How does Day and Night Venting Work?

I’m a big fan of cooling my house in the evening with the whole house fan. The rush of cool night air can make sleeping so much more comfortable at a cost 10 to 20 times cheaper than AC.

Conversely, there are times I’ve come home to a chilly house and thought to myself, It’s warmer outside than inside! I might even open up the windows to take advantage of this if I weren’t so lazy.

This is why I have been working for years to automate these processes. After developing such a system, I used temperature sensors to record inside and outside temperatures with using this system. The results are shown below in graph form.

Baseline, No Heating or Cooling

This graph shows a time when no heating or cool of any kind was applied. All systems were off.

Note the even sine wave of the inside temperature and that the daily range falls between 69 and 74 degrees F. Inside average and outside average are roughly the same.

Cooling with a Whole House Fan

This graph shows cooling using only night venting. No AC was used.

Note the rapid drop in slop of the inside temperature line as cool outside air is introduced. Even though outside average temperatures hover around 80 degrees F, the inside average remains around 74 Degrees F, roughly 5 degrees lower.

Heating with a Whole House Fan

This graphic shows heating using only ventilation. No heater was used.

Note the steep incline of the inside temperature when warm outside air is introduced. Average inside temperature was maintained around 5 degrees F above outside average.

The Big Picture

By knowing when and how much to heat an cool via ventilation, significant energy savings can be achieved during those times when daily outside temperature fluctuations intersect with the inside target range.  A 2004 California Energy Commission report concluded that a typical 2000 sq ft California home could save $450 a year using a ventilation controller though cooling savings alone.

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