Chilled water Meyrin consolidation Study 1 st Part Many thanks for their contribution to: Pasquale Alemanno, Fortunato Candito, Alexander Putzu

Outline Loads Proposed layouts System design Parameters “variations” Savings strategies Summary / Conclusions

Loads summary table Courtesy of F. Candito and A. Putzu

Present layout of Installed Cooling Power 378 kW kW 227 kW kW kW 50 kW Eau Perdu Total installed Cooling Power 4640 kW Courtesy of P. Alemanno

Actual cooling power used (Summer) 300 kW 43 m³/h 630 kW 90 m³/h 700 kW 100 m³/h 100 kW 14 m³/h 300 kW 43 m³/h 2195 kW (960 kW buildings kW PS) 315 m³/h Besides POPS (12/18° C), production is 6/12° C. Distribution flows calculated assuming 6 ° C ΔT. Total cooling power: 4225 kW.

Central Plant production/distribution Central Plant: ΔT 6 °C m³/h 249 m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN 65 5 MW cooling tower, axial fans. Centrifugal Chillers with VFD compressors. Chiller staging control. Primary/Secondary (VFD). No buffer tank. Two sets of chilled water pumps.

Two Main Plants production/distribution Summer Plant “PSB area”: ΔT 6 °C m³/h 249 m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN 65 Plant “PS area”: ΔT 6 °C m³/h

Two Main Plants production/distribution Winter (based on 50% load) Plant “PSB area”: Shut down 124 m³/h DN 150- DN m³/h DN m³/h DN m³/h DN m³/h DN m³/h DN 65 Plant “PS area”: ΔT 6 °C m³/h 193 m³/h DN 200

Standard flow vs Low flow 4225 kW cooling COP 6 -> 5 MW tower Condenser water inlet 25 ° C ( 21 ° C w.b.) Standard flowLow flow Chilled water Supply T (°C)66 Chilled water ΔT (°K)68 Condenser water ΔT (°K)510 Chilled water flow (m³/h) Condenser water flow (m³/h)861430

Standard (kW)Low flow (kW)Standard -> Low flow Chiller705753Higher lift due to higher condenser temperature, Chilled water pump17574Same pipes and accessories size ΔP=K*Flow 1.85 Cooling tower fans9060Tower 30% smaller Condenser water pump7035Smaller pipes, ΔP about the same, half flow TOTAL Power Comparison

Central Plant production/distribution Central Plant: ΔT 8 °C m³/h 187 m³/h DN m³/h DN 150-> m³/h DN m³/h DN 100-> m³/h DN 250-> m³/h DN 200-> m³/h DN 100->80 10 m³/h DN 65->50

Further analysis: Impact on AHUs (fan power with bigger batteries and/or different control valves). General considerations Low flow about 10% less power “hungry”. Assuming VFDs for cooling tower fans and chilled water pumps and constant condenser water flow, even at part load the chilled water system benefits from “Low flow”. Anyway, part load analysis needed with actual manufacturer data for cooling towers and chillers. Low flow can be used with standard flow (bigger) tower size, therefore approach can be reduced: colder condenser water. Higher lift will be offset by colder condenser water inlet. Keeping same piping size and tower as in standard flow conditions, would allow for future system expansion with a careful choice of new chiller parameters.

Further savings strategies Increase Chilled water supply temperature 6 °C -> 8 °C. This would represent a saving of about 7% on chiller power. Chilled water temperature reset at part load: about 0.5%- 1% /°C chiller power reduction. Reset condenser water temperature as w.b. falls: about 1% /°C chiller power reduction. Is there a real need for 6°C chilled water setpoint? Put in place all the means to monitor chilled water ΔT and energy consumption. Keep the ΔT as close as possible to design value: system balancing use of two way control valves, avoid unnecessary water bypasses, no three way valves (just for minimum flow and remote locations), shut off clients not using water, verify that the instrumentation is placed and calibrated well in order to avoid excessive valve opening, verify batteries cleanliness.

Foreseen budget for a central plant (VERY preliminary) Main componentsEuros Hydraulics and accessories for main plant (3 condenser pumps, 3 evaporator pumps, 4 distribution pumps, 2 cooling towers, piping and accessories) 1,200,000 3 Chillers600,000 Electricity400,000 Main distribution piping600,000 Terminal loads modifications (AHU batteries, heat exchangers,…) 500,000 Civil Engineering? Total3,300,000 + ?

Conclusions/Future study development Low flow system seems a better choice. Review the need of 6 °C chilled water supply temperature. Monitor the loads during the next summer and winter. Try to get an idea of future system expansion needs if any. Meet Chiller manufacturer (end of this month) for better understanding: equipment size, load split (1/3 + 2/3, 50%/50%, else….), VFD compressors, Cooling power redundancy (1 air cooled chiller as a backup during cooling tower maintenance or main chillers failure?), the phase out of HFC refrigerants in favour of more “green” refrigerants like HFO. Collect info from Cooling tower manufacturer (variation of size, fan power, approach…). Identify Life cycle costs (purchase price, installation, operation, maintenance,..) CE study for central plant vs two main plants. Heat exchanger economizer, heat recovery?