District heating is already a very efficient way of supplying heat to buildings, but it can become even more efficient if the temperature in the network is lowered. District heating has been in use in Denmark and other countries for more than a century. Instead of each building having its own heating source, water is heated to a certain temperature in a central location and then distributed to many buildings via a network of pipes, providing scale of magnitude savings. Once the heat has been released in the building, the cold water is returned for reheating via the district heating network.
Turning down the heat
Utility companies have therefore begun to lower the temperature in district heating networks, saving energy by operating with a lower temperature. In turn, this reduces heat loss in the network, reducing costs and CO2 emissions. Until fairly recently, the temperature in the network was lowered incrementally because it was difficult to lower temperatures systematically.
District energy management
One way of managing the temperature in district heating networks is by utilising advanced district energy network simulation software such as the TERMIS software application. Read the interview (click on the tab above "Interview: TERMIS benefits") with Thomas Østergaard, Chief Project and Market Manager at COWI and an expert on TERMIS. This makes it possible to combine information from the SCADA (supervisory control and data acquisition) system with pipe data for the network and the consumers, providing an advanced computer model that can calculate how the whole network is functioning in real time.
PHOTO: Thomas Østergaard, Chief Project and Market Manager, COWI
It can also simulate other elements of a district heating system including factors and variables such as:
• Pressure, temperature and flow in the network
• Forecasted outdoor temperature and wind conditions
• The behaviour of large consumers
• Actual electricity prices
• Limits at critical points in the network
With this knowledge available in real time, the operator can accurately forecast energy consumption and lower the temperature in the network to the minimum required.
Knowing the other 80% of the system
Most district heating systems already have a SCADA system to monitor and control temperature and flow data in the system. However, once the hot water is sent into the network, a SCADA system can only monitor the network by tracking the return flow.
The system cannot tell the operator how and why the network performs as it does, and with the distribution network accounting for up to 80% of capital and operating costs, there is an opportunity for significant savings if the operator can accurately model the whole system and its performance.
Providing a real picture of the network also assists operators in developing operational strategies and improving overall efficiency. A TERMIS system lets the operator simulate operational scenarios in pipeline systems ranging from transmission lines to complex looped distribution networks with many energy plants, heat exchangers, pumps, valves and other equipment.
To find out more about TERMIS and district heating, we talked to Thomas Østergaard, Chief Project and Market Manager at COWI. He has extensive experience of installing and operating the TERMIS system for COWI, who are a major Danish consulting group with 6,200 employees that has been in business for more than 80 years.
Click on the tab above (Interview: TERMIS benefits) to read more.
TERMIS has already been installed in more than 500 locations worldwide. Thomas Østergaard from COWI explains the benefits of temperature optimisation in district heating networks made possible by TERMIS.
What benefits does a TERMIS have?
Thomas Østergaard: Traditionally, district heating networks have been operated with a fixed temperature in the network that was high enough to ensure that there was sufficient heating available for all customers at all times. However, as research into energy saving has increased, optimisation of the operation of district heating networks has come into focus. One method for optimising is to reduce the temperature of the water in the network.
Right now TERMIS is both state-of-the-art and the most widespread system for temperature optimisation in the world. From an operational point-of-view, it has a number of advantages because a district heating network is a very dynamic system. No two networks are the same due to factors including the length and size of the pipes, insulation, types of consumer and their installations, methods of heat generation etc.
With TERMIS the operator can still monitor any system in real time and evaluate how the system functions to find the most cost-effective way of operation. Of course, this is a complex piece of software.
To install it the operator already needs to know a lot about a network, and have an organization capable of monitoring the system, plus good data, a SCADA system and detailed knowledge of the network. But then it is the most advanced way of lowering temperatures in a district heating network.
It provides the most precise overview of the system, so that even in Denmark, where the temperature in the district heating networks has already been lowered over the years, there are still potential savings. In networks outside of Denmark the potential for optimising temperatures and making savings is huge.
No two networks are the same due to factors including the length and size of the pipes, insulation, types of consumer and their installations, methods of heat generation, etc.
Thomas Østergaard, Chief Project and Market Manager, COWI
It can also be used to locate and understand breakdowns and other problems in the network. For making adjustments in the network, TERMIS can be used as a planning tool for consulting engineers that provides a level of accuracy and insight that exceeds anything else available.
Traditionally, district heating networks have been operated with a fixed temperature in the network that was high enough to ensure that there was sufficient heating available for all customers at all times.
Thomas Østergaard, Chief Project and Market Manager, COWI
Is there a minimum temperature for the water in a network?
Thomas Østergaard: There are actually two minimum temperatures: a higher one during the winter, determined by the minimum temperature for heating buildings, and a lower one during the summer, which depends on the supply of warm water for other uses. In a modern, optimised district heating network it is possible to lower temperatures to around 55°C (131°F) during the summer.
The minimum temperature is determined not only by the demand for warm water and the structure and flow of the network, but also by water safety regulations. Due to the dangers of Legionella and other bacteria, which grow in temperatures below 50°C, the temperature for producing warm water for bathing and other uses must be kept above 50°C.
How much can heat loss be reduced?
Thomas Østergaard: That really depends on where you start. If you take a district heating network where the temperature has not been optimised at all, then savings will obviously be greater than in Denmark. In Denmark, where the temperature in the district heating networks has been lowered over the years due to regulations, typical savings are around 10%. In other countries there is the potential for much higher savings.
For a large-scale district heating network, TERMIS has a payback time of as little as 1-1.5 years. It will also help utilities in Denmark and other European countries meet increasingly strict requirements for energy savings. And of course, it can also help achieve reductions for other district energy users such as campuses and the like.
Is there a limit to the size of a district heating network?
Thomas Østergaard: No. The largest network is found in Moscow, which is a city of more than 11 million people. However, there is a lower limit determined by population density. If there are too few people or they live too far from one another, then district heating will be too expensive to make sense in the first place. It is a solution for urban areas.
When it comes to district heating, Denmark is one of the countries that is leading the way. Denmark’s first district heating plant was built in 1903 and today 63% of homes in Denmark have district heating. There are 460 heating plants in Denmark using sources of energy including waste incineration, windmills, biomass and geothermal. One of the major advantages of district heating is that is can make use of multiple sources of energy, including renewable energy, and can combine different sources of energy.
District heating other countries as share of citizens served by district heating (Source: Euroheat & Power):
In the EU as a whole, less than 10% of heating production is provided via district heating.
PHOTO: A heating power plant supply district heating in Denmark
Facts about Grundfos and District Heating
Grundfos has delivered many pumps for district heating (and district cooling) networks, not only in Europe but also in North America, Asia and other countries. Grundfos supplies pumps to all levels of district heating networks, from in-line to end-suction pumps and from split case to multi stage pumps, as well as dosing pumps for water treatment. Grundfos also supplies control systems and support tools.