Fans in an enclosure, trying to understand the physics

[SinLA]

This may be a @Tom specific question, but I'm trying to wrap my head around how a fan works (or doesn't) with tortoises.

You have a night box or a hide or whatever, and its internal temperature is, say, 100 degrees.
You put a fan in the box, it "feels" cooler to mammals because of our skin sweats and the air passing over it makes us sweat and cool down, but a reptile will still feel 100 degrees, with no change from the fan on it. (I know some reptiles like the "feel" of air blowing from fans, but that's not this question)

An exhaust fan can, IN NO WAY can reduce the temperature inside (regardless of which direction it blows) and likely will just pull hotter air from outside in, making it actually hotter inside than it was before.

The only way to cool the inside is to force that is cooled by a mechanism (air conditioner, ice bags whatever), withing the box (or pushing into the box) itself.

Do I have the right? Absolutely no benefit to a fan whatsoever?

 

[Tim Carlisle]

I won't pretend to speak for Tom, but I disagree 100% with your assertion. I have 2 inline fans set up on the ceiling of my house; both connected to a thermostat. When the temp kicks past 90F, the exhaust fan kicks on. In the winter, a second inline fan circulates the warm air inside the house. If it weren't for the exhaust fan, the inside temps would reach >100F. With the fan, the highest I've ever recorded the temp was 91.3F. In the winter, the second fan circulates the air from ceiling to floor and maintains a constant 80F even when outside temps fall below 0F.

 

[SinLA]

I won't pretend to speak for Tom, but I disagree 100% with your assertion. I have 2 inline fans set up on the ceiling of my house; both connected to a thermostat. When the temp kicks past 90F, the exhaust fan kicks on. In the winter, a second inline fan circulates the warm air inside the house. If it weren't for the exhaust fan, the inside temps would reach >100F. With the fan, the highest I've ever recorded the temp was 91.3F. In the winter, the second fan circulates the air from ceiling to floor and maintains a constant 80F even when outside temps fall below 0F.

Ok in the winter, it is pushing hot air inside to out, and keeps it cooler. In the summer, how does it work for you?

 

[Tim Carlisle]

Ok in the winter, it is pushing hot air inside to out, and keeps it cooler. In the summer, how does it work for you?

I was mostly talking about summer. When the temp goes past 90, the fan kicks on and expels the hot air outside. I have a vent on the opposite wall that pulls cooler air inside while the fan is running. Today the temps outside were around 95F. His house was 89F inside.

 

[SinLA]

where is it getting the cooler air "from" though? the cooler air being pumped inside?

 

[Tim Carlisle]

Hopefully these pics will explain a little better. This is the air intake vent that draws cooler air from the outside to the inside:



This is the exhaust vent that blows hot air from the inside out:



This is the inline fan mounted to the ceiling that moves the air:




This is the thermostat I have it connected to:



And this is a pic of Ghost for added attention lol:

 

[Markw84]

I have a small muffin fan running in my night boxed 24/7. I do not have fans in any of my enclosures. So not sure what you are referring to in your question.

The reason for the fan in the night box is simply get an even distribution of heat and not let the ceiling temp get 10°+ warmer than the floor temp. With a well insulated, closed night box you would get a pretty good heat gradient top to bottom without a fan. By mixing the air I even out the temperatures and ensure the bottom corners are much the same temperatures as the ceiling. I also have my heaters mounted on a shelf towards the top of the box, so the fan is even more effective at mixing the air in the box to get the floor pretty close to the ceiling temperature.

I feel a night box is best kept with as uniform a temperature as possible throughout.

 

[wellington]

And I use a regular ceiling fan, like you might have mounted in your house, in my heated, insulated tortoise shed. In winter it pushes rising heat back down to tortoise level. I don't use it in summer, because the tortoises are in a different part of the shed for summer.
For my chickens shed, I have a solar fan that runs all day. It brings in air from the outside, into the shed and moves the air around and cools it slightly from what it would be if there was no fan moving the air.
Just moving air around, even if it's hot air, will help to make it feel a little cooler. But instead sheds, enclosures etc, where it heats up and is stagnant, a fan will help cool it some.

 

[jaizei]

This may be a @Tom specific question, but I'm trying to wrap my head around how a fan works (or doesn't) with tortoises.

You have a night box or a hide or whatever, and its internal temperature is, say, 100 degrees.
You put a fan in the box, it "feels" cooler to mammals because of our skin sweats and the air passing over it makes us sweat and cool down, but a reptile will still feel 100 degrees, with no change from the fan on it. (I know some reptiles like the "feel" of air blowing from fans, but that's not this question)

An exhaust fan can, IN NO WAY can reduce the temperature inside (regardless of which direction it blows) and likely will just pull hotter air from outside in, making it actually hotter inside than it was before.

The only way to cool the inside is to force that is cooled by a mechanism (air conditioner, ice bags whatever), withing the box (or pushing into the box) itself.

Do I have the right? Absolutely no benefit to a fan whatsoever?

A well insulated night box with a lower ceiling might not benefit much from an exhaust fan, especially ifs its not in direct sun, but if its more like a shed, has a higher ceiling/roof, or is less well insulated then an exhaust fan can help immensely with cooling. Spend an hour in a 140* attic and you'll cherish the 100* 'cool' air outside.

 

[wellington]

I do think it's funny that you thought this was a Tom thing. He has small night boxes that aren't very tall and probably doesn't use fans. Although, in the hottest of summer would help those boxes if they did get too hot.

 

[SinLA]

I do think it's funny that you thought this was a Tom thing. He has small night boxes that aren't very tall and probably doesn't use fans. Although, in the hottest of summer would help those boxes if they did get too hot.

more about things he said about fans not working with reptiles because moving air doesn’t cool them the way it does mammals and birds. The examples above that talk about the air being cooler I’m trying to figure out if that’s because mammals are “feeling“ cooler from the moving air, or because the temperature is actually cooler from the cooling mechanism of the fans , which would in turn cool the reptiles…

 

[wellington]

more about things he said about fans not working with reptiles because moving air doesn’t cool them the way it does mammals and birds. The examples above that talk about the air being cooler I’m trying to figure out if that’s because mammals are “feeling“ cooler from the moving air, or because the temperature is actually cooler from the cooling mechanism of the fans , which would in turn cool the reptiles…

I either didn't see that or don't remember.
I do remember, people saying, not on here, that a fan really doesn't cool you down. Not real sure that's a fact. I use fans all the time for my tortoises, chickens and oh yeah me. They sure feel like everything and me are getting cool. Even when the air outside is very warm, where the fan is blowing that warm at at ya, it still feels cooler.
Not sure if the tortoises feel the difference, but I know there is a difference. If you temp it, it will show the difference and so I do believe the tortoises feel it even if it's not that much.

 

[Tom]

This may be a @Tom specific question, but I'm trying to wrap my head around how a fan works (or doesn't) with tortoises.

You have a night box or a hide or whatever, and its internal temperature is, say, 100 degrees.
You put a fan in the box, it "feels" cooler to mammals because of our skin sweats and the air passing over it makes us sweat and cool down, but a reptile will still feel 100 degrees, with no change from the fan on it. (I know some reptiles like the "feel" of air blowing from fans, but that's not this question)

An exhaust fan can, IN NO WAY can reduce the temperature inside (regardless of which direction it blows) and likely will just pull hotter air from outside in, making it actually hotter inside than it was before.

The only way to cool the inside is to force that is cooled by a mechanism (air conditioner, ice bags whatever), withing the box (or pushing into the box) itself.

Do I have the right? Absolutely no benefit to a fan whatsoever?

Yes. You have all of this correct. Its just physics.

Fans work on us through evaporative cooling. No evaporation = no cooling effect. Reptiles don't lose water through their skin, and they don't pant like a dog, so no evaporative cooling for them. If the tortoise is 90 degrees sitting in a 90 degree room filled with 90 degree air and you turn a fan on to the tortoise, it will not cool. It will just have moving 90 degree air around it instead of still 90 degree air. If you place the fan near a window with cooler air outside, then it will blow cooler air on the tortoise. If the air inside of your tortoise house is cooler than the air outside the tortoise house, and you place the fan near the door, you will indeed suck hotter air into the box and warm the interior or the box some more.

The only way an exhaust fan can work to cool a box is if the air being pulled into the box is cooler than the air outside the box. In my case during summer, the air outside is usually 100+ during the heat of the day, while the inside of my boxes remains in the high 80s, occasionally climbing into the low 90s when we have those 110 degree spells for a week at a time in summer. If I were to pull outside air into my box, the temp inside the box would soon be the same as the temp outside the box.

If a tall shed is getting heated by the sun with a "greenhouse" effect and the inside temp becomes hotter than the outside air temp, then an exhaust fan would indeed cool the shed back down to whatever the outside temp is. It would be pulling in air that is cooler than what is already in the shed. But if the shed is 90 degrees inside, and you turn on an exhaust fan that is pulling 100 degree air into the box, it will warm the box up to 100 degrees. If the shed is 90 degrees inside, and you turn the exhaust fan on after dark when the outside air is cooler, it will cool the shed.

My boxes are very well insulated and sealed. Insulation resists temperature change. It keeps warmth in in winter, and it keeps heat out in summer. My boxes tend to stay the average between the day time high and night time low. So if its 100 during the day and 60 at night, my boxes stay right around 80. if the outside temp is 110 during the day and 70 at night, then the boxes will get up to around 90. They don't cool too much at night or warm up too much during the day. My swimming pool does the same thing. Cooking in full sun all day is off set by evaporation at the surface. My pool stays right in the middle of the day time high and the night time low.

I do use small computer fans in some of my boxes to distribute the heat evenly, exactly as @Markw84 explained. If I recall correctly, I got the idea from him in the first place. These fans are not cooling anything. They are just moving the warm air around the box so that I don't get hot spots near the heater, or cold spots near the door or areas farthest from the heater.

 

[SinLA]

Yes. You have all of this correct. Its just physics.

Fans work on us through evaporative cooling. No evaporation = no cooling effect. Reptiles don't lose water through their skin, and they don't pant like a dog, so no evaporative cooling for them. If the tortoise is 90 degrees sitting in a 90 degree room filled with 90 degree air and you turn a fan on to the tortoise, it will not cool. It will just have moving 90 degree air around it instead of still 90 degree air. If you place the fan near a window with cooler air outside, then it will blow cooler air on the tortoise. If the air inside of your tortoise house is cooler than the air outside the tortoise house, and you place the fan near the door, you will indeed suck hotter air into the box and warm the interior or the box some more.

The only way an exhaust fan can work to cool a box is if the air being pulled into the box is cooler than the air outside the box. In my case during summer, the air outside is usually 100+ during the heat of the day, while the inside of my boxes remains in the high 80s, occasionally climbing into the low 90s when we have those 110 degree spells for a week at a time in summer. If I were to pull outside air into my box, the temp inside the box would soon be the same as the temp outside the box.

If a tall shed is getting heated by the sun with a "greenhouse" effect and the inside temp becomes hotter than the outside air temp, then an exhaust fan would indeed cool the shed back down to whatever the outside temp is. It would be pulling in air that is cooler than what is already in the shed. But if the shed is 90 degrees inside, and you turn on an exhaust fan that is pulling 100 degree air into the box, it will warm the box up to 100 degrees. If the shed is 90 degrees inside, and you turn the exhaust fan on after dark when the outside air is cooler, it will cool the shed.

My boxes are very well insulated and sealed. Insulation resists temperature change. It keeps warmth in in winter, and it keeps heat out in summer. My boxes tend to stay the average between the day time high and night time low. So if its 100 during the day and 60 at night, my boxes stay right around 80. if the outside temp is 110 during the day and 70 at night, then the boxes will get up to around 90. They don't cool too much at night or warm up too much during the day. My swimming pool does the same thing. Cooking in full sun all day is off set by evaporation at the surface. My pool stays right in the middle of the day time high and the night time low.

I do use small computer fans in some of my boxes to distribute the heat evenly, exactly as @Markw84 explained. If I recall correctly, I got the idea from him in the first place. These fans are not cooling anything. They are just moving the warm air around the box so that I don't get hot spots near the heater, or cold spots near the door or areas farthest from the heater.

ok @Tom, so looking at the @Tim Carlisle setup above, and assuming it’s hot outside, it only works to cool the shed down because the top of the shed is going to have stored/contained heat that is *hotter than* the outside air (greenhouse effect/heat rising/being in the sun/etc) so even the hot air from outside coming in will be cooler than the contained heat inside… if the shed did not have inside air hotter than the outside air then running the exhaust would not make it cooler inside for the tortoise. It would feel cooler to mammals but not actually have a lower temp inside (other than due to shade or whatever, but not because of the fan).

but it seems like people say running an exhaust fan does actually lower the temp cnad I can’t figure out how per this explanation…

 

[Tom]

but it seems like people say running an exhaust fan does actually lower the temp cnad I can’t figure out how per this explanation…

It can't unless the air being pulled in is cooler than the air being pushed out. This is not my opinion. This is a physical fact.

 

[Tim Carlisle]

ok @Tom, so looking at the @Tim Carlisle setup above, and assuming it’s hot outside, it only works to cool the shed down because the top of the shed is going to have stored/contained heat that is *hotter than* the outside air (greenhouse effect/heat rising/being in the sun/etc) so even the hot air from outside coming in will be cooler than the contained heat inside… if the shed did not have inside air hotter than the outside air then running the exhaust would not make it cooler inside for the tortoise. It would feel cooler to mammals but not actually have a lower temp inside (other than due to shade or whatever, but not because of the fan).

but it seems like people say running an exhaust fan does actually lower the temp cnad I can’t figure out how per this explanation…

The physics for a lower profile night box will be different than that of a higher profile shed-type house. A house like mine, while very well insulated, will still allow heat to rise and collect toward the ceiling. Night boxes - not so much. I had to create a shed-type house due some physical disabilities I have in order to maintain it easier. The fan system, in my case, makes a VERY noticeable difference. Added bonus: it tends to get rather dusty in there, and the exhaust fan helps to alleviate it a bit.

 

[Tom]

The physics for a lower profile night box will be different than that of a higher profile shed-type house. A house like mine, while very well insulated, will still allow heat to rise and collect toward the ceiling. Night boxes - not so much.

I agree with all of the above, but that still doesn't change the facts about the incoming air being hotter or cooler than the air inside the shelter. If the air you are pulling in is hotter than the air you are pushing out, the shelter will get warmer. In this regard, the height of the box does to matter.

 

[jsheffield - In Memoriam]

I count on fans in my enclosures to circulate air and temps, not to cool off the enclosures.

Jamie

 

[Tim Carlisle]

I agree with all of the above, but that still doesn't change the facts about the incoming air being hotter or cooler than the air inside the shelter. If the air you are pulling in is hotter than the air you are pushing out, the shelter will get warmer. In this regard, the height of the box does to matter.

That was kinda my point. With a higher profile, peaked roof such as mine, the ceiling temp inevitably gets hotter than the air being drawn in. Same concept as an attic in most peoples' homes. The fan serves to equalize that effect. For folks in SoCal, NM, and AZ..... perhaps not so much given the temps lately are in the 100's. I don't know how yall deal with that day in and day out!

 

[wellington]

That was kinda my point. With a higher profile, peaked roof such as mine, the ceiling temp inevitably gets hotter than the air being drawn in. Same concept as an attic in most peoples' homes. The fan serves to equalize that effect. For folks in SoCal, NM, and AZ..... perhaps not so much given the temps lately are in the 100's. I don't know how yall deal with that day in and day out!

Same way I deal with the cold. Except, I can put on as many clothes as I need to stay warm, they can only strip so much and still will be hot and maybe arrested lol. I have high heat bills, they have high AC bills. I might stay inside cuz it's too cold, they stay in cuz it's too hot. I can wait till the hottest part of the day to do stuff, they do their stuff early morning or later in the evening.
I hate the snow I get, don't mind the cold, I tolerate it well, but I sure wouldn't ever want that heat!
Fans here, in summer, can always cool the inside of the tortoise shed or chicken shed, it's always cooler outside that in the shed, but we have very few 100 days, but can have quite a few 90+ days. The sheds are always hotter than the outside. Sky lights and windows opened helps the tortoise shed too in summer.