As the European Union has set an ambitious target for greenhouse gases emission saving (from energy production) in order to reduce the impact on global warming, of 40% in energy consumption by 2030 and 80 - 95% by 2050 it is important to address efforts in the residential sector as it is responsible for 40% of the current total energy demand. District heating and cooling play an important role as centralized management for space heating / cooling has proven to be an effective way to reduce energy intensity (CO2 / kWh).
Since District Heating (DH) systems are built to provide a sensitive service in many countries across the northern hemisphere, and with additional capacities being deployed year after year due to the many advantages in comparison to individual heating solutions, DH systems have a high impact in energy consumption, and lately in the environment.
Life Cycle Analysis to assess the sustainability of DH systems
New DH systems have demonstrated a number of environmental benefits: they can reduce GHG emissions, air pollution, ozone depletion, and acid precipitation among others. When integrating renewable energy sources (RES), improving efficiency in equipment and moving from individual solutions to central heating systems, an environmental performance assessment to figure out environmental impacts of modernized DH systems is necessary. From the sustainable development point of view, DH systems are understood as a service, which makes it necessary to quantify the environmental impacts from providing it, since it is created and used to fulfill a need. From a holistic point of view, a ll products (goods or services) have a life cycle that can be represented as:
All these activities along the life cycle result in environmental impacts in terms of exploitation of biotic and abiotic resources, eco-system quality, and human health. Life Cycle Assessment (LCA) is recognized as one of the most powerful and widely used tool for undertaking holistic environmental sustainability assessments, as it assesses the product’s environmental impacts from cradle to grave with a multicriteria approach. The principle is to compute the materials and energy flow inputs and the emissions at all phases (stages) in the life cycle of a production process. LCA offers a broader perspective because it can be utilized to evaluate a wider range of environmental impact categories, beyond climate change, which is often the usual and only parameter considered when assessing environmental performance. One of the advantages of LCA is complementing local environmental impact assessments by analyzing the impacts from a global perspective, therefore avoiding the so-called “burden-shifting”. As a result, LCA is understood as a methodological framework to estimate the environmental impacts in terms of: climate change, stratospheric ozone depletion, tropospheric ozone creation (smog), eutrophication, acidification, toxicological stress on human health and ecosystems, resource depletion, water use, land use, noise, and others.
Methodologies to implement an LCA vary among studies, but the most common one remains to be the LCA ISO standard 14040 and 14044. The ISO 14040 (1997) describes the principles and framework for LCA while the ISO 14044 presents requirements and guidelines to perform it. According to the framework found in ISO 14040, a complete life cycle, with its associated material and energy flows is called the product system. In ISO 14044, the main four steps included in the LCA methodology are described as: goal and scope, life cycle inventory, life cycle impact assessment, and life cycle interpretation.
LCA role for sustainability assessment of DH systems: examples
Sustainable heating solutions have evolved over the last decades at the European level. Such solutions require an increase in the utilization of RES for DH purposes. This results in a reduction of fossil energy use, consequently cutting CO2 emissions and thus leading to a decrease of environmental impacts by DH. Furthermore, heating and cooling costs in the EU Member States can be reduced by 15%, which equals to approximately EUR 100 billion per year.
Besides, sustainable heating can be achieved by making use of low temperatures in DH. Low-temperature DH (LTDH) systems can lower energy losses, utilize industrial excess heat, balance the renewable energy in the electricity grid and have strong economic potential (if properly implemented). It can be confirmed with the results of several studies, for example, a case study on DH of Helsinki, which investigated the effects of the potential benefit of low temperatures in the distribution network of DH powered by combined heat and power (CHP) together with solar collector, boilers and heat pumps, found that the change of supply temperature from a range of 80 ° C to 110 ° C to a constant supply temperature of 65 ° C improves the system performance in terms of cost and emission reductions by 4%. Aforetime estimates of LTDH showed a possible reduction of heat loss by 75% in comparison to the medium temperature DH system. Such study mentions additional benefits to the reduction of heat losses, as a reduction of boiling risk, reduced thermal stress on materials along the pipeline, the utilization of thermal storage to handle peak loads without oversizing equipment, and improving heat to the steam ratio in steam CHP system to extract more power of the turbine.
A good example of LCA applied to the sustainability assessment of a DH system, was performed over the Belava Parish in the Gulbene municipality. In this case, four different scenarios were evaluated for the DH development, considering the current operational parameters and three potential future ones. As a result, it was found that a future scenario where RES (solar thermal systems), combined with new boiler technologies and low-temperature profiles for heat distribution, achieves an environmental impact reduction close to 30%. Furthermore, the results show that most of the reduction is attained in the human health area, which is usually the first area of concern to stakeholders compared to climate change, ecosystem quality, and resources. The impact in the human health area also turns to be easy to convert to monetary terms, as disability-adjusted in life-years can be properly economic internalized by society, which can give a quick glimpse into additional social and economic burdens.
In practice: how to build a LCA for DH
As mentioned LCA is a useful and practical tool to be use during every infrastructural design phase including (Low Temperature) DH facilitating the selection of optimal environmental and viable solutions by using specific environmental criteria. This will support a more global vision within the environmental assessment highlighting which systems, subsystem or section of the DH presents the major impact and thus how a redesign from a more focused environmental perspective can create a higher environmental performance for the whole infrastructure. The results from an LCA made for a DH system should be able to:
Define an updated data inventory of all DH subsystems to be used as further benchmarks;
Clarify which subsystems and past of a district heating system are effecting the overall environmental performance of the infrastructure.
Provide alternatives based on eco-design perspectives implementable in Municipality Energy strategies including SECAP and compare them with the business-as-usual DH scenario (e.g. distribution network using natural gas)
The LCA results may be of interest for energy planner and energy companies, engineers, DH operators, public officials and decision makers including municipal planning merging the environmental perceptive within new or updated planning processes for urban infrastructural development.
Hereafter we present a graphic example on how to build an LCA for a Pilot Energy Strategy in a DH system implementing a LTDH approach considering the proposed methodology in ISO 14044.
By following the methodology proposed for an LCA, decision makers can easily recognize the most impacted areas (human health, ecosystem quality, global warming, resources) and, depending on the type of LCA conducted (stand-alone or comparative) can also identify the optimal alternative from the environmental point of view.