Assessments - 3, GPA: 4.3 ( )

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We recommend aluminum foil tape. Stale Air Return System The stale air return system is used to draw air from the points in the building where the worst air quality problems occur. Balancing dampers and/or adjustable grilles are recommended on all return air lines which are used during installation to help balance the “draw” from different areas of the building. Alternately, the stale air may be drawn directly from the return air duct. When this system is used, the air handler’s blower must constantly operate. The exhaust takeoff connection must be at least a 3 ft (1 m) from a directly connected HRV/ERV supply duct if both are connected to the same duct run. Static pressure of the air handlers return system should be noted and compensated for if, it is apparent that the static pressure of the return in the air handler will exceed .1 to .15” W.C. A damper located just prior to the HRV/ERV is required to balance the stale air exhausted with the fresh air supply entering the building. Return air suction points should be located on the opposite side of the room from the fresh air inlet. The inlets may be located in the ceiling or high on the walls and fitted with inlet grilles. Many commercial activities produce air contaminants in the form of dusts, fumes, mists, vapours and gases. Contaminants should be controlled at the source so that they are not dispersed through the building nor allowed to increase to toxic concentration levels. The ventilator allows for economical operation of the HVAC system while effectively removing contaminants from the space. In designing the exhaust portion of the system the exhaust grilles are placed so as to remove the contaminants while not allowing them to enter the breathing zone of the occupants. For contaminants that are lighter than air, grilles should be located high on the wall. If contaminants are heavier than air, a lower placement of the grilles will be required. Information on a contaminants specific gravity and toxicity should be available from chemical data sheets. 14 Fresh Air Supply System The fresh air supply ductwork from the HRV/ERV may be directly connected to the return air duct of the forced air system. Check the air flow balance of the HRV/ERV with the air handler blower both “ON” and “OFF” to determine that it does not imbalance the HRV/ERV more than 10%. Also, it is advisable to include a short length of flex duct or other non-metallic connector in this hard ducted line in order to keep the HRV/ERV acoustically isolated and separately grounded (electrically) from the air handler. This will avoid a possible shock hazard to service people if a short to ground develops in one of the devices. It may be necessary to install a separate fresh air supply ductwork system if the heating is other than forced air. When installing an HRV/ERV, the designer and installer should be aware of local codes that may require smoke detectors and/or firestats in the HVAC or HRV/ERV ductwork. Because an HRV/ERV is designed to bring fresh air into the building, structures may require supply voltage interrupt when smoke or flame sensors are triggered, or when a central fire alarm system is activated. Supply air grilles may be ceiling or high wall mounted. Avoid locating incoming fresh air grilles that could cause a direct draft on the occupants as the incoming air may be below room temperature. A reheat duct heater can be installed to improve occupant comfort. The use of balancing dampers or adjustable grilles to balance the flow rates into various rooms is recommended. The use of balancing dampers or adjustable grilles as supply air diffusers and air exhaust covers are recommended. TECHGRILLES™ are round, efficient, sound absorbing devices available in 4”, 5”, 6” and 8” (100, 125, 150, and 200 mm) models. AIR FLOW SUPPLY AIR FLOW EXHAUST TECHGRILLE (optional) schematic The Integrated HVAC System Figure A and B The HRV/ERV has become an integral component of the HVAC system. Figure A shows an HRV/ERV unit providing fresh air directly to the return air plenum of a rooftop heat/cool unit. In the balanced airflow system, the HRV/ERV exhaust removes stale room air (eg. from lunch room, storage or copy area) and returns to the space an equal amount of fresh outdoor air, making the use of an economizer obsolete in conjunction with an HRV/ERV. Many buildings have ceiling return air plenum as in Figure B. Fresh air from the HRV/ERV can be introduced directly into the ceiling space but this should occur near the air handler’s intake. By operating the HRV/ERV on a 24 hour/7 day battery backed timer, the unit can be set to operate only when occupancy or indoor conditions require the air exchange. In installations where it is satisfactory to provide general exhaust from the space, the air to be exhausted may be taken directly from the return air plenum to the HRV/ERV as it is drawn back to the air handler. Fresh air supplied by the HRV/ERV is then introduced directly into the return air plenum...

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