The basement of our well-insulated and air-sealed 100+ year old home is dry, but enough moisture (as vapor) makes its way through our concrete walls and slab that dehumidification is a must from about April through October.
Dehumidification comes with a pretty big energy penalty, so I am proactive in managing this load: when I see that the weather and forecast is for a dry day, I start the day by opening up our half-dozen basement hopper windows, and then close them up at the end of the day (see Image #1 at the top of the page). This just takes a couple of minutes, and Mother Nature manages our basement humidity.
But there are many non-heating-season days when we manage the basement humidity with our off-the-shelf 50-pint Whirlpool dehumidifier (see Image #2 in the image gallery). It has done a fine job, but I got to wondering just how old the unit was, and how its efficiency was faring. The unit also seemed quite noisy (but honestly, maybe it was always that way).
I took the housing off the face of the dehumidifier unit to inspect the coils (see Image #3) and to check out the specs (see Image #4). The coils were a bit dirty, but easily cleaned. What really surprised me was that the unit was quite a bit older than I thought (manufactured in 2003, since the “P” in the serial number stands for a manufacturing date of 2003; see Whirlpool Date Codes) and its Energy Factor was just 1.35 (L/kWh: liters per kilowatt-hour) — not even Energy Star.
How has this unit’s efficiency held up over the many years?
Benchtop measurement of a dehumidifier’s Energy Factor
There is of course a standard test for Energy Factor; it used to be ASTM C 749 (as cited on the Whirlpool unit’s spec label — Image #4) but now is ANSI/AHAM DH-1 (as detailed in Appendix X to Subpart B of Part 430 – Uniform Test Method for Measuring the Energy Consumption of Dehumidifiers).
My version of the test was to hook up a Kill A Watt meter to the dehumidifier, and collect the condensate over a 24-hour period. I did that for the Whirlpool unit in our basement under these conditions:
- Initial basement temperature and relative humidity: 78°F/68% (as measured by a HOBO datalogger; see Image #5)
- Intermittent operation over the 24 hours, with constant operation “setting”
- Average operating power: 590 watts (see Image #6)
- Test period: 6 a.m. August 14 through 6 a.m. August 15
- Output: 6.3 liters
- Input: 4.32 kWh
Conclusion: The benchtop Energy Factor is 1.47 L/kWh.
Wow – pretty impressive efficiency considering the unit’s age. But it started out as pretty unimpressive. (A current version of this same Whirlpool dehumidifier would be the Whirlpool WHAD501AW. It’s EF is 2.0 and it retails for about $200.)
There is a long list of conditions that make my benchtop test different than a laboratory test done to all the specifications of a standard. The most meaningful comparison will be to the new high-performance dehumidifier, coming up next.
High-performance dehumidifier
For the last twenty years at least, the U.S. company Thermastor has been a key contributor to the Building America program, quietly but steadily educating builders about the importance of managing latent load, particularly in efficient homes with longer shoulder seasons.
As part of my work with Hanley Wood University’s Homebuilding Crossroads workshops , I have been doing a lot of tech-talk with Nikki Krueger at Thermastor. When she asked how I was keeping my own basement dry and I described my aged Whirlpool unit, she said, “Want to give our new Santa Fe Advance 100 a try?” I could see GBA benchtop testing written all over this offer.
So, earlier this week I installed the Santa Fe Advance 100 (a dehumidifier that retails for $1,799) in our basement (see Image #7). I did an identical benchtop Energy Factor test with the Advance 100:
- Initial basement temperature and relative humidity: 78F/68% (as measured by a HOBO datalogger; see Image #8)
- Intermittent operation over the 24 hours, with setting RH = 60%
- Average operating power: 660 watts (see Image 9)
- Test period: 6 a.m. August 15 through 6 a.m. August 16
- Output: 13.5 liters
- Input: 5.04 kWh
Conclusion: The benchtop Energy Factor is 2.68 L/kWh.
Pretty impressive efficiency. And pretty much inline with the EF reported on the SF Advance 100 spec sheet (see Image #10). But how else is the Advance 100 different or better than an off-the-shelf standard dehumidifier, such as the Whirlpool I had in my basement for all those years?
Beyond straight dehumidification
You can go to the Santa Fe website and get their version of the differences, but here is what I found:
- Much quieter operation – the fan motors are higher quality, with less vibration;
- Made mostly of metal, not plastic – the Advance 100 is a sturdier (and heavier) unit;
- Includes air filtration – MERV 8 pleated filter is very easy to change out;
- Includes “circulation” mode – a mode that pushes the fan to high speed to increase mixing and to even out the space’s relative humidity and temperature;
- Can be ducted – the unit is designed for and capable of being ducted so that the unit can be in a different space than the space it serves;
- Accurate sensors – the LED readout-panel on the Advance 100 was always within 1°F and 1% RH of the Hobo data logger in my basement;
- Remote internet-based operation (more on this below);
- Made in U.S.A. – pretty rare these days, and for me it translates into very responsive technical service.
As with most modern new appliances, the Advance 100 is tied to the internet. You download the Santa Fe Connect app, and from your phone you can see and set the operation of your Advance 100. Every half hour it updates weather conditions for your zip code, and the app sends alerts if there is anything awry regarding your setpoint and current RH (see Images #11 and #12). Very cool!
Now if I can just get an app that will open and close my basement windows when the weather is nice and dry…
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20 Comments
Peter,
Here are some observations on the payback implications of upgrading from a $200 dehumidifier to a $1,799 dehumidifier.
First of all, the expensive dehumidifier uses more electricity per day (5.04 kWh) than the cheap dehumidifier (4.32 kWh). So if you simply leave the expensive dehumidifier to run for 24 hours per day, your energy bills will be higher than they used to be.
However, the expensive dehumidifier is more efficient. If you install a 24-hour timer on the expensive dehumidifier so that it runs only 46% of the time, it will pull the same amount of moisture from your basement air as the cheap dehumidifer running for 24 hours per day.
With these assumptions, along with the assumption that you'll need a dehumidifier for half the year, the difference in operating cost between the cheap dehumidifier and the expensive dehumidifier on a timer to operate for 46% of the time is 788 kWh per year minus 429 kWh per year -- that is, a savings of 358 kWh per year, equivalent to $53.70 per year if your electricity costs 15 cents per kWh.
Since the incremental cost of the expensive dehumidifier is $1,599, the simple payback period is 30 years. That's not too impressive, since the equipment may not last that long.
Finally, note that if you buy a a cheap ($200) Whirlpool dehumidifier, the new model will be more efficient than the older Whirlpool model you tested. That fact further lengthens the already long payback period for the Thermastor dehumidifier.
Peter,
I did some new calculations -- this time based on the EF of the new Whirlpool model, which is 2.0 instead of 1.47 (the presumed EF of your current Whirlpool model).
The new Whirlpool model uses only 73.5% as much electricity as your Whirlpool model. So running a new Whirlpool dehumidifer will only require 579 kWh per year rather than 788 kWh per year.
That means that the annual savings of a new Whirlpool dehumidifier compared to the Thermastor is 150 kWh instead of 359 kWh. The annual savings are only worth $22.50.
So the payback period for the upgrade to a Thermastor unit stretches out to 71 years. Ouch.
I would be amazed if anyone upgraded to a dehumidifier like the Santa Fe Advance 100 based on energy savings payback alone. To me, comparing a standard portable dehumidifier to a unit like the Advance 100 is like comparing apples and oranges. The list of performance advantages--air filtration, circulation mode, smart-phone operation, can-be-ducted, fits in a crawlspace; operates to much lower air temperature--is why you pay the premium. Is it worth it? I guess that depends on how much you need or want the additional performance.
As soon as an Energy Star rated dehumidifier gets over 75 pints/day its EF must be 2.80 or greater, per the latest specifications:
https://www.energystar.gov/sites/default/files/ENERGY%20STAR_Dehumidifiers_V4%200_Specification_Final.pdf
Upgrading to a model similar to this Danby 95 pint unit:
https://www.homedepot.com/p/Danby-95-Pint-Dehumidifier-with-Pump-DDR095BDPWDB/305567168
...gets you 40% more efficiency for about 60% more money, but is also capable of pulling 90% more moisture (95 vs 50 pints) on a daily basis. If an efficient large-format dehumidifier is the goal, I see this making much more sense than an $1800 unit, unless ducting is an absolute requirement.
If ducting is a requirement, the $1400 Honeywell DR90 doesn't require additional ducting kits be purchased and is rated at the same 2.9 EF. If ducting, ultra-efficiency and Made In the USA are requirements, the $2400 Ultra-Aire XT105H (4.2 EF) may even make sense if long payback periods don't scare you away.
It's too bad Danby or someone else doesn't sell a 95 pint unit in a "whole house ducted" form factor. If it was in the $500 price range and took a commonly available furnace air filter they would have the market.
Great info Peter. I installed a ThermaStor dehumidifier in my house (https://www.greenbuildingadvisor.com/article/new-house-year-one-update) recently to help in the shoulder seasons since the house is so tight and I often end up with high RH and moderate temperatures. Since I don't have ducts, or a basement, I installed an intake an exhaust in the downstairs hallway. The big surprise was how much heat the unit puts out. I ran it when the RH was high and the outside temperature in the mid 70's. It did a fine job of removing moisture, but when I put an IR thermometer on the exhaust duct I discovered that it was pushing out air at 100 degrees. Had I installed a split dehumidifier during construction I could have avoided the added heat. I have since learned that when installed in a ducted system the heat dissipates, and the system often calls for air conditioning when the heat output starts to increase the indoor temperature. Since we don't get many cool days with high RH, I expect that I will not be able to take advantage of the dehumidifier as much as I had hoped, instead, I will likely run the AC at a lower temperature when I need additional dehumidification.
Carl, using your AC to dehumidify the house will require over-cooling if the house is already at the desired temperature. The Sensible Heat Ratio of your AC will determine how much dehumidification you get for a certain amount of cooling, usually about 25/75%.
The SHR of a split dehumidifier will lean favorably towards dehumidification, but it will still cool the house. Your best option is likely to use your dehumidifier as necessary and just allow the AC to handle the small added heat load. It sounds like a little added heat may even help out from time to time (house too cold).
If the dehumidifier's localized heat output bothers you, perhaps you can come up with a supply vent strategy that puts the hot air near the return of your AC, or distribute it throughout the house a bit better?
Great articles BTW!
The latent heat of vaporization of the moisture in the air as it is being condensed onto the evaporator coil is what is being converted to sensible heat at the condenser coil. Rather than surprising, fact that the exit air temperature the air coming out of the condensing coil is higher than the room temperature should be expected.
A dehumidifier just converts the latent load to a sensible load (with additional sensible heat from the compressor motor as a bonus. :-) )
Of course putting that sensible heat outdoors with a split system (or into a tank of domestic hot water) would be preferable to adding it to the indoor air during the cooling season.
Very interesting, per liter how many BTU does this add to the room?
About 2134 btu/liter of water - plus the heat from the compressor.
Interesting, can you explain the calculation?
The heat from the compressor is actually a bit more complicated because there's also fans that run constantly on some units, intermittently on others that don't show up in the EPA rating. But a kill a watt is a simple way to measure the electricity consumption no matter what the real rating is.
I will experiment with the dehumidifier on days when it is cool and humid but we don’t see many of those in GA. I was surprised at the heat coming out of the unit because I’m not educated enough in the physics of dehumidification, and as far as I can tell it hasn’t been widely discussed in the industry. I suppose that dehimifiers historically have been used as band aids for problems. As very high performance homes become more common people will be looking for solutions to high RH. I feel like we’re in a transitional stage and expect to see new solutions including possibly ERV/HRVs combined with dehumidification or true dehumidification integrated into HVAC systems. Damn climates just won’t cooperate.
Your praises had been heard 5 years ago by a Canadian manufacturer: Minotair. Their latest product, the PentaCare V12, is 4 machines in one: it's a HRV, a 1-ton heat pump, a HEPA filtration device (MERV 15, which is pretty good) and a dehumidifier capable of removing over 100 pints of moisture per day. Those units are mostly used in passive house and other high-performance buildings (single dwellings and multifamily units) as an all-in-one HVAC system. More info below:
https://www.minotair.com/wp-content/uploads/MINOTAIR_PENTACARE_V12_052018.pdf
They really seem to be on something as those units are really well-made, kind of a durable commercial grade (I saw one at the latest NESEA Boston show where their booth was one of the most crowded ones). The main goal of those units as stated on their brochure is to provide unrivaled levels of indoor comfort & health. Pricing is 6 grand.
There's also another manufacturer, Build Equinox with the CERV2. Pricing is lower at 5 grand but the capacity is way less on all aspects (and their "spec sheets" doesn't show any reference to any code or standard contrary to Minotair that shows many, having then a much more serious and rigorous spec sheet. On top of that size-wise, the PentaCare is almost 3 times smaller offering more possibility of where to install it. You can have a look here: https://www.buildequinox.com/thesystem/
Coming from Canada, those guys have an edge on residential ventilation as HRVs are mandatory and part of their national building code for more than 20 years. It also explains why most HRVs and ERVs being sold here in the US are made by Canadian firms (Fantech, Lifebreath, Venmar (makers of Broan/Nutone units) and of course Minotair).
And because the climate won't cooperate as you wrote, we really need those new machines from now on. Because at some point, when we start to suffer a bit in our homes, pricing and "pure" electrical efficiency of equipment become less important as our survival instincts will bring us to get what it works to get the job done to protect ourselves.
The latent heat of vaporization (condensation) is just one component of the temperature rise. The other one is the work that the unit is doing. That's where the EF comes in. A unit with a higher EF will add less of its own heat to the output air, but the heat of vaporization will be the same.
This is one reason I'm really starting to like heat pump water heaters , especially for warm climates. Using the waste heat from the dehumidifier automatically seems like a win.
Full disclosure: I just bought a cheapy Frigidaire (Energy Star) to replace my old, dead dehumidifier in the basement. I love Thermastor, but not the price. Yikes.
One newer option on the market is a super efficient minisplit with a 'dry' or 'dehumidify' option. These will run very efficiently sucking the moisture out of your home. And unlike heat, humidity will quickly equalize in the home especially with open or partially open doors. This will also do some cooling which generally is not an issue. It will also send all the heat outside unlike a stand-alone humidifier.
And when you want AC switch to that. Many are very efficient at AC also and auto zoned, and some have 'follow me' remotes, do heating as well, have wifi control (be careful with that one) and are super quiet for you and your neighbours. Some now are DIY, quick connectors and simply plug in and can be moved to a new room or new house with not much more work then a window AC unit. The efficient ones will quickly pay for themselves in a few years, especially if you install it yourself.
These could change AC energy hog Global Warming issues in quick order and save folks money.
Excellent point! $1800 will get you your choice of the two highest performing 3/4 ton minisplits on the market (minus accessories and installation):
https://www.acwholesalers.com/Fujitsu-9RLS3Y/p65507.html
https://www.acwholesalers.com/Mitsubishi-MZ-FH09NA/p56553.html
Either of these can provide highly efficient cooling or heating for reasonably large spaces, as well as offering a Dry mode that keeps the heat outside. Assuming they are capable of providing enough dehumidification for a home it kinda highlights the "value" in an $1800 dehumidifier-only device.
I wonder if the dry modes of these minisplits are able to dehumidify to the Energy Star EF of 2.8 L/kWh? Anyone know?
There are conventional air handlers (and furnaces) with dehumidification modes, too. I had a Carrier/Bryant FV4C installed in May. It has two DH modes that run the fan at 50% and 80%, respectively. I'm using the lowest fan speed and it's almost inaudible. The house is much more comfortable and I almost never have to make manual thermostat adjustments (RH stays between 50 and 55%). Dehumidification calls dominate system operation (CZ4a), with only occasional cooling calls on 90º+ days.
And the best part is that it was almost free, since I was planning for a variable speed AHU anyway. My HVAC guy wasn't familiar with the DH mode, so I wired it up to my Ecobee with a relay (unfortunately the thermostat doesn't support the exact Carrier wiring configuration to get max DH). I used this paper to help assess whether it would be adequate for my climate zone, along with the load calc I had performed:
https://www.energy.gov/sites/prod/files/2013/12/f6/humidity_control.pdf
While the efficiency of my 16/13 S/EER unit may not keep pace with mini-splits, at least the heat is being rejected outdoors, unlike the room dehumidifier in the basement...
Alan,
When water is condensed from the air, heat is released at the rate of about 1,000 BTU per pound (per pint). Evaporation of liquid water requires heat to be added to the water, while the condensation process releases heat from the water. That's physics.
I understand, i was just curious how much heat was involved.
By any chance would it make sense to use this for heating during shoulder seasons?
Peter, just a reminder about significant digits in calculations - if you have only a two digit value, the resulting calculation can't produce an accurate three digit value.
From the story:
Output: 6.3 liters
Input: 4.32 kWh
Conclusion: The benchtop Energy Factor is 1.47 L/kWh.
The result should have been 1.4 L/kWh (truncated) or if you were certain of the measurement accuracy - it might have been reported as 1.5L/kWh (rounded). OR you actually measured your output to 6.30 liters and didn't say so.
Ok, on to commenting on the rest of the story.
The measurement accuracy for the Kill-a-watt devices are also often misunderstood. Quick look at the brochure says 0.5%... but that is really the best accuracy when the device is measuring probably a 10A load at 120Vac. The current transformers used in the devices are NOT linear... at the low end the measurement error can increase to 2%. I often see people reporting that they had a 3W load or a 4W load as measured by a kill-a-watt... when really that number is in the noise margin of device when it is looking at VERY low loads. Also often missed is that the kill-a-watt device itself can add up to a 10Wmax load to the circuit.
Missing from your testing - is the RH chart of the room during the testing. Were they similar conditions?
Whirlpool when they tested the original models had indicated 1.35L/kWh. That testing would have done with some very accurate equipment and very precise measurement techniques. The tests would have likely (almost certainly) been done in controlled laboratory conditions with a known controlled temp&RH. Your results would infer that either the dehumidifier improved with age - or the measurements were not done with the same accuracy, precision or test conditions.
One of the leading complaints I've heard from customers about dehumidifiers is that they sometimes die prematurely. A co-worker had two in a row die after only 2 years. Even though he got free replacements for both under warranty, he finally bought a Therma-Stor dehumidifier to avoid the hassle.
The theory I've heard to explain why some dehumidifiers die early is that the plastic housing isn't as good at protecting against damage during shipping as the metal housings were back in the day. In addition, maybe a sea voyage from China increases the odds of damage compared to domestic shipping?
I'm biased because I've had cordial dealings with Therma-Stor over my many years in the efficiency biz here in Madison, Wisconsin. I particularly like their digital humidity gauges that beep when humidity gets above a limit.
When we bought our 1938 house nine years ago, I persuaded my wife that it was worth spending the ~$1000 on a Santa Fe Compact dehumidifier. (She's remarkably tolerant of my energy geek quirks.) Saving on operating costs was far down the list of reasons I offered.
The dehumidifier is on a timer so that it only runs off-peak (we're on the voluntary Time-Of-Use rate). The humidity doesn't rise beyond 60% RH during the 11 hours the dehumidifier is off. In a typical summer the dehumidifier would use about 300 kWh as measured by a Kill-a-Watt meter.
At the start of this cooling season we replaced our 17 year-old central AC (and a 27 year-old 90%-efficiency furnace) with Bryant Evolution variable speed equipment, including the Connex thermostat. I actually liked the previous Ecobee thermostat better, but it couldn't enable all the features of the furnace and AC. (Not endorsing Carrier/Bryant over other brands, just reporting what we bought from a dealer I've known for 30 years.)
When I looked at the Kill-a-Watt today, I was surprised to see that the dehumidifier had only used about 75 kWh so far this season. My best guess is that the new AC is dehumidifying more than the old one because it runs at 25% of its 2-ton capacity most of the time. Longer run time at lower capacity=a lower Sensible Heat Ratio (aka more dehumidification).
Jonathan
Climate Zone 6, Madison WI. (Where sticky Gulf air with dew points above 70F enters basements with 50F deep soil temps, with predictable results.)
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