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A Zero-Energy Community: Part 5

Project Manager Brad Liljequist chronicles the building of the zHome, a ten-unit townhome in Issaquah, Washington—the first multifamily zero-energy community in the United States. Part 5: How do ground source heat pumps and solar panels work?

 

Two of our most central technologies in achieving zero net energy are our ground source heat pump system (for heating and hot water), and our solar panels (which generate electricity). The two account for about 60% of getting to zero net energy, so obviously they play a key role. 

Ground source heat pumps are a well-known technology, but are generally not mainstream, especially here in the Pacific Northwest. The system combines three highly efficient processes which together result in a system which over three times more efficient than a typical forced air furnace. The slides give a good narrative to how the system works, but if you’d like more details, check out the ground source system sign from the zHome education signage—it is the second sign in sign package one.

Solar energy, surprisingly, works quite well in the Northwest—solar panels here put out about 70% of the solar energy of a panel in Sacramento. Solar energy quietly is becoming more and more cost effective, with prices coming down and efficiency going up. Currently solar panels convert about 15-20% of the solar energy hitting them to energy—quite efficient when you consider that photosynthesis is only a half a percent efficient! Also, solar panels are quite durable—many panels from the 1970’s are still functioning well.  There is little to go wrong in them. Given how little maintenance they require (simple occasional  cleaning) there is a huge amount going for them.
 

The first stage of the system is the ground source piping system. At zHome, we have fifteen 220-foot-deep boreholes, where we’ve inserted U-shaped one inch diameter pipes grouted into place and fused into one interconnected set of pipes, just below the ground surface. Through these we pump a water/ethanol mixture, which absorbs the average ground temperature of 51 degrees. This fluid is then pumped into each unit, where it is then further heated by the heat pump. The benefit of doing this is that the heating system is effectively always heating from that 51 degrees—as if it is in a perennially moderate climate.

Click here to read past installemts of Building A Zero-Energy Community.

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