Lower heating and cooling costs
 

I was thinking of a concept as it works with a fridge. It only cools off the inside when the temp rises above a certain set level. If there is nothing in there then it cools off faster and needs to be cooled off less once the desired temp is reached. But if there is food in there then it takes longer to cool off initially, but then it also requires more cycling more often. Does this work for a house? If most of the living space was open as opposed to having stuff all over the place then wouldn't that concept still apply? Any thoughts on this?

What you are talking about is called thermal mass. Its very important in heating and cooling systems, especially if you are looking into passive systems. I suggest reading up on it. BTW, you have it backwards. If there is more food in the refrigerator the compressor will cycle less often as the food sort of 'stores' the cold.

half right
 

You're half right. The empty fridge will cool off faster than one filled with room temp. contents. Once the contents of the fridge are cold they will not release their cool as quickly as the air that surrounds them. Therefore a fully stocked fridge, once cooled, will maintain it's lower temp longer than an empty fridge.

Ok. With those two things then. Would it be reasonable to assume that a room in a house would act the same way? And if it did (with difference because of furniture instead of food) would there be any benefit to have a lot of furniture in a room or less furniture?

Yes, more mass will change its temp less quickly than less mass. The number I've heard to be optimum for refridgerators is approx. 80% full. Hope that helps.

Yes, a room in a house will act the same way. More furniture (more of anything really) will help maintain a more constant temperature. Adding thermal mass means that it will take more energy to cool down everything in the room, but it will also warm up slower.

What is your goal here?

yeah build your kitchen table out of brick.

my house is passive solar. we don't have any a/c, don't need it. and when we were heating only with wood we used less than 2 cords a winter.
adding an inch or two of concrete to your floor will do alot more than filling the rooms with furniture.
good insulating curtains will do more than anything.

I have a vague memory of a passive solar, energy efficient house in which they had a crawl space beween floors with hundreds of one gallon plastic jugs of water. The mass of the water helped the temperature remain constant and they drew their air thru that space.

Yeah, the whole point of thermal mass really isn't to make your A/C go on and off less (although that will help a small amount). Its more about storing cool from the night for example, and slowly releasing it through the day to reduce A/C use completely. Same with heat, build up heat during the day and slowly release it through the night lessening required heating.