Chiller Optimiser Technical Specification

Transcription

1 Chiller Optimiser Technical Specification 1. System Description The Chiller Optimiser Millennium Series is a self contained solid state dedicated microprocessor system. It has been specifically designed to reduce the Energy consumption of centrifugal, screw, reciprocating or absorption Chiller systems. It is capable of operating a single Chiller or several Chillers in various lead / lag sequences. The Chiller Optimiser may be used as a stand-alone control or it can be interfaced with timers, load controllers, or central computer systems. 2. Soft Load The controller soft starts the Chiller compressor(s) at the lowest practical capacity level. This "soft" start saves money in two ways:

2 a) The system significantly reduces the electrical peak demand produced each time a compressor is started, overshooting the correct capacity level at start-up. b) Soft start does not impact on the supply and return inrush, which is frequently not charged to the customer by the utility company. 3. Variable Soft Load After the soft start, the Chiller Optimiser uses a variable soft load. This means that the Chiller is gradually brought up to match the building load, faster during the warmer months and after shutdowns and slower during cooler months. This is accomplished by having a variable step size that automatically adjusts from 2% to 10% of FLA depending on the requirements of the system. 4. Temperature Reset Most chillers produce a constant chilled water supply temperature all year round. While a user may occasionally reset this temperature or set point, it requires manual input which requires constant attention. Our system monitors outside air temperature and chilled water return temperature, using these parameters to adjust chiller loading to obtain an optimum setting, allowing an increase of 1 degree in chilled water temperature results in about a 1.5% to 2% savings in energy consumption and costs. During cooler weather, an increase of 6 degrees will result in a 9% to 12% cost savings. This is why the Chiller Optimiser has been designed to continuously and precisely adjust the water temperature to match current building conditions. 5. Low Load Shutdown Sequence During periods when the demand for cooling is low (at night for example), a chilled water system will reduce its capacity to a point where its operation is inefficient, from 3 or 4 times the power per ton. Additionally, operation at low loads frequently causes higher motor winding and bearing temperatures, and possibly compressor surging.

3 To avoid this problem, when the Chiller reaches its programmed minimum capacity level and the chilled water temperature is below the target by more than the programmed offset, the Optimiser Controller initiates the following sequence:- a) The low load timer starts, allowing the Chiller to operate at minimum for that time. If the time expires, and the water temperature is still below the target temperature, the Chiller is shut down, and will remain off for at least as long as the MIN" setting. b) If the demand for cooling does return within the time period allowed, then the MIN" is reset, and the sequence is ready to start again if minimum load is perceived. c) If the Chiller does get shut down, a subsequent increase in demand will re-start the Chiller, it will soft / start and soft / load in the normal manner. d) The net result is that the Chiller Optimiser low load cycle saves energy by operating the compressor at more favourable efficiency levels and by reducing unnecessary compressor cycling. 6. Air Temperature Lockout The Chiller Optimiser can be programmed to monitor outside air temperature and hold the chiller system off as long as the outside air temperature is colder than certain user programmable set points. A table has entries for the set points for the lead chiller and the lag chiller. Also, the system has a sophisticated method for choosing which chiller is lead and which is lag. Outside air temperature and the peak timer control this function. 7. Multiple Chiller Operation When a system has more than one chiller, the chiller can be programmed through combination up to eight different sequences (dependant on the number of chillers). The sequence is entered and changed from within the Master Configuration Table. For example, if you have five chillers, you may configure them to run in a 1,2,3,4,5 sequence or 1,5,4,3,2 or 2,1,4,3,5 and so on..., but you cannot have one sequence to start at 7:00 am and select another chiller or sequence at 9:00 am. The chillers are turned on based only on cooling demand and not on time-of-day. The Chiller Optimiser controller starts the subsequent chillers when the lead Chillers reach a user programmed threshold set point, between 75% and 100% capacity to satisfy cooling requirements. The lag chiller is soft started, when the Ready to Load (RTL) signal is received, our system will regulate the capacities of all chillers, reducing the loading of the lead chiller by the amount of loading on the subsequent chiller. The chiller loading is proportional to their full-scale capacities.

4 When the lead chiller(s) once again satisfy cooling requirements and lag chiller operation is no longer efficient, the controller shuts down the lag chiller and increases the capacity of the lead chiller, to replace the lag chiller capacity that was removed in the first instance. The lag chiller shut down is initiated by the "Low Load Off-Cycle" sequence described above. If the chillers have approximately the same capacity, they are loaded evenly. If they have different capacities, they are loaded proportionally. (The full load capacity of each chiller is entered in the Data Entry tables of the control). The aforementioned describes a typical simple lead / lag relation between chillers. Some climates require more sophisticated switching patterns to efficiently proportion the load to the chillers, therefore, other lead / lag switching options are provided (peak timer, mentioned above). Entries in software tables determine the lead / lag action. An explanation of the options is given on in the installation and operating manuals. 8. Load Shedding The Chiller Optimiser has the capability to receive an external load shedding signal from a load controller to reduce the electric Energy usage of the chiller. The system will also decrease chiller capacity by 10% per minute until the signal is terminated or until the "Minimum Operation %" level is reached. Routine capacity adjustments resume when the load shed signal is terminated. Some operations may require lag chiller lockout rather than load shedding, terminals 7 and 8 are used for either operation, and the program entry in a table determines which operation occurs at contact closure. (It is unnecessary to use both). 9. Additional Cooling Capacity Humidity monitors, critical temperature thermostats, or in the case of the Hotel, Ballroom Sensors can be used to request the chiller control to increase cooling capacity. When an additional cooling signal is received, the controller will lower the return water set point temperature by 1 degree, thereby requiring increased loading on the Chiller. The system water temperature will be returned to normal when the signal is terminated. 10. Control Safety - Override The Chiller Optimiser constantly monitors the system for potentially harmful conditions such as low temperature, high temperature, and control setting error, compressor failure, and electrical interference.

5 When any of these conditions are detected, front panel cue lights will come on and an alarm is generated on the PC. 11. General Specifications Electronic Circuits: Microprocessor: 16-bit AMD x 86 Series Program memory Flash User s Parameter Memory : Electrically Erasable Flash (non-volatile) Operator Interface : 16 tactile sealed membrane switch keys and 16-charactoer, dual line alphanumeric large format LCD display (back lighted) A/D Converter (with 8-input max): 12-bit binary, 0.5 LSB max inaccuracy D/A Converter: 12-bit binary, 1 LSB max inaccuracy Status (Logic) Inputs: Ready-to-load (110/220 VAC) Remote Start (Dry Contact Closure) Remote Lead / Lag (Dry Contact Closure) Remote Load Shed (Dry Contact Closure) Remote Additional Cooling (Dry Contact Closure) Logic Outputs: Chiller Start (Interlock) Load/Unload Chiller (Centrifugal s) Compressor On Solid State Relay (up to 12) for recip loading Chiller Fail Analogue Output: 4/20 ma for external demand limit, external living chilled water set-point, reset leaving water temperature Sensors: Three Platinum RTD temperature sensors (one return water sensor, one leaving water sensor and one outside air sensor) with 4-20 MA transmitters. Temperature range covered is 32/120 degf or 0/50 degc Models: Series C for Centrifugal Chillers

6 Ambient Temperature Range: 32/120 degree F or 0/50 degree C, 10-90% Relative Humidity (non-condensing) Weight: Master Unit 10 pounds / 4.5 kilograms Slave Unit 6 pound / 2.7 kilograms Power: 117 VAC (220 V) 10%, 15 watts max. Housing: Master Unit with one Optimiser - Wall Mounted NEMA 4X (fibreglass) cabinet with clear window. 14 x 12 x 8 /35.5cm x 30.5cm x 20.3cm. Slave Unit = 10 x 8 x 6 / 25.4cm x 20.3cm x 15.2cm. Standard System - Wall Mounted Schematic

7 Standard System Interface Schematic Notes: Energy Management or Building Automation Systems may interface with the Optimiser to Start/Stop the chillers, call for additional cooling, call for Load Shedding, call for Locking Out lag chillers or Bypass Optimiser. Maximum Demand software in conjunction with the kwh transducer may be used for auto load shedding, when building total demand is likely to be exceeded, 15-minute data is stored for retrieval via modem. PO Box 46320, Abu Dhabi, U.A.E Tel: +971 (0) or Tel: +971 (0) Web: