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You Asked, Chu Answered

Department of Energy Secretary Chu answers questions from the public on home energy efficiency.

Ed. Note: Cross-posted from the Department of Energy's blog. To learn more about events happening as part of National Energy Awareness Month, check out our calendar.

Last week Secretary Chu invited you to submit your questions on home energy efficiency and the response was tremendous. We sifted through your questions and recently discussed many of them with the Secretary.

 Here are the resources that the Secretary referenced during the discussion:

While the Secretary covered a lot of ground during the course of our discussion there were some thoughtful questions that we didn’t have a chance to ask, so we decided to ask the experts at Energy Efficiency and Renewable Energy to weigh in. You can check out their responses below.

Mayank A.
Do solar panels function differently in winter or summer assuming the same amount of sunlight is available?
ANSWER: Solar panels depend upon sunlight to generate power. In summer, solar radiation is more intense than in winter, so electrical output is generally greater. In winter, both solar intensity and the number of hours of sunlight are decreased, which can mean lower electrical output. If, however, the amount of solar radiation (meaning number of hours of sunlight AND intensity of that sunlight on the solar panels) were exactly the same, the solar panels would function about the same.

David F.
What is best way to get a discount on Solar and Wind equipment?
ANSWER: One of the biggest challenges for renewable energy equipment is the upfront cost. Major power developers face the same challenge that families do -- how to finance that upfront cost. Because, after all, with renewable energy, the fuel is free. Once you buy the equipment, there's no incremental cost to purchase fuel since sunlight and wind are free. Of course, you have to maintain the equipment, but you aren't buying coal or natural gas on a daily basis to generate electricity.

A good way to get a "discount" on renewable energy equipment is to look for financial incentives. For homeowners, the federal government will provide a 30% tax credit for newly installed solar and wind energy equipment (geothermal heat pumps and fuel cells get a credit too) through 2016. Click here for more information. There may also be incentives offered by your state, check here for more information.

L Darryl D.
I'm currently ordering dual pane polyolefin interior storm windows. I was wondering if there's an acceptable durable low-emissivity film to boost those units' performance to an R-3 air space or so in addition to tightening up the single pane existing window. ... additionally, is there a climate zone where the ROI for geothermal (ground loop) heat domestic HVAC heat pump is too slow to compete with say an SEER 16 air to air heat pump and perhaps a DOE map of the point where the payback is neutral for either choice.

ANSWER: There are really two questions here, so let's split this up. Your windows question: Adding a low-e film to a dual pane window has the potential to increase energy performance, but it is somewhat dependent on your climate zone. An interior, thin film, double pane storm window as you suggested is a good solution, however over a long period of time the visibility can diminish. Another potential solution is a storm window with low e glass that also has comparable energy performance but will be more durable. Since these options can become complex, and are highly dependent on your climate and energy prices, it's probably best to contact a window professional for a specific solution for you.

On geothermal heat pumps: When deciding whether to install a geothermal heat pump (GSHP), calling an accredited professional is essential. They can help you understand if the local climate and geology are suitable, whether you have enough space and which ground loop option makes the most sense (e.g. horizontal, vertical, surface water). Currently the only reliable way to determine the return on investment of a GSHP versus 16 SEER air source heat pump (ASHP ) for your application is to request quotes from qualified contractors for each. Accredited GSHP installers can be located on the International Ground Source Heat Pump Association web site. Application of this technology is highly variable between specific sites. The Oregon Institute of Technology Geo-Heat Center cites costs of ASHP verses GHP (both in their optimal zone where GSHP is 50 to 100% more efficient than ASHP). Total installed cost (10.5 kW – 3 tons) for a 2000 ft² home with duct work and controls, ASHP and Gas with AC ~ US$ 4 to 5,000 ($1300– 1,700/ton); Surface Water GHP ~ US$ 7,000 ($2,450/ton); Ground-coupled (horizontal) GHP ~ US$ 8 to 9,000 ($2,700 – 3,000/ton). For additional information, click here. A major reason these vary so much—and they vary non-linearly—is due to differences in air, soil and water temperature.

In general, the efficiency of an ASHP drops dramatically when the air temperature drops below freezing. They stop working entirely and must be supplemented with electric heating during prolonged periods of cold. The USDA plant hardiness map is actually a good way to see in detail the lowest temperatures that can be expected each year in the United States. These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986. To find out more, click here. DOE is, however, funding research on ASHPs that will perform better in cold conditions.

Conversely, GSHPs experience efficiency declines (not as dramatic) when the ground temperature heats up. The GSHP efficiency also depends on the ground ‘s conductivity which is related to its geology and soil moisture content at 100 feet. To find out more, click here. DOE also is funding research on hybrid heating and cooling systems that are better adapted to efficient operation in warmer climates.

Several GSHP manufacturers have calculators on their web sites that assist with system comparisons. Links to all the members of the International Ground Source Heat Pump Association (IGSHPA), including manufacturers, can be found here.

Robert Wu (via e-mail)
QUESTION: In China, on-demand water heaters are widely used, and no one uses water tanks to keep hot water around all the time.

When we remodeled our home in California three years ago, I wanted to install on-demand water heater to save gas, but the architect said that it is not widely used in the US and not available in our market. Wouldn't it save energy to not keep hot water ON all the time? It will certainly save on having to install a big water heater tank. Or is it an issue of changing consumer behavior? I hope the market has changed since my renovation and that on-demand water heaters are available now.

ANSWER: Water heating accounts for 12-15% of energy use in U.S. households, so better efficiency for water heaters will have a significant benefit for American families. The good news is that water heating technology is getting more efficient. ENERGY STAR(r) water heaters are now available in a variety of forms, including high-efficiency gas storage water heaters (these are the most traditional format), gas condensing water heaters, solar hot water heaters, heat pump water heaters, and on-demand water heaters. Each of these types of water heaters has its own advantages, but all of them save you money over the non-Energy Star models. Consumers that replace a water heater today have many more choices in technologies (and savings) than they did just a few years ago. Add in Federal tax credits available until December 31, 2010 and there's even more savings. There may also be rebates available in your state.

Andrei P.
QUESTION: Is there some resource you recommend for helping homeowners evaluate whether particular improvements make sense for their homes? I imagine it's not trivial to replace the skill of a professional with easy rules of thumb, but I'd find something like that useful. Getting a professional to come over and make customized recommendations requires quite some effort.

ANSWER: The best approach is to use a professional - a professional home energy assessment can help you identify areas of energy loss and set a plan to start saving. You'll get a prioritized report to help you identify which improvements to make first. Some utilities and local governments offer free home energy assessments. Click here for more on what to expect from a home energy assessment.

But there are some things you can do yourself: You can perform a do-it-yourself energy assessment as well. The results are not as precise, but it may help you identify some easy savings opportunities. Click here for more on that visit.

If you have an older home, the odds are pretty good that you need more insulation. Insulating (or adding insulation to) an attic or crawl space can make a significant difference both in your family's comfort and your energy bills. Click here for more information.

Because energy efficiency is closely linked to regional climate conditions, it's hard to provide a guideline that works nationwide. A few things to think about:
*check your attic insulation, if you have four inches or less of insulation, you'd likely save by adding more *replace the light bulbs you use most often with ENERGY STAR Compact Fluorescent Lights. *airseal and caulk - check around windows and doors, if you can feel air movement, you need to airseal. Be sure to check around basement rim joists (where the floor above connects to the walls), that's often a place with no insulation at all.

Also, check out the calculators available here.

John Schueler is a New Media Specialist with the Office of Public Affairs