uncertainty

The steady-state concentration of occupant generated carbon dioxide (CO2) is used in some applications as an indicator of compliance with a required ventilation rate. These applications assume that the CO2 is at a uniform concentration in the space being considered, and that the outdoor concentration, ventilation rate, and CO2 emission rate are all constant. Emission rates are often derived using an equation in the ASHRAE Fundamentals Handbook, which is poorly referenced and not based on the most recent understanding of the principles of human metabolism.

Building airtightness tests have become very common in several countries, either to comply with minimum requirements of regulations or programmes, or to justify input values in calculation methods. With more widespread use it has become increasingly important to understand and quantify the reliability of these tests.

Mandatory building airtightness testing has come gradually into force in European countries, mostly because of the increasing impact of building leakage on the overall energy performance of low-energy buildings.  Therefore, because of related legal and financial issues, the reliability of the airtightness test has become a crucial issue and has raised the question of the fan calibration process. 

Uncertainties in airtightness measured using fan pressurization test should not be defined by the scattering of the points around the line defined using ordinary least square method anymore. Its definition requires first to know the uncertainties in pressure and airflow measurements. This works aims at quantifying one of the component of the envelope pressure uncertainty: the uncertainty in zero-flow pressure approximation due to short-term fluctuation of wind speed and direction.

This paper analyses the contribution of a steady wind to the uncertainties in building pressurisation tests, using the approach developed in another paper (Carrié and Leprince, 2016). The uncertainty due to wind is compared to the uncertainties due to other sources of uncertainty (bias, precision and deviation of flow exponent).
The main results of this study are:

This paper discusses two particular points of the buildings airtightness measurement method (ISO 9972) in relation with the calculation of the combined standard uncertainty: (1) the zero-flow pressure difference and (2) the weighted line of organic correlation.

Existing protocols for the inspection of mechanical residential systems poorly address both the assessment of uncertainties and recommendations or specifications for measurement methods and devices to be used to guarantee low measurement uncertainties. This paper gives the major elements of a new protocol developed within the Promevent project to overcome this problem. We have analyzed results from 180 airflow measurements performed in laboratory conditions in accordance with this protocol.

Quantification of natural ventilation rates is an important issue in HVAC system design. Natural ventilation in buildings depends on many parameters whose uncertainty varies significantly, and hence the results from a standard deterministic simulation approach could be unreliable.

Although standards for single-zone air leakage tests are widely used, there are no existing standards for several multi-zone cases including: 1) testing air leakage between adjacent zones or 2) testing leakage to the outside from a single unit in a multi-zone building. While a range of test procedures have been used to determine inter-zone leakage using fan-pressurization, the accuracy of the methods can vary significantly. Using field measurements and simulations, we compared the uncertainty in the leakage between two adjacent zones for different measurement and calculation methods.

In this paper we present a series of leakage tests on extremely airtight dwellings (ACH50 < 0.6 upon completion) in which the durability of the airtightness and the measurement uncertainty involved are assessed. In literature, repeatability and reproducibility issues have been discussed by several authors, along with influences of weather. It remains unclear, however, to what extent the available uncertainty intervals are relative or absolute.