Letters: September/October 2007

Approaching Zero Energy

In reading the article “Zero-Energy Manufactured Home” (May/June ’07, p. 24), I expected to see net-zero-energy use for the year.  There is no definition for “zero-energy,” but the article suggests “affordable homes that create as much energy as they need each year.”  However, as I labor through the data, it looks like the home consumed 10,730 kWh of electricity, without knowing how the thermal energy provided by the solar hot water system was accounted for.  The way the information is presented, it is not clear how much water-heating energy was consumed, and how the measurements and conversions were made. 

The data show the 4.2 kW solar PV system provided 2,820 kWh, or a load factor of less than 8%, without describing whether inverter losses were included, or if the collectors or the home are expected to last long enough to pay for them.  There is also no mention of the economics, or what makes this home affordable.  My arithmetic infers that this manufactured home used about 7,900 kWh of purchased electricity.  How is that zero energy?
 
Larry Spielvogel, PE
L. G. Spielvogel, Incorporated
King of Prussia, Pennsylvania

Author Mike Lubliner replies:
We never expected this all-electric manufactured home to be an affordable net-zero-energy home.  However, “Affordable Net-Zero-Energy Manufactured Homes” is a long-term programmatic goal of the DOE Building America and Bonneville Power Administration research sponsors.  Few have been able to reach this goal to date, but work continues. Had our budget and roof area allowed us to triple the size of the PV system, we might have achieved net-zero energy.   
We expected better PV performance, but the inverter and the battery backup configuration reduced performance.  Had we to do it over again, we would not have invested in the backup battery system, and instead would have put the money into more PV panels. 

We have no idea how long the solar domestic hot water system and PV system will last. 

The article graphics give the monthly use, and the article summarizes the daily electric use, for space, water, and other. Your math summary is correct!


Water-Wise Gardening

In response to the Water/Energy Special Issue, I have a comment about irrigation. Much of the problem with irrigation is the fact that we want to have plants, any plants, any time, all the time, in our outdoor space.  Plan the outdoor space around the climate restrictions (choose dry-climate-adapted plants in dry climates); use drip irrigation techniques; minimize turf area; mulch, mulch, and of course, mulch.  If we must have wet-climate plants in a dry-climate, design the irrigation system to apply the required water to those plants, as they need it, not to all the plants because the wet-adapted plants need it. Also, there are other controllers that control to the evapotranspiration rate:  Rainmaster Eagle (commercial grade), Rain Bird ET Manager, and the Hunter ET system.  All are proven water savers.  Plus, optimize the system: minimize spray overlap and onto pavement, and never irrigate in daylight.

On the municipal side: Some communities require green lawns and then turn around and ding the homeowner if the system oversprays  onto the sidewalk.  Removing the requirement would save a lot of water.  The wet-climate-adapted lawns would die, of course, but different methods of landscaping would come to the fore (search “xeriscaping” on the Web), and just maybe we could adapt to a new world of natural beauty.
 
Robert Grindrod
Conservation Services Group
Westborough, Massachusetts


Errata

Unfortunately. Monroe Infrared Technology, Incorporated, was not listed among the trainers in the Training Guide for Home Performance Professionals (July/August ’07, p. 28). The company offers in 2, 3, 3 ½, and 4 ½ day classroom/hands-on training programs nationally on the use of thermal imaging systems for all building weatherization and home performance professionals. Certification and American Society for Nondestructive Testing qualification is offered through Infrared Training Center, Academy of Infrared Training, and Snell Infrared.

Monroe Infrared Technology
PO Box 1058
Kennebunk, ME 04043
Tel: (800)221-0163
E-mail: miti@monroeinfrared.com
Web site: www.monroeinfrared.com

The contact information for Pure Energy, another national home performance trainer, has changed since publication of the Training Guide. The current contact information is

Pure Energy
10 N Bausman Drive
Lancaster, PA 17603
Tel: (717)293-8990
E-mail:
tsterner@pureenergyaudits.com
Web site:
www.pureenergyaudits.com
 
A letter attributed to Jim Wickham on p. 4 of the July/August ’07 issue should have been attributed to Doug McEvers.

Finally, in the Water/Energy Special Issue, the article, “Southface Eco Office To Achieve 80% Water Savings” states on p. 16, “The urinals in the Eco Office are either Sloan Waterfree or Clivus Multrum foam-flush toilets.”  In fact, the Clivus Multrum foam-flush toilets are not urinals. The editors regret the errors.