b) DDC systems require less maintenance than
conventional control systems. With a personal controller (PC)
interface workstation, HVAC mechanics can quickly troubleshoot
HVAC problems. DDC systems efficiently operate building HVAC
systems by providing accurate sensing, maintaining setpoints, and
operating in the designed sequence.
c) One disadvantage of DDC is that DDC systems from
different manufacturers have different operating systems which
are proprietary and will not communicate with each other. In
some cases, this makes competitive bids for additions difficult.
Consider specifying DDC in the following
In most new construction,
In a major retrofit of HVAC systems,
(3) When complex or numerous HVAC systems are
included in the design,
In buildings over 20,000 square feet,
(5) When remote or local workstation monitoring
and troubleshooting of HVAC equipment is desired, and
When the customer desires DDC.
e) Acceptance of DDC by the user's operation and
maintenance personnel is extremely important. If not so
accepted, DDC should not be specified. The project manager
should directly contact station personnel to make this
determination of acceptance.
f) Consider conventional electric, analog electronic,
or pneumatic control systems when the following apply:
Small buildings where DDC is not cost
When package air handling units are specified,
When the customer or maintenance will not
Designing DDC Systems.
Design DDC systems using the