Saturday, August 28, 2010

Tightening up to Zero: the Blower Door test Blowout!

Creating a tight envelope is a critical goal in shooting for a zero energy home. And it is not enough to simply apply the correct techniques and materials, it is essential that we have a measure of their effectiveness. This is where the blower door test comes in. A blower door test is a diagnostic tool designed to test the air tightness of buildings.

A blower-door fan is sealed into an exterior doorway, all the house vents are temporarily sealed, and the calibrated fan blows air out of the house creating a pressure difference between the inside and outside, which draws air into all of the inadequately sealed cracks, holes and penetrations. A pressure sensing device is used to measure the rate of pressure change/leakage. The data is entered into a standardized formula and the number of Natural Air Changes per Hour (NACH) is derived. Typical production-built homes built under current building codes will score at about 0.5NACH or higher (one complete air change every two hours). A well built, near zero energy home aims for a score of 0.1-0.2NACH. EarthCraft Virginia officials, including Chuk Bowles, Technical Director (tending to the pressure monitor above) and KC McGurren, Executive Director, supervised the testing of our home this week.

As KC is indicating in the picture, the results were encouraging! We registered a score of 0.16NACH, reflecting approximately one complete air change every 6 hours, approximately 3 times tighter than a well built new conventional home! Mark Waring, our builder, said that he was very pleased with this performance, which reflects the tightest home he has built to date. This tightness will minimize the heating/cooling load, reducing the demand on the geothermal system and putting less draw on the solar PV array.

Tuesday, August 3, 2010

Zero in on Geothermal HVAC in Virginia

In a typical home, heating and cooling represents 56% of energy usage, the largest piece of the energy consumption pie. To strive for a zero energy home, it is logical to try to drive this heating and cooling load down as low as possible. Although we initially considered using solar thermal radiant heating, we soon abandoned this idea in favor of a geothermal heat pump in combination with solar PV. Solar PV is more "plug and play" than solar thermal, and when combined with geothermal, serves as one low energy solution to both heating and cooling needs, both of which are high demands in the temperate Virginia climate. A ground source geothermal heat pump uses the relatively constant temperature of the ground six feet below the surface, which in Virginia is estimated to be approximately 60 degrees, to heat or cool the home. An antifreeze solution is piped through loops in the ground where, depending on the season, heat is either absorbed and used to heat the home, or the unwanted heat from the home is expelled. As in a conventional heat pump, a compressor and an air handler are used to condense and distribute the heat exchange. A geothermal heat pump does not produce heat, but rather it extracts and moves heat. Where the most efficient gas furnace may approach 97% efficiency, a geothermal heat pump may approach 400% efficiency, in effect, extracting 4 units of heat energy for each unit of energy expended. Research suggests that a geothermal heat pump may result in energy savings of 69% over gas heat and 40% over air to air heat pump heat. Jim Satterfield of HVAC by JM LLC worked closely with our builder to assess our projected heating and cooling loads and recommended a 4 ton Comfort-Aire GeoMax2 split unit connected to 3200 feet of buried loop. The GeoMax2 is a rebranded Climatemaster Tranquility 27 Series, which has an EER rating of 16.6/23.7 and COP rating of 3.7/4.2, some of the highest ratings available. In comparison, Energy Star requirements for geothermal ground source heat pumps are 14.1 EER and 3.3 COP. The two stage compressor and variable speed fan coil contribute to the heightened efficiency while its reliance on R410-A refrigerant protects the ozone layer. The GeoMax2 includes a desuperheater, which uses excess heat to pre-heat your hot water, a nice added benefit. This a split unit, which means that the refrigerant/ compressor unit is seperated from the air handler unit, allowing them to more easily fit in the safety of the conditioned crawl space. The refrigerant/compressor unit is a small gray box about the size of a small bedside table. Once again, great things come in small packages!

The air handler is the same type of blower/ducting
system you have on your furnace.

But then lets not forget that buried loop I mentioned earlier. This involves 3200 feet of 3/4 inch high density polyethelene pipe buried in two 400 foot runs of trenches dug six feet deep and placed 10 feet apart. Suffice it to say that pretty much snaked over every available inch of our front, back and side yards. It looked like the mole from H_ll attacked our lot.

And in this case it was a big bright orange one!