CHAPTER 2
HVAC FUNDAMENTALS
OVERVIEW
The HVAC Section of this book is organized into eight chapters:
• Fundamentals (Chapter 2),
• HVAC Load Estimating (Chapter 3),
• HVAC Load Management (Chapter 4)
• HVAC Delivery Systems (Chapter 5)
• Heating and Cooling Production (Chapters 6 and 7) and
• Air Handling and Piping Equipment and Systems (Chapters 8 & 9)
Heat transfer and fluid flow are the governing principles for the design of HVAC systems. Other
information required in design includes the selection of weather date, properties of materials and
performance of equipment and its components. Essentials of these are included in these chapters
to illustrate the design process. These data are by no means complete, and should not be used in
actual design of construction projects. The Handbooks published by the American Society of
Heating, Refrigerating and Air Conditioning Engineers, Inc. (ASHRAE) should be used when
designing actual construction projects.
HVAC Fundamentals is an introduction to HVAC system technology used in design:
• Basics of energy and power
• Fuels
• Psychrometrics
• Fluid flow and pressure
• Energy transport by fluids
• Environmental comfort
CHAPTER 2
HVAC FUNDAMENTALS
QUESTIONS AND ANSWERS
2.1 If the lighting load for a 10,000–ft2 building is estimated at 1 W/ft2, what will be the
resulting heat generated by lighting in units of MBtu for 3000 hours of lights on?
2.2 If the lighting load were increased, what would be the effect on other building systems
in a Midwestern U.S. climate? Would you increase the capacity of the heating system?
The cooling system? What would the energy impact of higher lighting loads be on gas
for heating, electric for cooling, and overall electric usage?
2.3 How much heat (Btus) will be stored in a 100-ft2 concrete wall 1 ft thick if it is warmed
from 65°F to 85°F by exposure to sunlight?
2.4 What is the equivalent value of the heat in Question 2.3 compared with gas at $0.65 per
therm burned in a boiler at 85% efficiency? What equivalent value compare with
electric at $0.06 per kWh?
One therm is 100,000 Btu. If the boiler is 85% efficient, one therm will produce 85,000
2.5 Compare the annual cost of heating by propane at $2.00/gallon in a 85% efficient
furnace versus electric heat pump with a COP of 3 using electric at $0.06 per kWh. The
2.6 What is the difference between absolute humidity, often called humidity ratio, and
relative humidity? What are the units used to express each of these quantities?
2.7 If the dry-bulb temperature is 95°F and the wet-bulb temperature is also 78°F, what is
the relative humidity? What is the dew point? What is the humidity ratio? What is the
enthalpy?
2.8 If the dry-bulb temperature is 55°F and the wet-bulb temperature is also 55°F, what is
the relative humidity? What is the dew point? What is the humidity ratio? What is the
enthalpy?
2.9 If 20,000 CFM of air at the condition in Question 2.7 is cooled to the condition in
Question 2.8, what is the rate of sensible heat removal (Btuh)? What is the rate of latent
heat removal (Btuh)? What is the rate of total heat removal (Btuh)?
2.10 If 2000 CFM of air at 5°F is mixed with 8000 CFM of air at 75°F, what is the
temperature of the mixed air?
2.11 If the humidity ratio of the 5°F air in Question 2.10 is 0.002 lbs of H2O / lb of dry air,
and the humidity ratio of the 75°F air is 0.0093, what is the humidity ratio of the mixed
air? How much moisture in lbs/hour would be needed to raise the mixed air humidity
to 0.0093 lbs of H2O /lb of dry air?
2.12 A space has a heat gain of 40,000 Btuh sensible. How much 55°F air needs to be supplied
to the space to maintain the space temperature at 75°F? How much would be needed if
the supply air were 50°F?
2.13 If the 55°F air in Question 2.12 is being discharged in a saturated (100% RH) condition
from a chilled water coil, and the inlet air to the coil is 100% outside air at 95°F DB
and 78°F WB, what is the sensible load on the coil (Btuh)? Latent load? Total load?
2.14 If the chilled water is being supplied at 45°F, and the coil is selected so that the chilled
water temperature rise is 10°F, what is the required chilled water flow through the coil
in GPM?
2.15 A space has a 60,000 Btuh heat loss in winter. It is heated by a furnace discharging
110°F air. How much air will be needed to keep the space at 72°F?
2.16 If the space in Question 2.15 were heated with air from a hot water coil discharging air
at 110°F, what hot water flow would be required through the coil if the hot water supply
temperature is 140°F, and the hot water return temperature is 120°F?
2.17 If a steam coil were used in Question 2.16, what would be the required steam flow in
lbs/hr?
2.18 Discuss the effects of humidity on interior comfort. What would you recommend for
upper and lower limits during summer and winter? How does temperature influence
your answer?
2.19 What are the effects of excessively high and excessively low air velocities in occupied
spaces? What range of values might be appropriate for design?
2.20 In general, nonnumerical terms, how would you define good air quality?
2.21 How might you compensate for discomfort from a cold window?
2.22 Historically, what factors have caused variations in standards for ventilation of
buildings in the United States? What is the authoritative source of these values?