P

Pascal (Pa)
A unit measuring pressure; airtightness tests are commonly conducted with a pressure difference of 50 Pascals between inside and outside.

Position of sun
The position of the sun in the sky, and hence the direction of the solar beam, is described by the solar altitude and solar azimuth angles. The solar altitude is the angle between the line to the centre of the sun and the horizontal plane. When the sun is on the horizon, the solar altitude is 0°. When the sun is directly overhead, it is 90°. The azimuth is the angle between true south and the point on the horizon directly below the sun. By convention, it is negative before noon and positive after noon.

The altitude and azimuth angles vary from hour to hour and season to season.

Positive pressure
A pressure above atmospheric.

Predicted mean vote (PMV)
The predicted mean vote (PMV) is a thermal sensation scale. The mean opinion of a large group of individuals expressing a vote on their thermal feeling under different thermal circumstances has been used to provide an index to thermal comfort. A PMV value of zero provides the optimal thermal comfort conditions. A positive PMV value means that the temperature is higher than optimal and a negative value means that it is lower. The comfort zone is generally regarded as stretching from a slight feeling of cold (termed 'fresh', when the PMV is -1) to a slight feeling of warmth (termed 'mild', when the PMV is+1).

Predicted percentage of dissatisfied (PPD)
The predicted percentage of dissatisfied (PPD) is an indication of the percentage of people susceptible to feeling too warm or too cold in a given thermal environment. It can be deduced from the PMV. If, for instance, the PMV is in the range -1 to +1, then the PPD index shows that 25% of the population will be dissatisfied. To reduce this figure to 10%, then the PMV has to be in the range -0.5 to +0.5.

Primary energy (kWh or MJ)
The total amount of energy drawn from a primary source (oilfield, coalmine, etc.) to extract, process, transport and distribute the fuels used for domestic and other purposes; it is a quantity that is higher than the calorific value of those fuels (delivered energy) by an amount representing the energy cost of extraction, processing, transportation and distribution of fuels.

Provençal well
See Canadian well.