Static Pressure

[TEK723]

I've read here to take statis pressure readings berfore the evap coil and after the filter on a furnace. If you were checking a evap air handler, would you test further doen stream to avoid VP?

[udarrell]

The positive tip reading goes before the evap coil while the negative tip goes after the filter & before the blower on a furnace is the External Static Pressure (ESP) reading; the reading on which mfg'ers rate equipment.

If you know the initial drop through the filter, you could remove the filter, because as the filter loads its PD drop will keep increasing.

When you check pressure drop across any device, including evaporator coil, you check pressures upstream & downstream of the device.

The static pressure tip, when use correctly, is designed to measure static not Velocity Pressure (VP).

It is good to design to retain as much velocity pressure as possible, because the more velocity is restricted (due to too small - high FR ducting) in relationship to CFM flow volume - static pressures will increase.

http://www.udarrell.com/external_sta..._readings.html
- Darrell

[a0128958]

And are these 2 statements thus correct for a heat pump:

The measurement points are after the blower motor and before the evap coil?

If a filter is part of the unit, then meaure before the filter, and, look for a manufacturer's foot note (something like "Max ESP includes allowance for wet coil and standard filter")?

Thank you.

Bill

[beenthere]

Air handler. Between air filter and coil, and in supply plenum. Check foot notes for air filter allowances.
On heat pumps. You must also look for foot notes on the strip heaters.