Heat Flow Electric Furnaces energy efficient design lesson bungalow tampa lg squared inc

Whennd 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 as a result be more comfortable and use less energy. The sales team for the Midtown condo 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! If we only knew then what we know now!

In our first winter, we had an electric bill pushing $300…for 900 square feet!!!

Let me qualify one thing before I go in to what we have discovered over the last four-and-a-half years about this “energy hog” we call our home; Jodi 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

Heat Flow Electric Furnaces energy efficient design lesson midtown atlanta lg squared inc

her on 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 70 in winter, which is already much higher than we want to have to keep it, we are still layering up. It was that 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 in our first Atlanta 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? Even at the height of summer, the sun is "blocked" until about 6:00...in the evening!

Anywho!! The answers were over our head and beneath us…literally! But, that's not all.

Answer #1

Heat Flow Electric Furnaces energy efficient design lesson midtown atlanta post tention slab thermal bridge lg squared inc

One of the main design features of this building is all of the exposed concrete columns and ceilings, and one of the amenities are the cantilevered balconies in every unit. 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). A thermal break in the slab, between the balcony and the condo interior, would have stopped all heat loss and gain. Alas, our energy savings was less important to the developer than construction savings. It's not the only area they cut corners during construction.

Answer #2

Our heating and cooling (split) system is oversized, extremely in-efficient, and improperly designed. A combination that causes short-cycling and unbalanced air distribution.

  • The air conditioner is a 13 seer, 3-ton system (36,000 btu/h - remember, 900 s.f., which is even too big using the rule of thumb of 400-500 s.f./ton. Based on the Manual J load calculation, the system is over-sized by at least 1.2-tons, or it has 160% more capacity than it needs. (Cooling Load: 21,875 btu/h, mostly due to the poor glazing, thank you very much!!)
  • The heat is entirely supplied by an 8kw strip heater! Yes, it's 100% efficient, but that's not very good for electric heat. It's like heating the condo with a toaster...not good.
  • The static pressure levels and poor duct design cause as much as 5-8 degrees temperature differential between rooms.

Answer #3

The floor-to-ceiling windows on the west side of the condo is made with an aluminum storefront system with reflective, double-pane glazing. The aluminum frame has no thermal break, and despite its reflective properties, the glazing allows an unusual amount of heat in during the summer months. I'd like to say that this helps in the winter, being west facing, but nope! The glazing has a poor U-Value (thermal resistance) and SHGC (Solar Heat Gain Coefficient). The lack of a thermal break is the most apparent (or painful!) 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!)

What Are the Solutions?
  1. 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.
  2. Cantilevered Balconies. Cut the balconies off (wink-wink, this is not possible) and add a thermal break, like this one, 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 approach,  we would also need to insulate the rest of the slab edge (where there isn’t balcony), which is covered with a continuous aluminum trim to hide the exposed edge. (Piece of cake, right?).
  3. Storefront. Replace all storefront windows in the building with a system, like this one, that has a thermal break (nylon) within the frame, and better performing glazing. (Not cheap)
  4. Heating and Cooling. Replace the existing illegal electric furnace (not allowed by Georgia Energy Code) and A/C system with a right-sized, higher efficiency air source heat pump system (with variable speed), along with right-sized ductwork and new layout. Now we're talking. Better yet, replace it all with a ductless mini-split heat pump system that will be about 250% more efficient (3.5 COP) than the illegal electric furnace (1 COP) we have now.
  5. OR...the developer's design team could have approached the design the building with energy efficiency in mind. Even the slightest bit of effort could have saved a lot!
The case for energy efficient design
Heat Flow Electric Furnaces energy efficient design lesson energy efficient design lg squared inc

I'm not sure what the payback for upgrading our systems and replacing the windows throughout our building, but considering how inefficient everything is now, it may be relatively short.

Fixing the inefficiencies is not what we should have to do, though. Avoiding these fundamental flaws in the design and construction process is our biggest opportunity for reducing our energy use and increasing comfort and value!

As many of us do, I appreciate beautiful buildings. Designing them to be efficient, durable and comfy does not mean making them ugly.

It takes thought. That’s all.

Stay Tuned...

We did come up with two solutions for the inefficient HVAC system and ductwork. One of them we've been living with for the past 3 years, and it's reduced our energy use by as much as 20%. The other is under way, and it involves a fairly significant (and exciting) upgrade!


No items found.