Whole House Fan - So far so good.

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As mentioned earlier in this thread I am interested in this because I have a home overseas. Temps range from 80 to 100F. Humidity ranges from 70 to 90%. It is tropical.

Even with air conditioning it gets quite warm on the hotter days. When I built the house I purposely did not add gable or roof vents because the rains can be torrential there and with the wind will find any gap or hole. The soffit eaves are 30 inches. That is where I plan to vent the hot air out via a fan or fans located in the higher part of the attic
 

UncleDave

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As I sit in my beautifully conditioned A/C home the key to your plan is the low humidity. Today it was 94F and 38% humidity during the day but it was 79F and 79% humidity at 9:30 PM. Inside it's 68F and 50% humidity and I'm covered in a blanket watching TV...lol.
For sure its pretty dry here for half the year. Not desert dry, but not far from it.

My parents slay me- they walk around with full pants and light jackets on inside with the Ac blasting in the summer.

My living room is 77 and the wife is got a blanket on her - the large diameter ceiling fan makes the room feel much cooler than that.

I've got a killer AC system as well - lennox variable speed and capacity 21 seer 5 ton with a merv 16 25x20x5 carbon impregnated filter.
At .31c a KWH I do what I can to keep the Ac load down.
 
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UncleDave

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As mentioned earlier in this thread I am interested in this because I have a home overseas. Temps range from 80 to 100F. Humidity ranges from 70 to 90%. It is tropical.

Even with air conditioning it gets quite warm on the hotter days. When I built the house I purposely did not add gable or roof vents because the rains can be torrential there and with the wind will find any gap or hole. The soffit eaves are 30 inches. That is where I plan to vent the hot air out via a fan or fans located in the higher part of the attic

An attic fan will probably help.
The whole house fan isn't going to help in high humidity nights or days.
 
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An attic fan will probably help.
The whole house fan isn't going to help in high humidity nights or days.


I am hoping that as well. The roof is metal so a lot of heat transfer into the attic even though reflective insulation was installed.
 
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In Saskatchewan in the late 1970s/early 1980s they used what was called poor man's air conditioning. Houses had a thermostatically controlled fan in the gable end of the attic or a fan mounted in the roof itself. The fan would come on when the attic got hot and draw cooler air into the attic space through the soffits. I don't know if they still use them and if not, why not.

A doctor who had worked in India said they had a sprinkler on the roof. Evaporation of the water would have a real cooling effect.
I might have to try this. Not so much for my house, but for the swimming pool! Lately, swimming pool water has been getting up to 87 - 88 in the afternoon. I have solar heat panels on the roof, which are turned off before the sun comes up, so no additional heat.

The solar controller has a cooling feature though! If you run the pump at night, and the thermostat is set to a point LOWER than the water temp, water will be directed to the roof panels for cooling. I can lose 2 - 4 degrees on a normal 81 degree night.
BUT, if I put a sprinkler up there (most likely a misting nozzle) evaporative cooling might be a little more effective,
 

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I might have to try this. Not so much for my house, but for the swimming pool! Lately, swimming pool water has been getting up to 87 - 88 in the afternoon. I have solar heat panels on the roof, which are turned off before the sun comes up, so no additional heat.

The solar controller has a cooling feature though! If you run the pump at night, and the thermostat is set to a point LOWER than the water temp, water will be directed to the roof panels for cooling. I can lose 2 - 4 degrees on a normal 81 degree night.
BUT, if I put a sprinkler up there (most likely a misting nozzle) evaporative cooling might be a little more effective,

I have friends in arizona with this problem - most have gone to a heat pump that lets them cool vs. heat the water.

Ive heard of nighttime pumping through panels, never had to do it.
 
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I might have to try this. Not so much for my house, but for the swimming pool! Lately, swimming pool water has been getting up to 87 - 88 in the afternoon. I have solar heat panels on the roof, which are turned off before the sun comes up, so no additional heat.

The solar controller has a cooling feature though! If you run the pump at night, and the thermostat is set to a point LOWER than the water temp, water will be directed to the roof panels for cooling. I can lose 2 - 4 degrees on a normal 81 degree night.
BUT, if I put a sprinkler up there (most likely a misting nozzle) evaporative cooling might be a little more effective,
I don't think you'd need very much water to make this work. But the water would need to stay around long enough to evaporate.

I've always thought the roofs in question in India were absorbent, made out of clay tiles or something like that.

This is like the old "water in a canvas bag" trick. A bit of water seeps through the weave and evaporates. The highest energy molecules, that is the ones that are evaporating, take a greater than average amount of energy with them, leaving the bag with progressively less energy, which we observe as cooling. Anyway a canvas bag of water gradually cools off.
 

JC1

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It does today -it vents to the gable ends outside, but In a month or so I'll have a roof ridge above to vent directly outside.

Im torn on this as it cools the attic space the way it is.
I installed a ridge vent when. I changed my shingles. I didn't do any temp reading/comparisons before/after, but I think it makes a difference to get the hot air out of the attic.

I did use a thermal gun to measure temps under the shingles in my garage and it was 51 celcius (123 f) a month ago.
 

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I installed a ridge vent when. I changed my shingles. I didn't do any temp reading/comparisons before/after, but I think it makes a difference to get the hot air out of the attic.

I did use a thermal gun to measure temps under the shingles in my garage and it was 51 celcius (123 f) a month ago.

I'm putting a new roof on the place in a month and the roofer is going with a full length ridge vent.

Yeah they get brutally hot - and that heat ultimately heat the rest of the place up.
Cool shingles and roof last longer not to mention whatever you may be storing in the attic.
 
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UncleDave

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I am hoping that as well. The roof is metal so a lot of heat transfer into the attic even though reflective insulation was installed.

Place sounds great already....

I never got the straight scoop from a metal roof guy- It seems like the ultimate if done right but awful if done wrong.

I noticed my attic fan runs about 3 hours on a 93 degree day, It turns on at 105 and stops at 80.
 
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4WD

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I don't think you'd need very much water to make this work. But the water would need to stay around long enough to evaporate.

I've always thought the roofs in question in India were absorbent, made out of clay tiles or something like that.

This is like the old "water in a canvas bag" trick. A bit of water seeps through the weave and evaporates. The highest energy molecules, that is the ones that are evaporating, take a greater than average amount of energy with them, leaving the bag with progressively less energy, which we observe as cooling. Anyway a canvas bag of water gradually cools off.
Pretty much like an evaporative cooler (swamp cooler) … broke down and got one for the patio this summer - not as efficient as in dry areas - but makes sitting on the patio much nicer - and I often take a break in front of the cooler …

06618CCC-A17A-4014-B5F9-03ABAB4DFE8C.jpeg
 
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Attics in Texas get miserably hot, and it would seem counterintuitive to put in the HVAC air handler up there, but that's where mine is.

Got a new AC system put in several years ago, and the HVAC guy suggested I get attic fans cut into the roof to relieve the heat soak of the air handler. The roof already has vents, along with soffit vents, so I just bought a big industrial fan and mounted it to suck air up through the attic entrance, which is in the garage, and set the garage door opener to stop 2 inches before fully closed. Haven't measured the temperature difference, but I know that you can go up there now and actually be up there for a few minutes without feeling like you're going to die.
 
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It does today -it vents to the gable ends outside, but In a month or so I'll have a roof ridge above to vent directly outside.

Im torn on this as it cools the attic space the way it is.
I would be torn too, if the attic vents or even some additional vents can handle the air flow it’s a home run cooling down the attic.
With that said if you have a gas or oil heating unit in the attic one must be careful not to force CO into the house.

Also to make sure enough windows are always open in the home if there is a fossil fuel heating unit with exterior vent on one of the lower levels not to draw exhaust fumes into the house.
 
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I never got the straight scoop from a metal roof guy- It seems like the ultimate if done right but awful if done wrong.


I had never dealt with the stuff before. They installed it foil side down towards the rooms which confused me at first. After checking it was determined to be the right way. There has to be a air gap between the roof and the layer insulation as well.

So your attic fan has a temperature sensor? That would be a good idea.
 
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Just tossing in some ideas here. Attic ventilation systems vary by region. When I was studying this stuff a few years ago for our Michigan climate, I learned that sealed, unvented attic space is a system sometimes used in the southern U.S.. Attic fans, if not engineered and installed properly, can upset the existing attic ventilation system. And, if negative pressure is created in the attic, it can suck conditioned air out of the living space.

Research each system to make sure it is being executed properly. It is sometimes not intuitive.
 
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UncleDave

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Just tossing in some ideas here. Attic ventilation systems vary by region. When I was studying this stuff a few years ago for our Michigan climate, I learned that sealed, unvented attic space is a system sometimes used in the southern U.S.. Attic fans, if not engineered and installed properly, can upset the existing attic ventilation system. And, if negative pressure is created in the attic, it can suck conditioned air out of the living space.

Research each system to make sure it is being executed properly. It is sometimes not intuitive.

It sure can cause problems.
I have soffit vents the entire length of the attic.
I walked the length of the attic with the fan running and an incense stick and I dont get any air movement until a few feet away from the fan, much less anything like depressurization so the only thing its sucking air out of are the soffits next to it.

The subject of attic fans stirs quite the debate about this.
 
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UncleDave

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I had never dealt with the stuff before. They installed it foil side down towards the rooms which confused me at first. After checking it was determined to be the right way. There has to be a air gap between the roof and the layer insulation as well.

So your attic fan has a temperature sensor? That would be a good idea.
Yes it has a thermostat inline with power with a 20 degree swing - I set it to come in at 105, and it shuts off at about 85.

This temp happens around 3:30 and it runs till about 6:30.
 
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Whole house fans generally speaking are a bad idea. They waste energy by sending conditioned air into the atmosphere and suck in humid (obviously not applicable in a desert) outdoor air. They also leak conditioned air.
 
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In Saskatchewan in the late 1970s/early 1980s they used what was called poor man's air conditioning. Houses had a thermostatically controlled fan in the gable end of the attic or a fan mounted in the roof itself. The fan would come on when the attic got hot and draw cooler air into the attic space through the soffits. I don't know if they still use them and if not, why not.

A doctor who had worked in India said they had a sprinkler on the roof. Evaporation of the water would have a real cooling effect.
My dad took this even further in Indiana in the 80’s. We were on a well, and he took two hoses, laid them on either side of the peak, and drilled very small holes every 6” or so. He also had them on one of the timer valves, and around 11am they would kick on and stream water down the shingles & generate the evaporative cooling in the attic. The downspouts were all channeled into a drain which led to a small cistern that was there from an earlier owner, which had a small pond pump that would kick on when the cistern got full enough to lift a float, which would then water my mom’s plants & flowers around the house.
 
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Above is a study, Florida-based, of whole house fan cooling.
They were more popular before air conditioning became common.
 
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