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  1. #1
    Join Date
    Jul 2008
    Posts
    86

    How to best measure cycle frequency / run time

    I would like to be able to monitor how much of the time my system is running throughout the day. What is the best way to log the start and stop times? I would like something that would create a log file so I could see how the run time varies throughout the day. Maybe there is something a lot easier that would just give me a cumulative run time. I could determine the % of run time based on how long it had been accumulating run time.

    Anyway, what is the way you guys do it, short of sitting there with a stop watch?

    Thanks.

    DavidJ

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,289
    How to do it would tread close to DIY rules infraction. I know now how I'd do it so I wouldn't have to repeat what I did it the other day in my radiant barrier performance post, where I sat down with a magazine or two, a pad of paper and pen nearby, and recorded start and stop times. It was a hot, lazy Sunday afternoon...got some reading done. But...for longer data logging, that method obviously has limitations.

    The best I can say is you would need some sort of device that could detect when the system is running, and when it is not. I personally want to use such a device to obtain a run time trend in comparison to outdoor temperatures, attic temperatures, humidity, actual system performance, etc. It might take me some time to amass enough loggers for the project.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,727
    There are thermostats that have that ability.
    Ask your contractor about them.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    I do it with a Crestron automation controller. It has 8 Digital Analog inputs, or you can use a Crestron thermostat which allows you to log things without engineering your own hardware. If.. you are a programmer or if you find a ready progam you can easily log all kinds of parameters to a file. You could log...Qty(8) channels of 16-bit analog inputs at 1/second for about 4 years on a 4GB Compact Flash card.

    I'm sure there's more practical data loggers out. To make it simple, you could just find a temperature data logger, measure the temp at a register (No wiring to the HVAC required). If the temp is 50F someting, the AC is ON. if you get a blast of hot air it just turned on. When the temp ramps from 50's to 70's the AC turned OFF (ramp probably less than a minute). Get multiple loggers (Outside, attic, register) and syncronize your data start points at the PC. You'll find multi channel data loggers also. Just google it.

  5. #5
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    I forgot... I've seen one of these USB stick loggers. Pretty handy.

    http://www.tiptemp.com/Product.aspx?ProductID=1309

    You can record 16,000 Plus datapoints between 10s and 12 hour interval. Comes with software.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,289
    Well duh, I don't know why I didn't think of this earlier, and it doesn't strike me as a no DIY infringement.

    Throw a temperature and humidity data logger into your supply air stream. When you download the logger and chart the fluctuations in supply air temperature and humidity, that will equate to your run time/off time. This method is more effective if the indoor blower runs continuously, but if you do not normally run the blower continuously (which is not advisable in a hot, humid climate), you should not do so for data logging, IMO. With the blower in "auto", you should still be able to pick up differences between run and off cycles via discharge air conditions, particularly if your system has a blower off-delay, which many do these days.

    The other method I had in mind would involve electricity, which is why I balked at the DIY stipulation.

  7. #7
    Join Date
    Jun 2006
    Posts
    294
    I never did this but he cheapest way to do it IMO is to somehow hook up a 110 VAC electric clock to the furnace blower AC line ( must be 110 VAC) , but don't do it yourself. Get a sparky friend to do it.
    When power is not supplied the time "stops" and when power is on the clock runs, so that at the end of the test period you read the "time" and then subtract from the start "time " of the clock.

  8. #8
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    You know.. you could also put a NC relay for a 2nd clock voltage, and you would have both OFF and ON timers. However after the fire inspector found the root cause of the fire, your sparky friend would be looking for a new career. Not sure how your insurance company would react. Most chinese clocks were not designed to operate at 130F ambient.

  9. #9
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    The method that worked well for me, was a Logtag data logger placed in a supply vent. Within a minute of AC call, the temperature would go down quite a lot. I won't say "unmistakeably" because there were a few things happening where I had to make judgement calls. But with the simpler single-stage systems, your errors should average out to near zero.

    This kept me busy for two cooling seasons. You can look up Logtag products and pricing at:
    http://www.microdaq.com/
    Here is another product which looks interesting but I have not tried this one:
    http://www.tiptemp.com/Product.aspx?ProductID=1309

    Hope this helps -- Pstu

  10. #10
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    My thermostat tells me daily run times, weekly run times and total run time from the previous week...also monitors total run times for filter changes....

    Joe

  11. #11
    Join Date
    Jun 2006
    Posts
    294
    Quote Originally Posted by gonekuku View Post
    You know.. you could also put a NC relay for a 2nd clock voltage, and you would have both OFF and ON timers. However after the fire inspector found the root cause of the fire, your sparky friend would be looking for a new career. Not sure how your insurance company would react. Most chinese clocks were not designed to operate at 130F ambient.
    Last time I checked my ambient was 75 degrees.

  12. #12
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by pstu View Post
    The method that worked well for me, was a Logtag data logger placed in a supply vent. Within a minute of AC call, the temperature would go down quite a lot. I won't say "unmistakeably" because there were a few things happening where I had to make judgement calls. But with the simpler single-stage systems, your errors should average out to near zero.

    This kept me busy for two cooling seasons. You can look up Logtag products and pricing at:
    http://www.microdaq.com/
    Here is another product which looks interesting but I have not tried this one:
    http://www.tiptemp.com/Product.aspx?ProductID=1309

    Hope this helps -- Pstu
    Thanks to you and everyone for the very good thoughts on this. I ordered one from microdaq.com today. I didn't know such a cool USB device existed.

    DavidJ

  13. #13
    Join Date
    Sep 2002
    Posts
    2,718
    Fluke 289

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