How to perform chiller system testing for efficiency on site

How to perform chiller system testing for efficiency on site

Chillers are the major utilities in most of the buildings and consume a significant amount of energy due to the technology of vapour compression. It becomes at most important to assess the performance of the chiller system as it runs continuously throughout the year and any deviation in performance will leave us to pay higher energy bills at reduced comfort.

In this article, a simple step by step method on how to perform chiller system testing for efficiency on site will be discussed.

Before proceeding for energy performance testing of the chiller system, it is important to know the parameter which reflects the performance of a chiller. kW/TR can be considered as one of the best performance monitoring parameter to assess the energy performance of a chiller. This parameter gives us the specific power consumed by the chiller for delivering one TR of cooling. This value can be easily compared with the design value or the standard values given out by ASHRAE.

Equipment Required:      
Steps to do energy performance assessment
  • Identify the portion on a chilled water pipeline which is straight and away from bends and joints
  • Remove insulation of the pipe at the selected portion 
  • Measure the pipe circumference, the thickness of the insulation and find out the effective diameter of the pipe
                   Circumference = Diameter x Phi
                   Diameter = Circumference / Phi
                   Effective diameter of pipe = Diameter – (2 x Insulation thickness)
  • Insert the values of diameter, pipe thickness, chilled water temperature readings in ultrasonic water flow meter and get the effective distance required to place the sensors on the chilled water pipe.
  • Place the sensors on the pipe as per the displayed distance in the flow meter. Note down the flowrate in cubic meter per hour from the meter
  • Then with the help of temperature gun measure the surface temperatures of chilled water pipeline after removing insulation at both inlet and outlet sides.
  • Let water flow be denoted as M, inlet chilled water temperature as T1 and outlet chilled water temperature as T2
  •         Now calculate the tonnage value of cooling from above reading with the help of below formula
                                                                                                                                                                                           
  • TR Delivered = (M x Cx (T1 – T2) x 1000)/ 3024
    Where CP = Specific heat capacity of water = 1 Kcal/kg 0C
  • Now with the help of simple power analyzer measure the 3 Phase power of chiller compressor
  • Now divide the  measured power consumption in kW with obtained  TR value and calculate the specific power consumption of a chiller in kW / TR
  • Compare this value with designed value and estimate the deviation.
Generally for a water-cooled screw type chiller specific energy consumption value should be in the range of 0.7 – 0.9. For those chillers with SEC values higher than 1.2 kW/TR, replacement with energy-efficient chiller will be the best option as nowadays even 0.6 kW / TR machines are available.

The manufacturer will generally provide design performance value in terms of COP which is nothing but Coefficient of performance. This is the same as kW / TR where in this compares electrical input kW with thermal output TR but COP converts electrical input to thermal and compares with thermal output. COP can be converted to kW/TR or vice versa with the help of below formula

                                                        kW/ TR =  12 / ( COP x 3.412)

Seasonal Variation & Part Load performances:

Many chillers will be operating under partial loading conditions depending on different seasons and load requirements. Hence it becomes equally important to assess the performance of a chiller under part loads. Sometimes it is evident that part-load efficiencies of chillers will be better than full-load efficiencies and hence based on this assessment selection of chillers for part load and full load operations can be done perfectly.

IPLV (Integrated Part Load Value) is the term used to assess the performance of a chiller at part load condition. IPLV is derived considering weighted average of 4 loading points (25%, 50%, 75% & 100%) – most appropriate reference

IPLV=0.01A+0.42B+0.45C+0.12D; where A, B, C & D are the COP values at 4 loading points respectively

So monitoring IPLV rather than simple kW/TR will be more helpful.

Once you understand your chiller efficiency then it's time for correcting the same if any deviations were found and look for opportunities to improve chiller efficiency both by simple fine-tuning and by minimum retrofitting. Few energy-saving opportunities for chiller systems were listed as below.
  • Increase the chilled water temperature setpoint if possible.
  • Use the lowest temperature condenser water available that the chiller can handle (Reducing condensing temperature by 5.5°C, results in a 20 - 25% decrease in compressor power consumption)
  • Increase the evaporator temperature (5.5°C increase in evaporator temperature reduces compressor power consumption by 20 - 25%) - Chilled Water Reset Strategy
  • Use adiabatic cooling pads for air-cooled condensers.
  • Use an indirect evaporative cooling module to reduce the load on the cooling coil and see chiller power consumption.
  • Avoid low delta T syndrome by properly planning the distribution system.
  • Use pressure independent control vales near AHU units which are more energy efficient.
  • Clean heat exchangers when fouling indication is flagged. Generally, if the condenser approach is more than 4 Degree C it's evident that the fouling is present in condenser tubes (1 mm scale build-up on condenser tubes can increase energy consumption by 40%). Use ATCS instead that can maintain the condenser approach in the range of 2-4 Deg C
  • Optimize the condenser water flow rate and refrigerated water flow rate. There is an excellent opportunity in getting energy savings by reduced flow rate technique. 
  • Replace old chillers with High COP Maglev chillers.
  • Use water-cooled rather than air-cooled chiller condensers.
  • Replace belt-driven AHU fans with EC fans which have around 15 - 20% savings on electrical energy consumed
  • Use energy-efficient motors for continuous or near-continuous operation.
  • Specify appropriate fouling factors for condensers.
  • Do not overcharge oil.
  • Install active refrigerant agents to avoid oil fouling and get energy savings up to 7%
  • Install a control system to coordinate multiple chillers.
  • Study part-load characteristics and cycling costs to determine the most efficient mode for operating multiple chillers.
  • Run the chillers with the lowest operating cost or lowest SEC ( Find how to calculate SEC for your water-cooled chiller) to serve baseload.
  • Avoid oversizing -- match the connected load.
  • Isolate off-line chillers and cooling towers.
  • Establish a chiller efficiency-maintenance program. Start with an energy audit and follow-up, then make a chiller efficiency-maintenance program a part of your continuous energy management program.
  • Use simple Air Washers in case of industrial applications where humidity control is of not that important
  • Look for installation of alternate cooling solutions like Radiant cooling.

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