Tuesday, November 18, 2008

Ceiling Fans and Water Storage

Another exchange between an Open House visitor and myself - great questions about my DC ceiling fans and my water tanks in the house...

Hello Christian.  

First, I want to thank you for the open house you held in early October.  That was most kind of you to open your house up to strangers.  My wife and I arrived on Saturday and were treated to a very interesting and informative tour you provided.  We both learned a lot and am so impressed on the sensible and logical steps you took in energy conservation and house construction--a fine job, well done!

I have been curious about a couple items.  If I remember correctly, the ceiling fans in your living room run on low voltage DC power, but I believe the rest of your power is converted to 120 VAC.  Why did you select the low voltage fans instead of 120 volt AC?

The water storage arrangement really caught my attention and makes a lot of sense.  Why did you put the tanks in the basement of the house instead of burying them in the ground below the frost level?

I didn't find the answers to the above questions on your website, however if the answer is listed please direct me there and save your time in answering.

Thanks again Christian.  That was so enjoyable to learn about your project and receive such a wonderful tour of your house.


Thank you very much for your kind words! I'm happy to answer your insightful questions for you.

Low Voltage Fans

Motors running on direct current, or DC, are inherently more energy efficient then AC motors. In the case of my fans they use only about between 18-19 W due to the aerodynamic blade design and the fact that they are DC-powered. The standard run-of-the-mill Hunter Douglas fans that I looked at seem to have a power consumption of about 150 or 180 W -- which is why I went with the DC powered fans to be able to "afford" cooling in the summer at a reasonable cost (e.g., letting the fans run from, say, 10 AM to Midnight would be 0.25 kWh vs. 2.5 kWh on an average daily budget of 3.5 - 5.0 kWh)

Looking at Energy-star certified fans again now, it seems that efficiency has greatly improved - on medium a energy-star certified Hunter fan uses approximately 6 Watts @ 5,000 cfm (cubic feet per minute) or 75 cfm per Watt. My fan produces 3,400 cfm at 18.7 W or 180 cfm per Watt. Running the fan 14 hours like the example above would use about 0.92 kWh.

Water Storage

There were three primary reasons for putting the tanks into the house: 

  1. I didn't really need that much more basement space. 
  2. Putting them into the house gave me easy access to the plumbing - if anything would ever go wrong or need replacement I can easily replace parts (versus the connections being buried)
  3. Three 2,500 tanks were only about $3,500 whereas a poured-in-place tank based on my research would have cost more like $7,500 to $10,000.

If I had to do it again, though, I would go with a ground-buried tank to avoid the mold issue.

Thank you again for your good questions and I hope that you will find my answers satisfactory. 


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