PÉCLETBuilding Physics
PÉCLET / Disciplines / 06Q — kWh/m²a

Energy

Energy is not a discipline of its own. It is the arithmetic left over once the other five have been decided.

QuantityDemandTransportBalanceInteractionAdjust the measures on the left. The balance re-proportions and the residual demand updates.
Fig. 06 — Cooling-season balanceSwitch measures on and off
With no measures applied, the residual demand index stands at 100 against a baseline of 100. The largest remaining term is Solar gain at 32. Terms: Solar gain 32, Fabric conduction 21, Infiltration 18, Internal gain 17, Latent load 12.
Measures applied
An energy balance drawn as flowing ribbons. Gains enter from the left as solar and internal heat; losses leave to the right through fabric, ventilation and system inefficiency. Ribbon thickness is proportional to the size of each term, and the ribbons re-proportion themselves as the balance changes. A residual demand figure sits at the centre. The figures are an illustrative index in which the untreated baseline is defined as 100. They compare the relative effect of measures on one another and are not a calculation, prediction or claim about any building.

The position

Fabric loss, ventilation loss, solar gain, internal gain and system efficiency form a single balance. Improving one term while ignoring the others moves the number without improving the building.

The order matters: reduce demand through form and fabric, then meet what remains efficiently. Reversing that order buys equipment to solve a geometry problem.

What we ask

  • 01Which term in the balance actually dominates here?
  • 02What is the cheapest kilowatt-hour — the one never demanded?
  • 03Is the system sized for the building, or for the drawing of it?
  • 04Where does this design stop improving and start costing?

How we answer it

  • 01Whole-building energy balance modelling
  • 02Demand-reduction sequencing before system selection
  • 03Parametric option testing across fabric and services
  • 04Performance-target setting with the design team