More Q&A Spotlight
“Ben87” wants advice on dehumidifiers. He has a 1600-sq.-ft. slab-on-grade duplex under construction in Climate Zone 4A, and he knows it will need some type of dehumidification, but he’s not sure how to spend his money. He lists two options:
Option 1: He could buy a portable dehumidifier for about $300.
Option 2: He could buy a ducted, whole-house dehumidifier, such as the Santa Fe or Aprilaire e80 , both of which cost about $1500.
As Ben sees it, the whole-house system will last longer, but his research suggests that the efficiency boost is marginal (they’re all between 2 and 2.35 l/kwh). He asks: “Will they really last 5x as long? Are there other ductable units that are better options?”
If he goes with a portable unit, he’s not sure where to put it. He wants the unit to auto-drain, which limits the location choices. His first-floor mechanical closet is a possibility, but he doesn’t think the unit would effectively dehumidify the rest of the house.
An assortment of considerations
As one reader points out, portable units work for small spaces, but a whole-house dehumidification system can handle larger amounts of humidity over longer time periods, and they are more robust and long-lasting.
Ben wonders how he would duct a larger system, as space is tight, but because the house is under construction, there is still the possibility of integrating a whole-house dehumidifier into his HVAC system.
Charlie Sullivan recommends ThermaStor brands (Santa Fe, Phoenix, Quest), even though they aren’t on Energy Star lists because of their larger size. “To qualify for Energy Star,” he explains, “it needs to be physically small, but the extra technology that ThermaStor uses makes them larger. If you compare the numbers for the best SantaFe units, they are fantastic. But the best technology is found…
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30 Comments
Dehumidification is one of the uncharted frontiers in building science. Right now there isn't any methodology that I'm aware of to predict whether a building will require dehumidification, or whether air conditioning and ventilation will keep the humidity in a comfortable zone. There also isn't great information on the capacity of dehumidifiers, particularly in terms of modeling their impact. Basically we're stuck with trial and error.
So it's not surprising that basic questions about dehumidifier effectiveness are hard to answer.
The qualitative answer is that new builds that have good insulation in climates with high dew points during shoulder seasons will benefit and likely need dehumidification. But sizing it? You can calculate how much moisture an HRV brings in but internal humidity generation depends a lot on the occupants. And is diffusion through the walls also significant?
And then figuring out what degree of distribution is needed is another question. If you have ducted central HVAC, that fan can run and mix things around, but if you don't it's hard to know what is needed. Maybe just intake on one level and supply on another, but it's hard to know.
Seems like a good candidate for a major research project with some high-fidelity simulations and some test installations.
There's no reason why there couldn't be a single device that heats, cools and dehumidifies. It's easy to imagine, because at least one already exists, the Daikin Quaternity. It's a minisplit with two coils in the head, it can be configured so that both coils heat, both coils cool, or one cools and one heats, which is what a dehumidifier does.
Now, I have no direct experience with this device -- and they seem very rare in the wild -- but there doesn't seem to be any theoretical reason why this design couldn't be extended to ducted units. And there's no reason why your indoor comfort couldn't be controlled by both a thermostat and a humidistat.
The question remains about how one would engineer such a system. The maximum pure dehumidification would be both coils running full out, one cooling and one heating. Or half the cooling of the maximum cooling -- so around half the dehumidification. Would that be enough in all cases? Or would people find that the still need supplemental dehumidification? I don't know, and what's worse is, I don't know how to find out.
The advantage I see of using a "real" dehumidifier instead of one of those is the ability to include the efficiency boosting technologies that the best dehumidifiers use: heat exchangers between inflow and outflow from the cold coil and the new multiple expansion cycle system used on the ultra-efficient Quest models. Now if the air handling box had the ability to switch the airflow to go through a heat exchanger or not, that could be a great solution--wouldn't even need to split the coils if you want dehumidification without any heating.
Dehumidifiers put off a lot of heat. So you don't want heat exchange, unless you need heating you want heat parity -- keeping the temperature the same -- which means putting back less heat than you take out and exhausting the rest.
Systems like the Quaternity should really be described as having three coils --- two indoor, one outdoor. All three can either heat or cool, at any given time two of the three have to be doing one thing and the third the other thing. So when you're in dehumidification mode the outside coil is also shedding some heat. That's more efficient than running a stand-alone dehumidifier and then running AC to remove the heat it introduces.
No need to explain the Quaternity. I got that. But it seems like you haven't had the occasion to learn about the advanced setup that Thermastor uses in their most efficient Santa Fe dehumid models, their best ones short of the Quest models which have an even cooler system. Those Santa Fe models have the following air path:
1) Heat exch, which cools the air down towards the coil temp.
2) Evaporator coil. The already cool air gets cooled a little more but mostly has the latent heat removed--that is moisture dropped out.
3) Other direction through the heat exch. This warms the air back up towards room temperature--that's not really the goal in this case. The goal is just to use the coldness of it to cool the incoming air in step one, so step 2 is almost exclusively removing latent heat.
4) Across the condensor coil, to cool the coil, with the heating of the air mostly being a side effect (unless you want the heat).
You probably thought I meant that the second heat exch pass was after the condensor coil. That would be a terrible idea.
Thermastor has sometimes offered a split dehumidifier. That puts steps 1-3 indoors and puts the condensor outdoors so the heat is dumped outdoors. It achieves close to heat parity, with just minor cooling. The same effect could be achieved by adding a heat exch. to a normal air conditioner air path. That's what I was talking about.
If you want I could show you how this works on a psychr. chart but I think you'll probably understand now that you know where to put the heat exch for it to help.
OK, thanks. I’ve had the chance to think about this overnight and all I can say is “wow!”
I’ve been known to go overboard with enthusiasm for new ideas, but if this means what I think it means it could be the biggest thing in home comfort in a while.
To explain why I feel that way, I’m going to analyze four scenarios of different ways of doing dehumidification. In each scenario the inside air is at 75F, 55% RH, dewpoint 58F, a pretty typical point where you’d want some dehumidification. Air is being run over a cooling device that cools to 40F and it exits with a 40F dewpoint. I’m assuming a flow of 100 CFM.
In all scenarios, cooling 100CFM from 75F to 40 F takes 3780 BTU/hr (the sensible load) and dropping the dewpoint from 58F to 40F at 100 CFM takes 2444 BTU/hr (the latent load). This would remove roughly 60 pints of humidity per day. For all scenarios I’m going to assume a heat pump with a COP of 4.
Scenario one: A conventional dehumidifier. Air is sucked in, cooled, then run over the hot side of the heat pump and exhausted. The heat pump has to do 6224 BTU/hr of cooling for the sensible and latent loads. At COP 4 that requires 1556 BTU/hr of electricity, or 456 Watts. The exhaust stream has to take away the 6224 BTU/hr that were removed, plus the 1556 BTU/hr of heat from the electricity used, for a total of 7780 BTU/hr. This requires an exhaust stream at 112F.
In dehumidification, the 2444 BTU/hr of latent load and 1556 BTU/hr of electricity use are added to the environment. To remove that would require 4000 BTU/hr of cooling; at COP 4 that’s 293 Watts.
Total electricity usage for heat neutral dehumidification is 749 Watts.
Scenario Two: The three-coil system (Quaternity)
In this scenario air is sucked in, runs over the cooling coil and then a heating coil. The heating coil provides just enough heat to return the air to room temperature, the remainder of the heat is shed by an outside coil. The heat pump has to do the same 6224 BTU/hr of cooling as in the conventional dehumidifier scenario. At COP 4 it requires the same 456 Watts to do so. But that’s it.
Total electricity usage for heat neutral dehumidification is 456 Watts.
Scenario Three: Stand-alone dehumidifier with heat exchanger.
In this scenario, air is sucked in and is cooled by air coming off of the heat pump before going through the heat pump. Since this is standalone, the heat generated by the dehumidifier needs to be shed, so after the exhaust air has warmed to room temperature it is then used to convey away the excess heat.
I calculated the heat flow by starting backwards. Air comes off the heat pump at 40F, the warmest it can get is room temperature, or 75F. Warming it from 40F to 75F takes the same amount of sensible heat as it took to cool it to 40F from 75F, or 3780 BTU/hr. If you apply 3780 BTU/hr of cooling to air at 75F and 55% RH at 100 CFM, it comes out at 51F, 100% RH.
If you then take a stream of air at 51F, 100% RH at 100 CFM and cool it to 40F, it takes 1188 BTU/hr for the sensible cooling, 1306 BTU/hr for the latent cooling, total of 2494 BTU/hr.* That’s the work of the heat pump, and at COP 4 that takes 624 BTU/hr or 183 Watts.
The heat exhausted into the environment is the latent heat removed plus the electricity used, a total of 3068 BTU/hr. At COP 4, that would take 225 Watts of electricity to remove.
Total electricity usage for heat neutral dehumidification is 407 Watts.
*(There’s some rounding going on here by my dewpoint calculator. The amount of heat that is removed is the sensible load, 2444 BTU/hr. But 2494 is close enough.)
Scenario Four: Split system with heat exchanger.
In this scenario, air is sucked in and is cooled by air coming off of the heat pump. The heat pump is a split system and the heat removed from the air is exhausted outside.
As in the stand-alone with heat exchanger, the work of the heat pump is 2494 BTU/hr, which takes 183 Watts. There is no need for supplemental cooling.
Total electricity usage for heat neutral dehumidification is 183 Watts.
So we’ve gone from 749 Watts to 183 Watts. I hope you see why I’m excited. Equally important, it’s simplified to a single device. In fact, I could see this being implemented as an accessor on a conventional ducted air conditioner. The biggest challenge might be finding systems that can modulate low enough.
I thought you'd like it once you understood what I was describing. I'll try to double check your math when I get a chance but the general outline seems correct. And it might even better better, because the kind of operation the heat pump would need, modest ΔT and minimum speed, would be where the COP is up to 5 or even higher. And to address the minimum modulation issue, one can increase the airflow.
It could also be implemented in conjunction with an air-to-water heat pump. This company offers a commercial scale version of that and says it's patented.
https://dewaircorp.com/products/dehumidifiers/rh-cube-18-chill-water-dehumidifier/
I've been considering making a small scale version of that by hacking a chilled water coil between to of the ports of a heat-exchanger plus fan box that's sold as an HRV.
Thanks Charlie.
Yeah, one of my first thoughts was using it with air-to-water, one of the fundamental advantages of A2W is you can modulate arbitrarily low.
Also, when you go to A2W immediately people start asking about running cold water through the underfloor heating loops. Well, to do that you have to isolate the dehumidification. This provides a method of providing 100% latent cooling to complement the loops which would be 100% sensible.
From the DewAir website:
"In a decoupled system the air conditioner only provides cooling and the dehumidifier only provides dehumidification. When you have a decoupled system, selecting the desired environment becomes as simple as setting your thermostat and dehumidistat to any desired setting. Changing the humidity setting won’t affect the temperature and changing the temperature setting won’t affect the humidity."
That is music to my ears!
Sorry, but I have to disagree with Chuck and Jake: We live in zone 5a and I added an Aprilaire dehumidifier to our central HVAC system - because humidity can be an issue in Spring, Summer and Fall. During the peak of summer, the AC system keeps the temp and humidity down. On many days, however, the Aprilaire keeps the humidity down - eliminating the need to run the AC compressor as often, even if it is warm outside. This reduces our power bill. Plus the ducted Aprilaire ensures that dehumidified air is evenly distributed throughout our house.
By comparison, a standalone dehumidifier is cheap - but not the best value. Similar to a window-mounted AC unit, it will be nearly impossible to distribute dehumidified air around his house - particularly to bedrooms at night when the doors are closed. Even a central ducted airhandler won't solve this problem.
Just curious if you could elaborate on why you don't think running the central fan would distribute the air adequately?
Dear Ben: First, running a central airhandler (the ;blower.fan' in a central HVAC system) would obviously consume extra energy. Second, the 'source' for the airhandler would be the return from a room/area, rather than directly from a ducted dehumidifier, which is inefficient. Third, a standalone dehumidifier would not have the capacity to cover the entire house. (They are typically designed for <1,000 SF.) Fourth, high capacity standalone dehumidifiers are noisy because they need to move a lot of air, Fifth, an inexpensive standalone dehumidifier is not designed to run constantly - AKA "You get what you pay for." Finally, I can confirm all of the above because we have two standalone dehumidifiers in our ancient stone house in France (no ducts are possible!), and a ducted Aprilaire dehumidifer in our home along the shore in the USA. So I know how both perform, and I would always pick a ducted model - particularly if the house already has ducts and a central airhandler.
"First, running a central airhandler (the ;blower.fan' in a central HVAC system) would obviously consume extra energy."
Wouldn't this be the same amount of energy as running the fan for a ducted dehumidifier?
"Second, the 'source' for the airhandler would be the return from a room/area, rather than directly from a ducted dehumidifier, which is inefficient. "
Why is that inefficient?
"Third, a standalone dehumidifier would not have the capacity to cover the entire house. (They are typically designed for <1,000 SF.) "
The square feet ratings are stupid, but they're trying to quantify a difficult concept for most consumers to grasp. Even the more sophisticated pints-per-day measure has methodological issues, but it does allow apples-to-apples comparisons of units. If you look at the pints-per-day rating of ducted dehumidifiers they aren't any higher than the biggest standalone units. Crucially, nor do the ducted units use less energy to remove the same amount of humidity.
"Fourth, high capacity standalone dehumidifiers are noisy because they need to move a lot of air."
I have an Air Sponge brand ducted dehumidifier and it is the noisiest thing in my house.
"Fifth, an inexpensive standalone dehumidifier is not designed to run constantly - AKA "You get what you pay for.""
A lot of ducted dehumidifiers have reliability issues. I would agree with this on an overall basis but on an individual unit basis it's hard to generalize. The bigger issue is that by the time you learn that a unit is reliable it's probably been discontinued.
"Finally, I can confirm all of the above because we have two standalone dehumidifiers in our ancient stone house in France (no ducts are possible!),"
Your experience with standalone is limited to running in a ductless house.
Dear DBContrarian: Here are some answers to your questions.
(1) Power consumption: No, a ducted dehumidifer, e.g. Aprilaire, has a much smaller fan than a central airhandler, which runs only when dehumidification is needed. A central airhandler is typically triggered by the furnace / condenser linked to the HVAC system, or a 'circulation' setting on a smart thermostat.
(2) Source supply: A ducted dehumidifier supplies dehumidified air to the central plenum, for direct and even distribution to all registers. If a standalone dehumidifier is used, the more-dehumidified air in that room is mixed with air from other registers. So one area has more dehumidification, and others have less.
(3) Capacity: Almost all standalone dehumidifiers are designed for <1,000 SF. This is the standard capacity measurement for all manufacturers, because they cannot measure your specific humidity level etc. We had to buy a larger standalone dehumidifier for one room in our house in France, for example, because of more water infiltration. So the SF ratings are not 'stupid' - but simply a rough estimation of the unit that will fit your requirements.
(4) Noise: A ducted humidifier should be installed next to your HVAC plenum, to connect to the central supply lines. So the 'external' noise generated by the dehumidifier should be much lower than the airhandler. Second, noise transmitted via the ducts indicates a problem with the ducts; all straight runs should be R6 insulated flex, which sharply reduce noise compared to hard metal ducts - from all sources, including the airhandler and dehumidifier. Finally, standalone dehumidifiers have small exhaust registers - which drives up the noise as capacity increases. Our ducted Aprilaire, in contrast, has circular 6" intake and exhaust ports with much higher capacity - and lower noise as a result.
(5) Reliability: Clearly, you get what you pay for. No service or parts are available for standalone dehumidifiers, because they are sell-and-forget. Check the warranty period and terms. This tells you all you need to know. I had to disassemble one of our standalone dehumidifiers in France because it began to make a loud rattle - and make custom changes to the case. In contrast, good ducted dehumidifier manufacturers offer support and parts, e.g. Aprilaire.
(6) My experience: As noted above, I use both standalone and ducted dehumidifiers. I also explained why standalone is a bad choice if you have a central HVAC system, and why a ducted product is better.
"Capacity: Almost all standalone dehumidifiers are designed for <1,000 SF. This is the standard capacity measurement for all manufacturers, because they cannot measure your specific humidity level etc. "
From the EPA.gov website (https://www.energystar.gov/products/dehumidifiers): "The dehumidifier 'size' or capacity of the unit is usually measured in pints per 24 hours."
If you look at the EPA Energy Star ratings, they group dehumidifiers by their pint per 24 hour ratings. Those ratings are determined using standardized conditions, so it doesn't matter what the conditions in your house are, if one unit is rated for 50 pints per day and another is rated for 100 pints per day the second one is going to have twice the capacity of the first one.
Manufacturers of ducted units don't like to share their pints per 24 hours numbers, because they aren't any better than large standalone units and aren't very impressive.
"Power consumption: No, a ducted dehumidifer, e.g. Aprilaire, has a much smaller fan than a central airhandler, which runs only when dehumidification is needed. A central airhandler is typically triggered by the furnace / condenser linked to the HVAC system, or a 'circulation' setting on a smart thermostat."
Dehumidifiers use a lot of electricity, and the fan is a small part of that. The lion's share is the compressor, and there is nothing fundamentally different about the compressors in ducted units compared to standalone units.
"If a standalone dehumidifier is used, the more-dehumidified air in that room is mixed with air from other registers. So one area has more dehumidification, and others have less."
That's not an efficiency argument, that's an effectiveness argument. And if the dehumidifier is set next to a return, the entire house is going to get the same air.
Just noticed this article based on my question and wanted to say thanks for writing this up! I do indeed have a central fan and plan to run it for mixing and fresh air distribution even when there are no heating or cooling calls, so sounds like a portable unit should work well
Dear Ben: I hope you read my last replies - and choose a ducted dehumidifier. Performance, service and reliability will be significantly better - and I have used both.
Yes, I have. Thanks for fleshing that out. And I will weigh it. Even anecdotally, it's good to know you've had a good experience with the Aprilaire unit.
In response to your comments:
(1) "running a central airhandler (the ;blower.fan' in a central HVAC system) would obviously consume extra energy."
In my case, I have a variable speed blower that I'm already planning to run periodically for supplying fresh air & destratification. So I don't believe I would need to run it any extra. I do think I would wire a duct fan to run in sync with the dehumidifier to pull air from upstairs into the closet the dehumidifier would be running in. This would prevent the air in the closet from becoming significantly warmer & dryer than the air in the rest of the house and decreasing the dehumidifier's efficiency. It would cost maybe 20 watts of additional energy to run the fan, but not very significant compared to 500+watts for the dehumidifier.
(2) "the 'source' for the airhandler would be the return from a room/area, rather than directly from a ducted dehumidifier, which is inefficient."
Yes, I agree that you gain the efficiency of distributing the dehumidified air with minimal fan power/run time that way. But as I recall from this article (https://www.greenbuildingadvisor.com/article/four-ways-to-duct-a-dehumidifier) you risk compromising the dehumidifying efficiency of the air conditioner when you duct the dehumidifier into the return side. Supply side avoids that, though you have extra static pressure to overcome. Also, not sure how much air can pass when the blower fan is off, but seems like either side could risk re-evaporating moisture off of the coils. So sharing ductwork complicates things a bit.
(3) "a standalone dehumidifier would not have the capacity to cover the entire house. (They are typically designed for <1,000 SF.)"
Yeah it's a good question whether or not a single portable unit will be enough. Seems like the portable units tend to top out at 50ppd at I think 65degF and 60% RH. Ducted units are available with higher capacities. So that is an advantage of ducted. But I am also limited by space such that I can't really fit the larger ducted units anyway. I wish they had some with a vertical orientation like the portable units (I think santa fe does make one, but it's very large & expensive)
(4) "high capacity standalone dehumidifiers are noisy because they need to move a lot of air"
Yes, I'd imagine without ducts, the noise of the blowing air itself is higher. So that's a good consideration
(5) "an inexpensive standalone dehumidifier is not designed to run constantly - AKA "You get what you pay for.""
Yes I think that's generally true. But this question also sparked my initial post. B/c I've been surprised by how many people I'm finding reporting that their Santa fe or other top of the line dehumidifiers have died on them. I know the portable units are unreliable, but the question is how much more reliable are the ducted units? B/c at a 5x price hike, I can roll the dice on several portable units first.
But your good experience with Aprilaire is nice to hear. In general, from the reviews I've read, the reviews of the Aprilaire units are probably best. So that does encourage me that that could be a good option.
So as I said, will weigh your recommendation, and thanks for your engagement on this!
Dear Ben: Thanks for your reply and comments. Two more notea:
(1) Conflict: When your AC condenser is running, there is typically no need to run the dehummidifier - thanks to dehumidifcation created by the AC coil. Our Aprilaire runs on its own humidistat, and is wired so that it will not turn on or continue running when the AC compressor kicks in.
(2) Space: The Aprilaire 1730A in our house is fairly small, and 6" flex ducts are easy to run. You may want to measure your space to see how it could be installed. I attached a copy of the 1730A install guide and spec sheet, which include dimensions and suggestions for a closet installation etc. Note: elbows, e.g. 90 or 180 degree turs, should always be made with metal pipe - NOT flex. Also seal all of the joints and connections with foil HVAC tape, e.g. Nashua 324A from Home Depot. Press the foil tape flat to eliminate wrinkles that might leak air.
I hope this is helpful.
The unit referenced is rated for 65 pints per day (PPD) at 80F/60%RH. That's kind of mid-range for portable dehumidifiers, this one for example pulls 80 pints under the same conditions:
https://www.turbro.com/products/greenland-165-pint-large-dehumidifier-with-pump
Note that there are at least three standards for PPD, so to compare units you have to make sure they're using the same standard. Some manufacturers quote "saturation," 95F and 90%RH, which gives big numbers but isn't something you'd realistically see inside a house.
More common is the AHAM standard, the Association of Home Appliance Manufacturers. That's 80F/60% RH, that's what is quoted in the attached spec sheet.
Until 2019 the EPA and DOE used the AHAM standard for its Energy Star ratings. In 2020 they moved to a more stringent standard of 65F/60% RH. Energy Star ratings are typically about 60% of AHAM ratings.
For illustration, the Turbro unit I linked to is rated at 165 PPD saturation and 80 PPD AHAM. They don't give an Energy Star rating but I'd expect about 50 PPD. The Aprilaire only gives an AHAM rating of 65 PPD.
Dear DBContrarian:
I should have spec'd a current AprilAire model, rather than the old 1730A. Here are the specs for the AprilAire E080 and the TurBro GL150P. PDF copies of both spec sheets are attached. Note: TurBro does not include PPD in their spec sheet . This is obviously a basic spec, and it is curious that they left it out.
AprilAire E080 TurBro GL150P
PPD AHAM: 80 80 (not in spec sheet)
CFM 0wc: 185 278
Noise: 45 dBA 52 dBA (range is logarithmic)
Op Power: 4.8 amps 6.8 amps
Ducted: Yes No
Standalone: Yes Yes
Energy Star: Yes No
Refrigerant: R32 R32
Warranty: 5 years 1 year
If you review the AprilAire and TurBro websites, you will also find that AprilAire products are manufactured in the USA. TurBro is offshore. This can affect service and parts availability, particularly for products that are not major in the company's product line.
AprilAire specializes in HVAC. TurBro makes many products.
I hope this is helpful.
yes, thanks for sharing. I'd had my eye on the aprilaire E080, but hadn't really considered the 1730. It is a little more compact than most, so I do think it would fit. Especially with just 6" duct work. Looks like the fan is pretty strong.
However, based on the spec sheet, the capacity for the 1730 drops off a lot at cooler temperatures. It's only rated for 25ppd at 65degF and 60% RH. That's the energy star test conditions for portable units, and many of those are rated at 50ppd, so double the capacity
Dear Ben: Attached is a copy of the Energy Star report for the AprilAire E080. Note that it delivers 65 PPD under Energy Star standards. TurBro's Gl150P is not Energy Star rated - and they only show performance from AHAM 80/60 and UP - not DOWN. TurBro's marketing also leads with "165 PPD!" - the maximum 'saturation' level, which is deceptive. See:
https://www.turbro.com/products/greenland-165-pint-large-dehumidifier-with-pump?srsltid=AfmBOooaUqLK4MmzmKTrZQq2-5M0f_rCXw7QX2ZQeKLbXTfNFLGgS1tp
You're missing that the whole reason for installing a dehumidifier is that the air conditioning can't provide as much dehumidification as you want. The reason for de-conflicting them is not to make them work better, it's that because of the way they're connected they can't both work at the same time, their fans would be in conflict with each other.
Both will actually work better if they are independent of each other and the AC is controlled by a thermostat and the dehumidifier is controlled by a humidistat. The reason they will work better is that they will tend to have longer cycles. To understand why longer cycles are better, think about how a cooling appliance removes humidity. Air is run over a cold surface, as the air cools dew forms on the surface. Once enough dew has formed it starts to drip off and is drained away. So at the start of each cycle there is a lag until enough dew forms for it to start being removed. At the end of each cycle, the coil is wet, but it stops dripping and as it warms up whatever moisture is on it evaporates and is returned to the interior as the coil warms up. If cycling is particularly short no dehumidification happens, the coil just gets wet and dries off.
De-conflicting will by necessity cause the dehumidifier to run shorter cycles than it otherwise would. It also causes the AC to run shorter cycles. Part of the load on the AC comes from the heat put out by the dehumidifier, when the dehumidifier is de-conflicted that source of heat is removed and the AC faces less load. In a particularly bad situation you could have the AC and the dehumidifier alternating cycles with each other with both having trouble maintaining the setpoint.
Optimum comfort is achieved when the dehumidifier and AC run independent of each other.
Dear Ben: The AprilAire E080 is the current 80 PPD model, which I should have spec'd vs the older 1730A that I installed in our beach house ~5 years ago. I added a comparison between the AprilAire E080 and TurBro GL150P above, in a reply to DBContrarian - along with copies of the matching spec sheets. One important note on space and installation: You can attach one of the ducts to the top or end of the AprilAire. This is important if the length of the unit is a factor. Also include the length of a 6" 90 degree metal elbow, for the duct that exits from one end - which is approximately 10" Best of luck with your choice and installation!
One more note: The 5 year warranty for AprilAire vs the 1 year warranty for TurBro underscores my point: "You get what you pay for." Plus the availability of parts and service for an offshore product, that is not a major part of TurBro's product line.
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