Ventilation in Schools
Ventilation rates vary between building types depending on the occupancy levels, the sensory and pollution loads, the desired levels of indoor air quality, outdoor air quality at the air intake, moisture levels, ventilation effectiveness and the amount of fresh air necessary to meet the range of standards and regulations.
Ventilation rates in School buildings are outlined in several publications including the Building Regulations (Part F), CIBSE Guidelines A & B and BB101. At Sections 1.3, 1.4 and 1.5, BB101 (2006), it is stated “all occupied areas in a school building shall have controllable ventilation at a minimum rate of 3l/s of fresh air for each of the maximum number of persons the area will accommodate” – all teaching areas shall also be capable of being ventilated at a minimum rate of 8l/s for each of the usual number of people in those areas when such areas are occupied.
An air change rate is the amount of time it takes the completely replace the volume of air within a space during a period of 1 hour. For schools the air change rates can range from between 4 – 12 ac/h depending on the type of room and the surrounding conditions.
The area of opening required to ventilate a building is very much dependant on the type of building and the site conditions. As most classrooms are single sided, a single sided ventilation strategy can be modelled.
The speed of the air entering the room provides an indication of how far natural ventilation levels reach into a building space. With a single sided, single opening ventilation strategy CIBSE Guide B recommends a maximum of 2 times the floor to ceiling height.
Ventilation requirements can be modelled using IES Macroflow which an advanced dynamic simulation software programme providing valuable information to design teams. The following is a ventilation simulation modelled on a single sided, single opening window.
The ventilation simulation establishes the amount of hours the building exceeds 28°C during the period 0090 – 1530, Monday to Friday from the 1st May to 30th Sep (an amount of hours in excess of 120 would not comply with the recommendation as highlighted in BB101.
The following image outlines the number of hours the building exceeded 28°C during the reporting period.
It can be seen in the above the temperatures exceed 28°C during the entire simulation period which would not be in line with the requirements of BB101 and CIBSE Guide B. This is one of the many benefits of using dynamic simulation early on at the design stage of a development to confirm the outcomes of design decisions.
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