ZEB retrofit planning methodology for existing office buildings using building energy simulation

To achieve decarbonization, enhancing energy efficiency in existing buildings is crucial. Non-residential buildings often undergo equipment renewal (e.g., air conditioning and lighting) every 15-20 years, but these updates typically involve simple replacements rather than re-designs based on current conditions, missing significant energy and carbon savings potential.

To solve this problem, the author is developing technical guidelines and simulation tools for energy-efficient retrofitting. This paper presents findings from a trial ZEB (Net Zero Energy Building) retrofit planning of an actual office building (total area: 13,467 m², built in 1978) to gain insights into retrofit design.

The study defines three retrofit levels and conducts quantitative examinations using a building energy simulation tool for evaluating Japanese Building Energy Standards:

Level 1 (standard retrofit) uses Japanese building design standards, achieving a 10% energy reduction compared to the current situation (Level 0) with primary energy consumption of 2377.5 MJ/m².

Level 2 (ZEB Ready target) involves changing the air conditioning to an individually distributed system with packaged air conditioners and optimizing the sizing (capacity) of the system using dynamic load calculations, reducing primary energy consumption to 517.5 MJ/m².

Level 2+ includes the addition of 236 kW photovoltaic power, further reducing primary energy consumption to 349.6 MJ/m².

Cost-effectiveness analysis reveals significant differences: Level 2+ offers utility cost savings of 42.8 million yen/year and renovation costs of 614 million yen, with a payback period of 14.3 years from Level 1 to Level 2+.

The findings indicate that achieving ZEB is possible even for office buildings constructed in 1978. However, the long payback period for ZEB retrofitting suggests that additional benefits, such as improved indoor thermal environments, should be considered to promote such investments. Therefore, this paper examines non-energy benefits (NEBs) using the building energy simulation to enable a comprehensive evaluation of the ZEB retrofit.