Strong Data Modeling Approaches and the Benefits They Offer Your Building
In smart buildings, devices, software, and building equipment must work together seamlessly. This...
Hello and welcome to a new blog series on the riveting and surprisingly controversial subject of data modeling.
For this series, we’re going to assume you’re well versed in the importance of data modelling for creating an integrated data layer and have a basic understanding of what building ontologies are, and hopefully even what OAP is and why we started the project. If not, start your reading journey there and circle back. We’ll be here in the weeds for a while so there’s no need to rush it.
With this series, we plan to dive deep into the theories and philosophies behind data modelling for time-series building data and expose how we tinker with the nuts and bolts of our ontologies. We’ll talk about our own approaches to solving the myriad modelling conundrums we’ve faced in our efforts to implement a scalable standard across diverse (and global!) deployments.
We look forward to you following along on this journey through the depths of data modelling and we sincerely hope you will participate in the conversation with us!
Alright, now that we’ve set the stage for what’s to come, let’s dive into the deep end with a “fan” favorite.
It seems fitting to kick off a data modeling series with fans – one of the most elemental parts of a building HVAC system and one of the most frequently occurring entities in a building’s data model.
Below we dig into some of the nuance around how the OAP handles fans and their points and in so doing, reveal the guiding principles that we strive to execute across all equipment types defined in the ontology alignment effort.
Briefly, Some Basics
OAP is an ontology with roots in Project Haystack and as such it leverages many of the concepts that are defined there. However, there are some important things to note upfront:
Fanning out from there, we continue.
What are fans, in the ontological sense?
Fans are vital air-moving equipment that typically show up in HVAC systems within two contexts:
In the OAP, fans are a subtype of equipment. The OAP defines the following types of fans, and they can be specified either as an equip or nested inside another equipment.
Fan
Fans are generally sub-typed based on the class of air they deal with (discharge, exhaust, outside, return), but you will notice there are some application-specific fans that have been defined as well, such as “cooling tower fan” and “stairwell pressurization fan.”
In general, if a fan operates as a standalone equipment (i.e. it is not directly contained inside a larger piece of equipment), then it is typically modeled as its own entity.
Some common examples would be:
When fans are contained within other pieces of equipment, they are typically not modeled as standalone pieces of equipment and rather any points associated with them are “flattened” under the larger equipment. Equipment that often contains fans include:
Here’s a common example of how this flattening occurs. An air handler contains a discharge (commonly called “supply” fan) and return fan and there are points associated with each of those fans. These points would get modeled like this:
Air Handler
The exception to this rule is when a piece of equipment contains 2 or more of the same type of fan with identical point sets. In that case, the only way to disambiguate between the fan points would be to model the fan as separate entities. An example might be a cooling tower that contains 2 fans. Here’s how that would get modeled in OAP parlance:
Cooling Tower
When modelling points associated with a fan either on a fan equip or a parent equip that contains fans, it is important to keep context in mind. Here are some general guidelines for our approach to modelling fans.
When the parent equip is a fan:
In this case, the most generic version of fan points can be used and it is not necessary to specify the type of fan at the point level. Here’s an example:
Exhaust Fan
Note that while it is preferable to use the more generic fan points, it is also acceptable to use the more specific versions of points, but all points related to the fan should use the same level of specificity. For example,
Exhaust Fan
Is acceptable, while
Exhaust Fan
Is not acceptable since it mixes generic and specific versions of fan points.
When the parent equip is not a fan:
In this case, it is generally best to be as specific about the point as possible regardless of whether there are multiple fan types contained within the equipment. Here are some examples:
Air Handler
Fan-powered VAV
Note that in all these cases since we are flattening the points of a sub-equipment onto a parent equip, we want to be specific about what that sub-equipment is at the point level.
Great you made it this far! I’m a big fan of yours for that.
Now, we’re dying to know your thoughts – Does this match your approach to modelling fans and fan points? Would you suggest something different? Please share any perspective in the comments.
To kick it off, a poll:
Do you spell modeling with one “l” or two? Please vote in the comments below.
Annie Dehghani, PE is a Senior Building Systems Application Engineer with Buildings IOT. Annie's expertise centers around building systems analytics including everything from initial data modeling to developing fault detection diagnostics and predictive maintenance algorithms. Her background in sustainable engineering design and consulting gives a unique window into what buildings look like and where they are going. She leads the Ontology Alignment Project (OAP) advisory board and is an active member of the building data modelling community.
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