Abriliam Consulting — Industrial Energy Management
Low delta-T syndrome is one of the most common and costly problems in chilled water systems. When the temperature difference between supply and return water drops below design, the system must push more water to deliver the same cooling — dramatically increasing pump energy. It also degrades chiller performance by reducing evaporator heat transfer effectiveness.
This notebook diagnoses low-delta-T conditions in the dataset using a combination of threshold analysis, scatter diagnostics, and efficiency segmentation.
Plant kW/ton vs Wet-Bulb Temperature: At low wet-bulb conditions (below ~14°C), the plant should operate very efficiently since the chiller has a low lift. Instead, we see a cluster of high kW/ton points — the plant is working harder than it should when conditions are favorable. This is a hallmark of low-delta-T syndrome.
Plant Tons vs Calculated Evaporator Tons: Comparing the load signal against the evaporator-side calculation (flow x delta-T) reveals measurement consistency. Deviations suggest either flow measurement error or genuinely degraded heat transfer.
=== Low-WB thresholds (computed within low-WB subset) ===
n_points WB_cut_C bad_eff_thr_(top_q) low_dt_thr_(bot_q) high_flow_thr_(top_q) %bad_eff %low_dt %high_flow %classic_signature
351 14.0 5.72 4.128 93.393 10.256 10.256 10.256 0.0
=== Top 20 worst-efficiency hours within WB ≤ 14.0°C === wb_C plant_kw_per_ton tons chw_dT_C chw_flow_m3h chw_sup_C chw_ret_C chw_pump_kw plant_kw occ 11.035 7.591 40.000 6.557 19.288 6.411 12.968 6.000 303.639 0.353 12.349 7.416 40.000 5.835 21.103 6.471 12.306 6.000 296.654 0.169 11.275 7.370 40.000 6.299 18.926 6.417 12.716 6.154 294.781 0.064 11.468 7.203 40.000 3.911 33.551 6.594 10.505 12.791 288.102 0.308 11.033 7.106 41.937 6.172 21.577 6.191 12.363 6.576 297.999 0.295 9.290 6.972 46.516 6.497 21.207 6.143 12.640 8.213 324.317 0.082 9.132 6.942 40.000 5.853 21.457 6.155 12.008 6.000 277.672 0.110 10.329 6.881 46.003 4.772 30.524 6.224 10.995 10.476 316.536 0.309 11.216 6.866 56.495 3.216 53.598 6.505 9.721 26.659 387.872 0.195 10.008 6.802 40.000 6.043 20.280 6.226 12.269 8.941 272.066 0.165 8.546 6.674 40.000 6.003 21.358 6.397 12.400 13.101 266.944 0.152 11.093 6.596 56.312 3.794 47.327 6.617 10.411 17.358 371.464 0.114 10.402 6.542 40.000 5.625 21.622 6.424 12.049 7.303 261.663 0.246 11.510 6.518 44.844 5.786 23.022 6.261 12.048 7.182 292.299 0.131 7.674 6.509 40.000 6.240 19.443 6.371 12.611 6.000 260.350 0.147 8.714 6.507 47.670 6.366 22.564 6.082 12.448 7.881 310.210 0.396 11.317 6.430 45.190 6.241 21.627 6.376 12.617 6.909 290.557 0.018 10.489 6.373 41.647 5.835 22.480 6.466 12.302 6.000 265.424 0.387 10.780 6.347 47.399 6.260 22.699 6.213 12.473 6.777 300.818 0.193 10.419 6.308 40.000 5.561 21.231 6.249 11.810 6.770 252.301 0.125 Classic signature count: 0 / 351 (WB ≤ 14.0°C)
Isolating hours where wet-bulb temperature is below 14°C and examining the joint occurrence of:
The "classic signature" — all three conditions present simultaneously — identifies hours where the plant is definitively suffering from low-delta-T syndrome. The highlighted points in the kW/ton vs WB scatter plot cluster at low wet-bulb, confirming these are not weather-driven efficiency issues but hydraulic ones.
The delta-T vs flow diagnostic plot (colored by kW/ton) shows the expected pattern: as flow increases and delta-T drops, efficiency degrades. The dashed threshold lines partition the space into "healthy" and "syndrome" regions.
The Plant kW vs Tons scatter reveals a minimum power floor — even at very low cooling loads, the plant consumes a baseline amount of energy for pumps, fans, and ancillary systems. This power floor is particularly important because it means the plant's kW/ton metric degrades rapidly at part-load. Combined with low-delta-T syndrome (which increases pump power), part-load hours become disproportionately expensive.
Estimated plant power floor ≈ 142 kW Incremental kW per ton ≈ 2.87 kW/ton
Inefficient hours (kW/ton > 4.0): 233 / 1344 (17.3%)
=== Summary by efficiency class ===
n wb_med tons_med plant_kw_med dt_med flow_med pct
ineff
False 1111 20.33 231.20 812.63 5.58 133.29 82.66
True 233 11.90 95.96 422.10 5.43 53.67 17.34
Flagging hours where plant kW/ton exceeds 4.0 (a generous threshold) and examining their characteristics:
This analysis provides the evidence base for recommending operational changes: minimum load staging, CHW reset strategies, and pump speed optimization can all reduce the severity of low-delta-T syndrome.