Controls

Chilled-Water Reset

Chillers operate more efficiently when they provide chilled water at warmer temperatures. A familiar EMS controls application keeps close tabs on the building load by measuring the return fluid temperature and rate of flow, then increases the supply temperature to match this load. The EMS acts in a limited, supervisory capacity. The chiller’s integral controls start the unit and otherwise control the chiller operation, while the EMS instructs the chiller to provide the required temperature of chilled water. In combination with chiller sequencing, this operation […]

Controls

Sequencing of Chillers

A large facility that requires several chillers to satisfy the peak building load usually has chillers that have different capacities and efficiencies. As the building load increases from zero to the peak daily use, there’s an optimum sequence of operation that uses the available chillers to best advantage. The smallest chiller can handle the lowest loads, up to its capacity. Then a second chiller of higher capacity is brought online, replacing the small unit. It carries the load up to its maximum capacity, at which […]

Controls

Primary/Secondary Loop System

The ideal central plant design has a primary loop supplied by the chillers, i.e., a constant-volume loop. Each main branch will, for example, serve individual buildings on a small college campus. It has secondary pumps to provide the flow to AHUs in individual buildings. The secondary loop has a variable-flow arrangement, so the pump can be controlled by a variable-speed motor controller, set to maintain a constant pressure in the building loop. The distance between the secondary supply and return taps on the main loop […]

Controls

Optimized Start/Stop of Air-Handling Units

This is a more sophisticated use of the on/off controls of all the air- handling units in a building, typical for a dormitory type of building. Instead of a complete cutoff of power to a unit, the thermostat setting is set back at night and on weekends. The advantage over full on/off controls is that when units are turned off all night, they must work extra hard to return the space to the comfort zone in the morning. This is especially important during the heating […]

Controls

Controls Overview

The ultimate objective of any serious energy-conservation program is a central, computer-automated electronic controls system. This integrated system of remote sensors and control devices permits the optimum use of energy in all areas while simultaneously providing the best environment for building occupants. The equipment that should be included in this electronic harness can be divided into five major categories: 1. Air-handling units 2. Hot-water heaters 3. Cooling towers 4. Chillers 5. Boilers Noteworthy features of each of these categories have been discussed in previous chapters, […]