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Substantial technical challenges involved in designing an energy loop

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Much more than a simple heating network, an energy loop extends beyond a single building to serve several customers and sites. There are multiple resources available to help designers plan the system. It is not enough to simply reuse the mechanical engineering concepts used for commercial in small buildings. The scale of this type of system requires robustness and the system’s configuration will, in fact, incorporate several aspects particular to energy loops.
So designing and installing it takes specific skills to deal with the challenges involved, including those related to the piping and energy measurement. The solutions chosen must take into account the objectives and constraints related to the operation and maintenance of the equipment by the system operator.
For example, the infrastructure used (tunnel access instead of buried lines, energy mix, network temperatures, etc.) will directly depend on the project business model, the operating and maintenance requirements, and the equipment’s life cycle—all these factors will greatly influence the design.
 
Useful resources for the technical design
There are many articles and other resources available to help design these systems. The 2016 ASHRAE Handbook1 provides a good overview of the technical principles involved in designing district systems. For more detail, the 2013 District Heating Guide and District Cooling Guide as well as the International District Energy Association’s publications are worth consulting.
8861_vol33-n1-2-livresSome of the themes and technical issues covered in the ASHRAE guides:

Themes

A few essential considerations

Designing a hydronic network

  • Detailed studies and simulations needed
  • Thermal expansion systems
  • Pressure loss
  • Pipe sizing

Thermal factors

  • Adequate insulation for network types and temperatures
  • Asset servicing and maintenance
  • Buried pipe versus in tunnels

Thermal expansion

  • Sizing of the expansion loop
  • Section of prestressed lines

Operating the equipment

  • Water treatment
  • Servicing and replacement (life cycle of the equipment)

For example, it is essential that pipe expansion be taken into account when designing the system. The reader is reminded that a 12-inch pipe may need a 15 ft x 31 ft expansion loop, which can be complicated to integrate into a project.2 The use of prestressed or compensating section mechanisms can be considered, but each solution comes with its share of advantages and drawbacks.3
 
Figure 1: Example of a solution comparison presented for a given project

Source: Kristin Wild, M.A.Sc., P.Eng., KWL Consulting Engineers. As part of the IDEA2018 presentation, Vancouver, BC.
Source: Kristin Wild, M.A.Sc., P.Eng., KWL Consulting Engineers. As part of the IDEA2018 presentation, Vancouver, BC.
 
Fortunately, even though traditional strategies combining steel and insulation onsite are still used, specialized pipes and options can resolve certain challenges in many projects in order to lower the project costs or simplify implementation and ensure robust, durable installations.4

Sizing and operating context for resiliency
To benefit from the advantages of an energy loop, it is important to calculate the loads specifically for that solution. And it is worthwhile taking into account the diversity of the loads between several spaces. Thanks to the network and equipment sharing, the systems designed will be more durable and resilient, with fewer heating and cooling appliances compared to a traditional installation where the equipment is duplicated in every building. The resulting gains in space and maintenance are significant on the scale of a whole neighbourhood.
The fact that the equipment is designed to be robust and large capacity with a long service life makes it possible to incorporate very high efficiency, innovative, renewable solutions that would typically be less cost-effective for small, individually sized installations. On the other hand, these systems have to be rigorously monitored by an experienced operator to ensure proper control and continuous optimization of this high-performance equipment.
 
Measurement challenges and operating context
For many projects, one of the main distinctions of an energy loop versus a traditional hydronic solution is the crucial role played by energy measurement, which allows for accurate billing of the thermal energy consumed by the various users on the loop.
In Québec, energy loop projects are currently being carried out in an unregulated environment, which is to say there is no organization controlling the billing and operating framework. While this may not be a problem for a hospital complex or university campus which has its own facilities, it can be an issue in the sale and supply of energy to third parties.
A Measurement Canada committee is currently working on a regulatory framework for measuring the thermal energy of energy loops. The first drafts obtained refer to existing standards and the use of the C900 and EN-1434 standards. However, Isabelle Picard, engineer and Director of the Natural Gas Technologies Centre (NGTC), who worked on the related technical committee, advises caution: “EN-1434 has just been completely revised in Europe. It will probably not be enough to specify EN-1434 adherence to be in compliance […].” Canadian regulation is expected to be published in 2021, with compliance required by 2026. Designers should take precautions since corrections could be required, even in the case of more recent projects. That means adopting current best practices, fully mastering the concepts of measurement classes and managing measurement errors according to energy regulations. Replacement of measurement instruments could also be required in the short or medium term.
 
Groundwork for the future
While the advantages are many and favour building small-scale loops and systems, several factors are slowing the adoption of large-scale energy loops in the Québec context.
Fortunately, several experts are studying this solution, as well as a multidisciplinary team associated with the Institut de l’énergie Trottier (Polytechnique, Université de Montréal and McGill University) work together on the technological, socio-professional, political and legal barriers. The long-term goal is to realize the potential of district heating to contribute to urban redevelopment and create mixed-use neighbourhoods that are compact, diversified and efficient—in other words, sustainable.5
 
Mathieu Rondeau Eng., CEM, CMVP, LEED AE®
DATECH Advisor, Technology & Energy Efficiency, Énergir 

 
1. Source: 2016 ASHRAE Handbook – HVAC Systems and equipments, Chapter 12 – District heating and cooling
2. Source: 2016 ASHRAE Handbook – HVAC Systems and equipments, Chapter 12 – District heating and cooling
3. Source: “Targeted DPS Design for Cities, System Expansion and Modernization,” IDEA2018 presentation by Kristin Wild, M.A.Sc., P.Eng., KERR WOOD LEIDAL consulting engineers
4. Elizabeth Nolder and Stephen Pollard, “Underneath the ivy,” Direct Energy Magazine / First Quarter 2018. URL: https://www.districtenergy.org/blogs/district-energy/2018/01/16/underneath-the-ivy
5. https://iet.polymtl.ca/projets-finances/reseaux-de-chaleur-de-4e-generation-quartiers-durables/
 
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