1000 m³/h is not a ventilation system. What really determines how it works

The quotation states: ‘Supply air handling unit, airflow rate 1000 m³/h’. There is a price alongside it, so it seems that all that remains is to compare a few quotations. But the same airflow does not mean the same system: the figures may match while what you are buying differs.

First, clarify what those 1000 m³/h represent

Is this the outdoor airflow or the total airflow through the unit? In a recirculation system, these are different quantities. If the unit supplies 1000 m³/h of mixed air, of which 700 m³/h is returned from the rooms, only 300 m³/h of outdoor air enters.

Recirculation is not inherently a mistake, but this arrangement cannot be compared with a system supplying 1000 m³/h of outdoor air as though they were equivalent solutions. It also matters where the airflow is verified: in the fan specification, at the unit outlet or at the diffusers after installation.

Air needs more than simply moving

In winter, outdoor air needs heating. Take, for example, an airflow of 1000 m³/h, an outdoor temperature of −20 °C and a supply air temperature of +18 °C. Without heat recovery, the approximate heating duty is:

Q = 0,34 × 1000 × 38 / 1000 = 12,9 kW

This is the heating duty, not merely the fan’s electrical consumption. For an electric heater, it approximately corresponds to the electrical load; for a water heating coil, the heat must come from an external source. So the statement ‘the ventilation consumes less than a kilowatt’ may tell you nothing about winter heating.

The same airflow can conceal a different ductwork system

At 1000 m³/h, the average velocity in a 400 × 250 mm duct is about 2,8 m/s. In a 300 × 150 mm cross-section, it is already about 6,2 m/s.

v = L / (3600 × A)

These are illustrative figures, not universally acceptable limits. A smaller duct changes velocity, resistance and noise. Poorly arranged bends and transitions near the fan add losses that are not apparent from the label ‘1000 m³/h’.

What the quotation should define

Compare like-for-like design conditions: outdoor airflow, required external pressure, winter and summer air treatment, filtration, acoustics, controls and the scope of commissioning.

Record the scope boundaries separately: ductwork, power supply, heating coil pipework, condensate drainage, balancing and operating mode checks. Without this, comparing prices makes no engineering sense.

What you should buy is not ‘1000 cubic metres’, but an agreed outcome: what air the system will deliver, to which rooms and under what conditions once it is running.