CSE Pure Power - Fall 2008 - (Page 18)

❯❯ PURE POWER // FALL 2008 18 cover story the lower temperature inlet energy (microturbine exhaust gas). Because it is a double-effect device, the chiller effectively converts the input thermal energy to chilled water and achieves a coefﬁcient of performance of approximately 1.3. The double-effect feature also permits a manual changeover of the chiller to operate as either a chiller or heater. Thus, the CHP system can provide either space chilling or space heating. The control system includes a diverter valve in the duct between the microturbines and the chiller. If the chilling demand is zero, this valve diverts the microturbine exhaust to the atmosphere. If a chilling demand exists, the diverter is positioned to deliver the energy required for the chiller to meet the demand. The ability to isolate the chiller under no-load situations is important to avoid excessive concentrations within the chiller and possible solution crystallization. Fuel gas boosters (FGB) elevate the pressure of the natural gas fuel supplied by the gas utility to the level required by the microturbine. Each CHP system uses one FGB for a pair of microturbines. The FGB is powered by the dc power produced within one microturbine pair, and therefore that microturbine experiences a parasitic electrical load that diminishes its ac output. Table 1 details the performance speciﬁcations of the CHP system at 95 F and at 59 F. The net power levels include power for the two FGB. As indicated, the combined electrical and chilling capability results in CHP efﬁciency greater than 80%. To achieve this level in an application, the full system output capacity must be used productively by the building. SITE AND THERMAL INTEGRATION Based on historical data and analyses, the hotel energy demand averages 670 kW of electrical power and 1,200 kW of combined thermal energy use and power. The electrical demand during the year rarely dropped below 500 kW. 300 275 250 225 Chilled water ﬂow rate (gpm) 200 175 150 125 100 75 50 25 0 July 2 July 16 July 30 Aug. 13 Aug. 27 Sept. 10 Sept. 24 Oct. 8 Oct. 22 Nov. 5 Nov. 19 Dec. 3 Dec. 17 Dec. 31 Because of the hotel’s signiﬁcant and persistent air conditioning demand throughout the year, the CHP system was integrated only with the chilled water loop (see Figure 1). The absorption chiller operates in parallel with two existing 300 refrigeration ton (RT) electric chillers (a primary unit and a spare). However, the design chilled water ﬂow rate was much higher for the electric chiller than for the absorption chiller. To accommodate the different ﬂow rates and pressure drops, a bypass loop with motorized isolation valves was required to balance ﬂow rates during different operating modes. The “absorption chiller” mode (see Figure 1A) required that the motorized valves were positioned to allow returning chilled water to ﬂow only through the absorber and the bypass loop. The chilled water ﬂow rate setpoint through the absorber was 270 gpm measured by a ﬂow meter at the absorber exit. The bypass loop had a similar ﬂow rate. The “simultaneous chiller” mode (see Figure 1B) required the valve settings to allow ﬂow through both chillers, but not through the bypass. When this occurred, the lower ﬂow resistance of the electric chiller reduced the chilled water ﬂow through the absorber to 170 gpm. The “electric chiller” mode (see Figure 1C) required the valve positions to isolate the absorption chiller and bypass loop. The chilled water ﬂow rate through the active electric chiller was roughly 500 gpm. GRID INTERCONNECTION The hotel connects to Paciﬁc Gas & Electric Co.’s (PG&E) San Francisco network through multiple feeders to the site. The multiple supplies provide redundancy in the electricity supply, enhancing power reliability. However, they also require “network protectors” on each utility feeder on the customer side of the transformer. A network protector is a combination of a breaker and a reverse current protection relay to prevent the reverse ﬂow of current onto a feeder that experiences a fault. Figure 3: CHP system chilled water ﬂow rate. The data shown provide a clear picture of the chilled water ﬂow rate through absorption chiller during the absorption chiller mode (the higher data points between 260 and 270 gpm) and ﬂow through the absorption chiller during the simultaneous mode (lower data points between 160 and 175 gpm). Source: UTC Power www.purepowermagazine.com http://www.purepowermagazine.com

Table of Contents Feed for the Digital Edition of CSE Pure Power - Fall 2008

CSE Pure Power - Fall 2008 In the News Commissioning CHP Enhancing Emergency Lighting Data Centers for Uncle Sam Handling a Nuisance Trip Sustainable Projects and Partnerships New Products Ad Index

CSE Pure Power - Fall 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.