Certain components have fixed pressure drops published by manufacturers that cannot be calculated by friction formulas. Create a dedicated section for these terminal items:
Do not hardcode coefficients into your main calculation. Create a hidden reference table based on or ASHRAE Handbook - Fundamentals .
. Using an Excel sheet for these calculations allows for a systematic approach to identifying the critical path —the duct run with the highest total pressure drop. Core Components of an ESP Excel Sheet
Eliminates "human error" when reading lines on a friction chart.
The fixed resistance from accessories installed in the airstream (e.g., filters, dampers, coils, louvers). Step-by-Step Excel Sheet Architecture esp calculation hvac excel sheet
Air charts utilize round duct metrics. For rectangular ducts, use the Huebscher equation to find the circular equivalent diameter: = (1.30 * (D8 * E8)^0.625) / ((D8 + E8)^0.25) Use code with caution. (Where D8 is Width and E8 is Height) 2. Automating Air Velocity
A common engineering approximation for Galvanized steel is: $$\Delta P = 0.0307 \times \fracCFM^1.852D^5.01$$ (per 100ft)
VP = (Velocity_FPM / 4005)^2 Fitting_Loss_in_wc = C * VP
is the resistance the fan must overcome to move air through the external components of the system—namely the supply ducts, return ducts, grilles, filters, diffusers, and coils. Certain components have fixed pressure drops published by
De=1.30×(a×b)0.625(a+b)0.25cap D sub e equals 1.30 cross the fraction with numerator open paren a cross b close paren to the 0.625 power and denominator open paren a plus b close paren to the 0.25 power end-fraction Velocity Equation
ESP=Total Duct Friction Loss+Total Fitting Dynamic Losses+Component Pressure DropsESP equals Total Duct Friction Loss plus Total Fitting Dynamic Losses plus Component Pressure Drops
Dynamic loss (in w.c.) = C * (Velocity_Pressure) Where = (Velocity_fpm / 4005)^2
This hidden table maps fitting types to loss coefficients (C) from ASHRAE Fundamentals or SMACNA. The fixed resistance from accessories installed in the
If measured ESP exceeds design, Excel can suggest new RPM using Fan Law 1: RPM_new = RPM_rated × sqrt(ESP_design / ESP_actual)
This tab pulls data from the main sheet to present the final engineering results.
Fitting losses are calculated using local loss coefficients ( -factors) applied to the velocity pressure ( Vpcap V sub p First, calculate velocity ( ) in Feet Per Minute (FPM):