Advanced Search

Please click here to take a brief survey

Heat pumps: The Future has Hot Showers.
Craig Neilson, 19 Feb 08
Article Photo

Alex recently posted a charming video snippet that he described as "solutions porn" - the video shows a man in a dusty, un-named country installing a photovoltaic panel on his roof and enjoying a lengthy hot shower when the evening sets in. His family are in the next room boiling water and doing homework under a lamp. The 90 second spot took first place in the 2007 Commonwealth Vision Awards.

At first, I had a similar reaction to Rob Baxter's comment - that you'd never get that kind of energy from the rooftop setup shown in the video. Author Lucidpix has since commented on YouTube that the hot plate might have been a bit much.

But Lucidpix was too late, the unfamiliar feeling of doubt had thrown me into a fervent bright green tailspin of denial and I was determined to prove the video's apparent claim right.

From my reckoning, I'm convinced that the home in the video has a secret ingredient that is not shown: it's heating its water with a combination of a solar roof-unit and a heat pump.

A heat pump water heater removes thermal energy from a low temperature source like air, waste water or the Earth, and moves it to a high temperature water tank.

Electric heat elements are 100 percent efficient - so for each 1KW of electricity they use, they transfer 1KW of heat to the surrounding water.

In hot climates like the one shown, the electricity spent to drive a modern heat pump ends up heating the water at around 400 percent efficiency. Even in cooler climates, the efficiency of this process is around 250 percent. One hundred percent efficiency is not the maximum, in energy.

Heat pump systems have a continuous recovery cycle, so they work around the clock and into the night time when the air is a little cooler (this is when the video shows the hot water). It seems illogical, but even in cool climates there's more than enough thermal energy to heat water with no more electricity than it takes to run the mechanical work moving refrigerant and heat. Heat pumps are even efficient below freezing.

I met with Rod Innes, technical director of Energy Saving Concepts Ltd (ESCL) and he had some jaw-dropping statistics for me regarding the savings that would come from mass adoption of these solar convection heaters for residential hot water in New Zealand or Australia.

There are an estimated 1.1 million electric hot water cylinders in New Zealand, with 50,000 new units sold each year. Eighty percent of these new units are replacements, so assuming an even failure rate, the "fleet" is fully replaced in 25 years.

The consumption across all units in New Zealand is around 45 percent of domestic sector electricity and almost 20 percent of total annual electricity production. Heat pumps currently available on the market save around 70 percent of the electricity that would be used by an electric element water heater. Australia, which has similar usage figures, would reduce its annual carbon emissions by five million tonnes (PDF link) if heat pumps were widely adopted. If we replaced old elements with heat pumps as they failed (and installed heat pumps in all new houses), New Zealander would heat their water by solar convection as early as 2033.

The exciting opportunity here isn't just that 10 percent of the country's total electricity bill could be wiped, it's that there's still space for design innovation in heat pump systems. Rod showed me his key innovation - twisting the conductive tube that runs through coolant increases the surface area contact and improved conductivity by 300 percent. Adding a opposing twisted rod through the centre of the coil (a "turbulator") improves the heat exchange efficiency relative to space by a further twenty percent. That's an efficiency improvement to a mature product that already achieves between 250 and 400 percent efficiency. More details in the patent.


The video also shows a lamp and a hotplate. You'll need to use your imagination here, but I'm going to say that the incandescent bulb is actually a compact fluorescent bulb that's been cleverly disguised. The conventional electric heating element is also a trick: it's a 90% efficient induction cooker. We'll be a little generous (but not unrealistic) and say that she's saving 70% of the energy that an electric element would have used.

The solar panels have stored energy from the hot day in some batteries under the house, where their heat rises back to warm the floor (or the excess energy is fed back into the grid). The solar-assisted heat pump combination has the home's water cylinder at high temperature already, and the batteries/grid gives the induction cooker the boost it needs to bring it to boil. The compact florescent lamps in the three rooms shown would only require an extra 50 watts, easily drawn from solar-charged batteries.

The video is possible with today's technology. That's what's so exciting about the future.

Image credit: Thanks Flickr/T Buchtele!

Bookmark and Share


All that so-called "renewables" basically are is second hand nuclear energy, harvested from the environment. The geothermal heat of the earth is the result of radiation given off by uranium & thorium, hydro, wind, biofuels, and solar panels are powered by thermonuclear fusion within the sun, etc. Even fossil fuels are fossilized biofuels, fossilized photosynthetic nuclear fusion energy. Nuclear is the only green solution. Lets just build more reactors and capture the energy efficiently!

Posted by: pete on 19 Feb 08

Pete - that's akin to saying fire is a good source of home heating, so let's burn the house down. The point is about where you want your nuclear energy sources - personally I'd prefer mine to stay in the Earth and sky where they belong, rather than in leaky concrete boxes and holes in the ground we have to look after for the next 250,000 years.

Posted by: Andy Kenworthy on 19 Feb 08

I loved the spirit - and the facts - of your article. is this technology available in the US at this point?

Posted by: uli nagel on 19 Feb 08

Thanks, Uli Nagel! Heat pump technology is not new, but only now gaining popularity in New Zealand - surely available in the USA. Compact florescent bulbs are very common and popular in New Zealand, and I'm sure they are available in the US. Induction cookers are yet to catch on, but something I think every new kitchen should choose.

Posted by: Craig Neilson on 19 Feb 08

ok - so let me get this straight... we use PV panels at 15% efficiency to heat water through supposedly 100% efficient hot plates - they must be operating in a vacuum and have not radiative, conductive or convective losses?
Are there any real engineers around? Has anyone heard of solar hot water collectors that are proven (and have been used for > 100 yrs) at 70-90% efficient? These kinds of articles and video popularity remind me of the alchemists turning lead to gold. We need real science not pop science!

Posted by: Fred Klammt on 20 Feb 08

Fred - the method is that the solar panels are powering the heat pump, which transfers heat to the water from the air, earth or another body of water. Of course, by doing this it also makes the heat source colder.

By that method, the system has more than 100% electrical efficiency - of course there are losses elsewhere, but the heat transfered is greater than the electrical energy spent on it.

I think solar hot water collectors are great when there's no electrical source handy, but they depend on it being sunny outside (and at these times you may not want hot water). SWHs have slow recovery cycles, whereas heat pumps can bring water to the boil even when their panels are covered in ice.

Posted by: Craig Neilson on 20 Feb 08

Craig: Thanks for your reply. How do you figure 100%+ efficiency in a total system energy, mass balance equation? PV panels are at best 18% efficient. I can see the 'geothermal' heat pump element helping out, but only to preheat. Solar thermal uses storage tanks and fresh water modules (plate-plate heat exchangers, counterflow turbulent/laminar flow HX's, etc) that are much more efficient at converting, storing and using hot water for use during cloudy days and at nite. This science has been around a long time.
Using PV to generate hot water is extremely inefficient, but it is the 'new' solar thing and everyone wants it. Stay tuned to solar thermal's upcoming new wave.

Posted by: Fred Klammt on 20 Feb 08

Thanks, Fred. I think we may be talking about the same thing with solar-thermal heat exchanges.

In total, energy transferred to the water by this system is, of course, Thanks, Fred. I think we may be talking about the same thing with solar-thermal heat exchanges.

In total, energy transferred to the water by this system is, of course, <100% (even if the electrical efficiency is much higher). Heat pumping/exchanging is not just a pre-heating measure, it's a highly efficient way of moving abundant heat energy to the places you want it. But this process does need a bit of electricity to run the mechanical work - which is where I'm suggesting the PV's come into the picture.

Posted by: Craig Neilson on 20 Feb 08

I have been reading about these renewable engery sourses for a couple months now. But, rarely do any of the articales actually back themselves up with real world working devices. In the cause of "solar convection heaters" I can find only the old style water heaters, solar powered, with the 40 to 80 holding tank.

I understand this site is more theoretical and not practical, but wouldn't it be nice if a web link was included. There is one linking to Google for patent information. But, not one for the practical application.. If this web site is aout changing the world, shouldn't some of the ideas move from the living room to the garage were some of us might make them more "do-able" for others as well.

Posted by: Mark Repovich on 20 Feb 08

Mark, heat pump water heaters are highly available and enjoy quite a bit of competition in the marketplace, so I've been a bit careful not to name producers in this story. But here's the US Department of Energy's consumer guide. My neighboring city of Waitakere, which is known for its green initiatives, has a page about the eco-friendly home they talk about a device from Daikin. Here are some heat pumps that the "Energy Star" program recommends.

Posted by: Craig Neilson on 20 Feb 08

OK people, doesn't seem like anyone was actually paying much attention to the video..
At time: 37-38 seconds, on the left side of the screen one can clearly see the solar hot water heater and storage tank on the roof. The fella was installing his second photovoltaic panel, must of already had the first.. Also note that the optimum angle for solar (PV or thermal) panels near the equator is straight up or any where near that. Anyway the incadescent light bulb and electric stove top burner were probly just exagerations to get across the general concept. What was not shown was a battery system, but streetlights would indicate available grid - therefore grid-tied system. The PV panels looked like about maybe 40-80 watts each (guessing). So for a grid tied system, 6 good solar hours might offset an hour of 60watt incadescent and maybe 15 minutes on the stovetop... engineer whose intalled these things both in US and on the equator...

Posted by: John on 20 Feb 08

I think you need to do a little more digging and fact checking, including real power output, real-world coefficients of performance, etc. I don't say this to disparage heat pumps, which can be a useful technology in certain cases. I say it because, Craig, as someone who is essentially a journalist, you haven't really done your homework. Dig deeper, and don't say "Eureka!" after several hours of web surfing. What you advocate is worth doing, but it's much harder and more complicated than you're depicting. I love WorldChanging for its good news, but you're influential enough now that you have to be careful not to inflate your claims.

Posted by: David Foley on 21 Feb 08

Pete's comments about nuclear energy should not be dismissed so readily. Reactor technology has improved drastically during the last 30 years. France now generates more than 70 percent of its electricity with nuclear reactors, and there's never been a significant accident there. Germany, Japan and Britain generate approximately 25 percent of their electricity with nuclear reactors, and they haven't had any disasters, either. There is no silver bullet; many and various forms of carbon-free fuel generation are going to have to be implemented on a large scale in the next few decades. To exclude the nuclear option because of outdated and ill-informed fear of catastrophic reactor leaks is shortsighted and foolish.

Posted by: Timothy Sullivan on 24 Feb 08



MESSAGE (optional):

Search Worldchanging

Worldchanging Newsletter Get good news for a change —
Click here to sign up!


Website Design by Eben Design | Logo Design by Egg Hosting | Hosted by Amazon AWS | Problems with the site? Send email to tech /at/
Architecture for Humanity - all rights reserved except where otherwise indicated.

Find_us_on_facebook_badge.gif twitter-logo.jpg