What's a typical range for air conditioned air temperature coming out of the vents?

In my office it’s coming out of the vents at 32.7 F. The vents are overhead and a plume of frigid air keeps falling down my back. My office is in a factory and we use enough energy that the air conditioning even runs during January where our outdoor temps are running low or mid 30s lately.

How unusual is this?

The typical temp at the vents is 20°F cooler than the returning air temperature. 32.7° is quite cold.

Sounds like it is low on refrigerant.


To expand on the post #2 from CookingWithGas

The delta in the temperature is what is important here. It should be between around 15 to 25 degrees cooler than the input air for mechanical AC.

As the air coming in is much cooler than that, your building is probably using an airside economizer which will use outside air when it is cool enough in order to save energy.

As the exact definition changes with standards I am talking about the ASHRAE Standard 90.1-2004 definition of:

Being in a factory they probably maximize the temperature differential, where in a typical office building they would mix the outside air to have a lower and more comfortable temperature differential but which is not as energy efficient.

Being low on refrigerant would *lower *the temperature? (note: temps in the OP are in Fahrenheit)

Yes, it’s a classic symptom. The pressure in the evaporator is lower then it should be leading to a drop in temperature. It is not a good condition as the coils will ice over and block air flow. And if the delivered air is 32.7 degrees, those coils are icing.


I too am of the opinion that they are discharging (probably 100%) outside air.

Is it feasible for the OP to partially or fully close his vents? Yeah, I know, maybe not convenient or even possible, but sometimes you gotta do what you gotta do.

Is there a maintenance manager in your factory that you can ask about this? Your office may have a variable position duct damper that is malfunctioning.

We installed an outdoor air economizer in our office at my last job because the building had a lot of lights and few windows, so even in winter it would be running the a/c. There was a temperature sensor that came with the economizer package that was supposed to keep the supply duct temperature at no lower than 50º by limiting the amount of outdoor air it would mix in. That would reduce drafts and be more than adequate to cool the space. At some point that sensor or one of the control components failed, so the economizer would just open up to 100% outdoor air, leading to those cold blasts and also a lot of short-cycling of the system.

A lower fan speed also requires a wider range in supply temperatures to achieve the same set point. The tradeoff for a higher speed is more wind for not-as-cold of a temperature. That could be another possible fix, but it may not actually improve your comfort.

I don’t think I can close vents. They’re motorized and they raise up and lower down out of the ceiling, driven by some motor. The whole system is programmable but if I change anything it reverts to default within one hour. It’s frustrating as hell.

I’ve spoken to a couple of the engineers responsible for it and they’re bringing in somebody to work on it.

32.7 degrees?
1st I have to ask how do you know it is 32.7 degrees. I have had many tenants claim that their space is freezing and must be below 50 degrees when the space was only 68 degrees. That is why I ask.

But no 32.7 degree supply is not normal.
The economizer dampers not be working properly can be one cause.
Another cause can be the minimum air dampers. They are set to keep a minimum amount of fresh air coming into the building and to keep the CO2 levels down. Don’t want sick building sysdrome. I have worked in buildings that on cold days too much minimum outside air will be drawn into the building dropping the supply air temp.

Also in many buildings only the air vents on the edge of the building will have any reheat, the interior air vents only have cold deck air with no reheat. (sounds good on paper, pain in real life.)

So if you are on a interior air vent it may not have any reheat and if the economizers are dropping the supply air too low, the end results will be cold air coming out of the vents.

Fair enough. I used a Fluke Chub E-4 readout and a brand new Omega Type K thermocouple with PFA insulation, and got a minimum reading of 0.4133 C while probing around with it.

I seriously like thermometry.