Chris is a licensed architect and energy efficiency professional who leads Energy Vanguard’s Design and Technical Services.
Follow Chris on Twitter: @claumergiddens
When my wife and I moved from Tampa to Atlanta in 2008, we decided to try high rise living. We were living in a 1916 bungalow, which we loved dearly, and looked forward to something fresh and new. Something that would not leak like a sieve, and that wouldn’t use so much energy. The sales team for the Midtown condo development we now live in told us what we wanted to hear, “average electric bills will be around $50 – $80 for your 900 square foot unit.” Great! Sign us up!
Bubble Burst – Last winter, we had an electric bill pushing $300…for 900 square feet!
Let me qualify one thing before I go in to what I have discovered over the last two years about this “energy hog” we call our home; My wife and I have always been conscious about the amount of energy we use, and we’re constantly reminding each other to turn the light off when we’re not using it, and I’ve tried to sell my wife the idea, “If it’s yellow, let it mellow. If it’s brown, flush it down.” (Not happening!). We also layer up in the winter to keep the thermostat down, etc. The list goes on.
It turns out, even when we set the thermostat to 78 in winter, which is already much higher than we should have to keep it, we are still layering up. It was our first winter here that we realized that there is something strange, if not wrong, about the design of this “fancy-shmancy” brand new condo, with it’s post-tensioned slabs, floor-to-ceiling double-paned windows, and a ‘state-of-the-art’ fitness room. In fact, the summer months proved to be just as bad. We topped out this past August at $167! Have I mentioned it’s only 900 square feet?
So, what’s the problem? When we asked the developer, they offered little, other than, ‘Georgia Power this and that’ and ‘The building across the street blocks the sun.’ Seriously?
Anyway, the answers were over my head and beneath me…literally! But, that’s not all. The following is what we’ve discovered, so far:
Answer A
One of the great design features of this building is all of the exposed concrete columns and ceilings. And, one of the greatest amenities is the cantilevered balcony in every unit. But, they are also both among the leading contributors to our problem. All that wonderful heat being forced in to our condo in the winter from our electric furnace (I’ll talk about that next), is being sucked right out through those concrete slabs and columns that surround us in every room (and, vice versa in the summer). Due to the nature of post tension slabs and cantilevering, thermal breaks were not an option.
Answer B
Our heating and cooling (split) system is oversized, and improperly designed, causing short-cycling and unbalanced air distribution.
- The air conditioner is a 13 seer, 3-ton system (remember, 900 s.f.), which is even too big using the ‘rule of thumb’ of 400-500 s.f./ton. Based on the load calculation and rating I’ve done, it’s over-sized by at least 1.5-tons. (REM/Rate calculated a required cooling load of 11,700 btu/h.)
- The heat is entirely supplied by an 8kw strip heater! Yes, it’s 100% efficient, but that’s not very good for electric heat.
- The static pressure levels and inadequate duct layout cause some rooms to feel as much as 5-8 degrees cooler or warmer than the room with the thermostat.
Answer C
The “wall of glass” on the west side of the condo is an aluminum storefront system with reflective, double-pane glazing. Despite its reflective properties, the glazing allows an unusual amount of heat than expected during the summer months. I’d like to say that this helps in the winter, being west facing, but nope! Like with many things during the construction of the building, the developer cut corners. The glazing has a poor U-Value and SHGC (Solar Heat Gain Coefficient), and the storefront system they chose came without thermal breaks in the metal frames. This is most apparent in the winter, when the mullions are literally too cold to touch. (I dare you to stick your tongue to it! I triple-dog dare you!)
Solutions?
- Concrete Slab. Apply a few band-aids to the thermal bridging problem by adding rigid foam insulation to the floor, ceiling, and columns. Although we would lose the ‘exposed’ design feature, we might gain a little more efficiency and comfort.
- Concrete Slab. Cut the balconies off (impossible) and add a thermal break before reattaching the balconies with concrete or metal columns running the full height of the building. (That’s attractive!). To be completely effective with this logic, though, we would need to insulate the rest of the slab edge (where there isn’t a balcony), which is covered with a continuous aluminum trim to hide the exposed edge. (Piece of cake, right?).
- Storefront. Replace all storefront windows in the building with a system that has a thermal break (typically neoprene) within the frame, and better performing glazing. (Yeah, cheap fix.)
- Heating and Cooling. Replace the existing split A/C system with a right-sized, somewhat higher efficiency (14 or 15 SEER) air source heat pump system (with variable speed), along with right-sized ductwork and new layout. Now we’re talking.
- OR…the developer’s design team could have designed the building with energy efficiency in mind. Even the slightest bit of effort could have saved a lot!
The case for energy efficient design
The payback for the upgrade of our HVAC system would be approximately 3-5 years, and we will most likely end up doing this. But, fixing the problems is not the point of this article. How to avoid inefficiencies and sucking energy is.
The fundamental flaws are in the design and construction approach of the building.
As many of us do, I fully appreciate beautiful buildings, and that sacrifices are sometimes made to achieve beauty over performance. But, there are a great number of high performance buildings that are just as amazing as any other structure out there. In fact, some of the more notable high performance buildings (homes included) have used energy efficient features successfully as design features.
It takes thought. That’s all.
