Hello, I have a building with a total of 7 separate air conditioning units. Each unit has it's own programmable thermostat in seperate zones of the building. I would like to install a device that would only allow only one unit to run at a time. I'm thinking of inputting the 7- 24 vac outputs from each of the thermostats into a ARDUINO device. The outputs would be the same seven 24 vac signals to each respective AC unit. In effect I would like to have a traffic cop to control all seven units. What ARDUINO unit would I want to purchase providing that this project is fees able?
Thanks
With 7 input, 7 output and pins for a lcd screen and any extra functions like a keypad, then you probably will have to go for a Mega 2560.
You will ideally need opto couplers to isolate/convert the 24Vac to 5v and a set of relays or similar to output the 24v ac to each of the A/C units.
That all sounds quiet easy to do, though you do not mention where the traffic cop gets its intelligence from to direct the appropriate signal. Some other factor/s in deciding which of the 7 A/C units should come on ?
Are the 7 units close enough that you could run wires from each thermostat to a central location and back again and still have everything work properly?
Leaving aside the connection issues any Arduino could control 7 outputs.
If the AC units are far apart it may make more sense to have an Arduino at each unit and a master to control them - possibly by wireless aor at least with much simpler interconnect wiring.
I'm not clear from your description what is the purpose of the "traffic cop". Why do you only want one running at any one time?
...R
The Reason that I wish to allow only one AC unit to operate at a time is to limit the kWh rate of usage. This building is on a commercial rate plan which means that it has a electrical meter that logs the highest maximaun rate within a 15 minute window each month. Silmutaneously operation of multiple units can greatly increase the monthly fee that is charged to our account. This building actually has too many units for it's own good but it's what we have. The units are close enough to allow wiring to the Arduino unit. The traffic cop concept was to allow operation of one unit at a time for the reason stated above. I was looking at an Eaton smart relay to perform the task. It would do so, however by the time The unit plus software and programming cable were purchased: $700. Would be spent. I was wondering what ARDUINO units were needed to emulate something like the Eaton smart relay. I thought that ARDUINO had a unit with a CPU and I/O that would accomplish this and could be programmed with a PC and the ARDUINO software without needing an LCD display or keypad. In short: 7 inputs to correspond to 7 outputs. If no inputs are active then no outputs are active. If anywhere between 1-7 inputs are active then each corresponding output may be active but only one at a time until all of the inputs conditions are satisfied.
Thanks
As I said in Reply #2 there would be no problem controlling 7 things with an Arduino. The simplest solution might be to have the Arduino control 7 relays.
You have not said how the Arduino is expected to decide which of the 7 units should be on at any time.
...R
You might make it magnificent and add a 3.2" LCD to the arduino mega2560 and bring back the actual temps
from each zone and display all that and even target temps.. then let the arduino enable the one zone
that is fursthest from the target temp.. that would be more logical than just a round-robin way..
I would make sure one unit is turned off for a few seconds before enabling the next zone so there is no power usage overlap..
Yes, it would work fine to have the ARDUINO control 7 relays. The building cools pretty efficiently and the units don't usually run that long. So would it be possible to put each input in queue and and allow the next in queue to operate as the one currently operating turns off? I appreciate the advice on an LCD display and bringing back the temperatures but to start out with I would like to try the simplest solution that might achieve my goals. If it doesn't work as well as I thought then we could get fancier. I also agree that there should be a delay between the switching of units to eliminate power overlap. So what do you folks think? 7 inputs with the ARDUINO putting the active ones in queue to control 7 relays one active at a time. What do I need to accomplish that?
Thanks
Masseyman:
Hello, I have a building with a total of 7 separate air conditioning units. Each unit has it's own programmable thermostat in seperate zones of the building. I would like to install a device that would only allow only one unit to run at a time. I'm thinking of inputting the 7- 24 vac outputs from each of the thermostats into a ARDUINO device. The outputs would be the same seven 24 vac signals to each respective AC unit. In effect I would like to have a traffic cop to control all seven units. What ARDUINO unit would I want to purchase providing that this project is fees able?
Thanks
You do not say why you need to do this.
Any microcontroller will probably do what you want but this seems to me that a proper analysis from a HIVAC speciallist is needed.
Arduino is primarily a hobby device, industrial PLC are available that are approved for connection to utility mains.
Using home brew in this situation could cause all sorts of code / insurance problems.
If your system has remote control, there are a couple of people around here have hacked the IR remote controls for HIVAC systems that may solve the problem.
"You do not say why you need to do this."
The why was quite clearly explained earlier re: electrical rates determined by monthly usage:
"This building is on a commercial rate plan which means that it has a electrical meter that logs the highest maximaun rate within a 15 minute window each month. Silmutaneously operation of multiple units can greatly increase the monthly fee that is charged to our account. "
CrossRoads:
"You do not say why you need to do this."The why was quite clearly explained earlier re: electrical rates determined by monthly usage:
"This building is on a commercial rate plan which means that it has a electrical meter that logs the highest maximaun rate within a 15 minute window each month. Silmutaneously operation of multiple units can greatly increase the monthly fee that is charged to our account. "
CrossRoads:
"You do not say why you need to do this."The why was quite clearly explained earlier re: electrical rates determined by monthly usage:
"This building is on a commercial rate plan which means that it has a electrical meter that logs the highest maximaun rate within a 15 minute window each month. Silmutaneously operation of multiple units can greatly increase the monthly fee that is charged to our account. "
Sorry i missed that.
But same comments apply.
Modifying an industrial or domestic installation requires suitably qualified people.
If aircon has remote control its possible to hack the remotes.
Doing it other wise requires a lot of expensive qualified work.
Masseyman:
So would it be possible to put each input in queue and and allow the next in queue to operate as the one currently operating turns off?
Yes.
And I agree with @BoardBurner2 about this
Modifying an industrial or domestic installation requires suitably qualified people.
...R
Okay, please bear with me but l beleive that this has strayed from the original scope and intent. Yes I do some automation and control as well as some hvac work. I simply don't want to invest the resources into a device that will not perform the tasks that I outlined. I don't understand the risks. This is not in an explosive class 1 div 1 environment nor is there any real fire hazard risk. We are talking about low voltage thermostat signals the same singnals that are run by thermostat wiring through walls to a wall mounted thermostat. Regardless I am planning on mounting the ARDUINO device into a NEMA rated enclosure. My system is not remote controlled and even if it was installing an ARDUINO device would not effect that one way or another would it? If the concern is wireless capabilities on an ARDUINO unit could it be disabled? What are the real risks? Say it malfunctioned and the AC system did not operate; there is no code that requires the building to be air conditioned in the first place. Say ift malfunctioned and the AC did not turn off; well now we have a cold building and wasted a little electricity. I see a lot of boasting about ARDUINO and even heard of them being used for automation and process controls in small factory and lab environments. But now I'm getting the impression that it is a kids toy incapable of doing anything serious. Is controlling 7 AC units in a 6000 SF building really that serious? Again I appreciate the replies but it harkens me back to when I was designing the hydronic heating system in the concrete floors of my house. Reading posts on some HVAC sites told me that I needed to have multiple set-point controllers to manage the system effectively and avoid extreme temperature swings. I ended up installing a total of 5 Honeywell T87 round thermostats. Yes the simple dumb thermostat manages the temperature absolutely perfect at a constant 72.5 degrees regardless of 80 degree swings outside. I understand the attraction to bells and whistles but in this case I'm looking for simple. If it works- great! If not then what am I really out? I understand all of the disclaimers but do not understand the concern of liability with a system of so low energy potential. Anyhow back to the original intent: if there is a ARDUINO device or two that will perform the previously outlined functions, then what might they be?
Thanks again.
Masseyman:
I don't understand the risks.
Which is why a qualified professional was suggested
nor is there any real fire hazard risk.
That means there is some fire risk - have you discussed the matter with your insurers?
What are the real risks?
Something will go wrong that never occurred to you and you or your employer will be be sued for $millions. What will you say when the Judge asks "what professional advice did you get?"
...R
Masseyman:
environments. But now I'm getting the impression that it is a kids toy incapable of doing anything serious.
Thanks again.
It is anything but a toy.
The atmel chip it uses is often used in industrial control systems and is very rugged.
The arduino that uses it however is a cheap mass market development system.
It can do what you want but is not certified for industrial use, Both UL and CE or equivalent approvals are expensive.
Some i have discovered will not work below 0 deg C although the chip itself can work down to -40.
Provided you use approved industrial components for the power and just use the arduino as the control element i think you would be OK.These can be costly and require a competent person to install them.
Unless you have a modern smart meter , of peak electricity is likely to be provided by separate metered circuits and those can get complicated.
All domestic thermostats i have seen use mains voltage with the exception of the radio ones.
Masseyman:
Reading posts on some HVAC sites told me that I needed to have multiple set-point controllers to manage the system effectively and avoid extreme temperature swings.
It may be worth asking on those sites WHY multiple set point controllers are needed.
There is probably a good reason for them.
An arduino should be able to cope with that anyway.
It sounds like you are trying to do what is called 'load shedding'.
An arduino should be able to do this provided you can get the thermostat connections done according to code.
That is likely to be costly , and in my experience getting a qualified professional to install the required interface for you to control yourself may be difficult.
They do not want the risk of installing something which could backfire on them.
Many only understand what they have been taught or told they can do.
I had a control relay installed at home i could control with 10V signal (industrial controller).
Went through several domestic installers before i found a fully qualified sparkie prepared to do it, and i had to explain first what i was doing.
No, I am a professional with two technical degrees an an electrical engineering degree. I work with PLC's and DPC's mostly Bristol Babcock and Siemens plus a little TI for a living and have licenses. The only thing that I admit to being stupid about is the capabilities of ARDUINO, which by now I should have just bought one and read the book but I wanted to cut to the chase to know whether to pursue or cut bait. This has nothing to do with my employer and I don't see any boogie man that is going to jump out at me. A 24vac 40va transformer with short circuit protection can not create enough potential to overheat thermostat wiring even if the device shorted out. A ARDUINO powered by a battery or 9v 650 ma wall wart ain't gonna do it either. Again, the unit will be mounted in a NEMA rated metal enclosure in a double sheet rock fire rated room with the furnaces. The thermostats are mounted to a double sheet rock wall as well. The mention of the set-point controllers was an example from years ago on another system that I built. It was only mentioned to stress the point that sometimes- not always how a really complicated and expensive solution will function no better than a simple less expensive solution. Which I thought was the spirit of ARDUINO?....an inexpensive logic device with open source programming? I realize that there are parts of the country where one practically needs a permit or approval to change a roll of toilet paper. I don't live in an area like that fortunately. If it would make everyone feel better then let's say I Want to control battery powered lights on a toy doll house. Using the aforementioned logic just substitute thermostats for switches and AC unit for light.
Thanks again
Masseyman:
powered lights on a toy doll house. Using the aforementioned logic just substitute thermostats for switches and AC unit for light.
Thanks again
Arduino will do this just fine.
Many times there are questions related to mains control where advice could possibly cause safety problems.
Many users of arduino systems wish to control mains voltage and although the arduino is an effective brain, practical use requires connection to mains supply. School children of 14 yrs or younger can ask this type of problem. They may also try to implement these systems using relays without their parents knowledge at home.
Masseyman:
No, I am a professional with two technical degrees an an electrical engineering degree. I work with PLC's and DPC's mostly Bristol Babcock and Siemens plus a little TI for a living and have licenses.
It would have short circuited a lot of wasted words if you had said that up front.
Being a professional I'm sure you will agree with us that we should have expressed caution in case the person asking questions was not adequately experienced.
...R