7 Comments

1. GBA Editor
   Allison A. Bailes III, PhD | Jul 12, 2012 06:17pm | #1

   What about load calculations?
   That's not a bad start for someone who's never owned an air conditioner, Alex. :~) For those of us in the Southeast, who have difficulty even imagining life without air conditioning anymore, there's a bit more about this subject that should be said. First, let's go right to the humidity issue. You said:

   If humidity is a problem, look for models that are effective at moisture removal.

   The first step, though, would be to make sure you get an air conditioner that's not oversized. To do that, you need to know what size is appropriate. The most common way to do that is with software based on the Manual J heating and cooling load calculation protocol from the Air Conditioning Contractors of America. It's not just about getting the right type of equipment.

   Also, I'm pretty sure that heat pumps are not excluded from the minimum SEER rule and have to be rated at 13 SEER or higher, same as air conditioners. I don't know that I've actually seen the rule from the US DOE, but every reference to it I've ever seen puts air conditioners and heat pumps in the same category here.

   Then there's the distribution system. Unless you're going with a window unit or ductless mini-split heat pump, you'll need ducts. My advice: Spend more on getting the best duct system you can and forget the super high efficiency equipment. I see people make this mistake all the time, and it's so frustrating to see, for example, an 18 SEER AC attached to a crappy duct system that might be 50% efficient.

   And finally, I agree with you about mini-splits. I like them a lot for the reasons you mentioned and more. The condensing units are whisper quiet, and you can get them in smaller sizes, too.

2. 
   user-1030217 | Jul 15, 2012 01:07am | #2

   heat pumps are indeed subject to minimum SEER standards
   CFR 430.32 covers energy efficiency standards see:

   http://bit.ly/MqvLOW

   Under the current rule, split heat pumps and air conditioners must have minimum SEER of 13. Beginning January 1, 2015, the minimums change, depending on the region. In the north, straight AC will stay at 13 but heat pumps will increase to 14 SEER. Furnaces in northern states will have to be at least 90%. That part takes affect in less than 10 months!

   Here's a summary of the changes from ACEEE. Note: this document pre-dates the final rule, so the implementation schedule shown is incorrect.

   http://www.aceee.org/files/pdf/1009hvac_fact.pdf

   As for the rest, I'm with Allison... I can't believe I just read an article on choosing an A/C without any mention of proper sizing, especially given the attention to moisture removal. If an air conditioner is significantly oversized (thus leading to short cycling), the coil may never get cold enough to condense any moisture. And BTW, for an air conditioner, moisture removal capacity is typically specified in terms of latent capacity or sensible heat ratio, not in pints per hour. That sounds more like a dehumidifier spec.

3. 
   LetsDoThis | Jul 19, 2012 01:10am | #3

   Beyond Condensers and Heat Pumps to New Chiller Technologies
   IMHO it goes without saying that properly sizing the equipment based on the load calculations (and whether or not buildings are properly air-sealed and insulated, etc.) is necessary, and I suggest Alex presumed readers would instinctively realize that.

   Also, an entire article could be written addressing all the steps necessary to properly prepare a building so that loads may be more precisely calculated and correctly sized equipment installed.

   I would like to note that Alex did not cover the new chiller technology (water source heat pumps) recently developed by Mestek Industries SpacePak divison, or the SDHV air management technologies that are now sweeping the globe.

   Already in use by the US military for years and found in installations on every continent, SDHV systems transcend current rules for minimum SEER requirements. Numerous drafts have been in development for the establishment of the standards for the energy efficiency testing and life-cycle analysis of these systems since about 2000, yet none as of yet have been ratified and adopted by the DOE. See here:
   http://www1.eere.energy.gov/buildings/appliance_standards/residential/small_duct_ac.html

   Nevertheless, these systems have been gaining in popularity over recent years due to their documented extremely high efficiency. Using super-silent high velocity VFS fans that create an air column which draws air in a room towards it, causing an aspiration effect, it more quickly blends with room-temperature air instead of attempting to replace it. Because these systems don't work on the same principles as conventional HVAC equipment, they use dramatically less energy to process less air more quickly, and standardized testing methods for conventional HVAC systems don't apply.

   One of the "coolest" things about these systems is the supply air termination. They're almost invisible in most installations; there are no unsightly supply vent grilles, returns may be nearly anywhere in the envelope. The newest air cell technology even eliminates the need for thermostats, and the DC VSD fan motors use less than 180 watts when running at full capacity, with an average energy consumption of less than a 90 watt light bulb when supplying air to a single zone.

   See more here: http://spacepak.com/products/aircell-efficient-airhandler.asp

   The SEER equivalency ratings might be well into the 30's, and because it does process a smaller amount of air so much more quickly, it draws the humidity out at nearly three times the rate of a conventional HVAC system.

   There's also an interesting slideshow on the FutureSource Initiative at http://abidesystems.com that points out requirements for current and upcoming DOE building efficiencies.

4. 
   recentcoin | Jul 19, 2012 06:30pm | #4

   Texas Summers
   I have always been taught that when a customer is bordering on needing the next size unit to oversize the AC. The prevailing wisdom here is that choosing to oversize AC units here because of the extreme summer heat keeps the unit from straining under peak load and results in more efficient operation. My acedotal experience bears this out. If somone has studies to the contrary I would like to see them.

5. 
   DavidButler | Jul 21, 2012 03:28pm | #5

   high velocity not inherently more efficient
   @Mic, the tenor of your comment sounds like you have a vested interest in promoting this product. I'm aware of the rulemaking attempt for SDHV systems such as SpacePak and Unico. There's a good reason this has gone nowhere. While these systems are great for solving access issues -- for example, in older homes with radiators -- it's ludicrous to think high velocity systems are somehow inherently more efficient than similar conventional systems, since all else being equal, HV blowers consume more power per BTU delivered. That's why they've had trouble meeting Federal minimum efficiency ratings.

   Comparisons touted on the manufacturer's websites are never based on equivalent systems -- PSC vs PSC, ECM vs ECM, ducts inside the envelope vs ducts inside the envelope. Tight ducts vs tight ducts. SDHV propoents always like to compare to a non-equivalent (poor) baseline. These companies would have you believe their equipment is better than everything else, all the time. It's simply not true.

   The argument for establishing a separate efficiency procedure originated with the idea that these systems have tighter ducts with significantly less surface area than conventional equipment. Less surface area means less conducted heat loss to unconditioned spaces and smaller leakage paths. True enough. However, reduced duct surface area provides virtually no benefit if the ducts are installed inside the envelope. Virtually all of the systems I design have conventional duct systems inside the envelope, and all are verified to meet strict air leakage standards.

   More importantly, duct system efficiency should never be reflected in manufactured equipment ratings since design and installation practice has such a large impact on in-situ performance.

   Admittedly I'm unfamiliar with spacepak's new new ground source chiller and aircell technology, but if it uses high static, high velocity air distribution, it cannot be as efficient as a similar product on an apples-apples basis.

6. 
   hootie | Aug 20, 2012 05:58pm | #6

   Dave Butler's comment vs RP Mick's
   Ironically, there was an ad for Unico on this very page, and it captured my interest.
   I think new technology is a good thing and we need some out of the box thinking.
   If the chillers can remove 30% more moisture out of the air in HOT and Humid climates, I think it might be worth a try.

   Has anyone reading this ever had one installed in their home?

   As I found out first hand with over sized air conditioners, if it short cycles, it is a good case for black mold issues in the house.

7. 
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