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THERMA-FUSER™
MAINTENANCE, CONTROLLING THE SYSTEM & MINIMUM FLOW
Maintenance
The moving parts of the TL Therma-Fuser 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 (TL-C and TL-CW)
References:
•
System Design, p 5, TL brochure, Form 21.1.
•
Chapters 2.2, 3.1 and 3.2, pp 6, 7 and 8, Designing
Modular VAV Systems, Form 5.2.
Supply Air Temperature
The source of cooling is 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. These objectives are best achieved by modulating chilled
water valves, and other variable equipment from supply air temperature. On/off equipment such as DX compressors are cycled
from supply air temperature. Use a discharge air sensor for the supply air temperature signal.
For TL-CW models, mode change between heating, recirculation and cooling is controlled from room temperature. Signals from
one or more room temperature sensors may be used for mode change. When using more than one sensor, a "majority rules"
approach is recommended. Constant volume heating temperature for TL-CW models should be as low as possible but no lower
than 80°F / 26.5° C.
Static Air Pressure
As with all VAV systems, the fan must run continuously during occupied times. 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 avoid diffuser noise by
limiting static pressure at both full flow and turndown 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, discharge
dampers, zone dampers, and fan control (variable speed 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.
MINIMUM FLOW (TL-C and TL-CW)
Standard TL units have a 10% leakage. To obtain higher minimum flows, a shorter length of blade gasket (foam) for each blade
can be factory installed or it can be field removed per the table below. The blade gasket must be removed at the end opposite
from the induction slot.
Amount of Gasket to be Removed from each Blade
Length Designation
24
36
48
60
Minimum Flow as a % of Maximum Flow
20%
5 in. / 128 mm
8 in. / 204 mm
11 in. / 280 mm
14 in. / 356 mm
•
Air Handling and Fan Coil Units Subzoned with Therma-
Fuser VAV modules, Form 6.7.
•
DX Equipment Zoned with Therma-Fuser VAV Modules,
Form 6.5.
30%
10 in. / 254 mm
11 in. / 280 mm
16 in. / 407 mm
28 in. / 712 mm
acutherm.com | THERMA-FUSER™ - Manual
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