Air changes per hour


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Air changes per hour

(ACH)
A metric of the air-tightness of a structure, often expressed as ACH50, which is the air changes per hour when the house is depressurized to50 pascals during a blower door test. The term ACHn or NACH refers to “natural” air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. ACHn or NACH is used by many in the residential HVAC industry for system sizing calculations.
References in periodicals archive ?
The Queen had been absolutely right; the number of air changes per hour was totally inadequate, and straight away we took all sorts of steps to improve the conditions.
We modeled room ventilation rates of 0.5 and 2 air changes per hour that correspond to 18 [ft.sup.3] and 72 [ft.sup.3] (0.5 [m.sup.3] and 2.0 [m.sup.3]) per minute.
Hunter Fan Co., a leading proponent of the system, calls CADR "the single most important piece of information needed to make a head-to-head comparison of an air cleaner's performance [because] CADR gauges the real-world performance of an air purifier," not filter effectiveness or air changes per hour.
The report set out to estimate volatile organic compound (VOC) concentrations in a new or renovated standard-sized classroom measuring 40 feet by 24 feet by 8 1/2 feet with a ventilation rate of 0.9 air changes per hour, and in a standard-sized state office that is 10 feet by 12 feet by 8 1/2 feet with a ventilation rate of 0.75 air changes per hour.
* Place patient in an airborne-isolation room, with monitored negative air pressure and 6-12 air changes per hour.
This solution produces up to 15 air changes per hour, well above the standard office air conditioning rate of six air changes per hour.
A lab's self-contained HVAC unit must have an increased number of air changes per hour, which means how often the room is completely replaced with fresh air from outside.
We have spent weeks with engineers calculating the number of air changes per hour required in various parts of the building.
For instance, in the 1997 California study, the air exchange rate in a 1997 Ford Explorer standing still with the vents on the "recirculate" setting and the fan on "low" was 1.8 air changes per hour, more than in the average home.
If this 13.7 percent had used plastic housewraps, greenhouse gas emissions could have been reduced by two to nine million tons ([CO.sup.2]) equivalent (depending on the percentage reduction in air changes per hour) - that's the same amount of [CO.sup.2] generated from the operation of between 100,000 and 450,000 cars over the same period.
Although nine air changes per hour might seem more than adequate, the total amount of outside air being supplied to the natatorium was only 2,000 cubic feet per minute (cfm).
The room should have at least six air changes per hour and should be maintained at negative pressure so that air flows from the halls into the room, preventing contaminated air from escaping.