2^nd GUIDE Europe case study: DTI’s ammonia heat pump concept with split condenser

The ammonia heat pump concept developed with the support of the Danish ELFORSK program has provided valuable insight into the potential of splitting a condenser into two parts and the circumstances, under which this is favourable. The split condenser concept makes it possible to obtain smaller temperature approaches, whereby the heat pump efficiency is improved at an equal heat exchanger area, when compared to the traditional solution with separate condenser and desuperheater.

 

The ammonia heat pump has been built by Svedan Industrial Refrigeration (Svedan Industri Køleanlæg).

 

 

In the project, an ammonia heat pump with high pressure reciprocating compressor and a novel split condenser was developed to prove potential for efficiency optimization. The split of the condenser in two parts can be utilized to obtain smaller temperature approaches and, thereby, improved heat pump efficiency at an equal heat exchanger area, when compared to the traditional solution with separate condenser and desuperheater. The split condenser design can also be exploited for heating a significant share of the total heating capacity to a temperature far above the condensing temperature. 

 

 

The prototype heat pump was equipped with a plate type evaporator combined with a U-turn separator with a minimum liquid height and a liquid pump with the purpose of creating optimum liquid circulation ratio for the highest possible heat transfer coefficients at the lowest possible pressure drop.

 

 

The test results successfully confirmed the highest possible efficiency of the heat pump. In the system, a coefficient of performance (COP) of 4.3 was obtained when heating water from 40°C to 80°C while operating with evaporating/condensing temperatures of +20°C/+73°C. With this total efficiency, it was possible to deliver approximately 25% of the flow at 100 °C and 75% at approximately 74 °C.

 

 

The calculation of the heat exchangers has to be performed manually with the use of the relevant design software from the supplier. This is very time consuming and in order to facilitate widespread use of this technology, a new project group has been formed, and an application for funding by the Energy Technology Development and Demonstration Programme (EUDP) has been submitted to The Danish Energy Agency. The aim of this project group is to enable commercialization by modifying the calculation software for ease of use as well as to extend the use to other refrigerants. Another important area is the application window with regard to the optimal temperature profiles and the control strategy especially in relation to optimizing part load operation.

 

 

Danish Technological Institute (DTI) specialises in research and development of refrigeration and heat pump technology and the use of natural refrigerants. Other key areas of expertise are e.g. solar energy, industrial drying and process optimization as well as preparing and carrying out training courses. The advanced state-of-the-art laboratories are used for research and development of new technology as well as for accredited testing of systems such as heat pumps.