas fired hydronic has a bit going for it, the radiant heat is wonderful, its just inefficient.
as for the heat pump, well on a cold canberra -5 degree winter's day you won't get much heat out of a heat pump, they work well when you need them least them.
sorry to be picking on you but I too live in Canberra and there are better options

Posted Tuesday 7 Sep 2010 @ 12:32:03 pm from IP #
PV2010
Member

what about a ground source heat pump? used widely by our northern hemisphere friends?

Posted Wednesday 8 Sep 2010 @ 8:49:32 am from IP #
ghostgum
Member

From what I have read about ground source heat pumps, these are similar to using an reverse cycle air conditioner as a heater, but because the heat source is closer to the target output temperature, the efficiency is about 6 for ground source, and 3 for air source. So twice as good, but still uses electricity. The downside is a cost of about $20k for ground source heat pump. If your annual heating bill is $2000 in a cold northern climate, then the ground source heat pump would pay itself off over time. If your annual heating bill in a warmer Australian climate is $500, then it may not be worth the investment.

An alternative to this is the one at mtbest.net, which uses sun on a black poly pipe to be the heat source, and then a heat pump to transfer that to a storage tank at higher temperature, which is then used for heating the house. This requires more space than a surburban block.

Posted Wednesday 8 Sep 2010 @ 12:21:42 pm from IP #
dymonite69
Member

I believe such a heat pumps has to be 'tuned' for different the different temperature ranges. It appears to be bespoke solution. You couldn't use an off the shelf unit.

Posted Wednesday 8 Sep 2010 @ 1:08:35 pm from IP #
dymonite69
Member

Interesting stuff:

http://www.ausscig.org/

Posted Wednesday 19 Oct 2011 @ 1:02:02 pm from IP #
gazmo88
Member

Sure is.

I used to have a kerosine fridge. Wonderful device, worked fantastically and didn't need to generate much heat - it just had a simple small burner..

For years I wondered when somebody would replace the kero with solar.

More sun more cooling .... Just what you need. Add some eutectic plates to carry it through the nights and cloudy days and no moving parts. Perfect.

Scale up to cool your house.

Bring it on

Posted Thursday 20 Oct 2011 @ 12:15:53 pm from IP #
milljeenath
Member

Great post! I was really looking for this kind of stuff, thanks for sharing a lot.

jacuzzi filters | filters for hot tub | hot tub spa filter

Posted Thursday 10 Nov 2011 @ 4:45:10 am from IP #
jimferguson
Member

Solar heating systems use a solar energy to generate heat and cells to generate power that drives a ventilating system. HRV system is a generic term given to powered systems that recover heat from outgoing air and transfer it to incoming air.

Overland Park heating and cooling | Kansas City heating and cooling

Posted Wednesday 18 Jan 2012 @ 10:07:06 am from IP #

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