I have never done this math before and I am happy to see that my experience and instincts were correct.
It's nearly impossible to buy an air conditioner that won't out-perform, out-price, out-efficient, and out-last the best dehumidifiers you can buy.

Oh look! Did I find YOUR dehumidifier because it is Top Rated by Consumer Reports, not because I was looking for that "dh" you mentioned in post #25. I thought you meant De Humidifier, not a DH model by Honeywell.

No, I have a Frigidaire. I was just using "DH" as shorthand. Frigidaire seems to dominate the ratings but I'm not impressed with one that fails after 6 years.

Very interesting analysis. You should write an article and get it published. Really, I mean it. This information is tough for a consumer to find. I'm sure we could find plenty of technical articles in ASHRAE but that doesn't help the average homeowner.

Your water removal estimates, once adjusted to standardized conditions, seem similar to the numbers quoted by the manufacturers. But here's what I see when I compare popular DH models to popular window A/C units.

• The Fridgidaire FFAD50333R1 dehumidifier is a popular 50 pint model selling for $189 (Amazon). The specs show it draws 530W and gives a 1.85L per kWh efficiency (EEV).

• The Fridgidaire FFRA0811R1 window air conditioner is a popular 8000BTU model selling for $200 (Amazon). The specs for the near-identical Q1 show it draws 816W and removes 41 pints per day. It has a mediocre EER of 9.8, but that doesn't fully account for the much lower L/kWh ability.

I'm having a hard time seeing that the A/C would be better than the DH in this comparison. It's tough to judge durability but on the surface you would assume machines at similar cost from the same manufacturer ought to be similar in build and design.

 

how exactly do you explain how someone buys an equivalently rated unit to replace an old one and the new one doesn't come close to being able to cool as well? Shouldn't 12,000 BTU rating give equal cooling capacity regardless of who made it?

I don't explain, I measure. If the new machine is deficient, I will soon know why by measuring its temperatures and pressures. Personally, I'm as skeptical as you, but in the opposite direction. I have never had a complaint about quality or performance...wait..there was one. A Physician wanted his doctoring office cooled but he didn't tell us there was one special room he used for physical activities until 3 weeks after the design was finished and approved by The City of Saint Sumthinerother. I massaged the numbers and changed some duct sizes. When the doc complained to the Inspector, the answer he got was, "He has this place 20 degrees below the outside temperature. What more do you want?" (Standard methods approved by The Government only allow for 17 degrees of difference between outside and inside.) Then the dumba$$ added a wall and asked me why he had walled off a small room that didn't have any A/C vents in it and it wasn't as cold as the rest of the building.

Idiot customers aside, I don't know how one machine rated the same as the other performs differently. Mine don't.

I have to go to work now. The heat index will be 108F today and the good news is that I'm doing plumbing...the air conditioner works.

 

That cheap-@$$ A/C will drop.......... 72.68 pints per day for 540 watts and cost $100 less than
a top rated dehumidifier that drops... 70.00 pints per day for 820 watts

Hmmm... The specs for that 6000BTU A/C ($229 on Amazon) say it will drop only 1.3pints/hr, or 31.2 pints per day, not 72.68.

129 pints per day per ton. (129 pints per 12,000 BTUs)

I guess a "rule of thumb" might be 1% of the BTUs is how many pints per day.

The Frigidaire 12,000BTU A/C (with a EER of 12.0, $379 on Amazon) specs say it will dehumidify at 3.8 pints per hour or 91.2 per day. So I was incorrect when I said your values are similar to the manufacturer's info. I did the comparison in my head and goofed. The manufacturers don't claim nearly as much dehumidification as your calculation. The two machines discussed here are 62 and 91 pints per ton, or $7.32 per pint-per-day or $4.15 per pint-per-day for the bigger model.

The 50 pint DH I linked to above is $3.78 per pint-per-day.

So the big, efficient A/C costs only a little more on a pint-per-day basis. That'd be fine if I knew it would last longer. But why would Frigidaire over-design their A/C units and under-design their DH units?

 

Interesting post about dehumidifier reliability. It's not good!
Another one at Consumer Reports, who admits they rate based on performance and have no insight on reliability.

I could not find a similar hatred for the poor reliability of window A/C units. It doesn't make sense to me, but it does appear that a $200 Frigidaire dehumidifier is lucky to go 5 years while a $200 Frigidaire A/C lasts much longer. What the heck?

 

One of the problems you are seeing is that, "The air conditioner is rated at pints per day" under conditions specified for an air conditioner. I went through 3 hours of look-ups and calculations in order to specify the air conditioner under the same conditions used to specify the dehumidifiers. You are still talking about how difficult it is to compare two machines that are rated under different conditions after I did the math to make them compare under the same conditions as each other. You don't need to compare apples to oranges, I just showed you how to compare them as both being apples.

Specifically, the dehumidifier is rated at 80F and 60% RH. Air conditioners are rated at 70F and 50% RH. Of course the A/C is going to be labeled as less effective as a dehumidifier. It's rated at lower temperature AND lower humidity. When I did the math to find out how a completely unmodified air conditioner would rate under the "standard" conditions for a dehumidifier, I showed you the pints per ton-day in post #35.

Then, in post #37, I showed you the relative pints per watt-hour based on a cheap air conditioner and an expensive dehumidifier, and the air conditioner still won in every aspect from purchase price to pints per watt-hour.

Very interesting analysis. You should write an article and get it published.

I thought I just did.
You must be talking about some other way to publish it.

 

Well as most HVAC techs would put it. I don't know, but it sounds like it's something I will have to charge a lot more for.

 

You don't need to compare apples to oranges, I just showed you how to compare them as both being apples.....
You must be talking about some other way to publish it.

I see, and yes, I am. I suspected as much, and have spent the afternoon getting ready to pull the trigger on a new A/C unit instead of yet another dehumidifier.

There's one final wrinkle to come to grips with. Some (most? all?) modern window units use a slinger fan to throw the condensed water at the hot condenser. That's a clever way to improve efficiency although users complain about the noise and the free shower that their neighbors get. This innovation is obviously not useful in a dehumidifier. I can drill a hole as well as any one, but that immediately voids the warranty. And I wonder how much of the design depends on water being available for condenser cooling. Maybe manufacturers are skimping on the condenser heat exchanger, whereas they cannot do that in their DH designs? I'm not sure the modern units can meet their published specifications without that additional cooling on their condensers. It's almost impossible to identify models with or without slingers before buying one.

 

There's one final wrinkle to come to grips with. Some (most? all?) modern window units use a slinger fan to throw the condensed water at the hot condenser. That's a clever way to improve efficiency although users complain about the noise and the free shower that their neighbors get. This innovation is obviously not useful in a dehumidifier. I can drill a hole as well as any one, but that immediately voids the warranty. And I wonder how much of the design depends on water being available for condenser cooling. Maybe manufacturers are skimping on the condenser heat exchanger, whereas they cannot do that in their DH designs? I'm not sure the modern units can meet their published specifications without that additional cooling on their condensers. It's almost impossible to identify models with or without slingers before buying one.

Pretty much every window AC unit built used that method to remove their condensation so it's not a new thing.

The only cheat to get the water out without drilling the hole is to mount the unit on a slant so that it runs out the overflow lip or tube first. That or add a piece of cotton or similar cord that will wick the water up over the edge of the pan and let it follow the cord down to point lower and drip off that. Or a bit of both.

Personally, I would just drill the hole and be done with it. The odds ar the thing is going to be built just well enough that it will never breakdown until the warranty is up.

Either that or as I mentioned earlier in the thread find an old beater window AC unit at a garage or yard sale clean it up and play with that for the experiment. Heck, If you were near me I would just say stop by and pick one for my collection old but still well functioning beaters and go nuts!

 

I can drill a hole as well as any one,

Or you can find the tube that carries water from the front to the rear and re-route it.

I'm not sure the modern units can meet their published specifications without that additional cooling on their condensers.

All air conditioners start with the rear pan dry, therefore they must be able to survive with a dry water pan.

Maybe manufacturers are skimping on the condenser heat exchanger, whereas they cannot do that in their DH designs?

You think they don't skimp on the DH designs, but the dehumidifiers die in about 5 years while air conditioners last from 10 to 20 years? Think a little harder.

Even if you kill a $200 air conditioner in 5 years, while you could have killed a $300 dehumidifier in the same amount of time...and all the while the air conditioner was producing more water per watt-hour...what's the problem? Afraid you'll save $100?

I'm about done with this. I did all the math, did a real world comparison, both of them giving the dehumidifier unfair advantage, showed you how to do it, and still you worry. Go ahead and don't believe the math. If that doesn't convince you, I'm out of weapons.

 

What's missing is an explanation of why this situation exists. This is all old technology. (I found a 1966 reference that mentions the slinger ring as obsolete technology. Now it's back.) There shouldn't be an opportunity for a DIY solution to be broadly superior to an off-the-shelf commercial product. If the answer is so clear, why does the DH market even exist? Why wouldn't Frigidaire not clobber all competitors by, for instance, selling a reconfigured A/C and offering a 10 year warranty to go with it? Everybody else's market share would go to zero.

I'm not doubting you at all, so please don't get frustrated and interpret my sluggishness as a lack of confidence in your assessment. I'm slow because I'm puzzled.

BTW, I brought the old unit upstairs today – into warmer air – and watched it freeze up. Its evaporator coils progressively froze from the bottom up.

 

Sorry to sound like a broken record but, it's lack of air flow through the coils.
It seems eminently logical that if the ambient air flow (which is well above freezing) is great enough, than the cooling ability of the unit won't be sufficient to keep the coils below freezing and the vapor in the air will condense to water, not ice.
Add an external fan blowing through the coils, if necessary, to keep the coils warmer than freezing.

 

Not so. The airflow is strong. The problem is low freon, causing evaporation of the freon at too low a temperature. The coil then goes to a temperature below the frost point of the ambient air. This is a widely recognized mode of failure of these dehumidifier units. Your auto A/C can do the same thing, and you'll see the ice disappear as you get to the ideal freon level in the system. If the freon falls even farther, the ice will disappear because the air flow will bring more heat than the punt freon can cause to frost.

With an impractically large airflow, you might be able to prevent the ice formation but then I suspect you would not get any water forming on the coil either, except in that one spot where you have forced an equilibrium heat flow.

I may try to develop a DIY repair for the low freon condition. It seems to me there is a need for such a thing, as all the DH units on the market tend to fail in 5 years or so because of this mode. I've done freon addition to both cars and central home units, so to me the problem is merely a plumbing problem. These DH units don't have service ports like and automotive or home system. It would be an easy fix if it did, so why not add one?

 

So you are saying that the system works more efficiently with low freon?
That makes no sense to me.

 

It makes the coil colder. That's not the same as moving more heat or removing more water. Once the coil ices, not much heat moves and no water is removed. That's why the icing happens slowly. One area of coil can't freeze until the area just before it ices over. Then the freon stays cold longer as it passes into the coil. That freezes the next section and the front advances until the whole thing is ice.

So it's very inefficient because it's using power and not removing water. It just runs the fan, and the small freon flow keeps the coils iced over.

 

I may try to develop a DIY repair for the low freon condition. It seems to me there is a need for such a thing, as all the DH units on the market tend to fail in 5 years or so because of this mode. I've done freon addition to both cars and central home units, so to me the problem is merely a plumbing problem. These DH units don't have service ports like and automotive or home system. It would be an easy fix if it did, so why not add one?

Easy to do. Just pick yourself up a set of Refrigeration Access Service Valves and solder one of them in where the original filling line/port pigtail is crimped and brazed shut.

A package of 10 costs around $12 - $15 on eBay or Amazon.

Option two would be to put a simple timer on the compressor that shuts it down for a few minutes every so often to let the ice clear off.

 

It makes the coil colder. That's not the same as moving more heat or removing more water. ..........

How can you say it's not removing more heat if the coil is colder?

 

It's colder in a small area until it becomes coated with frost, then there is very little heat transfer through the ice. The cold spot keeps moving until there is no unfrozen area left. Surely you aren't suggesting iced up coils are more effective than bare copper with aluminum fins?

 

Easy to do. Just pick yourself up a set of Refrigeration Access Service Valves and solder one of them in where the original filling line/port pigtail is crimped and brazed shut.

The Frigidaire specs for my unit say it uses R134a. Great! I even have some already on hand since that's what is used in some cars. So I opened up my DH and found plenty of tubing where I could splice in a fitting. I'm halfway there!

Then I read on the compressor that it actually uses R410a, which is effectively unobtainable by consumers. They probably lied about the refrigerant because everyone knows it's easy to find R134a and might be reluctant to buy a unit with no hope of repair. Bastards.

Now all I can do is strip off the interesting bits and send the shell to the trash like everyone else. Grrrr.

@#12 will be glad to hear that a new A/C is on its way to me. I'll keep this thread alive to report back on how that experiment goes. I'll have to disable the water collection system without voiding the warranty, but hopefully that won't be too tough.

If anyone finds this thread and is interested in the ratings of dehumidifiers, I found that they are undergoing a government-forced change right now and will be completely different by this time in 2019. See https://www.regulations.gov/#!documentDetail;D=EERE-2012-BT-STD-0027-0045
One thing in there made me chuckle. Electrolux (maker of Frigidaire) complained that the new ratings would cause a 70 pint unit today to become a 46 pint unit, placing it in a different category for required efficiency (water removed per kWh). The ruling would ironically lead to a reduction in efficiency.
A summary article in the trade press here: https://www.nrdc.org/experts/lauren...standards-help-make-summer-little-less-sticky

 

http://www.ebay.com/itm/410a-R410a-...889378?hash=item2ee9cafaa2:g:RuwAAOSw9eVXXHTT

Then I read on the compressor that it actually uses R410a, which is effectively unobtainable by consumers.

BS. Anyone can buy it on eBay. http://www.ebay.com/itm/410a-R410a-...889378?hash=item2ee9cafaa2:g:RuwAAOSw9eVXXHTT

If you know how the system works there are all sorts of legal ways around the supposed rules the HVAC weasels have.

 

Hahaha, yeah, I know I can buy large quantities but I need all of 10 oz. I'm sure I could find someone to sell me what I need but it's becoming a not-worth-the-hassle thing. I've called around and NO service shops will do a recharge, so that tells me something.