Assessments - 2, GPA: 5
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Facilidade de uso
When this system is used the air handler's blower will constantly operate. The exhaust takeoff connection must be at least a meter from a directly connected HRV supply duct if both are connected to the same duct run. A damper located just prior to the HRV is required to balance the stale air exhausted with the fresh air supply entering the building. Return air suction points should be located at the opposite side of the room to the fresh air inlet. The inlets may be located in the ceiling or high on the walls and fitted with inlet grilles. In residential applications the gyproc and studs of the wall can be used as a "duct" for high wall returns. When using wall cavities this way, they should be lined with either galvanized sheet metal or polyethylene (check Local Codes). The wall plate and the floor ply must be cut out to accept either ducting or the proper sized sheet metal boot. 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 heat recovery 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 the chemical data sheets. FRESH AIR SUPPLY SYSTEM The fresh air supply ductwork from the HRV may be directly connected to the return air duct of the forced air system. When directly connected it is recommended that the air handler blower be in constant operation to move the fresh air about the building. Also, it is advisable to include a short length of fabric flex duct or other non-metallic connector in this hard ducted line in order to keep the HRV 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, the designer and installer should be aware of local codes that may require smoke detectors and / or firestats in th HVAC or HRV ductwork. Because an HRV is designed to bring fresh air into the building, structures may require a supply voltage interrupt when smoke or flame sensors are triggered or 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 as supply air diffusers and air exhaust grilles are recommended. TECHGRILLES™ (from NUTECH) are round, efficient, sound absorbing devices available in 4", 5", 6" (100,125 and 150 mm). 5 THE INTEGRATED HVAC SYSTEM The HRV has become an integral component of the HVAC system. Figure 4A shows an HRV unit providing fresh air directly to the return air plenum of a Rooftop heat/cool unit. An economizer if installed on the air handler may be used to provide first stage free cooling, but the outside air damper is to be set at its minimum opening or 0° position. In the balanced airflow system, the HRV 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. Many buildings have a ceiling return air plenum as in Figure 4B. Fresh air from the HRV can be introduced directly into the ceiling space but this should occur near the air handler’s intake. By operating the HRV 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 as it is drawn back to the air handler. Fresh air supplied by the HRV is then introduced directly into the return air plenum but at a location closer to the air handler. The air handler would have a constant running blower to effectively distribute the fresh air and remove the stale air. Bal...
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