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Which energy savings pay back first?

Describe an example building and its energy bill. See the low-cost measures ranked by payback, with each saving taken from the bill that is left.

Worked example · about 2 minutes

What it does

Finds low-cost ways to cut an energy bill and ranks them by how quickly each pays for itself.

What you need

The floor area, the yearly energy bill in euro, and a few answers about how the building runs.

What you get

Each measure with its cost, saving and payback, and the bill shrinking step by step, counted honestly.

What it is not

Not an energy audit and not advice. The figures are rules of thumb, not measurements of a real building.

Read this first

This is a teaching example. It works on an example building and uses rules of thumb and published averages, so its answers are rough guides, not advice. It is not a design, a survey, a quote or a valuation. Before you act on anything about a real building, ask a qualified engineer who has seen it.

What you type stays on your device. This page sends nothing anywhere and keeps nothing.

The example building

The example is a made-up 2,500 m² office open weekdays, with a €180,000 energy bill.

Often wrong: adding the savings together. If lighting saves 10% and controls save 8%, the pair do not save 18%. They save 17.2%, because the second saving comes off a bill the first has already cut. This page applies each saving to the bill that is left.

About this worked example

Words used here

Payback
How long a measure takes to pay for itself from the money it saves. Three months is quick; three years is slow for a quick win.
Controls
The timers, thermostats and building management system that switch heating, cooling and lighting on and off.
Weather compensation
A boiler setting that runs the water cooler on mild days, saving gas without anyone noticing.
Sub-metering
Extra meters on the big loads, so you can see where the energy actually goes.
Applied in turn
Each saving comes off the bill that is left after the ones before it, which is why savings cannot simply be added.

What it does not do

  • The cost and saving figures are rules of thumb, labelled Judgement, not measurements of your building.
  • It does not check whether a measure suits a particular building or its occupants.
  • It ignores price changes and grants.
  • It is not design advice.

Start learning free

DC-LEARN’s first three modules are free, with no account needed: what a building’s power and cooling systems do, and where the energy goes.

Start DC-LEARN free