Negative pressure is mostly used in new sheds – sucking the air out using fans and bringing the air in via wall or ceiling air inlets. Using many air inlets spread out means better air distribution and air quality. For this to work the shed needs to be airtight otherwise your air comes into the shed through all the gaps and holes – especially via effluent drains. Pull plug flushing systems are completely airtight so they make good sense in shed design.
Installing a false ceiling in a controlled environment shed improves the ventilation because it allows you to place ceiling air inlets throughout the room to get fresh air to all areas. It also keeps the room warmer in winter and cooler in summer.
Positive pressure forces air into the building and the air escapes via various gaps or openings, similar to evaporative cooling a house. Positive pressure is often the best method to install a ventilation system to an older shed because sealing up all the gaps is often difficult.
To get the best advice about ventilation, heating and cooling contact Mundigo for a appraisal of an existing shed or design of a new one.