Heating/Cooling Element (Gas Simulator): This element, located just under the container, allows you to heat or cool the container,  keep it at a constant temperature (default), or "insulate" the container to prevent any heat energy exchange with  the surrounding environment. Choose to make it a heater or cooler in the heating/cooling element's Properties Box. To prevent heat exchange (the adiabatic case), select no heat transfer.  If you change the temperature control option during Run mode, the container's movable wall automatically returns to its default position in the middle of the container.

The simulator represents heating by a fire with red arrows pointing up. It represents cooling by an ice block with blue arrows pointing down. Note that you cannot use the push-pull (move top wall) tool in conjunction with the heater or cooler options.  

Use the energy bars tool to explore the consequences of not allowing heat energy transfer, or of keeping the temperature constant, when using the push-pull tool.