Handbook of air conditioning and refrigeration / Shan K

5.66 CHAPTER FIVE
5.16 CONTROLS IN ASHRAE/IESNA STANDARD 90.1-1999
General
Off-Hour Controls
ASHRAE/IESNA Standard 90.1-1999, Energy Standard for Buildings Except Low-Rise Residential
Buildings, specifies the following mandatory provisions for HVAC&R controls. For exceptions and
details refer to Standard 90.1-1999.
● Thermostatic controls. The supply of heating and cooling energy to each zone shall be controlled
individually by thermostatic controls using the zone temperature as the response. A dwelling unit
is permitted to be considered as a single zone.
● Dead band. When both heating and cooling are controlled, zone thermostatic controls shall be capable
of providing a temperature range or dead band of at least 5°F (2.8°C). Within that range the
heating and cooling energy supplied to the zone is shut off.
● Set-point overlap. When heating and cooling supply to a zone are controlled by separate zone
thermostatic controls, means such as limit switches, mechanical stops, and software for DDC systems,
shall be provided to prevent the heating set point exceeding the cooling set point minus any
proportional band.
HVAC systems with a design heating or cooling capacity greater than 65,000 Btu/h (19,050 W) and
3 fan system power greater than �4 hp (0.56 kW) shall have all the following off-hour controls: automatic
shutdown, setback controls, optimum start controls, shutoff damper controls, and zone isolation.
● Automatic shutdown. HVAC systems shall be equipped with at least one of the following:
1. Controls that can start and stop the system under different time schedules, are capable of retaining
programming and time setting during loss of power for a period at least 10 hours, and
include an accessible manual override or equivalent that allows temporary operation of the
system for up to 2 hours.
2. An occupancy sensor that can shut the system off when no occupant is sensed for a period of
up to 30 minutes.
3. A manual operated timer that can adjust the system for two hours.
4. An interlock to a security system which shuts the system off when the security system is
activated.
● Setback controls. A heating system located where the heating outdoor design temperature is 40°F
(4.4°C) or less shall be equipped with controls that can automatically restart and temporarily operate
the system as required to maintain zone temperature above a heating set point adjustable
down to 55°F (12.8°C) or lower. A cooling system located where the cooling outdoor design temperature
is greater than 100°F (37.8°C) shall be equipped with controls that can automatically
restart and temporarily operate the system as required to maintain zone temperature below a cooling
set point adjustable up to 90°F (32.2°C) or higher or to prevent high space humidity.
● Optimum start controls. An air system with a supply volume flow rate exceeding 10,000 cfm
(4720 L/s), served by one or more supply fans, shall have optimum controls. The optimum start
shall be at least a function of the difference between space temperature and occupied setpoint, and
the amount of time prior to scheduled occupancy.
● Shutoff damper controls. Both outdoor air supply and exhaust system shall be installed with motorized
dampers that will automatically shut off when the systems or the space are not in use. Out-