Model TB Therma-Fuser diffusers are 24” x 24” (600mm sq.) ceiling diffusers with built-in temperature controls and VAV damper. The round damper moves up to close and down to open, metering air flow into the room in response to room temperature. The damper is mechanically positioned by a thermostat/actuator that is both room thermostat and damper motor. The room thermostat/actuator is a large brass cylinder containing a petroleum-based wax. The wax melts and expands when heated, pushing the piston outward. A spring pulls the piston inward when the wax cools.

The Therma-Fuser diffuser is a simple stand alone device that pro- vides VAV control when supplied with air in a suitable range of tem- perature and pressure.

Therma-Fuser™ VAV diffusers allow for all low-pressure system designs. No energy is required to operate the diffuser’s controls. As U.S. Green Building Council members, Acutherm is proud to produce energy efficient VAV diffusers that prevent over cooling and over heating — producing 15%-47% energy savings when compared to traditional VAV Systems.

High-performance air systems demand modern design approaches with leading-edge products and technology in order to optimize comfort while greatly reducing energy consumption. A comfortable environment is achieved by providing the smallest possible zones of temperature control, allowing for individual temperature distribution and better air movement. Reduction in energy is realized by designing a low-pressure HVAC system that allows for maximum turn down while maintaining temperatures.

As energy costs continue to rise, the management of energy while balancing tenant comfort and operational costs is a significant challenge for commercial building owners and managers. A Building Automation System (BAS) is an option that provides monitoring of entire building systems with single source control and troubleshooting.

Acutherm’s Therma-Fuser VAV System is designed to work cooperatively with the wide range of BAS options available. Whether you're looking for simple individual temperature control, requiring no energy for operation, or full-scale networking for system scheduling, monitoring, reporting, troubleshooting and more, this guide will help you determine what is best for your building needs and budget. Six basic options are compared using the quick chart on the following page, then each option is described in more detail throughout.

Individual temperature control is the principle goal of the Therma-Fuser VAV application in direct expansion (DX) cooling systems. Therma-Fuser diffusers can subzone SYSTEMS AS SMALL AS TWO TONS into individual temperature control.

Acutherm’s thermally powered VAV diffusers have been meeting people’s individual comfort requirements since 1978. With over one million installations throughout the world, the Therma- Fuser VAV diffuser has proven to be reliable, efficient, flexible, affordable and the sustainable design solution for providing individual temperature control.

Manual dampers will not satisfy these objectives because the pressure drop across them varies as the air 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 vanes, etc.). In addition, R-Rings, unique to VAV diffusers, provide bypass at the dif-fuser where the system has a ceiling plenum return

The rule of thumb when installing Therma-Fuser™ diffusers is that obstacles should not extend more than 1/16 in/1.5 mm below the plane of the bottom of the diffuser. Breaking this plane reduces the throw and destroys throw completely at low air flows.

The rule of thumb when installing Therma-Fuser diffusers in special ceil- ings is that obstacles should not go below the plane of the diffuser casing extended. Breaking this plane reduces the throw and destroys throw completely

The built-in transducer is connected with ¼” / 6mm tubing by others to a static pressure fitting located in the duct at the point of control. This transducer is a mass airflow sensor which measures the airflow (0.007cfm / 0.003 l/s max.) from the duct to a port open to atmosphere and converts that to a voltage output indicating differential pressure. For differential pressure above set point, zone dampers are rotated closed and bypass dampers rotated open. The opposite happens when the differential pressure is below set point. Dual motors provide the rotation—one operating clockwise and the other counterclockwise.

The Acu-Zone electric heater is equipped with the most advanced modulating airflow sensor. When the room temperature drops below the room mode control thermostat set point, the heating coil is energized. Airflow is measured by the patented airflow sensor and power to the heating coil is modulated by a SCR proportional heat controller to produce a constant discharge air temperature even at extremely low air-flow conditions.

The Acu-Zone electric heater is equipped with the most advanced modulating airflow sensor. When the room temperature drops below the room mode control thermostat set point, the heating coil is energized. Airflow is measured by the patented airflow sensor and power to the heating coil is modulated by a SCR proportional heat controller to produce a constant discharge air temperature even at extremely low air-flow conditions.

Bypass R-Rings are used to bypass supply air into the ceiling plenum when Therma-Fuser VAV diffusers turn down. The purpose of the bypass is to limit diffuser noise by limiting inlet static pressure. A Therma-Fuser diffuser with a bypass R-Ring has a constant volume air flow to it and, therefore, also over the balancing damper. This results in a constant pressure drop over the balancing damper which, in turn, limits the static pressure at the diffuser at both full flow and turn down.

Because supply air is bypassed into the ceiling plenum, R-Rings can not be used with a ducted return. They also require a four way blow pattern as three, two or one way patterns upset the bypass.

R-Rings are available in three nominal inlet sizes of 6 in./150mm, 8 in./200 mm and 10 in./250mm. There is no 12 in./300mm inlet R-Ring.

Every Therma-Fuser™ diffuser is a VAV zone of temperature control providing pleasing comfort in both heating and cooling. A wide range of control with comfort set points adjustable from 55-95˚F/13- 35˚C. The electric motor delivers a consistent response for control of room temperature, and when required, a quick response to commands. The Wall Adjuster provides easy access for unit configuration and for the occupant to adjust comfort set points

The swirl face provides a modern aesthetically pleasing appearance and every Therma-Fuser™ diffuser is a VAV zone of temperature control providing pleasing comfort in both heating and cooling. A wide range of control with comfort set points adjustable from 55-95˚F/13- 35˚C. The electric motor delivers a consistent response for control of room temperature, and when required, a quick response to commands. The Wall Adjuster provides easy access for unit configuration and for the occupant to adjust comfort set points

Every Therma-Fuser™ diffuser is a VAV zone of temperature control providing pleasing comfort in both heating and cooling. A wide range of control is available with comfort set points adjustable from 55-95˚F/13-35˚C. The electric motor delivers a consistent response for control of room temperature, and when required, a quick response to commands. The Wall Adjuster provides easy access for unit configuration and for the occupant to adjust comfort set points.

Model ML Therma-Fuser diffusers are linear slot ceiling diffusers with built-in DDC controller, temperature sensors and VAV damper. The damper blade(s) open and close to meter airflow (hot or cold) into the room in response to room temperature. The damper(s) is modulated by a brushless DC stepper motor. The electric motor, rigorously tested to provide many years of reliable service, directly drives a threaded shaft connected with a linkage to the damper blade(s).

The controller uses an ‘expert system’ control similar to having an “expert” sitting there making the adjustments. Unlike PID control ‘expert system’ control does not require filed tuning. Every 10 second it determines if the flow should be adjusted and the amount of any adjustment based on temperat

The VA-HC Therma-Fuser module i s the same as the TF-HC except for a simple modification. A plenum for ventilation air i s added t o the top which is connected b y four ducts t o the four induction nozzles. In addition, two of the induction nozzles are enlarged for more ventilation air capacity. Ventilation air is introduced to the space through the induction nozzles and rapidly mixes with the thermal air. The mixture is distributed throughout the occupied por- tion o f the space.

The VA-HC Therma-Fuser module is the same as the TF-HC except for a simple modification. A plenum for ventilation air is added to the top which is connected by four ducts to the four induction nozzles. In addition, two of the induction nozzles are enlarged for more ventilation air capacity. Ventilation air is introduced to the space through the induction nozzles and rapidly mixes with the thermal air. The mixture is distributed throughout the occupied portion of the space.

Apart from the induction nozzles, the VA-HC works the same as the TF-HC

Low temperature air must be introduced into the room so that it does not reach the occupied zone. VAV boxes with fixed diffusers can not always do this because the more dense low temperature air drops or dumps at low flows.

A common answer is to use a series (continuous) fan powered box to mix the cold supply air with air from the return plenum, raising air temperature before introducing it to the room. The risk of low temperature air reaching the occupied zone is reduced by delivering a constant volume of warmer air to the room.

The temperature control level (set point) of the Therma-Fuser diffuser is lowered by adding heat to the thermostat/ actuator. A small resistance heater attached to the thermostat warms it and adds just enough heat to create a precise thermal differential between the temperature sensed at the Therma- Fuser diffuser thermostat and actual temperature in the space. This bias heat causes the thermostat to control at the lower temperature selected at the Wall Adjuster.

Model TF Therma-Fuser diffusers are 24” (600mm) square ceiling diffusers with built in temperature controls and VAV damper. Four blade dampers move up to close and down to open, metering air flow (warm or cool) into the room in response to room temperature. The dampers are mechanically positioned by thermostat/actuators which are both a room thermostat and damper motor. The room thermostat/actuators are a large brass cylinder containing a petroleum based wax. The wax melts and expands when heated, driving a piston out. A spring retracts the piston when the wax cools and contracts. The movement of the piston positions the dampers in a proportional manner.

Model ST Therma-Fuser diffusers are 24” (600mm) square ceiling diffusers with built-in temperature controls and VAV damper. The round damper moves up to close and down to open, metering air flow (warm or cool) into the room in response to room temperature. The damper is mechanically positioned by a thermostat/ actuator which is both a room thermostat and damper motor.

The room thermostat/actuator is a large brass cylinder containing a petroleum based wax. The wax melts and expands when heated, pushing against a fixed piston which moves the thermostat outward. A heavy spring pulls the thermostat inward when the wax cools and contracts. Thumbwheels on the room thermostat push the two offset axles of the control arm to move the damper up or down.

Round model STR Therma-Fuser diffusers are 24 inch diameter ceiling diffusers with built in temperature controls and VAV damper. The round damper moves up to close and down to open, metering air flow (warm or cool) into the room in response to room temperature. The damper is mechanically positioned by a thermostat/actuator which is both a room thermostat and damper motor.

The room thermostat/actuator is a large brass cylinder containing a petroleum based wax. The wax melts and expands when heated, pushing against a fixed piston which moves the thermostat outward. A heavy spring pulls the thermostat inward when the wax cools and contracts. Thumbwheels on the room thermostat push the two offset axles of the control arm to move the damper up or down.

Model TB Therma-Fuser diffusers are 24” x 24” (600mm sq.) ceiling diffusers with built-in temperature controls and VAV damper. The round damper moves up to close and down to open, metering air flow into the room in response to room temperature. The damper is mechanically positioned by a thermostat/actuator that is both room thermostat and damper motor. The room thermostat/actuator is a large brass cylinder containing a petroleum-based wax. The wax melts and expands when heated, pushing the piston outward. A spring pulls the piston inward when the wax cools.

The built-in transducer is connected with ¼” / 6mm tubing by others to a static pressure fitting located in the duct at the point of control. This transducer is a mass airflow sensor which measures the airflow (0.007cfm / 0.003 l/s max.) from the duct to a port open to atmosphere and converts that to a voltage output indicating differential pressure. For differential pressure above set point, zone dampers are rotated closed and bypass dampers rotated open. The opposite happens when the differential pressure is below set point. Dual motors provide the rotation—one operating clockwise and the other counterclockwise.

Model TL Therma-Fuser diffusers are linear ceiling diffusers with built-in temperature controls and VAV damper. The damper blades open and close, metering airflow into the room in response to room temperature. The damper is mechanically positioned by a thermostat/ actuator, that is both room thermostat and damper motor.

The room thermostat/actuator is a large brass cylinder containing a petroleum- based wax. The wax melts and expands when heated, pushing against a fixed piston that moves the thermostat outward. A heavy spring pulls the thermostat inward when the wax cools and contracts. Four-slot models have two thermostat/ actuators.

Model TLW-C and TLW-CW Therma-Fuser diffusers are sidewall diffusers with built-in temperature controls and VAV damper. The damper blades open and close, metering airflow into the room in response to room temperature. The damper is mechanically positioned by a thermostat/actuator that is both room thermostat and damper motor.

The room thermostat/actuator is a large brass cylinder containing a petroleum-based wax. The wax melts and expands when heated, pushing against a fixed piston which moves the thermostat outward. A heavy spring pulls the thermostat inward when the wax cools and contracts. Four-slot models have two thermostat/actuators.

The model TK Therma-Fuser diffuser is a 12 5/8in / 320mm square ceiling diffuser with built-in temperature controls. The TK has four dampers that open and close to meter airflow (warm or cold) into the room in response to room temperature. The dampers are mechanically actuated by thermal actuator/thermostats.

Each thermostat/actuator is a small brass cylinder containing a petroleum- based wax. The wax expands when heated, driving a piston out. A spring retracts the piston when the wax cools and contracts. The movement of the piston positions the dampers in a proportional manner.

The Model TN Therma-Fuser diffuser is a 12 5/8 in / 320mm square ceiling diffuser with built-in temperature controls and VAV damper. The round damper moves up to close and down to open, metering airflow into the room in response to room temperature. The damper is mechanically positioned by a thermal actuator/thermostat.

Each thermostat/actuator is a small brass cylinder containing a petroleum- based wax. The wax expands when heated, driving a piston out. A spring retracts the piston when the wax cools and contracts. The movement of the piston positions the damper in a proportional manner.