Technical Paper | District Heating and Heat Pumps Abstract The Heat Roadmap Europe (HRE4) models the thermal capacity needed to decarbonize heating scenarios by 2050. Large-scale heat pumps constitute one of the most important technologies in decarbonizing heating supplies in the future. This paper provides a quantitative overview of demand for decarbonized heating in the EU. Based on this future heating challenge, it is important that large-scale heat pump suppliers and developers take up the challenge and seize the opportunities available. This paper will also describe how district heating grids and heat sources can assess appropriate heat pump technologies. Finally, the paper considers the opportunities for addressing decentralized heating providers like supermarkets and air conditioning chillers, that are traditionally intended for cooling only. Under the Auspices of the Italian Ministry for the Environment | 18th European Conference | The Latest Technology in Refrigeration and Air Conditioning | Milan, 6-7 June 2019 EU decarbonization of heating calls for large scale heat pump innovation By: Torben Funder-Kristensen, Ph.D. Head of Public & Industry Affairs, Danfoss Cooling Jan Eric Thorsen, M.Sc. Director of Heating Application Centre, Danfoss Heating Drew Turner, M.Sc. Global Marketing Manager, Danfoss Cooling Leping Zhang, M.Sc. System Architect, Danfoss Cooling airconditioning.danfoss.com
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Technical Paper | District Heating and Heat Pumps
AbstractThe Heat Roadmap Europe (HRE4) models the thermal capacity needed to decarbonize heating scenarios by 2050. Large-scale heat pumps constitute one of the most important technologies in decarbonizing heating supplies in the future. This paper provides a quantitative overview of demand for decarbonized heating in the EU. Based on this future heating challenge, it is important that large-scale heat pump suppliers and developers
take up the challenge and seize the opportunities available. This paper will also describe how district heating grids and heat sources can assess appropriate heat pump technologies. Finally, the paper considers the opportunities for addressing decentralized heating providers like supermarkets and air conditioning chillers, that are traditionally intended for cooling only.
Under the Auspices of the Italian Ministry for the Environment | 18th European Conference | The Latest Technology in Refrigeration and Air Conditioning | Milan, 6-7 June 2019
EU decarbonization of heating calls for large scale heat pump innovation
By:Torben Funder-Kristensen, Ph.D. Head of Public & Industry Affairs, Danfoss CoolingJan Eric Thorsen, M.Sc. Director of Heating Application Centre, Danfoss HeatingDrew Turner, M.Sc. Global Marketing Manager, Danfoss CoolingLeping Zhang, M.Sc. System Architect, Danfoss Cooling
The EU energy targets for 2030 and the long-term 2050 decarbonization aspiration call for the most efficient innovative solutions spanning multiple sectors. Heating buildings consumes the largest amount of energy, and produces the highest CO₂ emissions. So, the focus is on planning for a resilient and efficient system that can provide affordable heat for all. To minimize investments, energy demand must be reduced by applying energy efficiency measures to buildings and optimizing the performance of technical building systems. There is also a need to establish efficient, decarbonized heating supply systems that put a focus on renewable energy. The nature of renewable primary energy supply will force the demand and supply sides to become much more integrated. This will in turn call for new applications and technologies like demand side flexibility and thermal or electrical energy storage. In the Heat Roadmap Europe (HRE) studies 1 and 2, it has been shown that increasing district heating to cover 50% of the total heat demand, together with a 40 GW heat pump capacity, can address up to 15% of total heat demand
on average. In periods with a surplus of renewable electricity, heat pumps are supposed to continue operating and using thermal storage to capture excess heat due to unused compressor capacity.
Large-scale heat pumps are estimated to produce 520 TWh/year with a coefficient of performance (COP) of 3 (see figure 2). Such an increase means they can better use alternative sources of heat like ground source thermal heat and waste heat from data centers. At the same time, they can use intermittent renewable electricity.
While realized COP in cooling systems is important, it might not be considered a primary business factor due to existing business models. However, in heating, the ‘realized COP’ of heat pumps is a primary business factor for district heating (DH) operators. The realized COP depends on some basic factors like temperature lift, as well as the technology behind the heat pump systems.
Introduction
Bioenergyfuels
Combustionengines
Wind etc. Electrofuels
Fuel storage
Resources Conversion Demands
Mobility
Cooling
Solar etc.
Heating
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exchange
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Combinedheat & power
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Fig. 1: Operation of a Smart Energy System when there is integration of wind power [1].
DH source shares in BL 2050 DH source shares in HRE 2050
CHP plants
Electric boilers Fuil boilers Waste incineration Fuel production heat recovery
Geothermal Heat pumps Solar thermal Industrial excess
Fig. 2: Source HRE roadmap. 2050 DH source share. HRE is the “decarbonised scenario” [1].
Sources for District Heating
Temperature lift is the difference between the temperature of the heat source inlet and the temperature supplied to the DH system outlet. DH grids have developed over the last 130 years. This development can be divided into four generations, each often referred to by generation names like 3G or 4G. The main parameter characterizing the G-level of the system is the flow line temperature. 3G systems have a flow temperature below 100°C while new 4G systems will go as low as 40°C [4].
As the flow temperature decreases, there are overall system efficiency increases, as well as more opportunities to apply decentralized heat sources like heat pumps or waste heat from supermarkets. The first parameter in determining how low the flow temperature can go is the size of the heating surfaces in buildings. For example, large surfaces using floor heating might use 40°C water, while old radiators in poorly-insulated buildings will demand 80°C during cold periods. Low temperature heating is still rare in the majority of building stock in the EU, but is expected to grow as old building stock is renovated. For new city areas, low temperature DH is an obvious choice. Specific high temperature needs will then be handled by dedicated heat pumps.
Another parameter determining the DH flow temperature is the architecture of the DH system. Pipe diameter, distance between heat supply sources and end consumer density are all important factors in DH system design.
Seasonal variations in heat demand will set the constraints for the flow line temperatures—but the trend is towards lower temperatures, even during winter. Good practice is to lower the temperature until the most demanding heat consumer calls. Then specific action (such as installing better insulation) can be taken to raise performance for that specific consumer.
Each city has unique opportunities to use large heat sources like combined heat and power plants, industrial plants, data centers, sea water etc. This will of course be subject to the outline of the DH system and flow temperature, as some heat sources may have higher temperatures than others.
The flow line temperature does not necessarily reflect demand from end consumers, as it can often be based on grid piping constraints or specific heat sources. A lower temperature that ensures sufficient capacity throughout the grid can be �
HP supply temp. Temp. can be lowered during o�-peak season
Temperature of �exiblecentral heat sourcee.g. CHP plant
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Fig. 3. Source Danfoss. DH flow line temp. compared to demand needs.
Fig. 4. Source HRE roadmap Europe and Danfoss. HP COP versus temp. lift; data from [1].
Flow line temperatures and demand needs
Connection between Heat Pump efficiency and temperature lift
� obtained by having multiple, decentralized distributed energy sources like heat pumps. Smaller heat pumps can boost 4G flow temperatures for apartments or multi-apartment buildings, while large heat pumps can supply heat to the grid via ground source. Supermarkets have also shown they can deliver extra heat to the DH. This issue has already shown to be an important factor to
discuss when planning the introduction of heat pumps to the district heating grid. The lesson is that the necessary temperature lift may often be smaller than the official flow temperature. This is an important parameter to consider when discussing heat delivery.
Heat pumps larger than 1 MW are often based on well-known ammonia technology. While CO₂ heat pumps can be a good source of high temperature DH, this technology is not common yet.
The HFO refrigerant R1234ze(E) has been introduced to the market over the last few years. Due to its high critical point (109,4°C), R1234ze(E) offers very good performance in heating applications. Furthermore, it can be used in centrifugal compressors due to its high molecular weight.
Assuming a temperature lift of 30-50°C, two or three stages of compression are normally suitable. However, CO₂ can use counterflow heat exchanger technology, and be effective for one stage compression as well, because of its transcritical properties.
A survey [1] shows COP values from 149 large heat pumps installed in the EU with capacities of up to 230 MW and average capacity of 10 MW. Even with a clear trend line seen in Figure 6, one can see a high deviation variance in the COP results. This can be explained by differences in the system architecture, such as on/off duty cycle or variable-speed drive, level of maintenance, etc. As a rule of thumb, the higher the capacity of the system, the higher the efficiency. This is due to these systems having more complexity and optimization procedures. It should be noted that potential future rollout of large ground source heat pumps would have capacity limits around 5-10 MW, and would call for more modular system designs.
Technology behind the low-GWP heat pump systems
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TDH [°C]Heating
WW-HPCOP System/Refrigerant
1919/1212/5
55-6545-5534-45
4,7Centr. oil free
1234ze(E)
26/1919/1212/5
55-6545-5534-45
4,0 Screw/NH₃
26/1919/1212/5
35/65 3,9 Recip/CO₂
26/1955-6545-5534-45
5,4Centr. oil free
1234ze(E)
15/855-6545-5534-45
3,9Centr. oil free
1234ze(E)
26/19 35-65 4,6 Recip/CO₂
15/8 35-65 3,5 Recip/CO₂
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Performance comparison between system setups, compressor technologies and refrigerants
Figure 5: Source Danfoss. TWS = Temperature of the Heating Water Source / TDH = Temperature of the District Heating Supply.
The energy outlooks for Europe call for ambitious investments in DH networks. Large-scale heat pumps will be necessary to power district heating and adapt to the increasing amount of renewable electricity being generated.
The temperature demands of the district heating grid have decreased continuously over time. It’s anticipated that future DH grids will go as low as 40°C, allowing for decentralized heat suppliers like supermarkets.
Heat pumps can be introduced effectively on a mass scale as decentralized zero carbon heat suppliers. System simplicity, low noise levels and refrigerant safety are all important factors that could establish MW-sized pumps within cities.
Heat pumps’ efficiency is also key to delivering affordable heating. By using oil-free heat pump systems, we can ensure heat pumps are efficient, safe and silent.
1: Andrei David et al ; Heat Roadmap Europe: Large-Scale Electric Heat Pumps in District Heating Systems; Energies 2017, 10, 578; www.mdpi.com/journal/energies2: Connolly, D. et al ; Heat Roadmap Europe: First Pre-Study for EU27; Aalborg University: Aalborg, Denmark, 2012. 7. 3: Connolly, D. et al; Heat Roadmap Europe: Second Pre-Study; Aalborg University: Aalborg, Denmark, 2013.4: Lund, H. et. al. (2014) ; 4th Generation District Heating (4GDH). Integrating Smart Thermal Grids into Future Sustainable Energy
Systems. Energy 68; (2014) 1-11.5: Zühlsdorf B., et al; Heat pump working fluid selection—economic and thermodynamic comparison of criteria and boundary
conditions, International Journal of Refrigeration 98 (2019) 500–513.
Thanks to their high compressor RPM and contact-free operation, oil-free air conditioning chillers using centrifugal compressors have strong energy efficiency, a small size and low noise levels. Even though oil-free systems have not yet been used for large-scale heat pumps, they are remarkable due to their high efficiency and quiet operation. These qualities make them well suited for use in densely populated areas.
To evaluate the efficiency of these systems compared to other low-GWP refrigerants, we performed some basic simulations comparing CO₂ reciprocating technology and NH3 screw compressor technology with state-of-the-art oil-free systems for heat pumps with an approximate 2 MW capacity. In the future,
as research into using tailor-made low GWP refrigerant blends suitable for counterflow heat exchangers continues, it’s likely that efficiency will increase [5].
All the systems used an economizer. However, CO₂ and NH₃ systems are more complex due to the need to manage oil. The CO₂ systems evaluated do not use ejectors or parallel compression. The results show system COP values of 3.5-5.4 depending on whether water supply temperatures were 15°C (high temperature level ground source) or 26°C (data center source). The oil-free system shows significant results without as much complexity, making it suitable for large-scale system production.
