UE 12 - Buildings and heat Flashcards
Energy sources + sector coupling for climate-friendly district heating generation
What technologies do you know?
- CHP or heating plants
–> H2
–> CH4 + CCS
–> Synthetic CH4
–> Biomass - Waste heat
–> From industry, wastewater, water bodies and waste
–> E.g. data centers - Large-scale heat pumps
–> Water source HP
–> Ground source HP
–> Air source HP
–> HP using waste heat - Power-to-Heat
–> Electrode boiler
–> Resistance boiler - Deep geothermal energy
- Solar thermal energy
What is missing?
Power-to-heat systems are comparable to “…” that work according to “…”. If there is a lot of surplus renewable electricity in the grid, it is used in the system to generate heat. If the heat load is low, “…” and thus supports sector coupling.
“large kettles (“Wasserkochern”)”
“the immersion heater principle (‘Tauchsiederprinzip’)”
“the renewable heat is stored in a heat storage for later use”
What challenges do you think could arise in the use of P2H and heat storages in the context of district heating?
- High electricity prices or taxes can make P2H uneconomical, especially if heat from gas or waste incineration is cheaper
- Grid capacity limitations may restrict how much electricity can be used during peak times.
- Temporal discrepancies of RES supply and heat demand
- Thermal energy storage (TES) helps decouple electricity use from heat delivery — but:
–> Large tanks take up space
–> Long-term seasonal storage still faces efficiency losses and cost barriers
What challenges do you think could arise in the use of large-scale heat pumps in district heating?
- High upfront investment costs
-
Heat source availability and suitability
–> Not all locations have accessible or adequate low-temperature heat sources (like rivers, sewage, or waste heat).
–> Seasonal changes (e.g. colder rivers in winter) can affect efficiency and performance. -
Integration into existing heating networks
–> Many existing district heating networks operate at high temperatures (80–120°C), while low-source HP (LSHP) work best at low to medium temperatures (up to ~70°C).
–> Efficiency (COP) drops significantly when higher output temps are required. -
Electricity demand and grid impact
–> Large heat pumps consume significant amounts of electricity, especially during winter.
–> Could stress local electrical grids if not properly managed.
–> Electricity prices may be volatile or unfavorable compared to gas or waste heat. -
Regulatory and planning complexity
–> Large infrastructure projects face lengthy planning, permitting, and environmental approval processes.
–> Rules around using ambient water, groundwater, or wastewater vary widely.
What challenges do you think could arise in the use of biomass in the context of district heating?
-
Sustainability and land use concerns
–> Large-scale biomass demand can lead to: Deforestation, monoculture plantations, loss of biodiversity -
Competition for biomass resources
–> Biomass is in high demand for: heat and power generation, biofuels, industrial use (e.g., steel or cement) -
Logistics and Infrastructure
–> Biomass is bulky and heavy, requiring: frequent deliveries, storage facilities, transport infrastructure -
Air quality and emissions
–> Biomass plants contribute to air pollution
What is missing?
Geothermal energy: “…”
With geothermal energy, heat from underground can be harnessed with the help of various technologies. This requires drilling up to several kilometers into the ground. A major advantage of geothermal energy “…”. In addition, the underground can also be used as a seasonal heat store (aquifer storage).
“the constant source of heat underground”
“is the high number of operating hours and thus the year-round use of renewable heat in the base load”
What challenges do you think could arise in the use of geothermal in the context of district heating?
-
Geological uncertainty
–> The biggest risk: You don’t know exactly what’s underground until you drill, there might be possible issues (insufficient temperatures, unfavourable rock formations) - High upfront investment costs
- Long project development time
-
Corrosion, scaling, and maintenance
–> Geothermal fluids often contain dissolved minerals and gases (e.g., H₂S, CO₂, iron, silica).
–> This can cause scaling and corrosion in pipes and heat exchangers.
What challenges do you think could arise in the use of hydrogen in the context of district heating?
- Green H2 production has a low overall efficiency which leads to fuel costs
-
Infrastructure limitations
–> Hydrogen needs dedicated pipelines, burners, and storage systems - Technical performance of hydrogen boilers
–> Hydrogen combustion produces very high flame temperatures, which can increase NOX emissions if not properly controlled
What is missing?
Overview CHP Technologies
“…”
- Power: 1 to 40 𝑘𝑊𝑒𝑙
- Fuel: External combustion (Wood, gas)
“…”
- Power: 20 𝑘𝑊𝑒𝑙 to 10 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
“…”
- Power: 0 to 250 𝑘𝑊𝑒𝑙
- Fuel: Hydrogen, natural gas, methanol, biogas
“…”
- Power: 1 to 100 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
“…”
- Power: 20 to 500 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
Overview CHP Technologies
Stirling engine
- Power: 1 to 40 𝑘𝑊𝑒𝑙
- Fuel: External combustion (Wood, gas)
Combustion engine
- Power: 20 𝑘𝑊𝑒𝑙 to 10 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
Fuel cell
- Power: 0 to 250 𝑘𝑊𝑒𝑙
- Fuel: Hydrogen, natural gas, methanol, biogas
Gas turbine
- Power: 1 to 100 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
Gas and steam turbine
- Power: 20 to 500 𝑀𝑊𝑒𝑙
- Fuel: Oil, natural gas, LPG, biogas, hydrogen
Name conventional technologies for district heating.
Conventional technologies for district heating
- CHP
- Heating plants
What is missing?
“…” are heat supply systems that supply residential and industrial areas with solar heat via “…” and heat networks.
“Solar district heating systems”
“large collector fields”
Visualization
Renewable district heating: Deep geothermal energy
Compare slide 32
Thermal water cycle
Production well
Injection well
District heating cycle
Plate heat exchange
Pump
District heating network
Outlet (e.g. 50°C)
Inlet (e.g. 80°C)
Hot water cycle
Heat exchange station
There are two different types of gas heating systems. Name and explain them.
Gas boiler
–> Uses the calorific value of the gas
Gas condensing boiler
–> Uses the calorific value through condensation of the water vapour
a) Name conventional technologies for decentral heating.
b) Name technologies for renewable decentral heating.
Conventional technologies for decentral heating
- Gas boiler
- Gas condensing boiler
- Oil Heating
Technologies for renewable decentral heating
- Heat pumps
- Pellet Heating
- CHP Systems Based on Fuel Cells
- Solar thermal system
- Geothermal heating system
What is missing?
For process heat, several different technologies exist but processes must often be adapted to switch from conventional to electric heating.
Not all processes can be switched to electric heating due to:
- “…”
- “…”
“High temperature levels (e.g. porcelain production)”
“Need of carbon as feedstock (e.g. steal)”
True or false?
Near-Surface Geothermal Energy
1) “…”
2) Heat pumps
- Heat transfer to refrigerant
- Compression
- Heat exchanger
- Expansion
3) Storage hot water
4) Storage heating circuit
“Horizontal geothermal energy collector OR geothermal probe”
Near-Surface Geothermal Energy
Explain the difference between a …
a) … horizontal geothermal energy collector
and
b) … geothermal probe
a) Horizontal geothermal energy collector
- Collectors work with a horizontal pipe system that lays at a depth of about 1,5 metres
- The area required depends mainly on the size of the area to be heated up and the rainwater permeability (‘Durchlässigkeit’) of the soil
–> It is usually one and a half times the heating surface.
b) Geothermal probe
- In geothermal probes, a frost-proof liquid (the brine) circulates in a closed circuit through a plastic pipe
- At a depth of 10 metres, temperature is almost constant throughout the year. It is therefore independent of seasonal
fluctuations. - Are very effective in winter and in the summer they are suitable for passive cooling
Name and explain technologies using only electricity to heat water
- Heating rod / resistance heater
–> The flow of electric current through conductive (‘leitend’) material heats it. The heat is then transferred to the water. - Electrode boiler
–> The water is heated directly without resistance elements
–> It operates in AC mode to prevent the electrolytic decomposition of the water
What types of heat storages are there?
Heat storage
- Sensible
–> Stores heat by changing the temperature of a material - no phase change - Latent
–> Stores heat via phase change, typically from solid ↔ liquid (e.g. melting or freezing) - Thermo-chemical
–> Stores heat via reversible chemical reactions (endothermic ↔ exothermic).
