# A/C Control System

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I am looking for an economic alternative to monitor and control the air conditioner of several distributed substations in order to detect their failure before the electronical equipment, that they contain, fails
because of the heat. Any suggestion?

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#### Bob Welker

Can you provide any specifics (distance between stations, any notable environmental concerns (i.e. - high voltage substations), degree of
sophistication (should the system phone someone, send email, turn on a buzzer, etc.)?

One possibility is get an inexpensive temperature controller with one or two alarm outputs, set it up for on/off (rather than PID) control, and then
maybe do something like this:

Setpoint - Hotter than normal. Turn on early warning alarm
Alarm 1 - Getting close to equipment max. temperature specs.
Alarm 2 - If practical, shut down heat producing equipment before damage
occurs.

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#### Larry Kiel

You didn't mention what type of air conditioning units you have but here are some of the options we use. If your air conditioning system has duct work installed, an easy detection method to see if the system is on, is to install a flow switch in the duct. This however, doesn't guarantee that the air is cold, it just means the air is flowing. Another option is to install a temperature switch or sensor. This could be mounted in the duct (faster response to a problem) or in the room. If it's installed in the room you would want to locate the sensor so you get the best response to a failure, some place where you don't have to wait a long time to see a temperature change. A less accurate indication is to monitor the auxiliary contacts on
the circuit breaker or motor starter that feeds the air handler motor.

You may want to look at how you intend to monitor the sensor you chose. If all you have is a digital monitoring system then you want to look at things like switches (temperature, flow, or pressure) or contacts (auxiliary). If you have access to an analog monitoring system then you can look at actual temperature measurement.

If you have a wall unit air conditioner then you would not be able to try the duct insertion methods above however, the room temperature monitoring and the auxiliary contacts would still apply.

One last thing to consider. I assume the system is active 24 hours a day. However, if the air handler cycles because it's on some type of schedule (say for energy management) then the flow switch idea is lot harder to implement.

A room temperature switch may be your simplest choice, assuming your response to a failure is in the range of hours.

Hope this helps.

867-1415.

Larry Kiel
Kennedy Space Center

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#### Eric M. Klintworth

You could use a simple autodialer to monitor the room temperature and call someone (and/or a pager) if the temperature goes outside the normal
range. This detects any sort of failure, even something as simple as "the guy changing the filter forgot to turn the A/C unit back on".

One unit I have used is a Sensaphone Model 1104, list price $400. We have several in service. They also detect and dial out on power failure. You just need 120VAC power and a phone line. Their main downside is that they must be programmed locally (numbers to dial, etc.). See www.sensaphone.com Hope that helps. E-mail me if you have more questions. Eric M. Klintworth, P.E. Columbus, Ohio A #### Ali Jazbi Dear Betty You can see Andoce Control Company part list, some of its product like tcx840 may be useful for you. Regards Ali jazbi R #### Roger Irwin http://www.satchwell.co.uk Allthougth not on thier website, thier economic IAC400 box is capable of this job. Awful graphical programming environment with no possibility of writing straightforward routines (god knows why these people think all users are idiots), but if you can put up with that they could be your solution. A #### Amr Elaguizy Betty, If you are looking for a cheap solution i.e. no out of pocket$! then you might consider two alternatives:
1. If you have a transformer in each substation which feeds, your switchgear and/or MCC within this station, and if the transformer has an ammeter to display the current with a couple of dry contacts alarms, hopefully one of the alarms contacts are not used. Then you could adjust the alarm to close the contacts at a certain amps value equivalent to a rough estimate of rise in temperature in the substation. Then with the help of some of your house electricians run contacts from the AC starter which compares both signal and if both signals are not on within some
time delay then a lamp will be lit, probably located in the electrical shop to alert the electrician to check out this alarm.
2. Another alternative which was implemented, many moons ago, in a paper mill in the S. E
region of the USA, which worked great. Have the shift electrician at the start of his shift, record in a form all the reading in the substation, while he is filling the form let him check the temperature of the substation for
any discrepancies he could see, and report it. Few issues need to be addressed, keep the forms in each substation, thus will make it easier for everyone, not in someone desk!! Few gains will be achieved if sold to the electricians, they feel a sense of ownership to the equipment, you have an excellent records of the loading conditions within your substation. Do not use this information for reprimanding any of the personnel or eventually the whole system will die for lack of team work and resentment.

As far as the second item, generally speaking off shift personnel usually have a lot of time in their hands, when they are not fighting any major fires.

Regards,
Amr Elaguizy

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#### Eric M. Klintworth

You could use a simple autodialer to monitor the room temperature and call someone (and/or a pager) if the temperature goes outside the normal
range. This detects any sort of failure, even something as simple as "the guy changing the filter forgot to turn the A/C unit back on".

One unit I have used is a Sensaphone Model 1104, list price \$400. We have several in service. They also detect and dial out on power failure. You just need 120VAC power and a phone line. Their main downside is that they must be programmed locally (numbers to dial, etc.). See www.sensaphone.com

Hope that helps. E-mail me if you have more questions.

Eric M. Klintworth, P.E.
Columbus, Ohio