Although I’m not a big fan of my power company, they do provide me with some good information about my swamp cooler, and energy use in general. NV Energy has an online feature that allows you to get your actual energy costs in 15 minute increments. The information is very telling.
The picture above is my personal usage on hot, humid day in late July last year. I picked a day that was humid enough where I would not be able to use a swamp cooler and would have to use traditional air conditioning. This would allow me to see the actual costs of running the a/c.
To get my swamp cooler power costs, I used a Kill-a-watt meter and ran the cooler for several days. Some of the days were run on “low” and at other times on “high”. The "low" setting used .35 kWh (at $0.13 per kWh costs me $0.045 cents per hour to run), and at the “high” speed used .62 kWh to run (at $0.13 per kWh cost me $0.08 cents per hour to run). So depending on the speed, if I ran the swamp cooler 24 hours per day, my cost would be between $1.08-1.92 per day in electricity.
Shifting to air conditioning, if you look at the graph above, you can see spikes in the usage. These are times when the air conditioner turns on. The tall spikes between Noon and 8pm indicate times when both air conditioners are running simultaneously.
On this day, it looks like my baseline electricity usage is about .75 kWh every 15 minutes (way too high). When the air conditioners turn on, the kWh usage rises by approximately 2 kWh every 15 minutes (or about 8 kWh per hour!). At it’s peak usage, that would cost $1.04 PER HOUR for air conditioning only! According to the graph, that would be the maximum. I arrived at this my deducting the baseline amount from the peak usage.
You can easily calculate the energy cost of seasonal usage, in this case air conditioning. Whether you use all electric or have a combustion source for heat, such as natural gas or propane, using your power bill is a handy tool.
You will need to have a twelve month history of your power consumption. Most invoices will have a graph that will allow you to approximate the usage, although you may need to call your utility for the information. You will be determining your baseload consumption and seasonal consumption. Baseload consumption are things that don’t vary with the seasons like lighting, the refrigerator, and other appliances. Seasonal energy use includes heating and cooling. We will focus on cooling here and the energy costs associated with it.
With twelve months of electricity consumption in front of you, find the three lowest months and add them together. Then divide this amount by three (this will give you an average for the lowest months of the year). Then multiply this amount by 12 for the approximate annual baseload energy usage. You now have your annual baseload figure. *Be careful here as some utilities will show daily usage by month, in which case you will need to multiply this baseload figure by 365 to get the annual figure. You will need to read your bill to determine if you need to do this.
To determine the seasonal use for your cooling, add the actual kWh (Kilowatt hours) used for all twelve months to arrive an an actual electric usage. Now we just need to subtract our baseload figure from the annual figure to arrive at the seasonal consumption in kWh. Then multiply this kWh by the cost on your power bill to get your dollar cost of seasonal cooling.