Heat Pumps And Hot Showers  

WorldChanging has a post on the startlingly large improvements in energy efficiency to be had by using heat pumps to heat water.

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 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 Zealanders 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.