June Energy Report

Summer is here so it's time to review energy use during the start of the air-conditioning season.

June HVAC
At 211 Cooling Degree Days (CDD), this June was about 30% above the historical average. The following graph from our Weather Underground station shows the daily temperatures for the month.  It's a bit hard to read but the key information is that we had several days in the mid 80's with a high of 87.  The average temperature for the month was 75.

By comparison, the average June temperature in downtown Atlanta was 81.4 and the high was 100.2.  The climate on the mountain is much more moderate.   Although the average temperature was only 6 degrees cooler here, the extreme high was 13 degrees less which makes a BIG difference in air conditioning.

We rarely run the AC unless the temperature goes above 85. In June we ran the AC for 2 1/2 days.  The total HVAC energy use was 15 kWh or roughly $1.50.  Not Bad for a month that was 30% warmer than average.

ISSUES
While it hasn't been hot enough to make the house uncomfortable, we have a lot of days where the indoor temperature gets into the low to mid 80's. Although this hasn't forced us to run the AC very much there are a couple of issues that I need to solve which will make the house more comfortable.

The temperature at night is generally in the upper 60's or low 70s.  In theory, we should be able to open the windows at night to cool the house down and close it up during the day to keep the heat out. But, we are failing on a couple of accounts.

It's around 9:00 AM right now.  The picture below shows that it's currently 73 degrees outside but the slab is still at 77 degrees from the day before.  In the late afternoon the slab temps will go into the low 80's and stay in the upper 70's all night.

The first issue, is the large amount of west-facing glass.   I knew this would be an issue when we designed the house but we wanted the view (it's awesome) and wide-open access to the deck. The windows are shaded most of the day but the sun pours in for two - three hours starting around 4:00.

There's roughly 120 square feet of west-facing glass so just a few hours of sun contributes a lot of heat.

Obviously the best way to keep a house cool is to keep the sun out in the first place. However, we hate to block the view.  I will probably use shades as a temporary solution but plan to build a pergola on the deck next summer.  This should shade the windows without blocking the breeze.


The second issue is insufficient ventilation.  Although it gets cool at night and the air temperature in the house is comfortable there just isn't enough air flow to pull the heat out of the slab.  If we can get the slab down to 70 degrees at night then it will keep the house cool all day.

Opening the big accordion door dramatically improves the ventilation but we don't have a giant screen for it so we never leave it open at night.  One of our current priorities is to find a screen system that will allow us to get full benefit from this door.