Page 296 - Mechanical Engineers' Handbook (Volume 4)

2 Performing an Energy Audit—Analyzing Energy Use 285

controllers can also cause energy waste. While major failures of thermostats can usually be
detected as a result of occupant complaints or behavior (e.g., leaving windows open on cold
days), drifts in these controls that are too small to cause complaints can still lead to sub-
stantial waste. Other controls, especially reset controls, can sometimes fail completely and
cause an increase in energy consumption without affecting occupant comfort.
After investigating HVAC operation and maintenance practices, the auditor should make
measurements of system performance. Typical measurements will include air temperature in
rooms and ducts, water temperatures, air flow rates, pressure drops in air ducts, excess air
in stack gases, and current drawn by electric motors operating fans and pumps. Instruments
required include a thermometer, a pitot tube or anemometer, a manometer, a strobe light, a
combustion test kit, and an ammeter. The importance of making measurements instead of
relying on design data cannot be emphasized too strongly. Many, if not most, buildings
operate far from their design points. Measurements may point to needed adjustments in
temperature settings or air flow rates. Table 4 gives recommended air flow rates for various
applications. Detailed analysis of the measured data requires a knowledge of HVAC system
principles.
After measuring HVAC system performance, the auditor should make rough calculations
of the relative importance of the different sources of HVAC system loads. These are primarily
radiative and conductive heat gains and losses through the building’s exterior surfaces, gains
and losses from air exchange, and gains from internal heat sources. Rough calculations are
usually sufficient to guide the auditor in selecting conservation measures for consideration.
More detailed analyses can await the selection of specific measures.

Table 4 Recommended Rates of Outside-Air Flow for
Various Applications 3
1. Office Buildings
Work space 5 cfm/person
Heavy smoking areas 15 cfm/person
Lounges 5 cfm/person
Cafeteria 5 cfm/person
Conference rooms 15 cfm/person
Doctors’ offices 5 cfm/person
Toilet rooms 10 air changes/hr
Lobbies 0
Unoccupied spaces 0
2. Retail Stores
Trade areas 6 cfm/customer
Street level with heavy use
2
(less than 5000 ft. with
single or double outside
door) 0
Unoccupied spaces 0
3. Religious Buildings
Halls of worship 5 cfm/person
Meeting rooms 10 cfm/person
Unoccupied spaces 0