Topic: Question for an electrician.. I think

[Bob Wessner]

Is there any way, or some device that I can plug in between some appliance, etc. and the A/C outlet that will accumulate the amount of time the device/appliance was running and drawing current over a period of time?

[CrisPDuk]

There is, it's called an electric meter, and electricity companies use them to decide how much to (over)charge you

Not sure there is a commercially available 'lightweight' version available that's more suitable for your application, but any competent trade electrical supplier should be able to tell you.

[Bob Wessner]

There is, it's called an electric meter, and electricity companies use them to decide how much to (over)charge you

Yup, have one of those. You should see that sucker hum when the A/C is on in the summer and the elec. clothes dryer is going. 

[tsflstb]

Would a clamp-on ammeter work?  Some of the nicer ones have some memory functions, max load, etc...you could do a little math and get the power consumption.

Man I love Harbor Freight.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=42397

I see what you're after though.  Something to plug between the outlet and appliance.  I bet it exists out there.

[crazypj]

Is there any way, or some device that I can plug in between some appliance, etc. and the A/C outlet that will accumulate the amount of time the device/appliance was running and drawing current over a period of time?

I think its called a clock
Probably something like an hour meter as fitted to construction equipment? (and lawn mowers )
I'm sure there is something, as running time meters are used in industry for machine maintenance schedules
PJ

[TwoTired]

Yes. It's the Kill A Watt.

http://www.ambientweather.com/tdp4400.html

I have one. Works great.

Cheers,

[Bob Wessner]

Yes. It's the Kill A Watt.

http://www.ambientweather.com/tdp4400.html

I have one. Works great.

Cheers,

I've heard of these. I see it lists "8 critical functions." Is one of them time? I'm not so much interested in power consumption at any given moment, or min/max draw so much as accumulating the appliance/device useage over a period of time, (e.g., how many minutes was it in use, or drawing current over a 24 hour period?

[TwoTired]

There is a KWH button.  Which gives the power used on this outlet branch since you plugged it in.  It has no built in time of day clock or facility to record when an appliance was drawing power or not.  It does give you cumulative time it has been on, though.

But, if you plug it in at, say, 5pm today and then check it at 5 pm tomorrow, you have the power used in a 24 hr period.  If you check it again next week at 5 PM, you have the weekly useage, and so on.  With this device I was able to determine that a new refrigerator and freezer would pay for themselves in 8 months, and be saving me money thereafter on power bills.

I don't use it often, but it has paid for itself many times over in power bill savings.
Here is a review:
http://www.the-gadgeteer.com/review/kill_a_watt_electric_usage_monitor_review

Cheers,

[Bob Wessner]

Thanks, just the information I was looking for.

[csendker]

The Kill-A-Watt's the way to go for the basic homeowner stuff.  It's a residential grade data logger, whereas a regular data-logger would be the preferred device.  Preferred that is, if you work for an engineering company that has a box full of them and the associated software package.

Not sure what you're exactly after, but the KWH feature would be the one to use if you're looking to justify a new appliance purchase.  At least you could determine the amount of energy utilized by your existing appliance; you'll still have to go on the manufacturer's word for the proposed consumption.  And, of course, the trick is how you compare the appliances.

There are way too many assumptions taken in the basic “EnergyGuide” tag.  (From my new front-load washing machine: “Based on eight loads a week and a 2000 US government national average cost of 8.03 cents per KWH for electricity…”)  With two young kids, we probably do triple that and I sure as heck pay waaaaaaay more than 8.03 cents/KWH.  And I also bet you don’t want to record for a full year to do your comparison either (of course you could divide it out).  So here’s a suggestion:

Watts = amps x volts

Your voltage is 110V (better yet, measure it with your handy-dandy voltmeter, just remember it’s not a 12VDC bike system).  You can usually get the amp draw off the equipment nameplate.  This may be a weak link, but unless you have the right equipment and really know what you’re doing, you probably don’t want to measure the actual amp draw for verification.  As most appliances are “On-Off” devices (as opposed to a variable draw) you can multiply the amps times the volts to get watts.  Divide by 1,000 to get kilowatts.

KWH consumption is the number of kilowatts drawn times the hours used, accumulated over a given period.  So you take this number, divide by the (steady-state) KW draw you figured out earlier and you’ll get the run time over whatever period you chose.  Then you use this run time to reverse engineer the equation based on the proposed appliance amp draw.

It’s far from perfect, but gets you in the ballpark.  Different wash cycles will draw different power loads.  Ice makers will skew things a bit, etc. but it’s good enough for a simple appliance justification.

But do keep in mind the snowball effect some appliances will have.  Like that clothes washer I got, it uses a whole lot less electricity than my old clunker.  But as a front loader, it also uses about a third of the hot water as the old top-loader, saving me a bunch of natural gas in my domestic water heater.  And the spin cycle is about twice the speed, getting everything dryer coming out of the washing machine, so I save even more electricity and gas in my clothes dryer (automatic ‘moisture-sensing’ setting…).  

Ice dispensers in the freezer door means opening the door less, saving energy.  Front-access mini-doors for getting milk or whatever from the fridge compartment do the same thing.  New furnaces have variable-speed fans and two-stage or modulating gas valves.  And NYS has (had last year, at least) a tax credit for upgrading your furnace - don't forget to watch for that stuff too.  And remember the compact fluorescent light bulbs.  I replaced every one in my house that’s not on a dimmer.  I got the cheap ones from HD, and they’re not as white as the real good ones.  I think they’re closer to incandescent.  13 watts instead of 60 watts is a no-brainer.  And thay last a lot longer before they konk out.  I conservatively calculated about a $10/mo savings and then pseudo-verified it in my bills.

Ugh, I think I’m rambling on here….

[Bob Wessner]

Actually, what I'm trying to do is a comparison between keeping the thermostat at a given, constant temp. vs. a 10 degree set-back at night. Common theory is that it saves energy to set it back. I'm curious to know if it is as effective as they say and is there some point, or set of conditions where it's questionable.

On two recent occasions we returned home in the evening after a trip and it was bitterly cold, it was near or below zero during this time. The furnace ran intermittently and maintained the proper temp. as one would expect, hope and. According to the program it set-back 10^o at 10:30 P.M. for 6 hours. Usually, we lose about 1^o per hour. Assuming it never lost 10 degrees overnight (though it did, because I heard the furnace cycle before 4:30 rise program) you would assume 6 hours of no furnace time.

When the thermostat did call for it to rise again at 4:30, it ran 6 hours or so straight, as no cycling, to get to the set temperature. Being curious (my wife calls it sceptical  by nature, I'm just trying to verify and quantify it somehow.

[csendker]

Now you have a dichotomy on your hands: energy vs. comfort.  Setting your t-stat back will save BTU's, but at the expense of comfort, particularly when it's bitterly cold outside.  The basic heat-loss equation is:

BTU = U x A x deltaT

BTU/h = energy (the less used is better)
U = the thermal resistance / area (that one divided by R, like R-19 insulation; a constant unless someone steals your insulation in the middle of the night)
A = the area of your walls & roof, etc.
Delta T = indoor temp minus outdoor temp

Keep in mind that you set your thermostat back 10 degrees just about the same time Mother Nature sets her thermostat back too.  So while the delta-T may not change much or even increase, it’s still 10 degrees less than it would have been (say 68 indoor – 15 outdoor = 53 DT daytime & 58 indoor – 0 outdoor = 58 DT nighttime which is still better than a 68 DT). You save energy, period.  That’s the energy half.

Now the comfort half: Forced-air furnaces heat the air, not the stuff in your house.  Radiant heat (fin-tube or radiant piping) heats your stuff and not so much the air.  So us folks with the furnaces have to suffer through with cold stuff until it slowly heats back up.  When it’s bitterly cold outside, your walls cool off significantly, becoming cold-bodies, and suck the heat out of anything that comes close (I-squared R…), exasperating the situation.  And while it’s taking its sweet time to heat back up, we have a major cold-body radiant cooling thing going on (the comfort part). 

Being from Michigan, you've HAD to have gone to a hockey game or two.  The air temperature is pretty consistent down around the ice, but you ever notice it’s a lot colder right next to the boards than it is across the walkway?  That’s radiant cooling at its best.  Ok, so officially there is no such thing as cold, just a major-league lack of heat but we won’t go there.  The radiant cooling makes you ‘feel’ a lot colder because the cold stuff, notably your walls, are sucking the heat out of you.

As for the excessive run-time, your furnace is sized to meet the worst-case heat loss expected to occur in your house.  That’s typically the ASHRAE 2-1/2 percentile, I’m guessing probably somewhere around -5 or -10 for Ann Arbor (its +2 degrees for Buffalo).  When the temperature is down in that neck of the woods, your furnace is near capacity, or just meets the heat loss of your house (hopefully).  It takes a long run-time to pull the temperature back up because there’s not a lot of excess capacity.  Efficiency-wise that’s a good thing because short-cycling your furnace (the typically wildly oversized unit) wastes energy.  But you still saved the energy throughout the night.  Personally, when it’s really, really cold out, like the last night or two, I’ll hold the temperature up for comfort reasons, knowing that I’ll be paying for it when the gas bill arrives.  Peace in the family is well worth it.

[Bob Wessner]

Thanks for all the detail, it's interesting. Perceived comfort aside, I was going pretty much by the temp reading in the house rather than how it felt. Ultimately I guess this is going to come to a decision about the exterior wall insulation. The house is 65 yrs old and there isn't any to speak of. Plaster interior, wood lap which has since had vinyl siding over it. Over the years I've buttoned things up quite a bit. There is now about 18" of glass blanket in the ceilings, all new construction and additions have thermo-pane glass and inslulation naturally, but some older double-hung wood (orig.) windows exist though they have storms over them. Right now is seems there is about an 8^o difference in the wall temperature between original outer walls and insulated walls in additions and such.

[csendker]

You can start by tightening up the building envelope; follow the airflow.  Cut down the air movement through your walls then address the heat loss.  I always put those little insulators behind all my outlet and switch cover plates.  The plastic window insulation kits really do work great.  If you're feeling aggressive you can pop off the inside moulding around your old windows & insulate the annular space - nasty heat loss through there.   There's a couple of different blown-in or foam insulation alternatives for your walls.  The switch plate insulators and window kits you can do now, the rest I'd wait for some warmer weather before I'd tackle them.

[Bob Wessner]

Thanks for the suggestions. I caught onto the airflow issue some time ago (i.e., switch plates, etc.). We have an old, but works well, exhaust fan in the kitchen. Found out early that it lowers the pressure on the entire first floor enough to suck in cold air (or hot in the summer) big time. I sealed the fireplace off long ago, temp of course but it was like a gale coming down that flue. I'll look into insulating around the window casings when the next interior repaint job is due.. which according to my wife is now. 

[jbailey]

Here's a link for the Kill-A-Watt:

http://www.p3international.com/products/special/P4400/P4400-CE.html