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

Question 10 of 14: Heat-Recovery Ventilator Efficiency

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 2.6: Heat-Recovery Ventilator Efficiency (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. Rearrange the given efficiency definition to solve directly for $t_{OA}'$, the temperature of outdoor air leaving the HRV core.

1. Rearrange and substitute. $$t_{OA}' = t_{OA}-\eta(t_{OA}-t_{IA}) = 36-0.60(36-26)$$
2. Evaluate. $$\boxed{t_{OA}' = 36-6=30\,{}^{\circ}\text{C}}$$

Final Result

Answer: (a) 30°C

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