Hate to show up late to the party but if your looking to have some fun and build a custom system them you may want to check out http://www.tri-plc.com this company makes pretty good PLC's and are affordable. The M series allows you to program in ladder logic and t-basic for custom functions comes with pleny of ports for various hook-ups, remote monitoring / modem. Also if you know any programming lang. (Visual basic, C ) you can write your own front end program and interigate the PLC at will for data. I found that this PLC is great for people wanting to learn automation for less then $400.00 bucks!
And if you really wanted to get fancy try building your own room sensors with LM335 transistors great learning experience simple to do. Very powerfull PLC and very affordable.
My apologies for not responding to your post earlier... been out of town on business.
I checked the URL you provided and I found it most educational and a technology that I had not considered...Thanks for the heads up.
BTW I happen to read all the posts to that HVAC Procedures thread... mercy sakes...very interesting to say the least.
Anyway, one of the posts that stood out to me during the feeding frenzy, that caught my eye was yours [Quoted below]. I found it extremely professional and educational, and I can assure you I am going to be asking my HVAC guy why he is not providing me with that kind of data on my system.
"As far as leaving behind a paper trail, you and I in this case see eye to eye. Nothing is more annoying to me then not having past service reports or maintenance reports on the job. I have a separate "tear-out" on my tickets just for a "Job-site file". Also a detailed start-up sheet that shows Velocity pressure, CFM (actual) and (rated), External static pressure, Comp. and motor amps, Voltage, Air temps (delta), Line size, etc....
On the Commercial end I like to go deeper into it Pully (fan) rpm, Pully sizes, air flow readings, motor nameplate info, brake horsepower, belt size, Evap coil performance, etc.... Then after all this is performed the Customer MUST sign off on it and copies are left on the job (in folder) for future troubleshooting, and system evaluation."
Originally posted by aguada I am in the process of developing my own user interface program to monitor my HVAC equipment.
I would like to have a USB interface between the sensor circuit board and my PC.
Anyone have any suggestions for a mfgr for a HVAC monitoring (only) circuit board and matching sensors?
Just ran across your post. And read it and some of the responses.
Hmmm. Seems to me that perhaps for the objective you state that you wish to achieve, that perhaps you're getting a bit complicated? As were some of the responders.
After all, how much does a home type furnace/AC system cost? How much would one wish to invest in a monitoring system? What's your level of technical expertise? And if it's not up to the task of accomplishing the project of installing the components, setting them up or calibrating, and testing ... then you'd need to hire someone to do it. Which isn't gonna be cheap.
It's all fine and well to talk about monitoring pressures, currents, delta T's, so on and so forth. But the equipment to do so adequately enough to be worth the effort in the first place isn't cheap. And can involve some installation activities which would be a snap for a good HVAC tech, but which may well be beyond a homeowner's skills. Add, determining WHAT are good minimum and maximum values for each might be a chore for you to determine.
Sems to me it might well be simpler and cheaper to reduce the inputs to the basics, and KISS. Then use commonly available, not very expensive, off the shelf items to get it done.
ie Sail switch or equivalent to detect that the fan is in fact producing air flow. Two standard capillary tube type temperature controllers. Exact make and model unimportant. Each simply needs an appropriate range, and a stick type or coiled cap type sensing element which can be installed in the appropriate place. One for monitoring a call for heat, one for monitoring a call for cooling. What else? How complicated do yah want to get? One or two CTs (current sensors) to verify fan motor and/or compressor motor is drawing current. Maybe a freeze stat located right next to evaporator coils (to warn of icing conditions). Line monitor? To monitor electrical power supply to unit. One can find then in single phase or 3 phase types. Single phase, which is what you would most likely need can be set to trip at a determined by you low voltage setpoint. Or, heck, just wire in a standard relay to the unit power supply. Relay having coil rated for same voltage as unit uses. Couple wires connected to common and normally closed contacts will give yah feedback as to whether or not you've blown a breaker or fuse. Etc.
With whatever of the above you decide to be important enough to know to spend the money on, the only other thing you need is some wire, some misc standard relays, and a few solid state time delay relays. Plus, maybe a 120 to 24 volt transformer, electrical enclosure cabinet, etc. Depends on your design.
Extra relays are used to prevent alarm point monitoring except when proper condition exists. ie They make or break signal line for fan status if fan is called for, or not called for. Same for temperature controller being used as temperature sensor. You want that signal line locked OPEN by a relay unless and until a call for cooling occurs. You'd also add a time delay relay, which would delay the lockout relay from making for a period of time after the call for cool commences. After all, it'll take a while for compressor to start, and coils to start cooling. Set temperature controller/monitor to some reasonable value, ie perhaps 55 or 60 degrees. Wire it so contacts break if temp at coil is less than set point, make if above setpoint. Now you'll have an open or closed dry contact (binary zero or one)which after a suitabe startup delay, after the call for cool, will tell you whether or not unit the coil is getting cold enough to be of any use to you.
Same principle works for the other monitored points.
Pretty simple system, actually. Not all that expensive if you have the skills to do it yourself. Just need to understand basic electricity. Be able to use a drill, screwdriver, wire stripper/cutter, etc. Outputs can be sent to any of many readily available I/O boards that'll plug into most desktop or laptop computers. You only need digital inputs. And a program to read the status of those bits of input. Or, just get some simple 24 volt neon lights that just require you to drill appropriate sized holes in you electrical enclosure cabinet, insert lights and wire em. Some plug in with built in spring clamps that'll hold em in place, others just require you to screw on a retaining nut/washer. Label indicator lights on cabinet door. Done. Simple.
Such scheme as I mention is an old one. And reliable. It works. When I worked for one of the major telecom corporations we had thousands and thousands of such simple monitoring systems. In main and remote switchhouses all over the country. In our case, at the time, we had system both lighting up indicator light on panel inside the switchhouse, so local phone guy knew he had a problem. Plus we sent same info out over a network. Central trouble dispatch center then called me or one of my guys, or one of my peers in another region. Computer program just looked at 8 bit byte to see which bit or bits was set, looked up a table and then produced simple message. "No electrical power to AC Unit 2". Or, "No air flow, AC Unit #3". Or, "High discharge temp on call for cool, Unit #1"
Wasn't much info, but it was something. Better than nothing. At least we knew something was wrong. And almost always knew it BEFORE building temperatures got critically high or critically low. Meaning that regularly a tech was able to get on site before TSHTF.
Of course, at later times we started putting in more advanced systems, DDC type monitoring and control. With remote access which was nice as I could do some rather in depth troubleshooting from home. Perhaps even get enough info to see that while we had a problem, it'd wait til next work day without problems. Thus saving an after hours call out and the overtime associated with it. Which suited most of us just fine as we really didn't want the overtime. Would as soon be in bed.
But even when we went to DDC systems, we didn't install that on every system in every building. We considered a cost-risk ratio. Facilites with a total value below a certain level were left with the simpler (and cheaper) monitoring systems. ie Just didn't make sense to install a total and complete monitoring system with all it's sensors and labor costs involved on something like a Bard wall hanger. Montoring equipment would have cost more than the AC unit cost to replace. Especially if the Bard was hanging on some small remote switch building out in the sticks somewhere. Now if it was a major, urban switch, a different matter. Those buildings had millions of dollars of electronics in em.