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HKUST holds 400 watts of solid-state cooling through a million cycles
A Hong Kong lab kept 400 watts and a 41-kelvin span steady across a million cycles of its TiNiCuCo refrigerant. Anyone evaluating solid-state cooling now has a durability figure to quote back at a vendor.
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What happened
- HKUST said its elastocaloric cooler held a constant 400 watts of cooling power and a 41-kelvin temperature span across one million operating cycles with no measured degradation.
- The failure mode it targets is functional fatigue in the commercial NiTi shape-memory alloy used as the refrigerant in most elastocaloric devices, whose cooling power declines over extended use.
- The fix pairs a fatigue-resistant TiNiCuCo alloy with a redesigned refrigerant structure, and accelerated testing of that refrigerant showed no functional degradation after 100 million cycles.
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Why it matters
- capability Procurement can ask a solid-state cooling supplier for a cycle count tied to a stated power and temperature span.
- constraint Capacity and durability still sit in two different machines from the same lab, so anyone specifying room-scale cooling has to choose which of the two a single line item covers.
- decision Whoever drafts the warranty has to decide whether roughly 36 days of equivalent duty, at the lab's own implied cycling rate, supports a service life quoted in years.
- precedent Coupon-level fatigue figures in the hundreds of millions will keep turning up in rival announcements; the device-level count at fixed power and span is the harder one to match and is now the published mark.
For anyone specifying a chiller, the useful question about a million cycles is how many days of running it stands for. The report does not give the device's cycling frequency [13]. HKUST's own service projection supplies a rate: the TiNiCuCo refrigerant survived 100 million cycles in accelerated testing [6] and is expected to run reliably for more than a decade in real conditions [7]. Spread over ten years, that is roughly 27,400 cycles a day, about one every three seconds [1]. Hold the assembled device to the same rate and its million-cycle run covers about 36 days [2].
Those two tests answer different questions. The 100 million cycles were run on the refrigerant alone [6]. The million cycles were run on a device built from multiple refrigerant units [12], holding 400 watts and a 41-kelvin span throughout [5]. HKUST says it tackled material functional fatigue and structural reliability together [4], and the second half of that covers the structure the alloy sits in.
Then there is capacity. Durability was demonstrated at 400 watts [5], while the same group's 2025 kilowatt-scale elastocaloric device was rated at 1,284 watts [11], so the zero-degradation result runs at about 31 percent of the cooling power HKUST has already published [3]. The account, reported by Interesting Engineering, treats the 2025 machine as answering a different part of the commercialization problem [14].
Sun Qingping, the corresponding author and a chair professor in the Department of Mechanical and Aerospace Engineering at HKUST, said: "While significant progress has been made in cooling performance over the past decade, long-term cooling stability is crucial for practical deployment. By integrating advanced shape memory alloy materials with innovative device engineering, we have tackled this key challenge." [8] He also said, "We are currently developing an air-conditioner based on this technology." [9]
Who can use this today is the person drafting a maintenance interval or a warranty term for a cooling system that has not shipped. For them the usable figure is a cycle count with a power and a span attached to it, because the failure mode being cleared here is gradual: commercial NiTi refrigerant does not break, its cooling power declines with use [3].
A durability claim in this field is checkable when it gives four things: the cooling power held, the temperature span held, the cycle count, and whether those cycles ran on the assembly or on a sample of alloy. A supplier that offers only the cycle count is describing a material. The line to quote back until someone beats it is 400 watts at a 41-kelvin span, held for a million cycles on a working device [5].
What to watch
- Whether the air conditioner HKUST says it is building is rated near 400 watts or near the 1,284 watts of its 2025 device.
- Publication of a cycling frequency for the device test. That figure is what turns cycles into hours of runtime.
- Whether competing groups respond with device-level cycle counts at a stated power and span, or keep reporting material-only fatigue data.