Lower Operating Temperatures
Identified Upgrade Needs
Represent current building
requirements
“These results are very promising for similar operational buildings to connect to district heating networks without having to replace all heating emitters. Temperature lowering testing can help buildings owners with potential to connect to a district heating network evaluate the capital costs, and can encourage more existing buildings to transition to a low carbon energy source.”
Andrea Mackenzie
Graduate Engineer, FairHeat
Background
Buildings across the United Kingdom have aspirational, but necessary carbon targets to be met in the coming years. However, many of these buildings are ageing, and it is becoming more apparent that these buildings do not have a clear scope for lowering temperatures to facilitate low-carbon heating technologies, such as connecting to district heating networks (DHNs) and building-level heat pumps.
The following case study describes the process for investigating if heating system operating temperatures can be lowered for a University building during a recent heating season, whilst minimising disruption to normal building operation.
Challenge
Older buildings within the UK are often found to operate their heating systems at flow and return temperatures, and for this case study the building was operating at a temperature profile of 82/71 °C. This presents a challenge for transitioning these buildings to low carbon technologies, as high flow and return temperatures will result in the desired performance criteria for these technologies not being achieved.
Two of the main hurdles for developing a suitable scope to lower operating temperatures are a) emitter replacements can be expensive for buildings with constrained budgets, and b) many buildings, such as hospitals, schools and courts, do not have the option of significant disruption to their normal day-to-day operation.
Therefore there is a driver to develop a performance test which can keep the building operation in situ and identify if the building can already operate at lower temperatures.
FairHeat Solution
The process began with an initial site visit to strategically locate temperature sensors to monitor the room comfort temperature key performance indicator (KPI) room before, and during the test. This is typically 19-21°C.
The maximum average emitter temperature permitted by the District Heating Network was 65°C. For this case study, the boiler temperature was lowered at the beginning of the test in order to achieve an actual average emitter temperature of 62.5°C, which allows for some contingency.
Figure 1 shows the majority of the spaces achieve the comfort temperature KPI at the lower heating temperatures, and in some cases exceed it. Some areas achieved their comfort temperature KPI with an average emitter temperature of 55°C. For these spaces, there is an increased confidence that emitter upgrades are unlikely to be required to enable a DHN connection.
Figure 2 shows that Room 1 was struggling to maintain its set point prior to the test starting, which indicates that there is a pre-existing issue in this space. For Room 2, this space experiences a decrease in room temperature during the test – this shows that emitter upgrades are required in this space.
The case study also investigated plantroom operating temperatures before, and during the test. Figure 3 illustrates the point at which the operating temperatures were reduced, where it is seen that the boiler flow temperature reduces to 65°C. The system return temperatures are monitored in order to provide an indication if return temperature lowering measures are required.
The DHN requires the heating system to operate with an average emitter temperature of 65°C or lower, and Table 1 shows all recorded circuits were recorded to be operating at an average temperature of 57.6°C or lower. However at the plantroom the boiler return temperature was 57°C, which is greater than the maximum allowable return temperature to the DHN. This indicates that return temperature limiting works will be required to comply with the DHN requirements.
Results
The test has highlighted that the majority of emitters can operate at the required DHN temperatures, an average temperature of 62.5 °C, therefore emitter replacement works are less likely to be required in these areas in order to connect. The test showed there is potential to lower the operating temperatures, as some areas operated with an average emitter temperature of 55 °C and achieved their room temperature KPIs during the coldest period. Note that there is also potential in future that district heating schemes could offer lower tariffs to those who run at lower return temperatures, making it economically advantageous to know the limits of lowering temperatures.
However, the test did indicate that return temperature limiting works are required both at the emitters and within the plantroom in order to achieve the temperatures required by the DHN. Examples could involve removing low loss headers, closing fixed bypasses and improving flow control within the plantroom, and installing pressure-independent flow limiting valves to individual emitters.
Overall, this information allows the building to target key areas for improving performance, and develop a derisked and cost-effective temperature lowering scope to facilitate a connection to a DHN.
Most areas of the building were able to meet comfort temperature targets at lower operating temperatures (62.5°C), reducing the need for costly emitter replacements.
The testing pinpointed particular areas (e.g., Room 1 and Room 2) where temperature targets were not consistently met, indicating a focused need for emitter upgrades only in select spaces.
In situ testing allows a data driven approach to be adopted which is reflective of the buildings operation rather than using theoretical benchmarks.
Recommendations for Operators
- Assess Current Operating Temperatures: Evaluate if existing heating systems can operate at lower temperatures (e.g., 65°C or below), as high flow and return temperatures can hinder DHN compatibility and efficiency.
- Targeted Temperature-Lowering Testing: Conduct a temperature-lowering test across different zones within the building to identify specific areas that may need modifications or upgrades. This can help ensure comfort standards while minimising unnecessary upgrades.
- Prioritise Emitter and Flow Control Adjustments: Avoid blanket emitter replacements by focusing on areas with pre-identified heating issues. In the plant room, consider return temperature control measures, such as adding flow-limiting valves and removing low-loss headers, to meet DHN requirements and improve system efficiency.
- Minimise Disruptions: For buildings with high operational demands, like universities or hospitals, plan for in situ testing and gradual upgrades that avoid major interruptions. Strategic planning helps reduce impact on day-to-day building activities.
- Optimise Plant Room Operations: Adjust plant room setup by installing pressure-independent flow limiting valves, optimising pump speeds, and implementing bypass control improvements to support lower temperature operation, ensuring a smooth transition to DHN integration.
- Engage with DHN Providers Early: Collaborate closely with DHN providers to understand their specific requirements and align your upgrades accordingly. Early engagement ensures that building modifications are well-suited to the DHN's standards and future-proofed for long-term low-carbon goals.
