Benny - what temp do you think is necessary for comfort in a forced air system? I haven't measured what comes out of my electric fan and am not certain what sort of temp I should have as a target. Does 30 deg feel warm or just not cold when it blows over exposed skin?
Solar Air Heaters - Anyone tried evacuated tubes?
(60 posts) (21 voices)-
Eamon,
Good stuff linking to the thermal mass wall manual, pity about the old imperial units. Interesting reading anyway.Seeing the high performance of the water walls reminds me of the 'Autonomous House' build by Sydney Uni Architecture students in the mid 70s, with a wall of water filled beer bottles between the North facing greenhouse and the living area. My brother (UNSW Arch) took me to have a look, as I was still at school back then.
Posted Wednesday 1 Jul 2009 @ 8:31:54 am from IP # -
Benny
MemberMunter - I think you need to aim for at least 25C for the outlet temp if its going to be blowing directly on you. Anything less than this and it feels cold (to me anyway) even though its warming up the room. I have the thermostat up in the heater set to start the fans running at 28C. I particularly positioned the warm air outlet in my home office right under my desk so I get max effect from it while working - I don't expect it to heat up the entire house.
Posted Thursday 2 Jul 2009 @ 1:13:19 am from IP # -
OK - thanks for the advice. I've come up with a small evacuated tube collector second hand from Victoria and got the chance to look over it on the weekend. Given that it included a frame and all the glass I need I think it may come out at a similar price to my buying the components for a lower tech collector panel.
Yesterday I opened up the top case and had a look at the manifold and heat pipes. I think I'll be able to convert it to heat air while stille keeping open the option of "un-converting" it back to a hot water heater if the experiment fails. The concentration of heat is very impressive - after a period in the sun the top manifold was too hot to touch. Even more impressivee was how hot it stayed after the sun went down. I put the panel back in the garage in the dark and later in the evening the manifold (with no insulation around it) was still hot.
Anyway - I rigged up a temporary duct made from cardboard and blew air through it with an electric fan and while the airflow rate was low, I did get a temperature increase of around 10 degrees. This seems a bit low and I'm sure I'll get a lot more with a less temporary (read: bodgy) arrangement for the duct. I think the manifold surface area is low to minimise heat loss but in my application I want it high, to maximise heat transfer to the air. My next few weekends will be busy!Posted Monday 6 Jul 2009 @ 2:57:21 am from IP # -
Benny
MemberGood luck with the project Munter - post some photos for us (-;
One hint re efficient heat transfer from hot surface to the air - you want to deliberately make the airflow turbulent. Not so much obviously that you restrict the airflow, but a turbulent flow increases the heat transfer to the air tremendously. Try putting small air deflectors on the surface of whatever is hot, so that the air is disturbed as it flows across it.
Posted Monday 6 Jul 2009 @ 4:00:44 am from IP # -
Eskimoau
MemberI know you prefer not to use water as a heat transfer medium but this seems like a good compromise http://www.everbreeze.com.au/LifeBreath.htm
You could connect the air system to your evacuated tube HWS and effective have solar heating.
Posted Wednesday 8 Jul 2009 @ 11:25:24 pm from IP # -
Bushpilot
MemberI dont know if this forum provides for images uploads; if it doesn't you have a couple of options:
1. Put them up on your facebook or any other webpage that allows open access, then post the URL on this thread, or
2. Email me the images (to my private email) and I will put them up and post the URL here.. Let me know if you want my email address.Posted Sunday 19 Jul 2009 @ 12:21:01 pm from IP # -
jg
MemberHi Munter,
How did you get on with your solar ventilation system?
If you want to drop me an email perhaps we can have a discussion about what you are trying to achieve. There are many other less expensive mediums you can use to collect solar heat. Oh, something else to consider is sizing the system to achieve a satisfactory outcome.
Did you know when disigning a on demand heating system you need upto 6 air changes an hour. A well designed system along the path you are considering would at best possibly increase the core temperature of a building by 3 degrees celsius and feel drafty while doing this. It may be possible to achieve more but there is a lot to consider.
I think several long phone discussions may be warranted if you would like to get a detailed understanding of the concepts for solar warm air ventilation.Posted Tuesday 13 Aug 2013 @ 11:45:30 am from IP # -
TonyT
MemberBenny
At
http://www.ata.org.au/forums/topic/147#post-688
you asked
"Has anyone done the basic calculations on how much heating you could get ? e.e. 2msq collector, at say 50% efficiency, collects a max of about 1kW, but only maybe 4-5kwh per day - how much air could that heat from say 10 - 25degC ? ( I realise it has to heat up the house + contents as well)."
To bring a room up to temperature the Rule of Thumb is heat input of 100W/sqm.
In the Adelaide Hills, for a room with a low energy rating (2 stars), the daily heat input needed to maintain temperature is about 0.9kWh/day per sqm of floor area (40W/sqm).
With better insulation (6 stars) the heat input drops to 0.3kWh/day per sqm (13W/sqm).
Estimates for the kWh of solar heat energy that can be captured are at
http://www.ata.org.au/forums/topic/9614#post-44635
and in earlier posts in that thread.Posted Wednesday 14 Aug 2013 @ 8:50:20 pm from IP # -
Chip
MemberWe have a home made 3 sq m solar air heater on roof with a duct through roof space discharging air through ceiling vent into room below. Currently 10am, sunny, outside temp 9 degrees, inside 16 and air coming into room is 30 degrees and will be near 40 at midday. Releasing air through a wide vent in ceiling above a doorway minimises any drafts. The warm air layer gradually moves down lower during the day. It is a non return system and our main leakages would be near floor level so our coldest air is being driven out. Cheap, simple, gentle, effective.
We are about to build a new house and will have a 30 sq m solar air heater for the southern side of the house. Contemplating using excess capacity to provide some under slab heating - a bank for the next cloudy day. Thinking of a grid of 40mm pvc pipes fed from/to 100mm manifolds all in the 150mm sand bed that is under the stiffened raft slab. Would put the underslab insulation under the sand bed. Any ideas on how this might work?
Posted Thursday 15 Aug 2013 @ 12:46:22 am from IP # -
Benny
MemberThanks TonyT but did you look at the date on those posts ? 2009. I've learned a lot (some from you thanks) since then. Watch out for these resurrected threads.
Chip - you heater sounds interesting - what sort of collector did you use ? Shadecloth in box or black flat plate ? Any blog showing pictures ? Thought of doing an article for ATA Renew ?Posted Friday 16 Aug 2013 @ 3:01:01 am from IP # -
Chip
MemberBenny - our small collector is flat black plate using stuff I had on hand as follows starting from bottom: a 4m sheet of roofing sheet (cliplock or trimdek) ribs down, then a layer of anticon insulation foil side up then a layer of chicken wire (to hold anticon down and increase turbulence) then a flat black painted sheet of same roofing, ribs down. I pop riveted a few offcuts of aluminium under the trays of the top sheet for added conductivity and turbulence. Then tied it on to the roof and attached 90mm pvc outlet for each tray, feeding into 100mm with inline fan bringing it down through roof and ceiling. Air is drawn in the opposite end of each tray. It probably brings in about 2 m3 per minute. If it was a return air system I'd go for a bigger fan since the total energy harvested is greater if volume is set to decrease temp of incoming air and therefore increase differential between collector surface and its internal air. It is only on a manual switch so it has a cooling effect if we forget to switch it off in time! All good experience for a better future model. I like the idea of using air as the solar energy transfer medium as my guess is that the upfront system costs and complexity are less per Kw of energy brought into the house plus air is easier to tame. Cheers
Posted Friday 16 Aug 2013 @ 10:02:26 am from IP # -
I have spent the last couple of months building some air heaters - first a couple of test models and finally the MK 3 version: it's 4.8m long x 1m high and is a simple timber frame box, plywood back, insulated foamboard back wall, and three layers of black aluminium fly screen laid inside. It's well sealed, glazed with twin wall polycarbonate and I used metal angles to seal the edges.
I have a couple of medium sized inline ducting fans and on a 60-70 degree tilt facing north I get a peak of 60-65 degree air coming out around noon, and above 35 degrees from 9am-3pm. It's amazing the heat it generates just from the fresh air running over the fly screen
My issue is getting the heat into the house - the heater is fairly heavy and we dont have any easy places to mount it on the roof or a vertical wall....or at least none that are proximal to the rooms we want to heat - which is a big issue with air heaters vs hydronic heating. You can move water much easier than air.
I like the sound of your build Chip - the metal backing would be much lighter.
Posted Monday 19 Aug 2013 @ 12:18:16 pm from IP # -
Johnnojack
MemberChip I take it your collector has no glazing? If that is right it would be great if you could duct tape some plastic wrap over it and check temperatures again for a few days to see if it is worth glazing properly with something. I think I once read about an air heater which was unglazed but drew air in thru many small holes in the black painted collector. Because the heat was immediately being taken away from the collector plate it was quite efficient and didn't suffer the losses of a normal unglazed collector. anyone know more on this one?
Good work Darryn, will the Mk 4 version fit on your roof?Posted Monday 19 Aug 2013 @ 1:27:21 pm from IP # -
Chip
MemberJohnnojack - no we have no glazing. This collector was originally used for drying food by forcing warm dry air down through an old fridge full of food so efficiency wasn't paramount. Our transfer fan is too small to allow accurate measurement of the difference a sheet of plastic might make. For a future model I'm drawn towards making a bigger version of a simple design rather than introducing complexity for marginal improvement. It gets pretty dusty here in summer so glazing would need to be carefully installed to remain effective. Is condensation between the glazing and the plate a potential problem? Out of curiousity I might get a sheet of black corro and cover a quarter in flat perspex, a quarter in glass, a quarter in corro polycarbonate and leave quarter as control then see which feels hottest underneath.
Posted Monday 19 Aug 2013 @ 10:53:18 pm from IP # -
garyt
MemberI haven't read every post but i think oil would be better it keeps heat much longer than water or air you could use some system like a car radiators with fans and ducting to blow hot air into rooms and as oil can get very hot venting may not be a issue and it will be a closed loop system and such a large amount of oil would keep it's heat much longer than water or air anyway. You would want to use the warm air from the house then to blow back through the system to loose as little heat as you can from the oil once the sun was gone.
Just a thought.Posted Monday 6 Jan 2014 @ 1:32:29 am from IP # -
darrynm said:
I have spent the last couple of months building some air heaters - first a couple of test models and finally the MK 3 version: it's 4.8m long x 1m high and is a simple timber frame box, plywood back, insulated foamboard back wall, and three layers of black aluminium fly screen laid inside. It's well sealed, glazed with twin wall polycarbonate and I used metal angles to seal the edges.I have a couple of medium sized inline ducting fans and on a 60-70 degree tilt facing north I get a peak of 60-65 degree air coming out around noon, and above 35 degrees from 9am-3pm. It's amazing the heat it generates just from the fresh air running over the fly screen
My issue is getting the heat into the house - the heater is fairly heavy and we dont have any easy places to mount it on the roof or a vertical wall....or at least none that are proximal to the rooms we want to heat - which is a big issue with air heaters vs hydronic heating. You can move water much easier than air.
I like the sound of your build Chip - the metal backing would be much lighter.
Great work you have put into this project Darrnym. It also looks as the returns/efficiency are what a good four bed house would require. In the MK3 version, could you estimate how much time you spent to build it and what what your material costs were. I know the polycarb and aluminium mesh does not come cheap. I am trying to asses overall build cost as against overall purchase cost in respect of return. This does not include the pleasure of the build or intrigue in designing the project. Thanks, eamon.
Posted Friday 14 Feb 2014 @ 11:06:40 pm from IP # -
I had been thinking of a way to heat my large pole barn with a solar air heater. I have two small ones already, but they only raise the large room a few degrees. There is a product on the market that I am thinking of using for the front, to let a lot of light through, yet insulate the heat within. I am thinking of building a 4' x 8' box of treated wood, perhaps 8" deep. Inside will br three layers of black aluminum screen. I heard that worked well to absorb heat. I will not use plexiglass as I did for the front of the others, but polycarbonate twinwall. ( https://www.interstateplastics.com/Polycarbonate-Twinwall-Clear-Sheet-POLCE~~SW.php?&kitoptionpk=197&src=adwordspla&utm_source=adwordsfroogle&utm_campaign=adwordsfroogle&utm_medium=na&utm_content=plastic+sheets-POLCE++SW&keyword=GOOGLEPLA-sheets-POLCESW-kits197&gclid=CJ-zseeNsdICFZG6wAodphcFSQ ) Instead of having the back of the inner part of the box painted black, I think it would be best to cover it with reflective mylar as used on survival blankets.
The air inlet and outlet would be what I used on my other heaters, for 6" pipe. Since this project is much more expensive than most I have seen, I would like a few opinions about it and whether or not the polycarbonate twinwall would be a good idea. Plexiglass on my others sags at about 180 degrees f. Polycarbonate would not. Appreciate any comments anyone may have.Posted Saturday 18 Mar 2017 @ 1:40:53 am from IP # -
Johnnojack
MemberAluminium fly mesh is expensive, why not use 2 layers of black shade cloth? Also i would price glass against the twin wall polycarbonate as I know that is exxy as well. Glass will work better.
Chip had plans, hopefully he will chip in herePosted Saturday 18 Mar 2017 @ 11:23:50 am from IP # -
I've made one with metal fly screen - the plastic stuff or shade cloth I'd keep away from because of potential off gassing from the plastic breaking down in the heat.
I used twin wall polycarb - great product and nice to work with being flat vs corrugated polycarb.
I used Foilboard as the backing for insulation and painted it black.
Some photos here: http://www.mckayphotography.com.au/photos/solar-mk3/ and here: http://www.mckayphotography.com.au/photos/solar3/
Posted Tuesday 4 Apr 2017 @ 9:47:34 am from IP # -
scott drew
MemberHi Darrynm,
They look nice, the pics. Couple of questions, do you have an air inlet diagonally opposite the outlet? Does your inlet grab air from inside the house or external to the house? What do you do with this in summer? What temps does it reach in summer?
SD.
Posted Tuesday 4 Apr 2017 @ 1:20:56 pm from IP # -
Yes I have an air intake bottom right side of the heater - then it exits top left side. It draws from the outside air but using air from the house would be much better and is on my list of things to do!
In summer I cover half of it with a sheet of corrugated iron and this stops the fan kicking in / stops it heating up. If not for the cover it would be getting up to 60-80 degrees which can't be good for the polycarb and other parts.
Posted Tuesday 4 Apr 2017 @ 2:53:21 pm from IP # -
HowardH
Membersorry to bump an old thread but have anyone found a decent commercially brought solar air heater?
I'm thinking of buying one to heat my lounge room which is around 70m2
will something like this mounted on the wall work better than the roof mounted ones which push hot air from the ceiling?
https://reductionrevolution.com.au/products/solar-air-heater
Posted Tuesday 29 Aug 2017 @ 5:49:21 am from IP # -
Wall mounted would be ideal - it captures more heat in winter & (usually) means a shorter or zero ducting run (long runs reduce efficiency).
Here's a NSW based company: http://solrheating.com.au/
Posted Tuesday 29 Aug 2017 @ 6:16:30 am from IP # -
I had a look at the one you linked to - I reckon it's much too small for a 70sqm lounge so you may not get a lot from it. Have you seen the http://www.builditsolar.com/ site? Lots of real life projects on there so you'd be able to get an idea on sizing.
Posted Tuesday 29 Aug 2017 @ 6:21:02 am from IP # -
HowardH
MemberHey Darryn,
I will check out that site, theres so many articles in there!
Not sure if most of the projects can be incoporated into my build since i do not have any north facing windows, atm the only way i could think of is using some sort of heater with solar panels attached to the roof.
Posted Tuesday 29 Aug 2017 @ 8:37:29 am from IP # -
Benny
MemberCan I ask HowardH what your reason for considering this is ? I think these solar air heaters are great and made one myself years ago but only because I made it - buying they seem to be very expensive. Do you care about how much heat they produce and at what cost or are you just wanting to do it as an environmental initiative and don't care about cost ?
Posted Tuesday 29 Aug 2017 @ 8:44:25 am from IP #
