I grew up in Pennsylvania without an Air Conditioner, and I vividly remember when we got central AC installed when I was in High School (1987 to be exact). Fast forward 10 years to my first trip to Texas in the late 1990’s (I married a Texas girl) and I remember thinking how COLD most houses were in Texas. Freaking boiling outside, and an icebox inside.
Why do many Southern US homes keep their thermostat at 68 degrees? I think it’s because they’re using the AC to deal with humidity issues much of the year. I’m very comfortable in my house with the T-stat set to 78 as long as the humidity is low.
So…What’s the main purpose of an HVAC system?
1. To Deliver Comfort
2. Delivery that everywhere & evenly in the house (and do it quietly)
3. Be efficient with Electricity (cooling is greater than 50% of energy use for Southern US Homes)
If you’ve followed my blog you’ll know that I think standard HVAC systems are far from delivering on those three goals above. In fact, I think most HVAC systems are missing something. HVAC+D. The D stands for De-humidification. You might say, doesn’t the Air Conditioner coil take care of dehumidifying the air? Yes it does, AC’s take care of sensible and latent cooling. Latent refers to the water vapor that’s in the air. However, your AC will only dehumidify when it’s running. (Remember, the air conditioner needs to run longer than 10 minutes before it starts to remove moisture from the air). With today’s building codes requiring a tighter envelope (in Austin we require 5ACH50 on the blower door test), and with the tendency for HVAC contractors (and builders) to choose the next size up in equipment I believe a stand-alone dehumidifier is required.
The “Gold Standard” Dehumidifier I install in my houses has been the Ultra-Aire XT105. This is my favorite model from Ultra-Aire’s great lineup of equipment and works for about 75% of the houses I build.
The XT105H is super efficient and removes 105 pints per day while only using 4.9Amps of electricity! But, the one down-side of a Dehum inside your house is that it will heat up the space where it’s running. A Dehum works like a mini-AC all in one box. It uses refrigerant & a compressor just like your AC except that the condenser coil (The “AC” box outside your house) is inside the same box as the cold evaporator coil. Fine Homebuilding has a terrific “How it Works” article I’d recommend reading in the May 2014 issue. When the XT105 runs it brings down the humidity inside the house but it also adds some heat.
Ok, so what makes the new Ultra-Aire SD12 so revolutionary? The big deal about the SD12 is that they’ve moved the Condenser coil outside the house! That means that there is no added heat inside the house. It also means that the SD12 provides some sensible cooling and basically acts as a first stage Air Conditioner! The SD12 removes 184 pints/day while providing 4300 BTU/hour of cooling. That’s equivalent to a 1/3rd Ton AC which is super helpful in the hot/humid South.
I’m about to install my first SD12 in a house I’m building on Lake Austin. The house is primarily a weekend and vacation house which makes it the ideal candidate for the SD12. I’ll coach my clients to keep their house thermostat set to 90-92 degrees while they aren’t there, and the SD12 will be set for 50%RH (all year). The SD12 will keep the house air dry/dehumidified, and will provide some cooling too! This house where I’m using the SD12 is a super-insulated & super-tight house so there will be little hot/humid air leaking inside and the house will ride the summer temp spikes with little AC. It’s actually my first Timber Frame project with Bensonwood Homes from This Old House fame.
The stable humidity (thanks to the SD12) in the house will keep mold & dust mite activity low, it’ll keep the hardwoods stable, it’ll keep the caulk in the house stable (greatly reducing cracking), the sheetrock/paint/studs more stable, their piano tuned, and it’ll smell fresh/clean when they arrive on a Friday for the weekend. I’m installing Nest Thermostats so they can grab their iPhone on Friday morning and set the Nest Thermostat to 76 and the house will cool from the 90 it’s been at all week to 76 prior to their arrival. 76 Degrees and 50% RH is ideal for the Hot/Humid South. This SD12 is a game changer and I’m excited to install my first one. I’ll post a video review after we get it installed.
If you’d like to see an XT150 review video here’s one I did two years ago.
Thanks for hanging with me on this long post. I’d love to hear your comments. Drop me a line below and I’ll respond quickly.
Best,
Matt Risinger
– Risinger Homes in Austin, TX
Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.
Be sure to check out my video blog on YouTube, and follow me on Twitter @MattRisinger
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View Comments
Hey Matt - I love hearing someone talk about hot weather! And thanks for the review - does any other manufacturer make a similar model, or is Ultra-Aire the only one?
Chuck Bickford, FHB
@ChuckB: This is the only split degum I know of in the marketplace. Ultra-Aire is the leader in Dehum's for residential use and this new SD-12 is unique out there. I'm excited to get a few installed so I can review them further. It's really first-stage cooling as well as dehumidification. Come visit anytime Chuck! It's going to be 70 today in Austin...
Best, Matt
Matt,
I am excited about your Blog and especially this Ultra-Aire SD-12 and all your other equipment recommendations. I am building a house in the Virginia near the Potomac river, which is in area 4 so our areas are different, and we sure do get humidity & rain in summers & cold winters. The house is an ICF full basement Cape Cod style with an open floor plan great room and a 1 bath and 2 BR's in the 2nd floor room truss (I know not the best for efficiency but looks great in the river community).
I am working very hard on the design to radically air-seal/spray foam insulate the home as well as the top cord or the roof so that any plumbing is in conditioned air space (goal is <2.0 ACH@50 Pa). I was taking notes during one of your presentation on the HVAC systems (or better yet "HAC +V+H"). However I would like your opinion on how, and even were, to place some of the equipment. My equipment selection based on you and others are: VRF mini-split; Venmar HRV or ERV (not sure since I will also use Dehumidifier for summer but need to retain humidity for the winter, to complicated for me, my head hurts); Ultra-Aire SD-12; and also perhaps an Aprilaire Media Cleaner #2210 (not sure about UV Light). So... how do I connect all this stuff. I know the VRF is basically separate; but since I will be using the ERV to remove stale air and feed fresh air ... can I somehow use the ERV distribution tubes to distribute and connect the Dehumidifier into the how deal and also the media cleaner??? Are they best kept entirely separate? Aarrgg... V/r, Eric Kessler
I realize this question is the antithesis of the basis of your article, but up here in the north, humidification during the winter is a necessity. Any suggestions for a system that is compatible with a Unico high velocity forced air system?
Matt, I live in the Florida Panhandle so dehumidification is necessary every month of the year. I have a relatively new single stage heat pump with variable speed blower which normally does a good job of controlling indoor humidity, except during those periods when there is not much call for heating or cooling. Some of the literature that came with the thermostat warns against running the cooling cycle when the outdoor temperature is 50 or below. Would the split Ultra-Aire system have a similar caution? Also, are the other Ultra-Aire units as noisy as portable dehumidifiers?
Great info, Thanks !!!
The home we built is super energy efficient and also tight (0.02 exchanges per hour by blower door test). We heat and cool with radiant driven by a ground source heat pump. Dehumidification is copper tubing on the walls over windows with a gutter below for drainage. Refrigerant runs through the copper tubes. Cool water in the floor tubing. Nice system but, dehumidification only works when system is running. It runs very little so we don't have enough dehumidification. Now, with your info, I'm weighing these options: 1) changing my controller to run the GS heat pump on dehumidification demand rather than temp so it will run more (will need to valve off hydronic tank so it doesn't get too cold) or, 2) putting in a separate Ultra-Aire. We don't have typical ducting, except, we do have an HRV pulling from 4 location and returning to 1. Could couple into this system I think. It's in the conditioned attic and has a drain line.
Thoughts?
@ejkessler: Dang, great questions. First, it sounds like a cool house you are building. Under 2ACH50 is a great goal for air tightness. My initial recommendation would be to run your HRV separate from your HVAC system (go VRF!). Your HVAC+D system is easier to run as a system with the filtration and the Ultra-Aire Dehum in line. Your climate is a bit on the border with needing the cooling benefit of the SD-12. You might be better served with an XT105 as the waste heat inside your conditioned space may not be as big of a deal. That being said I lived outside of DC for seven years and I remember summers being HOT and HUMID! Austin Summers are HOT but not as humid, it's the spring/fall that's a bear hear. 90 degrees outside and 85% RH isn't much fun.
I hope this helps.
Matt
Thanks Matt,
You really helped push me toward another decision ... the water heater. I was really struggling with the two piece SD-12 and another hole in my foundation plus the added cost, vice the XD105 simplicity and it too was making my head hurt. While I did not want the added heat from the XD105 in my equipment room I was also thinking about a Heat Pump water heater (in combo with a modest PV array) and how it sucked heat out of a room. So perhaps between the added heat of the XD105 and the heat robbing Heat pump water heater all in the same closed equipment room, perhaps it will balance out. thanks.
But I do have a follow-on regarding the HRV vice ERV issue if I am using the "Ultra-Aire Dehum in line."
- Which is correct or best, the HRV or the ERV since in the winter the humidity is low and I likely want to retain that at some controlled level in such a tight house (say the 50-60% range)? If I understand the ERV helps retain humidity ... but won't that create problems in line with Ultra-Aire?
- Do really tight houses really need to worry about too much retained humidity?
Thanks again!
@looselumber: I've never used a high velocity HVAC system before. I'm not sure about integration. These Ultra-Aire dehums and specifically the SD-12 are pretty simple to duct as a stand-alone system however. You just need a good return and supply grille. Humidity inside a house is generally pretty even (unlike temperature) so one location ducting for the Dehum and you'll be able to handle the whole house easily. Hope that helps. Best, Matt
@rickrobson: I'm not sure I've got much advice on your current system. I'm not a GSHP expert. I would however tell you that a stand-alone application for a Dehumidifier would work very well. The Ultra-Aire SD12 or the all-in-one Dehums like the XT105 are pretty easy to install in a stand-alone duct fashion. One return grille, and one supply and you can easily dehumidify the whole house. That might be the simplest installation for your house. Best, Matt Risinger
@humperdink: I see no reason why this SD-12 would have any problems running below 50 outside. You might call them to verify before purchase, but I don't see why it would have a problem at that outdoor temp. Regarding your sound question, yes these units when running do make noise. The SD-12 is much quieter because the compressor is outside so it's mainly fan noise. The other all-in-one units like the XT105 make more noise as the compressor/condensor is all in one package. Debra Judge Silber did a great "How it Works" article in this months' issue that shows the inner workings of the Ultra-Aire XT105. Here's the link https://www.finehomebuilding.com/how-to/departments/how-it-works/dehumidifiers.aspx
I've been putting Dehums in my houses for about 4 years now and I've yet to get a noise complaint. Best, Matt
@ejkessler : ERV vs HRV is a frequent question for people in the middle 1/3rd of America like you. North of you is all HRV country, South is all ERV. You probably could go either way. Remember that an ERV is not dehumidifying your inside air. It's simply rejecting SOME of the incoming moisture from the air stream coming from outside. If you are dealing with humidity issues the stand alone Dehum is the way to go. Martin Holiday has a great article on GBA about this topic.
http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv
Regarding the heat pump water heater and the XT105 Dehum, I think those would work well together in your basement. The Dehum will produce "some" heat and the HPWH will product some cool air when running. Depending on the model you can get 1/3-3/4 Ton of AC when it's making hot water, but remember that it's going to run mainly after hot water events like showers/baths/laundry/etc.
Hope this helps, Matt
Wow Matt,
That is excellent. I've read a fair number of articles but never heard it stated so clearly that the ERV did not dehumidifying my inside air but that it was only rejecting SOME of the Incoming humidity moisture. Thanks you!
- So its best to just get the HRV and somehow connect it to the XT105 Dehumidifiers?
- Do the Venmar HRV and XT105 output/input tubes the same size?
- should the XT105 be in line Before or After the Venmar HRV ?
Thanks so much again,
Eric
Sorry Matt,
in my above question, I forgot to include the Aprilaire Media Cleaner #2210 (not sure about UV Light) and what order/arrangement the media cleaner, Dehumid & HRV all connect?
Thx,
Eric