Page 22 - Guidelines for cities to achieve carbon Net Zero through digital transformation

Figure 4: Hungary Green Bus Program

Source: Hungary Today

Building efficiency

Lake water heating and cooling for buildings

In some cities, water from natural sources is utilized to provide heating and cooling for buildings.
This system is known as a lake water cooling or heating system.

During the winter months, water is drawn from the deeper, warmer layers of the lake, where the
temperature remains relatively constant, typically around 4–6 degrees Celsius (39–43 degrees
Fahrenheit). This water is then pumped through a heat exchanger, where its heat is transferred
to a closed-loop system containing a heat exchange fluid. The heated fluid is then distributed to
buildings for space heating, providing warmth and reducing the need for conventional heating
systems.

Conversely, during the warmer months, the system operates in reverse. Cold water is drawn from
the lake's surface, which remains cooler than the surrounding air due to its depth and thermal
inertia. This cold water is used to cool the heat exchange fluid in the closed-loop system, effectively
absorbing excess heat from the buildings' interiors. The heated lake water is then returned to the
lake, and the cooled heat exchange fluid continues to circulate and provide cooling to the buildings.

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