Energy Star tax credits
Simple is as simple does. It works. Its easier to understand. Easier to fix. The real world does not reward complexity.
An important aspect of good design is simplicity. HVAC can be complicated enough, given the need to maintain various spaces at set temperatures, relative humidity and cleanliness. HVAC systems are also expected to maintain certain pressurization and [code required] outside air exchange. All while keeping to the highest possible energy efficiency. We also need and expect them to respond precisely and correctly to changing variables.
Simplicity in controls are also key to this. The simplest controls are on-off. Simplicity is not obvious everywhere. But in reality, as software development theory teaches, you can find the simple by decomposing the complicated.
Consider these concepts before the initial Basis of Design is established. Decompose the various functions needed and decide how the system will be controlled. Many designers have their personal preferences and presumptions, but these must be put aside in favor of open-mindedness in the beginning of the decision making process. Yes, energy and size calculations may be useful, but not as important as what and how to control the various environmental parameters.
Diagrams of the systems, 
Mass-flows, temperatures, and pressures. For lighting, its watts and lumens per square foot. And using natural ambient light wherever available.
Get these right the first time, and you will save all kinds of hassle. During design, keep the diagrams as a guide and reference. It will keep also you focused and directed.
Next subject: Dedicated outside air systems (DOAS) These kinds of systems separate the ventilation "function" from the building internal HVAC. Tens of millions of buildings have no way to split this from the basic heating and cooling. Which makes the controls complicated. DOAS is especially good for high occupancy rooms and in situations where air change requirements are more exacting. Its an economic question and we have to decide how and whether this is worth the trouble. Most significant in schools, assembly rooms, theaters, health care,
In many existing buildings, DOAS, which require separate main ducts, may be impossible to retrofit due to space limitations and structural issues. But DOAS divides the work that HVAC systems do, they can be used to recover energy that is lost by exhaust systems. Furthermore, because DOAS central units can be physically remote, so they do not contribute noise to the occupied space and finally, they incorporate the potential to increase net rentable space!
An alternative, if the above is not economically feasible, is to keep and/or update the existing systems, measure carbon dioxide levels (a proxy for stale air), and control the entering outside air according to that parameter. This is "Demand Controlled Ventilation" control, which I described in this previous post in November.
