CHILLER SYSTEM

CONTENTS CHILLER BASICS WORKING PRINCIPLE OF CHILLER REFRIGERATION CYCLE CHILLER COMPONENTS COMPONENTS FUNCTIONS & COMPARISON LOAD TERMINAL CONTROL OPTIONS CHILLER SYSTEM CONFIGURATION TECHNICAL TERMINOLOGY CHILLLER PERFORMANCE MEASUREMENT

CHILLER BASICS What is a Chiller? The refrigeration machine that produces chilled water is referred to as a “Chiller”. A chiller is a water-cooled air conditioning system that cools inside air, creating a more comfortable and productive environment. Basically, there are two types of chillers based upon the refrigeration cycle: Vapour Compression Chiller Absorption Refrigeration Chiller Based upon the condensation process of working fluid , there are two types of chiller: Air-Cooled Chiller Water Cooled Chiller

WORKING OF CHILLER SYSTEM Chillers circulate chilled water to air-handlers(AHU’s) in order to transfer heat from air to water. This water then returns to the evaporator side of the chiller where the heat is passed from the water to a liquid (LP) refrigerant . The refrigerant leaves the evaporator as a cold vapor (LP) and enters the compressor where it is compressed into a hot vapor (HP). Upon leaving the compressor, the vapor enters the condenser side of the chiller where heat is transferred from the refrigerant to the air/water side of the condenser where it is circulated to an ACC/open cooling tower for the final removal of heat from the refrigerant as a liquid (HP). (Water Cycle) (Air/Water Cycle) AHU Evaporator Compressor Condenser C.Tower (Refrigerant Cycle)

AIR-COOLED CHILLER

WATER-COOLED CHILLER

HEAT TRANSFER LOOP

HEAT TRANSFER LOOP Heat Transfer Loops In Refrigeration System Thermal energy moves from left to right as it is extracted from the space and expelled into the outdoors through five loops of heat transfer: – Air loop. Air is driven by the supply air fan through a cooling coil, where it transfers its heat to chilled water. The cool air then cools the building space. – Chilled water loop. Driven by the chilled water pump, water returns from the cooling coil to the chiller’s evaporator to be re-cooled. – Refrigerant loop. Using a phase-change refrigerant, the chiller’s compressor pumps heat from the chilled water to the condenser water. – Condenser water loop. Water absorbs heat from the chiller’s condenser, and the condenser water pump sends it to the cooling tower. – Cooling tower loop. The cooling tower’s fan drives air across an open flow of the hot condenser water, transferring the heat to the outdoors.

VAPOUR COMPRESSION CYCLE

VAPOUR COMPRESSION CYCLE

Vapour Compression Cycle

ABSORPTION REFRIGERATION CYCLE

Vapour Compression Chiller Absorption Water Chiller Use a Compressor to move refrigerant around the system. Energy source for the compressor is an electric motor. Use heat to drive the refrigeration cycle. Energy sorce are steam, hot water or burning of oil or natural gas Vary by type of compressor such as reciprocating, scroll, screw, centrifugal. Use of absorption refrigeration cycle. Lower initial cost Higher initial cost due to additional cost of heat transfer tubes & absorbent. In emergency situation, continous electricity required for electricity-driven chillers. Minimal electricaity needed for generator during emergemcy situations Not applicble Waste heat recovery - Wasted energy can be used to fuel an absorption chiller Application in Cogeneration system

CHILLER SYSTEM COMPONENTS

CHILLED WATER SYTEM COMPONENETS Chiller (Evaporator) Compressors Chilled Water Pumps ACC in Air Cooled Chiller Cooling Tower in Water-cooled Chiller Condensate water pumps in water-cooled chiller Load Terminals (chilled water cooling coils) Chilled and condenser-water distribution systems include piping, expansion valve, control valve, check valves, strainers etc.

COMPRESSORS Reciprocating Compressor Used in small chiller Available in capacity up to 100 tons (350kw) Multiple Compressor used in a single chiller for capacities up to 200 tons(700kW) Scroll Compressor Used in small water chiller less than 200 tons (700kw) 10 to 15% more efficienct than reciprocating because of 60% fewer moving parts Available in hermetic configurations in capacity up to 15 tons (53kW) for use in water chiller Multiple are used in single chiller to meet larger capacities Helical Rotary (Or Screw) Used in medium sized water chiller 50 to 500 tons (175 to 1750kw) More reliable & better efficiency due to fewer moving parts Centrifugal Compressor Used in large water chiller Available in prefabricated chiller from 100 to 3000 tons (350 to 10500kW) & up to 8500 tons (30000kW) as built-up machines High efficiency, superior reliability, reduced sound levels, relatively low cost as compared to others

CONDENSER

Water Cooled Condensor Air Cooled Condensor Water Cooled Condensor Available from 7.5 to 500tons (25 to 1580kW) Available from 10 to 3000tons (35 to 10500kW) Packaged System - Reduced design time , simplified installation, higher reliability & single source responsibility. Additional requirement of condenser-water piping, pump, CT & associated controls. Better low-ambient operation (i.e. below frezing weather conditions) Cooling tower require special control sequences, basin heaters or even an indoor sump for safe operatin in freezing weather Elimination of cooling tower Cooling tower in the system Lower Maintenace - Eliminates concers & maintenance requirements related to cooling tower Mainteance requirements associated with water treatment, chiller condensor-tube cleaning, tower mechanical maintenance , freeze protection & availability of make up water with its quality Reduce Operating Costs of cooling tower Additional Costs of cooling tower & condensor pump

Water Cooled Condensor Air Cooled Condensor Water Cooled Condensor Refrigerant Condensing temperature is higher due to dependent on DBT Refrigerant Condensing temperature is lower due to dependent on condensor-water temperature, which is dependent on WBT. Higher condensing temperature & therefore higher condensing pressure means compressor to do more work & consume more enrgy. Greater Energy Efiiciency due to lower condensing temperature & pressure More preferable at Part load conditions because DBT tends to drop faster than WBT in a day (from day to night). Less preferable to work at part load conditions Efficency advatage lessen at part load condition Efficiency advantage much less due to additional cost of CT & pump. Life approx. 15 to 20 yrs. (Outdoor installation) Longer equipment life 20 to 30 yrs. (Indoor Installation & water as condensing fluid operate at lower pressures)

AIR COOLED v/s WATER COOLED CONDENSER

AIR COOLED V/S WATER COOLED CONDENSER

AIR COOLED V/S WATER COOLED CONDENSER

LOAD TERMINAL CONTROL OPTIONS

LOAD TERMINAL CONTROL OPTIONS

LOAD TERMINAL CONTROL OPTIONS

LOAD TERMINAL CONTROL OPTIONS

LOAD TERMINAL CONTROL OPTIONS

SINGLE CHILLER SYSTEM

PARALLEL CHILLER SYSTEM

TERMINOLOGY Tons of refrigeration (TR): One ton of refrigeration is the amount of cooling obtained by one ton of ice melting in one day i.e . 3024 kcal/h or 3.516 thermal kW. 2. Net Refrigerating Capacity: A quantity defined as the mass flow rate of the evaporator water multiplied by the difference in enthalpy of water entering and leaving the cooler, expressed in kcal/h, tons of Refrigeration. 3. kW/ton rating: Commonly referred to as efficiency, but actually power input to compressor motor divided by tons of cooling produced, or kilowatts per ton (kW/ton). Lower kW/ton indicates higher efficiency.

TERMINOLOGY 4. Coefficient of Performance (COP): Chiller efficiency measured in cooling output (kcal/hr) divided by electric power input. 5. Energy Efficiency Ratio (EER): Performance of smaller chillers and rooftop units is frequently measured in EER rather than kW/ton. EER is calculated by dividing a chiller's cooling capacity (in kcal/h) by its power input (in watts) at full-load conditions. The higher the EER, the more efficient the unit.

PERFORMANCE ASSESSMENT OF CHILLER SYSTEM ● The refrigeration TR is assessed as TR = Q x Cp x (Ti – To) / 3024 Where Q is mass flow rate of coolant in kg/hr Cp is coolant specific heat in kCal /kg deg C Ti is inlet, temperature of coolant to evaporator (chiller) in °C To is outlet temperature of coolant from evaporator (chiller) in °C. The above TR is also called as chiller tonnage. ● The specific power consumption kW/TR is a useful indicator of the performance of refrigeration system. By measuring refrigeration duty performed in TR and the kiloWatt inputs, kW/TR is used as a reference energy performance indicator.

PERFORMANCE ASSESSMENT OF CHILLER SYSTEM ● In a centralized chilled water system, apart from the compressor unit, power is also consumed by the chilled water (secondary) coolant pump as well condenser water (for heat rejection to cooling tower) pump and cooling tower fan in the cooling tower. Effectively, the overall energy consumption would be towards: – Compressor kW – Chilled water pump kW – Condenser water pump kW – Cooling tower fan kW, for induced / forced draft towers

PERFORMANCE ASSESSMENT OF CHILLER SYSTEM ● An indicative TR load profile for air conditioning is presented as follows: Small office cabins = 0.1 TR /m2 Medium size office i.e., = 0.06 TR/ m2 10 – 30 people occupancy with central A/C Large multi-storeyed office = 0.04 TR/ m2 complexes with central A/C

PERFORMANCE ASSESSMENT OF CHILLER SYSTEM S.No. Parameters UOM TG Chillers - 3nos.(2W+1SB) Design Chiller No.1 Chiller No.3 Actual 1 Chilled water Outlet Set Temp. deg.C 5 to 25 10 10.1 2 Power Consumption of Compressor kW 210 94.86 93.3 3 Power Consumption of Fan 11 8.28 8.41 4 Power Consumption of Chiller Pump 22 18.2 18.69 5 Total Power Consumption 194 121.34 120.40 6 Total Pump Flow m3/hr 105 81.5 7 Inlet Chilled water temp. (entering into Evaporator) 12 12.1 11.9 8 Outlet Chilled water temp. (leaving Evaporator) 9.2 8.9 9 Chilled water temp difference across chiller 5.0 2.9 Refrigeration Effect of Chiller Plant kcal/hr 529200 236350 244500 TR 175 78.16 80.85 Specific Power Consumption kW/TR 1.11 1.55 1.49

PERFORMANCE ASSESSMENT OF CHILLER SYSTEM S.No. Parameters UOM ESP Chillers - 2nos.(1W+1SB) Chiller No.1 Design Actual 1 Chilled water Outlet Set Temp. deg.C 5 to 25 10 2 Power Consumption of Compressor kW 310 92.00 3 Power Consumption of Fan 35.2 12.47 4 Power Consumption of Chiller Pump 15 12.49 5 Total Power Consumption 288 116.96 6 Total Pump Flow m3/hr 125 85 7 Inlet Chilled water temp. (entering into Evaporator) 12 12.8 8 Outlet Chilled water temp. (leaving Evaporator) 9.9 9 Chilled water temp difference across chillar 5.6 2.9 Refrigeration Effect of Chiller Plant kcal/hr 695520 246500 11 TR 230 81.51 Specific Power Consumption kW/TR 1.25 1.43

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