Energy Saving Estimate ReminderWednesday 10th October 2012
Let’s get a little more serious today and think about energy saving and estimating what the cost savings could be particularly for businesses.
It can be easy to make a mistake by using a too simple a method to predict savings, you need to remember that averaging out a monthly electricity bill to estimate savings can be grossly inaccurate.
You need to be careful as most non-residential consumers are charged for how fast they use electricity (kW) as well as how much they use (kWh). The “how fast” refers to what is called “peak demand” and can account for as much as 50% of an electricity bill.
So don’t just divide the monthly total cost of electricity only by the kWh used over the month - or whatever period you are focussing on, as by doing this would include the cost of peak demand.
To explain further - if motion sensors for lighting control were installed they are very likely going to save substantial amounts of kWh, but are unlikely to affect peak demand (kW) by themselves.
They may contribute as a building fills up and all the lights may come on, along with everything else starting up. As the lights shut off during the day as rooms are left unoccupied the peak has already been reached and the charges for peak demand (kW) applied - the motion sensors save but only on the kWh, so using an average electric price will overestimate the cost savings - in reality only savings on the kWh part of the bill should be used.
So to make an estimate of savings the peak demand needs to be analyzed, this can often only be done with high quality energy monitoring. To underline this, real-time energy monitoring helped an educational centre save thousands on their electricity bill. The energy use data revealed a huge spike of energy early in the morning, this was shown to be a number of pumps starting all at once from an off position, this was overcome by leaving them on standby, still using energy but reducing the electricity costs due to a lot lower peak demand figure.
Wednesday 10th October 2012