Cold district heating is a technical variant of a district heating network that operates at low transmission temperatures well below those of conventional district heating systems and can provide both space heating and cooling.
Transmission temperatures in the range of approx. 10 to 25 °C (50–77 °F) are common, allowing different consumers to heat and cool simultaneously and independently of each other. Hot water is produced and the building heated by water heat pumps, which obtain their thermal energy from the heating network, while cooling can be provided either directly via the cold heat network or, if necessary, indirectly via chillers.
Cold local heating is sometimes also referred to as an anergy network. The collective term for such systems in scientific terminology is 5th generation district heating and cooling (5GDHC).
Due to the possibility of being operated entirely by renewable energies and at the same time contributing to balancing the fluctuating production of wind turbines and photovoltaic systems, cold local heating networks are considered a promising option for a sustainable, potentially greenhouse gas and emission-free heat supply.
A funny idea that one could also use thermal reservoirs to store heat in the summer, extracting cold medium of, say 20°C, and extract this heat again in the winter, cooling the reservoir. Which would be more efficient than to use river water, for example.
This has been proven to work well on relatively small scale (a couple multi-party houses) as “seasonal heat storage”. The key insight is that the amount of energy stored - being proportional to the volume - grows with the third power of the dimension of the storage, while the amount of insulation needed grows only with the second power, because it is proportional to the surface area. Therefore, a storage tank which is ten times as large by size, would be able to store one thousand times more heat, but only need one hundred times more insulation.
Pretty much anywhere humans live there is similar “heat” a few meters into the ground even during winter. If you need a heat-pump to upgrade the heat, you might as well attach it to a ground-loop and extract the heat that way.