ArcGIS for District Energy: Tracing Thermal Energy
ArcGIS for District Energy: Tracing Thermal Energy
By Tom DeWitte and Tom Coolidge
The purpose of a district energy system is to transport thermal energy to customers (district heating) or to transport thermal energy away from customers (district cooling). It sounds simple, yet the looped nature of district energy pipe networks makes them some of the most complicated utility pipe networks.
Modeling flow through this complicated network of energy plants, pipes, pumps, valves, and eventually buildings is not easy. Yet, it is vital to planners, engineers, and operators of the pipe network to understand how their product moves to and from their customers. This gets even more complicated if the district energy organization utilizes circulation zones with heat exchangers. In that system configuration, the water flow is not the same as the thermal energy flow. This requires an application and data model smart enough to differentiate between water flow and thermal energy flow.
This is where ArcGIS with its ArcGIS Utility Network capability and District Energy Data Model can help.
Thermal Energy and District Heating
When modeling a district heating pipe network, it is vital to understand where the energy starts and where it goes.
For district heating, the start is typically the energy plant. From the energy plant the heated water or steam transports the thermal energy through pipes, pumps, heat exchangers, valves, more pipes and eventually it to a building. The customer in that building consumes the thermal energy to heat their home. In a full loop system, the now cooled water returns to the energy plant to be reheated.
Thermal Energy and District Cooling
When modeling a district cooling pipe network, the thermal energy starts with the customer and is delivered to the cooling plant where it is typically released into the air.
In a full loop system, after the thermal energy is released to the air, it is sent to chiller units to further remove thermal energy. This results in an additional decrease to the water temperature. Once cooled it is transported through pipes, pumps, heat exchangers, valves, and more pipes before it reaches the customer's building. At the building the chilled water absorbs the customer’s waste heat and transports it back to the cooling plant.
Leveraging Utility Network
Modeling this real-world transportation of thermal energy through a pipe network, requires more than an understanding of how the pipes, pumps, heat exchangers, valves and other components are connected. It requires the ability to understand which pumps are operating, and which valves are closed. It also needs to differentiate between cathodic protection wires and leak detection wires. These wires are connected to the pipes but do not transmit thermal energy. To accurately represent these additional real-world complexities, we need a more advanced connectivity model. We need to leverage the Utility Network.
The Utility Network is an extension to ArcGIS. ArcGIS is the geographic information system (GIS) provided by Esri.
What Stops Thermal Energy Flow
With a Utility Network comes the Trace geoprocessing tool. A configuration of this tool is what will be used to perform the thermal energy flow trace. To correctly configure the thermal energy flow trace requires a real-world understanding of what can stop the thermal energy flow.
In the real-world devices which are closed, such as a valve, or are not operating, such as a pump, will impede the flow of the thermal energy. Add to this list any pipe segment or device which is not in service, such as retired pipe segments or pipe segments which are proposed but have not yet been built. Lastly, there is the need to exclude the cathodic protection wires and leak detection wires which are part of the pipe network but do not conduct thermal energy flow.
When using the District Energy Utility Network Foundation data model, those constraints look like this:
- Pipe segment or asset is not in service: Lifecycle Status Does not equal In Service
- Valve is closed: Device Status is equal to closed
- Pump is not operating: Device Status is equal to closed
- Cathodic Protection wires: Category is equal to CP Only
- Leak detection wires: Category is equal to Leak Detection Only
Configuring the Trace Tool
The Trace geoprocessing tool in ArcGIS Pro has many parameters. Here is how to transpose the constraints into the specific settings in the Trace tool.
The type of trace will be a downstream trace, leveraging the DHC domain network, and the DHC Energy Tier. Setting the Tier to “DHC Energy Tier” is important as it sets the flow source as the energy plant/chiller plant, versus the “DHC Pressure” tier which would set the source as in-system pumps.
The constraints will be added as Traversability Barriers. If any one constraint is true, the trace will not traverse beyond the asset.
When this trace is run, it will return all pipe segments, devices, fittings, and customer service points which are receiving thermal energy from the designated start location.
This includes both the supply and return portions of the pipe network.
If you are a district heating organization and only interested in the thermal energy flow supplying energy to the customer, you can add a filter barrier:
- Pipe segments are only supply lines: Line Asset Type does not equal supply
This will return a selection set of the pipe network which shows how the thermal energy traverses the pipe network from the designated location to the customer.
The same configuration will work on the district cooling pipe network.
Sharing the Trace
Now that you know how to configure the trace tool to perform a thermal energy flow trace, how do you share this with others in your organization. And, how do you share it in a way that does not require everyone to manually perform this configuration of the Trace Tool. This is where the new functionality introduced at ArcGIS 10.9, called Trace Configurations is useful.
Trace Configurations is the ability to store a configuration of the Trace Tool within the Geodatabase. When the Thermal Energy Flow trace is stored in the Geodatabase, other desktop, web, and mobile users do not need to know how to configure the tool.
A simple check of the “Use Trace Configuration” option removes all the configuration options and replaces it with a simple pulldown menu for the end user to select from.
Having the trace configuration centrally stored and accessible to end users ensures that everyone is running a properly configured thermal energy flow trace.
Summary
Planners, engineers, and operators require this type of advanced flow modeling to help them perform their daily activities. Thermal energy flow modeling is just one of the many types of water, thermal, cathodic protection, leak detection flow analysis which can be configured with the ArcGIS Utility Network. These trace capabilities help to remove some of the complexity of maintaining and operating a district energy pipe system.
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