WHY PRE-INSULATED PIPE SYSTEMS FOR DISTRICT COOLING?

Worldwide, the need for comfort cooling buildings is at least the same as the need for heating buildings. The need for comfort cooling buildings is self-evident in countries like, e.g., the Middle East region and the southern part of Europe. But also in the more northern situated countries like, e.g., Sweden, Finland, Norway, and Denmark, there is a need for comfort cooling. Here, cooling is needed for office buildings, large shopping malls, hospitals, hotels, etc.

By Peter Jorsal, Product & Academy Manager, LOGSTOR

District cooling with a centrally produced cooling agent distributed in a district cooling pipe system would be the obvious choice to supply these types of buildings with cooling regardless of the climate being hot or cold.

This article deals with pre-insulated pipe systems for district cooling.

Advantages of District Cooling compared to Individual Cooling

FOR THE CUSTOMERS:

• High security of supply
• Less maintenance
• Less tied-up capital
• Competitive price
• Space-saving – frees up m² in the building for other purposes
• No noise/vibration from local cooling unit

FOR SOCIETY:

• The most energy-efficient solution – up to 50% reduction in energy consumption to produce the cooling
• Many different sources to produce the cooling agent from e.g. surplus heat, surplus power from windmill production, free cooling with the use of lake or sea water etc.
• Reduced CO₂ An up to 65% reduction in CO₂ emission as a result of the possibility of using renewable energy sources in connection with district cooling
• Improvement of the townscape as regards aesthetic and noise

FOR DISTRICT HEATING COMPANIES:

• New product to existing customers
• Growth potential for the energy companies
• Supports the corporate social responsibility and image of the energy companies

The Challenges of District Cooling

The big challenge is the large investments for the production unit and the district cooling pipe system, and the payback time of the initial investment, as well as the need to integrate the district cooling solution in due time in the planning phase.

Often people ask, ”Why use insulated pipes for district cooling systems, when the temperature of the cooling agent, which typically ranges between 5 – 15 °C, is close to the temperature of the ambient soil? Can’t we simply use coated steel pipes or plastic service pipes and install them directly in the trench?”

The answer is that a pre-insulated pipe system ensures the lowest Total Cost of Ownership, when the investment, operation, service life, repairs etc. are evaluated.

• The most energy-efficient operation will be obtained in a pre-insulated pipe system. Even in northern situated countries, where the operation is optimized by minimizing the cooling loss from the pipes, the soil temperature varies relatively much. In southern situated countries the soil temperature is constantly high compared to the service pipe temperature, and choosing a pre-insulated pipe system is natural
• A pre-insulated pipe system minimizes the cooling loss and ensures the correct temperature of the cooling agent at the consumer’s
• The pre-insulated pipe system is established with a surveillance system detecting any moist in the insulation due to damages on the service pipe or outer casing. This enables you to respond as soon as the damage occurs and prevent the damage from spreading and in worst case resulting in a system breakdown, so cooling cannot be delivered to the consumers
• No uninsulated parts to paint or coat to corrosion protect them
• No need for corrosion protection (cathodic protection), because the entire system is pre-insulated and therefore leak-proof
• It is easy to budget the operational costs without unforeseen expenses
• The pipe system can also be used for crossing water bodies
• No condensation on pipes when they are installed indoor or above ground
• The pipe system can lie in aggressive soil
• Long service life of the system

All in all, there are a lot of reasons to choose pre-insulated pipes for district cooling pipe systems.

District cooling systems can reduce energy consumption by up to 50%

… and up to 65% reduction in CO2 emission

The Pre-insulated Pipe System

A pre-insulated pipe system for district cooling is designed in insulation series 0, 1 or 2, where series 0 and 1 are the most frequently used insulation series. By comparison, a pre-insulated pipe system for district heating is designed in insulation series 1, 2, or 3.

This means that the insulation thickness of pre-insulated pipes for district cooling is typically lower than that of the same service pipe dimension for district heating. The reason is that the temperature difference between the medium and the soil is smaller in a district cooling system than in a district heating system.

The pipe dimension for district cooling systems range between DN20 – 1200.

A district cooling system typically requires the following components which must all be insulated from the factory:

• 6, 12, and 16 m long pipes
• Bends
• Branches
• Reductions
• Ball valves
• Butterfly valves
• Casing joints

European Standards for Pre-insulated District Cooling Products

Just like there have been European standards for pre-insulated district heating pipes for many years, European standards for pre-insulated district cooling pipes are being worked on. The work is at an advanced stage. The standard for pre-insulated district cooling pipes with steel service pipe has already become effective. Standards for pre-insulated fittings and valves with steel service pipe as well as standards for pre-insulated pipe systems with plastic service pipe are in the hearing phase.

The fundamental principle is that the European standards describe a minimum requirement to the pre-insulated components.

For an energy company it becomes simpler to prepare the tender material for pre-insulated pipes for district cooling pipe systems. The energy company only has to describe that the products as a minimum comply with the requirements in the European standards and then ask the pipe suppliers to describe what services and customer values they offer in addition to the minimum requirements in the standard. That may e.g. be advanced surveillance systems for district cooling systems, pipes with diffusion barrier, making sure that there is no water vapour diffusion from the surroundings into the insulation etc.

Surveillance System for the Pre-insulated District Cooling Pipe System

A well-functioning, active surveillance system is decisive for a long and faultless service life of the pipe system. If moist enters the insulation either due to an untight steel weld, a damage on the casing or an untight casing joint, the surveillance system must immediately notify you of this, so immediate action can be taken to mend the fault.

Immediate response to an alarm from the surveillance system is decisive to prevent the damage from spreading and becoming extensive and in worst case resulting in breakdown of the district cooling system, so the customers cannot be supplied with cooling. Example of this below where a welding fault between two pipes caused a major rupture.

When planning the surveillance system for your district cooling system, you must consider which principle is most appropriate.

There are two principles:

• Active system, based on a resistance measuring principle, telling whether moist is in the insulation or not. The surveillance system is a so-called Nordic system with two copper wires

• Active system, based on the impedance principle. The system can locate any fault in the system

A surveillance system for district cooling faces particular challenges compared to a surveillance system for district heating. It is well-known that over time, a minor quantity of moisture (condensation) may accumulate in the insulation of the district cooling system. This condensation accumulation is especially problematic at untight joints, damages, and repairs or connections when the plant is in operation, and the ambient temperature is higher than the service pipe temperature. It is, therefore, essential to make sure that the pre-insulated system is completely leak-proof before system start-up at terminations, vents, and in buildings.

If the ambient temperature is higher than the service pipe temperature, any repair in the pipe system requires that a tent is placed around the casing joint location, and the air temperature is cooled to the service pipe temperature or, alternatively, that the operation is planned at another time, where the ambient temperature is the same as that of the service pipe, if possible.

An active system with the Nordic system (2 copper wires) is particularly sensitive in regard to this issue.

By using insulated 3dc cables, the system can operate even though moisture/condensation accumulates in the insulation. This is ensured by establishing new reference curves, which take the built-in moisture into account.

It is therefore recommended to use impedance-based surveillance systems with 3dc cables for district cooling systems.

Different Types of District Cooling Projects

In the following three different district cooling projects are described.