HEATING, VENTILATING, AND AIR CONDITIONING (HVAC): TYPICAL DESIGN PROCESSES


HVAC systems usually involve a minimum of three design stages. In the preliminary design phase, the
most general combinations of comfort needs and climate characteristics are considered:

Activity comfort needs are listed.
An activity schedule is developed.
Site energy resources are analyzed.
Climate design strategies are listed.
Building form alternatives are considered.
Combinations of passive and active systems are considered.
One or several alternatives are sized by general design guidelines.

For smaller buildings, this analysis is often done by the architect alone. For innovative or unusual systems in smaller buildings, and especially for larger, multiple-zone buildings, consultants such as engineers and
landscape architects often are included.

The team approach is particularly valuable in assessing the strengths of various design alternatives. The architect and the consultants have very different perspectives, and when mutual goals can be clearly agreed on early in the design process, these perspectives are not only mutually supporting but can produce striking innovations whose benefits extend far beyond services to the clients of a particular building.

By setting an example, the team can make available better environments for less energy for hundreds of
subsequent buildings. With inspired teamwork, the distribution of HVAC services can enhance building
form, as many examples in this chapter show.

By the time the design development phase is reached, one of the design alternatives has probably been chosen as the most promising combination of aesthetic, social, and technical solutions for the program.

The consulting engineer (or architect, on a smaller job) is furnished with the latest set of drawings
and the program. Typically, the architectural or mechanical engineer then:

I. Establishes design conditions.
A. By activity, lists the range of acceptable air and surface temperatures, air motions, relative humidities, lighting levels, and background noise levels.
B. Establishes the schedule of operations.

II. Determines the HVAC zones, considering:
A. Activities.
B. Schedule.

C. Orientation.
D. Internal heat gains.

III. Estimates the thermal loads on each zone:
A. For worst winter conditions.
B. For worst summer conditions.
C. For the average condition or conditions that represent the great majority of the building’s
operating hours.
D. Frequently, an estimate of annual energy consumption is made.

IV. Selects the HVAC systems.
Often, several systems will be used within one large building because orientation, activity, or scheduling differences may dictate different mechanical solutions. Especially common is one system for the all-interior zones of large buildings and another system for the perimeter zones.

V. Identifies the HVAC components and their locations.
A. Mechanical rooms.
B. Distribution trees—vertical chases, horizontal runs.
C. Typical in-space components, such as under-window fan-coil units, air grilles,
and so on.

VI. Sizes the components.

VII. Lays out the system. At this stage, conflicts with other systems (structure, plumbing, fire safety, circulation, etc.) are most likely to become evident. Because insufficient vertical clearance is one of the most common building coordination problems with HVAC systems, the layouts must include sections as well as plans.

Opportunities for integration with other systems also become more apparent at this stage: air ducts can also help distribute daylighting, act as sunshading devices, or fulfill other functions.

After the architect and the other consultants hold conferences in which HVAC system layout drawings are compared to those for other primary systems (structure, plumbing, electrical, etc.), design finalizing occurs.

At this final stage, the HVAC system designer verifies the match between the loads on each component and the component’s capacity to meet the load. Final layout drawings then are completed.

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1 comment:

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