This is promising: Ecogeek reports on a new GE water heater that could cut energy consumption in half. The trick: it uses a heat pump to preheat the water coming into the tank.
I’ve waxed rhapsodic about the magic of heat pumps before. Start with a glass of lukewarm water, and a heat pump can turn it into a half glass of warm water, and a half glass of cold water, in a process that takes less energy than warming up a half cup of water on a stove top. If done right, heating your home with a heat pump—particularly one that draws heat from water that’s circulated underground—can be more climate-friendly than even the most efficient gas furnace. So this new heater is really just an application of a tried-and-true technology, but in a slightly new way.
The heater isn’t commercially available yet, but the announcement coincided with the release of new Energy Star ratings for hot water heaters. (Both press releases were dated April 1, but I don’t think anyone’s pulling my leg here…) Obviously, it’s a little premature to rave about a technology that’s not even available in stores yet. After all, nobody knows whether the technology will pan out, or whether any increased sales cost will be worth the energy savings.
Still, the announcement is a useful reminder: there are loads of efficiency opportunities left out there, and we don’t have to wait for radically new technologies to capitalize on them. Heat pumps, have been around since the days of Lord Kelvin; and household water heaters consume more electricity than home lighting. Still, it’s taken over 150 years to put the two needs together.
If I had to guess, there are plenty of similar opportunities out there—energy-saving technologies that are perfectly obvious, and are just crying out for a little bit of capital and engineering muscle. (For instance: why doesn’t my fridge connect to the outside world? In wintertime, there’s plenty of cold air for free, just outside my window. In summertime, the hot air from the fridge’s air pump gets recirculated into my already-overheated house. Seems like a problem looking for a solution. Any takers?)
Matt the Engineer
Any takers?”A very simple and inexpensive refrigerant-to-water heat exchanger connected just before the refrigerant-to-air heat exchanger on the back of one’s refrigerator would be a simple way to preheat water to your hot water heater. It would take perhaps $5 worth of parts if mass-produced into a refrigerator, but save dozens to hundreds of dollars a year. Plus, if you don’t hook it up to anything then it functions exactly like any other refrigerator (which is how most users would use it at first).This would make your refrigerator more efficient, recover heat energy in the summer, and in warm climates (or anywhere with air conditioning) reduce cooling energy.
Richard
There are huge savings in energy and carbon emissions to be had by making our buildings greener. Having something like this in hotels and businesses would be a nice start. Then I’d like one, for those in our family who take very long showers. Someone is going to make quite a bit of money along the way.
Alex
Clark:http://www.worldchanging.com/archives/007951.html
Matt Leber
Clark, you and I think too much alike. I have thought about ways to tap my fridge for “free hot water” for quite some time. But then I realized this: My fridge uses just over one kilowatt per day (465 kWh per year according to the Energy start rating). Even if you could cut these numbers by 50%, you are only talking about $20 or so per year in saved electricity bills. Put a different way, you’re talking about roughly 800,000 BTU of “free hot water”—not particularly earth shattering. Even that is being charitable since I’m assuming 50% savings over 365 days. I suspect once you insulate the home really well, install efficient lighting, tighten down the efficiency of the home heating and hot water systems and eliminate phantom loads, the bulk of the work in the home is done. Alex’s post regarding the Freeaire refrigeration shows that these kinds of systems will be best utilized for commercial purposes. Ever been in an ice cream shop in summer? (Side note: There should be a law requiring ice cream shops to use heat pump water heaters.) Another growth area: Co-locating businesses with symbiotic energy requirements. I’ve always thought a good combination of businesses would be an ice-cream shop next to a Laundromat. Or how about a data center next to a food processing plant… Then we’re talking serious energy savings.
Matt the Engineer
Let’s look at Matt’s refrigerator in more detail. In the winter, we’re taking heat that is rejected indoors and moving this to hot water heat. This will make the refrigerator more efficient but not really save natural gas (saving at the water heater, but having to heat the house more).In the summer, we’re saving from a more efficient refrigerator and saving natural gas, since we wouldn’t be heating our house. If this were a warm region we’d also be saving air conditioning costs.I’ll use current electric rate: $0.097/kWhRefrigerator savings = 465/2*.097 = $22.50/year savings.We’ll call winter 8 months long (sigh). The energy saved for hot water isn’t the same as the refrigerator uses. A refrigerator is a heat pump and moves heat from one place to another. Assuming a coefficient of performance of 1 for a normal refrigerator and 2 for water-cooled refrigerator, This means that in our water cooled refrigerator one unit of energy moves two units of energy. Water heater savings = 465/2*3*(4/12 months)*.097 = $22.50/year savings.So Matt’s refrigerator would save him around $45 per year*. This doesn’t sound like much, but if this really was a $5 piece to add to a refrigerator and perhaps $100 to pipe up the water heater for the first time (though this could be much more depending on his house), then this is around a 2.5 year payback. That’s not bad. That’s $900 over the 20-year life of his refrigerator. It sounds like a pretty good deal to me.Although I admit it’s hard to get excited over $45 a year if enough people take this step then we’re looking at serious greenhouse savings.
Matt the Engineer
In 1995 there were 106 million refrigerators in the US. If we added heat recovery to these refrigerators (which should be due for an update by now), we’d save 49.2 billion kWh/year – which would switch off around 36 coal power plants working at full capacity.
Matt Leber
Hmmm… This is what happens when I start dabbling in engineering…I’m still a little suspicious of the details, but I see where you are going with this. The question now is how much all of the plumbing and labor will cost to connect my fridge to my hot water tank. Oh, and don’t forget the electricity to pump the water from the fridge to the hot water tank.If you really think this is possible, I have a built-in fridge located directly over our utility room where our hot water tank sits. (If you cut a hole in the floor under the fridge, it would literally drop on top of the hot water tank). I don’t think you could find a more ideal setup. Care to void the warranty on our fridge? 😉
Dave Brook
Another company with a heat pump water heater is the E-Tech (http://aers.com/etech_residential_water_heating.html). While they are expensive, they are certainly a good investment for a family with larger hot water needs (better payback than solar), especially if they are heating hot water with propane. As discussed, using heated house air is not a good application for HPWHs. A good location for one is in an unheated basement, attic or garage in a mild climate. In new construction the best application is installed as part of a whole-house ventilation system (in Oregon the state Residential Energy Tax Credit provides a substantial incentive ($560) in these applications.The California Energy Commission’s PIER program looked into refrigerator-water heater combo units a while back and while they’re certainly technically feasible, as the discussion above shows, I wouldn’t hold my breath – figuring how to keep the tank close to the refrigerator, etc. will make them difficult to install. I could imagine some high end built-in refrigerator company offering it as an option for new homes. I’m told that in Japan multizone minisplit heat pumps have a water heater option.For energy bozos: the waste heat from a standard refrigerator is not wasted in the winter but contributes to a warmer house (and possible air conditioner run time) in the summer. They provide as much summer cooling as a small window air conditioner.
Matt the Engineer
Matt, You don’t need a pump for this heat exchanger. Just split off your main water line, through the heat exchanger, and into the HW heater. The only reason you’d need any pumping is if you already had very low water pressure – a shell-and-tube heat exchanger won’t reduce pressure much.In new construction or in a case such as yours, installation would be simple – involving perhaps 30 minutes of skilled labor or 3 hours of homeowner labor (including runs to Lowes). All you’d need to do is cut the water inlet to your water heater, install fittings to PEX tubing, and run the PEX up to threaded connections at the refrigerator. PEX is flexable and easy to install.However, that assumes there’s a shell-and-tube heat exchanger built into your refrigerator (there isn’t). To actually install one after-market would be quite difficult, involving draining the refrigerant, cutting into the refrigerant line, brazing on a heat exchanger (not to mention designing a heat exchanger and having it manufactured to your specifications), then refilling the refrigerant.This is really something that would have to start with the refrigerator manufacturer, likely as a green bullet point for sales.
MRBeyer
I had heard of this idea from a co-worker. How difficult would it be to build a shell around the coils of an existing refrigerator and run your supply line through there then on to the water heater?