FEBRUARY 2020 · VOLUME 19.1

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Air apparentHow residential AC can save the world.

C O V E R F E A T U R E

The Global Cooling Prize is addressing one of the pressure points of climate change by challenging the world’s innovators to build a more sustainable room air conditioner. Eight finalists have now been chosen,

but as Mark Vender reveals, there may be many winners.

Innovation prizes are a sure‑fire way to capture our imagination. Whether it’s designing a solar‑powered vehicle to travel from Darwin to Adelaide, or a robotic spacecraft to travel from Earth to the Moon, these competitions hold the promise of great innovation and achievement. What better arena could there be for human endeavour than setting a lofty goal and letting participants decide how to reach it?

The Global Cooling Prize brings this kind of excitement to a topic that, until now, has not generated much public interest: air conditioning. But as we become more aware of the climate emergency, that is changing.

There are 1.2 billion room air conditioning units in service around the world today, and it is estimated

this number will increase to 4.5 billion by 2050. Many of these are inefficient and will place a significant burden on electricity grid infrastructure and consumers in developing countries. Transformation of residential cooling technology through innovation can improve people’s health, productivity, and wellbeing, all while avoiding runaway climate change.

The prize is a timely challenge to innovators around the world. The goal: to design a residential cooling solution that will have at least five times less climate impact than a typical unit on the market today. Such a system must reduce indirect emissions (energy use), as well as direct emissions (global warming refrigerants).

The winning solution must also operate within limits on refrigerants,

water, full‑load power consumption, emissions, volumetric size, materials, and operational requirements. And perhaps most importantly, it must be affordable to typical consumers, costing no more than twice the retail price of today’s standard units at assessed industrial scale.

The eight finalists – announced at a ceremony in New Delhi in November last year – each received US$200,000 (AU$291,000) to develop and ship their prototypes to India for testing during the country’s summer, starting in May.

The overall winner will be announced in November of 2020 and awarded more than US$1 million (AU$1,454,000) in prize money, as well as commercial opportunities to scale the technology and take it to market.

Air apparent

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WHO MADE THE GRADE?In total, 139 detailed technical applications were submitted, and these were whittled down to just eight finalists. These include some of the world’s largest AC manufacturers: Daikin, Gree, Haier, Godrej and Boyce.

Iain Campbell, senior fellow at the Rocky Mountain Institute (RMI) – one of the organisers of the prize –says this was a gratifying result.

“There are many prizes where the only people who respond are universities and start‑ups, and somehow industry doesn’t get engaged,” he says. “That was always one of the concerns we had, because the start‑ups and universities are great, and they may be approaching things from a different angle. But there are companies that have been at this for close to 100 years, and it would be nice to have some of them involved to bring in their experience and capability and capital.”

Another feature of the finalists is that most are working in teams. Only three entries are single entities;

the other six bring together experts and technologies from different sectors.

This was probably due, in part, to the difficulty of the challenge. As well as the exacting criteria outlined above, the testing regime contemplates both sensible and latent heat.

“We often look at efficiency in relation to being able to meet sensible load, and we somehow forget the latent loads,” Campbell says. “Measuring the energy consumption to get down to a sensible temperature is not a good proxy for what really happens. Because if you’re down at 27°C and you’re at 80 per cent relative humidity, not only is that uncomfortable, you’re probably going to grow mould. And people will overcool, because you have to get the moisture out of the air.”

This led to a wide range of solutions (see breakouts), including smart hybrid designs of vapour‑compression and evaporative cooling systems, as well as solid‑state technologies.

“I’m excited about the diversity of technologies and approaches that we’re

seeing,” says Campbell. “In some ways this is the most exciting time for the prize. It’s kind of an anticlimax of selecting down to one or two winners.”

INNOVATION COMES IN DIFFERENT FORMSRather than looking way outside the box for solutions, many of the teams have integrated existing technologies in clever, low‑cost ways. The Gree entry, for example, features split evaporative coils to separate dehumidification and cooling needs. It also has evaporative cooling – which can be used both for direct evaporative cooling and for cooling the condensing unit – and ventilation.

“Then based on the outdoor temperature, the outdoor humidity levels, the air quality, the indoor desired temperature, and the indoor desired humidity level, the controls figure out which combination of these technologies can best meet the needs for the lowest energy use,” says Campbell.

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“Not only is it absolutely ingenious, you’d have a more comfortable environment than we have today where sometimes it’s humid and sometimes, because you’re too lazy to open windows, you’re air conditioning when the outdoor temperature’s low enough that you could do a simple air exchange. Having a control that can take care of all of that is amazing. And that’s just typical of many of the entries, not just of the Gree application.”

At the other end of the scale are startling new technologies at earlier stages of development, such as the solid‑state solution from Barocal Ltd, a new spin‑out from a University of Cambridge lab. This barocaloric technology is built around advances in material science.

Campbell reveals that he read about the breakthrough in Science Direct and contacted the professor behind it.

“I called him and said, ‘Hey, we’re running a cooling prize here, why

don’t you apply?’ He hadn’t heard of it, so I sent him all the stuff and he applied,” Campbell recalls. “He had a great application, so we selected him to go forward. This is one where the ‘show me’ phase is really important to prove how much more efficient the material is than the refrigerants that we’re using today. We believe that it is more efficient and potentially multiple times more efficient, but we have to take it into the testing phase.”

Another less traditional entry comes from the Kraton Corporation team. They have created a polymer that is extremely efficient at transmitting moisture, and is activated with a small electric charge. It was originally developed as a coating on sports gear to remove moisture from athletes working out or competing in very hot conditions.

“But they never really got it to take off,” says Campbell. “And when they saw the Global Cooling Prize they thought,

Panel discussion as finalists are named.

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‘Maybe that’s the application we go with’. So, they teamed up with some evaporative cooling folks, and they’re using it for electro‑osmosis for moisture removal.”

PRIZE POTENTIALThis reveals another potential benefit of the prize. Although it seems aimed at finding one “silver bullet” cooling solution, it could also publicise technologies that could be incorporated into existing systems.

At the finalist ceremony, representatives from the big manufacturers were seen assiduously handing their cards out to the researchers and start‑ups behind the new technologies. And Campbell believes this interest could easily spread to the wider industry.

“Manufacturers might ask why they are using their compressors to remove moisture from the air, when they can simply do it with a small electric charge and this polymer,” says Campbell.

“And it’s something that would be a very simple add.

“I can see some of these innovations being incorporated in today’s products. They won’t be five times lower climate impact, but they could be three, and to see that step‑change with big industry players behind it, that would be huge.”

Victory, it seems, may come in many forms. And if the prize achieves its objective, the ultimate winner will be the planet. ❚

Iain Campbell.

C O V E R F E A T U R E

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The Global Cooling Prize was initiated by the Rocky Mountain Institute (RMI), the Department of Science and Technology, the Government of India, and Mission Innovation. It is administered by RMI, Conservation X Labs, the Alliance for an Energy Efficient Economy, and CEPT University.

AIRAH is an outreach partner of the Global Cooling Prize.

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DAIKIN AND NIKKEN SEKKEI

For its entry, Daikin has teamed up with Nikken Sekkei, a top Japan-based architecture and engineering company.

The solution adopts a multi-split method to connect three indoor units with one outdoor unit. Refrigerant flow rate for each indoor unit is optimised depending on an ever-changing cooling load, and refrigerant-control technology is used to closely modulate the capacity.

The system also integrates a direct evaporative cooling system. This method improves the system efficiency by using heat of vaporisation to lower the heat of the air that the outdoor unit takes in.

Control technology is being developed to measure the outdoor temperature with sensors and automatically spray water when ambient temperatures and the cooling load are particularly high.

The solution uses HFO-1234ze, with a GWP of less than one. At the same time, Daikin has stated that it still considers R32 the most balanced refrigerant, and will continue to promote it. ❚

GODREJ AND BOYCE IN PARTNERSHIP WITH ATE ENTERPRISES

The Indian AC giant has partnered with ATE Enterprises, a leading evaporative cooling technology company, to develop an advanced hybrid solution.

The system integrates Godrej’s own well-established high-efficiency vapour-compression system with a natural low-GWP refrigerant and advanced evaporative cooling technology. It is expected to have a significantly lower climate impact than typical RAC units sold today.

The evaporative cooling technology reduces the air temperature without adding to its humidity level. This cool air is then either supplied directly to the indoor space or passes through the vapour-compression system, which optimises compressor performance depending on the set indoor temperature and humidity requirements of the space.

The grid electricity consumption of the cooling system is further reduced by improving the heat exchanger efficiency and by using a small solar PV panel. Smart controls optimise the performance of this integrated solution. ❚

GREE AND TSINGHUA UNIVERSITY

One of the world’s largest residential AC manufacturers is collaborating with one of the top universities to develop a super-efficient and climate-smart residential cooling solution.

The hybrid solution is designed for automatic, climate-smart operation in three modes: vapour-compression refrigeration, direct evaporative cooling, and ventilation. It will switch between these or operate them in parallel depending on outside weather conditions.

Key attributes include a newly developed dual-suction, dual-discharge, twin-cylinder compressor; a low-frequency-oriented inverter; a fully redesigned evaporator and evaporative condenser; a low-GWP refrigerant; and an AI-assisted controller. The solution also has a small PV panel integrated into the outdoor unit to further lower grid-electricity consumption.

According to the team, this hybrid cooling solution not only demonstrates the application of a low-GWP refrigerant, it also highlights the extent to which the efficiency of vapour-compression technology can be expanded through smart, hybrid design. ❚

KRATON CORPORATION, IIT BOMBAY, PORUS LABORATORIES, AND INFOSYS

Kraton Corporation, a global specialty chemical company, is collaborating with three other companies to develop a hybrid cooling solution using a membrane dehumidification system based on Nexar polymer.

NexarCool technology integrates an electro-osmotic membrane dehumidifier with a water-based direct evaporative cooling system to achieve air conditioning without using any refrigerant.

By applying a small voltage across the membrane dehumidifier system, water vapor from the indoor air is ejected to the outside air, drying the indoor air in the process. The indoor air is then cooled via a direct evaporative cooling process.

This integrated approach to cooling is expected to have significantly lower energy consumption than today’s conventional air conditioners. Because no refrigerant is used, the technology has the potential to dramatically lower climate impact. ❚

AND THE FINALISTS ARE …

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M2 THERMAL SOLUTIONS

This US-based start-up is developing a solution that uses a combination of evaporative cooler and membrane technologies to independently cool and remove moisture from room air. The system requires no compressor or refrigerant.

An evaporative cooler first operates to cool the room air while increasing its humidity. The cool and humid air is then passed through a membrane system to remove the excess water vapour, decreasing its humidity. The solution also has the capability to bypass either of these processes and only use a ventilation mode, depending on outdoor weather conditions.

Most of the water supplied to the evaporative cooler is generated by the membrane system – thus minimising the water footprint of the solution. With no compressor or refrigerant, and an innovative approach to independent cooling and dehumidification, it has the potential to achieve significantly lower climate impact than typical AC units sold today. ❚

S&S DESIGN STARTUP SOLUTION

A group of mechanical engineering researchers and innovators with expertise in air conditioning are developing a hybrid solution. It combines a two-stage cooling system with direct evaporative cooling of the condenser to significantly improve efficiency. The two-stage cooling system integrates a water loop and a traditional vapour-compression system to optimise performance. The water loop pre-cools the room air, which is subsequently cooled and dehumidified at the evaporator of the vapour-compression system.

At the condenser, a part of this conditioned air is further cooled using direct evaporative cooling, thus significantly improving condensing efficiency.

The performance is further optimised by using a variable-speed compressor. And with a natural, low-GWP refrigerant, the proposed solution has the potential to achieve dramatically lower climate impact. Finally, DC electrical componentry allows for easy integration with renewable power sources. ❚

TRANSAERA INC. IN PARTNERSHIP WITH HAIER

Transaera, a manufacturing start-up from the Massachusetts Institute of Technology (MIT), is collaborating with Haier on this hybrid cooling solution. A high-efficiency room air conditioner operates in parallel with a moisture storage battery (MSB) to provide cooling and dehumidification.

The MSB contains a novel desiccant material discovered at MIT that can adsorb a large amount of moisture, allowing room air to dehumidify. The high-efficiency AC unit can then cool the air more easily, reducing the overall electricity consumption.

While typical desiccant materials require high temperatures for regeneration, the MSB material can regenerate using waste heat from the vapour-compression system.

The solution has a provision for direct evaporative cooling of the air at the condenser inlet to improve condensing efficiency, a small integrated solar PV panel, and battery to reduce grid consumption. It also uses rainwater to reduce overall environmental impact. ❚

BAROCAL LTD, A NEW SPIN-OUT FROM A UNIVERSITY OF CAMBRIDGE LAB

Researchers at the University of Cambridge’s Department of Materials Science and Metallurgy in the UK are developing a solid-state cooling technology to solve the cooling challenge.

Instead of using refrigerants, barocaloric cooling technology takes advantage of the properties of solid organic “plastic crystal” materials to provide cooling. The process of continuously applying and releasing pressure on the barocaloric material results in solid-to-solid phase changes in the crystals, causing large thermal changes due to molecular reconfiguration. This produces a cooling effect, which can be delivered either to the room air or to produce chilled water for cooling.

The plastic crystals are flexible materials that are widely available, low-cost and non-toxic. Research shows that their thermodynamic behaviour is very similar to commonly used refrigerants, meaning they could offer a viable alternative to vapour-compression technology. ❚

AND THE FINALISTS ARE …