Separate efficiency from service demand

Hold the service constant before claiming efficiency

Two devices can use different energy amounts because one is more efficient, because their services differ, or because people use them differently. Begin by writing a functional service unit. In the supplied example, one unnamed device needs 2 kWh per unit and another needs 1. The units represent the same stipulated service, not merely two devices operating for equal time.

Predict their inputs for ten service units. Device A uses 20 kWh and B uses 10. The second uses half as much input for the same request under the assumptions. That is a matched-service efficiency comparison. It does not establish measured performance, cost, emissions or adequacy for a particular household.

Separate efficiency from a change in use

Now let B provide 25 units. Its energy input is 25 × 1 = 25 kWh, exceeding A’s original 20. This is a changed-use scenario, not evidence that B lost its per-unit efficiency advantage. The arithmetic shows why improved efficiency alone does not guarantee lower total energy use.

Rebound describes increased use that can offset some expected savings, but this paper card does not measure behavior or assign a universal rebound percentage. Record the assumed use change explicitly rather than presenting it as an observed response to a new device.

A third option reduces A’s requested service from ten units to eight. Input becomes 8 × 2 = 16 kWh. This changes service quantity; it is not the same-service efficiency comparison. A sufficiency proposal must explain whether the reduced request remains adequate and who experiences the change. The energy calculation cannot decide those objectives by itself.

Explain a heat pump without creating energy

For a supplied heat-service case, a heat pump with coefficient of performance, COP, equal to 3 provides 12 kWh of heat using 4 kWh electricity. The other 8 kWh comes from heat extracted from its surroundings. At this boundary, output heat equals work input plus transferred environmental heat.

An ideal resistance heater would require 12 kWh electricity for the same 12 kWh heat. The heat pump’s COP exceeds one because it transfers heat as well as using work, not because electricity is multiplied or energy created. Revisit heat-pump COP for the energy balance and constraints.

The IEA heat-pump explanation supports this transfer mechanism. The authored COP 3 is a stipulated example, not a seasonal rating or observation of an installed appliance. Weather, operating conditions and system design would matter to an actual comparison, and no emissions factor is supplied here.

Connect efficient service with dispatch honestly

The live lab keeps its electrical request fixed at 4 kW across four bins. Its controls change generation timing and storage, not device efficiency, temperature settings or requested services. Compare ideal fast and lossy fast storage at the same timing: a loss profile changes the electricity needed to support a given delivered amount.

Capture that comparison and separate it from your paper device calculation. The dispatch model can show loss and grid support at its bus, but it cannot establish whether its electricity produces equal useful lighting or heat in different buildings. Keep boundaries consistent when building a portfolio argument.

Transfer: change both efficiency and service

A fictional old device uses 3 kWh per unit for six units. A replacement uses 2 kWh per unit for ten units. Calculate the two totals and explain how efficiency improved while total use changed. Name one additional question before recommending reduced service.