Heating/cooling networks

A district heating/cooling network is an infrastructure that distributes thermal energy to several buildings from one or more sources (biomass, geothermal, waste heat recovery, solar thermal, chillers, etc.). In its recent version, known as a tempered loop (4th/5th generation), the water circulates at a "neutral" temperature (approximately 10–30 °C). Each building then extracts heat or cooling via its own heat pump to produce heating, cooling, and sometimes domestic hot water. The interface point is called the substation: a heat exchange station that transfers energy, measures consumption, and regulates the system, without mixing the water between the network and the building's internal heating system.

Heating/cooling networks: operational definition

A "traditional" network supplies hot water (e.g., 70–95 °C) and returns a cooler water; a district cooling network typically supplies 6–12 °C. The tempered loop, on the other hand, circulates water at around 15–25 °C. Each building connects a reversible heat pump to this loop, which raises the temperature for heating/domestic hot water or lowers it for cooling, achieving excellent COPs because the temperature difference is reduced. Another advantage is the exchange of energy between users (the cooling needs of one building can cover the heating needs of another).

On the substation side, you'll generally find: plate heat exchangers, control valves, pumps, filters, expansion vessels, energy meters (heating/cooling), and a programmable logic controller (PLC) connected to the building management system (BMS). Overall performance depends on a good temperature difference (ΔT) in the network, rigorous hydraulic balancing, and flow and temperature control based on usage and season. Production can be hybrid (biomass + waste heat + chillers + geothermal), with storage (tanks, chilled water tanks, ground loops) to smooth out peak demand.

Advantages, limitations and points to consider

Interests:

• Scaling up renewable energy and reducing carbon footprint at the neighbourhood level.
• Pooling resources and smoothing OPEX (splitting effect).
• Improving the COP of heat pumps thanks to small temperature differences.
• Simplify building boiler rooms (fewer heavy generators on site).

Boundaries :

• CAPEX for infrastructure (trenches, pipelines, substations).
• Dependence on the quality of operation (bad ΔT = overconsumption).
• Governance and contractual framework to be defined (concession, tariffs, indexations).

Points to consider:

• Water quality (corrosion, scaling) and section insulation.
• Emitter compatibility (low vs high temperature) on the building side.
• Domestic hot water hygiene (anti-legionella procedures) when domestic hot water is produced locally.
• Measurement and remote metering for fair cost allocation and precise management.

Anecdote — "The exchange that makes all the difference"

In a neighborhood blending offices, shops, and residences, open-plan offices demanded cooling during the hottest hours, while residential buildings needed heat for domestic hot water in the evening. The installation of a temperature-controlled loop with substations and reversible heat pumps enabled energy exchange: the heat extracted from the offices covered a portion of the domestic hot water needs of neighboring residences. The result: reduced production capacity, smoothed consumption, and a building manager delighted to see that meetings were less… heated. Proof that, when well-organized, a network can become an energy-sharing hub between neighbors.