Economizer, reheat coil and preheat coil.

[Muhammad Riyas]

I am HVAC Engineer new to this field, Though I search through internet, I have some uncleared questions,

1. Economizer - A packaged unit consists of a economizer, cooling coil and a heating coil. If my room design temperature is 23°C and outdoor temperature falls to 15°C, when will the heating coil starts to work.

2. What is Preheat coil and what is the purpose of it? What happens if there is no preheat coil in cold regions?

3. What is Reheat coil and what is the purpose of it?

 

[apollowolfe]

1) You would utilize the economizer in that situation. The heat coil would activate when you are bringing in the minimum required outdoor air and your leaving air temperature is below desired.

2)The preheat coil is utilized to raise outdoor air above freezing in hydronic units. In a cold climate you need to protect the hydronic coils from freezing and getting damaged.

3)You will need to learn the psychometric chart. If you need dry air you will need to cool it down to remove the moisture and then reheat it to desired temperatures.