HVAC engineering firm: ventilation, air conditioning, heating

The HVAC engineering firm produces a chain of technical and regulatory deliverables covering the entire project cycle. Kytom frames this scope from the sketch stage to avoid grey areas between the MEP, electrical and finishing packages.

• Thermal calculation notes: summer/winter assessment for heating and air quality, internal occupant gains 80 W, LED lighting 8 to 12 W/m², office equipment 100 to 150 W/workstation.
• Airflow and hydraulic drawings: duct networks, target velocity 4 to 6 m/s in main ducts, 2 to 3 m/s in plenum return.
• HVAC technical specifications: equipment requirements, filtration classes ePM1 60% minimum in urban areas, network tightness class C.
• Tender documents and bid analysis: multi-criteria technical comparison grid.
• Execution monitoring: weekly visits during the construction phase, snag clearance.
• Commissioning: 8 weeks of post-delivery adjustments, flow readings, hydraulic balancing.

Our reading differs from common practice on this precise point: the profession still treats commissioning as a budgetary option. Our site experience systematically shows a significant gap between theoretical performance and measured real comfort when this phase is removed, a risk we refuse to pass on to the client. Dynamic thermal modelling under Pléiades or DesignBuilder anticipates the gaps between theoretical and real performance, often significant in the absence of serious post-delivery adjustments.

When this full approach is not justified: below 200 m² of floor space, the complete chain with commissioning makes the fees/savings ratio unprofitable. Kytom then switches to a streamlined mission (calculation notes, technical specifications and simple acceptance) and steers the client towards a standardised monosplit or multi-split solution rather than a VRF with BMS.

4 HVAC types for offices from 100 to 5,000 m²

The choice of type determines a majority share of perceived thermal comfort and annual consumption, with significant gaps between types on comparable floor plates. Kytom frames four families according to building configuration and occupant density.

• Monosplit: one indoor unit, one outdoor unit. Recommended for a server room or cellular office of 15 to 25 m². Cost generally between €1,500 and €3,500 per unit depending on configuration. Limitation: facade saturation beyond 4 zones.
• Multi-split: 2 to 8 indoor units on one condenser. Individual control per zone, significant facade space savings vs monosplit. Constraint: single mode heat OR cool, incompatible with mixed server/office buildings.
• 3-pipe VRF with simultaneous recovery: heat transfer between hot and cold zones, with an investment level generally higher than a 2-pipe system. Preferred on floor plates over 500 m² with BMS control.
• Tempered water loop: dedicated to dense urban buildings without authorisation for facade or roof condensers, a solution whose investment remains significantly higher than conventional VRF systems.

Kytom rules out the monosplit in open-plan spaces beyond 4 zones. Coordination under the raised floor requires 3 to 5 meetings between the HVAC engineering firm, electrical, plumbing and architect. Below 150 mm of clear height, air distribution switches to the ceiling, which changes the acoustic assessment with a retained target of 30 to 35 dB(A) in tertiary open-plan spaces.

When the 3-pipe VRF is not the right choice: on a single-zone plate below 300 m² with homogeneous use, the VRF surcharge vs multi-split generally does not pay off over a standard operating period, which steers towards a multi-split solution with zone-based control.

For the thermal engineer and energy manager: as a calculation framework, not as a declarative constraint

The tertiary regulation (decree no. 2019-771 of 23 July 2019, articles R174-22 to R174-32 of the Construction Code) requires an energy consumption reduction of 40% by 2030, 50% by 2040 and 60% by 2050, relative to a reference year chosen between 2010 and 2019. Annual declarations are centralised on a national platform dedicated to monitoring the energy performance of the tertiary building stock. For the thermal engineer and energy manager, this framework is not an annual form but a calculation framework that must be injected from the detailed design stage: choosing the reference year, calibrating the sub-metering and fixing the trajectory determine the success of the technical levers. The MEP item represents a majority share of tertiary consumption, so the bulk of the potential lies with the HVAC engineering firm.

Five levers structure the trajectory:

• Heat recovery on extracted air: plate heat exchanger with 75 to 85% efficiency according to NF EN 308, enabling significant savings on heating.
• Mechanical or natural free-cooling: use of outside air between 8 and 18°C to noticeably reduce air conditioning needs.
• Variable air volume (VAV): modulation according to actual occupancy via CO₂ sensors, for substantial savings on ventilation.
• Centralised BMS control: schedule programming, overrides, consumption monitoring per zone.
• Sub-metering by use: separate meters for heating, air conditioning, ventilation, lighting, others, in accordance with the regulatory requirements applicable to the tertiary building stock.

Kytom validates the meter breakdown from the detailed design stage. In our experience, retrofitting the sub-metering after delivery represents a significant additional cost per m²: an avoidable cost if the energy manager is involved in the technical specifications. MEP coordination synchronises air distribution, high-voltage electrical, IT cabling and condensate drainage under a raised floor of 100 to 300 mm, with a minimum 30 cm separation between power and IT cabling according to NF C 15-100.