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Even in a medium-sized building project, mechanical services require far more fan motors than most people expect. Air handling units, exhaust fans, fresh-air supply blowers, jet fans and roof aspirators each run on motors of different power, different speed and different mounting type. In HVAC projects the correct listing of these motors, their timely supply and their passage through consultant approval form the key link in the mechanical installation schedule. Wrong selection, late delivery or failing approval directly locks the installation programme and triggers a chain that can reach as far as liquidated-damage penalties.
In this article we cover how to translate the fan list into a motor list in an HVAC project, the advantages of project-based bulk supply, and how to prepare an equivalence-approval file. The aim is to let you bring dozens of different items down to site from a single source, on time and approved.
Why Is the Fan Motor Requirement in HVAC Projects So Complex?
In a building project fans are not a single type. Even on the same floor, one exhaust fan may run on a small 0.37 kW motor while an air handling unit's supply fan may need a 15 kW motor. When different speeds, protection classes and drive (frequency inverter) requirements are added, dozens of different motor variants emerge across the project.
The way to manage this complexity is to treat the whole project as a single entity rather than making scattered one-off purchases. Translating the entire fan list into a motor list from the outset and planning supply from a single source optimises both cost and lead time. Our broad range of electric motors makes it possible to cover most of the project's different power and speed items from one source.
Translating the Fan List Into a Motor List
In a mechanical design, fans are usually defined by flow (m³/h) and pressure (Pa). To translate these values into motor selection, the following steps are followed:
- Determine the required shaft power for each fan; read it from the fan manufacturer's curve or selection software.
- Add a safety margin to the shaft power and round the rated motor power up to the next standard value.
- Determine the speed (2, 4, 6 poles) according to the fan's operating speed.
- Select the mounting type (foot, flange, B5/B14) according to the fan's construction.
- Determine the protection class according to the environment (for example a higher IP for exhaust fans).
- For fans running with a drive, add an inverter-compatible motor and thermistor protection if required.
When these steps are complete, the fan list turns into a clear motor list: each line carries power, speed, mounting type, protection class and quantity. This list forms the basis of both the bulk supply and the consultant approval.
The Advantages of Project-Based Bulk Supply
Supplying motors on a project basis rather than buying them one by one as needs arise offers clear advantages:
- Single-point coordination: When all motors come from the same source, the delivery schedule and documentation are managed from one point.
- Stock assurance: The project's standard items can be reserved from stock and dispatched in batches according to the installation programme.
- Consistent documentation: The nameplate, conformity and technical files of all motors are presented in the same format, which speeds up the approval process.
- Cost predictability: A bulk quote obtained at the start of the project reduces budget deviations.
Bulk supply prevents the installation crew from waiting, especially in projects with a tight schedule. Creating a batch-based dispatch plan aligned to the project's different phases makes it possible to take delivery when needed without piling up motor stock on site.
Equivalent Selection and the Consultant Approval File
In HVAC projects the mechanical specification may name a specific brand or model. However, most specifications allow the offer of an equivalent product, provided the technical values are met exactly and the consultant approves. When proposing an equivalent motor, an approval file should be prepared to ease consultant approval. This file should contain:
- The technical values of the motor required in the specification (power, speed, IP, insulation class, efficiency class).
- A comparison table showing that the proposed equivalent motor meets the same values.
- The motor's technical catalogue, dimensional drawing and conformity documents.
- Documents proving that energy requirements such as the efficiency class (for example IE3) are met.
A well-prepared equivalence-approval file prevents the consultant from saying "not compliant" and reduces the approval process from days to hours. This file is one of the project's most valuable documents, both technically and commercially, because no motor can come down to site without approval.
Synchronisation With the Installation Schedule
Selecting and approving the motors correctly is not enough; they must also be on site at the right time. For this, the supply plan must be synchronised with the mechanical installation schedule. The motors of the phases to be commissioned first are dispatched as a priority; items to be installed later are held in stock. This synchronisation prevents both the installation crew waiting idle and unnecessary stock piling up on site. Single-source supply makes managing this synchronisation markedly easier.
Frequently Asked Questions
Can I offer an equivalent motor if the specification names a brand?
Most mechanical specifications allow an equivalent product through the phrase "or equivalent." Provided your proposed motor meets all the technical values in the specification (power, speed, protection class, efficiency class) and you demonstrate this with documents, consultant approval can be obtained with the approval file you prepare. If the specification sets a strict brand requirement, equivalence acceptance should first be confirmed with the client.
Do I have to buy all the project motors at the start?
No. In project-based supply the motors are planned in bulk but can be dispatched in batches according to the installation schedule. This balances the budget and stock burden; only the motors needed for that phase are present on site. The important thing is that the planning is done from a single source at the outset.
What should I watch for in fan motors running with a drive?
For motors running with a frequency inverter, it is important that the motor has inverter-compatible insulation and, if needed, includes a thermistor (PTC) for winding protection. Also, because cooling decreases at low speeds, forced cooling or a suitable motor selection should be considered for fans that will run continuously at low speed. These details should be stated from the outset when the motor list is prepared.
