How is the ice for indoor rinks made?

Nitrogenous substances and other chemicals are added to water to raise the freezing point of water, so that water will not melt at a temperature slightly higher than the freezing point of ordinary water (0℃). On the one hand, it can prevent people who are active on the ice from being too cold, on the other hand, it can reduce the dependence on the refrigeration system.
The temperature inside the general indoor skating rink remains relatively constant, ranging from 0℃ to 17 ℃, while the ice itself maintains a consistent temperature between -5℃ and 0 ℃. The formation of ice in the indoor rink is achieved through the freezing of water, with the addition of certain chemicals as necessary. To rapidly cooling into ice, a liquid ammonia refrigeration system is applied. Initially, water is filled into the pool and then liquid ammonia is injected into laid pipes. Given that only a thin layer of ice (approximately 1 to 2 inches or 2.5 to 5 cm) needs to be formed and that this process occurs within a short time , so specialized machines are subsequently utilized for further ice maintenance. Additionally, introducing of nitrogen and other chemicals into the water can elevate its freezing point slightly above that of regular water (0℃), thereby preventing it from melting at temperatures marginally higher than freezing point. This approach serves two purposes: firstly, it prevents individuals engaging in activities on the ice from becoming excessively cold; secondly, it helps reduce reliance on refrigeration systems.