Pressure loss and static pressure
Combine supply and return static readings to find TESP and compare an entered equipment rating.
Add signed supply and return static-pressure readings at a documented equipment boundary, then optionally compare the measured TESP with that equipment's entered rated maximum.
TESP describes the static-pressure difference across the equipment’s defined external boundary. With the supported sign convention, the supply reading is nonnegative and the return reading is nonpositive, so subtracting return pressure adds its suction magnitude. The pressure total is meaningful only when both readings use the same gauge reference and the manufacturer-defined tap locations.
The optional rating comparison divides measured TESP by the supplied equipment maximum and reports the remaining pressure margin. It does not infer airflow from that percentage. Filters, coils and accessories may fall inside or outside the applicable external boundary depending on the equipment documentation; including a component twice or moving a tap across it changes what is being compared.
TESP = Psupply − Preturn = |Psupply| + |Preturn| for the documented convention Psupply ≥ 0 and Preturn ≤ 0; comparison margin = rated maximum ESP − TESP; share = 100 × TESP / rated maximum ESP.
Psupply/Preturn = signed supply/return gauge static pressures (in. w.g.) at the documented equipment taps. TESP and the rated maximum ESP share that boundary; margin is in. w.g. and share is percent.
Below, at or above refers only to the entered rated maximum under the documented operating condition. Retain the supply and return readings and boundary description; TESP alone does not locate a restriction or select a corrective action.
Inputs: Daikin DD96TN installation-instruction example: supply static +0.3 in. w.g. and return static −0.1 in. w.g.; measurements are taken at the manual's shown equipment test openings.
Calculation: TESP = +0.3 − (−0.1) = 0.4 in. w.g.
Result: 0.4 in. w.g. TESP. The manual's example verifies the arithmetic; on a job, use the actual equipment's measurement boundary and operating condition.
Inputs: Constructed comparison case: supply static +0.45 in. w.g.; return static −0.30 in. w.g.; exact equipment-rated maximum ESP entered as 0.50 in. w.g.
Calculation: TESP = +0.45 − (−0.30) = 0.75 in. w.g.; margin = 0.50 − 0.75 = −0.25 in. w.g.; share = 0.75 / 0.50 × 100 = 150%.
Result: 0.75 in. w.g. TESP; above the entered 0.50 in. w.g. rating. The example maximum is user-supplied and is not a generic equipment limit.
Enter its signed gauge reading. This form expects a nonpositive return value and a nonnegative supply value. Check probe connections and the documented reference when polarity is opposite rather than silently changing the signs.
It only establishes the entered pressure comparison. Airflow depends on the actual blower setting and equipment performance, so use matching blower data or an appropriate measurement to evaluate it.