Bypass line sizing. This critical information is needed to identify the quantity and desired performance requirements of the equipment. As the chilled water valve begins to open, the chilled water differential pressure transmitter senses a drop in system pressure. Chilled water is centrally produced and distributed throughout the campus, and this district cooling system shall be utilized wherever possible. The circuits are wired in series, which means all conditions must be satisfied prior to allowing the unit to operate. %PDF-1.3 document: chw-1-rev1 . this sequence shall be carefully reviewed and edited with respect to application … the cooling coil. The lead pump shall run first. The CWSAT uses inputs of the chilled water system equipment and operating . The design output capacity of a chiller exists only for a short period of time during the cooling season. Primary-Secondary pumping is not appropriate for … revision: 1.0 . After viewing this information, you may wish to alter the equipment specifications or apply one of several operating cost … Chilled Water System Sequence of Operations --SAMPLE-- Overview The chiller system is comprised of three chillers: two larger centrifugals (CH-1 and 2) with good part load efficiency down to 25% and one reciprocating chiller (CH-3) about 1/3 the size of the centrifugals which has excellent part load efficiencies with eight stages of unloading. The challenge for design engineers is just how to maximize the comfort requirements while keeping energy costs to a minimum. To provide chilled water, a variable-primary-flow system includes two variable speed pumps that pump water through a first chiller and a second chiller. As this occurs, the total system water flow and chilled water temperature difference is monitored along with the chiller power consumption. As the chilled water flow is increased, the additional load is noted at the chiller by an increased return water temperature. This is accomplished by unloading cylinders in the reciprocating unit, modulating a slide valve in a screw-type compressor, or controlling refrigerant flow with a variable speed drive or inlet vanes on a centrifugal compressor. This will provide a profile of the power requirements and efficiencies. Another added control feature is to have the leaving water temperature reset based on the outdoor air wet bulb temperature. Search Products And Discover New Innovations In Your Industry. Figure 1 illustrates the flow of water at the cross-over bridge piping under normal flow. Two large chilled water storage tanks totaling ten million gallons--one located behind Creekside Residence Hall and the other at the northwest corner of Red River and Martin Luther King, Jr. As long as the space was cooler than the outdoors, a 5 or 10 F temperature swing was just fine. PART 3 - EXECUTION 3.01 SEQUENCE … The designer has total flexibility in identifying sensing points, alarm circuits, and control strategies. Some designers use a current transducer on the motor that indicates the pump is running. Determining Optimized Sequences Chilled Water Pump Control Chilled Water Temperature and DP Setpoint Reset Tower Fan Speed Control Condenser Water Pump Control Chiller Staging Waterside Economizer Control. and water flow to meet chilled water needs and save operating energy costs. Cooling tower capacity and performance is based on the outdoor wet bulb temperature and the ability of the equipment to match the wet bulb temperature and the tower leaving water temperature, which is known as the approach temperature. There are several control strategies for condenser water pump control. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. Division 23 equipment Sections detailing package controllers. Ice detection sensors protect the towers in cold climate operations as well as initiate a de-icing operation. Modulate (vary) the speed of the secondary pump VFD to maintain a constant differential pressure. This all begins with either single or multiple sensors, located in a space or controlling a process temperature. As additional water flow is presented to the cooling towers, an outdoor wet bulb sensor is used to reset the leaving water temperature controller. Cooling towers incorporate vibration sensors in the event a fan goes out of balance. Pump speed is controlled by differential pressure transmitters located throughout the chilled water system. Horsepower changes exponentially to the third power in relationship to flow. COOLING ONLY OPERATION: The Cooling thermostat shall cycle the water control valve, via a cooling signal, to maintain the desired space temperature in … It is important not just to have a grasp of the maximum and minimum load requirements, but also to understand the building load profile that identifies the time duration during part load events. The more fill, the more surface area—and the better the heat transfer. On the chilled water side, most pumping configurations use variable flow strategies. When towers are operated during freezing conditions, there must be a control algorithm that maintains a minimum flow through the tower to prevent ice buildup on the fill material. Using a room thermostat as a starting point, the following events would occur: So here we have an abbreviated outline of interoperability, demonstrating that a change in any one component will have an effect on overall system performance. parameters to calculate the system’s energy consumption. rev. The HVAC with controls shall be installed and programmed to perform as described in this section, and as applicable to the specific project. Back then and even now, the on/off concept is simple and works, although it does have a detrimental effect on operational life of the equipment. As software becomes more sophisticated, the control sequences/operation will have an intuitive nature, preventing rapid system fluctuations due to a single data point change. The tiered cooling approach decouples the latent Related Sections include the following: 1. Chillers and constant flow primary pumps are enabled in pairs, making the primary flow rate a step function. The Indivent system requires only one compact, room saving air duct system since the heat loads are being removed via a compact chilled water system. Sensing pressure after the pump discharge check valve will not work, especially in a multiple-pump common header design. The pumps are designed to operate in a parallel configuration. The chilled water is then pumped, via the chilled-water distribution system to the building's air-handling units. A compressor that can have the refrigerant flow controlled infinitely will be more successful matching the loads and maintaining efficiency. Sequence of Operations (excerpt) Chilled Water System Consists of one (1) 600 cooling ton Trane CVHE 3 stage centrifugal chiller, with associated chilled water pumps, condenser water pumps and one (1) two stage cooling tower, supplies chilled water to all fan unit cold deck coils for building cooling. A simple analogy would be trying to fit rectangular objects under a curve—the larger and fewer the objects, the more open area under or above the curve. System – Air handling unit for supply fan. 1.8.5 Consolidation of chilled water systems 48 1.8.6 Chiller sequencing strategies 51 1.8.7 Chilled and condenser water temperature reset 54 1.8.8 Condenser tube cleaning and water treatment 61 1.9 Thermal energy storage systems 62 1.10 District cooling systems 66 2. The chilled water supply is pumped through the chiller and to the building’s various air conditioning units such as air handling units (AHUs) and fan coil units (FCUs): In the AHUs and FCUs, the chilled water is passed through a heat exchanging coil … Rising energy costs and the demand for more precise temperature control are the driving factors for properly and efficiently controlling a chiller plant. The objectives are to maintain the unit operation during part load conditions, avoid on/off cycles, and minimize energy consumption. Water-cooled Chillers . SEQUENCE OF OPERATION 15985 - 1 SECTION 15985 - SEQUENCE OF OPERATION 1.01 SUBMITTALS A. In a primary– secondary system, a chiller and its primary pump typically operate in tandem. A large percentage of operating hours are spent at some point between off and 100% loaded. A poor system design and construction will result in low delta-T syndrome. As the system load changes, the flow requirements change as well as system head. A single pumping system is simple because a single system curve is followed; a parallel pumping system becomes a little more complex. Water flow is modulated with VFD controlled variable flow primary pumps based on the differential pressure across the water system. However, if the pump uses a coupling to attach the pump shaft to the motor shaft, and that shears, the motor runs but the pump is not operational. notes: 1. this sequence is intended to provide the design professional with a basic guideline of minimum requirements for a typical building chilled water pumping system. There is a certain irony in the design and control of a chiller plant. The chilled water control valve must modulate open to provide additional cooling and lower the space temperature. date: july 22, 2011 . Change only one thing; too many variables will never work. The offset would be higher efficiency at the chillers, resulting in a net energy reduction for the system. The most important component of good chiller plant control is understanding the full and part load requirements and then matching them to system performance. The smaller and more frequent the rectangles, the closer you get to match the curve. PART 2 – PRODUCTS 2.1 SEQUENCES OF OPERATION A. A stable condenser water temperature will result in consistent chiller operation and efficiency. The secondary chilled water pump (SCHWP) sets will be controlled through VFD drives to … Safety controls are usually inherent to the manufacturer and should not be altered. This also includes the physical layout and configuration of the plant. 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