Western Cooling Challenge Update: Results from the Lab and Field
Progress on the Cooling Challenge is heating up. This month's Newsletter focuses on two different field studies of Cooling Challenge equipment and one laboratory report for a dedicated outdoor air unit. The results for each of these studies show significant energy savings:
Field Results: Dual-Evaporative Pre-Cooling Retrofit | Palmdale, CA
The product tested in this project takes advantage of indirect evaporative cooling to cool the ventilation air stream on a conventional rooftop unit, and uses direct evaporative cooling to cool air at the condenser inlet. This dual design reduces energy by reducing the temperature of incoming ventilation air and by lowering the condensing temperature. Since the dual evaporative pre-cooling technology incorporates with a conventional air conditioner, the combined system still maintains latent cooling capacity for applications where dehumidification is required. These dual processes work together to increase cooling capacity and to improve efficiency for the vapor compression system. The second effect is mainly caused by a lower heat sink temperature for the refrigeration cycle. Laboratory measurements for the dual evaporative pre-cooling technology installed on a similar rooftop air conditioner indicated 43% reduction in power draw at peak.
Download the Case Study »
Field Results: DualCool Hybrid Rooftop Unit Field Test | Ontario, CA
The product tested in this project takes advantage of indirect evaporative cooling to cool the ventilation air stream on a conventional rooftop unit, and uses direct evaporative cooling to cool air at the condenser inlet. This dual design reduces energy consumption by reducing the temperature of incoming ventilation air and by lowering the condensing temperature. Since the dual evaporative pre-cooling technology can incorporate with any conventional air conditioner, the combined system still maintains latent cooling capacity for applications where dehumidification is required. These two cooling processes work together to increase cooling capacity and to improve efficiency for the vapor compression system. The second effect is mainly caused by a lower heat sink temperature for the refrigeration cycle.
Three variable speed Trane Voyager units with DualCool® were installed in Ontario CA for the purposes of this study. Two were installed on the administrative offices for a mall (M12-14, M15-15), and one was installed to cool the kitchen for a restaurant and bakery (AC7).
Download the Case Study »
Lab Results: Hybrid Dedicated Outdoor Air Unit | San Ramon, CA
This report presents analysis of results from laboratory testing of the Munters EPX 5000 - one example of a commercial DOAS product that incorporates indirect evaporative cooling, vapor compression, and heat recovery. The laboratory examination was conducted at PG&E Applied Technology Services in San Ramon, California. Tests were organized in a way to measure the cooling capacity and energy consumption for the system in each mode of operation, and across a range of operating conditions.
RESULTS IN BRIEF
The results from this report indicate a 20% reduction in electrical demand from the whole building HVAC at Western Cooling Challenge peak conditions, and 10% reduction at Western Cooling Challenge annual conditions. Moreover, the analysis indicates that while the baseline scenario requires roughly 42 tons (net nominal) conventional rooftop unit cooling capacity, the EPX 5000 scenario only requires 29 tons (net nominal). This means that an existing building with five conventional rooftop units could downsize to three or four conventional units by shifting the ventilation cooling load over to a new 5000 cfm DOAS.
Download the Report »
Rainwater Storage for Evaporative Systems
Previous research successfully show the viability in both sufficient quantity and quality of rainwater for use in evaporative systems. The water demand for a season of evaporative cooling was met from a few rain events, and the water meets EPA guidelines for use in evaporative systems even after being stored for months. The next phase of research will determine the effects that rainwater may have on a copper condenser coil. In order to investigate both tap water and rainwater effects in cooling systems, a laboratory test with a small-scale, copper coil evaporative condensing unit was used. Various water sources for use in a residential evaporative condenser, representing tap water characteristics typical to California, were tested. The potential sources included groundwater-derived municipal water, surface-water-derived municipal water, and harvested rainwater. The project evaluated the interplay between water quality, evaporative-condenser fouling and performance, and water burden for each water source.
Systematic testing of influential water quality parameters
The effects of various water quality parameters were assessed to determine their influence on scale formation. Water quality parameters includde two water quality scenarios to represent the breadth of water quality conditions in CA, being sure to adequately capture the range of water conditions in California’s drinking water supply. In WCEC's experimentst, four setups were examined in parallel with low (about 7%) bleed rate systems with two different tap water qualities. Bleeding of a system is defined as the rejection of a portion of the cooling water in the system either continuously or at regular intervals during operation. The volume removed was replaced with the tap water source.
The small scale apparatus was designed to run up to four tests simultaneously to reduce the variability in test conditions. The strategy applied was to compare low hardness and high hardness water source systems in a small scale of aqua chill and also to have an understanding of the effect and the presence of previously precipitated solids in the system, by using a newly made copper coil and an old copper coil (previously coated with solids from the previous experiment). The four parallel small scale units were run for 15 days.
Evaporation of water increases the concentration of minerals and if the process is carried in a sufficient time the sump is supersaturated. Vaporization of water over the copper coil leads to direct deposition on the surface of the coil. Figure 2 shows the summary results of solution mineral analysis for the experiment. The amount of precipitation for each test was calculated based on the measured influent and effluent concentrations.
Calcium was observed to be largely precipitated (about 90% precipitation) in the first and third test (Low Hardness) and the sump concentrations of calcium were actually lower than that of influent. The calcium concentration in sump was 0.03 mM for new coil test and 0.12 mM for the old coil test.
Calcium precipitated in the second and fourth test (High Hardness) about 25% for the new coil and 22% for the old coil.
Magnesium scale (probably magnesium carbonate) formed in all cases. Magnesium was observed to be precipitated (about 9% precipitation) in the first and third tests (Low Hardness). Magnesium concentration in sump was 0.02 mM for new coil test and 0.03 mM for the old coil test. Magnesium precipitated in the second and fourth test (High Hardness) systems about 3% for the new coil and 12% for the old coil. In the high hardness systems, magnesium contributed higher to mineral scale formation compared to the low hardness systems. The amount of precipitation was increased with the old coil system ( 400% increase). indicating that previously precipitated solids on the coil can lead to excessive precipitation and therefore reduces solution concentration especially when the influent concentration is high such as the foruth test. In the other words, the presence of nucleation sites on the copper coil may encourage the formation of scale on the surface. This effect was lower (45% increase) when the effluent had a low concentration as was observed in low hardness systems such as the first and third test.
Older, already seasoned coils, encourage the formation of even more scale on their surface.