Room Temperature

I think there are many variables to consider.

Is the room empty?

Are there any sources of heat, such as a person, cat, fire, appliances, etc?

If the room has no heat influences, and has been sitting that way for a long time, i would think that the room temperature will maintain roughly the ambient, or average temperature of its environment. The room will more or less hold the average temp while the environment fluctuates between day/night etc. The insulating properties of the room will determine how much fluctuation in inside temperature will be seen due to the fluctuations of outside temp.

this is just a thought rattling around my cranium, as I have no real qualifications when it comes to thermodynamics and such.

............ it also depends on wind and solar radation

I don't know if you are GUEST or you have the same proffessor, but check here:

http://cr4.globalspec.com/thread/39079/Stone-Walls-and-Room-Temperature

IS THIS HOMEWORK?

yes I'm the guest

I couldn't find where it was my post so i decided to write again

it is not a homework. it is a real problem. we want to keep in this room a big amout of vegetables. the vegetables need an interior temparature aroud 2 celsius degree. in winter will be really cold outside, will be minus 18 Celsius degree. there won't be any source heat. in calculation we won't consider the gain heat from the vegetables.now the room has the thermal resisdence, R1, R2, R3. the final goal will be to know which will be the interior temperature after I will isolate the room (I know how to calculate R1, R2, R3- i will try diferent tipes of insulation, but first i need a formula for finding the interior temperature) and the exterior temperature will be minus 18 Celsius degree.

I don't know if You undertand what I wanted to explain.

Do not calculate. Measure it, when outside is -18

Are we really helping you out with vegetables or some other type of green leafy plants?

Quote form Steven Wright

"No matter what room you are in, it's always room temperature"

You have already asked this question and got a lot of answers.

Click here for your previous attempt:-

http://cr4.globalspec.com/thread/39079#newcomments

Your question here is OTT.....

The stated problem is un-solvable. Consider a highly-simplified version of the problem. Suppose you had a small box (your farm room) made of walls with known R-values. Place said box within a larger box that has completely controlled conditions (your -18C, free of any random radiative or convective influences) so that the only mode of transfer is conductive. The temperature within the smaller box would be time dependant, and only calculable if you knew the starting temperature. Sorry.

I really hope that there it is a way of finding what I want to know.

Thank You for answed to me.

Follow here to your previous and the answers

But the answer is the same - no heat - same temp as outside no matter insulation.

Is this room isolated from living quarters?

Is this room above or below the ground? From your description I believe it is above ground.

If you could make an underground room that was below the frost level (at least most of it) the interior temperature of the room would be more constant.

How thick are the walls?

How thick is the ceiling?

How often will somebody be going into this room? Every day? once a week? once a month?

I think there are too many variables to solve. The interior temperature will vary with the amount of sunlight, the strength of the wind, etc.

Do you have resources to make changes to this room? Is there any source of power?

I know that was a lot of questions, but I think there is a chance of modifying that room to prevent the freezing of the vegetables.

me1234: And what are the dimensions of your room? Also, what is the initial temperature inside the room?

When you asked first I gave you the equation how to compute the temperature inside. But as you present the problem the temperature will be -18°C if the outside temperature is -18°C a time long enough which ever insulation you will use and without respect to how much you will invest. In one of the comments I even gave an equation to compute the time constant of the cooling in case you have not any heat source in the room.

If you do not understand it then it is not possible to help you.

Sorry

" if there are any questions please let me know "

1. Is this homework?

2. What is the temperature and thermal conductivity of the 'land'?

3. IS THERE ANY HEAT INPUT?

If the answer to (3) is No, then the interior temperature when the system is in equilibrium will probably be ≈-18°C (assuming uniform cloud cover), but the exact result will depend on the answer to (2), among other things.

I think the easiest way for you to understand this problem is to consider your system like an oven. You have an interior with insulating walls and an exterior at a given temperature which is lower than the interior temperature. If you heat the oven to say 200 degrees and then turn off the elements/burners/douse the fire it will start at 200 degrees. The problem is that, now you have an oven that at the moment is hot, but if you leave it, it will slowly radiate heat into the surrounding room, getting colder while it does it. The only way you can maintain a temperature is to keep the burners going.

In other words, if you want this farm room to stay warm you need to put some source of heat into the system to make it warm. Now, if your barn/farm has a soil floor, one could assume that the ground is a heat source, as i doubt that the ground will be -18 deg C.

However, the system you have provided us with as reference is an oven without a burner. You have nothing to keep the heat in the room. If the external conditions vary (i.e. seasonal variation) you may have a time transient system which will have the walls, roof and the floor being a heat source in winter and a heat sink in summer. This variation would need to be taken into account.

thank you for answer me

The temperature is about $10.

Why won't you take care of your own grammar before correcting others?

Why not build a storage box inside the room with enough square footage to store your food supply. Your description sounds like it is not in a livable area. around the outside of this storage shed, pile bales of hay, or straw, and place a 150 watt light bulb inside the storage area. When I was a boy, that's what we did on a farm we lived at. Most of the time the straw kept things okay. On really cold nights we would leave the light on. The area was built in the lower section of a barn with stone walls and really drafty wood sheathing. The area was about 12' x 12' x 7'. -18c you would probably need a couple 100w bulbs.

Just a thought.

You could even rig up a thermostat to automatically turn the bulb on and off for next to no cost.

you also need to take into account the thermal mass of the stone which will act as a heat storage system as well as a heat absorber. Also, the building will not be hermetically sealed, any air exchange will alter the results. Also the stone will absorb moisture and evaporation of it will have a cooling effect.

bottom line, the only way to be certain is measure it. Testing provides "ground truth" that no amount of calculations will alter.

so just the earth=land will be heating source for the room.

the earth has few plus celsius degree

Only deep down in winter.....so it may only go down to -16 inside when its -18 outside - big deal!!

yes, it is true

the vegetables should be in a room which is in the ground, a kind of basement. there won't be need probably a heat source

Only if it is deep enough considering the soil properties at the spot!

The depth depends on the called "heat diffusibility" which depends on several factors as heat conduction and heat accumulation. The minimal depth depends as well on the length of the cool period= the longer the deeper.

Impossible to answer. If there is no internal heat source and you leave it long enough the temperature will fall to -18°C, but I don't suppose that's the answer you're looking for.

If there is a heat source it can be estimated, but it's a mistake to calculate on basis of inside surfaces at T°C, outside surfaces at -18°C, and use the conductivity of the walls/roof/floor. Heat transfer is resisted by convection from inside air to inside surface, conduction through walls/roof/floor, and convection from outside surface to outside air. All these in series for each.

Total heat flow of course = heat input from source, so equilibrium temperature can be calculated.

Good luck!........Codey