One of the greatest gifts our modern
human technologies have brought us is the ability to maintain safe comfortable
temperatures in our living and working spaces without the need to find blocks of ice
to cool down or firewood to keep warm. But of course we all now know the environmental
and climate costs of those technologies, most of which use fossil fuels in one form or
another, either directly for heating or indirectly via national electricity grids. According to
the International Energy Agency the use of air conditioners and electric cooling fans accounts
for nearly 20% of the total electricity used in buildings around the world, and that number
is much higher if you include mobile cooling in private vehicles and on public transport
plus industrial and commercial refrigeration for keeping food fresh and for chilling critical
products like pharmaceuticals. There's something like 3.6 billion cooling appliances in use today
all over the world and that number is going up by about 10 devices every second. And
as we move rapidly away from gas and oil and towards electric heat pumps for space heating
even greater demand will be placed on our grids. These things draw a lot of energy and many of them
use hydrofluorocarbons or HFCs as a refrigerant gas. HFCs aren't quite as disastrous as the
CFCs that were banned by the Montreal Protocol 30 years ago. They don't wreck the ozone layer.
But they're still extremely potent greenhouse gases - often hundreds of times more powerful than
carbon dioxide. So the race is on to find better solutions to the rapidly growing challenge of
heating and cooling with better energy efficiency and without potentially harmful emissions. Now
a British company looks like they've achieved precisely that with an elegantly simple system
inspired by this thing - the sterling engine Hello and welcome to Just Have a Think. Stirling
engines are an example of an external combustion engine. The energy that drives them comes
from outside the closed system, as opposed to an internal combustion engine where the fuel is
burnt inside the combustion chamber. So how does it work? Well in this little model I've got here
we've got two metal plates at the top and bottom and then we've got this little block of foam
sitting in an enclosed chamber in the middle. If I put the model onto something hot like
a cup of coffee the heat energy from the coffee warms up the bottom plate and that
makes the air inside the chamber expand. And as it expands it pushes this little piston
upwards. The piston is attached to the wheel via this rod, so as the piston goes up, the
wheel starts to turn. But the wheel is also attached to the foam block, so as it turns
it pushes the block downwards. That forces the air to flow past the block and come into
contact with the top plate, which is cooler. The cooling air contracts, pulling the piston back
down, which turns the wheel a little bit more. And as the wheel continues to turn it pulls
the foam block back up, forcing the air back down to the hot side, and the whole cycle starts
again. As long as there's a temperature difference between the top plate and the bottom plate then
the engine will keep running. In fact you could put this thing on top of a block of ice and it'd
still work, albeit with the wheel turning in the opposite direction, because the top plate would
then be warmer than the bottom plate. The greater the temperature difference between the two plates
the more efficiently the system will run, and conversely if there's no temperature difference
at all the whole thing grinds to a halt. But Stirling's invention is one of the few cycles
that can be run in reverse to effectively make it a heat pump instead of a heat engine. If I use
the energy in my arm to manually turn the wheel, or in a more sophisticated version if I attached
a drive shaft to it powered by a little electric motor, then the expansion and compression of the
air would make one plate hot and the other plate cold. And if that system was scaled up then you
could theoretically draw the heat or the cold off from one plate or the other depending on whether
you wanted to heat a space or cooler space. Sounds simple right? So why don't we run all our
heaters and coolers that way instead of using air conditioning units that contain all that horrible
hydrofluorocarbon refrigerant fluid stuff? Well it all has to do with something called
the Carnot cycle and whether a gas is expanding isothermally or adiabatically. I know - science
jargon! I know. The full explanation of the Carnot cycle is beyond the scope of this
video, but suffice to say it represents the theoretical maximum efficiency of a heat pump
or a heat engine. Isothermal just means constant temperature, so if a gas is expanded or compressed
isothermally it stays at the same temperature all the time. It's much more normal though for a
gas to be compressed or expanded adiabatically, which means its temperature increases or decreases
as it's compressed or expanded. To achieve the ideal efficiency of the Carnot cycle a Stirling
heat pump would have to run 100% isothermally so that the gas was able to lose all its heat energy
as it was being compressed and draw in enough heat energy to stay at a constant temperature while it
was being expanded. That kind of energy exchange might be possible for the gas molecules
right next to the outer wall of the chamber, but the molecules in the middle of the chamber
are a very long way away, so to achieve a fully isothermal cycle you'd have to run it extremely
slowly to allow time for all those molecules to either give up or take in energy. That's just
not practical for any real world application. You'd be waiting hours or days for your room to
cool down or heat up. So instead air conditioners and refrigeration units around the world today use
vapor compressor heat pump technology that's been around for more than 160 years and which relies
on those nasty refrigerants with very high global warming potential or GWP. And they still only
achieve about 40% of the Carnot cycle efficiency. But now this new system has been created that
takes the elegant simplicity of the Stirling cycle and applies some good old engineering lateral
thinking to the challenge of heat energy transfer to produce a working heat pump that can reach 60%
of Carnot without using any gases with high GWP values. The design is the brainchild of hydraulic
engineer Michael Crowley and is being developed by his company Fluid Mechanics who are specialists
in the design, analysis and modelling of hydraulic systems. Several prototypes have been built and
tested since the beginning of the project back in 2015. All of them are based on the principle of
pistons and cylinders to achieve a similar effect to this version of a Stirling engine known as an
Alpha Type. Essentially the gas in the expansion cylinder is heated externally and the gas in the
compression cylinder is cooled externally. That sets up the temperature differential needed to
make the pistons move to rotate the drive shaft, just like in my little model version. The gas
is able to flow between the two cylinders, which it does via this channel known as a regenerative
heat exchanger. The heat pump developed by Fluid Mechanics also has two cylinders, just like the
Alpha Type Stirling engine. In fact the working model will actually have another pair of cylinders
at the back to optimize the mechanical balance of the system. Each set of two pistons are attached
to each other via something called a Ross Yoke, which is a clever piece of existing technology
designed to keep them out of phase with each other by about 120 degrees. Again, very similar
to the Alpha Type Stirling engine. The gas is expanding and compressing, and we've also got a
regenerative heat exchanger moving the gas between the cylinders. So far so samey! But remember the
Fluid Mechanics system is set up to be a heat pump not a heat engine. That means the drive shaft is
providing the input power to move the pistons up and down rather than vice versa. So now we've
got to find a way of removing the heat from one cylinder and the cold from the other. The Fluid
Mechanics system achieves that in two ways. Firstly by using helium as the
working fluid rather than ambient air, and secondly by adding a series of thin
metal fins to the bottom of each piston. Helium molecules are much smaller than air
molecules so they can move much faster and that means they can transport energy more quickly too.
In fact the thermal conductivity of helium is 10 times greater than air, and according to Michael
you could just as effectively use hydrogen gas for exactly the same reasons. The helium gas is
held between the metal fins at the base of each piston. The distance between the fins is just
two millimetres, so the average distance that the helium molecule has to travel to get to a
fin is just 0.5 millimetres. And that means heat transfer out of or into the gas is extremely
rapid indeed. As each piston completes a cycle the fins are plunged into a sump of silicon oil
where they're quenched. Depending on which side of the system the quenching takes place, the oil
is either heated up a bit or cooled down a bit. A circulating pump moves the oil constantly
around an external circuit via a heat exchanger where it heats up water on the hot side and cools
it down on the cold side. To measure the basic system efficiency, Fluid Dynamics created this
test rig which looks a bit like something out of Back to the Future, but is in fact a very
carefully calibrated scientific instrument. Based on measurements of the pressures inside
the chambers, the rig demonstrated that it was achieving 95% isothermal efficiency. Very close to
that theoretical maximum of the Carnot cycle, with an overall real world working efficiency of about
60% once all the system losses are accounted for. The performance of all heat pumps improves
as the temperature difference between what you've got outside and what you want inside
gets smaller. It's a function known as the Coefficient of Performance or COP. So if the
ambient temperature is 19 degrees C and you want say your room or your car to be at 21C, then
your system will have no trouble at all. but if it's 45 degrees Celsius outside and you're trying
to get to 18 degrees inside then the COP number will drop significantly. That's the same for all
heat pump systems, and Fluid Mechanics' design is no different. Nevertheless, early test
results suggest that the Fluid Mechanics system will achieve a higher COP than a typical air
source heat pump available on the market today. And their current 2.7 kilowatt prototype is
capable of generating a temperature difference of 60 degrees Celsius between hot and cold. The next
development model will be a 10 kilowatt unit with improved technology that Fluid Mechanics expect to
reach temperature differences of about 80 degrees Celsius. That could happily run an industrial
freezer in a building where the external temperature was over 30 degrees Celsius, or if
it was configured as a heating device it could provide hot water at about 60 degrees Celsius when
the external temperature was less than minus 10! In principle the design can be scaled all the
way up to one megawatt of cooling capacity. Something that's attracted interest and funding
from the navy, who currently cool their ships with air conditioning units that leak refrigerant gases
all the time, making it extremely difficult for them to achieve their emissions reductions targets
as part of the Paris Agreement. So there it is. A system that achieves a 30% energy saving
versus the current technology with absolutely no high GWP refrigerant gases and which, by the
way, also operates much more quietly than a traditional refrigeration unit. And the potential
applications are everywhere, from air conditioners in buildings to refrigeration units on lorries
and even cabin heaters in electric vehicles. Fluid Mechanics reckon they're about
three years from full production capacity but if they can successfully bring this
innovation to market then it could potentially have a hugely beneficial impact on the energy
requirements of our rapidly warming world. If you've got feedback and views on this one, or
if you work in the HVAC or refrigeration industry and you've got insight that you can share,
then jump down to the comments section below and leave your thoughts there. That's it for
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hello moderators, if you do not feel this is 'close enough' to boring company news i understand if you want to delete it,
But this heat transfer technology will be a major reason why cities and counties will want bore tunnels all over the world in the thousands