Spring is in the air (but we still have some snow too in the north central region) and as our thoughts turn to COOLING, we need to look at the ECONOMIZER. Economizers still are the most misunderstood, misdiagnosed, most often “GUTTED” control system we have in our industry, when, in essence, it really is simple if you take the time to learn it.
I have taught Economizers most of my career and, there have been very few changes to the controls or modules or motors. The only real change was the introduction of “DC” driven motors and IAQ capability of the modules. Otherwise, the enthalpy sensor and the discharge (or mixed) air sensor have remained the same. We added dry bulb out-door air sensors. We went from the W7459 logic module to the W7212 module. We went from the M7415 actuators to theM7215 actuators. Through all of this, the wiring has not changed as far as field wiring was concerned. With the 2 changes to the module and actuator, now you were able to add IAQ sensors and could control the power exhaust without an end switch attached to the crank arm of the actuator. As the saying goes, ” We’ve come a long way baby”!
Well, now we move to the next generation of controls for economizers. The wiring, believe it or not, hasn’t really changed but a lot of the components have changed. Honeywell has introduced the JADE economizer controls. These will eventually replace all the existing economizer controls they have made for years (almost). What will remain for the basic economizer is the M7215 actuators. This will work with the new module. The new LOGIC MODULE is the W722o:
This is a field programmable controls that also does its own diagnostics. That, in itself, is a real plus for the Service Tech out in the field. That in itself should help eliminate economizers from being GUTTED like they have in the past. As you can see below in the wiring diagram, there really is not much of a change:
One nice thing is, if you are doing a “dry bulb” economizer, both the discharge (or mixed) air sensor and outdoor air sensor are the same. It is Honeywell’s part number C7250 and is a 20K NTC sensor.
Now, if you want to go with outdoor temperature and humidity (enthalpy) sensors, you do need to use a new C7400S SYLK BUS SENSOR.
Unlike the old enthalpy sensors, this is NOT polarity sensitive. In fact, none of the sensors are polarity sensitive according to Honeywell.
Here is the wiring diagram for using ENTHALPY sensor(s). Please note that they tie into the “S” Bus on the module and not to the OAT sensor connections:
The new enthalpy control and Jade control give you much better set point control of how the economizer will function:
So, if you want to upgrade the economizer controls in a unit and you have the M7215 actuator, you can use the new JADE control and change the sensors and you’ll be “good to go”. This control has a lot of nice features — especially the built-in diagnostics.
In my next post, I’ll cover “set up” and “diagnostics” using the display and the arrows. Stay tuned for that post. In the mean time, please don’t GUT old economizers!