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 o
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Advanced HVAC Topics
5.1 Introduction 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.
5.2 Air Loops Recall that Air Loop are a series of Objects representing HVAC systems that conditions air, which is provided to Thermal Zones for heating, cooling, and ventilation.
5.2.1 Air Loop Configuration In OpenStudio, an Air Loop is represented by the diagram shown in Fig. 5.1. Air always flows in the directions shown by the red arrows. An Air Loop, assuming it has an outdoor air system with an outdoor air intake and exhaust, is an open system, where some amount of the return air is exhausted and replaced with fresh outdoor air for ventilation. As shown in Fig. 5.2, an Air Loop can first be broken into two pieces, supply and demand sides.
© Springer International Publishing AG, part of Springer Nature 2018 L. Brackney et al., Building Energy Modeling with OpenStudio, https://doi.org/10.1007/978-3-319-77809-9_5
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5 Advanced HVAC Topics
Fig. 5.1 Flow direction in an empty Air Loop
Fig. 5.2 Supply and demand sides of an empty Air Loop
5.2.1.1 Air Loop Supply Side The supply side of an Air Loop is responsible for: • • • • •
Consuming air returning from Thermal Zones via the supply inlet Node, Exhausting some of that air to an outdoor air system, Consuming replacement air via an outdoor air system, Heating, cooling, and humidifying it to the correct supply air conditions, and Supplying it to the Thermal Zones via a supply outlet Node.
An empty supply side portion of an Air Loop is shown in Fig. 5.3. Supply side components may be added to Loop between the supply inlet and outlet Nodes.
5.2 Air Loops
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Fig. 5.3 Empty supply side Air Loop detail Fig. 5.4 Typical fan locations within an Air Loop
Outdoor air system components may be added just below the outdoor air exhaust and intake Nodes. In EnergyPlus, an Air Loop must contain at least one fan on the supply side but may include more than one. Figure 5.4 illustrates three typical locations for a fan. A fan positioned before the outdoor air system is commonly called a return fan. A fan positioned adjacent to the outdoor air system exhaust Node is frequently referred to as an exhaust or relief fan. A fan positioned downstream of the outdoor air system is often called a supply fan. In EnergyPlus, unlike in real HVAC systems, fans do not drive airflow around the loop. Instead fan Objects utilize the amount of air flowing through them along with prescribed pressure drop and efficiency curves to calculate the energy that would be consumed to move that much air. Supply and return fans must accommodate the full flow rate o
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