Concept
Log Processing Trend Log
A log processing trend log enables calculation within or between various trend logs. With this feature, building managers can gather new information about how the building is operating, they can view historical data that is calculated against new data and in this way detect new trends, they can compare various values and calculate a new trend log displaying relativised behavior, or unify measurements made with different units. The results from these calculations can indicate anomalies that have other reasons than the naturally varying conditions, so that it becomes easier to find problems with the building.
Examples
For instance, you use a log processing trend log in the following contexts:
Use a log processing trend log to compute the amount of the energy used during some given period of time, depending on the degree of the outdoor temperature. You can log this value along with, or instead of, the value of the outdoor temperature. You can also use some other energy measure such as degree days or an energy index listed in MSCI World Index. For this calculation you use the formula expressing the following function: “Energy consumption divided by energy index"
Use a log processing trend log to compute how much the light level differs from the natural light level. For this calculation you use the formula expressing the following function: "natural light level minus light level in the room".
Use a log processing trend log to store in a new log the average, or the minimum or the maximum temperature for a given period of time. You can log this value along with, or instead of, the value of the temperature. It can be further used by a 3rd party reporting tool. For this calculation you use one of the formulas expressing one of the following functions: "average(temp)" or "min(temp)" or again "max(temp)".
Use a log processing trend log to store in a new log the value of the total energy usage. You can log this value along with, or instead of, the values of the partial energy indicators. For this calculation you use the formula expressing the following function: "a sum of energy usage measured by multiple meters where there is no main meter".
Mathematical Operators Used in Calculations
The formulas for the calculations use operators discribed in the C++ Mathematical Expression Toolkit Library (ExprTk). For more information, see: https://github.com/ArashPartow/exprtk Scroll down to [SECTION 01 - CAPABILITIES] and [SECTION 02 - EXAMPLE EXPRESSIONS].
For instance, use:
(01) Basic operators: +, -, *, /, %, ^
(02) Assignment: :=, +=, -=, *=, /=, %=
(03) Equalities & Inequalities: =, ==, <>, !=, <, <=, >, >=
(04) Logic operators: and, mand, mor, nand, nor, not, or, shl, shr, xnor, xor, true, false
(05) @(My Trend Log:Count) will give you the number of records in the calculated period.
Non-Persisted Data
If data isn't persisted, calculation will be executed on the latest value while data is received. The latest value can change value until the period is finished. If data is persisted, calculation on the latest value will be executed first when the period is done. Views can then differ between a non-persisted log and a persisted log.
Trend Log Types
Creating a Log Processing Trend Log
Configuring Log Processing Trend Log
Creating a Log Processing Trend Log Item