Energy-Saving HVAC System and Design Methods Utilizing Medium-Temperature Chilled Water for Office Buildings

This paper presents an energy-saving HVAC system and design method using medium- temperature chilled water for office buildings. The proposed heat load calculation method focuses only on necessary areas, reducing air volume load compared to conventional methods. It separates heat load calculations for interior and ceiling spaces. The air volume is calculated based on the interior load, while the ceiling space load—mainly from lighting and skin load—is included in coil load but excluded from air volume load. Typically, air cooling uses chilled water at around 7°C. This system adopts a two-step cooling process using medium-temperature chilled water and chilled water to increase chiller outlet temperature and improve efficiency by approximately 25%. Outside or return air is first pre-cooled with medium-temperature chilled water, then cooled further to the required temperature. In this system, outside air is cooled to 16°C and supply air to 12°C. About 50% of the total heat load can be handled by medium-temperature chilled water, allowing the chiller to operate at a higher outlet temperature and achieve greater efficiency.