Bring up any topic regarding the environment and you will be sure to hear at least two opinions. Actually, if you bring up any topic to a group of 10 engineers, you will probably hear at least 9 different opinions. This is true when talking about energy-modeling.

          To avoid argument, let's consider energy in terms of absolute truths. Apart from members of the "Flat-earth society", almost everyone considers scientific law to be an absolute truth. So, let's look at energy-modeling in terms of Laws. With it being related to energy, there is no better place to start than the Laws of Thermodynamics. 

        I know what you are thinking, "Yeah, I already know that energy can't be created..." Well, for once, we are not going to focus on the First Law, but rather it's younger sibling, the Second Law. If you don't know the Second Law, Google it. 

        So what's this word? Entropy? It is always increasing? Huh? It's a tough concept for some because Powerpoint presos can't illustrate it. Anyway, let's just say in layman's terms:

-High Quality energy becomes low quality energy.

-No process can be completed without the loss of energy.

-Email Mythbusters all you want, THERE IS NO SUCH THING AS PERPETUAL MOTION.

        If we look at a building as a closed system, the energy degradation goes something like this: Electricity becomes mechanical energy which becomes high temperature heat, which becomes low temperature heat.

        Since buildings are in fact open systems, we can always bring in more high quality energy, but at a cost. So let's ask ourselves: do we need high quality energy (electricity) for tasks such as reheat, preheat, regeneration? Wouldn't it be great if we could simulate just how much of this "waste" energy we could put to use and therefore design to those specs? This is exactly what we can do with energy-modeling.

     Now, if we look at the bigger picture, yes, the earth too is an open system, but not in terms of our currently used resources (no matter how ample or limited you believe them to be, they are in fact finite, ie we don't get hit by many oil-based asteroids).

         Based on the Laws of Supply and Demand,  the cost of high quality energy resources will continue to be substantial. Simple logic tells us that we should therefore use this energy in the best manner possible. Luckily for us, energy follows rules and laws. Therefore, it can be simulated in a fictitious environment (and at relatively low energy consumption), and thus the invention of energy-modeling, which allows us to accurately predict what energy and forms will be used in a building. It prevents us from taking shots in the dark (as energy modeling tells us that savings is not always as expected). Therefore, energy-models allow us to minimize high expense energy in favor of using byproducts (waste heat) where applicable. Since this is possible, and since it has proven to be economical, it follows that regardless of the reason, it is plain and simply economical to simulate a building ahead of time.

Unless you can do this in your mind, it leaves you to perform an energy-model.