For buildings which operate exhaust systems, whether they be for the purposes of general room extract, process extract or dust/fume extract, a fresh air make-up supply is typically installed to maintain a satisfactory room or building pressure balance. The desired pressure will be dependent on the application. For example, a cleanroom facility will typically require to be maintained at a positive pressure condition to minimise contamination from the external environment. An industrial kitchen area will conversely require to be kept at a negative pressure condition to prevent the potential spread of odours and cooking oil vapours/smoke spreading to adjacent restaurants or cafeteria areas. This does however not preclude the requirement for a fresh air make-up system, as in this example, large extraction rates are typical and make-up air must be introduced at (or usually close to) the same rate that contaminated air is exhausted.

Operating a building at an excessively negative pressure condition can, in some instances, create poor environmental conditions due to one or more of the following:

  • Inefficient exhaust system operation due to excessive static pressure resistance being presented to the fan.
  • Excessive infiltration rates, which in turn can cause occupant discomfort due to localised draughts, most typically close to the perimeter walls at low level.
  • Poor room temperature uniformity (cold at low level, warm at high level), potentially leading to higher heating system operational costs.
  • Difficulties with opening or closing doorsets between rooms.
  • Interference with the operation of exhaust hoods, fume cupboards and other process equipment utilising localised extract ventilation (LEV).
  • Contamination and pollutants being introduced from the external environment or adjacent building spaces.

It is therefore of critical importance that where required, a fresh air make-up system is carefully designed and installed to achieve the desired room and overall building pressure balance. Fresh air make-up systems designed for operation in the UK, typically incorporate as a minimum, a supply fan, filtration to remove particulate and other pollutants and pre-heating so that the air is supplied at a temperature which avoids occupancy discomfort and/or disruption to any research or manufacturing process.

Callidus Design can provide the design and specification of fresh air make-up systems to either resolve an existing pressure regime problem or as part of a new ventilation installation.

Callidus Design offer a number of services for ventilation installations, including design and specification of entire systems, system modifications and extensions, condition surveys, refurbishment and troubleshooting.