Low cost DIY AC/fridge duty cycle and dryer and water heater kWh estimator

[ICanHas]

This novel idea uses simple household devices within easy reach of students, hobbyists and conservation enthusiasts to accurately collect the average run-time percentage of refrigeration or air conditioning compressors and other utility operated cyclic devices. This implement utilizes very simple, yet tried and true principle of synchronous motor electromechanical analog integration.
It does not use digital circuitry of any kind. The device is electromechanical and the run time is accumulated very accurately in an entirely analog process.

This allows the accumulation of run time over a fairly long period to provide you a good, repeatable and accurate run time and cycle percentage.

It can also be used to estimate the kWh consumption of devices such as electric dryers, water heaters and electric furnaces with a greater accuracy than estimating from the whole-house kWh reading. More than one sets can be used when multiple points must be observed.

It involves accessing hazardous voltage and a great care is required as with any electrical projects. It is very robust, simple and do not require specialized training in computer programs, digital electronics or specialized laboratory tools. The principle of operation is very simple and easily understood by the average people.

You need a plug-in AC analog or a flip plate type clock, which you can find at thrift stores or maybe even new at Walmart.

To allow measurement of 240v sources, a 50W transformer type 240v to 120v travel adapter is used which is economically available at department stores. The transformer is not necessary when measuring 120v equipment.

The clock runs when energized and stops when deenergized. Unlike digital microcontroller embedded systems based clock, it is easily stopped and started without special knowledge of electronics.

The advancement of time relative to elapsed time is the duty cycle. For example, if you set the clock to current time and you observe it has elapsed 4 hrs 30 minutes after 10 hours, the run duty cycle is 45%.

For something like a dryer, one set would be wired to the heating element which is thermostatically controlled and another set wired to the motor.
the advance of time on motor represents the total run time and heater clock represents the heater run time during cycle. The motor and heater power can be easily determined by the ampere measurement.

120v x amps through motor = motor watts
240 x heater amps = heater watts.



Let's say the two clock are set at 12:00 and you place one across the motor, and another across the heater through a travel transformer.

At the end of cycle, the motor clock reads 1:15, heater clock reads 12:45

Using previously measured data, you can estimate that motor: 3A = 360W (the series wound type motor or PSC type have pretty close to 1.0 PF)
Say heater measures 20A =4800W
360W x 1.25 hrs = 450Wh

(45min/60min/hr = 0.75 hours)
0.75hr x 4800W = 3,600Wh

3600+450. Estimated power use for that drying cycle is 4.05kWh or 13,822 BTU
To gather power use with a greater accuracy, a two-wattmeter real time integrating energy meter such as a revenue grade kWh must be used, however for educational and estimation purpose, I find this setup to be adequate.

The starting weight of wet load minus the weight of clothes + lint(hopefully not much. that's fabric wear) will allow you to calculate the latent heat of water in BTU.

The latent BTU divided by BTU of kWh usage is the dryer efficiency.

You could use also use two setup to independently monitor upper and lower elements of water heater, so you know if upper element ever gets used. If the upper element almost never sees use, the water heater is over sized.