CPD Programme
CPD Programme
The CIBSE Journal CPD Programme programme is free and can be used by any
Members of the Chartered Institution of reader. It is organised jointly by CIBSE Journal
Building Services Engineers (CIBSE) and other and London South Bank University, and will
professional bodies are required to maintain help you to meet CIBSE’s requirement for
their professional competence throughout CPD. It will equally assist members of other
their careers. Continuing professional institutions, who should record CPD activities
development (CPD) means the systematic in accordance with their institution’s guidance.
maintenance, improvement and broadening Simply study the module and complete the
of your knowledge and skills, and is therefore questionnaire on the final page, following the
a long-term commitment to enhancing your instructions for its submission. Modules will
competence. CPD is a requirement of both remain available online at www.cibsejournal.
CIBSE and the Register of the Engineering com/cpd while the information they contain
Council (UK). remains current. You can also undertake the
CIBSE Journal is pleased to offer this questionnaire online, and receive your results
module in its CPD programme. The back by return email.
The Basic Psychrometric Processes
The CPD articles in the April and August editions of the CIBSE Journal have
considered the main properties of moist air that may be determined from a
pair of coincident properties using the Psychrometric Chart and how values
may be calculated in the absence of a chart.
This article moves on to develop the core processes that are plotted on the
chart as means of illustrating and investigating the changes that take place to
the properties of humid air as it is ‘conditioned’. Symbols are defined in the
box at the end of the article – you may also find it useful to be able to refer to
those earlier articles (both are available online at www.cibsejournal.com)
The start of the process photo-enlarged chart (or a specific area from include both latent and sensible change the
The outline of the chart is as shown in Figure the chart produced by computer software) individual processes are simplified to straight
1 and it may be used for individual rooms or will improve the resolution. lines. The lines that join the start and end
processes as well as describing the changes points on ‘real world’ processes that include
to properties that take place in a complete air Plotting the air point latent heat transfer may curve; however, for
handling system. When illustrating the air When lines are drawn on the chart they reflect HVAC analysis it is normally just the start and
condition in a project or job notes it might changes in sensible heat or latent heat or a end points that are important.
be clearer to refer to a printed chart (possibly combination of the two. Sensible heat is that Sensible heating is shown in Figure 2. This
conveniently plastic coated and reusable) added to, (or taken from), moist air without a may be achieved, for example, with a heater
to read off the data and then convert that change in moisture content and latent heat is battery made up from rows of hot water or
into a sketch similar to that shown in the that added to, (or taken from), moist air without steam coils, or electric resistance heaters or as
figure where the data and processes are not a change of dry bulb temperature. The energy the result of some heat recovery mechanism
lost in the plethora of printed lines. When contained in the air (as indicated by Enthalpy, (such as a flat plate heat recovery device). The
considering whole processes on a standard h) relating to both the sensible and latent opposite process, sensible cooling, is shown
CIBSE Psychrometric chart (particularly energy increases towards the right and the top in Figure 3. For a cooling coil to provide
when considering ‘summer’ cycles) the of the chart as each of dry-bulb temperature sensible cooling only (and no latent cooling)
individual process lines can be quite tightly and moisture content increase. When using the coil surface temperature must be greater
bunched and difficult to discriminate. A the Psychrometric Chart for plotting cycles that than the dew-point temperature of the air. >
www.cibsejournal.com October 2009 CIBSE Journal 59
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