Static pressure and ac charge

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csp0202
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Static pressure and ac charge

Postby csp0202 » Thu Sep 17, 2015 9:06 pm

I know air flow has to be correct when checking chare of ac system. Is static pressure the best way to check proper air flow?

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Re: Static pressure and ac charge

Postby csp0202 » Thu Sep 17, 2015 9:10 pm

Charge*

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Re: Static pressure and ac charge

Postby CEO1 » Thu Sep 17, 2015 11:06 pm

The simplest approach is SST and superheat evaluation. If the SST is significantly less than 40˚ and superheat low or normal, depending on the metering device, the airflow is low. Read the second topic down from this one..."Practical Airflow Considerations". Hopefully, someone else will offer a reply, 'cause I never attempt to measure airflow.

You could evaluate air flow with static measurements if you could get an accurate measurement of total static, and had a "fan performance chart" for the particular unit. Measuring static in residential ducting can be misleading, because of turbulence resulting from "inefficient" duct geometry's.

If you're dead set on calculating airflow, I'd suggest an anemometer and the airflow formula... CFM = Velocity X Area, where velocity is in ft/min units, and area of the opening in ft2.
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Re: Static pressure and ac charge

Postby CEO1 » Thu Sep 17, 2015 11:16 pm

csp0202 wrote:Charge*


You can edit/fix posting mistakes..

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..by clicking on the little "pencil" in the menu at the top of the submitted post. ;)


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Re: Static pressure and ac charge

Postby CEO1 » Fri Sep 18, 2015 12:05 pm

Here's another topic with a Jim Bergmann PDF attachment that offers a lot of insight about high temp refrigeration systems. It's got a bit of "marketing talk" in it, relative to digital gauges, but gets into the stuff you need to know about how systems are supposed to operate...

AC Applications
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Re: Static pressure and ac charge

Postby JCtech » Fri Sep 18, 2015 6:56 pm

csp0202 wrote:Is static pressure the best way to check proper air flow?

For us in the field, I would have to say yes. You can refer to the airflow data table in the indoor unit fan curve chart and get a pretty good idea. Also, just having an abnormally hi static on either return or supply will steer you in the right direction. Usually its return, BTW. But like Wayne said, an airflow problem bad enough to effect operation significantly will most likely be obvious in your operating conditions, especially with a fixed metering device. Not enough air means not enough HEAT to boil away the gas in your evaporator, so you will see lo press and lo superheat. A TXV will compensate for the superheat issues in some cases, but then you will be looking at subcooling, and usually finding it lo.
As far as other methods to verify airflow, there are several, but most are cumbersome and not pragmatic on your typical service call, IMO. My favorite way is the flow hood, but its time consuming and the tool is very expensive and large. I'm sure some of the other fellas around here will have other ideas. Pay good close attention to the Jim Bergman stuff ;)


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