A new a/c mystery

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Old 08-22-15, 09:47 AM
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A new a/c mystery

I had a brand new central A/C (a 16 SEER Carrier) installed at my house in early July to replace the old one. It has been working very well; however, just in the last 5-6 days, I've noticed increased power consumption. I'm pretty sure of that because I've been recording my electric meter's readings daily (I was curious to see how much more efficient the new A/C would be compared to the old one.) And of course I know the outside temperatures and cooling degree days, so I'm quite certain that I'm not imagining things. Everything else in the house is just the way it's always been, so it has to be the A/C. I've also been checking the air temperature coming out of the vents and that seems to be fine. Yet, I've been clearly using about 20% more electricity in comparable weather conditions over the last 5-6 days.

What could it possibly be? And if it is the A/C, why would things suddenly change after about 6-7 weeks of use?
 
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Old 08-22-15, 11:20 AM
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Have you replaced the air filter? If the filter is dirty, that can reduce the efficiency. Also, you have to take into account the humidity as well as the temperature. When the humidity is high, a lot of the cooling energy is used to dehumidify the air. I don't know where in NY you're located, but in my area (Western NY between Buffalo & Rochester, it's been very humid the past week or so (humidity broke late yesterday).
 
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Old 08-22-15, 12:35 PM
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I've noticed my consumption has been up the last week here in northern NJ too.
 
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Old 08-22-15, 03:21 PM
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Thanks, Bob. The air filter is clean, but I didn't consider the humidity factor. It had indeed been very humid here (in Hudson Valley) until yesterday. However, I thought that only a two-stage compressor would be affected by humidity. Mine is a one stage. Am I wrong?
 
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Old 08-22-15, 04:29 PM
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It doesn't matter whether you have a 1 stage or a 2 stage, it still takes a lot of energy to dehumidify the air. When it's very humid, the initial cooling action is spent dehumidifying the air, once the RH gets down to ~50%, then it starts cooling faster. With my A/C, if it's 65-70% RH in the house when I turn the A/C on, it may run for close to 2 hours before I see even a 1 degree change in temperature. However, I do see the RH come down, and then once it gets in the 50% range, then the house begins to cool noticeably.
 
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Old 08-25-15, 04:29 AM
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IMO; The older units before the +13-seer craze had larger volumetric capacity compressors that pulled the suction pressure/temp down lower in high humidity conditions; they would condense more moisture out of the indoor air faster at real high indoor humidity conditions than the higher seer units.

IMO; At real high indoor humidity conditions the real high seer units could have problems getting the suction pressure/temps low enough to get the coil cold enough for optimal condensation work.
 
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