P & ID's in HVAC Industry 5

[pmover]

for those experienced in hvac industry design activities.

lately, i've reviewed several hvac design dwgs - plot / plan / elevation - and not a single detailed p & id! although my background is the oil & gas industry, where detailed p&id's are the standard, why is it that p&id's are not created for hvac systems to the detailed level that the o&g eng firms generate?

i can understand client requests for not generating p&id's, but does the hvac design industry, as a general rule, create effective p&id's in which to build from?

references or documentation relating to p&id generation in hvac designs are appreciated.
thanks!
-pmover

 

[rajeshbidani]

It seems it is still not clear to many that what exactly goes into a D&ID. In HVAC industry it is not called P&ID. It is Duct and Instrumentation Diagram(D&ID) and it not product specific. I have worked onshore projetcs as well as off-shore/oil & gas and have used D&ID extensively. If some one need to have a look at what exactly a D&ID look like call at rajeshb@dsme.co.kr and i will mail PDF file

 

[lilliput1]

To read P&IDs you need to understand ANSI/ISA S5.1-1984(R 1992) instrumentation symbols. Each symbol is constructed using alphabetical & numeric identification codes, abbreviation, function blocks, connecting lines.

 

[lilliput1]

Here is a link on how to read P&IDs

http://lamspeople.epfl.ch/kirrmann/Slides/HowToReadP&ID.htm

 

[wilg]

To summarize (steal some of what has already been said
and add some of my own thoughts to this)...
We have individuals from various areas requesting "maps" when they mean floor plans and "H"- "vac" coverage diagrams
when they should be asking for H.V.A.C. Zoning Plans, but real confusion is occurring with the actual definition of
HVAC Control Diagram, HVAC Airflow Diagram, HVAC P&ID and HVAC D&ID.

The question of what constitutes or what is the difference between an HVAC Control Diagram, HVAC Airflow Diagram,
HVAC P&ID and D&ID has been brought up on several occasions and the terms although similar have distinctly
different usage.

The attached document may be a handy reference if someone outside of the technical field requires you to define
or point out the difference between "HVAC P&ID", "D&ID", "Air flow diagram" or "Control Diagram", it also represents an attempt to bring resolution to this nuisance contradiction in terminology.
For those with backgrounds in the Piping field, where detailed P&ID’s are the standard, it seems strange that P&ID’s are not generated for hvac systems to the detailed level that they are for piping systems. The question of what constitutes an HVAC Control Diagram, HVAC Airflow Diagram and an HVAC P&ID has been brought up on several occasions. This document is an attempt to answer the question of why detailed P&ID’s are not generally produced for the HVAC discipline.
Simply put, the term P&ID is an acronym for Piping and Instrumentation Diagram (the P does not stand for
Process, Process is shown on PFD’s or Process Flow Diagrams).

Control drawings (produced by an AE firm or general engineering office), also termed air and water schematics, which are very similar to P&ID's are produced for various projects by multi-disciplinary design offices, (these drawings often indicate viz. sensors, dampers, simple motor controls etc.)
show general location of components and are produced to correspond with the system sequence of operation document and are more likely to be used by the estimators and controls manufacturer to produce a points list / controls count than to actually be used as a construction document (the system sequence of operation document indicates the engineers intent and supersedes the control drawing if the two documents are in conflict).

For compliance pharmaceutical companies, prepare single line air flow diagrams of HVAC Systems. They consist of schematic diagrams of AHUs and their major components (viz., cooling coils, heating coils, Filtration Systems etc.) which show in and out flow directions of air through each controlled space
(hence the term air flow should only show air flow and design conditions in each space).
Control instruments like pressure gauges, temperature sensors, RH sensors and manometers are not indicated.

Air flow diagrams are compulsory and prevent the USFDA from issuing 483 (non compliance) complaints to Pharmaceutical companies which do not provide this information, detailed HVAC P&ID’s are not compulsory for compliance.

It saves time & money not to do P&ID drawings for typical HVAC systems. Instead the design engineer concentrates on describing the sequences of operation. It is up to the winning control system vendor to provide control equipment and control diagrams (which may or may not be in P&ID format depending if shop & as built drawings are required). Typical HVAC controls are not like process controls that would need special PLC type controls and accurate diagrams for all to check the control logic. Instead typical control vendors have DDC system design that incorporates numerous software & hardware enhancements built in. Shop drawings & equipment data are submitted for the engineer to check prior to fabrication.

The person responsible for the BAS system provides an Input / Output Summary which helps the control manufacturer select controllers, sensors, etc. Typical single line flow diagrams are also manufactured during projects, but differ from the process industry. Once a shop drawing is made with sections taken out at critical areas, they become self sufficient. The HVAC industry is part of Building Services not Process Services which directly produce the product and relate directly to a products formulation through various steps of manufacture.

P&IDs are generated as schematic piping drawings and form part of the drawings issued for piping.
The terminology of P&ID is not normally used in the HVAC industry. Nevertheless, there are schematics, flow diagrams, made and issued in most cases. Many times, typical connection details at AHUs, Chillers, pumps, etc., are issued as part of a standard detail and coupled with the schematic piping drawing and flow diagram for ducting serving the function of the P&ID drawings. A new term has recently surfaced,
D&ID (Duct and Instrumentation Diagram) basically this is the same as P&ID but with a new guise.
The typical HVAC construction set is the design without the design intent. There is a continuous reliance on the automatic temperature controls (ATC) submittal process which involves the controls manufacturer, to detail the system and to carry out the engineer’s intent.

P&ID’s for general HVAC are an example of over engineering. Consulting firms have to make a profit to survive & finish work within budget and on time. They are able to communicate design intent using written description of sequences of operation. Translating this to a P&ID is a mere duplication of effort. After installation, it will be the control vendors shop drawing submission that will be finalized for the as built part of the project. The P&ID (D&ID) drawing will not be used. The building operator would use and understand a written sequence of operation instead of a P&ID. Providing a P&ID (D&ID) for HVAC other than that for process is an inefficient use of man hours.
wilg5404@aol.com

 

[pmover]

wilg,

thanks for the correction on the definition of p&id (a blundering oversight on my part - i know better) and the overall explanation - good job!

-pmover

 

[wilg]

pmover...you started an excellent thread and my thanks to all who participated.