For efficient cooling in your living room on the ground floor, it is not necessary to compute the open upstairs area on the second floor or its hallway. Air conditioning systems are typically designed to cool specific zones or rooms independently, based on the cooling load and the desired comfort level in each area.
The cooling requirements and thermal characteristics of the living room on the ground floor are generally different from those of the upstairs area and its hallway. Therefore, it is more practical and energy-efficient to focus on cooling the individual zones separately.
However, keep in mind that factors such as insulation, airflow, and heat transfer between different floors can influence the overall temperature distribution in the building. So, it's essential to ensure that there is proper insulation and sealing to minimize heat transfer between floors, which can affect the cooling efficiency of the ground floor.
If you have a multi-story house with central air conditioning, it's advisable to have the system properly sized and zoned to cater to the cooling needs of each floor separately. This allows for better control and efficiency, as the cooling system can be optimized for each zone based on its specific requirements. Consulting with an HVAC professional can help determine the best approach for cooling your living room and the overall comfort of your home.