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BACNET™ MOTORIZED VAV DIFFUSER
MAINTENANCE & CONTROLLING THE SYSTEM
Maintenance
The moving parts of the EF-B diffuser have no maintenance or lubrication requirements. We are often asked to recommend
periodic maintenance procedures and a spare parts stock. Recommended maintenance is to clean the outer surfaces of the
Therma-Fuser diffuser - nothing else. We do not recommend stocking any spare parts. Our customers also confirm that stocking
is unnecessary.
Controlling the System
References:
•
System Design section of EF-B Brochure (Form 091.101).
•
Chapters 2.2, 3.1 and 3.2, pg. 6, 7 and 8, Designing
Modular VAV Systems (Form 5.2).
Supply Air Temperature
The sources of cooling and heating are controlled from supply air temperature. As with all VAV systems the goals are to achieve a
constant supply air temperature (may be reset to another constant supply air temperature) and to limit the supply air temperature.
Limits for supply air temperature should be between 50˚F/10˚C and 68˚F/20˚C when cooling and between 80˚F/26.5˚C and
120˚F/49˚C when heating. The heating temperature limit should be as low as possible. These objectives are best achieved by
modulating chilled water valves, hot water valves and other variable equipment from supply air temperature. On/off equipment
such as DX compressors and electric heat are cycled from supply air temperature. Use a discharge air sensor for the supply air
temperature signal.
Mode change between heating, recirculation and cooling is controlled from room temperature. Object analog_input_0 (oRmTemp)
from the EF-B Therma- Fuser diffuser may be used for mode change. A "majority rules" approach is recommended.
Static Air Pressure
As with all VAV systems, the fan must run continuously during the occupied hours. Goals of static pressure control are to provide
enough static pressure to obtain the required air volume especially at the diffuser farthest from the fan, to limit static pressure at
both full flow and turndown, to avoid diffuser noise and to provide pressure independence or consistent operation as the system
flow changes. These objectives can be achieved with the usual methods of automatic static pressure control: bypass dampers,
zone dampers, and fan speed control (variable frequency drives, inlet dampers, etc.). Locate the static pressure sensor as far
down the duct as possible - at least 2/3 down the duct from the first takeoff.
•
Air Handling and Fan Coil Units Subzoned with Therma-
Fuser VAV Diffusers (Form 6.7).
•
Dx Equipment Zoned with Therma-Fuser VAV Diffusers
(Form 6.5).
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