Fig. 37-41 Recoverable Heat vs. Cooling Load for 950 Ton Reciprocating Engine-Driven Chiller. Source: York International


fuel input to the combined output of the vapor compression chiller, plus the absorption chiller which operates on heat recovered from the engine.

Figure 37-41 plots the recoverable heat, in MBtu/h, versus cooling load for this system. Assuming a displaced boiler efficiency of 82%, at full load, the recovered heat would produce a fuel credit of about 3,100 Btu/ton-h (0.26 kWhh/kWhr). Subtracting that from the full load fuel input of about 6,200 Btu/ton-h (0.52 kWhh/kWhr) yields a net fuel rate of about 3,100 Btu/ton-h (0.26 kWhh/kWhr), for a COPnet of 3.9. While this net COP is significantly higher than the total COP achieved with the add-on recovered heat-powered absorption chiller, the performance enhancement achieved with the absorption chiller feature would be an attractive option if there were limited opportunities to displace other facility fuel use with recovered heat.

Fig. 37-40 COP vs. Cooling Load for 950 Ton Reciprocating Engine-Driven Chiller With and Without Recovered Heat Powered Absorption Chiller. Source: York International


Reciprocating engine-driven vapor compression systems have relatively high maintenance frequency requirements. In seasonal space conditioning applications, however, which typically operate fewer hours than other applications, maintenance frequency is somewhat less of a concern. As such, the lower maintenance and longer life benefits of the lower-speed, heavy-duty industrial-grade engines may not affect the economics sufficiently to offset higher first cost. Additionally, seasonal applications allow for off-season maintenance programs to be completed without the pressure to quickly bring a unit back on line.

Complete life-cycle OM&R costs for the engine drive will vary widely, ranging from $0.005 to $0.02 per ton-h ($0.002 to $0.006 per kWhr). OM&R costs for most mid-sized, medium-speed engines will be typically less than $0.010/ton-h ($0.003/kWhr). Complete service contracts are commonly procured for reciprocating engine-driven vapor compression systems to allow a facility to capture the benefits of the system without absorbing additional maintenance and repair responsibility and risk.

Application Examples

Reciprocating engines have been widely applied for driving vapor compression systems. Applications are fairly common with reciprocating, screw, and centrifugal compressors and range from small DX units to extremely large water-cooled systems. Figures 37-42 through 37-47 provide several application examples.

Figure 37-42 shows a 98 ton (345 kW), roof-mounted, air-cooled chiller system. This system features two

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