DWDI incorporable backward-curved — maximum efficiency for high-performance AHU and nZEB systems

DWDI incorporable fans with backward-curved impeller represent the top of range for centrifugal AHU components — the combination with the highest overall efficiency available: DWDI double inlet for high airflow in a compact footprint, backward-curved blades for maximum aerodynamic efficiency and self-limiting characteristic, and EC motor for 90–95% electrical efficiency. The three factors act synergistically — each amplifies the others.

Direct comparison in AHU design context:

AHU design criterion	Plug backward	DWDI forward	DWDI backward
Inlet type	Single (no casing)	Double inlet	Double inlet
Airflow at same motor diameter	Medium	Highest	High
Aerodynamic efficiency	High	Medium	Maximum
Self-limiting motor power	Yes	No	Yes
Safe VAV operation	Yes	With caution	Yes — recommended
Total system efficiency (TTE)	55–68%	45–58%	62–76%
nZEB certification suitability	Possible	Limited	Recommended

Why self-limiting matters in real AHU operation: an AHU goes through dozens of operating regime changes daily — filters gradually clog increasing resistance, VAV dampers open and close changing airflow, outdoor air temperature varies changing air density. With forward-curved blades, all these variations can push the motor beyond its power limit if not actively supervised. With backward-curved blades, the power-airflow curve is self-limiting — the motor physically cannot be overloaded, regardless of the combination of conditions in the installation. This eliminates an entire category of risk for the AHU designer.

Total system efficiency (TTE) and regulatory relevance: European energy efficiency regulations (ErP, EU Regulation 1253/2014 for AHUs) impose minimum limits on total ventilation system efficiency. DWDI backward-curved + EC is the configuration that most easily achieves the TTE values required for nZEB buildings and for BREEAM, LEED or WELL energy certifications. Designers who need to document fan efficiency in building energy calculations will find the most favourable TTE values in this configuration.

Specific applications where this combination is the standard selection: AHUs for hospitals (continuous 24/7 operation, HEPA filtration with high and variable resistance), clean rooms ISO 5–8 for pharmaceutical and semiconductor industries (precise airflow and pressure control at any point on the curve), nZEB ventilation plants where fan self-consumption is audited, AHUs with complex VAV systems where the motor runs for hours at 30–60% of nominal airflow, and any AHU undergoing building energy certification.

AHU installation: the DWDI scroll casing is fixed to the internal structure of the unit. The bilateral inlet connections (right and left) collect air from the AHU central plenum, and discharge passes through a single outlet directed towards the filtration or thermal treatment section. The plug and play EC driver is mounted on the casing — connect power and control signal (0-10V or Modbus RS485) without further configuration.

👉 Plug backward curved incorporable EC — for AHUs with minimum space, no own casing 👉 DWDI forward curved incorporable EC — when maximum airflow takes priority over peak efficiency