Latent heat and cold storage: Engineering and performance

How a basement tank of ice cools a 53-storey tower

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

Ice and PCM stores move cooling or heating in time rather than producing electricity, so their value is measured in avoided peak demand. Sizes run from household units to the tens of MWh of a skyscraper.

Round-trip efficiency

Mixed

None of the sources gives a measured round-trip efficiency for ice storage. Making ice means running chillers colder, which uses more energy per unit of cooling, partly offset by cooler night-time air; vendors argue the system mainly shifts when energy is used. For high-temperature PCMs, 1414 Degrees says it expects over 90% heat-to-heat efficiency against 75% for burning gas. Losses through the tank walls are the other drain.²⁸

Silicon store, heat out (company claim) over 90%⁸ Gas combustion comparator (same source) 75%⁸

Power and energy decoupling

Favourable

Partly. Energy is set by the number of tanks and power by the chiller and heat exchangers, so adding tanks extends duration cheaply. A CALMAC 1320CSF tank holds 324 usable ton-hours, enough for 40 tons of cooling for 8 hours, and costs about USD 30,000, roughly USD 26 per kWh of cooling (calculated, 1 ton-hour is 3.517 kWh). But in a PCM block, heat must travel through a poor conductor, so faster charging needs more heat-exchange surface.²⁵

CALMAC 1320CSF tank 324 ton-hours; 40 tons for 8 hours² Tank equipment cost about USD 30,000 each, about USD 26 per kWh of cooling (calculated)²

Footprint and siting flexibility

Favourable

Ice tanks fit in basements, car parks or roofs: an average CALMAC tank measures about 9 by 8 ft, about half a parking space (company data). Ice and PCMs hold far more per m3 than chilled water, which is why chilled water suits district plants with room for big tanks: a worked example for a 40,000 ton-hour district cooling store, using a 7.2 C temperature rise and 90% storage efficiency, needs nearly 5 million US gallons (about 18,600 m3), roughly 7.6 kWh of cooling per m3 (calculated). The ice store at 55 Water Street, a 53-storey Manhattan office tower, holds 16,000 ton-hours, about 56 MWh of cooling (calculated); NYSERDA lists its capacity as up to 12.6 MWh, which appears to be the chiller electricity shifted rather than the cooling stored. Silicon or aluminium stores are compact but need heavy insulation.²³¹¹

Average CALMAC tank about 9 ft by 8 ft (company data)² 55 Water Street, 53-storey New York office tower 16,000 ton-hours, about 56 MWh of cooling (calculated); listed as up to 12.6 MWh³ Chilled water store, 40,000 ton-hours about 18,600 m3; about 7.6 kWh per m3 (calculated)¹¹

Safety and thermal runaway risk

Favourable

Ice and chilled water are benign; the main hazards are glycol leaks and refrigerants. Paraffin and fatty-acid PCMs are flammable and need fire-rated containment in buildings. Salt hydrates are corrosive. Liquid nitrogen displaces oxygen in closed rooms, and molten metals carry burn and steam-explosion risks if water gets in. No thermal runaway in the battery sense applies.⁵⁶

Sources

Thermal Battery systems: CALMAC ice storage (Trane sales brochure IB-SLB001, company data) Trane Technologies, 2020
Energy storage case study: ice thermal storage in a 53-storey Manhattan office building (ES-newwater-cs) NYSERDA, 2018
Review of Low-Cost Organic and Inorganic Phase Change Materials with Phase Change Temperature between 0 C and 65 C (Hirschey et al., Purdue High Performance Buildings Conference) Oak Ridge National Laboratory, 2021
Study on the hybrid energy storage for industrial park energy systems, Table 2: thermal storage materials (National Science Open 3(3)) National Science Open, 2024
SiBox competitive with fossil fuels (ASX announcement, company data) 1414 Degrees, 2023
Evaluating chilled-water storage for district cooling systems HPAC Engineering, 2016