Large language models (LLMs) have shown human-level capabilities in solving various complex tasks. However

it is still unknown whether state-of-the-art LLMs master sufficient knowledge related to heating

ventilation and air conditioning (HVAC) systems. It will be inspiring if LLMs can think and learn like professionals in the HVAC industry. Hence

this study investigates the performance of LLMs on mastering the knowledge and skills related to the HVAC industry by letting them take the ASHRAE Certified HVAC Designer examination

an authoritative examination in the HVAC industry. Three key knowledge capabilities are explored: recall

analysis and application. Twelve representative LLMs are tested such as GPT-3.5

GPT-4 and LLaMA. According to the results

GPT-4 passes the ASHRAE Certified HVAC Designer examination with scores from 74 to 78

which is higher than about half of human examinees. Besides

GPT-3.5 passes the examination twice out of five times. It demonstrates that some LLMs such as GPT-4 and GPT-3.5 have great potential to assist or replace humans in designing and operating HVAC systems. However

they still make some mistakes sometimes due to the lack of knowledge

poor reasoning capabilities and unsatisfactory equation calculation abilities. Accordingly

four future research directions are proposed to reveal how to utilize and improve LLMs in the HVAC industry: teaching LLMs to use design tools or software in the HVAC industry

enabling LLMs to read and analyze the operational data from HVAC systems

developing tailored corpuses for the HVAC industry

and assessing the performance of LLMs in real-world HVAC design and operation scenarios.