Efficiency, Cooling Power Demand, and Heat Pumps
In a previous post, I wrote about
new ultra-efficient air conditioners being tested in India, where high humidity
levels tend to reduce efficiency. This is one cooling innovation that is most
applicable to humid climates. Here, I will focus on more widely applicable
cooling innovations. One important part of the super-efficient air conditioners
tested in India is the use of more efficient refrigerants like R32, with
potential for the use of propane-based R290.
Power demand for space
cooling, mainly air conditioning, is expected to grow considerably, about
one-third faster than power demand for AI data centers. Demand for each is
expected to triple by 2035. More than 80% of new A/C demand is expected to come
from developing countries in response to economic growth. Most are in tropical
and subtropical regions where extreme heat is common. David Elliott for
Mitsubishi Heavy Industries (MHI) explains how cooling impacts power grids in
these regions:
“The capacity of the grid in the hottest regions, for
example, needs to cover a doubling of electricity demand compared with milder
months. In these places, cooling can account for more than 70% of peak
electricity demand.”
As noted in the graph below, India is expected to be a major demand driver for cooling.
More efficient air
conditioners, stronger insulation, better shading, green walls, and green roofs
can all help reduce heat island effects in urban environments. In contrast,
traditional air conditioners also give off waste heat, which can contribute to
urban heat island effects.
The secret power of
air-source heat pumps is reliable and much cheaper air conditioning compared to
traditional electric air conditioning. I enjoy mine very much!
The IEA emphasizes that
regulations, information, and incentives are important policy moves to support
sustainable cooling, as noted below. While I agree that incentives are good, I
don’t like the idea of mandates for building energy optimization.
District Cooling
District cooling projects are
being explored in many cities where water is chilled at a central plant and
then distributed to buildings via underground pipes. There are distribution
lines and return lines. This kind of collective cooling provides economies of
scale over individual cooling units. These projects are achieving 20-35%
reductions in electricity use compared to traditional A/C. The chiller plants
used for district cooling are centrifugal chillers. MHI makes these and their
pumping units. There are ongoing district cooling projects in Dubai, Saudi
Arabia, Paris, Munich, Hong Kong, Singapore, and Toronto. Elliott notes:
“District cooling systems are also often combined with
thermal storage, in which overcapacity during the night is stored for use
during the day. In Singapore’s Marina Bay financial district, one of the
chillers supplied by MHI can be switched to ice-storage mode during off-peak
times when the cost of power is lower, creating a huge ice storage tank that
can chill water throughout the day.”
Hotels, hospitals, and
universities may be able to integrate district cooling. Chilling can also be
achieved or contributed to by natural cold from rivers, groundwater, lakes, or
the sea. Chilling ice at night and using it for cooling during the day can be a
feature as well.
For large tropical cities
like Singapore, district cooling offers a more efficient method of cooling. The
city-state hosts the world’s largest district cooling system. According to John
McKenna for MHI:
“Based around a central subterranean plant, the system
channels water along 5 kilometers of closed-loop pipe network, giving it the
power to lower temperatures across a substantial neighborhood of buildings.
Cold supply water flows along the pipes, entering the heat exchanger in each
building, where it absorbs heat and cools the building before making its way
back to the central plant.”
A centrifugal chiller
converts refrigerant from liquid to gas and back again to chill the water in
the system’s pipes, but it does it on a larger scale than other refrigeration
devices.
“The largest chiller units measure around 12 meters
long, six meters tall and wide, and weigh more than 160 metric tons, each with
a cooling capacity equivalent to approximately 3,600 residential air
conditioning units. The centrifugal chillers use a highly efficient compressor
design with an aerodynamic profile that minimizes mechanical energy loss.”
The Marina Bay district
cooling system in Singapore utilizes 16 centrifugal chillers, including one
that can be switched to ice-making mode. It is estimated that the district
cooling system cuts energy demand for cooling by 40%. Maintenance costs are
lower for district cooling since they can be pooled. Less space is needed than
would be needed for above-ground chilling systems.
Absorption Chillers
Chilling can also come from
heat! In Vienna, waste heat from a trash incineration plant is used to power an
absorption chiller. Absorption chillers utilize refrigerant cycles of
absorption and condensation to efficiently cool. In Europe, it has become the
trend to lay combined cooling and heating networks at optimum temperatures to
minimize heat loss or gain.
According to Thermo max:
“The process of absorption cooling is dependent on a
thermochemical ‘compressor’. Two different fluids are used: a refrigerant and
an absorbent. The fluids have high “affinity” for each other, which means one
dissolves easily in the other. In a water-lithium bromide vapour absorption
refrigeration system, water is used as the refrigerant while lithium bromide
(Li Br) is used as the absorbent. In the absorber, the lithium bromide absorbs
the water refrigerant, creating a solution of water and lithium bromide.”
Geothermal Cooling
As noted, the demand for
cooling makes up 70% of power demand in some cities. An article by Source
Geothermal notes that cities in the Middle East are in this category and can
benefit from geothermal cooling technology. This can be in the form of
ground-source geothermal, where cooler ground temperatures facilitate optimized
geoexchange of heat for hot areas. It can also be in the form of utilization of
heat generated by deeper geothermal in closed-loop horizontal well configurations,
like the company Eaver is building. They also note that geothermal can help
power the desalination plants that are vital for the region. The Middle East
region as a whole has been assessed to have abundant geothermal resource
potential for heat, cooling, and electricity. They note that closed-loop
geothermal can function as thermal storage for excess renewables. They also
note the engineering culture of Saudi Arabia, where there is a trained
workforce and supply chains for oil & gas drilling and producing. There is also
heat.
“Several geological basins—particularly in western and
central Saudi Arabia—show characteristics suitable for superhot-rock geothermal
systems, which operate at temperatures exceeding 400 °C. These resources could
deliver up to ten times the power of conventional systems per well. In
parallel, the same deep formations could serve as thermal energy storage sites,
holding surplus solar or wind energy for later release as cooling or power.”
They note that according to
Robert Stephens’ Environmental Cooling Challenges presentation:
“We believe the time has come for geothermal cooling to
step out of the shadows. It’s scalable, predictable, and uniquely suited to the
world’s hottest climates.”
Some places in the U.S.
Southwest are the most suitable places in the country for geothermal storage
and cooling.
Cool Roofs
A cool roof is designed to
reflect more sunlight than a conventional roof, absorbing less solar energy.
Roofs can get as hot as 150 deg F, and cool roofs can lower roof temperatures
by as much as 50 deg F. The downside of cool roofs is that they can incur a
winter heating penalty. For this reason, they are more optimizable in warmer
climates.
Green roofs that utilize
vegetation are another form of cool roof. These are ideal for urban buildings
with low-sloped or shallow-pit roofs. These are more expensive, heavier, and
harder to maintain than other roofs. The cooling mechanism is different for
green roofs. The evaporation of water from plant surfaces gives off heat,
cooling those surfaces.
References:
Cooling
buildings will drive power demand — new tech can help. David Elliott.
Mitsubishi Heavy Industries. Spectra. November 11, 2025. Cooling buildings will drive power
demand — new tech can help | Spectra by MHI
Below
the surface of Singapore lies the future of keeping cool. John McKenna. Mitsubishi Heavy Industries. Spectra.
July 28, 2020. Below the surface of Singapore lies
the future of keeping cool | Spectra by MHI
Geothermal
Cooling: The Middle East’s Next Clean-Energy Frontier. Source Geothermal. October
27, 2025. Geothermal Cooling: The Middle East’s
Next Clean-Energy Frontier – Source Geothermal
District
cooling: A better alternative to air conditioning? Gero Rueter. DW. September
8, 2023. District cooling: A better
alternative to air conditioning? – DW – 09/08/2023
How do
absorption chillers work? Thermax Global. How do absorption chillers work? -
Thermax | Trusted Partner in Energy Transition
Centrifugal
Chiller. Mitsubishi Heavy Industries. Centrifugal Chiller | Mitsubishi
Heavy Industries
Staying
cool without overheating the energy system. International Energy Agency. July
28, 2025. Staying cool without overheating the
energy system – Analysis - IEA
Cool
Roofs. U.S. Department of Energy. Cool Roofs | Department of
Energy
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