this is a very common mistake alot of people make.they go out and buy a thermostat that they can set to say turn the temp up while they are gone working during the day,and then say 5 p.m. or so they have it drop the temp so when they get home it's cool.this scenario reminds me of a retailer i had years ago.i work on vending machines and had an issue with a machine.the guy said he was losing like 20 to 50 cents a week.which was'nt much but it bugged the heck out of me.well i was talking to him about brown out type power loss and how that will affect the bill and coin acceptor and he replied that he had a surge suppressor so why was that an issue.well turns out that he had my machine and a pop machine plugged into the same suppressor.AND he turned it off ever night.i thought WTF.your plugging a pop machine into a surge suppressor,and you are cooling that machine all day then turning it off at night,no wonder my machine was getting the raw end of the deal.what an idiot!if he would have left it plugged in full time it would have used less power.and wouldn't have been an issue.

Both statements are factually incorrect.

If you dehumidify without attempting to cool, the latent heat from condensation is dumped into the space. You have a drier but much warmer space.

If you cool and dehumidify, the latent heat from condensation is minimized by the cooling action.

Running the a/c and heater at the same time is completely counterproductive. The heater won't dehumidify anything............it will simply raise the temperature in the space and, of course, decrease the relative humidity in the process. That accomplishes nothing.

This isn't a common mistake if the system has the capability to cool relatively quickly. If the system can cool in two hours or so, it's far more efficient to raise the temperature during the warmest part of the day (presumably about eight hours) than to force the system to maintain temperature throughout the day.

However, on a whole house system that may take eight hours to drop eight degrees, this approach is not feasible.

Actually, it can accomplish reduced humidity while maintaining setpoint temperature by artificially increasing the load on the AC, causing it to run more and extract more water from the air. From an energy conservation standpoint, the practice is frowned upon, but it does work.

I agree, however, it's about the most inefficient way to decrease humidity.

Why not run a dehumidifier.............you actually get a decrease in humidity and simultaneously increase the load on the a/c............for much less cost?

Guys, much of your content is either something that I've lived in the various dwellings I've spent time in, either fixed or mobile, my entire life.

This tonnage to SF is a quandry to figure out, but apparently the engineer that prescribed my Brother's home missed the mark.

I have what I believe is a tight relationship with my HVAC guy that I hired to renovate my home's HVAC system in 2001. He has worked for friend's of mine here locally for several decades, and I felt I could trust him in quality and pricing and workmanship working for me.

I recall asking Jim (his actual name) about whether my replacement system had a ramping-up, variable speed fan works that I had heard would save me money in power usage. He said, the unit I had that he installed had an option on it for fan speed of 50% of what it is now, but did not have the ramping up feature. My rationale was that less fan speed==less energy consumption. While the wintertime would work for my home, the severe heat of 98* every day much of the Summer in Dallas, TX., needs the high fan speed.

I'm wondering if there is a "50%" switch available on my Brother's Carrier central air-conditioning unit, thereby, not allowing the home to cool so quickly? Seems like part of my querying of the process is to ask my Brother how long in the course of say an hour in the hot mid-day sun, does the central AC unit run? That would seem to be the first Q and may help solve the whole deal.

Well, all this is coming home in my mind in regards my Brother's Carrier system - perhaps the calibration selection for fan speed should be lessened, or, an analysis of the total time spent running should be learned?

I totally am on-board, understand, and agree with Brian's summation that the fan works of an AC unit should run much of the time. In the case of my home on the most brutally hot days, my unit runs approx. 50% of the time to keep the interior a nice 76*. Brian's "75%" is of course a good number for a unit trying to achieve the desired reasonable interior thermostat setting, while ridding the air of HUMIDITY!

Brian's description of his window unit going to idle with fan only (no compressor) once the unit achieves the desired temp. is what I have to endure in my mobile unit's operating sequence. I hate it. What it does, is it draws in warm, exterior air, thereby heating-up the interior that was just cooled in a big, quick way. What I would prefer, is a window unit that cycles OFF, instead of the fan continuous running. However, be advised that I realize that if the fan did not run continuously, the fins would not have a chance to warm up, and not ice. Thereby dropping their water into a draining collection tray to the outside. I've got all that. The trouble I have is that the onset of the compressor kicking on again in a matter of minutes - is totally aggravating when you're try to sleep.

Brian, the better window units seem to have a fan that totally shuts off. At least perhaps that is the missing link here in cooling the room w/o the damm room heating up too quickly, because the fan is drawing outside air in in the non-compressor phase while de-icing the A-Frame?! Perhaps the best scenario, is a room where the AC window unit can never really achieve say 68*, whereby it stays 'on' the entire time?

I will endeavor to convey much of this to my Brother, to try to get to the truth of the matter here. I will be in Omaha for a couple weeks shortly, and will try to give my .02 to the situation if at all possible.

I'm in a bit of a quandry about reducing fan speed. In theory, if the fan speed is reduced, the airflow across the evaporator is reduced and the evaporator doesn't need as much refrigerant flow to maintain temperature. Accordingly, this should result in the compressor operating LESS than it would otherwise operate at full fan speed.

That being said, the window units will run the compressors flat out, independent of fan speed, until the desired room temperature is attained. Why the compressor doesn't freeze the evaporator under these conditions with very low fan speed is a bit of a mystery.

If you run the window unit at low fan speed for several hours to reduce temperature, the resulting humidity will be about eight points lower than it would otherwise have been on high fan speed. Of course, once it reaches temperature, it all goes to hell anyway.............the humidity climbs dramatically.

There usually is a selector switch on the unit for opening or closing outside air. If the compressor shuts down and the outside air door is open, it will definitely draw moist air into the conditioned space with undesirable results. This outside air door should usually remain closed.

If the unit cannot pull air from the outside, running the fan only circulates air from the conditioned space, largely a waste of energy.

You have correctly observed that the newer units have the option of killing the fan when the compressor shuts down. I'm not a personal fan of this approach due to the cycling of noise.............seems to be more benign if it runs all the time, sometimes with the quiet whisper of the fan and sometimes with the low growl of the compressor.

I will say that my Panasonic unit of about eight years is the most quiet machine I have every observed. It is just about impossible to tell that the compressor is engaged and the fan is whisper quiet, even on the high setting. It's truly in a class by itself. If you have a chance to get a good used one..............do it.

Well, Brian, I appreciate the learned feedback about window units. The ability to close the outside air is what feature my mobile unit does not have. Getting a good night's sleep/rest on the road is essential to me.

In another setting of perhaps cooling-off the room(s)/space in a big way for the night, one could just kill the unit. That, is not an option where the killing of the window unit, has you waking up a couple hours later with the ambient temp. in the low 80s.

I have none of these above troubles in my residence. My central unit has been right-on for comfort in the Summer.:) In the Winter? The heatpump is great to about 35*/40* for it's behaviors.:(

I'll report back as this deal in my Brother's home unfolds - thanks for the expertise of ya'll!

Skid,

Does his unit have a condensation drain that is plugged up?

BS

But, if you have to run the heat and ac together, look for another problem. This would be a maintenance operation, not an ongoing operation.

My mom's house was having the same sort of issue last summer. We brought in a different contractor, who said that the cold air returns were too small and not pulling enough air. We had the ducting replaced with larger returns, and it works well now.

Not sure if it could be the problem in your case, but it's worth looking at.

I cannot imagine how you could ever get to 96% humidity in a building that is without some sort of massive water leak or similar. Either that is the case or the humidity gauge is incorrect in its display.

I keep a humidity gauge above the thermostat in the bedroom. It records and keeps both the high and the low. I haven't looked at the high or the low for at least one year.

Took a look last night and the high was 84% and the low was 26%. At the time, just prior to getting some sleep, the reading was 56%. The temperature had dropped to 75F. after the unit had run for two hours continuous (compressor full time).

I lowered the fan speed and checked the gauge in the morning. The temperature stabilized at 74F. but the humidity climbed right back up to just about the ambient humidity: 70%.

A classic example of the problem with humidity when the unit begins cycling with an estimated 30% duty cycle (ambient temperature had dropped to about 76F. overnight).


I also agree that 96% humidity would be unlikely.............but 90% is definitely possible on a very warm and rainy day.

I am going to have to get one of these humidity sensors. Ive had the humidity so high in my house my clothes were wet and I had water condensing on the walls in the bathroom. I had a leak in there..

INTERIOR TEMP / HUMIDITY / EXTERIOR TEMP
 

Indicator in my kitchen right now. / Exterior temp. from cheap, battery operated, hand-held device in shade right now.

Indicator is from the 1960s (belonged to my Grandmother, then my folks when they were alive) - I do not have another measuring device of humidity.

I too, would like to purchase a relative humidity indicator from perhaps Lowe's? Perhaps they're cheap, hand-held instant digital devices nowadays......