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 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 and 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'm a proponent of 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. Thus, HVAC+D. 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 project with the famous 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.
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