In multi-roomed buildings, closing interior doors during heating and or cooling is lowers energy efficiency. All HVAC equipment, whether heaters or air conditioners, have fans that blow air around in massive quantities; 1000-2000 cubic meters per minute. Open interior doors enable the fan-moved air to circulate without restrictions but closed interior doors inhibit air flow, pressurizing the rooms.
Increased energy efficiency from open interior doors
Increasing pressure cannot be contained, and the already conditioned air is forced out of a room through holes, slits, and other openings in order to relieve the pressure. However, since the doors are still closed (limiting air circulation space), and the heating/ cooling equipments are still running, the rooms remain pressurized. In pressurized rooms, the vacuum created by expelled air is replaced with outdoor air that is sucked into the building through fire flues and other unobstructed openings.
Reduced energy efficiency
In closed doors rooms, conditioned air is wasted through the forceful eviction of air that results from the pressurization of the rooms, and this means that HVAC systems have to restart the air conditioning process all over. Since optimum indoor air quality (IAQ) is not achieved, the excessive heat, cold and moisture form conducive conditions for the growth, circulation, and increment of pathogens such as mold, bacteria, and mites. The elimination of these pollutants requires additional costs invested in elimination equipment, as well as the energy required to run those equipments. A re-run of an HVAC equipment translates to additional energy consumption.
It is to be noted that the expulsion of conditioned air is not the only problem that forces HVAC systems to run longer than necessary to condition air. External air that gets sucked into a room is not conditioned; it is full of pollutants and extreme temperatures. HVAC systems are forced to run longer and consume additional energy in order to condition (purify, cool or heat) the new air in order to ensure that the quality of indoor air is as pure, warm or cool as the building occupants require.
Since it is not possible for every building/ occupant to leave his/ her interior doors open all the time, people should apply any of the following energy efficiency tips. First, construction of buildings should put into consideration the need for pressure relievers. Gaps can be left above or below doors, and transfer grills can be installed on room-dividing walls. Alternatively, and whenever possible, building occupants/ owners should purchase HVAC systems that have return air ducts.