# Biomass District Heating Systems Based on Agriculture Residues
## 3 Methodology  
In this section is presented a methodology for evaluating the potential for forest/agriculture residues BioDH systems in a region. It evaluates the factors that affect to the viability of these systems though a top-down/bottom-up methodology integrating the renewable forest biomass energy source and complemented with agriculture residues. This global methodology is summarized in Figure 2.  
The methodology analyzes the critical factors that directly affect to the economic viability of BioDH systems and their sustainability. These factors and the stages where they are evaluated within the methodology are: availability of the biomass resource (stage 5); thermal energy demand (stage 2); environmental factors (stage 3); socio-economic factors, such as energy poverty, housing occupation or the age of buildings (stage 4). Figure 1: (**a**) Universal Network Heating model; (**b**) Integrated management between different universal heating networks of the forestry resource, extrapolated from [6]. Step 1. Regional characterization and selection area of study  
The region under study is defined through the energy characterization and available resources. In a first approach three main types can be identified for district heating analyses: (i) industrial areas, where the heat source comes from residual processes and cogeneration; (ii) urban areas, with high population density, scarcity of available spaces and, usually, natural gas network. In them the logistic associated to the use of biomass at certain scale can be complex; and (iii) rural areas where usually population density is low or moderate and biomass resource is available with a relatively easier management for logistic and supply. Step 2. Thermal System assessment. Preliminary evaluation  
It comprises the Sanitary Hot Water (SHW) and heating demands of the set of building to be connected to the heating network. The former can be estimated from adjusted estimation of the consumption rates, usually defined in local regulations. The heating demand can be evaluated through the evaluation of energy losses through buildings envelope and the contribution of internal and external heat gains [8]. Once estimated the thermal demand, the linear heat density (LHD) can be used as first approximation to the systems viability, based on a mean length of the network defined as function of the buildings density. The BioDH systems are designed for supplying the whole thermal demand, and no auxiliary backup systems are considered for these urban heating networks. They are considered to be reliable systems and, once implanted, with lower fuel costs than those with fossil fuels. Although in some biomass district heating systems gas or diesel boilers are used for peak demand, this study has opted for full decarbonization of the heating system by using only local renewable resources, even though in some cases it may penalize the investment costs of the boilers. Step 3. Assessment of viability factors  
Rural BioDH systems require specific evaluation of the factors that directly influence their viability:  
* Biomass resources: Cost and availability must be analyzed. This can be done by means of GIS tools or statistical data. * Environmental factors for thermal plant location: this includes characteristics of available and feasible spaces for thermal station plant implementation, available area, affections, contaminants and particles dispersion and safety distances. * Socioeconomic factors. These should include analyses of energy poverty and occupancy of dwellings. Step 4. Municipality assessment  
After the classification of potential BioDH locations in previous steps, this step goes into the detail of the specific BioDH at the selected locations. Heating demand is the main factor for the viability of the systems. It goes up to 90% of the total energy consumption in the DH. An accurate demand estimation allows an accurate prediction of incomes and system profitability.