Ways to graph air conditioning run times?
I’d like to be able to graph and visually see the cycling pattern of my traditional split system heat pump here in Central Florida. The thought is that if I can determine that it is off, say, 25% of the time in the afternoon on the hottest summer days, that I could probably downsize the tonnage by 25% when it comes time for replacement. Of course, I would want to make sure that my system was properly charged and operating before conducting such a test.
There are various models of whole house or circuit level monitors that have software interfaces that can display consumption activity. I wonder if there is something simpler and more cost effective. I’m thinking maybe some device that can interface with the thermostat wiring, for example.
Thanks for your thoughts.
David
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I realize that people might reply that that is what Manual J is for but it seems like it would be hard to argue with actual system performance provided that the system is functioning optimally and that duct work is sealed at least as good as it will be on the replacement system. Provided that that is all in place, then it seems like such a test would bring all the variables that would go into a load calc into the real world with the opportunity to simply monitor the cycling ratios on one of the hotter days of summer. David
David,
Allison Bailes wrote an article describing two ways to accomplish what want to do. If you don't want to invest in equipment, you can sit near the equipment with a stop watch on a hot afternoon. The easier (but more expensive) way is to use a sensor; Bailes used a Hobo UX90-004 from Onset (which can be purchased online for $92).
Here is a link to Bailes's article: How to Tell If Your Air Conditioner Is Oversized.
Some options if you don't want to spend a day in a utility room or $92 on a logger:
1) This $23 "hour meter" can track the total number of hours of on-time of a 24VAC source such as a thermostat signal. If you look at it after 8 hours and see that it accumulated 5 hours of run time, that means it ran 5/8 of the time. Depending on where you wire it in, you might end up accumulating off time rather than on time, but either way you can figure the % on time. The downside is that you don't get to see how short or long the cycles were, on the cumulative on time.
http://www.digikey.com/product-detail/en/curtis-instruments-inc/700LN001N1248D2060A/267-1028-ND/408445
2) Make a digital audio recording of the HVAC system. If you viewed a graph of the audio file, you'd easily see when it was on vs. off, assuming the A/C is the loudest equipment in the vicinity. Buying audio equipment for that purpose would be expensive, but you might already have something, such as a smartphone, that could do the job. Perhaps you have an old device you can use so you don't need to experience smartphone separation anxiety.
Charlie- simply logging the on time over a significant number of hours will show you the average duty cycle, but not the peak duty cycle information that you're looking for. (This really needs the audio equipment. :-) ) The duty cycle during the heaviest load 1-2 hours is the relevant information for sizing the equipment, not the average.
If there's an instrumentation budget, you could do worse than a $200 single channel TED 5000 which provides more information than the $92 Hobo UX90-004, which only gives you on-time information, not peak power draw total power use, etc.
http://www.theenergydetective.com/downloads/QuickStartInstallation%20v110711.pdf
http://www.theenergydetective.com/5000docs