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The first blower door was further used to test the airtightness of the Saskatchewan Conservation House built in 1977, which was tested at 0.5 ach at 50 Pa. These early research efforts demonstrated the potential power of blower door testing in revealing otherwise unaccounted for energy losses in homes.
A third test method to determine if ductwork is leaking to the outside is to use a pressure pan, which is a register cover with a pressure tap for a hose connection. With the house pressurized (or depressurized) to 50 Pa (-50 Pa) using a blower door, a pressure gauge is attached to the pressure pan by means of a hose.
Building airtightness levels can be measured by using a fan, temporarily installed in the building envelope (a blower door) to pressurize the building. Air flow through the fan creates an internal, uniform, static pressure within the building.
It is worth noting that ACH measured with the blower door test, at a differential pressure of 50 pascals, mimics the situation of a sustained 20 mph (32 km/h) wind outside. The natural air leakage, under calmer conditions, is likely to be much less. As a result, the so-called natural ACH may be a factor of 10-25 times smaller. [14]
A typical commercial air curtain enclosure. In North America, the more commonly-used term for an air door is "air curtain". The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines an air door as follows: "In its simplest application, an air curtain is a continuous broad stream of air circulated across a doorway of a conditioned space.
There are two major systems to classify ductwork airtightness, one based on European standards, the other based on ASHRAE standard 90.1-2010.Both are based on the leakage airflow rate at a given ductwork pressure divided by the product of the ductwork surface area and the same ductwork pressure raised to the power 0.65.
Small air handlers, for local use, are called terminal units, and may only include an air filter, coil, and blower; these simple terminal units are called blower coils or fan coil units. A larger air handler that conditions 100% outside air, and no recirculated air, is known as a makeup air unit ( MAU ) or fresh air handling unit ( FAHU ).
Figure 1: Components of a centrifugal fan An external motor belt driven inline centrifugal fan discharging inline to the exterior of a building through a duct. Unlike non-inline/non-concentric impeller casing design with a cutoff blade above, the concentrically symetric cylinder casing and impeller geometry of inline type redirects the outflow around so that it is parallel to the inflow of gases.