ASHRAE Journal - November 2013 - B9

be created individually. Most BAS vendors have supported this
trend log multiple functionality in their front ends in a proprietary manner. This new object type allows this functionality to be provided by vendors in an interoperable manner so a
user can trend multiple points on a common time period from
the same BACnet device or from different devices supplied by
multiple vendors.
For example, the Trend Log Multiple object type allows a
user to trend outdoor air temperature in one vendor's controller
and boiler supply water setpoint in another vendor's controller.
A third trend log such as Btu consumption from yet another
vendor's BACnet Btu meter can be added to this object. These
three trends from different devices are trended with a common
time base. This example shows how Trend Log Multiple will
help users analyse boiler plant efﬁciency in an interoperable
manner.
There is a suite of BIBBs for this object that is similar to the
Trend Log object type.

New Value Object Types
The new suite of Value objects now allow for more than just
the binary, analog and multistate values to be represented in
a network visible manner to other BACnet devices. Here is a
brief description of these new value objects.
CharacterString Value. This value object allows a device
manufacturer to represent a character string such as a HIGH
DRIVE TEMPERATURE ALARM!!! in a variable speed drive
as the present value of an object, instead of as a Multistate
Value of say, 27, that needs to be converted into human understandable text for the user.
Large Analog Value. A BACnet device can use a Large Analog Value object to make any kind of double precision data
value accessible to other BACnet devices. One excellent use
for this object is to represent kWh from an electricity meter.
Integer Value. This object allows one to represent a negative integer such as -1238 or a positive integer such as +8321.
This object type can be used to represent positive values for
clockwise rpm and negative values for counterclockwise rpm.
Positive Integer Value. This object allows one to represent
only a positive integer such as +1238. This object type could
represent count of the number of ofﬁce spaces in a building
calling for heating.
Time Value. This object allows one to represent a single speciﬁc time value like 12:34:56.77.
Date Value. This object allows one to represent a single speciﬁc date like 07-August-2013.
Time Pattern Value. Time Pattern Value objects allow for
wildcard characters like the asterisk (*) to represent any value
in the ﬁeld. The wildcard value of the Time Pattern Value object
could have a present value of 12.*.*.*. The asterisks between the
periods represent any minute, second or hundredths of a second.
Date Pattern Value. The wildcard value of the Date Pattern
Value object could have a present value of 07-*-2013. The asterisk in this case represents any day in July.
DateTime Value. This object allows one to represent a single
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speciﬁc date and time like 07-August-2013, 12:34:56.77.
DateTime Pattern Value. By combining the concepts of the
Date and Time Value objects together, the present value of this
object could look like 07-*-2013, 12.*.*.*. Besides representing any value, the asterisk can represent even or odd days or
months.
BitString and OctetString Values are mentioned for completeness but are not covered in this article. The BACnet standard contains more details on these object types.

Global Group Object Type
The Global Group object type deﬁnes a standardized means
of representing a collection of properties from one or more objects. A Global Group object is used to simplify the exchange
of information between BACnet devices by providing a shorthand way to specify all members of the group at once (e.g.,
all space temperatures in a building). The Global Group also
supports intrinsic event reporting, and it exposes a method for
sending periodic Change of Value (COV) notiﬁcations. This
object type can initiate an event notiﬁcation message conveying the values of all of the members of the group at once.
A Global Group object type differs from a Group object
types in that its members are not restricted to the same device
where the Group object is located. Global Group members can
be from any device on the BACnet internetwork.
This object type also differs from the Structured View object type. The Global Group gives present values of referenced
object properties whereas Structured View deﬁnes the object
location, allowing the client device to ﬁnd the object and read
its present value.

Notification Forwarder Object Type
The Notiﬁcation Forwarder object type allows devices that
can distribute notiﬁcations to a small number of destinations
to have their notiﬁcations received by many destinations. This
object types differs from a Notiﬁcation Class object type in that
the Notiﬁcation Forwarder object type is not used for originating event notiﬁcations, but rather is used to forward event
notiﬁcations to a different and potentially larger number of recipients.
Figure 1 shows how this object works. It can be thought of as
a list of recipients who must be notiﬁed when the burglar alarm
goes off. The building security system sends the alarm to the
alarm company. The company (representing the Notiﬁcation
Forwarder object type in the ﬁgure) then notiﬁes staff and the
police that an alarm has occurred.
This object is ideally suited to small devices, such as VAV
boxes. The box sends the notiﬁcation to a supervisory controller, which in turn sends the event to a Recipient_List in a Notiﬁcation Class object.

Alert Enrollment Object Type
This object provides an easy way for a device to notify another device that an event has occurred. Alerts give users ﬂexibility
as they do not use BACnet's standard event algorithms such as

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ASHRAE Journal - November 2013

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