The power use of various stuff around the house
 

So I am trying to audit power use of electrical items one-by-one to get an idea of what I'm wasting. I listed things that generally gets left on all day as kWh/day and things that you only turn on as needed as watts.



It's the surprising little things wasting more power than I expect.

Small freezer: 0.85kWh/day based on 14 day average
Energy Star. Circa 2011 6-7 cu.ft.
Room temperature normally kept at 75F

0.48kWh/day the AO Smith Smart Energy module thingy on water heater. The control board sits on top of the tank and it draws 20.5W even when the heater is off. I measured the voltage at heaters and I didn't find either elements operating at reduced voltage. The 20.5W is dissipated right at the control board with the heater doing nothing.

The control board for water heater using more than half the power of my freezer is stupid. The electronic board that simply does what normal thermostat does wastes 180kWh/year. :(


Airhandler with X-13: 0.144kWh/day standby power.
185W when running

1.44kWh/day Small computer UPS, alarm clock, smoke detector, printer, TV.
broadband router is always on. Everything else powered down, but plugged in.

An additional 3.6kWh/day when the desktop PC is left on.

What kind of tank is this?

One of those "smart" storage heater that steps down a few degrees every time the bottom heater kicks on, then steps up some when upper heater has to kick in to tune the water temperature setting.

But 175kWh/year to feed the electronic board itself is absurdity.
http://i.imgur.com/c7413Ge.jpg

On the board, you'll see four relays. They're all single pole normally open type (give power to coil, contacts close).

The outer two relays (contactors ) are energized whenever there is power and each switches each side of the line. The middle two acts as a power switch. One for the upper, one for the lower.

So, there's a considerable holding power for these heavy duty 30A relays. Standby power consumption is 20W 24/7.
When the heating element is on, it has to go through three relays. The controls loss into the air is probably ~50W range when the heater is on with three coils energized and 20A having to go through three relays.

The triple redundancy design is probably to compensate for the reliability issues of digitally controlled embedded system based design from becoming a liability claim.

If you put that Energy Smart water heater on a timer, it still works, but doesn't draw any current for the hours it is not running. If you fish your hand around the cover, you'll find a warm spot toward the right side where most of your continuous 20W is converting from electrical energy to heat energy. I have the Whirlpool version with that brain board, and mine has been living on a timer for over a year. I also downgraded the heating elements in mine after reading numerous reviews indicating the boards (more likely the relays) were not holding up well on the Whirlpool version. I've never had an issue with the brain board in 5+ years.

But, overall its a useless piece of gadget. If you have it set to 130F, it will turn down to 115F but not less. Since I can get away with setting at 120F, the smart logic is not doing anything that a ordinary water heater isn't doing. If it had a built-in timer, so that separate permit is not needed to install it legally, it would sweeten the deal.

It claims to learn your usage over a long period of time, so the learning effect is probably gone too if you put it on a timer. I've noticed some iffy reviews no this too such as failures related to the proprietary board and the lack of economical immediately available replacement parts. If I knew it at the time, I would've avoided it.

I need to measure the standby loss of tank itself, but that would require not using hot water for about a week and metering the kWh usage in order to get a reasonably accurate data. the problem is that the 175kWh that it wastes away is coming off from the control board which is on the outside and does not offset heat losses from the tank shell, but an additional loss.

http://www.descoenergy.com/pdf/Gas%2...cal%20Side.pdf

Take a look at this. It's interesting to note that ECM has a higher standby power use on the average, but they fail to factor this into efficiency evaluation. It's just a symptom of the underlying problem of the excess applications of embedded systems based appliances. :rolleyes:

You seem to be an electronics wiz. Why not just replace it with a control system of your own design?

EcoRenovator is a place to develop solutions to issues. The industry very rarely makes things exactly how you want them. We find ways to fix things to our liking here.

That water heater may or may not be incredibly useful for the average wasteful US household. That .48 kWh may be saving hundreds per year. The aweful embedded electronics may work great for them. But, if it doesn't work for you go ahead and fix it. You obviously know how.

If you want to save power, turn the breaker off when you don't need it or buy and install a timer. Most hot water tanks made have enough insulation to keep the remaining water hot for at least 8 hours.
With your electrical knowledge, you could turn that energy saver into something more useful.

Well, 115-120F is pretty much the lower limit from practical sense so you have warm enough water for usage. Residential water heaters are designed for upper bound of 150F.

So, all that controller is designed to go move back and forth between 115F and upper set point set by the user and since people don't set it at 150F for safety reasons, you're talking about insignificant reduction in standing from going down 10-15F at the most, which I think is easily dwarfed by 0.45kWh/day loss at the control board. Unfortunately, this style is less flexible too.


So, the solution here is confessing to my mistake of buying that thing and I will be going back to the traditional style. The traditional style lets you do something like setting the upper element at 115F and lower at 130F and putting the timer just on lower element so that it works on time of use schedule, but the upper element will come on whenever if you use enough water such that upper element falls under 115F.

If you put a timer at the heater on the electronic board, it throws an error thinking the heating element is out.

That's what i do with all the electric tanks I put in as backup for my solar systems. We have pretty good off peak rates here so it only comes on during those times, if needed.

I have found that 107F seems to be the optimum temperature for showering in my case, which is of particular significance with a heat pump water heater. Dishwashing needs somewhat higher (120F or above, as high as 140F for some detergents), but if it's a plain electric water heater, using the one built into the dishwasher would always be more efficient as it's on demand. (In the case of a heat pump water heater, put in some automation to temporarily boost the setpoint just for dishwashing!)