Hello dear readers! I hope that all of you are doing fine. In this article, I will explain the Cooling Coil Design. Here, I will cover the following:
What is a cooling coil? Types of cooling coil, functions of the cooling coil, different parts of the cooling coil, material of construction of cooling coil, and the design parameters of cooling coil.
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When you study a topic in the form of some short questions, interest will grow within you and you will feel that some topics you have learned.
So, without wasting your time, let us start the short questions on the cooling coil to know what is it, and how it works.
Table of Contents
Cooling Coil Details
Whenever you want to change the temperature, you need a heat transfer phenomenon to occur. Heat transfer takes place through the cooling coil. Whenever you want a heat transfer phenomenon, you need a cooling coil. I will discuss the entire Cooling Coil Details including the types, designing parameters, the material of construction, etc.
What is Cooling Coil?
Cooling coils are the components that exchange heat between two fluids. It can remove the heat from equipment or machines. How much heat it can remove depends on its capacity.
Therefore, a cooling coil is one type of heat exchanger.
In air-conditioning system, the AHU unit is having cooling coil within which chilled water flows and the room air transfers its heat to the cooling coil. Also, there is another set of cooling coils within the chiller unit where heat transfer takes place between chilled water and the refrigerant. Further Condenser is also having a set of cooling coils where heat transfer takes place between water and air.
What are the Different Types of Cooling Coils?
There are mainly two types of cooling coils- Condenser coil and Evaporator coil. Evaporator coils are of two types- dry type and flooded type. It can also be classified as frosting cooling coils and non-frosting cooling coils.
Also, there are 4 different types of cooling coil depending on the type of fluid it carries:
- Chilled water coil
- Hot water
- Direct expansion
Further, there are 4 different types of cooling coil depending on where it is mounted:
- Duct-mounted cooling coil
- DX cooling coil
- PAC mounted cooling coil
- TFA Coil
What are the functions of cooling coils?
The functions of the Cooling coil are to dehumidify and cool the surrounding room/equipment/machines. The refrigerant flows within the cooling coil. It absorbs the heat from the room’s air. Hence, room air becomes cold and the refrigerant changes its phase from liquid to vapor.
If you use an oversized cooling coil in the Treated Fresh Air Unit and pass the hot and humid air of the outside area through this cooling coil, you will get overcooled air as an output. Next, if you use a heat pipe inside which heating coil is there, you will get comfortable and dry air.
What are the Different Parts of the Cooling Coil?
The following parts are in the cooling coil:
- Flanges or casing
The tubes are of small diameter pipes within which the heat transfer fluid flows. There are some standard diameter pipes that are available in the market. They are 3/8”, ½”, and 5/8”.
These tubes have arranged either parallel to one another or in staggered positions along the length of the coil. Tubes take turns with the help of return bends or hairpins.
Fins are added to increase the heat transfer area. Fins are basically thin metal plates attached to the periphery of the tubes.
Cooling coils are covered by casing and supported by flanges.
There are either 4 or 6 or 8 rows of tubes. All the supply tubes are connected with a common supply header. Similarly, all the return tubes are connected with the return header. These headers are made of either copper or steel.
In chilled water/ steam coil, the inlet is always from the top side so that it can allow the condensation from the system can be taken away from the bottom with the help of a drain pan. Condensate drain pans are made of galvanized or of stainless steel.
What are the Materials of Different Parts of Cooling Coil?
Flanges/ Casing – these are made of non-ferrous/steel.
Drain pan – Stainless steel, galvanized
How to Design the Cooling Coil?
Design parameters to focus on while designing the cooling coil are as follows:
Coil size, number of rows, total coil face area, coil face velocity, Fin spacing, and number of tubes.
Fin spacing- normally 10-12 fins/inch. It varies along with the OD of the tubes.
½” OD Tubes: 11-18 fins per inch
5/8” OD Tubes: 6-14 fins/inch
3/8” OD Tubes: 10-18 fins/inch
A number of rows deep
It means the number of rows of tubes within the cooling coil. Normally for a chilled water coil, the number of rows is 3 to 12 whereas in the case of hot water coils it is 1 or 2 rows and condenser water coils are 1-8 rows.
Chilled water coils are generally constructed from ½” OD tubes or 5/8” OD tubes.
The cooling coil efficiency is measured by (1-B.F) where B.F is the bypass factor.
Length of fins
There is no such fixed length of fins. It depends on the design patterns of the cooling coil. However, for every 50” length of the fin, there are requirements of support which are also known as Center Support or Tube support.
Maximum face velocity to be considered as 3 m/sec.
If you want the leaving temperature high, you have to size the cooling coil deeper and velocity higher. Deeper than 6 numbers of rows are very difficult to clean.
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