Can the SDopers give me a crash course in HVAC controls? Please help fill me in on typical means of controlling HVAC systems, whether old or new. So far, I am finding there are:
Direct Digital Control Systems (DDCs)
Hydraulic controls
Pneuamtic controls (I guess) like a vacuum system, perhaps?
Now, what about just a probe with a wire coming off it, like a temperature probe? Does that fall under DDC, or is DDC something much more specific?
Also, where would a thermostat fall under? There must be some general “categories” that controls fall into, but what are they? Perhaps, I first need to break them into (a) mechanical (i.e. hydraulics) and (b) electrical which would then break down into analog, or digital???
I don’t even know enough to know what to ask, so perhaps the SDopers can help clue me in!
In part: pneumatic controls are run on dried compressed air. The compressed air flow is controlled by a thermostat to operate pilot valves and power pistosn to move dampers controlling hot and cool air flow to meet the temperatue demand.
If you are serious about learning about HVAC control systems you should get a book or study guide covering the subject. It is far too extensive for short answers.
Yes, I recognize this is a BIG topic, and thanks for your input. Not being EE, I did at least confirm that there are mechanical and electrical controls. And, the electrical controls can be electric or electronic devices.
Also, I should recognize that controls marries sensors and probes, gauges and dials, transmitters and recorders, alarms and actuators…all through feedback loops and the magic of electricity! Whew!
So, can you recommend a good primer reference? I don’t need the nitty-gritty, just an overview as to the types of “animals” I might come across, what they do (in general), and what might be paired-up with what. Thanks, Jinx
I hope people can answer various parts of this question:
a) Can you help me define “ventilation” concerning commercial buildings? My reference book will say it is amounts of Outside Air (OA) needed to dilute odors in buildings and keep the air fresh…as set by Code and ASHRAE stds. OK, but then they also say ventilation combats infiltration by maintaining air pressure just high enough to offset infiltration. BUT THEN! The examples only show how cfm is used to combat infiltration…isn’t there a pressure associated with this? (Let’s assume a one-room building, and I’m asking about the air pressure in that room. How many inches of water will it be above atmospheric?
b) Also, a simple example they give seems illogical. A room with an exhaust fan has an infiltration rate of 500 cfm and the fan exhausts at 200 cfm. They claim you MUST provide 700 cfm ventilation air to exfiltrate 500 cfm and exhaust 200 cfm. But, cant’ we say the 500 cfm infiltrated will just be 500 cfm exfiltrated? To me, the example is saying 500 cfm infiltrated + 700 cfm ventilation air from a blower WOULD BE 1200 cfm total INTO the room! Is there some unspoken assumption that 500 cfm is being returned, or something?
c) When supplying air to a room, do you add the cfm req’d for cooling that room PLUS the ventilation requirement to find the total Supply Air (SA) req’d?
The above question posted in the WRONG place! Please ignore…
It’s all because the SDope Board once had a different format, and I can’t break away from the old habits! Grrrrr! :mad:
For controls and other questions you might try finding the ASHRAE Handbooks at your local library. The various HVAC manufacturers (Trane, Carrier, etc.) also produce manuals that you might be able to find on eBay or elsewhere.