Project - Optimisation of hot-gas defrost in industrial refrigeration systems

Jannie Guldmann Würtz

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Project - Optimisation of hot-gas defrost in industrial refrigeration systems

Optimisation of hot-gas defrost in industrial refrigeration systems

Project started January 1st 2015. Ended in December 2017.

Purpose of project
This project will explore the possibility for reducing the condensing pressure by optimizing the design of the evaporator, system and control strate-gy but also by introducing a serial compressor for defrosting, so that only the necessary amount of hot gas is lifted to the desired temperature level, allowing the rest of the plant to run at a lower condensing temperature. This is expected to lower the total yearly energy consump-tion of the system by about 14%.

The evaporation temperature – and thereby the evaporator surface temperature – in refrigera-tion plants operating below 5-8 °C will be below 0 °C. This will lead to frost formation on the evaporator surfaces and periodic defrosting is necessary to maintain the cooling capacity. Hot-gas defrosting is commonly used in large industrial refrigeration plants like blast freezing tun-nels. To get a high temperature and pressure of the hot gas used for defrosting many plants run with a relatively high minimum condensing temperature. This leads to unnecessary energy consumption since the air temperature in Denmark in most part of the year is low enough to decrease the condensing pressure further.


The project is divided into 8 work packages:

  1. Kick-off and start-up
  2. Simulationsmodel
  3. Designing the pilotplant
  4. Experiments on alternative system designs
  5. Determination of pilot plant design
  6. Instillation and measurements on pilot plant
  7. Validation of the model
  8. Dissemination


  • Danish Technological Institute
  • Johnsons Controls Denmark ApS
  • Danfoss A/S
  • Ringsted Slagteri
  • Claus Sørensen, Engesvang

The project is funded by ELFORSK.