Quite often, design engineers choose decentralized HVAC systems because of first-cost benefit, packaged equipment, simplicity of design, and the repetitiveness of the installation, to mention just a few of the features. One should read chapter two of the 2016 ASHRAE HVAC Systems and Equipment Handbook for a more detailed discussion on decentralized HVAC.
That said, decentralized equipment includes packaged units with self-contained refrigeration, remote air-cooled and water-cooled condensing units, heat pump units, VRF units, specialty units (e.g., computer room packaged units) and/or rooftop units. Included in the decentralization design can be fan coil units and other terminal HVAC equipment distributed throughout the building.
When this type of system is selected, the design engineer will most likely produce the following contract documents:
Show the terminal unit with limited sheet metal distribution and branch piping.
Standard detail of terminal unit because of the repetitiveness of the installation showing typical piping valves and fittings.
Automatic control diagram, which may be two different diagrams because the terminal unit may come with some self-contained control features provided by the equipment manufacturer.
Equipment schedule detailing the terminal unit criteria, e.g., heating output, cooling output, horsepower.
Equipment contract specification detailing the terminal unit construction, accessories, and other criteria.
In another section of the contract, documents will be vague specification criteria addressing terminal equipment startup, O&M, and training requirements.
Also in a separate section of the contract documents will be the commissioning criteria, including the functional performance test sheet.
So there it all is! Seven separate documents for repetitive terminal units that may show up 150 times on the contract drawing floor plans. In fact, the design engineer may choose to duplicate this drafting effort by producing two drawings per floor plan, a sheet metal distribution floor plan, and a pipe distribution floor plan. Following the floor plans will be a detail sheet drawing, automatic control drawings, and a schedule sheet drawing.
The contract specification will have HVAC requirements found in Division 1 General Requirements and Supplementary Conditions pertaining to the terminal equipment shop drawings, system startup, O&M manuals, training, and warranty. The design engineer will duplicate the contract specification criteria and often not coordinate the specification language with Division 1 when he or she writes the HVAC specification. The third-party commissioning engineer will need to peruse all these documents to find the data he or she is looking for to assist in writing the commissioning specification requirements pertaining to all the above.
As for the bidding contractors, they will need to most likely focus on the HVAC contract drawings and contract specification to pull all the pieces together to come up with their best estimate to furnish, install, startup, warrantee the standardized terminal equipment, and provide the contract-required owner personnel training.
For the building owner’s O&M staff this distributed method of contract documents and contract requirements will be delivered, as noted earlier, when the record documents are delivered to this owner.
How can something so repetitive be so complicated to produce? Streamlining the decentralized system design for these various HVAC applications offers the design engineer the opportunity to value-engineer the contract document production through the use of specification that can eliminate the need to go into such great detail beginning with the drafting of the piping and sheet metal floor plans. Instead of showing every branch runout to a drafting symbol that represents the repetitive terminal unit, the pipe runouts really don’t need to be shown at all because the standard detail covers the piping and sheet metal requirements including fittings, number of elbows, valves, etc. This is just the first suggestion to minimize the detailed drafting exercise shown on the floor plans.
To continue with this theme, the standard detail doesn’t even need to be shown on a contract drawing along with the associated equipment schedule drawing and automatic control drawing. For the cost-conscious design engineer, combining all of these contract document criteria can be located in one spot: the contract specification document. How does this work?
Next month, I’ll go into the details of producing a more streamlined method of documentation that will reduce contract drawings, improve contract specification, project closeout, and O&M routine maintenance after owner occupancy.
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