When the A/C season was at its height in 2008, I was using up to about 1200 kWh per month. At the height of the heating season, I racked up over 3,300 kWh/mo. (My heat pump is much less efficient when it heats the house than when it cools it.) I wanted to try to find out how much electric power I was using for heating and cooling alone.
In order to do this, I decided to find out how much power my house uses when the heating-cooling system is completely turned off, along with all appliances, devices, and lighting not on 24/7. Now, I have a number of things that are always on. These include high-tech stuff: two computers, two TiVo digital video recorders, a cable-TV DVR, two Apple TV devices for pumping video and audio from iTunes to a TV, several Apple AirPort devices for wireless home networking, several hard drives, etc. There are also some fluorescent lights that I keep on about half the time to make my indoor plants happy. I turned half of these fluorescents off along with the heat pump-based heating-cooling system, and checked my electric meter to determine how much power my house consumes in "baseline" mode.
The easy way to do this, if you, like me, have a typical (non-digital) electric meter, is to look at the spinning wheel below the five dials on the meter's face. This wheel is mounted horizontally in the meter such that you look at it edge-on. You can time how many seconds it takes the wheel to make one full revolution, then plug the result into this formula:
kW = (3.6 X Kh )/ no. of seconds per revolution
Here, 3.6 is a constant which makes the formula yield the number of kilowatts of power that is being used, and Kh is a numerical factor that is printed on the face of the meter, and is usually 7.2. (My Kh is in fact 7.2; it may be different, however, for your meter.)
I found in my experiment that my wheel revolved once every 58 seconds, so I determined that (3.6 X 7.2)/58 came to about 0.447 kW, or 447 watts. So my house draws approximately that many watts of electric power in its "baseline" mode. Multiplying that figure by 24 hours per day, my house uses about 10.7 kWh a day of "baseline" power, or (in a 30-day month) 321.8 kWh.
At that point, I decided it would be wise to up that figure just slightly to allow for "non-discretionary" appliances like my refrigerator and water heater that come on automatically at various times during the day, but were probably not on when I checked the meter. I accordingly decided to use 350 kWh per month as my actual baseline figure.
If I assume a 350-kWh baseline for everything except A/C and heat, my total yearly usage would be just 4,200 kWh. That means roughly 15,000 to 16,000 kWh (just under 80%) of my annual electric power usage goes to power (a) things that are occasionally on at my discretion during various waking hours or (b) supposedly non-discretionary heating and cooling.
Among the "discretionary" (a) things are:
- electric lights, which until recently were a mix of incandescent, halogen, fluorescent, and compact fluorescent — though I've lately been going around the house replacing incandescent light bulbs with compact fluorescents. I've also been more consistently turning off lights when I leave the room, instead of leaving them on much of the day. But during the last twelve months I was, I am ashamed to admit, customarily more wasteful
- my two computers in their "working" mode, with their LCD screens brightly lit, and not in their nighttime "sleep" mode with their screens off or dimmed
- my three high-definition TVs ... though at most one is typically on at a time
- my household appliances that are used only sporadically, such as my electric range, dishwasher, washing machine and dryer
- a space heater in my basement that I generally keep on all the time in the dead of winter, but off in spring, summer, and fall
In the past twelve months, my lowest electric bill (in September 2008) showed that I used about 750 kWh that month. September 2008 was a month of moderate temperatures here in Maryland in which I did not run my heating-cooling system much at all. I'm willing to assume for the sake of further discussion that I used only roughly 100 kWh for cooling my house during that mild month — meaning that my discretionary usage in September was about
750 (total) - 100 (cooling) - 350 (baseline) = 300 kWh.
Now, I know I can lower my discretionary power usage somewhat through such conservation measures as switching to energy-efficient lighting and turning lights off when I leave the room. Still, assuming a monthly baseline 350 kWh and a typical discretionary usage of 300 kWh during the last twelve months, I feel justified in believing that anything over the sum of those (650 kWh in any given month) was getting sucked up by my heating and air conditioning use.
650 kWh per month times 12 months per year is 7,800 kWh per year. But in the last twelve months I actually consumed 19,828 kWh of power, meaning that about 12,000 kWh went for indoor comfort — 1,000 kWh per month, on average. At 14.5 cents per kWh, I paid $1,740 in electric power charges just for comfort in the last 12 months. I paid just $1,136 for everything else I used electric power for. So 60 percent of my total electric bill went just for heat and air conditioning, while 40 percent went for everything else.
Now, these figures are very rough estimates, and they may be off by a considerable amount. Yet it's clear that my switching to compact fluorescent bulbs and keeping the lights off when I'm not in the room is not going to save terribly much on my electric bill. But if I can get my annual heating and A/C power consumption down by 65 percent, I'll save a whopping 650 kWh/mo. on average — enough to power everything else in my household "for free."
So my first imperative would seem to be to do what I intended to do last spring, but put off: replace all 11 windows in my nearly-30 year old town home with windows that are super-energy efficient. My present windows are the "el cheapo" single-glazed aluminum jobs that the original builder installed back when energy was cheap and the term "global warming" was unknown. These windows don't have newer ones' two glass panes separated by a mixture of argon and nitrogen for greater insulating capacity. Plus, the metal they are made from conducts heat into the house in summer and out of the house in winter. Add to that the fact that they use old-fashioned, non-airtight storm window inserts and are themselves air-leaky owing to the house having settled over 27 years, and you have a recipe for terrible home heating and cooling efficiency right there.
I should also note with a great deal of sheepishness at this point that last winter I neglected to deploy the storm windows. Out of sheer inattention, I let ungodly amounts of indoor heat escape into the great outdoors through my windows' lower sashes that did not have their storm window inserts in place. Coupled with the fact that my heat pump is not nearly as efficient in heating mode as it is in cooling mode — and that when the outside temperature is well below freezing, I actually am better off using the "emergency" resistance heat from my indoor electric furnace — my failure to deploy storm windows boosted my power usage during the winter of 2007-2008, and thus during the entire period of the last twelve months, by an unknown but sizable amount.
Needless to say, I now have my storm windows in place for the onset of winter 2008-2009. Also, I have in fact arranged for all eleven of my windows to be replaced in late January 2009 with extremely energy-efficient ones. So my electric bills can henceforth be expected to be much lower than they were one year ago.
How long it will take for the energy savings of the window replacement project to offset my up-front costs of a little over $800 per window, installed, will comprise a period of six-to-eight years, according to the salesman. That guesstimate is probably on the optimistic side, but if the roughly $9,100 cost of the project generates just $910 a year in electric-bill savings for me, the whole thing will pay for itself in ten years.
$910 is roughly half my $1,740 current yearly outlay for heating and cooling. It's not the 65 percent reduction I'm ultimately looking for — and it remains to be seen whether that reduction can actually be achieved — but it's a start.
If you are thinking about replacing your windows, keep in mind that you can get considerably cheaper windows than I'm getting, if you go for vinyl or clad-wood replacements. The kind I'm getting from Renewal by Andersen are made of an extremely durable material called Fibrex that will deteriorate less quickly over time. Also, these windows never need painting or maintenance. I figure these high-end windows will add enough extra to the resale value of my house to justify the extra expense.
Also, whatever price you pay for replacement windows, as long as they meet minimum standards of energy efficiency, they can generate up to $500 of federal income tax credits, spread over three tax years. In my case, the credits amount to roughly five percent of my out-of-pocket costs. If you get fewer and/or cheaper windows, the percentage would most likely go up.
Once I get the windows replaced, my next moves will likely include:
- getting an "energy audit" to determine where else my house is wasting energy
- possibly adding more insulation in my attic, if the audit so indicates
- replacing my 15-year-old heat pump and backup heating system with one that hopefully will be more efficient, particularly in its wintertime heating mode
Possibly doing all those things will get me up to the magic 65 percent level of savings!
No comments:
Post a Comment