Building Automation Class A (EN ISO 52120)

Upgrading the building automation system from Class C/D to Class A, the highest efficiency level.

How does Class A building automation work?

The standard EN ISO 52120-1 (successor to EN 15232) assesses how strongly building automation and technical building management influence energy consumption. It divides systems into four efficiency classes: Class D stands for non-energy-efficient installations without automation, Class C is the reference standard, Class B describes advanced automation and Class A the highest level. Class A comprises room-by-room demand-based control of heating and cooling, time schedules, demand-controlled ventilation based on CO2 or occupancy, optimised heating and cooling curves and integrated energy monitoring. The effect is expressed through so-called BAC factors (Building Automation and Control): for non-residential buildings, the typical thermal factors are D = 1.51, C = 1.00, B = 0.80 and A = 0.70. Moving from Class D to A therefore cuts calculated heat demand by more than half; for electricity, the factors are of a similar order.

Which buildings benefit from an upgrade to Class A?

The prerequisite is an existing DDC outstation or BACnet-capable hardware, or alternatively a replacement of the control equipment. Engineering capacity for design, programming and commissioning is also needed. Typical properties are office buildings, hospitals, hotels and air-conditioned industrial buildings, that is, buildings with complex plant and variable use. Very small buildings under 500 m² generally do not pay off, because the engineering effort exceeds the saving. Guidance from eu.bac and REHVA confirms that offices, hotels and schools benefit particularly from Class A.

What does Class A building automation actually deliver?

Compared with the Class C reference level, savings of 20 to 35 % on heat and 10 to 20 % on electricity are realistic; compared with an unregulated Class D starting point, considerably more. For an office building with 600,000 kWh/a heat demand, the jump from D to A corresponds to around 322,000 kWh/a. Investment is €30 to €80 per m² of gross floor area for a complete system; isolated upgrades are cheaper. Payback is 5 to 12 years over a 15-year service life. In Austria, the standard is referenced in the Energy Efficiency Directive Regulation (Energieeffizienz-Richtlinienverordnung) as a recognised assessment method.

Energy carrier

Erdgas, Heizöl, Fernwärme, Strom → Erdgas, Heizöl, Fernwärme, Strom

Savings potential

20-35 % thermisch, 10-20 % Strom

Worked example

A 5,000 m² office building with a heat demand of 600,000 kWh/a is operated with outdated controls without demand-based functions, corresponding to Class D under EN ISO 52120 (BAC factor 1.51). As part of a building automation refurbishment, the system is brought up to Class A: room-by-room control, time schedules, demand-controlled ventilation and energy monitoring (BAC factor 0.70). The saving is derived from the previous consumption multiplied by (1 − new BAC factor / old BAC factor), i.e. 600,000 × (1 − 0.70/1.51) = 600,000 × 0.537 = 321,852 kWh/a. That is around 322,000 kWh/a less heat demand, which with natural gas as the reference avoids roughly 65 t CO2 per year. For large non-residential buildings, this is one of the biggest single levers available.

Investment & payback

Komplettsystem 30-80 €/m² BGF; isolierte Upgrades günstiger · Service life: 15 a · Payback: 5-12 a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

What is the difference between building automation Class A, B, C and D?

EN ISO 52120-1 distinguishes four efficiency classes of building automation. Class D means no or inefficient automation, Class C is the reference standard with basic functions, Class B covers advanced control and Class A the highest level with room-by-room demand-based control, demand-controlled ventilation and energy monitoring. Each class is assigned a BAC factor that indicates the relative energy demand compared with Class C.

How much energy does Class A building automation save?

Compared with Class C, Class A typically saves 20 to 35 % of heating energy and 10 to 20 % of electricity. In calculation terms, the BAC factor drops from 1.00 to 0.70. Coming from Class D (factor 1.51), heat demand can be reduced by over 50 %. An office building with 600,000 kWh/a heat demand saves around 322,000 kWh/a when jumping from D to A.

How much does upgrading building automation to Class A cost?

A complete Class A system costs €30 to €80 per m² of gross floor area. Isolated upgrades of individual functions such as time schedules, heating curve optimisation or demand-controlled ventilation are considerably cheaper if DDC or BACnet-capable hardware is already in place. Payback is 5 to 12 years, with a service life of around 15 years.

Is Class A building automation worth it for small buildings?

For buildings under 500 m², a full Class A system is usually not worthwhile, because engineering and programming involve a fixed effort that the small saving does not cover. The measure becomes sensible from medium-sized office buildings, hotels, hospitals and air-conditioned industrial buildings upwards, where complex plant and variable use offer large control potential.

Is EN ISO 52120 mandatory in Austria?

EN ISO 52120-1 is an assessment standard, not a direct obligation for existing buildings. In Austria, the method is referenced in the Energy Efficiency Directive Regulation as a recognised procedure for assessing savings from building automation. The EU Energy Performance of Buildings Directive additionally requires building automation covering Class A functions such as monitoring and fault detection for larger non-residential buildings with heating or air conditioning systems above 290 kW rated output.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Schnittstelle DDC ↔ LineMetrics Cloud via Modbus/BACnet/MQTT erlaubt langfristiges Trending + Auswertungen für Audit. EDM Toolbox liefert Energiekennzahlen pro Bereich/Nutzung.

All measures