home a/c efficiency

Is there incentive from the local utility provider to change your behavior?

Out here they’ll charge more during “peak times” therefore prompting thought on changing your comfort parameters.

Her parents (who live 5 doors down from us) say “meh” to this and they leave their house at 73 all the time.

Us on the other hand (remember my CFO is thrifty) sets the thermostat higher at 78-80 then we turn it down at night to 72.

All depends on the equation and your comfort.

 

How efficient is your AC? Older unit?

We installed a new 2 stage unit when we moved into our house (the old unit was 22 years old and you could hear it run on the other side of the house).

The 2 stage unit runs at 3 tons and if it needs more due to load or settings, runs at 5 tons. For us, we have a 2 story and we shut the upper thermostat off during the day as no one is up there.

At night just before we go up there for good we set it to 73 F and the 5 tons does it’s job quickly.

With an older unit, I’d not try to make it run any harder than you need to (unless you’re looking to upgrade), so a consistent setting would be easier on the components IMO.

 

Sounds like there might be an opportunity in the air flow and intake space.

We had a similar thing in a house we had in Richmond, VA. When we installed a new unit there, we changed the air flow to make more sense.

That helped a lot.

 

The longer it runs, the more you’ll spend. With today’s heat in the eastern USA I don’t think it’s going to run any less set to 74°F.

 

When the outside temp is X and the interior temp is Y, heat gain is directly related to the delta between X and Y. Keeping the interior of the home warmer will reduce the heat gain and reduce the amount of energy needed to maintain that temperature.

This is independent of any direct solar gain and shading.

 

My point was that the thermostat may already be in hysteresis at 74, so setting it to 72 wouldn’t be likely to back it down from an enduring all-day duty demand on the output terminals.

 

if it’s already running flat-out, leaving the thermostat set low from the night before isn’t likely to help. If it is still only cranking part time then leaving it low in the morning is only going to make it run more.

 

How’s the insulation in the cape?

If you’re not sealed up well, that could be an issue.


A lot goes into the equation .

 

No. The longer you leave the home at higher temperature, the less energy required to keep it at that temperature.

If your system is old or undersized or struggling in the first place, the downward temperature changes could challenge it. Otherwise, it will cool the house to the lower temperature when commanded.

 

No. If it’s only running part time then I didn’t give your system enough credit.

When you slack it back to 74 in the morning it spends less time running to maintain it vs. leaving it at 72. Keep doing that to maintain your savings, you’re already doing it right.

 

It just depends on the end game too

• Is 72 F more desirable for the occupants?
• Is 74 F acceptable?
• Is the system operating and not overworking?
• Is this an experiment to see capability?
• Is this an experiment to see cost effects?
• Etc

I like data based decisions and understanding the ‘why’.

 

While that might SEEM to be the efficient thing to do, sometimes it isn't as good as you think.

Often there is very little insulation BETWEEN rooms......so letting some of then rise to 10 or more degrees hotter tends to make the adjoining rooms feel hotter too.

Also a ceiling fan on LOW can be very beneficial in the bedroom. Might allow you to set the main thermostat up one or two degrees higher.

My programmed thermostat is set similar to what you said......but it only toggles down once; one degree a half hour before our "normal" bed time and back up the next morning.

 

If you get an energy logger like the Spyder you’d be able to get real statistics on how much time it spends running and what it draws. Much better feedback than just waiting for the power bill.