Ventilation
Most people think of ventilating a building or room only when they feel uncomfortably hot. Until they feel the discomfort caused by accumulated hot air, the idea of ventilation seldom occurs. There are other reasons for ventilating a building which are less prevalent. 80% of enquiries received by Lorenz and Associates are prompted by excessive heat within buildings.

The word “ventilate” is defined in the dictionary as “to let fresh air into (a room or building)” and a “ventilator” is defined as “an opening or device, such as a fan, used to let fresh air into a room or building.”

A room or building needs ventilation for one or more of the following reasons:

1. Trapped air accumulates heat
2. Trapped air becomes contaminated with toxic fumes, particles and odours
3. Trapped air becomes saturated with water vapour
4. Trapped air becomes depleted of oxygen causing stuffiness
5. Smoke and fumes from fire choke inhabitants and cause the fire to spread

The most cost effective form of ventilation would be a hole in the roof, as this would allow the air to escape naturally. However this is generally impractical as a hole will allow dust, rain etc. to enter the building.

Mechanical vs. Natural Ventilation
The manner in which a building is ventilated can take one of two forms; mechanical or natural. Mechanical ventilation employs power such as electricity, gas, coal, oil etc. and natural ventilation harnesses nature’s forces.

Natural Ventilation
Natural ventilation will solve, on average, 75% of a given ventilation problem. Solving the remaining 25% usually turns out to be too expensive. A turbine ventilator moves air constantly, causing trapped air to be replaced with cleaner, cooler air from outside.

Stack Effect
Natural ventilation is driven by pressure differences, like the wind, air density differences due to temperature differences between indoor and outdoor, and the operation of equipment generating heat inside the building.

Temperature differences between indoor and outdoor cause air density differences, and therefore pressure differences. The taller the building and the less internal resistance to airflow, the stronger the stack effect.

Types of ventilation products
Static ventilators in all shapes and sizes have been used traditionally on industrial buildings. Recently, however, turbines have begun to replace the static ventilator.

Within the industrial environment, the static ventilator is the major opposition to the turbines. The static ventilator is, however, less effective as it only relies on the upward motion of hot air to perform its function.

Due to the necessary weatherproofing of these ventilators their effectiveness is usually around 60% of their free area. The static ventilators have been around for many years and have been the standard for ventilation. Lorenz and Associates’s objective is to make the Gladiators the number one choice of specifiers.

Mechanical ventilation usually takes the form of extraction fans that are electrically powered. There is sometimes no substitute for mechanical ventilation when huge or precise amounts of air have to be moved. They are however expensive (maintenance and electricity) and are often not switched on due to the high noise levels they create. Therefore, turbines are sometimes a better solution than electric fans.

Before the advent of turbines, there was no viable form of natural ventilation for residential roofs other than wall vents. In the USA 95% of turbines are sold to the homeowner.

Benefits of turbines

• The turbine is maintenance free
• Works all the time, even when the building is closed
• Silent operation
• Performs better than static ventilators
• Lightweight construction means roofs do not need reinforcing
• Does not impact on the environment

Applications for the turbines
The turbines must be installed on the roof of a building where there is access to the wind from all directions to be most effective. It can withstand intermittent winds of hurricane strength. When installing a turbine be sure to keep it away from parapet walls, the walls of adjacent buildings and the like. From this, it is obvious that the types of applications are only as limited as your imagination.

Roofs
The turbine is ideally suited to installation on steel roofs such as IBR and corrugated iron (they allow solar radiation through into the building very easily), having said that the turbines can, and have been, installed on slate, tiles (low amplitude), fibreglass sheeting, asbestos, thatch, chimneys, vehicles, and poly-carbonate skylights.

Undesirable applications

1. Internal rooms
2. Large closely populated rooms where distribution of natural ventilation would be inadequate(rooms occupied by more than 50 people).
3. Rooms where volume per occupant is too low for efficient natural ventilation (under 3,5 m³ per person).
4. In cases where the close control of environment is required.
5. Where natural ventilation is impossible because windows cannot be opened because of external pollution or noise.
6. Where the extraction at the source is needed for dealing with fumes or smells from cooking or other special processes.
7. Removing particles such as sawdust etc. where high velocities of extraction are required.
8. Where bylaws determine a specific extraction rate, or fume concentration in the air.
9. When there is a negative pressure inside the building caused by other mechanical extraction equipment (This will cause the turbine to rotate the wrong way).

Fumes
Fumes are another reason for ventilating a building. Fumes should be dealt with wherever possible at the source. The use of turbines to extract fumes should only be used for the excess or spillover fumes. Be very careful when offering the turbine as a solution to the removal of fumes as the vent rate is very low compared to mechanical ventilation, and if the fumes are dangerous to health of the people and/or environment the turbine cannot be used because the air is vented outside. e.g. Asbestos plants.

Where odours and dust are objectionable, the turbine can be used to increase the air changes in the building to dilute the effect of the fumes. Attached is a list of recommended air changes suggested for various types of industries and activities.

To calculate the number of turbines needed to obtain the required air changes per hour, calculate the volume of the building by multiplying the length by the breadth by the height. Then multiply the number of air changes by the volume then divide by the extraction rate of the turbine into this result to establish the number of turbines.

Transport Garage
Removing diesel and petrol fumes requires that you provide a minimum removal rate of 250 m³/hour for every horse power of the motor. The temperature of diesel fumes is very high ± 150°C, therefore it rises very quickly. As long as enough ventilation has been provided, and the fumes are removed quickly before they cool down again extraction can be efficient.

Petrol fumes are emitted at a much lower temperature (32°C) and therefore low level extraction is normally required. However the air change method will provide a vast improvement by allowing the dilution of the fumes.

Moisture
Moist air is less dense than dry air and consequently has a tendency to rise. Upper corners of rooms which are often colder than lower areas in buildings, are therefore exposed particularly to rising currents of moist air from below.

The problems of condensation are most common in the winter months. This is due to the fact that the outside temperature causes the surface temperature of the roof, walls and glass to be colder than the dew point of the moist air inside the building. This is very noticeable in plants where steam or water of a high temperature are used. The steam or water vapour rises to the level of the roof and the moment it touches the cold ceiling it turns into water droplets, falling like rain onto machinery, people etc., causing damage.

It is always better to treat the emission of the moisture vapour at the source by using mechanical extraction hoods, and not to expect the turbine to do it. Often the air being drawn into the building has to be heated to prevent cold air entering the building and increasing the problem by creating a fog. It has been known for roof sheets to be heated in a factory to prevent the formation of water droplets.

Domestic Structures
Stack effects are important elements in air movements in buildings and during winter substantial volumes of air will rise. This encourages concentration of moisture and is particularly critical in buildings where most of the moisture input is on the ground floor while the first floor may be less well heated.

It is typical for nearly half the air lost from buildings as ventilation to make its way into the roof space. Condensation can result, particularly where the ceiling is insulated and the temperature in the roof space is low. Much of the air lost by ventilation in houses enters the roof space through cracks and pipe openings.This conveys moisture from the interior into the roof space. In traditional buildings large quantities of fresh air entered the roof space at the eaves and the moisture was dissipated.

If insulation is installed in roofs, they usually have little effect on the penetration of air from the building below but they can, by blocking the eaves, reduce the inflow of fresh air to the roof and allow moisture levels to rise unacceptably.

In addition, the insulation prevents heat from reaching the roof space which thus, in a well insulated building, is very much colder than in the past. There is an increased risk of condensation.

Turbines on the roof can be used to increase the level of ventilation and thereby reducing the level of moisture of the air, which reduces the condensation risk.

In summary, use the turbine only for the spillover of moisture, and even then be very careful, if water droplets are being formed on the underside of the roof, it is highly unlikely that increased ventilation by means of the turbine will stop the problem - heating of the roof sheet or additional mechanical extraction is needed.

Stuffiness
Air movement to prevent a feeling of stuffiness can be achieved with very low air speeds e.g. 0,1 m/s. The removal of factory heat and the cooling of the body are the most important aspects of ventilation.

It is however, recommended that the minimum quantity of fresh air introduced per hour into a non-air-conditioned factory should not be less than 28.80 m³ per person or 5.40 m³ per m² of floor area.

(These quantities are generally accepted as necessary to remove odours and maintain oxygen and carbon dioxide levels).

Fire
The turbines have not been passed as a fire ventilators. Under no circumstances are they to be sold as such as there is strict legislature governing the construction and operation of fire ventilators.