The communications interface has two aspects – the physical interface and the logical interface.
The physical communications interfacedescribes the physical connection through which event signals are received, and shall meet the following requirements:
1. The OCST shall be capable of receiving signals that have been transmitted using a non-proprietary communications protocol. This shall include, at a minimum, one of the following:
a. connecting to a Wi-Fi network compliant with Institute of Electrical and Electronics Engineers (IEEE) Standard 802.11,
b. connecting to a Zigbee network compliant with IEEE Standard 802.15.4, or
c. for nonresidential, high-rise residential, and hotel-motel buildings, connecting to an Ethernet network compliant with IEEE Standard 802.3.
Manufacturers may choose to include additional wireless or wired physical communication interfaces.
2. The physical communication interface shall be capable of bi-directional exchange of information over its communication path.
The logical communication interface within the OCST hardware, which describes the messaging protocol and information model used in representation and interpretation of demand response signals, shall comply at a minimum, with any individual or combination of the following open-based standards: OpenADR 2.03 or Smart Energy Profile (SEP) 1.14 which are listed the Smart Grid Interoperability Panel (SGIP) Catalog of Standards (CoS)5. Manufacturers may choose to provide additional logical communication protocols. Builders, HVAC installer, architects, and all other Title 24 professionals should check with the local utility where the property is located) on guidance when choosing the DR signal standard for the OCST.
Using receipt of a demand response signal via the physical communication interface, and interpretation of the signal via the logical communication interface, the OCST shall be capable of automatically initiating demand responsive control.
The expansion port allows for the installation of a removable module to enable physical and logical communication as described in Section 5.3.1.
When the Expansion port is unpopulated, the thermostat shall function as a programmable setback thermostat and shall meet the requirements of Sections 110.2(b) and (c).
The removable module may also provide a means of memory storage, logging, and firmware upgrade. The requirements associated with the expansion port are:
(a) The expansion port shall be readily accessible to the occupant for installing and removing the communication module.
(b) Installation of the module shall upgrade the programmable setback thermostat to an OCST.
(c) After communications are enabled6 and the occupant has enrolled in a Demand Response program or subscribed to receive demand response related messages or information updates, the OCST shall be capable of both receiving and responding to Demand Response Signals.
The expansion port has no mandated configuration or design specification.
When onboard communication devices are present, the thermostat or HVAC control system shall be equipped with the capability to enable or disable the onboard communication device(s). The switch or interface to enable or disable onboard communications shall be readily accessible to the occupant.
When onboard communications are disabled, the thermostat shall function as a programmable setback thermostat and shall meet the requirements of Section 110.2(c). Thermostats for heat pumps shall also meet the requirements of Section 110.2(b).
The OCST shall have the capability to display information to the user. The following information shall be readily available whenever the OCST display is active:
(a) communications system connection status,
(b) an indication that a Demand Response Period or pricing event is in progress,
(c) other maintenance-related information,
(d) the currently sensed temperature,
(e) the current setpoint.
(a) Clock Operation. The clock mechanism enables the OCST to execute temperature setpoints scheduled by the occupant. It also supports other timing functions such as start-time, end-time and duration for coordination of Demand Response Periods and price signal response.
The OCST shall provide a pair of programmable thermostat setpoint time and temperature parameters for at least four operating periods that collectively govern thermostat operation during the 24-hour day.
Accuracy to a precision of one minute is acceptable for this operating environment and the applications being considered.
The clock in an OCST may be set by the occupant, using the OCST’s human-machine interface. Alternatively, an OCST with communications enabled may be set or synchronized by the occupant’s selected service provider.
(b) Normal Operation. Normal operation of an OCST is defined to be the OCST’s prevailing mode of operation as determined by the occupant’s prior settings and use of features7 provided by the OCST manufacturer’s design. Aspects of normal operation of an OCST may be modified or interrupted in response to occupant subscribed price signals or when Demand Response Periods are in progress, but only to the extent specified by occupants or their representatives.
Unless an occupant has elected to connect the OCST to an energy management control system or service that provides for alternate strategies, the OCST shall provide a mode of operation whereby it controls temperature by following the scheduled temperature setpoints.
Occupants shall always have the ability to change OCST settings or use other features of an OCST during an event. Those changes may alter what is considered to be the prevailing mode of operation when a Demand Response Period is terminated and the OCST returns to normal operation.
(c) Demand Responsive Control. Upon receiving a price signal or a Demand Response Signal, OCSTs shall be capable of automatic event response by adjusting the currently applicable temperature setpoint by the number of degrees indicated in the temperature offset (heating or cooling, as appropriate).
Override: OCSTs shall allow an occupant or their representative to alter or eliminate the default response to price signals or Demand Response Signals, and to override any individual price response or Demand Responsive Control and allow the occupant to choose any temperature setpoint at any time including during a price event or a Demand Response Period.
When the price signal changes to a non-response level or the Demand Response Period is concluded, OCSTs shall return to normal operation. The thermostat setpoint shall be set to the setpoint that is programmed for the point in time that the event ends or to the manually established setpoint that existed just prior to the Demand Response Period.
The OCST shall also be equipped with the capability to allow occupants to define setpoints for cooling and heating in response to price signals or Demand Response Signals as an alternative to the default event response. The default setpoint definitions unless redefined by the occupant shall be as follows:
1. The default price response or Demand Response Period setpoint in the cooling mode for OCSTs shall be 82°F. The OCST shall allow the occupant to change the default event setpoint to any other value.
2. The default price response or Demand Response Period setpoint in the heating mode for OCSTs shall be 60°F. The OCST shall allow the occupant to change the default event setpoint to any other value.
3. The OCST shall ignore price response or Demand Response Period setpoints that are lower (in cooling mode) or higher (in heating mode) than the programmed or occupant selected prevailing setpoint temperature upon initiation of the price event or Demand Response Period.
4. By default, thermostats shall not be remotely set above 90°F or below 50°F. Occupants shall have the ability to redefine these limits. This measure protects occupant premises from extreme temperatures that might otherwise be imposed by event responses, should the occupant already have a very high or low temperature setpoint in effect.
The occupant may still override or change the setpoint during all price events and Demand Response Periods. Price signal response and Demand Responsive Control only modify the operating range of the thermostat. They do not otherwise affect the operation and use of features provided by the manufacturer’s design.
The OCST shall include the capability to allow the occupant to restore the factory installed default settings.
Demand Response Signal security attributes and requirements shall be specified within both the communications standard and the messaging protocol utilized by the utility or other entity selected by the occupant. The OCST communications system shall consider relevant security issues and potential cyber-attacks8.