HVAC system control principles


Thread Starter

Alex Nikulin


For a HVAC system, control of room comfort conditions by is a difficult and complex task. When I have one heater module, and one fan, it's possible to use simple control of a temperature, b.e. PI or PID algorithm. But what should I do with more complex system?

Possible, we have some HVAC system - central conditioner (supply and extract fans and dampers, mixing module with return air damper, pre-heater, cooler, humidifier, after-heater) with sensors and comunications. We have task - control of a comfort conditions in a single large room with many peaple. When I can find principles of control all of this equipment for this task? B.e., what should do an after-heater, and cooler, to meet goal and herewith not to disturb to each other?

Peter Whalley

Hi Alex,

Possible sources of information:

1. HVAC consulting engineers - engage them to design the system including control strategy. If the design is particularly complex you may well need an engineer with the right experiance and training to do the work.

2. HVAC control system contractor - include control strategy as part of their contract to provide the control equipment.

3. Ask your local HVAC control equiment suppliers if they have any application notes they can provide.

4. See if you can get hold of the Honeywell publication "Engineering Manual for Automatic Control of Commercial Buildings" Library of Congress Card No 97-77856.


Peter Whalley

Johan Bengtsson

Well, the answer to one part of your question, how to make them not fight each other:

Use one controller to determine the heating/cooling power in a way that makes some point on the scale mean 0 power, values below that means negative power (ie cooling), values above mean positive power (ie heating).

So define your scale from maximum cooling to maximum heating, assign the task to one controller to ouput the needed power.

Take this signal and break it up to the various places where heat can be added or removed.

/Johan Bengtsson

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