12.2 Overall Energy Demand: Delivered Energy, Fuels & End Uses

12.2 Overall Energy Demand: Delivered Energy, Fuels & End Uses

Exam Focus: Sub-topic 4.2.3 "Overall energy demand of buildings" underpins every other energy sub-topic in Domain 4.0. Questions test whether you understand what number EDGE is actually reporting.

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The Multi-Fuel Problem

A real building rarely runs on one energy carrier. A hotel might draw grid electricity for lighting and cooling, natural gas for kitchens, diesel for a standby generator, and district cooling for part of its load. You cannot add kilowatt-hours of electricity to litres of diesel.

EDGE resolves this by converting energy from all carriers into a single delivered energy metric. The Methodology Report explains both the mechanism and the reason:

Since a building generally uses more than one fuel from different carriers (e.g. electricity, natural gas, diesel, or district cooling/heating), EDGE converts primary energy into "delivered" energy values to provide a common metric. The combined outputs for energy use are relayed as delivered energy (rather than primary energy or carbon dioxide emissions) to best communicate efficiency gains to users, who relate more easily to results when expressed as lower utility bills.

Delivered vs primary energy

The choice is communicative, not accidental. A developer understands "your building uses less electricity"; a primary energy factor is an abstraction. The Methodology Report notes that as EDGE evolves, primary energy projections may also be provided.

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The Eight End-Use Categories

EDGE assesses a building's energy performance across these categories:

1. Space heating
2. Space cooling
3. Fans
4. Pumps
5. Lighting
6. Other (appliances)
7. Hot water
8. Cooking

Two observations worth carrying into the exam. First, fans and pumps are separate line items from space heating and cooling — distribution energy is not folded into generation energy, which is why variable speed drives on pumps and fans register as their own saving. Second, appliances and cooking are included, which is the non-regulated energy discussed in Section 11.1. Many national codes exclude them; EDGE does not.

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How On-Site Renewables Are Treated

The rule is simple and specific:

Renewable energy generated on site (e.g. electricity from solar photovoltaics or hot water from solar collectors) is deducted from the building's improved case and is expressed as "energy savings."

Three consequences:

• Renewables act on the improved case only. The base case has none, so every kilowatt-hour generated is a full kilowatt-hour of saving.
• The saving is expressed in the energy category, with no materials-category penalty in EDGE for the panels themselves. This is one reason on-site PV is a favoured route to the 40% EDGE Advanced threshold.
• Solar thermal counts too. Hot water from solar collectors is treated the same way as PV electricity, which is easily forgotten because "renewables" is often heard as "photovoltaics".

Remember the threshold rule from Section 1.3: the 40% for EDGE Advanced must be achieved on-site. Off-site renewable purchase and offsets belong to EDGE Zero Carbon, not to the Advanced threshold.

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Hot Water Demand in Detail

EDGE bases hot water algorithms on EN 15316-3, which supplies both the hot water requirements for different building types and the energy calculations to meet them. The parameters used are:

• Cold water supply temperature, derived from the mean annual temperature of the project location.
• Hot water delivery temperature, set at 40 °C.
• Daily hot water demand, based on water usage patterns and the number of days used.
• Energy need for hot water — hot water consumption per day × the water usage factor × days per year ÷ boiler efficiency.
• Fuel energy needed, accounting for fuel calorific value and boiler efficiency.

The examinable insight is the temperature difference. Energy needed is proportional to the gap between cold feed and 40 °C delivery. In a cold-climate city with a 10 °C cold feed the water heater must lift 30 °C; in a tropical city with a 26 °C cold feed it lifts only 14 °C. The identical showerhead therefore saves roughly twice as much energy per litre in the cold-climate project. This is why hot water measures rank very differently between locations.

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Lighting Demand in Detail

EDGE uses the "quick method" under EN 15193 to estimate annual lighting energy. The calculation is based on:

• installed lighting power, and
• annualised usage according to building type, occupancy and lighting controls.

Both halves are levers. Reducing installed power — lower lighting power density through more efficacious sources — cuts the first term. Adding occupancy sensors and daylight-responsive dimming cuts the second by reducing annualised usage hours. A project that installs LEDs but leaves them on a manual switch in a daylit perimeter zone has taken only half the available saving.

And recall the interaction from Section 9.3: lower installed lighting power also reduces internal heat gain, which reduces the space-cooling line item in a cooling-dominated climate. The lighting upgrade shows up twice in the energy result.

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Reading the Energy Result Correctly

When you present an EDGE energy figure, you are presenting: delivered energy, across eight end uses including non-regulated loads, net of on-site renewable generation, inclusive of virtual energy for comfort where no conditioning is specified, benchmarked against a localised base case. Every clause in that sentence is a place where a naive comparison to another building or another rating system breaks down.