|
|
Acutherm Modular VAV Systems
The TF-HC Therma-Fuser
Thermally Powered VAV Module Page - 4
The TF-HC Therma-Fuser
THERMA-FUSER™ THERMALLY POWERED VAV MODULE
SYSTEM MODULE
The best control for heating/cooling units supplying air to VAV terminals is a discharge thermostat which maintains a constant supply air temperature. With DX equipment these are a high and low limit. For hybrid systems (part VAV and part constant volume) control the heating/cooling supply unit with a thermostat in one of the rooms with a constant volume diffuser, preferably the space with the greatest load. For both VAV or hybrid systems, the fan should run continuously.
The constant discharge velocity of Therma-Fuser modules at varying air flow provides good room circulation which reduces stratification. Keeping heating supply air temperatures as low as possible will further reduce room air stratification to a negligible level.
Static pressure at the inlet of the Therma-Fuser module should be between .05" wg./12Pa and .25"wg./62Pa at full and partial air flows. Static pressure below .05" wg./12Pa will result in low air flow and less induction. Above .25"wg./62Pa, Therma-Fuser modules operate well but excessive noise may result. Use minimum flow stops where Therma-Fuser tight shut off is not needed.
If the system turns down more than 30%, static pressure should be controlled. Included in the options for static pressure control are bypass, fan control and discharge dampers. Zone dampers are recommended where several zones share a higher pressure duct or riser.
When designing ducts, if Therma-Fuser modules are to deliver nominal volume at inlet SP of .15"wg./37Pa and if a maximum SP of .25"wg./62Pa is to be held for quiet operation, size the duct for a maximum pressure drop of .1"wg./25Pa between the first and last takeoff.
Because Therma-Fuser modules control from temperature by sensing room air induced up the center of the space, care should be taken not to disturb room air induction and entrainment. For example, location next to walls or dropped lights results in the reflection of primary air back at the Therma-Fuser module. Avoid this with a three-way blow pattern or relocate either the Therma-Fuser module or the light.
Acutherm has "how to" system design brochures for almost every ducted air system. For specific recommendations refer to the brochure for your system.
GUIDE SPECIFICATION
Thermally powered variable air volume modules shall be Therma-Fuser model TF-HC manufactured by Acutherm, Hayward, CA. Each module shall be a complete VAV terminal and thermostat self-contained in a nominal 2' x 2' diffuser. External wiring or pneumatics shall not be allowed.
The modules shall vary the supply air volume to provide both VAV heating and VAV cooling. They shall be thermally powered using two room temperature sensing thermostats and one changeover thermostat. The room temperature settings for heating and cooling shall be separately adjustable in the field by separately adjusting each of the two room thermostats.
One room temperature sensing thermostat shall sense room temperature and vary the supply air when cooling. The other room temperature sensing thermostat shall sense room temperature and vary the supply air when heating and shall be biased to offset room temperature stratification.
Each room sensing thermostat shall have a micrometer type temperature set point adjustment with an indicator that moves along a 70°F/21°C to 78°F/26°C temperature scale. Initial set point shall be factory set at 74°F/23°C.
The changeover thermostat shall be factory installed and adjusted to engage the heating mode when the supply air temperature rises above 80°F/27°C and return to the cooling mode when the supply air temperature falls below 68°F/20°C. The changeover mechanism shall not extend above the neck of the diffuser.
Each unit shall have four perimeter dampers to provide 66 lineal inches of variable discharge area at the perimeter of the diffuser for maximum Coanda effect and to avoid dumping. Each module shall be factory tested.
The manufacturer shall warrant that the module shall be free from defects in materials and workmanship for a period of ten years from date of shipment. Each module shall have a hinged appearance panel that can be unlatched and folded down to hang allowing hands to be free for adjusting temperature set points. Instructions for the module shall be on the inside of the appearance panel.
DIMENSIONS
Inlet Designation |
OD |
|
Inches ±1/16 |
mm ±3 |
|
6 |
5 15/16 |
150 |
8 |
7 15/16 |
200 |
10 |
9 15/16 |
250 |
12 |
11 15/16 |
300 |
TEN YEAR WARRANTY Acutherm warrants that its Therma-Fuser modules, exclusive of any options and accessories (whether factory or field installed) shall be free from defects in material or workmanship for a period of ten (10) years from the date of shipment and agrees to repair or replace, at its option, any parts that fail during said ten (10) year period due to any such defects which would not have occurred had reasonable care been taken, provided that such parts have been inspected by Acutherm and found defective and provided the modules have been given normal and proper usage and all parts and controls remain unaltered. Acutherm makes NO WARRANTY OF MERCHANTABILITY OF PRODUCTS OR OF THEIR FITNESS FOR ANY PURPOSE OR ANY OTHER EXPRESS OR IMPLIED WARRANTY WHICH EXTENDS BEYOND THE LIMITED WARRANTY ABOVE. ACUTHERM'S LIABILITY FOR ANY AND ALL LOSSES AND DAMAGES RESULTING FROM DEFECTS SHALL IN NO EVENT EXCEED THE COST OF REPAIR OR REPLACEMENT OF PARTS FOUND DEFECTIVE UPON EXAMINATION BY ACUTHERM. IN NO EVENT SHALL ACUTHERM BE LIABLE FOR INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR DAMAGES FOR INJURY TO PERSONS OR PROPERTY. Acutherm shall not be responsible for freight to or from its plant in connection with the inspection, repair or replacement of parts under the terms of this limited warranty nor for cost of removal of installation. |
1766 Sabre Street
Hayward, CA 94545
(510) 785-0510
FAX: (510) 785-2517