On July 12, 2006, Rensselaer Polytechnic Institute (RPI) researcher Steven Van Dessel and his colleagues will announce their most recent progress--including a computer model to help them simulate the climate within their test structure atop the RPI Student Union--at the Solar 2006 Conference in Denver, Colo.

For 4 years, the researchers have been working on their prototype Active Building Envelope (ABE) system. Comprised of solar panels, solid-state, thermoelectric heat pumps and a storage device to provide energy on rainy days (literally), the ABE system accomplishes the jobs of both cooling and heating, yet operates silently with no moving parts. NSF is supporting the team to determine if a microscale version of the technology will function effectively.

According to Van Dessel, thin-film advances could potentially lead to functional thermal coatings composed of transparent ABE systems. Such systems might vastly improve the efficiency of temperature-control systems.

"The ease of application would make it possible to seamlessly attach the system to various building surfaces," he added, "possibly rendering conventional air conditioning and heating equipment obsolete."

Van Dessel hopes a thin-film version of the ABE system will see uses in a range of industries, from aerospace--in advanced thermal control systems in future space missions--to the automotive industry, where it could be applied to windshields and sun roofs, giving them the ability to heat or cool a car's interior.

"It also may be possible to one day use the ABE system to create packaging materials for thermal control," he added, "which could lead to things like self-cooling soda bottles."

Active Building Envelope Systems

Active Building Envelope (ABE) systems are a new technology for space heating and cooling, which integrate photovoltaic (PV) and thermoelectric (TE) technologies. In the ABE systems, a PV system is used to transfer solar energy directly into the electrical energy; this electrical energy is subsequently used to power a TE system.

Depending on the direction of electrical current applied to the TE system, ABE systems can operate in a heating or cooling mode, and can compensate for thermal losses or gains that occur through a building's envelop or other thermal enclosure.

ABE systems make use of solar energy, a clean and renewable energy resource. In order to assess the feasibility of the ABE system, we have developed a prototype ABE-window system.

In conjunction with developing this prototype, we have also developed an outdoor testing room to test our ABE window system. Our current experimental setup allows us to measure the temperatures inside and outside of this window testing room.

To assess the effectiveness of the ABE system while in operation in the testing room, it is necessary to determine the comparative temperature for the same testing room without the TE system operating, for similar environmental conditions. There are two main methods to establish such control.

The first method is to develop two identical experiments and test them simultaneously, one with, and one without, the ABE system in operating mode. The second method involves computing the indoor temperature through a simulation method. In our research we have opted for this second method.

In this study, we have built a computational model to predict the indoor temperature of an outdoor testing room and its integrated ABE system. The computational model uses the finite differential method, and includes the computation of solar radiation, heat transfer through the testing room surfaces and the ABE-window, and a model for the indoor air.

We have verified the model's accuracy by comparing the simulation results of this model with actual temperature data. We have found that there was good correlation between the model's prediction for indoor temperature, and the actual temperature measurements for our testing room. The model will be used in further studies to assess the effectiveness of the ABE system.

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