Posts Tagged ‘hybrid’

Heat pump water heaters–an interesting choice, but not a one-size-fits-all solution

March 19, 2011

An evolving water-heater technology has been moving more mainstream over the past couple of years.  This technology uses a heat pump (think air-conditioner working in reverse), to heat the water.  I’ll focus on GE’s GeoSpring Hybrid water heater for discussion purposes.

GE's "hybrid" water heater

The good news is that this technology is ready to roll.  Heat Pump Water Heaters (HPWH) can be twice as efficient as a standard electric resistance water heater, and that increased efficiency can add up to big savings over time.  This can be a great choice for many homeowners.

It’s not for everyone, however.  In most cases, if you heat you water with natural gas, it won’t make sense to switch to the heat pump.  This does depend on things like the gas and electric utility rates, usage patterns, and climate.

The GE model is only available in a 50-gal tank, and it won’t provide either the capacity nor the efficiency benefits for high-usage situations.  The heat pump is more efficient, but it takes long to recover—that is it takes longer to make the water hot.  To compensate for this there is a standard heating element that you can use to speed things up in “high demand” situations.  In fact, you can set it to standard mode and it will function just like a regular electric resistance heater.  However, the more you heat water using the electric element instead of the heat pump, the less you save.

Because of the compressor and fan, a heat pump water heat does make some noise while it’s running—about the same as a full-size microwave.  Since water heaters are often in basements, garages, or otherwise isolated from the living space, this may not be an issue.  But it’s something to be aware of.

In simple terms, the heat pump uses heat from the air and transfers it to the water.  A secondary effect is that it cools the air around it.  This is actually a nice side benefit in cooling climates.  However, in colder climates where you’re paying to heat your home for much of the year, in some sense you’re robbing Peter to pay Paul, and I don’t think this technology makes sense in the northern U.S., snow country.  In the north, where inlet water temps (the temperature of the water is it hits your home from the city lines or your well) can be quite cold, you’ll also be in the “high demand” mode much of the time, again, reducing your savings.

Height can also be issue, and this won’t fit in some shorter crawlspace where a “low-boy” water heater is needed.

Bottom line:  A HPWH can be good choice in cooling climates where you heat your water with electricity—especially where electric rates are high.  Not the best choice if you already heat with gas or see snow for half the year.


What’s Greener: A Prius or a Home Energy Retrofit?

August 5, 2010

Thinking about purchasing a Prius to reduce your environmental impact?

You may want to consider all of your choices before stepping into a shiny new hybrid because in many cases, investing in a home energy retrofit may have a bigger impact on your carbon footprint and a faster return on your investment than purchasing a Prius.

number crunching

The Prius vs. A Home Energy Retrofit

So, how does buying a Prius compare with improving your home’s energy efficiency in terms of reducing your carbon footprint and seeing a return on your investment? While these the answers to this question will vary depending on the driver and the driver’s home, our team did some research and found that what might shrink your neighbor’s carbon footprint might not be as cost effective for you.

We’ve crunched a bunch of numbers in hopes of getting people thinking about energy efficiency from a new perspective. The points made here are not meant to convince you that you shouldn’t buy a Prius. We’re using the Prius as a symbol of a more fuel-efficient way to get around; we could have done the same calculations with any fuel-efficient car.

Let’s do a little example to illustrate.

Meet Rebecca — An average driver with a home built in the ’90s. Rebecca drives 12,000 miles per year in a car that gets an average of 23 mpg, and she lives in a house built in 1992.

Buying a Prius:

Rebecca would double her fuel efficiency to 46 mph by purchasing a new Prius. As long as she continues to drive 12,000 miles per year with gas costing $3 a gallon, Rebecca will:

  • Use 267 fewer gallons of gasoline per year
  • Reduce her annual carbon footprint by 1,530 pounds
  • Save $800 in fuel every year
  • See an annual 3.2 percent return on her $25,000 investment

From a carbon footprint perspective, the manufacturing of a new Prius is an energy intensive process – the equivalent of consuming 1000 gallons of gasoline. So, Rebecca will spend the first four years with her new Prius paying off the “carbon debt” associated with making the Prius.

Cost-Benefit of a New Prius for Rebecca: $25,000 invested, 3.2% ROI. Assuming she keeps her car for 7 years, her average annual carbon savings will be 655 lbs per year.

Making Home Energy Upgrade: In a 1990’s era home, comfort and indoor air quality issues are common, and duct sealing is typically the single greatest opportunity for energy savings, followed by air sealing and improvements in the ventilation system. In a house of this era, it is reasonable to expect a savings of 10 – 30 percent in energy efficiency from a $3,000 investment.

Let’s say Rebecca consumes 12,000 kilowatt-hours (average residential consumption) of electricity per year in her home, and purchases her electricity at 10 cents per kWh (the national average). If she improves her home’s efficiency by 20 percent, she will:

  • Save 2,400 kWh of electricity per year
  • Lower her annual utility bills by $240
  • See an 8 percent return on her $3,000 investment
  • Reduce her carbon footprint by 1,360 pounds (with coal as primary fuel source)

Cost-Benefit of an Energy Retrofit for Rebecca: $3,000 invested, 8% ROI, annual carbon savings 1,360 lbs.

P.S. — Rebecca might be able to save a big chunk of the initial investment if she took advantage of all the tax credits and other incentives for retrofitting her home.

Which is the Greener choice?

In this example, an audit and retrofit of her house will provide Rebecca — an average mileage driver in average mileage vehicle living in a newer house — with a greater return on her investment and nearly twice the reduction in her carbon footprint as buying a Prius, for one-eight of the cost.

Of course, we left out a lot of detailed factors on both sides in an attempt to simplify the numbers. But if you think we missed something important, or you’re in Toyota’s marketing department and you want to argue with us, contact us and share your thoughts.

What is the greener choice for you?

Whether you’re better off retrofitting or buying a Prius depends on your unique set of factors: what era house you live in, how much you drive, your current vehicle’s mpg, etc. However, there are tremendous opportunities to reduce your carbon footprint and fuel costs, both at home and on the road. And, while choosing a more fuel efficient vehicle is an obvious step towards reducing your carbon footprint, investing in a more comfortable and energy efficient home can often provide an equal, if not greater, reduction in your carbon emissions — and, in many cases – at a fraction of the cost!

Scott Case is the VP of Product Management for, a company dedicated to making energy efficiency easy and accessible for homeowners throughout the U.S. through tools and resources such as an online energy audit and a directory of energy tax credits and rebates.

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