How to Select a Condensing Unit for a Cold Room?

Proper selection of a condensing unit for a cold room is crucial for the installation's performance, stability of maintained temperature, electrical energy consumption, and compressor durability.

An undersized unit may not provide the required cooling capacity, especially during high ambient temperatures or intensive loading of the room. Conversely, an oversized unit, particularly one lacking appropriate capacity control, may operate in frequent on-off cycles, adversely affecting operational efficiency.

The selection of a refrigeration unit should not be based solely on the room's volume or the nominal power of the compressor given in HP. the basis is the actual thermal load and the unit's capacity under specific operating conditions.

1. Determining Cold Room Parameters

The first step in selecting a condensing unit is gathering data on the designed or existing installation.

The most important parameters are:

• Internal dimensions of the room: length, width, and height.
• Required internal temperature.
• Design ambient temperature of the room and unit.
• Thickness and thermal conductivity of the insulation of walls, ceiling, and floor.
• Type of stored products.
• Mass of products introduced into the room daily.
• Temperature of products during loading.
• Frequency and duration of door openings.
• Number and power of electrical devices inside the room.
• Required cooling time for products.

Two rooms with identical volume may have completely different cooling power requirements. For example, a room used solely for storing pre-cooled products usually requires less capacity than a room regularly receiving warm products.

2. How to Calculate Cooling Power Requirements?

The total cooling load of the room consists of several basic elements.

Heat Gains Through Partitions

Heat penetrates the room through walls, ceiling, floor, and structural connections.

For a homogeneous partition, the simplified heat flow can be determined by the formula:

Q = U × A × ΔT

Where:

• Q – heat flow [W];
• U – thermal transmittance of the partition [W/(m²·K)];
• A – area of the partition [m²];
• ΔT – temperature difference between the environment and the room interior [K].

Calculations should be conducted for all significant partitions, considering their actual thermal conditions.

Load Related to Product Cooling

For products requiring temperature reduction, the amount of heat necessary to be removed during their cooling must be calculated.

For products without phase change, the relationship can be applied:

E = m × c × ΔT

Where:

• E – thermal energy [kJ];
• m – mass of the product [kg];
• c – specific heat of the product [kJ/(kg·K)];
• ΔT – required temperature reduction [K].

If the product undergoes freezing, it is necessary to additionally consider the heat of phase change and the properties of the product before and after freezing.

Heat Gains from Door Openings

Opening doors causes the influx of warmer and often more humid air.

The magnitude of this load depends on the opening area, temperature, humidity, duration of door opening, and the use of strip or air curtains.

Internal Heat Sources

It is also necessary to consider:

• air cooler fans;
• lighting;
• presence of personnel;
• transport equipment and other heat sources;
• the impact of defrost cycles.

The total required capacity of the installation must account for all significant heat gains and the assumed available cooling operation time.

3. Example of Selecting a Condensing Unit for a Cold Room

Let's consider an example cold room for storing food products.

Assuming that after accounting for heat transfer, air exchange, product load, and internal heat sources, the daily demand of the room is 36 kWh of cooling energy.

Assuming 18 hours of effective refrigeration system operation per day:

Q₀ = 36 kWh / 18 h = 2.0 kW

If for this example we additionally assume a 10% design reserve:

Q₀,proj = 2.0 × 1.10 = 2.2 kW

We obtain an indicative required cooling capacity of 2.2 kW.

This is an educational example. The daily load of 36 kWh was assumed and not determined based on a complete balance. Final selection requires checking actual operating conditions, peak loads, and equipment characteristics.

4. How to Determine the Evaporation Temperature?

The evaporation temperature of the refrigerant is one of the most important parameters affecting the performance of the condensing unit.

In typical air cooling systems, the evaporation temperature is lower than the temperature required inside the room.

For example, for a room maintained at +2°C, the design evaporation temperature may be around –6°C if an 8 K difference is assumed.

However, this is not a universal value.

The proper temperature difference depends on the selection of the air cooler, required humidity, control method, type of product, and system operating characteristics.

The lower the evaporation temperature with other conditions unchanged, the generally lower the cooling capacity of the compressor and the lower the energy efficiency of the system.

Therefore, the condensing unit should be selected for the design evaporation temperature, not solely for the temperature inside the room.

5. Condensing Temperature and Operating Conditions of the Condensing Unit

The second key parameter is the condensing temperature.

It depends, among other factors, on the ambient temperature of the condensing unit, the design and capacity of the condenser, airflow, and the method of controlling condensing pressure.

For an air-cooled condensing unit operating at an ambient temperature of +35°C, an example condensing temperature may be +45°C.

However, this value should be confirmed based on design assumptions and condenser parameters.

When comparing two condensing units, their performance should be checked at the same evaporation temperature, condensing temperature, and the same refrigerant.

Comparing only nominal HP ratings does not reliably determine which unit will provide the required cooling capacity.

6. Selection of the Appropriate Refrigerant

The type of refrigerant affects the achieved cooling capacity, compressor operating conditions, installation safety, and legal requirements.

Before selecting a condensing unit, check:

• the list of refrigerants approved by the manufacturer;
• cooling capacity for the selected refrigerant;
• range of permissible temperatures and pressures;
• compatibility of other installation components;
• safety class of the refrigerant;
• applicable F-gas regulations and restrictions for specific applications.

Do not assume that a condensing unit can operate with any refrigerant just because its thermodynamic parameters are similar.

For refrigerants with flammability class A2L, it is necessary to consider appropriate safety requirements and confirm the approval of the entire system for such operation.

7. Standard or Inverter Condensing Unit?

In a traditional condensing unit, the compressor operating at a constant rotational speed has limited direct capacity control capabilities.

An inverter condensing unit uses the change in compressor rotational speed to adjust the cooling capacity to variable load.

When is it worth using an inverter condensing unit?

Inverter technology is particularly interesting in installations where the thermal load changes throughout the day.

Potential benefits include:

• smoother capacity adjustment to demand;
• reduction in the number of compressor starts;
• more stable temperature control;
• possibility to reduce electricity consumption under appropriate operating conditions.

However, it is necessary to verify the minimum and maximum capacity of the device, permissible compressor frequency range, and control and oil return requirements.

An inverter condensing unit will not always be the most economical solution. The decision should consider the load profile and total operating costs.

8. Common Mistakes When Selecting a Condensing Unit

Selection based solely on cold room volume

Volume does not determine the amount of heat introduced into the cold room or the load resulting from cooling products.

Selection based solely on power in HP

The nominal power of the compressor is not equivalent to cooling capacity in kW.

Omission of summer conditions

A condensing unit selected for too low ambient temperature may not provide the required capacity during heatwaves.

Failure to consider product cooling time

A large amount of warm product can significantly increase the instantaneous cooling capacity demand.

Excessive oversizing of the condensing unit

Too high capacity can lead to short operating cycles and regulation difficulties, especially under low load.

Lack of verification of compatibility between the air cooler and the condensing unit

The cooling capacity of the air cooler and the condensing unit must be appropriately matched at the actual operating point.

9. BOYARD Condensing Units in the blueref.pl Offer

The blueref.pl offer includes BOYARD condensing units designed for professional refrigeration installations, including standard devices and models with inverter control.

Available solutions can be used in appropriately designed refrigeration systems for cold rooms, showcases, refrigeration furniture, and other commercial installations.

The selection of a specific device should be based on the required operating point, actual cooling capacity, and permissible application range indicated by the manufacturer.

Check the offer of BOYARD condensing units at blueref.pl and take advantage of technical assistance when selecting a device.

10. What Data to Provide for Condensing Unit Selection?

To prepare a correct selection of a condensing unit, the following information should be provided:

1. Dimensions of the cold room and type of insulation.
2. Required internal temperature.
3. Design ambient temperature of the condensing unit.
4. Type and daily mass of stored products.
5. Temperature of products during loading.
6. Time allocated for cooling the products.
7. Type and availability of refrigerant.
8. Available electrical supply.
9. Preferred method of capacity control.
10. Any additional installation requirements.

Based on this data, a cooling load analysis can be conducted, the appropriate condensing unit selected, and the compatibility of other system components assessed.

11. Summary

Correct selection of a condensing unit for a cold room requires determining the actual cooling capacity demand and analysing the operating conditions of the entire installation.

The most important factors are: heat load, evaporation temperature, condensation temperature, type of refrigerant, and capacity control characteristics.

Choosing equipment based solely on the dimensions of the room or the nominal power of the compressor can lead to design errors and unnecessary operating costs.

Are you looking for the right condensing unit for your installation?

Contact the technical department at blueref.pl. We will help analyse the required operating parameters and select the appropriate BOYARD condensing unit for the planned application.

See BOYARD Condensing Units