Minnesota State CARD Grant Independent Testing October 31, 2025 By Baris Karagun Energy Efficiency Potential of Nanofluids Conservation Applied Research and Development (CARD) FINAL Report Prepared for: Minnesota Department of Commerce, Division of Energy Resources Prepared by: Michaels Energy CARD Final Report Template, Version 31 (04/17/2021) (DO NOT REMOVE THIS UNTIL DER REVIEWS) Dakota County Air Cooled Chiller System Description The Dakota County Annex is an addition to the Dakota County Administration facility and functions as a municipal office building. A separate chilled water plant provides mechanical cooling to a variable volume air handler dedicated to the addition. The air handling unit mixes outdoor air with return air from the conditioned spaces in the building to a mixed air state. This mixed air undergoes both sensible and latent cooling as it passes across the cooling coil. The air handling unit distributes the conditioned supply air to the building spaces. The chilled water plant consists of an air-cooled chiller with a rotary screw compressor. Redundant constant speed pumps deliver chilled water to the air handler. The air handler contains a three-way valve to control chilled water input to the cooling coil. The working heat transfer fluid in the system is a mixture of 30% ethylene glycol and 70% water. Table 1 shows the specifications of the primary system components. Table 1. Air Cooled Chiller Equipment Specifications Equipment Type Qty Size Units Chiller Screw 1 100 Ton Chilled Water Pumps Centrifugal 2 7.5 HP Air Handler – Supply Fan Centrifugal 1 50 HP Air Handler – Return Fan Centrifugal 1 15 HP Figure 1 shows a diagram of the air-cooled system. Figure 1. Air-Cooled Chilled Water System Figure 2. Air Cooled Chiller Data Collection The air handler is the only end-use served by the chilled water loop. Therefore, the load on the air handler chilled water coil was utilized to determine the load on the chiller. Table 2 lists the data points collected from the facility’s digital automation system. Table 2. Air Cooled Chiller Data Points BAS Data Point Units Collection Interval (Min) Outdoor Air Dry Bulb Temperature Deg F 5 Outdoor Air Wet Bulb Temperature Deg F 60 Outdoor Air Humidity % 60 Air Handler Outdoor Air Volume CFM 5 Chiller Power kW 3 BAS Data Point Units Collection Interval (Min) Chiller Evaporator Flow Rate Gallons per Minute 3 Chilled Water Supply Temperature Deg F 3 Chilled Water Return Temperature Deg F 3 Air Handler Return Air Humidity % 5 Air Handler Return Air Volume CFM 5 Air Handler Mixed Air Temperature Deg F 5 Air Handler Supply Air Temperature Deg F 5 Air Handler Supply Volume Cubic Feet Per Minute 5 Air Handler Supply Fan Speed Percent 5 Cooling Valve Position Percent Open 5 The chiller system utilized a glycol/water mixture as the heat transfer medium in the baseline condition. The mixture contained approximately 30% glycol, providing freeze protection at 7°F outdoor air temperature. The baseline monitoring period occurred from August 12, 2020 to October 30, 2020. Data was collected from the building automation system in five-minute increments to capture system performance. To process the large amounts of data into identifiable trends, relevant data points were averaged based on outdoor air temperature bins of three degrees Fahrenheit. The baseline data collection period captured over 3,300 data points encompassing roughly 275 hours of chiller operation. Since the test period began in mid-August, the baseline monitoring period did not contain operating data where outdoor air temperatures exceeded 87°F. The fluid in the chiller system was replaced on April 13, 2021 with a mixture of 45% HYDROMX and 55% city water. The total loop volume of the chiller system was found to be 720 gallons. The air-cooled chiller system was monitored from May 3, 2021 to October 14, 2021. The nanofluid data collection period captured over 12,600 data points over the entire cooling season, equating to roughly 1,050 hours of chiller operation. Nanofluid kWh 39.094 Annual kWh Savings -6,927 Percent Savings -22% Annual Carbon Savings (lbs) -3,380 Simple Payback (Years) N/A Since the loading of the chiller system was abnormally low due to COVID-19 impacts, the savings were also calculated using the equivalent full load hours (EFLH) methodology for chillers presented in the Minnesota Technical Reference Manual, version 2.2. Error! Reference source not found. shows these results. The chiller’s integrated part-load values (IPLVs) using water and the nanofluid were estimated using the average kW/ton across the monitoring periods. This average efficiency was determined by dividing the kWh consumed by the total ton-hours of cooling produced by the chiller. The building served by the system is a low-rise structure in Zone 3; therefore, the calculation used 446 EFLH. This methodology shows that a typical cooling season would likely have four times the cooling load observed during the late summer of 2021, as the chiller only ran 107 EFLH during this monitoring System 2 – Dakota County Air-Cooled Chiller The operation of the Dakota County air cooled chiller is summarized by outdoor air temperature bins to present the data in an easy-to-consume format. The tables contain the number of data points per bin, average outdoor air dry bulb temperature, average chiller tons delivered, average power consumption of the chiller, chiller kW/ton, average air handler supply air volume, average outdoor air volume, average air handler supply temperature, mixed air temperature, and zone temperature. Baseline Results Table 3 displays the calculated kW/ton of the chiller system in the baseline condition, as well as other select system attributes broken down by outdoor air (dry bulb) temperature bin. Table 3. Baseline Results (Glycol-Water) Temp Range Observations Avg OAT (°F) Avg Tons Avg Chiller kW Avg kW/ton Avg Supply CFM Avg OA CFM Avg SAT Avg MAT Avg Zone Temp (°F) 87-84 104 85.4 14.3 19.9 1.38 10,947 2,005 62.2 75.8 73.6 84-81 209 81.9 11.0 15.9 1.45 9,393 1,873 63.4 75.0 73.5 81-78 625 79.4 9.2 13.4 1.46 8,650 1,830 64.0 74.6 73.4 78-75 354 76.6 9.2 12.9 1.41 9,102 2,611 63.9 74.4 73.3 75-72 433 73.3 9.1 12.3 1.35 9,146 3,273 63.9 74.3 73.3 72-69 612 70.5 7.9 10.6 1.35 8,862 5,632 64.2 73.5 73.2 69-66 604 67.4 8.2 10.4 1.27 8,867 8,024 63.5 72.6 73.4 66-63 386 64.6 6.2 9.1 1.47 8,208 8,005 64.0 71.4 73.3 63-60 188 61.8 6.2 8.2 1.33 8,528 5,998 64.1 71.4 73.1 60-57 115 58.6 11.1 14.4 1.30 9,413 2,381 62.1 74.7 74.0 Nanofluid Results Table 4 displays the calculated kW/ton of the chiller system in the nanofluid condition as well as other select system attributes broken down by outdoor air (dry bulb) temperature bin. Table 4. Nanofluid Results Temp Range Observations Avg OAT (°F) Avg Tons Avg Chiller kW Avg kW/ton Avg Supply CFM Avg OA CFM Avg SAT Avg MAT Avg Zone Temp (°F) 99-96 93 96.6 12.2 16.7 1.37 9,357 1,702 61.9 74.7 73.3 96-93 342 94.3 10.8 14.9 1.39 8,884 1,589 62.1 74.6 73.3 93-90 450 91.3 11.7 16.0 1.37 9,444 1,702 61.9 74.6 73.3 90-87 564 88.5 10.9 15.0 1.38 9,135 1,649 62.1 74.5 73.3 87-84 1022 85.3 11.2 15.2 1.36 9,123 1,632 62.1 74.6 73.2 Temp Range Observations Avg OAT (°F) Avg Tons Avg Chiller kW Avg kW/ton Avg Supply CFM Avg OA CFM Avg SAT Avg MAT Avg Zone Temp (°F) 84-81 1238 82.6 10.3 13.6 1.32 8,380 1,866 62.4 74.5 73.3 81-78 1357 79.4 10.1 13.1 1.30 8,460 2,284 62.3 74.4 73.3 78-75 1680 76.4 10.5 13.5 1.28 8,998 2,170 62.0 74.2 73.2 75-72 1759 73.5 11.1 13.1 1.18 9,352 2,627 62.1 74.0 73.1 72-69 1973 70.5 10.1 12.0 1.19 8,942 3,237 62.5 73.7 73.2 69-66 1182 67.7 10.5 12.1 1.16 9,331 4,807 61.1 72.5 72.8 66-63 952 64.4 10.3 11.6 1.12 8,302 2,944 60.3 72.8 72.5 63-60 666 61.9 11.0 12.6 1.15 9,264 3,051 59.8 72.9 72.2 60-57 228 59.0 7.6 8.2 1.07 6,097 2,300 57.5 72.1 71.8 The metered operating efficiency of the chiller improved by an average of 0.16 kW/ton. The efficiency gains in each temperature bin vary. Annual Savings Estimates The nanofluid installation resulted in energy savings or a more efficient (lower) kW/ton. While linear trends show more considerable efficiency gains at lower outdoor air temperatures and loadings, the efficiency increased at all temperature ranges after the nanofluid installation. A graphical comparison of the chiller efficiency across a range of outdoor air temperatures is shown in Figure 3. Figure 3. Chiller Efficiency vs Outdoor Air Temperature We created an efficiency regression curve plotting the efficiency impacts of the nanofluid installation against the outdoor air temperature in order to determine the efficiency gain of the system across the range of operating conditions. (This curve is shown later in the discussion section.) The baseline energy consumption of the system was normalized to the operating conditions observed during the nanofluid operation by applying the chiller efficiency gain regression curve to the metered data observed in summer 2021 for the nanofluid monitoring period. This approach yielded a savings of approximately 9% across the summer or 1,278 kWh, as shown in Table 5. Table 5. Air-Cooled Chiller Savings in 2021 Data Point Result Nanofluid kWh 13,682 Glycol kWh 14,960 kWh Savings 1,278 Percent Savings 9% Annual Carbon Savings (lbs) 624 Simple Payback (Years) 189 Since the loading of the chiller system was abnormally low due to COVID-19 impacts, the savings were also calculated using the equivalent full load hours (EFLH) methodology for chillers presented in the Minnesota Technical Reference Manual, version 2.2. Table 6. TRM Water-Cooled Chiller Savings Parameter Value Nanofluid IPLV 1.22 kW/ton Glycol IPLV 1.33 kW/ton Equivalent Full Load Hours (EFLH) 446 hours Chiller Capacity 100 Tons Minnesota TRM Equivalent Annual Savings 5,077 kWh Annual Carbon Savings 2,478 lbs Simple Payback 47.5 years The chiller system’s integrated part-load value (IPLV) using glycol and the nanofluid were estimated using the average kW/ton across the operating seasons, determined by dividing the average kWh consumed by the total ton-hours of cooling produced. The facility is a low-rise office building in zone 3; therefore, the calculation used 446 EFLH. As shown in Table 6, the TRM methodology shows that a typical cooling season would likely have four times the cooling load observed during the summer of 2021, as the chiller only ran 112 EFLH.
