Applied heat and thermodynamics.

In summary, the conversation discusses the task of making an abandoned town habitable, with a focus on the largest building in the area - a 40x9.5m shearing shed. The proposal is to create a roof cavity to insulate the building and prevent heat transfer, as the temperature fluctuates greatly from below freezing at night to around 50C during the day. While there is concern about the walls and their potential for heat loss through conduction, it is suggested that if the roof is well-insulated and a ceiling is installed, the warm air trapped in the roof cavity should keep the building warm enough at night. Additionally, painting the roof white or silver to reflect light and heat could further improve the building's temperature regulation.
  • #1
Harrybarlow
11
0
Okay, to give a little contextual background, for one of my units we have been given an abandoned town in south-west queensland (AU). It was inhabited by the natives for a while, then Australia was colonised, now no one lives there and there's a few garbagety buildings that are falling apart. The natives have recently been given the rights to the land, and we were tasked with the job of making the place habitable.

The largest building in the area, the shearing shed, is 40x9.5m and is just made from a layer of corrugated tin. Our proposal is to make a roof cavity, which is to insulate the roof preventing heat transfer and making the building livable. It should be noted that the temperature fluctuates from below freezing at night, to around 50C during the day.

Whilst i think that the roof cavity should prevent the rest of the building from getting too hot during the day(since most of the heat a building is absorbed through the roof via the EM radiation from the sun). I was concerned that, at night when thermal conductivity between the thin walls with a large surface area and the air would cause the building to be cold at night. I am struggling to find information on my problem, and was wondering if someone with a heat/thermo background could help me out. Thanks!
 
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  • #2
Harrybarlow said:
Okay, to give a little contextual background, for one of my units we have been given an abandoned town in south-west queensland (AU). It was inhabited by the natives for a while, then Australia was colonised, now no one lives there and there's a few garbagety buildings that are falling apart. The natives have recently been given the rights to the land, and we were tasked with the job of making the place habitable.

The largest building in the area, the shearing shed, is 40x9.5m and is just made from a layer of corrugated tin. Our proposal is to make a roof cavity, which is to insulate the roof preventing heat transfer and making the building livable. It should be noted that the temperature fluctuates from below freezing at night, to around 50C during the day.

Whilst i think that the roof cavity should prevent the rest of the building from getting too hot during the day(since most of the heat a building is absorbed through the roof via the EM radiation from the sun). I was concerned that, at night when thermal conductivity between the thin walls with a large surface area and the air would cause the building to be cold at night. I am struggling to find information on my problem, and was wondering if someone with a heat/thermo background could help me out. Thanks!
I would not worry about the walls. In addition to insulating the roof, if can you paint it white or silver to reflect light and heat, you will make it even cooler during the day and warmer at night.

AM
 
  • #3
I WOULD worry about the walls especially if they constitute a large area...heat transfer occurs in three ways conduction, convection and radiation.

basics here: http://en.wikipedia.org/wiki/Heat_transfer

You'd be most convcerned with conduction...with inside and outside temperatures the same, there will be none...but if inside is say 70 degrees F and the outside 0 degrees, there will be a LOT. With a 70 degree temperature difference, there will be 70 times the heat loss of a 1 degree difference.


Q = U [delta T], where U is heat exchanges, U is conductance and delta T the difference in temperature...where U is the inverse of R, the insulation value.
whatever Q, heat loss you calculate, will be the heat required to maintain daytime temps at the temperature difference you select...

http://en.wikipedia.org/wiki/Heat_conduction

R values for many materials are shown here:
http://en.wikipedia.org/wiki/Insulation_value

Your shed is almost certainly steel, not tin, but the R values are likely very close..


Here's another table, in different units..watts/ sq meter:
http://en.wikipedia.org/wiki/Thermal_conductivity

Looks like stainless steell might be 20 times as conductive as glass...1/20 the R value in other words, close enough for your calculation.
 
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  • #4
Naty1 said:
I WOULD worry about the walls especially if they constitute a large area...heat transfer occurs in three ways conduction, convection and radiation.

basics here: http://en.wikipedia.org/wiki/Heat_transfer
Here's why I wouldn't worry about the walls. If the roof is insulated and a ceiling installed, you will have a lot of very warm air trapped in the roof cavity that will tend to keep the building from getting too cool during the night. If the walls eliminate convection (ie. there are no large holes), you are likely not going to lose enough heat through radiation/conduction to cause a problem. If the temperature goes to a few degrees below 0C and all you want to do is maintain 20C temperature inside, I suspect the roof will keep you warm enough at night.

AM
 
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  • #5


I would suggest looking into the principles of heat transfer and thermodynamics to address this problem. The first step would be to calculate the heat transfer coefficient for the building's walls and roof, taking into account their materials and thickness. This will give an idea of how quickly heat can transfer through these surfaces.

Next, I would recommend considering the thermal conductivity of the proposed insulation material for the roof cavity. This will determine how well it can prevent heat transfer from the outside to the inside of the building during the day.

To address your concern about the building getting too cold at night, it would be important to also consider the thermal mass of the building. This refers to the ability of a material to store and release heat. In this case, the thick corrugated tin walls may have a high thermal mass, which can help regulate the temperature inside the building by absorbing heat during the day and releasing it at night.

Additionally, incorporating passive solar design principles such as shading and ventilation can also help regulate the temperature inside the building. This involves strategically placing windows and vents to allow for natural airflow and minimize direct sunlight during the hottest part of the day.

Overall, a thorough understanding of heat transfer and thermodynamics principles can help inform your proposal and ensure that the building is habitable in both hot and cold weather conditions.
 

1. What is the difference between heat and temperature?

Heat is a form of energy that is transferred from one object to another due to a difference in temperature. Temperature, on the other hand, is a measure of the average kinetic energy of the particles in a substance.

2. How does the Second Law of Thermodynamics apply to everyday life?

The Second Law of Thermodynamics states that in any natural process, the total entropy of a closed system will always increase. This means that energy will always flow from a hotter object to a colder one, and it is impossible to convert all energy into useful work. In everyday life, this can be seen in the fact that things tend to move from a state of order to a state of disorder, and that it is impossible to create a perfectly efficient machine.

3. What is the difference between conduction, convection, and radiation?

Conduction is the transfer of heat through direct contact between two objects. Convection is the transfer of heat through the movement of fluids, such as air or water. Radiation is the transfer of heat through electromagnetic waves, such as sunlight.

4. Can heat be converted into other forms of energy?

Yes, heat can be converted into other forms of energy, such as mechanical energy, electrical energy, or chemical energy. This is the basis of many power plants, where heat is used to produce steam, which then turns a turbine to generate electricity.

5. How does the study of thermodynamics impact our understanding of climate change?

Thermodynamics plays a crucial role in understanding the factors that contribute to climate change, such as the transfer of heat between the Earth and its atmosphere, the effects of greenhouse gases on temperature, and the overall energy balance of the planet. It also helps us to develop sustainable energy solutions that can mitigate the impacts of climate change.

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