Background and objectives

Many industrial processes in Norway have heating demands in the temperature range of 90-120 °C. At the same time, waste heat holding typically a temperature of 30-50 °C is available. Efficient heat pumping technologies are therefore attractive in order to reduce the specific energy consumption (kWh/product amount). The limitation in heat pump alternatives for temperatures above 100 °C after the high temperature refrigerant R114 was abandoned has turned the focus on alternative heat pump processes using natural working fluids.

Heat pump description

IFE has built a 60 kW pilot compression/absorption type heat pump. By adding water to a standard ammonia heat pump cycle and including a solution circuit, a high temperature heat pump concept can be obtained. Compared to conventional vapour compression type heat pumps, a compression/absorption heat pump has several advantages:

• For an ammonia/water system, the inclusion of water can increase the boiling point considerably. The heat can therefore be delivered at remarkably higher temperatures using a standard 20-bar compressor.
• Due to the two-component mixture, the heat exchanging process will have gliding temperature both at heat source and heat sink side and therefore reduced heat exchanging losses for source and sink fluids with large temperature changes. The operation of the compression/absorption heat pump can effectively be tailored to the heat sink and heat source temperature fluctuations since the mixture’s component composition can be changed.
• Capacity control by variation of the average solution composition circulating between the absorber and the desorber within given temperature limits.
  

The compression/absorption heat pump has been designed and built to evaluate the performance and long-term operation consequences. In order to reduce capital costs, standard components are used.

The heat pump system is designed to simultaneously deliver heat at 95 °C and cooling at 5°C using waste heat of 50 °C as heat source, with a COP of 3.4.

The final product

The most profitable installations will meet both a cooling and a heating demand. When the high temperature heat pump is used in the industrial market, the pay back time is expected to be from 2-5 years.

Projects related to the R&D activity

• Strategic Institute Program (1995-2002)
• Feasibility study, gas processing plant (1997-1998)
• Consequences of water in lubrication oil (1999-2000)
• Implementation of plate type heat exchangers in compression/absorption processes (1998-2000)
• Market and feasibility study, Norwegian industrial processes (1999-2000)
• Participation in IEA Heat Pump Programme Annex 24 (Ab-sorption Machines for Heating and Cooling in Future Energy Systems) (1997-2000)
• Prototype evaluation and design (2001-2002)
• Steam production by a hybrid heat pump (2004-2005)
• Hybrid heat pump for high temperature heat production (2005-2006)
• Use of screw compressor in a hybrid heat pump using NH3/H2O as working fluid (2006-2008)