Lloyd Alter
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Double Hung Window Basics
Why we like them
These windows have upper and lower moving sections that give a lot of flexibility; if you open the top and the bottom you can create a convection current in the room; If you open it at the bottom in one room and the top in another you can tune the windows to maximize ventilation.
Scientists at the Imperial College in London studied the use of double hung windows. Dr Gary Hunt of the Department of Civil and Environmental Engineering is quoted by the college:
"Many of us have forgotten how to correctly use the sash windows so carefully installed by the Edwardians and Victorians to maximise airflow."
"If used correctly it is possible to significantly improve comfort in the office or at home without using air conditioning units that place high demands on energy and increase carbon-dioxide emissions."
Using laboratory modeling techniques that accurately replicate the flow of air in small-scale physical models, Dr Hunt and his team are able to measure and clearly visualize how air circulates within rooms and buildings.
"The trick to getting the maximum flow of air through the window is to slide the sashes so the window is open equally at the top and bottom.
"By separating the in-flow and out-flow, cooler incoming air efficiently flushes the warm air out of the room. The warm air inside the room tumbles out of the top opening and the cooler air form the outside comes in through the lower opening," explains Dr Hunt.
What we worry about
Screens are on the outside and can get dirty. Some say that they don't seal as well as other kinds of windows and have a higher air infiltration rate. A maximum of 50% of the window can open, which some consider a disadvantage. The meeting rail crosses the center of the window, which some consider blocks the view.
Eco-factor of Double Hung Windows
Tuneable and long lasting. The classic.
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