Concerning the process chillers' operating temperature, two possibilities are given under Regulation (EU) 2015/1095: medium temperature or low temperature, in line with the definitions given in Article 2.1.t and article 2.1.u of the regulation. This means that for the purposes of the regulation no other choices are given to the manufacturer in terms of intended operating temperature, and, therefore, in terms of which requirements apply for a certain process chillers (i.e. either those for medium temperature or those for low temperature).
In terms of process chillers operating temperature, there is also a third possible case, i.e. the one of high temperature (article 2.1.v of Regulation (EU) 2015/1095); the process chillers with this operating temperature are in scope of the forthcoming regulation on air heating products, cooling products, high temperature process chillers and fan coil units.
These categories (low, medium and high temperature) were defined and identified also in collaboration with stakeholders, and there was a good agreement in terms of the chosen temperature levels. However, there can be specific situations of products sold for cooling temperatures which are somehow on the boundaries of the temperature limits defined in Regulation (EU) 2015/1095 such as the case mentioned in the question, i.e. process chillers "designed to operate between the temperature ranges of -7°C and +7°C and capable of reaching -8°C in some circumstances". In those cases, freedom is left to the manufacturer to identify and declare the process chiller operating temperature, under Regulation (EU) 2015/1095 (or, under the regulation on air heating products, cooling products, high temperature process chillers and fan coil units, in the case of high temperature process chillers).
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.