Free cooling on RTAF Chiller
Integrated option Water based free cooling principle.
• Use full aluminum (car radiator based) flat channel dry cooler exchangers. • Modulate 3 way valve to reach required free cooling capacity. • Need low air pressure drop coil to avoid upgrade of fans.
Oil Sep.
Evaporator
2 Technical proposition
• Alternative 1 : no change on condenser fan = lower EER, but no fan impact on cost, almost no impact on sound level
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Total Free cooling Total Free cooling Direct free cooling version (With glycol on customer loop) Glycol Free version (With water on customer loop)
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Partial Free cooling Partial Free cooling Direct free cooling version (With glycol on customer loop) Glycol Free version (With water on customer loop)
Trane FreeCool External drycooler
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3 External Dry cooler – Standard RTAF With or without glycol on customer loop Flow chart - Free cooling Direct free cooling version (With glycol on customer loop) 1 3
Service valve (Vent)
Dry cooler Dry cooler coils coils
Service valve (Vent) Tchill OUT Tevap IN
Free cooler Evaporator Modulating 2way valve Free cooler Tchill IN Bypass Optionnal 2way valve Pump package
Service valve (Drain)
4 Flow chart - Free cooling Glycol Free version (With water on customer loop) 2 4
Service valve (Vent)
Dry cooler Dry cooler coils coils
Service valve (Vent) Tchill OUT Tevap IN Water/glycol BPHE Tfc OUT Free cooler Evaporator Modulating 2way valve Exp.tank Free cooler Tchill IN Tfc IN Bypass Optionnal 2way valve Pump package
Service Service Circulating valve valve pump (Drain) (Drain)
5 Free cooling enabling condition
Condition to get free cooling active : • Unit is in active cooling mode. • Outdoor temperature shall be low enough. Cf. diagram here below
Free cooling enabled Proposed default value FC Offset = 3K (Min 0.5°K, max 15°K) FC Hysteresis = 1K (Min 0.5°K, max 3°K)
FC Offset
Free cooling disabled Water Cooling setpoint Outdoor air temperature FC setpoint = Active chilled water cooling setpoint – FC_offset FC Hysteresis
The free cooling function is enabled when outdoor air temperature is below (Active chilled water cooling set point minus FC_offset). An hysteresis shall be applied to avoid short cycling of FC enable logic. FC offset is the parameter adjusted by user to make free cooling active.
Free cooling becomes the 1st stage of cooling, whatever the compressor sequence selected: • If free cooling is enabled while compressor is running, then unload command of the algorithm shall apply to running compressor . In case of load command, then free cooling capacity shall be increase
6 Free cooling capacity modulation
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Dry cooler Dry cooler Dry cooler Dry cooler coils coils coils coils
2 2 Free cooler Free cooler Modulating Modulating Free cooler 2way valve 2way valve Free cooler Bypass 2way Bypass 2way 1 valve (ON-OFF) 1 valve (ON-OFF)
FC pump 4 FC disabled FC 1st step FC 2nd step
1 100%►0% for TFC 0% for TFC Bypass Valve 100% 100%►30% for PFC 30% for PFC
2 FC valve CLOSE 0%►100% (modulating) 100% 0% 0%►100% 3 Condenser fan Follow compressor fan or follow compressor fan or follow compressor fan airflow sequence sequence if compressor are still sequence if compressor are running still running 4 FC pump OFF ON ON 7 Freeze protection (only for Glycol free version)
If Free cooling is active, the pump is ON. At start up or when heat transfer over the drycooler increases, the glycol stored in the system could be very cold, resulting in freezing risk on the BPHE. To avoid this, the strategy is to run the pump with recirculation of the glycol in a short loop (dotted line arrow). The freeze protection mode is targeted to restore positive temperature at BPHE glycol inlet. The heat from return chilled water and from the pump heat loss will try to maintain the BPHE glycol temperature above 0°C. Difficulty here is to have quick enough system response to avoid partial freezing into the BPHE Condition to have freeze protection active: • Outdoor air temperature <3°C • Free cooling is active : Chiller water flow is present & there is a call for cooling. • If Tfc OUT is < chilled water freeze protection setpoint and FC pump is ON then we are in FC freeze protection mode
FC Freeze protection limiting mode : • Reduce Free cooling capacity to keep TfcOUT > chilled water freeze protection setpoint from 100% to 0% (following accelarated unload sequence). • If Tfc IN < chilled water freeze protection then • Lockout free cooling operation and report alarm. Auto reset when Outdoor temperature is >3°C.
To dry cooler coils
Tchill OUT Tevap IN Water/glycol BPHE Tfc OUT FC Evaporator Modulating 2way valve
FC Bypass Tchill IN Tfc IN Optionnal 2way valve Pump package
Service Service Circulating valve valve 8 pump (Drain) (Drain) Schedule
2015Q1 Q2Q3 Q4 2016Q1 Jan. Feb. Mar. Apr. May Jun. Jul. Aug Sep Oct. Nov Dec Jan. Feb. Mar. . . . .
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Jul-09 Program key steps Mockup build & Test Validation unit Ph1 Validation unit Ph2 build & Test build & Test
Industrialization Ph1 Industrialization Ph22
Literature update Ph1 Literature update Ph2
Phase 1 = All RTAF sizes – Direct free cooling Phase 1 : All RTAF sizes – Glycol FREE version - version - Partial and Total Free cooling Partial and Total Free cooling
Pre-annoucement
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