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New efficiency limits for condensing units!

Published Date 3/15/18 7:00 AM

Less than 4 months remain to prepare for more stringent limits on European condensing units! In detail, Ecodesign requires an increase in efficiency of between 6-14 %, depending on the categories, compared to the 2016 tiers. This comes at a crucial moment for HFC phase-down and with some uncertainty among condensing unit manufacturers regarding the alternative refrigerants to be used, which undoubtedly affect system efficiency.

Why is important to increase the condensing unit efficiency?

First of all, it is important to look at what “condensing unit” means in the Ecodesign regulation. The concept is not always clear, as the condensing unit itself is a part of all vapour-compression refrigeration units. This creates some confusion among stakeholders, and some overlapping of different regulations for the same products.

The Ecodesign Directive defines a condensing unit as a product integrating at least one electrically driven compressor and one condenser, capable of cooling down and continuously maintaining low or medium temperature inside a refrigerated appliance or system, using a vapour compression cycle once connected to an evaporator and an expansion device. The type of refrigerated appliance or system where the condensing unit is connected is not specified. However, it is well known that the most popular application for condensing units is convenience stores, where refrigerated appliances mean the refrigeration showcases in the store.

According to a study published by IIR, the annual electrical energy consumption in convenience stores is over 2000 kWh/m² of sales area against 700 kWh/m² of sales area in hypermarkets. In both cases, the refrigeration systems account for between 30% and 60% of the electricity consumed (lighting accounts for between 15% and 25%; HVAC equipment and other equipment such as bakery ovens account for the remainder).

Clearly, increasing the efficiency of condensing units allows convenience store owners to save significant amounts of money on their electricity bills. Without forgetting the reduction in CO₂ emissions into the atmosphere due to lower electricity consumption.

What parameters need to be measured?

Condensing units operating at low temperature (-35°C), medium temperature (-10°C) or both are covered by the Ecodesign regulation. Each of these classes is categorised into low and high capacities.

For low rated cooling capacity condensing units, the coefficient of performance (COP) has to be measured, whereas for high rated cooling capacities, the variations in temperature throughout the year are also considered, thus the seasonal energy performance ratio (SEPR) has to be calculated.

COP has traditionally been the coefficient to measure the performance of refrigeration units. The result comes simply by measuring the cooling capacity of the system in actual operating conditions and the electrical power input needed to reach that cooling capacity. In particular, the Ecodesign regulation dictates an evaporation temperature of -35°C for low temperature or -10°C for medium temperature, with a reference ambient temperature of 32°C for both.

In the latest regulations, SEPR needs to be calculated in order to have a more precise value of the real performance of the system in different operating conditions. In other words, the cooling capacity and electrical power input are measured at different ambient temperatures, so that the variations in load and ambient temperature throughout the year are taken into account.

To calculate the variations in outdoor temperatures across the year under average climate conditions in Europe, the Ecodesign regulation includes a table with the hours per year that a certain temperature occurs (this combination of temperature-hours is called a bin). Each bar in the following graph represents a bin.

In practice, the cooling capacity and the power input are measured at 4 different temperatures at full or part load (points A, B, C, D: represented in the graph by the red bars). The values obtained from the measurements in points B, C and D must be multiplied by the degradation coefficient in case of units that cannot achieve the required load by means of capacity modulation.

The cooling capacity and power input for the other temperatures are calculated by linear interpolation. The final result will be the sum of the parameters at each ambient temperature multiplied by the number of hours for each bin.

What will the new limits be?

Low capacity condensing units include those in the range 0.2-5 kW. As shown in the following graph, the minimum COP allowed for medium-temperature condensing units for capacities from 0.2 to 1 kW will increase from 1.2 to 1.4. This means an increase of 14%. For higher capacities (up to 5 kW) the increment over the 2016 requirements will be 13% (from 1.4 to 1.6). If the condensing unit is designed to operate at low temperature, the increase will be 6% for low capacities from 0.2-0.4 kW (from 0.75 to 0.8) and 11% (from 0.85 to 0.95) for capacities in the range 0.4-2 kW.

The Ecodesign tiers for high capacity condensing units (above 5 kW and up to 50 kW) are shown in the following graph. On the one hand, for medium-temperature condensing units at capacities in the range 5-20 kW, the minimum SEPR will vary from 2.25 to 2.55, namely +12%, whereas for capacities higher than 20 kW it will increase by 11% (from 2.35 to 2.65). On the other hand, the minimum SEPR for low-temperature condensing units will increase by 6% (from 1.5 to 1.6) up to 8 kW, and by 6% (from 1.6 to 1.7) from 10 kW up to 20 kW.

It should be noted that there is a low-GWP efficiency bonus that allows these limits to be reduced: if the condensing unit uses a refrigerant with a GWP < 150, such as R-744 (CO₂), the minimum COP and SEPR values specified for July 2018 can be reduced by 10%.

Are European condensing units ready?

If not already done, it is time to check whether the condensing units that will be placed on the European market from July comply with the limits. In any case, optimising the design of the unit by choosing highly-efficient components and systems will help when it comes to pay the electricity bill, also reducing CO₂ emissions. Most of the time, the cheaper option turns out to be more expensive, whereas the more expensive option turns out to be cheaper!