ASHRAE Psychrometrics and Moist Air Properties 3

Question 1

Which ASHRAE Handbook volume contains the primary psychrometric data, charts, and moist air property equations?

Accepted Answer

ASHRAE Handbook — Fundamentals

Answer

The ASHRAE Handbook — Fundamentals is the primary reference for psychrometric data, including property tables, equations, and the psychrometric chart used in HVAC design.

Question 2

How do psychrometric properties change at higher altitudes compared to sea level for the same dry-bulb temperature and relative humidity?

Accepted Answer

Humidity ratio and enthalpy values increase because lower atmospheric pressure allows more moisture per unit mass of dry air

Answer

At higher altitudes, reduced atmospheric pressure lowers the partial pressure of dry air, causing humidity ratio and enthalpy to increase for the same dry-bulb temperature and relative humidity condition.

Question 3

What is the approximate specific volume of standard air at 70°F (21°C) and standard sea-level pressure?

Accepted Answer

13.5 ft³/lb (0.843 m³/kg)

Answer

Standard air at approximately 70°F and sea-level pressure has a specific volume of about 13.5 ft³/lb (0.843 m³/kg), corresponding to a density of approximately 0.075 lb/ft³ commonly used in HVAC airflow calculations.

Question 4

What distinguishes the room sensible heat ratio (RSHR) from the effective sensible heat ratio (ESHR) in cooling system design?

Accepted Answer

RSHR applies only to the room thermal load; ESHR accounts for outdoor ventilation air mixed into the supply airstream

Answer

RSHR represents the sensible heat ratio for the conditioned space load only, while ESHR accounts for the combined effect of the room load plus the enthalpy of outdoor ventilation air introduced into the system.

Question 5

What is the primary engineering purpose of the psychrometric chart in HVAC system design?

Accepted Answer

To graphically represent thermodynamic properties of moist air and visualize HVAC processes for load calculations

Answer

The psychrometric chart plots all relevant moist air properties simultaneously, enabling engineers to graphically track heating, cooling, humidification, and dehumidification processes and calculate associated loads.

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test

ASHRAE Psychrometrics and Moist Air Properties 3