Dear reader,
with this 24th issue, we complete the first 2 years
of our heatbeat Research Newsletter.
In this time, we covered a wide range of topics
with relation to district heating from the demand
side and the network operation to the integration
of several kinds of renewable heat sources.
In addition to zooming in on these topics, we
surveyed and summarized the entire district heating
literature in our annual heatbeat District Heating
Trends (District
Heating Trends 2021, District
Heating Trends 2022).
To mark the occasion of this anniversary, we have
started to make improvements to the
newsletter-section on our website.
Until now, we had focused on our monthly newsletter
to keep you updated about district heating research
and we are looking forward to continue this in the
future.
The major change is that on our website, we have
extended the newsletter-section into a Blog
format.
This means that we will continue to update our
monthly Research Newsletter without any changes and
no need to worry:
We will not send you more emails than the 1
newsletter-update each month.
At the same time, we will have the opportunity to
also post insights from our projects and
development with a more practical focus on our new
Blog.
If you're interested, our first blog post takes a
look at the new German BEW subsidies
for the
operation of heat pumps in district heating
networks.
And after your positive feedback on our newsletter
issue 22, this
current issue will also look at a few very recent
research papers instead of diving deep into a
single paper.
A Review of Strategies to Reduce Supply
Temperatures in Existing Networks
In Reduction
of supply temperature in existing
district heating: A review of strategies and
implementations,
Guelpa et al. take a structured approach to the
challenge of reducing supply temperatures in
district heating.
They identify 3 types of limitations that can
hinder temperature reductions:
-
Network limitations: Increased pump costs as
well as pressure and velocity limits
-
Substation limitations: Limits of heat
exchangers and the temperature requirements for
DHW preparation to prevent legionella
-
Building limitations: Limited radiator areas
and thus limited heat transfer capacities
Based on this analysis, the paper suggests a wide
range of actions that can be taken to overcome the
limitations.
These actions include, among others, taking
advantage of capacity reserves in the system caused
by overdimensioning, modifications to the pressure
control strategies and pump setups, and using
storages and demand side management for peak
shaving, before modifying the pipe network itself.
In total, this paper provides a great guideline for
readers interested in a structured approach to
lower the supply temperatures in existing district
heating networks, which is a key to unlock the
potential of integrating renewable heat sources
into district heating.
CO₂-Emissions of Heat Pumps Depending on
Electricity Source
One key technology benefiting from lower supply
temperatures are of course heat pumps.
Yet, they are not a renewable heat source by
default, but depend to a large degree on the source
of electricity used to drive their operation.
In this context, 2 interesting preprints by Hurst
et al. were just published (General
numeric
determination of ecological operation of heat pumps
using power from
cogeneration
and Dependency
on external power supply to operate
large-scale heat pumps to decarbonize
Cogeneration-based District Heating
Networks).
While not final, these 2 papers take an interesting
look at the CO₂-emissions of heat pumps using
different electricity sources.
The authors compare heat pumps operated in tandem
with a Combined Heat and Power (CHP) plant directly
using its electricity output with electricity
sourced from the public German grid as well as from
local renewable sources.
The analysis shows that the impact of the
electricity source on the specific CO₂-emissions of
the generated heat is very large.
For the case of a heat pump working in tandem with
a CHP, the analysis arrives at CO₂-emissions which
are even higher than heat generated by the CHP
alone, if both generators are operated at the same
output temperatures (which is of course not ideal
for the heat pump). In comparison, operating a
large scale heat pump with electricity from the
German public grid with its current energy mix was
found to cause CO₂-emissions in a similar range
than the stand-alone CHP (depending on the CHP's
fuel).
And compared to that, using renewable electricity
sources for the heat pump operation was found to
reduce the CO₂-emissions by a factor of 5 - 15.
Thus, even while we hope that heat pumps will
benefit from lower CO₂-emissions of the total
electricity generation for the public grid, these 2
papers illustrate the benefit of using local
renewable sources as much as possible.
Survey of 5GDHC Networks in Germany
When thinking further about reducing network
temperatures and integrating renewable heat
sources, ultra-low temperature networks (sometimes
referred to as the 5th generation of district
heating and cooling 5GDHC) are a popular concept in
research.
To see how much that research has already
translated into actual change in the real world,
our former colleagues at RWTH Aachen Wirtz et al.
have just published a Survey
of 53
Fifth-Generation District Heating and Cooling
(5GDHC) Networks in
Germany.
This paper is also part of our joint efforts in the
TransUrban.NRW
research project and we are especially happy to see
the project's demo-sites together with some of our
other heatbeat projects as well as many further
networks in this comprehensive survey.
As such, the paper gives a very recent analysis on
the current state of 5GDHC in Germany.
In a way, this continues the work started by Buffa
et al. in 2019 (see our newsletter issue
3) which surveyed 40
different 5GDHC networks in Europe at the time, 15
of which are located in Germany.
So we can directly see a large increase in the
number of networks in Germany.
And in another interesting direction, the new
survey does not only look at the technology used,
but also into the business models and boundaries of
ownership between network operators and building
owners.
The results show that there is a wide variety of
both technology mixes and business models used.
This shows that there is currently no standard
solution that can be transferred to every location,
but that each case requires an in depth-look to
find the optimal solution for the location and the
stakeholders involved.
Resilient cooling through geothermal district
energy system
And even as summer has come to an end in the
northern hemisphere, the various heat waves in
recent months have shown that not only heating, but
also cooling is an important topic.
Offering insights into possible solutions, a recent
paper by Gautier et al. investigates Resilient
cooling through geothermal district energy
system.
For the investigation, the authors use dynamic
simulations to show how an ultra-low temperature
network (similar to those surveyed by Wirtz et al.)
connected to a geothermal borefield can not only
provide heating, but is also an efficient and
robust solution to maintain indoor thermal comfort
during heat waves when using the network to cool
buildings. We think that this is an aspect of such
networks
that will get more important if summers continue to
put heat stress on the built environment as
happened this year.
One aspect the paper also shows is that a
geothermal source can help to operate the network
at low temperatures which allow direct cooling of
the buildings without the need for a compression
chiller in the building.
This does not only help to reduce the electricity
demand of the cooling operation in general.
Furthermore, this reduces the electricity demand in
potentially critical times during heat waves when
the electric grid may also be under stress to meet
all demands.
Thus, the authors conclude that such a system can
be an important contribution to the resilience of
urban infrastructure.
Thanks for you continued interest after those 2 years of heatbeat Research Newsletter. The next issue of our newsletter will be published November 2.
Best regards,
Your heatbeat team
