Static Pressure

[catmanacman]

Can your static pressure be to low? This discussion came up at work today. You can imagine all of the opinions from people like me that dont really know. I came home at looked at mine, I have the Carrier Infinity control that shows it. My pressure at the moment is 0.05. I have a 4 Ton hp that was on low stage at this reading. The airflow CFM was 500. I dont think I have ever seen it over 0.1. Normally it never runs on a CFM over 1000. I have it set to comfort.

something is not correct a 4 ton heat pump on low should be flowing way more than 500 cfm

[energy star]

Nice. Have you inspected your ductwork lately?

[mgenius33]

Yes! If the supply pressure is too low you probably won't have a high enough velocity for proper and even diffuser throw or duct distribution.
Return should be as low as possible.

[kkmcewen]

Nice. Have you inspected your ductwork lately?

I have not.....what would I be cheking for and why?

[energy star]

Leaks

[kkmcewen]

something is not correct a 4 ton heat pump on low should be flowing way more than 500 cfm

I checked again....its on low and it shows 500CFM??

[kkmcewen]

something is not correct a 4 ton heat pump on low should be flowing way more than 500 cfm

I have to agree now after looking at some paper work I have. It says that if the outside temp is between 12-61;

3.5 x air flow multiplier x outside temp + 137 cfm/ton

3.5 x .63 x 32 + 548 = 618

Not sure why its not 618 instead of 500?

[beenthere]

Static pressure can be too low in my opinion. Take for example a direct drive blower. If you run it alone with no duct it will over amp and over heat.You cover part of the intake to add static pressure and it works fine.But how low is too low? Im shure there are alot more opinions than mine.Does someone know the minimum?

He has a VS ECM blower, so it doesn't work like your description of a PC blower.

His Infinity control could also be reporting the static pressure lower then it is.

[stickinit2thman]

He has a VS ECM blower, so it doesn't work like your description of a PC blower.

His Infinity control could also be reporting the static pressure lower then it is.

K I meant to ask that. So with the ECM it doesnt need and duct static? And thanks for acknowlaging my suggestion. Nice to see some here have respect.

[energy star]

beenthere, how is control actually capturing that data? Have you known a particular % of full scale that my be incorrect? I'm not to familiar with this control. He did state it was 32 outside. Not knowing the number of total supply diffusers, it just seems very low once we look at the possible number of supplies in the house divided by that five hundred.

[Redwood650]

Did you think to take an amp reading? The reason I ask is I would like to know if that low will cause over amp condition like I described in my previous post. If you are called back to a blower motor failure you know what caused it. Was it a ECM?

Yes and it wasn't over amping. It could overamp if the motor was older I would imagine. This system was abut 4 years old.

[second opinion]

beenthere, how is control actually capturing that data? Have you known a particular % of full scale that my be incorrect? I'm not to familiar with this control. He did state it was 32 outside. Not knowing the number of total supply diffusers, it just seems very low once we look at the possible number of supplies in the house divided by that five hundred.

Are you asking how the Infinity controller is calculating the static/CFM?

[beenthere]

The VS motor Carrier uses is a communicating motor(it communicates with the infinity control). They use to use the 2.5 version, but now are using the 3.0 version.

It won't always read the same as a manometer will. but that is mainly from placement of the static probe, from the few that i have checked.

But I wouldn't rely on it only, if you ant to know how much air the system is actually moving.