What size evaporator coil do I need? Check-list to design an evaporator coil
The function of an evaporator is to carry out heat exchange between refrigerant fluids. The evaporator or heat exchanger coil is where the transfer of energy from a medium, for example, the air in a cold room, to a liquid inside the evaporator takes place. The heat from the air is absorbed by the evaporator and is therefore cooled.
In order to meet the objective of cooling space, either to cool or to maintain a certain temperature, the evaporator or coil has to be custom-made based on parameters that must be known in advance to provide the optimal solution, both in terms of temperature achievement and cold production costs. These parameters are the following:
- Available space: it is necessary to take advantage of the maximum available space, the more space for the evaporator, the greater the heat exchange surface and the higher the performance. On the contrary, an excessive size will incur higher installation and production costs. The necessary dimensions to know to offer an evaporator are the total or external length (LT), height (H), and width or depth (D).
- Air direction: if the same airflow enters through the narrow side of the coil and travels across the wide side, it will have higher performance than if it enters through the wide side (this is mainly due to the fact that the air velocity will be higher in the first case). Therefore, it is necessary to know how it will be placed in the space to be cooled and where it will receive the airflow.
- Air flow rate: the higher the air flow rate, the more heat exchange power and therefore the smaller the evaporator size with consequent cost savings.
- Chamber temperature: i.e., what temperature we want to achieve in the space to be cooled.
- Evaporating temperature: will influence the temperature of the air in the chamber or room to be cooled and the humidity we will have. With the data of both temperatures, we will be able to know the need of performance that the battery has to have and therefore it will determine its configuration.
- Refrigerant: it is essential to know which refrigerant gas is going to be used by the manufacturer of the installation since some evaporate at a higher temperature than others and will determine the performance.
Other variables that can determine which evaporator coil should I use
There are other factors that can determine how to manufacture a coil. The most important ones to highlight:
- Corrosivity level of the air and its temperature: if the evaporator is going to work in a corrosive environment or because it is going to be used for the refrigeration of corrosive products, it will be necessary to apply an anti-corrosion paint treatment to the coil. Also, situations such as sudden temperature changes or very cold or hot peaks, as it can be the case of evaporators intended for environment simulation chambers (climatic chambers), will make it advisable to protect the coil with this type of paint to protect the metallic components of the evaporator, mainly the tube.
- Working temperature: although it is already commented, if the evaporator is going to work at temperatures below zero, this will imply the space between the fins, in such a way that it will be necessary that this is not less than 5 mm to avoid that the formation of ice prevents the passage of the air between the fins.
- Location of connections to the evaporator: depending on the arrangement provided by the refrigeration system manufacturer, the coil inlet and outlet should be placed in a specific location on one side of the evaporator.
- Evaporator installation: this will determine the configuration of the headers, usually the system manufacturer designs the headers to fit the space where the evaporator will be fixed.