The PHCC project is the design and development a prototypical, modular system for a Passive House Compact Core. PHCC is a prefabricated, technologically optimized and spatially minimized modular space-conditioning HVAC core for Passive Houses of sizes between 1,000 to 4,000 square feet (and possibly beyond). Most Passive Houses in the U.S. are constructed within these size perimeters, with the numbers of Passive Houses growing due to an increased interest in these highly energy-efficient, yet cost-effective buildings. From a purely technologically standpoint, Passive Houses share one common challenge: their HVAC and control systems are usually a more or less complex accumulation of different and highly customized systems that are designed as individual prototypes for each distinct building. This grant project is about the product development of a PHCC – to develop, assemble, test and evaluate a simple, yet flexible modular system that is solely based on market-ready products, to be installed and maintained by standard trades within standard building processes. Grounded on the experiences of the 125 Haus project by AJR Atelier Jörg Rügemer, this system will be easily understood and used by the end consumer. The expected outcome is to be a marketable product.