Restating and ranking the stakes
We have studied your refurbishment project for the Hélios office building with the greatest interest. Our in-depth analysis of the consultation file allowed us to identify the key objectives that condition the success of this project:
• Technical and energy performance: the main challenge is to replace existing systems with modern direct-expansion installations, both efficient and energy-saving, to ensure optimal thermal comfort while controlling operating costs.
• Reliability and durability: equipment selection and installation quality must ensure flawless reliability of the new HVAC installations over the long term.
• Schedule compliance: we are aware of the binding nature of the deadlines and of the need for rigorous organisation to deliver the project within contractual milestones.
• Controlled-site execution: although the building is currently empty, we integrate exemplary site management into our methodology, minimising disturbance and ensuring seamless coordination with other trades.
- The project is named ("Hélios") rather than treated as an anonymous file: a strong personalisation signal.
- Four ranked stakes (energy performance, reliability, schedule, coordination) that mirror the typical expectations of a tertiary real estate client.
- Each stake is phrased as a response, not as an observation: the project manager already sees the operational promise.
- The closing sentence explicitly commits the team ("point by point"), reassuring on completeness.
- Citing the targeted energy label (BREEAM, HQE) or BBC Refurbishment target would have anchored the response even more in tertiary standards.
- A sentence on service continuity for neighbouring building occupants would have been welcome.
Exhaustive and explicit list of deliverables
As holder of the HVAC lot, our mission encompasses all the studies, supplies and works required for the complete refurbishment of the building's climate engineering installations. Our intervention will cover the following services:
• Complete execution studies, including calculation notes, layout plans and principle diagrams.
• Retrofit of the NORTH and SOUTH air handling units, including coil replacement and installation of high-efficiency motors.
• Supply and installation of new VRV-type direct-expansion systems for all office floors, landings and the Hall.
• Replacement of MVHR and extraction casings on the roof and basement.
• Complete sanitisation of the retained air ducts, with the creation of necessary inspection hatches.
• Management of the interface with the future BMS to ensure perfect communication of the new installations.
• Tests, commissioning, training of operators and provision of as-built files (DOE).
- Structured list covering studies → supplies → works → handover: zero contractual ambiguity possible.
- Explicit mention of NORTH and SOUTH AHUs: the company has read the plans and names existing equipment.
- Sanitisation of retained ducts is listed: a service often forgotten by competitors on retrofits.
- BMS interface is included in the scope from the start, not relegated to an option: anticipates a frequent question from the fluids engineering office.
- An explicit "out of scope" sentence (what the HVAC lot does not do) would further secure interfaces with electrical and structural lots.
Detailed professional software stack
To ensure reliability, consistency and traceability of studies, we mobilise a proven professional software stack:
• Thermal design and load calculations: Pleiades + Comfie (Izuba Énergies) for dynamic thermal simulation, ClimaWin and Perrenoud Bbio for steady-state heat loss and gain calculations.
• VRV system selection: Daikin VRV Xpress (equivalent length calculation, pipe diameter validation), Mitsubishi Electric MELCAD if equivalent variant proposed.
• Execution drawings and BIM: Autodesk Revit MEP 2024 and MagiCAD for 3D modelling, AutoCAD MEP for 2D detail drawings, IFC and DWG exports.
• Aeraulic calculation: AutoFluid (TraceoCad) for duct sizing and pre-balancing.
• Synthesis and clash detection: Autodesk Navisworks Manage with import of other lots' models.
• Electrical schematics and control: EPLAN Electric P8 for principle diagrams and control cabinets.
- Each software is named with its publisher and precise use: impossible to bluff at this level of detail.
- Coverage is complete (thermal, aeraulic, BIM, synthesis, electrical): the company proves it can handle the entire EXE chain.
- Mention of Navisworks for clash detection: a strong BIM maturity signal, sought after on tertiary operations.
- Reference to a Mitsubishi variant shows openness to technical equivalents: reassuring for the engineering office.
Phase 2 : Refrigerant networks (excerpt)
Refrigerant copper pipe: standard NF EN 12735-1, Cu-DHP work-hardened quality, factory-degreased and capped interior. Provisional suppliers: Wieland WICU, KME Sanco or Mueller. Diameters determined according to Daikin manufacturer chart based on equivalent network length.
Brazing: phosphorus-silver 5% alloy (BrazeTec 4505 or Castolin Eutectic 1801), melting point 645°C. Dry nitrogen sweep quality 4.5 (≤ 5 ppm O₂) at 5 to 10 L/min during and 30 seconds after brazing, to prevent internal scale formation.
Leak test: dry nitrogen test at 38 bar (1.1× the VRV service pressure of 33 bar) for 24h, with thermal compensation. Pressure readings every 2h, variation tolerance ≤ 0.5% at equivalent temperature. Signed test report.
Vacuum pull: two-stage vacuum pump Refco RL-4 or Robinair 15600 (113 L/min flow), pulldown to 270 µbar (3 mmHg) measured by electronic vacuum gauge, 1h hold to verify no rise.
Insulation: elastomer foam Armaflex AC or K-Flex ST class M1, thickness ≥ 19mm on suction line and 13mm on liquid line, bonding with Armaflex 520 adhesive on longitudinal joints.
- Operational technical detail level: standard cited (NF EN 12735-1), quantified values (38 bar, 270 µbar, 19 mm), manufacturer references.
- Nitrogen sweeping during brazing is explicit: signal of mastery of best DTU practices, often neglected.
- Leak test with signed report and hourly readings: the company commits to traceability.
- Several suppliers cited (Wieland, KME, Mueller / Armaflex, K-Flex): demonstrates competitive openness and supply security.
- Inserting a photo or schematic of a compliant brazed joint would further strengthen the visual demonstration.
Sanitisation of retained ducts
Standards mobilised: NF EN 15780 (air quality in buildings : cleanliness of ventilation systems) and NF X46-100 (procedure for indoor air quality qualification).
Preliminary inspection: endoscopic camera RIDGID SeeSnake CA-350 or Lifa Air Inspector, full path of retained ducts. Time-stamped photographic record serving as condition report.
Vacuum and brushing: mobile suction unit Lifa Connect or Gansow GS3-78 equipped with HEPA H13 filtration (99.95% efficiency at 0.3 µm), mechanical brushing with Lifa BR-90 robot (Ø200 to 1000 mm ducts).
Final disinfection: ULV (Ultra Low Volume) nebulisation with ECOCERT-certified product such as Sanyresine or Aniospray Quick, 30-minute contact time before recommissioning.
Controls and traceability: microbiological sampling before and after intervention (CFU/m² on Petri dish, COFRAC-accredited external laboratory), gravimetric control of residual dust (≤ 0.75 g/m² "medium" class NF EN 15780). Complete intervention report submitted to project management and client.
- Two standards cited upfront (NF EN 15780, NF X46-100): the company positions itself within the required framework.
- Time-stamped endoscopic condition report before intervention: protects the company and reassures the client.
- HEPA H13 filtration and ECOCERT product: health and environmental arguments directly usable for the occupant communication.
- Validation by independent COFRAC lab: the company accepts being audited, a strong trust signal.
Monthly milestones and acceptance tests
Our provisional schedule is structured around monthly milestones allowing fine project management for the works supervisor. The key milestones are as follows:
M1 : Start order, mobilisation of the engineering office, first iteration of EXE drawings.
M2 : MOE/BC validation of EXE drawings, launch of long-lead orders (VRV units, AHUs).
M3 : Site installation, start of removal and sanitisation of retained ducts.
M4 to M6 : Pulling of refrigerant and aeraulic networks, installation of indoor units floor by floor (R+1 to R+7).
M7 : Lifting of VRV units onto rooftop, connections, vacuum pull and charge.
M8 : COPREC acceptance tests series 1 and 2 in the presence of the inspection bureau.
- Monthly milestones (M1 to M8): readable at a glance for the project management.
- Explicit link between EXE validation in M2 and launch of long-lead orders: the company shows it anticipates factory lead times.
- Floor-by-floor phasing R+1 to R+7: the vertical progression strategy is explicit and auditable.
- Mention of COPREC series 1 and 2 + presence of the inspection bureau in M8: the company commits to the official acceptance procedure.
- Adding the critical path in colour on the appended Gantt would allow instant identification of slack.