The electricity bill paid over the life of a cold room is mostly several times the purchase price of the equipment. This is why efficiency is part of the investment decision. The COP (coefficient of performance) is the ratio of the cooling capacity to the electrical power drawn at a specific operating point: if 4 kW is drawn for 10 kW of cooling, the COP is 2.5. But the COP describes a single condition; the equipment does not spend most of the year in that condition. The design condition is seen on only a few days a year.
The SEPR (Seasonal Energy Performance Ratio) makes up for this shortcoming: it divides the annual cooling demand of the equipment by its annual electricity consumption; the distribution of the outside air temperature over the year and part-load behaviour are included in the calculation. The EU’s ecodesign regulation 2015/1095 sets the minimum COP and SEPR values for condensing units and process chillers; for condensing units the limit is roughly at the level of 2.5 at medium temperature and 1.6 at low temperature.
What really determines efficiency is two temperatures: evaporating and condensing. Every 1 K rise in evaporating temperature and every 1 K fall in condensing temperature reduces consumption by 2–3%. This is why large-surface evaporators and condensers, floating condensing control, an electronic expansion valve, EC fans and an inverter compressor are the options that raise seasonal efficiency the most. Of two units of the same capacity, the one with the higher SEPR is mostly the one with the larger heat exchangers.
The operating side is at least as important as the equipment. A dirty condenser, a frosted evaporator, a low charge, a worn door gasket and a room temperature set lower than necessary can reduce the efficiency of a good unit by 20–30%. Even raising the room setting by 1 K means a saving of a few points. Panel thickness and door arrangement determine the load, and therefore the consumption. The cooling load calculator shows the components of the load; in our catalog the equipment capacities are given by operating conditions.