Both buildings and biological organisms need energy to run their respective systems, so you could say they both have some form of digestive system. While biological organisms digest food to convert it energy, buildings could utilize an on-site PV system to convert solar energy to electricity. In a more indirect sense, if the building lacks on-site energy generation and needs to pull from the grid, you could argue that the grid ‘digests’ fossil fuels to convert it to energy for the building.