if you open a fridge for an hour, is the room warmer or colder than before?

Question

a random question i found on a game.

Answer 1

Just as a thought experiment, I think it would be warmer based on the laws of thermodynamics. The first law can be summarized (excessively briefly) to saying energy cannot be created nor destroyed. This means that when you run your refrigerator, the heat in it does not just vanish, it has to go somewhere. The refrigerator manages this by essentially pumping the heat out of the refrigerator and into the room. If the refrigerator were 100% efficient this would result in no temperature change of the room because the cooling would exactly equal the heat pumped into the room. In actuality because of the second law of thermodynamics, which says that the entropy of a system must always increase, the refrigerator cannot be 100% efficient. The refrigerator will use electricity to run a compressor but some of the electrical energy is wasted as heat, and the cooling is not as great as it could be. Because of this the final temperature of the room should be slightly warmer than it would be if the refrigerator door was closed.

Answer 2

I suspect it depends on the size of the room relative to the fridge, whether the fridge was running and down to temperature before you opened it and whether you can eliminate any other heating or cooling influences.

Opening the door will release a fridge-full of pre-cooled air so the room temperature will drop. Then the fridge motor will run continuously in at attempt to bring the fridge back down to the temperature set on its thermostat ... but any heat it extracts from the air will be released back into the room by the cooling fins on the back so there will be no net cooling after the original release of cold air. There *will* be some additional heating because the motor (the compressor) will be running all the time, using electricity and giving off heat.
So, if the heat given off by the motor running for an hour exceeds the cooling effect of the initial release of a fridge-full of cold air, the room will get warmer.

Answer 3

It will get slightly warmer.

At first it will get slightly colder, for an interesting reason. While the refrigerator door is closed, we don't consider the inside "part of the room." But when we open it, the cold air inside will begin to mix with the room air, and the overall temperature of the room (as measured by an extremely accurate thermometer) will drop slightly.

But then the refrigerator system will detect the warming of it's inside temperature and turn on in order to reduce that temperature. Refrigerators work by using electricity to drive a motor that compresses a gas (freon) and then expanding that gas (which results in a drop in temperature) which cools the inside. As that refridgerator motor tries unsuccessfully to bring down the inside temperature, the motor will generate a lot of heat, thus heating up the room.

Of course this is assuming there is no other loss or gain of heat in the room. So where is the new heat energy coming from? From the power cord of the refrigerator (as it is plugged into a wall outlet that is introducing energy into the room).

Clever question!

Answer 4

It depends on what other factors are taken into account.

1) If you switch the fridge off, so that it is not trying to cool things then the room will get very slightly cooler, and the fridge will warm up.
2) If the room is airtight, and the fridge is switched on, then the room will warm up. This is due to the fact that there is energy coming into the room via electricity to operate the fridge cooling mechanism.
3) If the room is not air-tight, then it will depend on the air temperature outside the room on if the room will warm up or cool down - that would have to be set against the effects of what was occurring inside the room.

Answer 5

I would say warmer because the heat exchange is inefficient (I am assuming that the warm part of the refrigeration unit is at the back of the fridge and not outside as it might be in an industrial or commercial unit). There is friction and other energy loss that adds to the room temperature; that is, the cooling inside the appliance is less than the warmng outside the appliance and the two do not balance so the room warms.

Answer 6

Warmer.

Let us assume a well insulated room with no net heat transfer out. Remember that the refrigerator is not 100% efficient, so it will add a net positive heat output into the room so it will be warmer after an hour. That assumes that the net heat capacity of the fridge contents is small compared with the remainder of the contents of the room outside the fridge.

Answer 7

The room will become warmer because energy powering the fridge,enters the room and as energy can not be lost,only changed from one state to another,it will become heat energy and so raise the room temperature.
This was a question I was first asked in the early 80s when studying applied thermodynamics and struggled with the answer for a long time.So the answer has stuck with me and I know it is correct

Answer 8

If you have a CLOSED fridge in a room, the room will get warmer because a fridge pushes heat out of it. If you leave an open fridge in a room, the fridge will simply fail to work hard enough and will burn out its motor.

Answer 9

Warmer.

A refrigerator operates by compressing air removing the heat and then pumping it outside of the container. Since not machine is perfect, and refrigeration is far from 100% efficient the fridge can't get rid of more heat than it produces in its motor.

Over a short period of time the room would get colder as the temperatures equalize, but as soon as the compressor motor starts to operate it generates heat and that would increase the temperature in the room. The refrigerator doesn't other wise increase or decrease heat it only transfers the heat from inside to outside.

Answer 10

It would warm up - the heat generated by the motor constantly running (it would be trying to cool the air in the fridge) is higher than the drop in temperature of the air inside the fridge due to inefficencies within the motor.

Although I'm certain the area close to the open door would see a reduction in temperature.