Dirty air conditioners: Energy implications of coil fouling - eScholarship

Dirty Air Conditioners: Energy Implications of Coil Fouling Jeffrey Siegel, Lawrence Berkeley National Laboratory/ UC Berkeley Iain Walker, Lawrence Berkeley National Laboratory Max Sherman, Lawrence Berkeley National Laboratory ABSTRACT Residential air conditioning is responsible for a substantial amount of peak electrical demand and energy consumption throughout most of the United States. Coil fouling, the deposition of indoor dusts and other particulate matter on evaporator heat exchangers, increases system pressure drop and, correspondingly, decreases system air flow and air conditioner performance. In this paper, we apply experimental and simulation results describing particle deposition on evaporator coils as well as research about indoor particle and dust concentrations to determine coil fouling rates. The results suggest that typical coils foul enough to double evaporator pressure drop in about 7.5 years, much sooner than the expected 15 - 30 year life time for an evaporator coil. The most important parameters in determining coil fouling times are the efficiency of the filter and indoor particle concentrations, although filter bypass and duct and coil design are important as well. The reduced air flows that result from coil fouling cause typical efficiency and capacity degradations of less than 5 %, however they can be much greater for marginal systems or extreme conditions. These energy issues, as well as possible indoor air quality issues resulting from fouling by biological aerosols, suggest that regular coil cleaning to ameliorate low flow and the elimination of filter bypass should be an important part of residential air conditioning commissioning and maintenance practices. Introduction Residential air conditioning is responsible for a substantial amount of energy consumption and peak demand in the United States. Fouling of indoor fin and tube heat exchangers, particularly air conditioner evaporators, causes a reduction in flow. Furthermore, air conditioner performance suffers from reduced airflow (for example, Parker et al., 1997; Proctor, 1998). Despite its potential importance, there has been relatively little research on residential evaporator coil fouling. There have been several anecdotal reports of HVAC heat exchanger fouling (e.g. RSC, 1987; Neal, 1992). In the engineering literature, Krafthefter and Bonne (1986) report that a typical residential heat pump condenser coil will foul sufficiently to cause a 20 % reduction in performance over a 4 to 7 year period. Although very useful in raising the importance of heat exchanger fouling, there is some reason to believe that the work of Krafthefter and Bonne (1986) might be an overestimate of the impacts of fouling because their analysis used indoor particle concentrations which are considerably larger than suggested by more recent literature, and they only consider removal by a high efficiency filter and deposition on the heat exchanger. Krafthefter et al. (1987) extend this work with further experiments and simulations to examine the role of high efficiency air cleaners in reducing heat exchanger fouling. For typical residential heat pump and air conditioning