HIOKI Clamp On Power Logger PW3360-20 for Energy Management of Chiller Plant
What is Energy Management?
Energy Management refers to the process of monitoring, controlling and conserving energy in a building or organization . The driving force for energy management is the conservation of energy as it affects energy costs, emission targets and legislation requirements. Figure 1.0 shows the steps involved in energy management for energy efficiency optimization, in a cyclical process.
Figure 1.0 Energy Management Steps – a Continuous Cycle
The Importance of Energy Management of Chiller Plant
In industrial factories and commercial buildings, air conditioning energy consumption accounts for over 50% of the energy cost . The chiller plant acts as the centralized cooling system to provide air conditioning for buildings and consists of four main components: a compressor, condenser, expansion valve, and evaporator (Figure 2.0).
Figure 2.0 Main Components of a Chiller
Due to the high cost of energy consumption, chiller plant energy efficiency is optimized through energy management to save cost. In addition, high rates of energy consumption of air conditioning negatively impact the environment, as illustrated in Figure 3.0.
Figure 3.0 Air Conditioning Energy Consumption Impact on Environment
Measurement Instrument for Energy Audit in Energy Management
In any Measurement and Verification (M&V) method to assess the Energy Efficiency (EE), accurately quantifying EE savings is a critical yet technically challenging aspect. One of the main concerns in an energy audit is the uncertainty (doubt) of the measurement instrument. This can be caused by several sources such as repeatability, reproducibility, stability, bias, drift, resolution, reference standard and reference standard stability .
Measurement uncertainty can affect risk assessment and decision-making, impacting financial goals, safety, and quality . Therefore, there is a need for regulatory guidelines to manage and mitigate this uncertainty. Figure 4.0 illustrates an example of the effect of uncertainty on the quantified EE savings, whereby the uncertainty is mitigated by decreasing the reported savings for conservative reporting.
Figure 4.0 Effect of Uncertainty on Energy Efficiency Savings
The Building and Construction Authority (BCA) Green Mark (Singapore) for Existing Non- Residential Buildings 2017 stipulates a 5% uncertainty for the instrumentation installed to calculate the resultant chiller plant operating system efficiency (kW/RT) . These include sensors, any signal conditioning, a data acquisition system, and wiring connecting the components.
Green Mark Requirements for M&V Instrumentation of Chiller Water System
HIOKI Power Logger PW3360 for Energy Management of Chiller Plant
Hioki's Power Logger PW3360-20 has the highest accuracy among all the available power loggers in the market, with a combined active power of + 0.6% rdg. + 0.11%f.s. (inclusive of 500A clamp-on sensor 9661). This important feature means the total uncertainty will not exceed the 5% limit inclusive of other instruments (Data Logger + Temperature + Flow sensors).
HIOKI Power Logger PW3360
HIOKI Clamp On Sensor 9661
In Energy Audit measurement, Energy Service Companies (ESCO) will use their portable power loggers, which are well-calibrated. However, there are some facilities with fixed power meters, but these meters' maintenance status can be doubtful. All the power measurements for the energy audit are at the chiller plant control panel (Figure 5.0).
Figure 5.0 Energy Audit Measurements are taken at the Chiller Control Panel
For energy management analysis and data demonstration purposes, this application note will use an example of a two-day duration data from a Water-Cooled Chilled-Water Plant system, which is most commonly used in our tropical climate. This system utilizes water as the cooling agent for the gaseous refrigerant in the condenser. For actual energy audit, a two weeks data measurement is taken at one minute interval and recorded to the 3rd decimal digit  (Figure 6.0).
Figure 6.0 Example of Screen Display on PW3360
Figure 7.0 shows the data measurement analysis process flow of the two days data collected for this application note. However, only Part B data will be shown in this application note as this is most relevant to energy management of a chiller plant.
Figure 7.0 Process Flow of Energy Management Data Analysis
The values obtained in Part A are used in the following formulas below to calculate the parameters in Part B.
Total Power Consumption Cooling Load, (kW)
Sum (PCH + PCH pump + PCD pump + PCT)
Cooling Load, (kW)
CWater * QCHW * ΔT(CHWR-CHWS), where CWater = Specific Heat Capacity of Water (constant value)
Cooling Load, (RT)
Cooling Load (kW) / TR (kW) , where TR = Tons of Refrigeration (constant value)
Heat Rejection Condenser Load, (kW)
CWater * QCDW * ΔT(CDWR-CDWS), where CWater = Specific Heat Capacity of Water (constant value)
Plant Efficiency, (kW/RT)
Total Power Consumption Cooling Load (kW) / Cooling Load (RT)
Heat Balance Error, (%)
Heatin – Heatout / Heatout x 100%
= (PCH + Cooling Load(kW)) – (Heat Rejection Condenser Load(KW)) / Heat Rejection Condenser Load(kW)) x 100%
i) The constant value for the specific heat capacity of water is 4.19 kJ/kg/°C
ii) The constant value of TR is 3.517kW (Defined as the heat transfer rate required to melt 1 ton (2000lbf) of ice at 32F in 1 day (24hr))
Figure 8.0 Daily Cooling Load Profile Over 24 Hours
Figure 8.0 shows the Cooling Load profile over 24 hours of both days. Day 1 cooling trend shows minimal fluctuations throughout the day, perhaps representing the weekend usage data trend. On the contrary, Day 2 data trend shows to be volatile throughout the day and a consistently higher cooling load usage between 7.00 am and 9.30 pm, representing a weekday usage trend. Usually, a two-week data with multiple line trends allow users to check for consistency in power consumption trend for weekdays and weekends. These multiple line trends are also needed to find the average instantaneous peak of the cooling load, which is required to determine the Green Mark efficiency rating category, as shown in Figure 9.0 below.
Figure 9.0 Green Mark Chiller Plant Efficiency Rating
Histogram distribution of the cooling load data (Figure 10.0) enables users to identify the most frequent cooling load occurrence; based on the two days' data, the two highest ranges are in 301RT - 400RT and 701RT - 800RT at 60.28% and 18.26%, respectively. The chiller with a cooling load within these two cooling load ranges will be the optimal choice for any future chiller replacement.
Figure 10.0 Histogram Distribution of Cooling Load
The chilled water plant efficiency profile by day over a 24-hour period (Figure 11.0) indicates a stable average trend around 0.6kW/RT - 0.7kW/RT throughout the day, except some outliers between 7.00 am and 7.30 am. The day's average, maximum, and minimum efficiency values are determined from the trend and used with the cooling load profile data to calculate the potential savings for any chiller replacement action.
Figure 11.0 Chilled Water Plant Efficiency Profile over 24 Hours
Based on the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) chiller plant efficiency benchmark , the most desired efficiency is less than 0.85kW/RT.
ASHRAE Chiller Plant Efficiency Benchmark
In the Green Mark Platinum rating requirement, the chiller efficiency needs to be less than 0.68kW/RT for <500RT cooling load. The efficiency versus load distribution (Figure 12.0) shows the user the 'sweet spot' for the chiller to operate most efficiently. Day 1 data shows that the chiller can achieve an efficiency of < 0.68kW/RT between a cooling load range of approximately 300RT - 425RT with high consistency and occurrence. For day 2 however, it is observed that there are three distinct groups of cooling load in the range of 300RT - 800RT performing with an efficiency range of 0.6kW/RT - 0.7kW/RT. Therefore, there is no specific 'sweet spot'.
Figure 12.0 Efficiency vs Load Distribution by Day
Using the heat balance (HB) profile on both days (Figure 13.0) and the Green Mark M&V Instrumentation criteria (See below) for heat balance computation, the summary of the heat balance analysis is shown in Table 1.0. It shows that there's no issue with Day 1's sensor integrity as >80% of the heat balance data is within the ± 5% range while for Day 2, it fails the targeted 80% level and requires further investigation on the temperature sensor to conclude whether recalibration/ replacement of the sensor is required.
Figure 13.0 Heat Balance (HB) Profile by Day
Green Mark Criteria for Heat Balance (HB) Computation of Chiller Water System
Table 1.0 Summary Data for Computation of Heat Balance (HB) based on Green Mark
For more information on other Code of Practice related to the energy efficiency of HVAC, please refer to the following documents of Singapore’s Standard Code of Practice:
■ SS 591: Code of practice for long term measurement of central chilled water system energy efficiency
■ SS 530: Code of practice for energy efficiency standard for building services and equipment
■ SS 553: Code of practice for air-conditioning and mechanical ventilation in buildings
■ BCA Green Mark for existing non-residential buildings
Aside from all the valuable parameters measurement above that fulfil the measurement instrument requirement of 5% uncertainty, Hioki PW3360-20 also comes with various value-added features as below:
■ Attractive pricing, which is affordable in terms of features- to- pricing in the market (Please check with our Hioki sales representatives)
■ Compact size and lightweight
■ Power measurement range up to 300.00 W to 9.0000 MW
■ Continuous measurement with no gap (critical for power profile measurement)
■ Built-in HTTP function allowing users to configure and monitor the instrument from a browser and FTP server to download the data. Multiple PW3360-20 and LR8450 Memory HiLogger can be connected for real-time logging using GENNECT One free software.
■ Storage to 2GB SD Card (Maximum recording period of 1 year based on 1-minute interval)
Hioki's Power Logger PW3360-20 features give users the confidence to execute energy audit data measurement required in Energy Management of Chiller Plant. It also fulfils the highly regarded and internationally recognized Green Mark rating M&V Instrumentation criteria.
For more product information, please click on the links below:
6. https://www1.bca.gov.sg/docs/default-source/docs-corp-buildsg/sustainability/green-mark-enrb-2017-technical-guide.pdf 7. https://optimumenergyco.com/how-to-optimize-an-hvac-system/