Mechanical Component of The Day - Economizer

[jar546]

An economizer in an HVAC system is like giving your building the ability to "sniff" the outside air. If the system detects that the outside air is cooler and more suitable than using the air conditioner, it will pull in that fresh outdoor air to cool the building. It's like opening a window on a cool day instead of using the AC, but it's done automatically by the system to save energy.

 

[mtlogcabin]

And when it malfunctions in the open position you will get 48-degree air at the register in January when it is 10 degrees outside.

 

[jar546]

And when it malfunctions in the open position you will get 48-degree air at the register in January when it is 10 degrees outside.

Excellent. It is still above freezing. And heaters don't work in the winter when they go bad.

 

[Robert]

An economizer in an HVAC system is like giving your building the ability to "sniff" the outside air. If the system detects that the outside air is cooler and more suitable than using the air conditioner, it will pull in that fresh outdoor air to cool the building. It's like opening a window on a cool day instead of using the AC, but it's done automatically by the system to save energy.

I'm currently remodeling a small restaurant with an existing economizer HVAC unit on the roof. The code requires a certain amount of fresh air supply in the restaurant. This building has no operable windows. I don't believe the commercial hood supply fan counts toward fresh air since that is balanced with the hood exhaust....but maybe I'm wrong about that. Could the economizer act as fresh air intake to satisfy the ventilation part of the code?

 

[ICE]

Could the economizer act as fresh air intake to satisfy the ventilation part of the code?

Can the economizer be controlled to meet the requirements for ventilation?

 

[klarenbeek]

The economizer can provide required occupancy air for the restaurant. The air from the makeup air unit can also serve the dual purpose of being both occupancy air and makeup air if designed properly. if distributed to the areas needing occupancy air and given an unobstructed airflow path to the hood area it can serve both purposes.

 

[Mech]

The economizer is to allow use of ambient air for cooling so the compressors do not need to run. I specify rooftop units with an adjustable potentiometer so that during occupied hours, the motorized damper opens to a predetermined setting to supply the proper OA rate. During economizer mode, the dampers modulate between the predetermined open setting and 100% open, to match the amount of outside / return air to offset the building heat loads.

Here is a nice write-up from Trane regarding economizers.
https://www.trane.com/content/dam/T...wsletters/airside-design/admapn020en-0406.pdf

A certain amount of outside air is required for the kitchen area whether there an exhaust hood is required or not. If the exhaust rate through the hood is greater than the kitchen outside air requirement, then the hood can be used to help satisfy the kitchen's outside air. I would place supply / outside air ductwork away from the hood so that the kitchen is ventilated rather than the supply / outside air being immediately exhausted.

The IMC section for transfer air allows air from the dining areas to be pulled into the kitchen as makeup air. I think if the dining area is supplied with more outside air than required for the dining area, the air can be pulled into the kitchen to serve as the kitchen outside air.