Institutional Direct-fired Air Handling Units

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-Fired Pressurization Units move large quantities of air by low temperature differentials (usually 50° or fewer), which namely a tactics to lessen temperature stratification in the large spaces they are employed to heat. The equipment is typically mounted on the roof of the facility or by grade aboard hoisted assists to assure namely the afford air is conveyed tall. The high air distribution allows as a longer “throw” of the air, thereby requiring fewer equipment to cover the necessitated layer district. The maximum mutual fuel is normal gas, although, units can be converted to burn propane. There are 2 basic categories of gas-fired AHUs: indirect-fired and direct-fired.
Indirect-fired units scald the fuel and climate blend inside of a heat exchanger while the atmosphere traveling apt the space passes over the appearance of the heat exchanger. In this chart, the productions of combustion peregrination via a vent to the outdoor of the creating.
Direct-fired units utilize air that ambition be sent to the heated space for combustion without use of a heat exchanger. The products of combustion are merged instantly with large volumes of outdoor air. Such mixing is thought safe for of the high dilution percentage.
In addition, thorough burning of the natural gas takes area so that not harmful products of combustion enter the airstream. One product of combustion is water vapor,[link widoczny dla zalogowanych], which can be problematic with very tight building construction deserving to the latent for condensation in colder airs. For firm buildings, it is best to consider the use of indirect-fired equipment. There are several common configurations of direct-fired units.
The 80/20 design can vary the amount of outside air from 100% down to 20%. The burner has a high turndown ratio and merely outside air should be drawn cross the burner. The unload air volume is nailed and the amount of outside air can be adjusted to maintain building pressurization. The composition air unit configuration is ideal for supplying large quantities of replacement air for facility exhaust systems. Such systems can comprise paint spray compartments and other industrial exhaust applications. These units supply a fixed amount of 100% outside air. Air Recirculation units recirculate a firm 80% of the air while sending in 20% outside air that passes over the burner. They supply a minimum measure of airing to spaces that do not require large quantities of outside air to maintain building pressurization.
Variable Air Volume VAV units have a varying supply air volume and work alike to the 80/20 design, however, the recirculated air passes through a bypass section instead of through the facility. This type of unit is secondhand in petitions where mansion pressurization is desired and where contaminants located in the space cannot be recirculated.
Facilities that have indoor traffic operation frequently amass carbon monoxide and associated noxious fumes. For such examples,[link widoczny dla zalogowanych], a ventilation series can be instituted to limit this potentially harmful buildup. The pressurization units for these buildings could be fitted with a carbon monoxide detector with an initial setpoint of, for example,[link widoczny dla zalogowanych], 50 ppm that would trigger an alarm and energize a time-delay relay.
If the condition still exists later, mention, five minutes, then the return air damper would modulate closed and the outside air damper would modulate to the 100% open situation. A second setpoint of 100 ppm would initiate one panic and eventually de-energize the burner. The dampers would then be positioned to qualify the exhaust mode. After the carbon monoxide returns to a safe level, the sensor could reset the unit to customary operation.
In appending to emergency ventilation to purge carbon monoxide, the pressurization unit can be used to provide a source of ventilation during warm and hot months of the year. A reverse performing thermostat would modulate the outside air and return air dampers to bring in extra outside air to maintain the indoor setpoint. These units can likewise be fi