I've been contacted by Trane on Static Pressure

[key1cc]

I wrote Trane with the questions below and to my suprise they actually wrote back. I've seen a lot of discussion on static pressure on this site so I will share Trane's reply to my questions.

1st Here are the questions I sent.

"The nameplate on my furnace indicates a static pressure maximum of 0.5 water column (for heating). Question 1. What is the max static pressure allowed for cooling? Question 2. How critical is it to hold to that max for example, when my 4 ton XL15i AC is set at the reccomended 400 CFM/ton, the static pressure due to the A-coil alone is 0.4 and if I add your new electronic filter "Clean Effects" that adds another 0.2, that would put my static at 0.6 which would be above your allowable maximum of 0.5 even before considering any duct work resistance. Thanks"

Now here is the reply.

"Thank you for your request

#1 The max static for cooling depends on air flow. For example if the blower data for your furnace says it will handle the required 1600 CFM for your outdoor unit at .8” WC then .8”WC is the max static for cooling. We stop our blower tables at .9”WC we prefer nothing higher than .9”WC at all.

#2 you should not allow the air flow for cooling to drop below 350 CFM per ton I recommend minimum 400 CFM per ton. Again the blower data that is in the service facts which was shipped with your new unit will provide a guide of how much static is available at given air flow.



Thank you for visiting our Website"

Well....there you have it from Mr Trane himself (or herself).

Key1

[dash]

So no explanation of why .5 is on the furnace as Max..

My theorey is "we have always done it that way".

[key1cc]

So no explanation of why .5 is on the furnace as Max..

My theorey is "we have always done it that way".

My nameplate actually states "0.5 max for heating"
It specifically said for heating that is why I asked about cooling. I do have a follow up question into Trane becaue I want to know if I should follow the service facts data that indicates I could go up to 0.9 for heating as well....or should I go by the nameplate thate states 0.5 max for heating.

Key1

[udarrell]

If you want blower motor operating efficiency, design to get all the components so the lowest possible ESP is achieved for the required CFM.

The higher the ESP the more duct leakage there will be, there is always some duct leakage, therefore that can make a big difference in cooling performance.

Present day blower wheels are engineered to handle higher static pressures, therefore because that results in increased back-pressure on the blower blades, the motor uses more amps when moving the same amount of air at those higher ESPs.

I personally, would design ductwork & all components to achieve 0.5" or less ESP. - udarrell

[mark beiser]

[B]I personally, would design ductwork & all components to achieve 0.5" or less ESP. - udarrell

Unfortunately, it is very often not possible to achieve that in the cooling mode.

[udarrell]

Unfortunately, it is very often not possible to achieve that in the cooling mode.

You are absolutely right Mark, quite often it may be unachievable.

Additionally, oft times we want a fair amount of static pressure & velocity at the Supply Air registers to achieve the desired throw.

All I was saying is that in the design stage, I would use .5" ESP as the desirable target to shoot for even at 425-CFM 'wet coil' per/ton of cooling. - Darrell

[Blacklabelman1]

i also belive that they are looking for total static pressure, and what are you using to measure you static pressure? i hope not a manometer with an open ended tube just poked into the duct work

[beenthere]

Just a guess.
.8" max static pressure for heat. Might mean in heat mode with a dry evap coil.

[key1cc]

Just a guess.
.8" max static pressure for heat. Might mean in heat mode with a dry evap coil.

In cooling mode my unit is set up for 400cfm/ton which the service facts sheet indicates would be 1666CFM with 0.5 static pressure.
In heat mode my unit is set on medium low which would give stage-2 CFM's about 200 CFM lower than that.
The lower CFM itself should lower the pressure for heating.

Also for cooling I use comfort R so for the 1st 1 minute it is at 50% blower demand and the next 7.5 minutes is at 80%. Thus during the 1st 8.5 min of every condenser start up my total ESP never goes above 0.69 even with dampers closed for air balancing (to make the whole house comfortable). After the 8.5 minutes are up the static goes to 0.92 (down from 1.1 with the changes that were made so far).

Key1

[key1cc]

i also belive that they are looking for total static pressure, and what are you using to measure you static pressure? i hope not a manometer with an open ended tube just poked into the duct work

My total static pressures were measured with a calibrated 0 to 1 Dwyer magnehelic guage in the blower box (before the blower) and BEFORE the coil (edited to correct).
The trane unit actually came with pre-drilled holes for static pressure testing.

My duct pro has been here frequently and tons of measurements were taken across the system at each phase as my basement duct work was being re-done.

key1

[jrbenny]

You (or the company you hired) are measuring incorrectly.

ESP is still greater than 1.0 IWC when measured correctly. Probably pushing 1.3 IWC with a wet coil.

[beenthere]

You (or the company you hired) are measuring incorrectly.

ESP is still greater than 1.0 IWC when measured correctly. Probably pushing 1.3 IWC with a wet coil.

In earlier post. He posted the static before the coil.
He has the correct measurements in other post.

[beenthere]

If your at .92" with 1666CFM in cooling with a wet coil.
Then in heat, at 1466 CFM, you should be around .70"

[jrbenny]

So, which is it? Before the coil or after the coil?

[key1cc]

You (or the company you hired) are measuring incorrectly.

ESP is still greater than 1.0 IWC when measured correctly. Probably pushing 1.3 IWC with a wet coil.

Sorry...I was recalling what he did incorrectly..I went down stairs and looked at the marked measuring spots and it is actually before the coil not after. Thanks for the correction so not to confuse anyone. Next time I'll have breakfast before attempting to post...
Key1

[beenthere]

If he's still using the Trane static pressure test holes, its before the coil.

[key1cc]

So, which is it? Before the coil or after the coil?

If you want to know some specifics....Before the fan was -0.26, after the fan but before the coil was 0.66, In the plenum after the coil was 0.26. There were a bunch more taken across different sections of the duct system but I believe I listed the most relevant ones....
You guys are on your toes.... .


Key1

[key1cc]

If your at .92" with 1666CFM in cooling with a wet coil.
Then in heat, at 1466 CFM, you should be around .70"

The 1666 CFM is the value stated in the service facts sheet at 0.5 static pressure. Since I am at 0.92 I get much less (1450 CFM) according to service facts sheet.

Since I have not run in the heating season yet, I'm not sure what the static will be so I can't check the service facts sheet yet and get the corresponding CFM's.

Key1

[beenthere]

Sure you can.

Turn the stat to heat, and turn it all the way up. When the furnace goes to second stage, you can measure it.

[Blacklabelman1]

Sure you can.

Turn the stat to heat, and turn it all the way up. When the furnace goes to second stage, you can measure it.

or you can jump it to run second stage