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Federal Technology Alert recovery unit (HRU), an indirect-fired, single-effect, 10-ton absorption chiller (ABSC), and direct-fired (DFDD) and indirect-fired (IFDD) desiccant dehumidifiers. Under normal conditions, the heated air or hot water input for these TATs is generated by natural gas firing. In the CHP configuration, the waste exhaust heat from the gas-fired microturbine provides the thermal energy input.1,2 The microturbine exhaust gas, at a temperature normally ranging from 250 to 293°C (482 to 560°F), can be directed through different paths depending on the configuration to be tested. Hot water ranging in temperature from 85 to 95°C (185 to 203°F) can be generated by directing the microturbine exhaust gas through an exhaust-gas-to liquid heat exchanger (e.g., an HRU). The hot water generated in the HRU can be input to either an indirect-fired desiccant dehumidification system or a 10-ton, indirect-fired, single-effect absorption chiller. The temperature of the exhaust gas leaving the HRU is ~120°C (~248°F). For testing a direct- fired desiccant system, the exhaust gas can be supplied directly to the desiccant system inlet plenum or passed through the HRU to generate hot water and then be directed to the direct-fired desiccant system inlet plenum.1,2 2.2 TEST FACILITY COMPONENTS1,2 2.2.1 Microturbine The microturbine, a three-phase 480 VAC/30-kW-rated unit, is designed to operate at a maximum speed of 96,000 rpm, generate 50 or 60 Hz power, produce a continuous phase current of 36 A at 480 VAC, and a near unity power factor when the unit is grid connected. The unit’s nominal phase-to neutral voltage is 277 VAC. The power-conditioning electronics of the turbine generator rectifies the high- frequency ac power from the generator to constant-voltage DC power, which is then inverted to 50 or 60-Hz constant- frequency ac power.1,2 The microturbine’s natural gas fuel is supplied by the gas distributor at a pressure of only 0.3 atm (5 psig) and the unit requires natural gas at a pressure of 3.7 atm (55 psig); therefore, a gas compressor is used to increase the pressure before it enters the microtur bine combustion chamber. An exhaust- gas-to-air heat exchanger/recuperator is used to preheat the air entering the combustion chamber, improving the electrical efficiency of the microturbine by ~10% from 13 to 23% based on the higher heating value (HHV) of the natural gas. 2.2.2 Heat Recovery Unit3–6 The HRU, an exhaust-gas-to-liquid heat exchanger, is used to recover a portion of the waste heat in the microturbine exhaust gas and produce hot water for heating, input to the IFDD system, or input to the absorption chiller. Although the HRU nominal water flow rate is ~4.3 m3/h (~19 gpm), CHP system configuration tests were performed with water flow rates as high as ~9 m3/h (~39.8 gpm). At a water flow rate of ~5.8 m3/h (~26 gpm) the maximum water temperature is ~91oC (~196oF). Actual water temperature depends on several parameters, such as microturbine power output, ambient temperature, and HRU water flow rate. The exhaust gas leaving the HRU has sufficient waste heat to potentially provide the thermal input to additional direct-fired TATs, such as a direct-fired desiccant dehumidification unit (DFDD). 2.2.3 Desiccant Dehumidifiers1,2,4,5,7 Desiccant dehumidifiers provide an alternative to mechanical refrigeration for removing moisture from air before it enters a conditioned space. The desiccant material attracts water from the air as a vapor rather than condensed liquid. The water vapor pressure difference between humid air (high vapor pressure) and dry desiccant (low vapor pressure) provides the potential that causes water molecule migration from the humid air to the desiccant. The desiccant dehumidifiers use a wheel of desiccant material mounted between two air streams—a process stream and a reactivation stream. As the wheel rotates between the two air streams, moisture is absorbed from the process stream to nearly saturate the desiccant, and the reactivation stream dries out the desiccant. Moisture released from the desiccant wheel is carried by the reactivation stream and discharged out of the building. Desiccant units that use heated reactiva tion air are called “active” to distinguish them from units that use dry building exhaust air for regeneration, which are called “passive.” The units in the Inte grated Test Facility are active units that can be further classified as “direct-fired” or “indirect-fired,” depending on the method used to heat the regeneration air. In a direct-fired unit, natural gas com bustion or other heat sources are used to directly heat the regeneration air as shown in Fig. 2. For the direct-fired unit tested in the Integrated Test Facility, hot exhaust from the microturbine mixed with outside air was used for regeneration air. When an indirect method, such as a hot water or steam-to-air heat exchanger, FEDERAL ENERGY MANAGEMENT PROGRAM –– 5PDF Image | Summary of Results from Testing a 30-kW-Microturbine and Combined Heat and Power (CHP) System
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