Wednesday, July 21, 2010

A Traitor in Our Midst

It is hot. Hot. Hawt.

For at least the past week the heat index has been at or above 100 degrees. For the next five days or so it promises to be the same. When I walked home from work yesterday the heat index was 107 degrees.

It's hot.

Gone are the glorious days of getting by with only the attic fan. Those were good days - we could run the attic fan for an hour in the morning and let it suck in all the cool air. Usually we could drop the household temperature down to nearly 74 degrees just by running the attic fan for an hour in the morning. Then we would shut the windows and close the curtains. By late afternoon it could be in the lower 90s outside, but the inside temperature of the house would rarely break 80 degrees. And then again in the evening we ran the attic fan for an hour to once again pull outside air in to cool down the house.

But you can only get by with that pattern if the nighttime temperatures drop below 75 degrees and the daytime temperatures and humidity aren't ridiculously high.

Friends, the daytime temperatures and humidity are ridiculously high. It's air conditioning time.

When we first caved in and decided to use air conditioning we agreed that we would keep the thermostat set at 85 degrees; cool enough to not suffer but warm enough to feel like we're still making sacrifices for the rationing program.

In retrospect, that was kinda a bad idea. See, the thermostat is on the main floor but the bedrooms are on the upper floor - and they typically run four to five degrees warmer. This means that we were sweating it out at near 90 degrees some evenings.

Research says that the ideal sleeping temperature is between 65 and 68 degrees. Friends, it is virtually impossible to sleep well at 90 degrees. You toss and turn, rotating body parts to expose to the nearby fan. You are cranky the next day. This is not good.

So we compromised again and decided that while the daytime thermostat temperature would still be set at 85 degrees, the nighttime thermostat temperature would be set at 81 degrees.
This definitely made for a slightly less cranky household. Still a little uncomfortable, but less crabby than before.

In the meantime, we were anxiously awaiting the monthly electricity bill. This summer and last summer started out very similar - a slightly cool May and June, with the exception of one week that was near 100 degrees. This similarity allowed for an apples to apples comparison to determine how much the attic fan was saving us in electricity (and money) during most of that period.

Since we didn't have the attic fan last year we didn't have an efficient way to pull in the nighttime air to cool down the house and avoid running the air conditioner during the day. So the kilowatts used this year should be noticeably lower, since the air conditioner (with it's big compressor and frequent cycles) was used more last year.

The electricity bill finally came this week. The results?

Kilowatts used in mid-June/mid-July 2009: 970 (32.3 per day)
Kilowatts used in mid-June/mid-July 2010: 1008 (32.3 per day)

Aack! Barely a difference - and actually a marginal, statistically insignificant increase! What gives?

True, we've been running floor fans when benefiting from the attic fan, but we still ran some floor fans last year when the air conditioning was on (although not quite as often).

True, the attic fan uses electricity, but surely running the attic fan for two hours a day uses less electricity than having the air conditioner on for 24/7?

Why, oh why, wasn't the electricity bill lower?

Floor by floor we reviewed the electricity being used, eventually ending up in the basement. And there, friends, we found our traitor: the dehumidifier.

Dehumidifier are notorious energy hogs. We knew that when we were shopping for a dehumidifier several year ago and chose an Energy Star model as a result. Unfortunately, even an Energy Star rated dehumidifier can still be an energy hog. And we think ours went a little wild in the last month.

While we were saving electricity by using the attic fan rather than the air conditioner, the result was higher household humidity levels. The higher humidity levels caused the dehumidifier to run more often than if we had instead run the air conditioner (which is, by itself, an effective dehumidifier).

Two steps forward, one step back. It was like we were sabotaged by an often-ignored appliance. Sigh.

So now what do we do? Keeping in mind the seemingly never-ending 100 degree heat wave, we basically have six options:

1. Screw the air conditioner and use only floor fans and the attic fan. Turn off the dehumidifier.
2. Screw the air conditioner and use only floor fans and the attic fan. Change the setting on the dehumidifier so that it does not run as often.
3. Run the air conditioner, but set the thermostat at a higher (80 to 85 degree) temperature. Because having the air conditioner set at a higher temperature means it does not run as often this, in turns, means the household humidity is a little higher. As a result the dehumidifier runs more often.
4. Same as above number 3, but change the setting on the dehumidifier so that it does not run as often.
5. Run the air conditioner, but set the thermostat at a more traditional temperature (78 to 80 degrees). Keep the dehumidifier setting as-is, with the understanding that it will still run frequently, but not as frequently as in the above scenarios.
6. Same as number 5, but adjust the dehumidifier controls so that it does not run as often.

The first two options are basically out since they would most likely result in a complete destruction of the Rational Living household (really, how did people survive the summer in the 1940s without becoming The Incredible Hulk?). I don't like the idea of higher humidity levels in the house, since this is an old house and it can get a good "old house funk" thing going when humidity levels get too high. But we still want to save energy.

So what would you do?

--Rational Mama


  1. I can't really say what I'd do, but I can share that we spend LESS money on electricity when we run our central air conditioner than when we turn it off and rely on windows only.

    I think that like you, we end up having our dehumidifier running more often when the air conditioner is turned off.

  2. I've found that the dehumidifier costs more to run than the air conditioner. When it's extremely hot and humid, I also find the air conditioner does a better job of pulling the moisture out of the house. If it was my decision for my household, I would shut off the dehumidifier when the air conditioner is running.

  3. I've had similar experience with dehumidifiers -- here's my cautionary tale:

    Putting on my home energy auditor hat for minute, it sounds like your dehumidifier is underpowered (too small) to be charged with dehumidifying the whole house. If getting rid of humidity without getting rid of heat were what you wanted to do, I would say get a bigger dehumidifier. But that's not what you want to do... your biggest humidity problem is also at the hottest time of year, and the dehumidifier is actually increasing the air temperature, so you're better off just running the AC that is sized appropriately for the house. So put the dehumidifier where the biggest humidity problem is (probably the basement) and use the AC to make upstairs tolerable.

    This is assuming that mold damage to your house and possessions is not part of the plan for WWII authenticity. ;-)

    I'm curious how the dehumidifier got below your period-appropriateness radar, Rational Mama... surely homes in the 40s without ACs also didn't have dehumidifiers, right? I mean, it's the same technology...

  4. The dehumidifier is only for the basement and does a sufficient job for that area. We weren't trying to have it dehumidify the entire house, but when the entire household humidity level was higher (including the basement) when the A/C was not running, then that triggered the dehumidifier in the basement to run more often. After reading your experience, Ben, I wonder if it is low on coolant. Maybe I should call the manufacturer?

    And yes, the dehumidifier is not period-appropriate, but it is an important component of maintaining the basement environment of this 100 year old house. As we've said on the blog before, we're going for the modern equivalent of rationing. :)

  5. I would go with the AC and decrease the dehumidifier. Have some sanity in this insane heat.

  6. Hi, I've been reading your blog almost since the beginning but have not commented before.

    In your picture on the post it says turn off appliances when not needed in order to save electricity. In my opinion, the air conditoner is needed not only for the people in your house to function but also to avoid repairs in your future. I say go for the air.

  7. Thanks for all the input! So the A/C is now set at 80 degrees during the day, 78 degrees at night and we've turn the dial down on the dehumidifier without negative consequences. Whew!

  8. BTW Michelle, I plan to use your dehumidifier story as an example in the "Non-Obvious Weatherization" class I'm offering tomorrow night at UUFT. Hope you don't mind; in fact, I hope you can be there!