Variable speed air handlers for hydro air systems

Constantin

... oversized ducts are advantageous to motors since they reduce the static pressure the fans have to overcome. Any thoughts from the air-experts?

rumn8r

Variable speed air handlers for hydro air systems

What variable speed air handlers (ECM motors) have you used for hydro air systems?

Techman

ECM air handlers

Hi! Carrier,Trane,Ruud/Rheem ,all very good!

Empire_2

Everyone tells me how goo they are, but

I still cannot get over the price when the ECM goes bad and is out of warranty.........Comfort is one thing, and a pain in the butt is another,,:-)

Mike T.

A.J.

Variable speed blower price

Sure they are more money but if you combine it with a electronic air cleaner it doesn't get any better.

rumn8r

Don't they save more money in electric costs than the cost difference for replacement?

Constantin

ECMs are expensive...

... all the more reason to install them only into systems where the ducts are the right size, etc. as any motor consistently strained beyond its allowable range will fail prematurely.

I hope that the cost of these motors is likely to fall in real terms as the technology gets more widespread, more motor manufacturers produce drop-in replacements for OEM units, etc.

rumn8r

Constantin,

My ducts are way oversized and I've been told that is not a problem. Do you agree?

Floyd

ECM motors are a two part deal....

Rarely the "motor" itself goes bad.. usually the problem is the"pot" or the control end of the motor. That part can be purchased for a rather modest cost and installed on the motor by connecting a molex plug connector and a couple of screws. Ecm motors by the nature in which they operate are inherently much more reliable than standard single phase motors.

Floyd

Brad White_9

Typically and Generally True

The lower the pressure requirements, the less strain on motors, fans, bearings and if belt-drive, sheaves and belts.. Not just duct sizing, which is the least of it, but the fittings are what really take a toll. In a typical air system of any length, the duct friction (airflow relative to size in straight duct) may be only 15-20% of a system's external pressure loss. Fittings, elbows, tees, offsets, make up the rest, externally. The internal losses of coils and filters often exceed that which occurs outside the unit.

The system has to be balanced correctly when set up for the first time and to make sure that the fan operates in a stable range. It must start as a good selection.

For example, if a fan has to move less air at a higher pressure, the operating point is at the high left side of a classic fan curve. There is a line at the far left called the "surge line" and the selection should be well to the right of this. When a fan operating point approaches the surge line, it seeks a balance between flow and pressure at available RPM. As it raises flow, so does pressure. As pressure increases, it drops flow. Hence the term "surging". It is in a range where it "hunts" and trades flow for pressure back and forth. Not stable as you can see.

The other side is what I call "over-shoot". A fan is operating in a stable range, SP and volume steady and in balance. Say a small constant volume system with dense filters such as a laboratory, running at what are low pressures external to the unit. The filters represent an unduly high percentage of the total system pressure drop.

Someone removes a set of the final filters (this has happened!). Suddenly, 35% of the total system pressure drop is gone, but the RPM remains the same. The operating point rapidly moves to the right, along a constant RPM curve, crossing the Brake HP curve and overloading the motor... Some fans my compensate for this by feathering (Backward inclined or airfoil blades) but a forward-curve fan will trip the breaker.

In small systems an ECM motor will compensate to some extent by balancing actual current to torque. (Do NOT ask me how it does this... I really do not know but will learn.. For now, call it F.M.

The scenario above, with constant volume systems overshooting is why I put VFD drives on any system that has the budget for them.

Granted this is commercial/industrial in application. Most systems in homes have fixed CFM and pressure within a range of speeds, so the "ductwork is designed for the fan" rather than designing the fan to suit the ductwork.

But the ECM motors and better yet, variable speed motors coming down to the more residential/retail level, have incredible potential.

Sorry of off-topic but I wanted to illustrate some of what Constantin was stating.