Frequently asked questions.

The term is used when storing energy as heat or cold, which can be released at a later stage. The heat or cold is usually stored when energy is cheap and then released when the heating or cooling demand is at a peak or the cost of energy is high.

PCM means Phase Change Material and refers to any material that changes state, for example from solid to liquid, when reaching a certain temperature. This phase change enables large amounts of energy to be absorbed or released. Water is one PCM, storing cold at zero degrees Celsius by changing phase to ice. Cartesian uses a wide variety of other materials, such as bio-based waxes, to store heat or cold at different temperatures.

For applications with HVAC systems, Cartesian's Thermal Box is not considered flammable. While some PCM might be flammable when they reach temperatures above 100 °C or more, the Thermal Box is designed to eliminate any risks of reaching flammability conditions in operations.

Cartesian offers only safe PCMs and primarily uses bio-based PCMs in the Thermal Box. The PCM will stay in the Thermal Box for its whole lifetime and is not consumed during operation. The Thermal Box is also designed to avoid any risk of PCM leakage.

The purpose of a water accumulator tank or buffer vessel and the Thermal Box is in many cases the same: storing thermal energy to be released later. However, the principle is different — the Thermal Box relies on phase change and latent heat, while the accumulator tank uses sensible heat. The result is that the Thermal Box requires three to eight times less volume for the same amount of stored energy. Another benefit is that the heat released while discharging the Thermal Box comes at a relatively constant temperature for several hours, which makes it a very good thermal buffer and a reliable alternative heat source.

No — each Thermal Box uses a specific phase change material adapted to a specific operating temperature range for storing the thermal energy. Cartesian can supply Thermal Boxes for both heating and cooling applications in the same building by using two separate units.

Yes. The Thermal Box can be installed inside or outside the building, depending on the space available. Whether it is in a technical room, outside on the parking lot, or in the underground parking, there is always a way to find the right space for the Thermal Box.

Our modules typically have a storage capacity in the range of 75–125 kWh. The range varies according to the properties of the PCM used for the specific application. When you add more modules, the capacity and the thermal output increase accordingly — there is no practical upper limit.

A Thermal Box module has the footprint of a Euro pallet — 0.8 m × 1.2 m — so it can be transported through standard doors into technical rooms inside the building. Several modules can then be connected once placed at their final location, and the insulation panels are fitted afterwards. Each module weighs 1 800–2 000 kg and can be transported using a standard pallet jack.

No maintenance is required for Cartesian's Thermal Box. The system is fully enclosed and has no moving parts.

If the Thermal Box is cycled once every day, a class A material will have consistent performance for more than 27 years without changing melting temperature or showing any capacity loss. Cartesian uses organic phase change materials that offer unmatched stability — the cyclic stability of PCM according to RAL-GZ 896 is >10 000 cycles for class A materials.

Yes — it can be retrofitted in all kinds of commercial buildings as long as the heating or cooling is constructed as a centralized hydronic system. Communication to the on-site Building Management System is handled with standard protocols such as BACnet IP or Modbus. Cartesian also offers data communication to cloud services via 4G/5G.

Two main sources of savings are typically considered. First, reduced investment and operating costs in HVAC equipment: instead of sizing heat pumps and cooling machinery for peak demand, the Thermal Box handles the peaks and lets the machinery run at a lower, constant load — downsizing the required installed capacity. Second, load shifting and peak shaving: storing thermal energy when energy is cheap or readily available (for example, excess PV) and releasing it later cuts operational costs and avoids high demand fees from the grid operator.

Payback depends on the case: application, the degree of HVAC downsizing possible, variable electricity costs, peak demand fees and available excess PV. Cartesian has the experience to quickly determine whether your project falls within our target of payback under 5 years. In any case, the Thermal Box has an expected lifetime of 25 years and will keep creating value long after payback is realised.