Blower Types
Forced air systems utilize a blower to create the air movement that delivers hot/cold air throughout the house. The type of blower you select can have a huge impact on the comfort and efficiency of your house. Here are the basics:
PSC (fixed-speed) blowers:
- These are blowers commonly found on lower-end equipment.
- Because these blowers operate at a "fixed speed," poor duct design often results in lower airflow. This frequently leads to longer operating times, higher energy bills, and reduced comfort due to the lack of airflow delivery.
- Comfort: duct systems commonly have more air resistance than these motors are optimally designed for, since the motor cannot adjust to this the result is less airflow and circulation of conditioned air, meaning less comfort
- If used with a multi-zoned system set-up, a bypass damper must be used. This can often lead to high air velocities and excessive noise.
Variable speed (ECM) blowers:
- These blowers are commonly seen on higher-end equipment.
- These blowers adjust their speed to move a fixed quantity of air (within a certain static pressure range). These blowers can essentially "overcome" the resistence created by poor duct design or excessive filter restriction (to a point).
- As a result of increasing their speed to deliver the "correct" amount of air, poor duct design can still create some issues:
- Higher energy use as a result of higher blower motor RPM's
- Noisy airflow resulting from high velocity
- Condensation "blow-off" in cooling mode - high velocity air blows condensate off of coil back into the duct system
- Non-draining condensate drain from high suction at blower (won't let the water go down the drain). This results in lack of dehumidification in cooling mode.
- When combined with properly sized ductwork and intelligent controls, these blowers provide great benefits:
- Greater efficiency
- Ability to modulate down to lower speeds to accomodate small zones, 2-stage compressors, and enhanced dehumidification in cooling mode.
The selection of the blower must be part of an overall improvmenet strategy that addresses the system's performance in a wholistic manner - ductwork included. While the ECM blower technology is indeed impressive, this technology doesn't eliminate the need for an intelligent ductwork design.
