Andrew Parker

Introduction to Building Energy Modeling

There is good reason that so much attention is paid to the concept of mathematical model in engineering and physics curriculum. Simple regressions derived from empirical data, differential equations based on first-principles, or detailed computational fluid dynamic simulations each provide an analytical framework that yields insight into the behavior of physical systems. In turn, those insights can lead to design decisions that have real impact on safety, cost, and performance of the cars we drive, the power grids that deliver our electricity, and the energy efficiency of the buildings we live and work in.

Parametric Analysis with OpenStudio

The previous chapter introduced the concept of OpenStudio Measures and how they can be applied individually and in combination to a Model to create and compare different Design Alternatives. While an improvement from modifying models by hand, generating results, and comparing them; the manual analysis workflow is still labor intensive, non-scalable, and will not necessarily yield the best solution for a given problem. In this chapter, we will discuss how OpenStudio enables automated creation and search of large building parameter spaces. We’ll also look at how these same approaches may be used to “tune” models of existing buildings to best match measured energy consumption data.

Building Envelope Specification

The most basic definition of a building is a man-made structure that isolates the interior from the outdoor environment. The portions of the building that separate the building’s interior from the outdoor environment (e.g. walls, roofs, floors) are often referred to as the building envelope. The envelope protects the interior from rain, snow, wind, and excessive heat or cold; helping to make the interior a safe, comfortable, and productive environment for its occupants. Often, a building’s interior is conditioned with Heating, Ventilation and Air Conditioning (HVAC) to maximize occupant comfort. There are many important considerations when designing a building envelope. The envelope must be sufficiently strong to support itself. It must effectively keep water or other unwanted environmental materials from damaging the building or its contents. It must be secure enough to keep unwanted pests (or people) out of it. It must be visually appealing. These aspects are all very important and there are numerous texts devoted to each of them. As this book is devoted to building energy modeling our focus will be on the transfer of energy through the building envelope.

Defining Energy Uses and Spaces

In Chap. 2 we defined the building envelope, the ambient weather conditions it is exposed to, and the interior Spaces that a building is subdivided into. Of course, the activities that take place in those Spaces are significant drivers for energy consumption as well as the reason buildings exist in the first place. In this Chapter, we will gain a better understanding of how Space occupancy and energy end uses are defined by OpenStudio. As with Constructions, the amount of data required to fully specify Space loads is significant, and we will come to appreciate how OpenStudio Libraries and data inheritance make this process both fast and consistent.

Introduction to HVAC Systems

As we observed in previous Chapter exercises, buildings generally benefit from HVAC systems that are designed to regulate their internal environmental conditions. As the name implies, in addition to heating and cooling, these systems also provide fresh outdoor (ventilation) air to dilute CO2 and other contaminants produced by building occupants, processes, and materials. Modeling HVAC systems correctly is one of the most challenging aspects of energy modeling because of the variety of systems and controls available and the design considerations that drive their selection. The goal of this Chapter is to discuss some of the general concepts needed to understand HVAC system modeling in the context of OpenStudio.

The OpenStudio Software Development Kit

As discussed in Chap. 1, OpenStudio is not a single energy modeling tool. Rather, it is an SDK or platform, designed to reduce the cost and time to create a variety of energy efficiency assessment applications. The OpenStudio Application and PAT, presented in previous chapters, are intended as examples of using the SDK to create software in C++ and Electron/Angular respectively. A third example of creating new functionality with the SDK is the OpenStudio Measure introduced in Chap. 6. OpenStudio Measures are the most accessible means of creating new capability with OpenStudio and represent the “gateway” to more advanced application development. For this reason, the bulk of Chap. 9 is devoted to adapting existing Measures or creating new ones to add functionality to the OpenStudio Application or PAT.

Advanced HVAC Topics

As described in Chap. 4, there are three main categories of HVAC Equipment in EnergyPlus: Plant Loops, Air Loops, and Zone Equipment. This chapter goes into more detail for each of these categories, describing their configuration, sizing, control, and operation. HVAC is a complex topic, and for that reason this chapter only covers the most critical concepts and topics. The authors suggest reading the EnergyPlus Engineering Reference as a supplement to this chapter to learn more.