Break Down

I finally broke down. At the same time we are "suffering" from record low high temperatures I finally broke down and will be replacing my AC unit next week.

While I had originally considered getting the most efficient system I could buy, I ended up moving from a 4-ton Carrier unit to 5-ton Ruud and from SEER 10/6 to a SEER 16/13 -- primarily due to economics. There are more efficient units, yes; however, as you run through the house energy calculations against the cost differential, a more efficient system really isn't all that cost effective, particularly as these systems are usually grouped together (condenser to heat exchanger) by whoever is trying to sell them.

Nonetheless, here's my estimated calculations on the energy draw:

My existing 4-ton unit, if allowed to run for 24 hours, would produce the same cooling effect as a four ton block of ice in my living room allowed to cool from ice to liquid. The latent heat of fusion for a ton of ice is 288,000 Btu. So on an hourly basis, divide by 24 and I get 12,000 Btu per ton of ice.

4 ton unit * 12,000Btu/h * 1,000h * $.15kWh / 10Btu/Wh / 1000W/kW = $720 per year...total yearly load -- 4,800kWh.

vs. a 5-ton unit producing equivalent cooling:

5 ton unit * 12,000Btu/h * 800h * $.15kWh / 16Btu/Wh / 1000W/kW = $450 per year....total yearly load -- 3,000 kWh.

So I should use about 1,800 kWh less next year, along with a $270 savings.

As I had mentioned earlier -- 1,800 kWh savings is almost 2/3rds my entire solar PV array output. And truthfully, the increased comfort level in my house is really what's driving my decision here -- our upstairs bedroom is painfully hot during the summer and this should help alleviate that.

Besides, immediately following the upgraded duct work I will get the R34 attic insulation installed which unfortunately isn't quite so easy to calculate the energy savings...but I will measure it in comfort, along with mental perception on how often the AC seems to stay on.

Hope this works for me...