Plants

Overview

This chapter covers plants used to produce thermal energy for cooling or heating. Haystack standardizes the following types of plants:

• chilled-water-plant: produces chilled water for cooling
• hot-water-plant: produces hot water for heating
• steam-plant: produces steam water

Typically, these plants supply AHUs and VAVs for HVAC applications. But they can also be used for industrial processes.

We typically use the term central plant to describe a plant that supplies a building or group of buildings. When the plant supplies a municipality, we use the term district plant. However, the Haystack modeling techniques described here are identical.

Haystack models an entire plant as a single blackbox equip entity. Equipment within the plant, including heat exchangers, pumps, boilers, and chillers, are modeled as children of the plant via the equipRef tag.

Chilled Water Plants

Chilled water plants are modeled as a single black box using the chilled-water-plant conjunct along with the equip tag. These plants are composed of the following types of sub-equipment:

• chiller
• coolingTower
• heatExchanger
• pump-motor
• valve-actuator

This diagram shows the salient equipment and fluid flows:

Hot Water Plants

Hot water plants are modeled using the hot-water-plant conjunct along with the equip tag. These plants are composed of the following types of sub-equipment:

• hot-water-boiler
• heatExchanger
• pump-motor
• valve-actuator

Steam Plants

Steam plants are modeled using the steam-plant conjunct along with the equip tag. These plants are composed of the following types of sub-equipment:

• steam-boiler
• heatExchanger
• pump-motor
• valve-actuator

Loops

Plants typically maintain a separation between the working fluid within the plant versus the fluid that supplies thermal energy to the building. We term the pipework within the central plant the primaryLoop and the pipework from the plant to the building the secondaryLoop. These two loops are connected through heat exchangers. In the case of a third loop connected to the second loop through a second set of heat exchangers we use the term tertiaryLoop.

For example, here is how we would model a heat exchanger with a temperature sensor on the primary entering pipe and on the secondary leaving pipe:

id: @hx
dis: "Heat Exchanger"
chilled
water
heatExchanger
equip
equipRef: @plant
siteRef: @site

id: @primary-temp
dis: "Primary Entering Temp Sensor"
chilled
water
primaryLoop
entering
temp
sensor
point
unit: "°C"
kind: "Number"
equipRef: @hx
siteRef: @site

id: @secondary-temp
dis: "Secondary Leaving Temp Sensor"
chilled
water
secondaryLoop
leaving
temp
sensor
point
unit: "°C"
kind: "Number"
equipRef: @hx
siteRef: @site