Heating the Home

Home energy use is represented by the graph to the left. We normally think about the cost of home heating, especially this year with natural gas prices going to record levels, but home heating is only 45% of the total energy use in the home. Hot water is 11%, lighting is 7%, etc....

Because we are shooting to be near zero net energy, we needed to think about energy use everywhere, but certainly tackle the big items first. Thus, we selected a ground sourced or geothermal heat pump system to minimize our heating load. The technology is straight forward ... heat in the ground (around 50-55oF all year) is captured by the heat pump and delivered to the home. In other words, the heat pump will operate in the 50oF range and deliver around 3-5 btus to the home for every btu used in energy. (BTU is a unit of energy called a British Thermal Unit.) (Click for More on Heat Pumps and How They Work)

One of the few subcontractors we (rather than Barrett our general contractor) selected was Wayne Medrud, Smart Energy Systems, Yelm, WA, pictured on the right. Wayne represents Econar Ground Sourced Heat Pumps in Washington State, and from previous experience I know that these are excellent units manufactured just up the road from where we used to live, in Elk River, MN. Wayne will be doing our radiant floor and ventilation system as well.

The ground sourced heat pump also will be used to heat water. On balance we hope to save around 65-70% of the energy used for home heating and hot water with the system ... saving around 38% of our total energy use compared to conventional space and hot water heating demand.

Heat pumps are basically refrigerators or air conditioner. In fact, the real benefit of a heat pump is that it heats and cools the house depending upon the season (we do not plan to use it for cooling, unless the climate really heats up.) The process works by having a fluid absorb energy, either from the air or in our case the ground, run it through a compressor that releases the heat.

As the cooled fluid expands, it is run back through the loop to collect more energy on the next pass. Run in reverse it collects heat from a home and delivers it outside thus cooling the home.

We have a 3 ton heat pump and the rule of thumb is 600 feet of piping for each ton, so we buried 1800 feet of piping under our site ... over 1/3rd of a mile. Since we only have a 0.75 acre lot, this was done by digging a 5 foot wide trench 5 feet deep, and approximately 300 feet long. Under the area of the lawn, we dug parallel trenches and snaked the tubing through the trench. Three loops are laid on the bottom of the trench, 2 feet of soil covers this layer and another 3 sets of piping is laid ... all covered by the final 3 feet of soil.

In the Pacific Northwest, the ground rarely freezes more than a couple of inches. In extreme conditions, it might freeze a foot. In colder climates like Minnesota, vertical wells are needed for the piping to get below the frost line.

Traditionally, heat pumps work best above 32oF. So, they make sense in the Western Washington climate, because it rarely gets below 20oF, and during most days the highs are well above freezing. If the Cold Climate Heat Pump is available buy it because it performs well down to 0oF.

These pictures are of the mechanical room where 2 dumb tanks are used, one to heat the domestic hot water and one to transfer heat to our radiant floor system.

We welcome your comments on this site.
You can email Christine Garst at cbgarst@aol.com
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Sunday December 17, 2006 05:34 PM -0800