Monthly Archives: July 2011

AC vs heating

99.6 °F in the shade at 2pm. Hotter here in MA than in FL today. Our house reports that it is expecting to use $1 worth of electricity today to keep cool by midnight. We’ll see how well the eMonitor guesses. (Well, $0 really if you count the PVs). But I *try* not to think of the PVs as an excuse to be extravagant.

And this kind of temperature is relatively rare here. Point being, I reckon our AC bill for a year will probably average 1/5 or 1/6 of our heating bill. Or something to that effect. So I can’t personally get too upset about that.

Aside: This is also the time of year when northern honeowners who wisely choose windows with a high SHGC (solar heat gain coefficient) are using a bit more in AC. But it will be offset by their greater savings in winter-time heating.

Sometime I will run a few informal experiments using a standalone dehumidifier instead of (or in addition to) the minisplit AC since sometimes it’s really the humidity (8 people in the house!), not the temperature. Though it definitely is sometimes both.

UPDATE: Actually eMonitor is saying 37 cents (3:30pm) and 16 cents more to go. So that would be 53 cents, not $1. (I have my settings set to $0.15/KWh since last I checked that is relatively close to what we actually pay Hudson Light and Power when you divide out at the end of the month)
So that would be 0.53/0.15 = 3.5 KWh for ONE 100F DAY. Versus, we probably use that much in 2 hours on a very cold day (0F).

See also:
– Here: Erik’s Blog: Latent vs Sensible Loads
– The New Yorker: an article about the rebound effect and the Jevons Paradox
David Owen, Annals of Environmentalism, “The Efficiency Dilemma,” The New Yorker, December 20, 2010, p. 78

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Hazy Hot and Humid

HHH today. 88F and humid and it’s only 11:30am. One funny thing about this house is that the basement is currently the DRYEST part of the house. (The temp/humidity sensors I have scattered about are telling me.) This despite also being where we often hang clothes to dry. (We don’t have/need a clothes dryer.) The basement is dry because of a few reasons I assume: 1) basement is very well sealed and insulated, just like the rest of the house. 2) more people upstairs… breathing, taking showers, cooking mac and cheese, etc. 3) we heat our hot water with a heat pump that sucks humidity out of the air (there is a condensate drain) and that’s in the basement.

Anyway, point is… it’s nice not having a dedicated dehumidifier running 24/7 in the basement.

Another interesting piece of info from the temperature sensors is that the HRV is bringing in that fresh 86F air and turning it into 78F air before it sends it out to the house. So we are getting fresh air even in the summer when the house is closed up for AC on HHH days. But that also means that the AC needs to run a tad more with the HRV running. Not that we used much. It’s projected we will use $8 in AC this July. We used $3 last month. And this is with 8 people living in this small house. So not bad.

I think people in more typical houses could achieve nearly the same thing in their basement if they insulate and seal their basements so that they are part of the “inside part” of their house. The walls and the rim joists are easy enough. One problem is the slab and whether there is insulation or poly underneath it keeping moisture out since that seems to be a tricky problem. I think the idea there is to insulate it and have a drainage mat that leads to an interior perimeter drain. Ask someone more clueful than me!

See also:
Marc’s basement retrofit (in 2 parts)
– A good overview of these issues is Deep Energy Retrofit Workshop
Foundation Insulation Retrofits –

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Filed under erik-green, passive house, superinsulation, zero energy home