Performance of Gas-Engine Driven Heat Pump Unit

Abstract

Airconditioning (cooling) for buildings is the single largest use of electricity in the United States (U.S.). This drives summer peak electric demand in much of the U.S. Improved airconditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated technologies (TAT), such as natural gas engine-driven heat pumps (GHP), can provide overall peak load reduction and electric grid relief for summer peak demand. GHP offers an attractive opportunity for commercial building owners to reduce electric demand charges and operating expenses. Engine-driven systems have several potential advantages over conventional single-speed or single-capacity electric motordriven units. Among them are variable speed operation, high part load efficiency, high temperature waste heat recovery from the engine, and reduced annual operating costs (SCGC 1998). Although gas engine-driven systems have been in use since the 1960s, current research is resulting in better performance, lower maintenance requirements, and longer operating lifetimes. Gas engine-driven systems are typically more expensive to purchase than comparable electric motor-driven systems, but they typically cost less to operate, especially for commercial building applications. Operating cost savings for commercial applications are primarily driven by electric demand charges. GHP operating costs are dominated by fuel costs, but also include maintenance costs. The reliability of gas cooling equipment has improved in the last few years and maintenance requirements have decreased (SCGC 1998, Yahagi et al. 2006). Another advantage of the GHP over electric motor-driven is the ability to use the heat rejected from the engine during heating operation. The recovered heat can be used to supplement the vapor compression cycle during heating or to supply other process loads, such as water heating. The use of the engine waste heat results in greater operating efficiency compared to conventional electric motor-driven units (SCGC 1998). In Japan, many hundreds of thousands of natural gas-driven heat pumps have been sold (typically 40,000 systems annually) (Yahagi et al. 2006). The goal of this program is to develop dependable and energy efficient GHPs suitable for U.S. commercial rooftop applications (the single largest commercial product segment). This study describes the laboratory performance evaluation of an integrated 10-ton GHP rooftop unit (a 900cc Daihatsu-Aisin natural gas engine) which uses R410A as the refrigerant (GEDAC #23). ORNL Thermally-Activated Heat Pump (TAHP) Environmental Chambers were used to evaluate this unit in a controlled laboratory environment. EXPERIMENTAL Temperature conditioning for each TAHP chamber is provided by a dedicated glycol fluid loop which circulates glycol at he appropriate temperature through the fluid-to-air heat exchanger in the room. Additional temperature conditioning is provided by sheathed electric heaters located directly in the air stream. Each glycol loo...

Gas Engine-Driven Heat Pumps for Small-Scale Applications: State-of-the-Art and Future Perspectives

“…Mahderekal et al [143][144][145][146][147][148][149][150][151] analysed GEHP technology on an experimental and simulation basis at the Oak Ridge National Heat Pump Laboratory (ORNL) in Tennessee (USA).…”

“…In [144], an experimental analysis on a GEHP is reported. The experimental tests were performed by varying outdoor air temperature, engine speed and the operating mode (heating, cooling).…”

“…Air-to-air [88,94,96,98,99,145,150,164,189] Air-to-water [85,122,123,162,175,176] Intense experimental activities have been carried out by many researchers all over the world through the analysis of GEHP units in laboratories, aiming to evaluate, by modifying different parameters, the performance, mainly at stationary conditions, though some studies also focused their attention on transient [85,105,119,137,144,157] conditions. In other cases, an investigation of GEHP performance reproducing daily heating and cooling loads has been considered [109][110][111].…”

“…In other studies, models based on experimental data by means of polynomials are considered for single components, such as engine [86,101,102,117,118,134,135,[138][139][140][141][142][143]146,173], heat pump [185], compressor [134,138,139,[141][142][143]146], the entire GEHP system [103,107,144], or for evaluating the system performance [134,165].…”

“…Simulation analysis has been performed mainly considering stationary conditions, but some studies considered transient operating conditions of GEHPs [101,103,124,144,157,192].…”