Re: Water kettle energy consumption logging

"Wu Ming"  wrote in message news:[email protected]...

Wu Ming <[email protected]> wrote:
> Energy payback: W1*(t-tcool)+Wh =W2*t
>
> Where:
> W1 is the average wattage at lower T
> W2 is the average wattage at 98°
> t is the number of hours
> tcool is the time to cool down from 98° to T
> Wh is the energy required to re-heat from T to 98°
>
> W1, W2 are known from my previous
> tcool is unknown and I tried to guesstimate it
> Wh is calculated as:
>
> T° C to 98° C Wh Wh *1.25
> 90 37.24 46.55
> 80 83.8 104.75
> 60 176.91 221.14
> After 6 hrs 21° 358.48 448.1
>
> Second column from an online calculator. Wolfram Alpha as example. Third
> accounts for the not perfect energy transfer.
>
> Solving for t is simple. Then the fun begins.
>

Formatting appears to be a mess. On my client at least. Doesn’t know how to
keep LF.
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You are on the right track.

Convection and air currents from the heating system and nearby people throw 
off the calculation of cooling rate which would be exponential to an 
asymptote at ambient by conduction alone. The professional way to get a good 
result is to record time and temperature and fit an equation to the 
observation, piecewise between power inputs. When I became a scientist in 
the 1960's we used paper chart recorders with mechanical ball integrators to 
give area under the curve, now spreadsheets can total automated readings.

The multimeter method I mentioned is my cheap home substitute for a 
datalogger, since I haven't found an inexpensive one that can record 
temperature, voltage and current. The meters are optically coupled to the 
laptop and don't create short circuits, allowing me to measure battery 
current with a shunt.

Water temperature is tricky to measure accurately even with an immersion 
probe. It will fluctuate due to convection cells in the water, rapidly 
during heating and slowly during cooling. I see this on the remote readout 
above my computer monitor for the temperature of food cooking downstairs on 
the wood stove. A probe on the outer surface is nearly useless unless in 
good contact and well insulated from the air.

The simple way is to guess a convenient procedure and measure the total 
energy consumed with a Wattmeter like the KAW or another smart plug. If you 
have only a few choices and can't spend hours watching and recording data it 
should be adequate. I've added PZEM-061s to several outlet strips to measure 
the energy demand of 120V and 240V appliances and machine tools during 
typical use.

I bought a thermal imager to find heat leaks on the house that I used to 
monitor a roasting chicken. It showed me the coolest areas immediately after 
I cut it open, where to insert a temperature probe near the breastbone, but 
wasn't otherwise better than an IR thermometer for cooking.