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air side economizer
- Thread starter xpsboy
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MechEngNCPE
Mechanical
An airside economizer is an attribute of an air handler that allows the unit to utilize "free cooling" when outside air temperature (or enthalpy) is lower than return air temperature (or enthalpy).
When the unit activates its economizer mode, the outside air damper modulates inversely with the return air damper to provide a mixed air condition as close to the discharge air temperature setpoint as possible. The unit is said to be in full economizer when the outside air damper is fully open, the return air damper is fully closed, the exhaust air damper fully open, the difference in supply airflow and exhaust airflow is just the air needed for pressurizing the building, and the supply air temperature setpoint is met. This means that there is no need for the cooling coil to provide cooling - either by d/x or chilled water.
Introducing this extra outside air brings up the need for more return air in order for the building pressure to stay at appropriate levels. In order to bring back this increased airflow there arises the need for an exhaust or return fan, depending on the static pressure loss of the return ductwork (if more than say 2 inches, the fan in the return position is probably the way to go.)
I would say there are many factors in designing these systems that cannot be learned from a tutorial - it usually takes an experienced collegue or mentor to get you to the point where you understand air handler design.
When the unit activates its economizer mode, the outside air damper modulates inversely with the return air damper to provide a mixed air condition as close to the discharge air temperature setpoint as possible. The unit is said to be in full economizer when the outside air damper is fully open, the return air damper is fully closed, the exhaust air damper fully open, the difference in supply airflow and exhaust airflow is just the air needed for pressurizing the building, and the supply air temperature setpoint is met. This means that there is no need for the cooling coil to provide cooling - either by d/x or chilled water.
Introducing this extra outside air brings up the need for more return air in order for the building pressure to stay at appropriate levels. In order to bring back this increased airflow there arises the need for an exhaust or return fan, depending on the static pressure loss of the return ductwork (if more than say 2 inches, the fan in the return position is probably the way to go.)
I would say there are many factors in designing these systems that cannot be learned from a tutorial - it usually takes an experienced collegue or mentor to get you to the point where you understand air handler design.
if you are designing a specific project then the best way is to consult the HVAC unit manufucturer that you have selected.
they will give you good information about specific job for thier unit.
commssioning of the air side economizer is a part of the HVAC unit commissioning, it can be getten from manufucturer procedure.
they will give you good information about specific job for thier unit.
commssioning of the air side economizer is a part of the HVAC unit commissioning, it can be getten from manufucturer procedure.
Got to have the reflex to google things out my friend - one hit in Google and here you go.... Extra, extra, read all about it.
If you’re not prepared to spend money on a proper maintenance then you’re probably wasting your time because estimates indicate that only about one in four economizers works properly, with the remaining three provid¬ing sub-par performance or, worse yet, wasting prodigious amounts of energy. Failures are a result of maintenance deficiencies, improper con¬trol, or systemic problems. For a better understanding of what I’m talking about please read the following:
mauricestoker
Mechanical
Imok2,
If you aren't prepared to spend O&M money, anything the designer does is going to be crap in a few years anyway. I've seen OA dampers shut or barely cracked, with economizer disabled. Starting to think it is just cheapness.
If you aren't prepared to spend O&M money, anything the designer does is going to be crap in a few years anyway. I've seen OA dampers shut or barely cracked, with economizer disabled. Starting to think it is just cheapness.
mauricestoker
Because I was a Refrigeration Fitter and worked in many areas of this industry doing construction and service I saw a lot of equipment that wasn't maintained properly because it was the first thing people did was cut the maintenance budget and when they got the repair costs they beside themselves so something like econimizers require a lot of attention. Opps there I go again sorry I get carried away :>)
Because I was a Refrigeration Fitter and worked in many areas of this industry doing construction and service I saw a lot of equipment that wasn't maintained properly because it was the first thing people did was cut the maintenance budget and when they got the repair costs they beside themselves so something like econimizers require a lot of attention. Opps there I go again sorry I get carried away :>)
Contractor currently in the field.
90% of maintenance personell don't understand economizers and disable them when they quit functioning, or when they thing they don't want 100 degree air being pulled into the building, OR they use poor filters and the evaporator becomes filthy diminishing capacity.
Just saying I see it..almost every time.
90% of maintenance personell don't understand economizers and disable them when they quit functioning, or when they thing they don't want 100 degree air being pulled into the building, OR they use poor filters and the evaporator becomes filthy diminishing capacity.
Just saying I see it..almost every time.
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