Feasibility limits of using low-grade industrial waste heat in symbiotic district heating and cooling networks

Abstract

Low-grade waste heat is an underutilized resource in process industries, which may consider investing in urban symbiosis projects that provide heating and cooling to proximal urban areas through district energy networks. A long distance between industrial areas and residential users is a barrier to the feasibility of such projects, given the high capital intensity of infrastructure, and alternative uses of waste heat, such as power generation, may be more profitable, in spite of limited efficiency. This paper introduces a parametric approach to explore the economic feasibility limits of waste heat-based district heating and cooling (DHC) of remote residential buildings depending on network extension. A parametric model for the comparative water–energy–carbon nexus analysis of waste heat-based DHC and Organic Rankine Cycles is also introduced, and applied to an Italian and to an Austrian setting. The results show that, for a generic 4 MW industrial waste heat flow steadily available at 95 °C, district heating and cooling is the best option from an energy–carbon perspective in both countries. Power generation is the best option in terms of water footprint in most scenarios, and is economically preferable to DHC in Italy. Maximum DHC feasibility threshold distances are in line with literature, and may reach up to 30 km for waste heat flows of 30 MW in Austria. However, preferability threshold distances, above which waste heat-to-power outperforms DHC from an economic viewpoint, are shorter, in the order of 20 km in Austria and 10 km in Italy for 30 MW waste heat flows.

Graphic abstract

ABS:

Absorption chiller

ASHRAE:

American society of heating, refrigerating and air conditioning engineers

AT:

Austria

CAPEX:

Capital expenses (Euro)

CO₂ :

Carbon dioxide

CO_2eq :

Carbon dioxide equivalent

COP:

Coefficient of performance (dimensionless)

CT:

Cooling towers

DC:

Dry cooling systems

DH:

District heating

DHC:

District heating and cooling

DHW:

Domestic hot water

El:

Electricity

IT:

Italy

IWH:

Industrial waste heat

LCC:

Life cycle cost (Euro)

LHV:

Latent vaporization heat (kJ/kg)

MVC:

Mechanical vapor compression chiller

NG:

Natural gas

OPEX:

Operating expenses (Euro/year)

ORC:

Organic Rankine cycles

PED:

Primary energy demand (TOE)

WEC:

Water–energy–carbon

equip :

Equipment (index)

\(C_{\text{cap,equip}}\) :

Capital cost of generic equipment (equip) (Euro)

\(C_{\text{cap,pipes}}\) :

Capital cost of the DH system (Euro/m)

\({\text{cCO}}_{{ 2 {\text{el}}}}\) :

Indirect carbon emissions factor for electricity (tCO_2eq/kWh)

\({\text{cCO}}_{{2{\text{fuel}}}}\) :

Indirect carbon emissions factor for fuel (tCO_2eq/kWh)

\({\text{cCO}}_{{ 2 {\text{m,equip}}}}\) :

Embodied carbon emission factor for equipment materials (kgCO₂/kW)

\({\text{cCO}}_{{2{\text{m,pipes}}}}\) :

Embodied carbon emission factor for pipe materials (kgCO₂/m)

\(Cp_{\text{equip}}\) :

Capacity of equipment (kW)

\(Cp_{\text{pipes}}\) :

Capacity of pipes (kW)

\({\text{CO}}_{{2{\text{d}}}}\) :

Direct carbon equivalent emissions (over 30 years) (kgCO₂)

\({\text{CO}}_{{2{\text{f}}}}\) :

Carbon footprint (over 30 years) (kgCO₂)

\({\text{CO}}_{{2{\text{m}}}}\) :

Embodied \({\text{CO}}_{{2{\text{eq}}}}\) emissions associated with equipment and pipe materials (kgCO₂)

\({\text{CO}}_{{2{\text{op}}}}\) :

Indirect carbon equivalent emissions during operation (over 30 years) (kgCO₂)

\(C_{\text{op}}\) :

Yearly operating cost (Euro/year)

\({\text{COP}}_{\text{a}}\) :

Coefficient of performance of absorption chiller (dimensionless)

\(c_{\text{p}}\) :

Specific heat of water (kJ/kgK)

\(C_{\text{PED,el}}\) :

Coefficient of primary energy demand for electricity (TOE/kWh)

\(C_{\text{PED,fuel}}\) :

Coefficient of primary energy demand for fuel (TOE/kWh)

\(cw_{\text{el}}\) :

Water consumption coefficient for electricity generation (m³/kWh)

\(cw_{\text{fuel}}\) :

Water consumption coefficient for  fuel (m³/kWh)

\(cw_{\text{m,equip}}\) :

Specific embodied water consumption coefficient for equipment materials (\({\text{m}}^{3} {\text{H}}_{2} {\text{O}}/{\text{kW}}\))

\(cw_{\text{m,pipes}}\) :

Specific embodied water consumption coefficient for pipe materials (\({\text{m}}^{3} {\text{H}}_{2} {\text{O/m}}\))

D :

Pipe diameter (mm)

\(E_{\text{el}}\) :

Net electricity demand (kWh)

\(E_{\text{fuel}}\) :

Net fuel demand (kWh)

G :

Volume flow rate (m³/s)

i :

Interest rate (%)

k :

Coefficient for water losses (dimensionless)

λ :

Frictional coefficient depending on flow conditions (dimensionless)

\(L_{\text{pipes}}\) :

Length of the district energy network (m)

\(N_{\text{equip}}\) :

Year of replacement (years)

\(N_{\text{h}}\) :

Duration of time span t (h/year)

\(N_{\text{l}}\) :

Useful lifetime (years)

\(P_{\text{cool}}\) :

Power demand of chillers (MVC) (kW_el)

\(P_{\text{diss}}\) :

Power demand of heat rejection units (kW_el)

\(P_{\text{ORC}}\) :

Power generated from ORC (kW_el)

\(P_{\text{pumps}}\) :

Power demand of pumps (kW_el)

q :

\(q = i + 1\) (dimensionless)

Q :

Heat load supplied (kW)

\(Q_{{{\text{C}}j}}\) :

Cooling load of jth building (kW)

\(Q_{\text{diss}}\) :

Heat load to be dissipated (kW)

\(Q_{{{\text{H}}j}}\) :

Heating load of jth building (kW)

\(Q_{\text{T}}\) :

Annual total heating (kW)

\(\rho\) :

Water density (kg/m³)

Re:

Reynolds’ number (dimensionless)

t :

Time span in duration curves (index)

V :

Building volume (m³)

\(v\) :

Water velocity in pipes (\({\text{m/s}}\))

\(W_{\text{m}}\) :

Water footprint of equipment construction materials (m³)

\(W_{\text{d}}\) :

Direct water consumption (over 30 years) (m³)

\(W_{\text{ev}}\) :

Evaporated water (CT) (m³/year)

\(W_{\text{f}}\) :

Blue water footprint (over 30 years) (m³)

\(W_{\text{op}}\) :

Indirect water footprint during system operation (30 years) (m³)

\(\Delta H\) :

Delivery lift (Pa)

\(\Delta H/L\) :

Pressure drop per unit length (Pa/m)

\(\Delta t\) :

Operating time (s/year)

\(\Delta \vartheta\) :

Temperature difference between the flow supply and return (°C or K)

η :

Efficiency (dimensionless)

\(\eta_{\text{pump}}\) :

Pump efficiency (dimensionless)

λ :

Frictional coefficient depending on flow conditions (dimensionless)

\(\rho\) :

Water density (kg/m³)

\(\psi\) :

Additional resistance coefficient accounting for local head losses (dimensionless)

This research was funded by the European Regional Development Fund—Interreg V-A Italia—Österreich 2014–2020—Axis 1.1 project IDEE ITAT1007—CUP G22F16000860007.

Authors and Affiliations

1. Dipartimento Politecnico di Ingegneria e Architettura, University of Udine, Via delle Scienze 206, Udine, Italy

   Maurizio Santin, Damiana Chinese & Alessandra De Angelis

2. Research Studio iSPACE, Schillerstraße 25, 5020, Salzburg, Austria

   Markus Biberacher

Corresponding author

Correspondence to Damiana Chinese.

Conflict of interest

The authors declare no conflict of interest.

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