Early Access: SwitchDamper

For years, DZ was able to control modulating dampers.

It seems, however, that bang-bang dampers still have their place, hence, SwitchDamper was added to Subversion and will become a part of the next release.

Now you can use DZ to control any HVAC actuator that is controlled by a switch. This includes, in particular, but not limited to:

• existing open/close dampers normally controlled by 24VAC;
• electric heaters that are configured as auxiliary heaters in a complex zoned system;
• hydronic, geothermal and steam system valves.

Note on Register Mechanical Design

I've just been told by one of DZ users that his design uses about 90° of servo motion to move from totally open to totally closed position. My kneejerk reaction was -

Design your registers so 180° of servo travel is necessary to move the damper from fully closed to fully open position.

Primary reason for this is that the torque required from the servo is proportionally less, hence, less stress, longer usable life and quieter operation - servos are becoming to growl as the load goes up, and as their age goes up.

There are several things you need to keep in mind when you're designing products using servos.

Servo range of motion

All servos, being analog devices, are different. Normally, servos are supposed to work with PWM control signal being between 200μsec and 2000μsec, but there are instances that can go as low as 160μsec and as high as 2300μsec.

Servo controller signal range

Not all servo controllers are created equal, either. Some of them support advanced range limiting and calibration options, some of them are incapable of producing anything other than a predefined range of signals with no calibration options whatsoever - the only calibration option would be to design the device in such a way that the servo travel is artificially limited, and later use software controlled range limiting to make things work properly.

Hardware vs. Software

DZ3 will support both range limit and calibration within coming weeks (DZ2 supported it already, and it's just a matter of porting it over), so your hardware (both servos and controllers) is the only limitation for your design.

On the picture: existing register designed to utilize 180° of servo travel.

What kind of actuators are you using?

I'm now working on a maintenance ("Undead") release for Servomaster, which was originally created to provide the driver layer for register or damper actuators (as shown here).

A lot has changed since last modification was made to Servomaster - the code turned out to be rock stable and low maintenance. I could accept that as a sign of the fact that the code is perfect - but I'd rather go the other way and ask if it is so off the mark that you guys are speechless and simply walked away from it because you can't use it.

It would be really nice if you looked at the poll (scheduled to close on December 5 2007) and gave me a hint on what to concentrate on.

Short Take: Modulating Dampers

A damper, in HVAC terminology, is an air valve used to regulate the flow of air through the duct.

There are two general kinds of dampers (definitions are probably not in line with HVAC terminology, but hopefully understandable enough):

• Simple, also known as bang-bang, dampers - these can only be in fully open or fully closed position;
• Modulating dampers are able to stay in any position between fully open and fully closed.

First kind is, of course, cheaper, but has serious drawbacks - first, the noise they make is quite noticeable (one can get used to it, though), second, they provide only limited control and are not suitable to advanced applications.

Modulating dampers, on the other hand, are silent by design and provide adequate control, but require more sophisticated control systems in order to utilize the capabilities.