OLEG SYSTEMS

A reliable ventilation system that can operate during a fire is both vital and essential. It prevents smoke logging, allows people to escape quickly, minimizes damages to property and contents and enables firemen to attack the fire without hindrance. Such power roof ventilators have the added advantage of providing normal day to day ventilation and in many cases can also be fitted with duct work for use in multi storey buildings.
Direct gas-fired equipment is the most efficient choice for makeup air. While indirect gas-fired equipment might have a nominal energy efficiency of 75% to 80%, a direct-fired unit will operate at a nominal 93%. Thus, the further north or more extreme the climate, the more valuable a direct-fired piece of equipment becomes. The type of make up air equipment used, as well as its size, is usually dependent on the climate. Humid areas of the country require considerably larger-capacity units to dehumidify outdoor air. The supply air requirements for occupant comfort are generally air temperatures of 70 degrees to 75 degrees F with an rh of 50%. A good design criteria for air-handlung units engineers is to specify the unit performance at two operating conditions - a design day and an off-peak period such as a 70 degrees rainy day. The off-peak times of the year are actually more critical to evaluate the unit performance because this is the lion's share of the unit operation. Engineers also need to specify the maximum allowable supply air dew points. It is also possible to experience condensation within the heat exchanger sections of indirect- fired units in very cold climates. If the heat exchanger is not properly pitched and drained and not constructed of stainless steel through all sections, then corrosion and premature failure can occur.
That's not to say that indirect gas-fired makeup air equipment doesn't have its place, but again, it comes down to the climate. Climates with high concentrations of combustible or potentially toxic elements in the air might not be suitable for direct-fired equipment as the air is directly exposed to the flame. Many applications allow the recirculation of some of the air from the space and return air that is laden with paint, solvents, or very fine powders would be better handled with an indirect gas-fired piece of equipment.