24-Bld-A4 Building Environmental Control Systems · May 2017

Question 11 of 14: Equipment Requiring Outdoor/Well-Ventilated Installation

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams May 2017 — 07-Bld-A4, Building Environmental Control Systems (Building Engineering). 3-hour closed-book exam: Section 1 (four 20-mark essay/calculation questions) + Section 2 (ten 2-mark multiple-choice questions).

Reference texts: ASHRAE Handbook — Fundamentals (2021 ed.); ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality (2022 ed.); McQuiston, Parker & Spitler, Heating, Ventilating, and Air Conditioning: Analysis and Design (6th ed.); National Building Code of Canada 2020 (NBCC); National Energy Code of Canada for Buildings 2020 (NECB).

Question 2.7: Equipment Requiring Outdoor/Well-Ventilated Installation (2 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given/Find. Identify which listed equipment MUST reject heat directly to (or draw combustion/cooling air freely from) the outdoor environment.

Eliminate indoor-only equipment. FCUs, WSHPs, AHUs and furnaces (as listed) all operate from an indoor mechanical space, rejecting/absorbing heat via water loops, refrigerant, or ducted air rather than requiring direct outdoor air contact for their own heat rejection.
Identify the outdoor-dependent equipment. An air-cooled chiller rejects its entire condenser heat load directly to ambient air across a large finned coil, so it must sit outdoors (or in a space with unrestricted, high-volume outdoor air circulation) or it will overheat.

Final Result
Answer: (e) Air-cooled chiller

Topic: Heat-rejection requirements by equipment type.

Key relations: equipment that condenses refrigerant directly against ambient air (air-cooled chillers, air-cooled condensing units, rooftop package units) needs unrestricted outdoor air; water- or refrigerant-loop-served equipment (WSHP, FCU, AHU coils, furnaces vented separately) does not.

Why this works: An air-cooled chiller's entire condenser heat rejection depends on continuously drawing large volumes of outdoor air across its coil; starving it of that air (an indoor mechanical room) causes head-pressure trip-outs and equipment failure.

Common pitfall: Confusing a WSHP (which rejects heat to a water loop, not directly to outdoor air) with an air-cooled machine.

Source: ASHRAE Handbook — HVAC Systems and Equipment, Ch. 44 (Air-Cooled Chillers); McQuiston, Parker & Spitler, equipment installation practice.

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