A Florida AC-only storage building is equally divided sections each with:
- a single hallway to provide access to storage units
- 3 doors (25 feet apart) provide building access into one of the hallways
- each section is designed the same as the others
- an AC handler is mounted in the hallway ceiling near the door and a thermostat
The design includes an electronic controller (one single-board computer and electronic relays) to signal for:
- cooling (Yellow wire)
- fan (Green wire).
Decision point: The relays can be placed either:
- proximal to the computer: requiring thermostat wiring to be run to the computer
- proximal to the each air handler: requiring wiring to be run between air handler and the computer
What are the questions & considerations that must be thought-out before making a decision as to where to locate the relays?
Best Answer
Here's what you don't want to do.
So I would lean seriously toward having the 24VAC wiring do the long haul.
However, if you want the gory details, you need to examine each option: determine the current that will flow on the long haul, and grind that through a voltage drop calculator given the expected wire size and distance.
The root of the problem is that a 0.5-volt drop only reduces 24V only 2%, but reduces 5 volts 10%. Much worse, to do the same practical work, 5V needs five times the current, so now you're looking at 2% versus 50%. In other words, voltage drop's practical burden is a function of voltage difference squared, so it is 25 times worse for 5V than 24V.