Packaged RTU Controllers for Diagnostics

[khvac]

Hello - I am trying to get a feel for how common microprocessor-based controllers are for packaged RTUs. My impression is that just about all new RTUs use them for unit control and logic-based diagnostics(using pressure and temperature switches, heating/cooling status, temperature measurements, etc.), and that a large portion of installed units also have them. Do you agree with this assessment?

Thanks.

[firstmech]

Yes and No, It all depends on the manufacture and the model. Microprocessor are more commonplace in the last few years especially on the higher end models. As for equipment price wars you will still find most manufactures carry a line of base models that have the bare minimum of components and safety devices. Alot of the manufactures also provide control configuration options that allow the contractor to order the equipment to intergrate with the existing building DDC system.

[khvac]

Thanks for the response.

If they are not using microprocessors for unit control and basic diagnostics, are they using electromechanical relay-based or other non-programmable (hard-wired) logic instead?

[firstmech]

Where microprocessors are not used we typically find basic elecctromechanial circuits and relays with intergrated safety lockout circuits requring manual reset of the control or main power circuit to the equipment in the event of a high priority safety componet trip. Other safety controls will simply recycle (low pressure controls).
A new trend we are seeing is the expanded use of electronic thermostats that incorporate scheduling, anti compressor short cycling, user configuration options, adjustable differentials, daylight savings, ect.

Equipment variations are vast I think most members would agree that the Lennox "L" series is setting the standard in equipment microprocessor controls, user service friendly and overall quality and still competing in the under 25 ton rooftop game.

I am not sure what specific info you are after as stated previously but typically in this business you get what you pay for, spend a few extra bucks and you get better quality, better efficency, more bells and whistles, ect.

GB