[This is the sixth installment of an ongoing series]
“You’re going about this the wrong way,” said my friend and architect Fredrick Zal.
“What you really need is a cold air stack.”
I had asked Fred for some easy, cost efficient ways to cool our house. It was a logical step in our family’s ongoing quest to reduce our energy bills by 25% or more while spending as little money as possible and without compromising our lifestyle.
To be honest, I had expected Fred to lecture me on how to use my air-conditioner more efficiently. After all, setting the thermostat a little higher and using fans can save 6%-8% on cooling costs for each degree above 78, according to the Department of Energy,
And, in an effort to show him that I had done my homework, I was fully prepared to counter his reasoning with my suggestion that an attic fan or a whole house vent could save even more money. Not only are both easy to install and relatively inexpensive, but the constant airflow can make you feel as much as six degrees cooler than you would in still air…air conditioned or not.
Either of these devices, according to my research, use only 10-20% as much electricity as our central air conditioner, which would put us significantly closer to our goal of an overall 25% reduction.
But, as he usually does, Fred cut right to the chase.
Turns out that “cold air stacks” have been around for thousands of years. The “stack effect” is based on the buoyancy principle, which is the difference between indoor and outdoor air density resulting from temperature and moisture differences.
“Buoyancy,” Fred explained, “creates a positive or negative force that can move more air than even the best air-conditioning units if conditions are right.”
And apparently conditions are right in our home. Fred noted that the high ceilings we have combined with a broad central staircase across two floors creates huge thermal differences between the hot air trapped near the ceiling and cooler air which collects on our first floor.
That’s why our air conditioner was working so hard in our hot Oregon summer, not to mention why our second floor is almost 10 degrees hotter than our first floor even with the AC going full blast.
We learned about that in science class,” our ten-year old son, Kunihiko, piped in, “Hot air rises so what you’ve really got to do Dad is cut a hole in the roof to let it out and draw cooler air in through open windows.”
Never one to rub it in, Fred grinned and said simply “bingo” as he pointed to the perfectly positioned skylight we have at the top of our staircase.
So much for my research abilities…
According to Fred, architects are well aware of cold air stacks, despite the fact that many have gotten away from using them in the United States. But, if you’ve ever been in a Middle Eastern home in the Mediterranean or spent time in the narrow hallways of Beijing’s hutongs, you’re cool as a cucumber even on the hottest days.
Also, homeowners in Japan and ancient Rome regularly wet the central courtyards of their traditional homes in the morning. And while that strikes us as strange or wasteful today, doing so set up an evaporative cooling effect that could last for 12 hours or more – something today’s “green” builders are trying their best to emulate.
While I was envisioning a complicated roofing project in the making, Fred suggested that all we have to do is convert our existing skylight at the top of the central staircase which is permanently sealed closed, to one that can open. That way the hot air collecting near the ceiling will naturally rise up and out of our home, while cool air is sucked in to replace it.
While there are many brands available, Fred suggested skylights made by Velux. They’re sold at most home centers including Home Depot (HD) and Lowe’s (LOW) and are easy to install thanks to a special flashing the company has developed – “Pretty much idiot proof” were his exact words.
Some quick online research suggests that we’ll probably pay between $300 – $600 for the skylight itself and another couple hundred for installation.
Now, I realize that many of you reading this may live in vastly different climates than what we have here in Oregon. “Even so,” Fred suggested, “you can still dramatically reduce your energy bills by using a combination of the cold air stack principle and whole house fans to complement existing air conditioning units or ceiling fans. This doesn’t cost a lot of money.
In fact, simply learning how Mother Nature wants to move air around and opening a few windows selectively might be all it takes to save some really big bucks.
Editor’s Note: Money Morning’s Investment Director Keith Fitz-Gerald is on a personal mission to reduce his household energy consumption by 25% or more through conservation – without altering or compromising his family’s lifestyle.
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