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Direct gas-fired unit
- Thread starter slav72
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AbbyNormal
Mechanical
In Canada, direct fired is allowed on 100% outside air with an interlocked exhaust. In the USA they may allow a bit of recirculation.
Take the "V" out of HVAC and you are left with a HAC(k) job.
Take the "V" out of HVAC and you are left with a HAC(k) job.
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- #4
Revisions from Engineered Systems website:
One of the biggest changes between the old and new standard is that under the old standard, engineers could specify a direct-fired recirculation unit as long as they provided a minimum of 4 cfm of outside air for every 1,000 Btuh of heat provided.
On January 1 of this year, it became necessary for the unit to operate in compliance with a sliding scale of outside air vs. "equivalent temperature rise." The greater the temperature rise, noted Mike Kaler, marketing manager for Applied Air, the greater the amount of outside air required by the standard.
Units must also be self-regulating or "adaptive." "They must be able to vary the amount of outside air, or the temperature rise, or both, in order to keep the unit in compliance at all times. The required amount of outside air could fluctuate from 100% down to as little as 10% or 15% depending upon the temperature rise through the burner section," said Kaler.
Allen Pirro, chief engineer for Intertek Inc., which tests equipment for the ETL mark, noted the revision addressed concerns about the testing methods to ensure that the heaters, when operated in the recirculating mode, would not produce amounts of CO and N[O.sub.2] in excess of national standards. "It meant some redesign and retesting to verify compliance."
One of the biggest changes between the old and new standard is that under the old standard, engineers could specify a direct-fired recirculation unit as long as they provided a minimum of 4 cfm of outside air for every 1,000 Btuh of heat provided.
On January 1 of this year, it became necessary for the unit to operate in compliance with a sliding scale of outside air vs. "equivalent temperature rise." The greater the temperature rise, noted Mike Kaler, marketing manager for Applied Air, the greater the amount of outside air required by the standard.
Units must also be self-regulating or "adaptive." "They must be able to vary the amount of outside air, or the temperature rise, or both, in order to keep the unit in compliance at all times. The required amount of outside air could fluctuate from 100% down to as little as 10% or 15% depending upon the temperature rise through the burner section," said Kaler.
Allen Pirro, chief engineer for Intertek Inc., which tests equipment for the ETL mark, noted the revision addressed concerns about the testing methods to ensure that the heaters, when operated in the recirculating mode, would not produce amounts of CO and N[O.sub.2] in excess of national standards. "It meant some redesign and retesting to verify compliance."
ANSI Z83.18 and Z83.4 should be the standards you would like to review
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