Energy consumption for a 8X5X7

[morrillt]

Hey guys I did a diy coldroom and am getting the following energy patterns with a 22000 btu lg residential system and coldbot. The system is set for 38, does this look "good"?


summary:
compressor fires using 2200 watts every 20 minutes for 4 minutes, baseline usage of 200 watts (fan mode)

34,000watts a day

[gvh_Dan]

An 8 x 5 x 7 walk in should be around 3,500 btu/hr heat load. Lets assume you are in an out of it a fair amount and that its a little "leaky" since it was DIY and double that number to 7,000 btu/hr.

Running a compressor made for window A/C down to that low of a temperature will probably drop the efficiency to .71 kW/ton = 0.06 watt-hr/btu.

7,000 btuh/hr (per hour) x 0.06 watt-hr/btu = 420 watt-hr (per hour) => 10.08 kWh every day.

Just a note, consumption of electricity is measured in kWh (KiloWatts/hr) while demand is in kWh/h or just kW. If you are small enough to be on a residential style rates, kWh is all you need to worry about. Larger businesses often move to a time-of-use rate where they are billed on both.

Looking at what you have, a 22,000 btu/hr unit pluss the fan. Applying the same numbers as before:

It runs 4 minutes out of every 20 or 12 minutes/hour.
22,000 btu/hr * 12/60 hr * 0.06 watt-hr/btu = 264 watt-hr (every hour) => 6.34 kWh every day

If the fan is running all the time at 200 watts, that is another 4.8 kWh every day so we are at 11.14 kWh every day. You seem to be in the right ballpark. I'm always amazed when cocktail napkin math works out!

On your numbers, I'm not sure where you got the 2,200 watts but if it is off the unit or from manufacturer's literature there are two corrections to make. First, the energy consumption of a window unit is based on a very specific set of A/C conditions. If you start forcing that compressor to odd ball conditions, the energy consumption is going to change. Second, if its based on FLA, motor hp or similar, the motor should be oversized for the actual load on the shaft so it would be pulling that full amount.

In other words, if you really want to get an accurate assessment of whether your Coolbot rigged unit is doing things right, you need to physically measure it. You can get a clamp on meter or most home stores offer plug in meters. You plug the meter into the wall and the unit into the meter and it records electrical consumption. Then compare to the numbers above or anything else someone posts up here to get an idea.