Why recover low-temperature waste heat?

14.02.2020 - Waste heat recovery is a measure that has been implemented in fourth-generation district heating and cooling (DHC) systems: the network distribute energy from a centralised generation plant to the customers. Waste heat recovered in these networks had to be collected from high temperature sources, mainly from industrial processes. Moreover, recovering such energy requires complex interventions in the process plants, limiting the number of possible cases.

Since the largest amount of waste heat available in the urban environment is rejected by low temperature sources and service facilities, the solution proposed is to recover such low temperature energy into DHC networks by means of heat pumps.

The idea is based on the water-loop concept used in commercial buildings and here extended to the district and city level: the district heating and cooling network can be fed by multiple waste heat sources, which contribute to balance out the energy drawings by heat users.

If a high temperature network is concerned, a heat pump is needed to rise waste heat temperature to the network’s level. On the contrary, if a low temperature network is considered, heat recovery can be performed directly (without heat pumps), but heat pumps is needed at consumers’ side to rise the temperature of the energy distributed to the useful levels (35°C to 55°C depending on the uses).

Exchange of energy between the network and the buildings

LIFE4HeatRecovery solutions will integrate effectively multiple waste heat sources from urban wastewater and service buildings, where they are available along the DHC network, by managing energy at different temperature levels. This will guarantee flexibility and scalability to the network design, and reliable, secure and clean thermal energy to the consumers.

Together with storages, control strategies optimizing harvest and re-use of waste heat are key from the technical and economic perspectives. On the one hand, strategies will be assessed that assure a thermal balance among diffused energy integration, storage and utilization. On the other, business models will be elaborated allowing to manage thermal energy purchasing from different sources, and electricity use when it is more convenient for customers and energy utility companies.

As infrastructural costs are a barrier hindering public investments in the DHC segment, LIFE4HeatRecovery will also elaborate innovative financing mechanisms based on Public Private Partnerships and active participation models. This strategy moves towards leveraging large private capitals, incorporating, in a unique action, customers, network owners and European interests - pursued through sustainability and recovery plans-, and investors profits.

As such, LIFE4HeatRecovery has a social dimension, creating new business opportunities and new participation, the energy users assuming a focal position and becoming protagonists in the heating and cooling market.