HVAC ELECTRICAL INTERFACE BASIC INFORMATION AND TUTORIALS


On a number of issues the HVAC designer must interface with the electrical designer, each sharing information and responding appropriately.

Motor loads: Motor sizes and locations derive from the HVAC equipment selections and equipment layouts.

Motor control features: HVAC control schemes determine many of the needed starter characteristics, e.g., hand-off-auto or start-stop, auxilary contact types and number, pilot light requirements, and control voltage transformer size if external devices needing control power are involved. Be sure to coordinate the specification and control of two speed motors and motor starters.

Fire and smoke detection and alarm: The electrical designer is usually responsible for fire detection and alarm, if such is required. But building codes require smoke detectors in the airstream of recirculation fan systems larger than 2000 ft3 /min.

If smoke is detected, fan systems are required to shut down. Similarly, if the building detection systems go into alarm, the fan systems must turn off. Further sophistication gets into smoke control in buildings, a separate topic by itself.

Lighting systems: The HVAC designer must fully understand the building lighting systems to be able to correctly respond to the cooling loads which develop.

Any inordinately high lighting loads may stimulate discussion and evaluation of lighting fixture selection. Automated lighting control may be included as a feature of a building automation system.

Transformer vaults: Electric transformers typically lose 2 to 5 percent of the power load (winding losses) to the ambient air. Building transformers may wind up in underground vaults, in secure rooms, in janitor closets, or in ceiling spaces.

Dissipation of the heat with ventilation is often a challenge. Note that even though the load may decrease, transformers seldom sleep; 24 h/day ventilation is required.

Building HVAC systems which follow a time-clock schedule are inadequate for transformer rooms. Some electronic monitoring and control devices cannot tolerate ambient air temperatures above
about 100 deg F.

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