Project - New sensor principle for cooling systems

Development of methods for increasing the flexibility in individual heat pumps' power consumption.

Project start: 2013. Ended in November 2015.

Goal of the project

The project is aimed at fully developing, testing and spreadind the knowledge of the new possibilities for great energy conservations by using a new control, regulation and monitoring of refrigerating plants with natural refrigerants. The focus is on supplying evaporators with liquid and securing against liquid shocks in compressors, which is based on the application of a newly developed sensor principle; HB-WDX Control System.

The void-fraction-sensor is developed with the purpose of registrering and calculating two-phased-flow in specific positions in the pibe systems of the cooling installations. Two-phased-flow means simultaneous flow of refrigerant in both the liquid and gas phase in arbitrarily variable size.The void-fraction-sensor is based on the measuring principle, where a change in the flow's degree of dryness (the relationship between gas and liquid phase) provides a change in the measurement of capacitance measured in [pF].

Thereby, the new void-fraction-sensor does not register the codition of the refrigerant in the outflow of a evaporator through the traditional measurement of the pressure and temperature of the refrigerant. By contrast, it registers the condition through registration and measurement of whether the refrigerant flow consists of one or two phases (liquid and gas) and the size of the two flows. With the sensor follows an electronic PC-configurable controller, which calibrates and handles the signal of the sensor used for management, regulation and monitoring the refrigerating plants.

Especially two positions in the pibing system of the cooling installations are important to know and/or register the amount of the gas and liguid flow of the refrigerant. The first position is an evaporator's outflow/decline, where registration and measurements of pressure, temperature and flow can be used for managing the supply of refrigerant for the evaporator's entry/accession with the purpose of achieving optimum refrigerant effect. The second position is the entry/accession of a compressor, which must not contain liquid, because it can result in liquid shocks. This is due to the fact that a cooling compressor fundamentally is constructed for compressing only refrigerant in the gas phase.

Cooling circuits are designed very differently, depending on, for example, the applied type of refrigerant. There is normally a distinction between dry (also called DX for Direct Expansion in smaller refrigerating plants) and flooded (also called wet in bigger refrigerating plants) evaporators for cooling of air and liquid. In both instances (dry and wet system designs), the application of the sensor can contribute with reducing the overheating and raise the pressure of the evaporator, by which the system's energy consumption is considerable reduced. Besides the mentioned potential for energy conservation through reduction of overheating and raising of the refrigerating plant's evaporator pressure (due to low drop of pressure), there are, among others, the following spin-offs:

• The sensor is not affected by an eventual water content in the ammonia
• Dry absorption from freezers minimizes the drop of pressure in vertical wet return pibes and enables greater flexibility in the pibing arrangement
• Rates of filling can be reduced considerably, which means that size of pibes for liquid and suction pibes can be reduced in proportion to the pump circulation systems, with so-called wet return

The design of the sensor is primarilly developed for the use of ammonia, which is among the most energy effective and environmentally friendly refrigerants in the world. This is due to the fact that HB Products has more than 20 years of experience with developing electronic sensors for exactly this industry. However, the sensor technology can in principle be used for any type of refrigerant, also CO2.

Participants

• HB Products A/S (project leader)
• Danish Tehnological Institute
• Thermofin GmbH
• Alfa Laval Copenhagen A/S
• Grundfos Holding A/S
• S.V.K. Energi A/S
• JH Development ApS

Activities

In the project, the following elements are used:

Phase 1: Project start 
Phase 2: Design/development
Phase 3: Laboratory test of sensor under stationary conditions
Phase 4: Laboratory test of sensor in dynamic evaporator systems
Phase 5: Site test of sensor built in real plants under real conditions
Phase 6: Documentation
Phase 7: Dissemination of knowledge
Phase 8: Project management and administration

If you want to know more

CEO Michael Elstrøm, HB Products A/S. Telephone: 8747 6203
Svenn Hansen, Danish Technological Institute. Telephone: 7220 1267