Photo Update #8 - Hearth Warming
Editor's note: To document construction of the Bullitt Center, the Bullitt Foundation has enlisted the help of John Stamets as project photographer. In addition to a keen eye, John brings a sharp wit, art for storytelling and attention to minute detail, all of which he will combine into regular project updates that will be posted in this blog. Read more about John's background here.
With no snow or Christmas lights around, it's hard to come up with a holiday image for you, but I do have a short hearth-warming story nevertheless.
That last missive on geothermal drilling generated some surprise that geothermal heating is even an option in Seattle. Obviously it would be an option at Yellowstone National Park or wherever else hot springs are at the earth's surface. However, it turns out geothermal heating works almost everywhere else too, just not to the same degrees.
Note: the term "geothermal" historically has meant heat derived from deep in the earth. Today the term has been expanded to include "ground source heat pumps" or GSHP, which derive stored solar heat from more shallow depths. Not everyone agrees with this expanded usage of the word geothermal.
For the ground source heat pump at the Bullitt Center they dug 26 wells for "geothermal" U-loops, each going 400 ft straight down. When a water-glycol mixture is pumped down one strand of a loop in wintertime, it will come back up the other strand warmer by about 5 to 10 degrees Fahrenheit. If needed, the water-glycol fluid can then be heated electrically within the building before being circulated beneath the floors via radiant heating tubes.
In wintertime, this heating boost is predicted to save about 50 percent of the electric power that would otherwise be needed to heat the building. In summertime, the same closed-loop system can be used to cool the building.
Within the vertical 400 ft wells, the water-glycol temperature ranges between about 50 to 65 degrees F over the course of the year. At any one time, the temperature differential is usually less than 10 degrees F. Despite that seemingly small amount, it adds up to significant energy savings when 26 wells are dug.
26 WELLS COMBINED IN 5 ZONES
The next step in the GSHP construction was to combine the input/output of five or six wells into larger "zone" pipes, as shown in the following photos. With a total of five zones covering different parts of the building, this allows the geothermal heating/cooling to be distributed more efficiently depending on local needs.
To improve performance, the GSHP tubing is wrapped with insulation once it comes out of the ground. The tubing itself is made of environmentally friendly HDPE, or high-density polyethylene.
The top two photos attached are the first floor plans, as photographed on site. The zone shown at bottom center of these plans corresponds to the zone shown in the other photos.
John Stamets
Dec 22, 2011
