Plate Heat Exchanger Pressure Drop: A Worked Sizing Example
Why pressure drop matters as much as effectiveness
An air-to-air heat exchanger recovers energy, but the fan has to push both airstreams through it. Every pascal of pressure drop becomes fan power and noise. A good design balances high heat effectiveness against acceptable pressure drop, and the two pull in opposite directions as you add surface area.
The plate channel model
A plate exchanger is a stack of thin corrugated plates forming narrow channels. Air flows in alternate channels, transferring heat through the plates. The pressure drop per channel follows the usual duct relation: delta P equals f times (L over D_h) times (rho V squared over 2), where f is the friction factor, L the channel length, D_h the hydraulic diameter, and V the mean velocity.
Our Plate Air-to-Air Heat Exchangers page describes the plate geometry; the worked numbers below use a typical corrugated channel.
Worked example
Take 10,000 m3/h of air per side through a plate core with 100 channels. Per-channel flow is 100 m3/h, or 0.0278 m3/s. With a 4 mm hydraulic diameter and a 0.6 m plate length, the mean velocity is about 0.0278 divided by (100 times pi times 0.002 squared), roughly 22 m/s. At that velocity the Reynolds number is well into the turbulent range, so a Blasius friction factor of about 0.02 applies. Plugging in: delta P is 0.02 times (0.6 over 0.004) times (1.2 times 22 squared over 2), or roughly 87 Pa per side. Total fan pressure including inlet and exit losses might land near 200 Pa.
Turning pressure drop into cost
Fan power is flow times pressure drop divided by efficiency. At 20,000 m3/h total and 200 Pa with a 60 percent fan, the recovered-side fan draws about (20000 divided by 3600) times 200 divided by 0.6, roughly 1.85 kW. Compare that against the recovered heat power using our savings guide: if the exchanger recovers 150 kW of heat, the 1.85 kW fan cost is trivial and the net saving is large. If you over-surface the plate to chase a few more points of effectiveness, the fan power can erase the gain.
Design rule of thumb
Keep face velocity and channel count in the range your fan can afford. Favour counter-flow plates for the best effectiveness-per-pascal. For cold-climate duty, plan defrost margin so the pressure drop does not spike when frost forms. See our frost-strategy article.
Bottom line
Size the plate exchanger on both effectiveness and pressure drop; the optimum is where added surface stops paying for its own fan power. For a sized proposal contact Qiyu (15753355505).