Reciprocating Compressors - Emissions
Reciprocating chiller emissions fall into two major categories: direct (or on-site), and indirect (or emissions resulting from the production of the energy used to operate the equipment).
Direct on-site emissions are confined to the release of refrigerant due to leaks or servicing. Federal law now mandates no intentional release. It is the responsibility of the user and service agency to minimize leaks and service release. Good preventive maintenance practices are imperative. Other factors affecting emissions include chiller age, application (whether it's a single package or split system), compressor type (open compressors with shaft seals tend to leak more than hermetic designs).
A typical semi-hermetic type chiller might lose about 3 to 5 percent of its charge annually. With the refrigerant charge running about 3 pounds per ton, the emission of refrigerant might total about 0.12 pounds per ton per year. An open chiller might lose 5 to 7 percent, and thus emit about 0.18 pounds per ton-year. To allow for less than ideal conditions, a conservative estimate of emissions might be 0.25 pounds per ton-year.
Natural Gas engine-driven reciprocating chillers must use open-type compressors. In addition to the same refrigerant emissions as an electric chiller, they also produce emissions from the combustion of the natural gas. Also, the leakage of natural gas into the atmosphere although small, is believed to contribute comparable greenhouse gases as refrigerant leakage.
These emissions can be estimated, based on the annual gas consumption. Typical gas engine driven chillers use about 9,300 Btu per ton-hour of natural gas (on a HHV basis). Using the annual ton-hours of cooling, the emissions of CO2 and the criteria gases can be estimated using these relative values of pounds per million Btu of fuel burned. The emissions of all gases other than NOx are relatively constant throughout the loading range. NOx emissions will vary considerably, depending on the annual load profile.
|On-site emissions in pounds per million Btu of Natural Gas burned|
*Particulates are 10 microns or less. Volatile organic compounds (VOC) includes hydrocarbons (HC).
While so-called "lean-burn engines" emit less NOX than conventional engines at full load, they emit more at part load conditions. Since chillers operate largely at part load, the added expense of a lean-burn engine is usually not justifiable.
Indirect emissions occur at the power plants generating the electricity used to power chillers. Remember that comparing different chillers (for example, electric versus gas) must include the effect of the chiller and system auxiliary energy consumption - not just the chiller's power use. These emissions can be estimated from the annual power consumption in kWh and the local electric utility's emission data.
Most utilities know their typical emissions of the various gases and particulates on a "per kWh" basis.