Roof space ventilation

[Joe Blake]

After about a dozen consecutive days of 38+ degree max temperatures, my house is starting to wilt. (New Year's day, it's 09:20 am and already 36.8 degrees in the back yard) I've had this view that if I get more than 2 consecutive days of consuming more power than I generate (in summer time) then there needs to be some investigation as something is wrong. Although the last three months have had my solar power producing more than I consumed (138%, 144%, and 118% for December '12) on a daily basis, it's been as low as 49%, which means I'm actually importing power to keep the house cool. (I'm still about $300 in credit on my power bill, so it's not a financial burden, but it still causes me some concern.)

So last week, using a non-contact infrared thermometer, I started taking house temperature readings and found that despite having double glazing on three windows and a door, and having fibreglass batt insulation in the roof space, the spot temperature on the ceiling was as high as 35 degrees C. The temperature underneath the roofing tiles was in places 60+ degrees, so clearly there was close to a furnace in the roof space. There are two "whirlybird" wind driven extractors mounted on the roof which, although they are clearly operating, do not seem to be doing too much to remove this mass of hot air.

A couple of years ago I'd seen some publicity for a solar powered extraction system. Yesterday I thought it was time to check it out, so although it was over 40 degrees I mounted the BMW and rode about 30 km south to the showroom to have a look. Anyway, to cut a long story short, I ordered one and it is (hopefully) going to be installed this Friday.

http://www.avantsolar.com.au/files/Sola ... 202011.pdf
http://i82.photobucket.com/albums/j245/saxeharp/general6/black20cma2030020dpi20print20copy1.jpg

A couple of things which caught my eye ... it only goes into operation if the roof space temperature goes above 23 degrees and claims to be able to shift "up to 730 litres of air per second". If it can move even 80% of that much air, that should make a significant difference.

Obviously I've already committed myself to installing it so I won't be asking for recommendations (or otherwise) but I'd still be interested to hear if people had experience with this system, or indeed other roof ventilating systems, because I feel that we are going to be in for a long hot summer (at least in Perth) and every little bit helps.

Joe

_________________

[Paul Bailey]

Happy new year Joe: After alot of years of following solar venting and looking at other options to keep the attic cool . Most mechanical venting systems are prone to fail eventually as with most moving parts . My father had whirlybird spinning roof vents next door that drove my mother nuts before they finally seized solid and they had peace again.. after considerable research I find all houses in North America attic ventilation undersized by at least 50% . So the temp keeps climbing as the venting is Clearly inadequate or it wouldn't get so hot . If you can keep within 5-8 deg f (4 degC) you know you good. . Mine was NOT good . I found my soffet vents pretty much plugged 75% with chaff and dust and dirt from I believe farmers feilds at certain times of the years.. I cut all the tight mesh screen out of every vent and refitted with Bee Screen on all soffet vents and Gable end Vents . Airflow was really moving now ,,, then I added 50% more venting in all areas and the differance is night and day in temps. I'll see if I can find some pics Paul:cheesy:

[Rob Beckers]

Most of the time it's under 30C in summer here, but we do get the occasional heat spell with 32 - 34C for a period of time. Over here there are two types of roof vents commonly used. Both passive. One is what's commonly referred to as "mushroom vents". They move next to no air, but are dirt cheap, that's why they're the most common thing seen here:

http://seattleareahomeinspector.com/image_store/uploads/7/2/5/3/8/ar124172557183527.JPG

They're nearly useless; besides just not having sufficient aperture to move air, the screen in them clogs to move even less air. As PV installers we love 'm though, because they are low enough so we can run panels right over top of them!

The other type seen here are "maximum vents":

http://www.atticsplus.ca/wp-content/uploads/2012/05/product-photo-model303.jpeg

They actually do move reasonable amounts of air, but again there is a screen in there and I suspect that over time it will clog. As an aside, we don't like 'm for solar PV, since they take up roof real estate and project shadows.

In my opinion, another part of attic venting that's usually overlooked is are the soffit vents. I usually see perforated aluminum soffit being used, and the blown-in attic insulation usually fouls the perforations. No holes in the top of the roof will work in moving air if it can't get in at the bottom. So take a look at your soffit and make sure it can move air into there.

-RoB-

[Jon Phillips]

Good point about the soffit vents, I was thinking about venting my roof space but didn't even cross my mind to look at the soffit. I wonder what our local hardware store (Bunnings) has that would enable a smooth flow of air into and out of the roof space?

[Joe Blake]

All went well yesterday, and the extractor was installed on the western side of the roof. The second whirlybird can be seen just poking its head over the roof ridge on the left.

http://i82.photobucket.com/albums/j245/saxeharp/vent012-1.jpg

http://i82.photobucket.com/albums/j245/saxeharp/vent011.jpg

We've got a predicted max of 37 degrees today (it was down to 17 overnight, so I was able to cool the house somewhat with the cross draft).

I never thought to test (other than the internal ceiling temperature) the "before" of the installation, but yesterday I hit upon an "after" test simply by lighting an incense stick and holding it up next to the open eave in the patio and watching the smoke get drawn into the roof space. I tried it again this morning (08:52 hrs, and already 29 in the back yard) but it was inconclusive as there was a variable breeze and the smoke moved in and out.
The fan has a temperature sensor set to trip at 23 degrees C and I've no certain way of knowing whether it's operating.

The ceiling temperature is about 22 degrees. However, it must be kept in mind that it took several days of 40+ degrees to get the inside temperature of the house to an uncomfortable level.

Watch this (ceiling) space.

Joe

[Joe Blake]

Our forecast is for some much cooler weather in the coming week so I thought I'd take a look and see if I can tease anything out of my preliminary results.

First up, a reminder that the hot spell had been going for about 10 days before I installed the solar vent, so the inside house temperatures were high and staying high, even with cooler intervening periods. The spreadsheet below gives some figures. Don't worry about the columns to the left of "V", except "A", which is the date of each set of readings. "W" is the number of kWh generated by my solar panels daily. Under present circumstances 10 is the maximum I have achieved. "X" is the number of kWh imported from the grid, "AA" is the number of units consumed (regardless of whether they are from the panels or the grid), "AB" is the difference between generation and consumption, and "AC" is the percentage generated (R%) from my rooftop. The figures show that the hot spell commenced on 25 December, 2012, when my R% dropped to 75%, and stayed pretty well negative for about a fornight. (Note that on a couple of days the generation figure dropped to 6 or below kWh, because of cloudiness and on one occasion a fairly substantial fall of rain, although the temperature didn't drop much at all.)

http://i82.photobucket.com/albums/j245/saxeharp/general6/solarventfigures.jpg

4 January the solar vent was installed.

My cooling for the house consists of a small refrigerated air cooler which draws roughly 1100 watts flat out. The solar panels can peak at 1650 watts, so under good conditions I can be cooling the house and still exporting power. The day before the vent was installed, the temperature of the air from the cooler was 28 degrees. The temperature can be set so that the cooler switches to "fan" if the chosen temperature is reached. My "comfortable" temperature is around about 24 degrees. The day the vent was installed (it was done by 9:30 in the morning) the temperature of the air from the cooler was 26 degrees, so whilst the cooler was running flat out as it had been the previous day, it was actually cooling more air, (presumably because the inside of the house was not heating as much because of the solar vent). The same pattern continued until 9 Jan when there was a break in the temperature cycle and the maximum (in the back yard) was 31.5 degrees. From looking at the column "AA" it can be seen that consumption was, for the most part abnormally high, 6 Jan is marked with a red triangle was my laundry day, when I had the washing machine running, and consumed roughly 1 kWh.

Although the figures don't reflect this, I felt more "comfortable" following the install of the solar vent, so I'd have to give it a "thumbs up", it didn't do MUCH but it did enough. I'll be interested to see what happens if and when another heat wave strikes, and the house starts off at a lower temperature. Hopefully the solar vent will slow the rising temperature, delaying the onset of discomfort.

An interesting sideline happened yesterday (9 Jan) when I decided to keep a closer watch on the happenings in my ceiling space, when I purchased a $30 electronic "weather station" with an independent sensor linked wirelessly to the base station. I placed the sensor in the ceiling offset from the solar vent by a metre and a half, sitting on the top of one of the joists. There was about a metre clearance beneath the roof tiles to reduce the effect of radiant heat (the temperature on the underside of the tiles measured 60 degrees in places) and just get the air temperature. The sensor was above the layer of fibreglass batts.

I was able to observe the actions of both the whirlybird extractor and the solar vent, and quite frankly it was a case of chalk and cheese. The whirlybird, while it was certainly rotating freely, was doing about 50-60 rpm, whereas the solar vent fan was moving too quickly for the eye to detect. As mentioned originally, the makers claimed it could move about 730 litres of air per second. From what I saw that figure would be quite a reasonable one, so on that score alone the solar vent does an excellent job compared to a whirlybird.

However, the interesting figure came when I'd got back to the ground level and waited for all the sensors to settle down. The air temperature in the ceiling space was 37.7 degrees, but when I measured the temperature of the ceiling (infrared non-contact thermometer) it showed 28 degrees, almost a full 10 degrees difference, thanks to the insulation of the fibreglass and the plasterboard of the ceiling.

[Rob Beckers]

Joe, have you considered a radiant heat barrier: Basically just a shiny (mylar) film that is supposed to reflect infrared back, instead of letting it pass through towards your ceiling. Those are cheap and easy to install. I've always wondered how well they work, and with your data monitoring skills we could find out!

Glad to hear the heat wave is coming to an end over there! Australia is really having a tough time with the heat and the subsequent forest fires all over the country.

-RoB-

[Joe Blake]

Some time ago I was getting some hot spots on the ceiling where it meets the external wall(s) and I worked out that it was probably being caused by radiant heat from the tiles where they come down to the eaves, and are only a few centimetres above the ceiling, and I thought about putting a radiant heat barrier of some sort on the timbers of the roof frame for the lowest metre or so. However after having a look in the ceiling space I found that there were areas with no fibreglass batt insulation, and when I had that installed correctly the problem was considerably reduced. I suspect that even without the solar vent the return on investment of money and time would be fairly minimal. Past events show that the number of "heat waves" (ie consecutive days with 35+ degrees I think is the official definition) per annum is relatively small.

I'd also read elsewhere that if not installed correctly, items like sarking can cause problems with air flow and maybe even condensation (unlikely in summer, but winters here are reasonably damp).

Sadly as far as the weather here is concerned, it's a case of we get it first in the west then it drifts east, so today the fire fighters over east are preparing for a return of nasty conditions cause by the last couple of hot days in Perth.

Joe

[Paul Bailey]

Hi Joe : I love the vent It looks good on that tile roof. . I found a couple more articles on Powered venting of attics that I had misplaced.

http://www.greenbuildingadvisor.com/blogs/dept/building-science/are-solar-powered-attic-ventilators-green

http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/

of course all attics would respond differantly depending on how its sealed. I see Home Depot in Canada is now selling solar powered attic ventillators.. . I'm sure they will sell as our Summers are getting hotter every year.:oh:

sorry the PDF article was to large to upload......

[Joe Blake]

Paul,

Thanks for those articles. As you say each attic space will react differently depending on its construction. My eaves are completely open so any air that is induced into the ceiling space will come from outside the house. But as long as it (ie external air) is cooler than the air in the roof (and more especially the temperature of the tiles themselves) it'll be a net gain in my view. Even doubly so since the unit is solar powered.

Unfortunately I don't have the advantage of performing a backlog of readings to get a firm baseload to work from, but really the installation was an act of last ditch desperation. Plan B. My plan D, which I've struggled to avoid, is to install a reverse cycle wall mounted cooler which will draw far more power than my PV set up will generate. A very expensive alternative given the small number of days it would be necessary, and the fact that the insulation already installed means that there is no heating necessary in winter.

Plan C, which I'm also trying to avoid, is to move my "office" from the living/dining room into a much smaller bedroom, and use my existing cooler in the way it was intended, a "room" cooler and not try and cool the living room and kitchen with it.

Currently, the meteorology gods (in Western Australia) are smiling and some relatively benign weather has been forecast for the medium term. The house has had a fairly good chance to cool down - currently 22-23 degrees C on the internal brick facing (via night-time cross drafts through windows etc) so if/when another hot spell arrives I'll be able to get a better idea of how well this little beastie works.

Current conditions. Time 09:00 hrs, External air temperature 34.0 degrees; house internal temperature 23.8 degrees; temperature on the underside of the roof tiles 33 degrees on the western (shaded) side of the roof, 37 degrees on the eastern (sunny) side, air temp in the ceiling space 23.6 degrees C (the fan kicks in at 23 degrees C).

Let's see what happens.

Joe

[Joe Blake]

As much for my own information as anything else, yesterday had a maximum of about 30 degrees, and was so pleasant outside I went for a ride on my bicycle. The internal house temperature overnight dropped to 20 degrees C, thanks to a nice cross breeze. Today looks like being the beginning of a spell of forecast hot weather, 38 (Sat), 42 (Sun):eek:, 38, 36 on Tuesday. (These temperatures are for Perth city proper - I can usually add 4-6 degrees at my place). Today (at 14:30 hours) it's 38.0 degrees. Internal house temp 24.5 degrees. Ceiling space temperature 41.8 degrees. The current temperature in Perth is 33 degrees. Forecast maximum was 35.

On edit: Measuring the temperature on the underside of the roof tiles is 68 degrees!!

My aim is to not let the internal house temperature reach a level where I feel "uncomfortable", whilst importing less than 2 kWh of power from the grid daily.

Let the battle commence.

Joe

If the Sunday temperature reaches 42 degrees (47 at my place) my big concern is the grid going down. Luckily it's not a working day so the CBD office blocks with air conditioning and elevators are not operating.

[Ralph Day]

Hi Joe

I think you should probably make a door and rack through the ceiling under the roof tiles. Mix up some batter and slide the cake or muffin tins onto the rack and presto, fresh baking provided by the sun:eek: Sounds like an oven up there anyway.

ralph

[Peter Klaassen]

Hi Joe, I doubt you have seen "Holmes on Homes" down under but it is a home DIY rescue show. An episode showed problems with roof venting and insulation. One thing I see which may be a problem with your new power vent is that it will draw air along the route of least resistance - maybe in from the turbine vent and out from the solar vent. I am not sure how to test this or fix it. Just something to consider after investing in the high tech. Your temperatures are certainly extreme compared to here, although we did wake up to -22 C this morning- an entirely different concern.
Pete

[Joe Blake]

Peter,

Thanks for that observation. Yes, that was a concern given that there were already two whirlybirds installed, one being in fairly close proximity to the solar vent, but I observed that the whirlybirds kept operating normally ie when there was wind they rotated in their normal direction and when there was no wind they stayed still. This indicated to me that if the air WAS being drawn down the 'bird then it was in a very small amount compared to the 700+ litres per second claimed for the solar vent. Further, the 'bird is mounted higher than the solar vent, so for hot air to come down it would have to go against the natural tendency for hot air to rise.

In Perth many of the houses have eaves which are completely open all the way round the house (a possible fire hazard giving access to burning embers from nearby bushfires I would have thought) and the first test I did was to try putting smoke up under the eaves with an incense stick (the latent hippy in me:D) and this indicated that there was a very slight drawing of air into the roof space.

That's certainly a valid point which could be of concern with a particular house design and worth thinking about.

We're well into our second heat wave, with a predicted 41 degrees C for today and 40 tomorrow, (at 9:30 this morning it was 32.6 degrees after an overnight minimum of about 24 degrees) after having a couple of near 40 days just gone. We're due for some cooler weather by Tuesday. I'll be posting further when the heat wave comes to an end, but I think I'm starting to have a good idea on keeping the house cool overall, not just the solar vent.

Watch this roof space.:blink1:

Joe

[Angie Joe]

I also have a solar greeen system in my home but this system is so attaractive and useful .I like it and get some useful points from it . Thanks great job .

[Marvin jordan]

I also have Solar system on my roof put not this much clean and managed.. Nice work man.

[Joe Blake]

It's been just over 12 months since I opened this thread, so it's good to be reminded of it and I can update.

Since Jan 2013 I've added another 1,600 watts of PV plus inverter so I now have a total of 3,200 watts maximum generation. This has been great since with the changing climate there have been more and more hot days, and worse, more sequences of hot days, which can defeat even the best insulation eventually. However, a couple of graphs might give some background on how I am progressing.

The first graph shows how much power I have consumed versus how much I generated versus how much I imported from the grid, from Jun 2009 till current.

http://i82.photobucket.com/albums/j245/saxeharp/convgen1402_zps971f30fe.jpg (http://s82.photobucket.com/user/saxeharp/media/convgen1402_zps971f30fe.jpg.html)

One of my latest toys is an automated weather station which stores and then downloads data (collected at 15 min intervals), which shows the internal temperature of the house versus the external temperature daily. This only goes back to January but you can get an idea of the temperature(s) and how much power is used to keep the house cool.

http://i82.photobucket.com/albums/j245/saxeharp/general10/temp01_zps2d532d8f.jpg (http://s82.photobucket.com/user/saxeharp/media/general10/temp01_zps2d532d8f.jpg.html)

Since my last power bill I have imported power from the grid to the tune of less than $12. (While having $500 credit).

My next door neighbour, with 3,600W of PV has just installed a BlueTooth compatible daily power logger, so he can keep track of how much he is generating, and I can give him my data so we can see how the weather might relate to our power generation.

And as a final interesting note, during the last week or so, when I have been using my 1,200 watt wheel around refrigerated air conditioner, I have been harvesting in the vicinity of 10-15 litres of condensed water per day. As we have had virtually no rain since November, this is pretty important.

http://i82.photobucket.com/albums/j245/saxeharp/rainfall1402_zps659f6493.jpg (http://s82.photobucket.com/user/saxeharp/media/rainfall1402_zps659f6493.jpg.html)

This amount of water is my total drinking, cooking, coffee, etc PLUS at least one toilet flush per day. I have a very nice little water filtering system which gives quite delicious water. And since I suspect that things are going to get worse before they get better (if at all) I've just taken delivery of another rainwater tank, 1,600 litres, in addition to my existing 2,000 litre capacity. The extra water will help to keep my vegetable garden from falling over.

I can't point to any specific figure or graph where I can say the solar powered extractor has made a difference, but despite the climatic changes, I'm still remaining comfortable.
:D
Joe

[Farhan Ahmed]

In our Area Also temperature in summer Average is 34°C and Max is 40-50°C, and it is very hot. thats why most of people on our area are using light colour paint on roof or some reflective paints and chemicals and they are very usefull and reflects most of heat back and inside temperature decreases to normal below 30-32° if outside is above 40°C. I suggest you use any kind of roof but ask to professionals about genuine ways of reducing heat that really reduce a large part of heat.
hope u understand. my grammar is not very well.

[Joe Blake]

Been a while everybody, end of the year looms. Once again the weather gods are delivering 40+ days (4 in a row) and time to put plan "E" into action. After several years of considering, my neighbour and I (we live in a duplex) decided to have our red tile roof painted with reflective paint.

https://blogger.googleusercontent.com/img/a/AVvXsEiN2W783yuH4nuhELT2b9iK7W4LtdA7HbeuS3Y0eHYO71 7rabrs8Sd2B7vzGMWb1QBo_R3SMKE1qDxHPkqWO4ZZF2uC2UZS E1J2xfqaieVRiJIODuGzr6REwDQqaG7ItOJffTufkLEXkPyafU 88HRzWsMMatFZW8hX9rQoT5XxxTx205FU2mPzLvJlrZA=s749

That was at the end of November, before the heat set in. The past few days we've been keeping an eye on things. I don't have solid figures for the temperature in the ceiling space, as the battery in my sensor went dead 12 months ago and I never replaced it until last week.

Whilst the external air temperature has been over 40 degrees, the internal house temp has been at 30 deg, as long as the air con is running. When I switch it off the temp indoors will slowly creep up to about 31-32 deg. On one night I had to leave the air-con running all night, but I was drawing power from the grid to keep the batteries charged. I imported 16 kWh for the day instead of the normal 3, but since the power was coming in during "off-peak" (15.36 cents/ unit as cif 59.12 "on-peak") it only cost a couple of dollars on my bill - which is still in credit.

So in summary, I'd say the reflective paint was a wise investment, given that climate change is here and will get worse as time goes by.

https://lh3.googleusercontent.com/-CCsbY0lOrbI/Ycw67QgcwnI/AAAAAAAAAg8/k78762OR3SIU63xIjh4gRqPhLYz2uiDvQCNcBGAsYHQ/h120/RoofpaintSmall.jpg
I put these two tiles out in the sun facing north and measured their surface temperature - reflective was 49 deg C and red was 61 deg C after several hours of direct sunshine.

(Sorry about the size of the pictures - I didn't realise they were that large until I'd posted them. Will try and change.)

[Rob Beckers]

Interesting Joe!
Simple things just as colour can make quite a difference. Do you have access the attic space? A reflective barrier (glorified bubble-wrap with aluminum foil on one side) would likely help quite a bit too. It doesn't provide much insulation, but reflects the infrared back so it doesn't go towards heating up your attic.

-RoB-

[Joe Blake]

The attic space (it's a rather grand title- I can't stand upright in there) is already insulated with fibreglass batts, which was one of the first things I did - even before I bought the house - I recall that on a day when it was 40 degrees outside, it was almost the same inside. The only way to cool off was to stand in the shower!

According to the spec sheet for the paint that was used, the particular light colour chosen had a Total Solar Reflection factor of 75%, whereas the original colour had TSR of about 26%.

Re the bubble stuff - I fitted my eastern facing window with internal Venetian blinds, but they didn't make much difference with the heat; once the heat was through the window glass it warmed up the blinds because the glass would not transmit the infra-red back out, so warmed up the living room. However, once I fitted an external roller blind to the window it made a big difference.

https://www.blindsonline.com.au/content/product-images/shade-it-black-84-outdoor-window-blind-1.jpg

Although one can get an electric motor fitted, this model is manually operated, like mine. But I only bring it down at the end of spring and put it up again in autumn.

I took the same view with the roof painting - stop the heat getting into the tiles and attic space. When I put the two tiles out in the sun for several hours and measured the underside temperature there was little difference between topside and down side - just between the two tiles.

Luckily the weather people are telling us that we have a week of low 30's coming up, so a chance for things to cool down a bit.

All the best for 2022 everybody.

[Rob Beckers]

Mild weather here too Joe: +2C today! That's pretty toasty this time of year here! No worries though, just around the corner is the more usual -20C coming Monday...

Happy New Year everyone!

-RoB-