"Integrative design" is another name for "whole system design." The key concept is that optimizing each component of a system independently leads to non-optimal complete systems, especially when energy efficiency becomes a goal.
Consider a very simple example. Assume you are designing a pumping system that consists of a pump and a pipe. The normal approach to designing this system would be to determine how big a pipe to install based on how much liquid you have to pump, given a certain "acceptable" amount of friction in the pipe. The bigger the pipe, the more expensive it is, so you don't want to get it too big. Once the pipe is sized, you then size the pump. but this approach turns out to only optimize the pipe.
But the pump is part of the system, too, and it turns out that if you reduce the friction in the pipe to nothing - that is, buy a large diameter, more expensive pipe - you can use a much smaller pump. Smaller pumps are much less expensive than larger pumps, and in fact with the money you save by reducing the size of the pump, you have some money left over to buy a more efficient pump, which saves you energy.
The combined system of smaller but more efficient pump plus larger and more expensive pipe is still less expensive than the standard configuration of larger pump and smaller pipe. And, you're saving a lot of operational costs because of the smaller more efficient pump. By using a systems approach to the design, you've not only saved money on the initial build out, but you're also saving operational costs because of the reduced energy need. One way to think of this is that the larger pipe is serving multiple purposes - it's transporting the fluid, but it's also providing a low friction system to pump against, and so you get multiple benefits, which offset its higher cost.
Integrative design entails more work upfront from the designers, and often requires a multi-disciplinary team to find and optimize all the multiple purposes that each component of the larger system can serve.
Amory Lovins of the
If you were to ask most engineers how thick your insulation should be in a very cold place, you’d probably be told, “Just as much as will pay for itself over the years in saved heating fuel.” That seems to make sense—you don’t want to pay more than it’s worth, do you?—but it’s wrong, because it leaves out something important. I don’t mean the environment, though it leaves that out too. It leaves out the capital cost of the heating system: not just the furnace but the ducts and fans and pipes and pumps and wires and controls and fuel supply that have to be paid for before you can get any heat, and yet none of that is counted in the normal calculation. But when you put in enough superinsulation and superwindows and air-to-air heat exchangers, you don’t need the furnace any more, and these other features cost less to install than a heating system would have cost.
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