Internal Temperature Behavior During Summer Excessive Heat Wave
Among the many interesting features in sustainable design are the research based on actual observation of temperature behavior. This allows to learn how material interact with various external factors such as high temperature, wind and solar radiations. The consequence of this material interaction is how the internal temperature fluctuates. Locally in Lebanon the overwhelming construction is done using what is technically labelled as thermal mass materials: These are nothing other than the common hollow block masonry units for external & internal walls, the external and internal cement based plastering , the reinforced concrete for slabs and roofs and the stones for external cladding and internal tiling. These materials, when exposed to a heat source, have the physical ability to absorb a large amount of heat, store it and release it at a later time.
The graph spanning August 24 till September 4, show both internal and external temperature fluctuation of what can be described as a typical local residential building in terms of construction with no particular attention to any sustainable feature. The room monitored is facing west and is used more than a few hours daily by one person as a work/laptop station. The approximate floor and window areas are 12sqm and 3sqm respectively, for an internal height of 3m. The room is within an intermediate apartment (between a lower and upper floor). Windows are opened at random times, yet during the heatwave they were kept closed, unless for not more than 30min a day to get some (warm) fresh air. There is no mechanical cooling within the room, nor within the apartment. Fans are used during high peak temperature periods.
The first few days (Aug 24-26) external temperature is moderate with a clear drop between day and night temperature. Typically, inertial temperature during the larger part of the day (morning and noon) are lower than the external ones, and this even if when the windows are open. Internal temperature starts to rise when the afternoon sun hits the room. When this happens dark brown aluminum shutter are closed during later afternoon till the early evening when the window is open for a short time, before being closed again for the night.
During the night and with the regular external temperature drops, internal temperature is more often warmer, and this even with the windows open. (These are typical temperature behaviors, observed now in various locations in Lebanon, with more than a few published articles, by us, in international journals and conferences showcasing the issue).
What is interesting this time is the observation within this phenomenal heat wave that is happening, with temperature reaching 39.4oC as a record (since summer 2012) for a Davis weather station located in Ballouneh, at 705m above sea level and some 15Km north east from Beirut. The observed room is within the same building as the station.
This heat wave happened in two phase, August 29-31 and September 3-4. During these two phases, temperature sore from previous days’ peak of an average of 8oC (from high 20’s to high 30’s). Furthermore, the expected night dropped is still comparable to the regular night drops, yet since it started at a high peak it remained considerably hot (varying between 28-32oC).
For the full three days of the first heat wave, internal temperature remained cooler than the external temperature. The afternoon regular peak remained, but as a trend the internal temperature is slowly rising.
The two days of cooler external temperature (September 1 and 2) allowed the internal temperature a limited cooling down, but the new heat wave started again.
This interesting phenomena of internal temperature considerably cooler than the outside, is interesting at various levels: it can be the key that leads to keeping internal spaces within the users’ summer comfort zone. Nevertheless, it would require further detailed studies that allows a full understanding of the behavior of the material, and more specifically on how to be able to control this to the users’ advantage.