The IBES (Interconnected Building Energy eco-System) concept is modeled after the behavior of natural ecosystems, in which the waste product of any one organism is the food for another organism. Within the context of IBES, we can say that the waste energy of one process in a building is the useful energy for another process. To give a specific example, certain systems, such as air conditioners and refrigerators, exhaust heat, whereas other systems, such as water heaters, require heat. If the building infrastructure is designed so that these systems are allowed to exchange heat, the result is a significant improvement in the net energy efficiency of the building. The IBES design principle can be broken into three practical steps:
1 - Locally recover heat that would be otherwise wasted, as in the form of hot water flowing down the shower or sink drain.
2 - Cycle heat between systems that produce heat and those that require heat, thereby improving the efficiency of the net system.
3 - In order to make maximum use of recovered heat that might otherwise be wasted, pump heat through a Sterling engine or similar device to generate useful electricity.
Accomplishing the first step requires the routing of certain drain pipes and supply pipes through a heat exchanger. The heat exchanger can be as simple as a water-filled tub, enclosing interleaving supply and drain lines. In the case of a shower (illustrated below) the supply water leaving the heat exchanger will be significantly warmer than when it arrived at the home. Although it will still need to be heated up before being used as hot water, the amount of energy required to bring it to an acceptable temperature will be significantly less than it would be without the heat exchanger.
Implementing the second step makes use of a significant amount of heat normally wasted through AC and refrigeration systems. The following data (California Energy Commission Electricity Outlook Report Feb 2002) shows that the majority of peak electricity usage in California homes supplies air conditioning systems.
The following diagram illustrates how water can be routed through a secondary AC heat exchanger, thereby improving the efficiency of the AC, as well as providing hot water for the home.
Using a water-based heat exchanger to cool the exhaust portion of the AC and/or refrigerator can reduce electricity consumption by 30% to 50% compared to exhausting the heat to outside air, depending on the geographic region and time of year.
The third IBES design principle addresses the fact that homes in many regions would produce more hot water than could be recycled within the home. By storing the excess heat, and exhausting the heat during cool nighttime conditions through a device such as a Sterling engine, useful electricity can be generated. Such a system is illustrated below, where the direction of heat flow (into or out of the building) depends on whether it is nighttime or daytime.
The maximum energy efficiency improvements available from IBES depend on the temperature gradients among the components of the building, and the efficiency of the various components, such as the heat exchangers. In order to generate realistic estimates of the energy efficiency of prospective building designs, we have developed a mathematical framework to describe the energy flow of a building, including energy loss and storage mechanisms. This mathematical framework is also the basis for an approach to maximizing the energy efficiency of the building, given the parameters of the building and an available set of flow control and heat exchange devices.
