How is simple payback calculated?

Simple payback is the project cost divided by the annual money saved. A 2,000 unit LED retrofit that saves 800 units a year pays back in 2.5 years. It ignores interest and rising energy prices, so it is a conservative first-pass screen for an investment case.

What efficiency figures do motors and HVAC use?

For a motor or compressor, savings come from the same mechanical output delivered at higher efficiency: old kW input minus new kW input. For HVAC, improving the coefficient of performance (COP) or SEER reduces the electrical input needed for the same heating or cooling output.

How accurate is the kWh saved figure?

It is as accurate as your inputs. The arithmetic is exact, but real savings depend on actual run hours, load profiles, and weather. Use measured baseline data where possible and treat the result as a planning estimate, not a guaranteed bill reduction.

Why include CO2 savings?

Many efficiency projects are now justified partly on carbon, not just cost. Multiplying kWh saved by your grid's carbon intensity in grams CO2e per kWh shows the emissions avoided, which supports net-zero reporting and ESG disclosures alongside the financial case.

Does lighting use a different model?

Lighting savings are the difference between old and new fixture wattage, multiplied by the number of fixtures and annual burn hours. A 36 watt fluorescent replaced by an 18 watt LED across 100 fixtures running 3,000 hours saves 5,400 kWh a year.

What is the Energy Efficiency kWh Savings Estimator?

Select an upgrade type (HVAC, lighting, motors, compressed air, building fabric) and input baseline and improved power or efficiency parameters to compute annual kWh saved, cost reduction, simple payback, and CO2e avoided. Supports investment-case preparation for energy managers. It runs free in your browser on Gera Tools, with nothing uploaded.

Energy Efficiency kWh Savings Estimator

Name: Energy Efficiency kWh Savings Estimator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Energy efficiency upgrades only get funded when the savings are quantified. This estimator takes a baseline and an improved case for five common upgrade types and computes the annual kWh saved, the money that translates to, the simple payback against your capital cost, and the CO2 emissions avoided — everything an energy manager needs for a one-page investment case.

How it works

All five upgrade types reduce to the same core idea — power saved multiplied by operating hours — but the way you derive the power difference varies:

Lighting:   kW saved = (old W − new W) × fixtures / 1000
Motor/comp: kW saved = old input kW − new input kW
HVAC:       new input kW = output kW / new COP
            kW saved     = (output / old COP) − (output / new COP)
Fabric:     kW saved entered directly as avoided demand

annual kWh saved = kW saved × annual hours
annual money     = kWh saved × electricity price
payback (years)  = project cost / annual money
CO2e avoided (kg)= kWh saved × carbon g/kWh / 1000

For HVAC, a higher coefficient of performance means less electricity is needed to move the same amount of heat, so the saving grows as the gap between the old and new COP widens.

Worked example: LED retrofit

Replacing 100 fixtures of 36 W fluorescent with 18 W LED, running 3,000 hours a year at 0.20 per kWh, saves 5,400 kWh and 1,080 in energy per year. A project cost of 2,000 pays back in under two years and avoids roughly 1.35 tonnes of CO2e on a 250 g/kWh grid — a clear business case in one paragraph.

Worked example: HVAC improvement

A 20 kW cooling output served by an old chiller with a COP of 2.5 draws 8.0 kW of electrical input. Replacing it with a unit with a COP of 4.0 drops input to 5.0 kW — a saving of 3.0 kW. Over 2,000 annual operating hours that is 6,000 kWh saved, worth 1,200 at 0.20 per kWh, against a higher upfront cost offset by reduced maintenance and refrigerant charges.

What affects the result most

The three input numbers with the biggest influence are annual operating hours, the baseline power draw, and the electricity price. Overstating run time is the most common way efficiency business cases disappoint in practice — use metered or logged data rather than nameplate hours. For motors and compressors, real-world load factor matters too: a motor running at 60% load draws significantly less than its rated kW, so measure actual input power rather than using the nameplate.

Using this for carbon accounting

The CO2e figure is calculated by multiplying annual kWh saved by the grid carbon intensity you enter in grams per kWh. National grids vary widely and change year to year as the generation mix shifts. For UK projects the government publishes annual grid intensity figures; for global projects use the country’s most recent published grid factor. Over the project lifetime a single LED retrofit can avoid several tonnes of CO2e, which is increasingly relevant for net-zero reporting and EPC-linked planning conditions.