What's the verdict on attic fans?

[aerohead]

Originally Posted by cRiPpLe_rOoStEr

As construction methods in my country often differ a lot compared to what is done in the USA, Tyvek and similar materials are more often placed below the roof tiles, and it's still not much common. But anyway, besides preventing the moisture from being trapped inside, another matter of concern for me would be the air renewal, exhausting CO² too.

In the USA, all industrial / institutional / commercial buildings are designed to to provide around 10% outside 'makeup' air for all forced-air systems.
Rooftop units have an outside-air damper, which can be adjusted during air-balancing, which helps guard against 'sick building syndrome.'
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For residential applications, MITSUBISHI offers a fine, air-to-air heat-exchanger, which thermally marries incoming outdoor fresh air, with out-going exhaust air, which works year round, to guarantee air-exchanges.
Electrostatic precipitators and HEPA filters are typically installed inline to provide top quality airflow.
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If one lives in a region known for haboob, or dirt storms, like Phoenix, Arizona, or Lubbock, Texas, the outside inlet can be closed off, and the entire house brought to a higher static pressure than the wind force, to prevent unwanted infiltration of the particulates.

[aerohead]

The reasoning according to ASHRAE is that, if you don't have living space on the inside of the 'roof', or AC equipment and ducting in the attic space, you're throwing money away.
Thermal insulation works on the difference in outdoor and indoor dry-bulb temperature. It doesn't experience' infrared. However, check your temp where the roof pitch is near the attic insulation. If it roof infrared is 'baking' the top of the insulation, it's going to raise the air temp on top of the fiberglass batting or blown-in fibers, cellulose, etc..
If exterior walls are exposed to solar incidence, 'Tech-Shield', or something like it ( OSB with foil facing ) could help.
The best thing is just to keep the sun off exterior surfaces ( load avoidance ).
Trees and landscaping can do that. Solar fabrics and awnings.

[freebeard]

The best thing is just to keep the sun off exterior surfaces ( load avoidance ).
Trees and landscaping can do that. Solar fabrics and awnings.

If one lives in a region known for haboob, or dirt storms, like Phoenix, Arizona, or Lubbock, Texas, the outside inlet can be closed off, and the entire house brought to a higher static pressure than the wind force, to prevent unwanted infiltration of the particulates.

Here in Antifa-fueled-wildfire country, I have a whole-house fan like this one:


https://www.herstylecode.com/wp-cont...Attic-Fans.jpg

It blows directly into a MERV-[8? 11?] 14" square filter in a ceiling vent. Noisy though.

[cRiPpLe_rOoStEr]

Originally Posted by aerohead

In the USA, all industrial / institutional / commercial buildings are designed to to provide around 10% outside 'makeup' air for all forced-air systems.
Rooftop units have an outside-air damper, which can be adjusted during air-balancing, which helps guard against 'sick building syndrome.'

I'm not sure about the regulations here in Brazil, but temperature control seems to be treated as more important than a renewal of the air flow.

For residential applications, MITSUBISHI offers a fine, air-to-air heat-exchanger, which thermally marries incoming outdoor fresh air, with out-going exhaust air, which works year round, to guarantee air-exchanges.
Electrostatic precipitators and HEPA filters are typically installed inline to provide top quality airflow.

I don't see anything similar for residential applications in Brazil.

If one lives in a region known for haboob, or dirt storms, like Phoenix, Arizona, or Lubbock, Texas, the outside inlet can be closed off, and the entire house brought to a higher static pressure than the wind force, to prevent unwanted infiltration of the particulates.

Not sure about dirt storms being common anywhere in Brazil, even though in some regions an excessive amount of particulate matter coming from burnt bushes or burning sugarcane fields prior to the harvesting is a serious issue. What I don't understand is, as there are swamp-coolers and air conditioners meant to be used on agricultural machinery fitted with filters to clean the incoming air from the outside to the inside, the residential swamp-coolers that I often see and similar devices meant for commercial and institutional uses don't have this same feature.

[hayden55]

Originally Posted by cRiPpLe_rOoStEr

I'm not sure about the regulations here in Brazil, but temperature control seems to be treated as more important than a renewal of the air flow.




I don't see anything similar for residential applications in Brazil.




Not sure about dirt storms being common anywhere in Brazil, even though in some regions an excessive amount of particulate matter coming from burnt bushes or burning sugarcane fields prior to the harvesting is a serious issue. What I don't understand is, as there are swamp-coolers and air conditioners meant to be used on agricultural machinery fitted with filters to clean the incoming air from the outside to the inside, the residential swamp-coolers that I often see and similar devices meant for commercial and institutional uses don't have this same feature.

Yeah for the most part the builder just knows he isn't building a tight house so he doesn't worry about it. A friend in a 1985 home in good shape just got a blower door test done. Efficiency wise he isn't far off what i was besides lack of insulation. But ACH50 he got a 7.9 ACH (air changes per hour). Rough conversion at like around 4 pascals which is closer to normal air changes thats around a 0.5 ACH. So half of the air in the room gets replaced per hour. I think minimum is 5ach50 which is around 1/3 of the room air exchange per hour and if you go below it you need to add an actual ventilation system per whatever code your area has.

Rooster you can look up "ERV" Energy recovery ventilation. I hear they exchange air with around a 90% efficient energy transfer now on some of them. I doubt the roi is good enough to retrofit but a purpose built house would be neat

[redpoint5]

Seems to me things shouldn't be built so sloppily we can assume way more than sufficient air exchange. A good system would measure the things that build up or become deficient in the air and set thresholds triggering air exchange.

I'm not sure what the biggest health concerns are with lack of exchange. Moisture buildup? Radon accumulation? I doubt it's CO2 buildup due to the sheer volume of air in houses.

[freebeard]

Black mold.

[Piotrsko]

Too much water vapor/humidity rise. Places like Pheonix or Bakersfield it makes the building intolerable even with cooling.

[hayden55]

Originally Posted by Piotrsko

Too much water vapor/humidity rise. Places like Pheonix or Bakersfield it makes the building intolerable even with cooling.

Especially in the summer. Most of us have oversized units that don't run for long enough to remove humidity in the air so they end up very humid inside.
My current house I have calculated can keep my house cooled to 75 from ~135 degrees and warmed to 70 degrees from -41 degrees. Needless to say i didn't freeze in the -5 the other day as the furnace only ran for 9 hours. lol
But yeah typically the newbies down here trying to do spray foamed sealed houses end up delivering extremely efficient but humid and moldy houses.

[redpoint5]

Originally Posted by hayden55

Especially in the summer. Most of us have oversized units that don't run for long enough to remove humidity in the air so they end up very humid inside.
My current house I have calculated can keep my house cooled to 75 from ~135 degrees and warmed to 70 degrees from -41 degrees. Needless to say i didn't freeze in the -5 the other day as the furnace only ran for 9 hours. lol
But yeah typically the newbies down here trying to do spray foamed sealed houses end up delivering extremely efficient but humid and moldy houses.

My 5-ton AC is a 10SEER (I think), probably whatever the legal minimum requirement was in 2003. It runs continuously in the summer from 3pm-7pm on a 100 degree day and can barely move the temperature down from my 78 degree setpoint. That particular day consumed 54 kWh. That's like $7!

Total AC consumption for 2022 was 987 kWh for $126.

I'll have to do some calculations as you've suggested to see if my experience matches the calcs. Could indicate problems if not.