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Load Analysis and Example Calculations

loads - lab
Health labs contain multiple types of loads; here there is lighting, air conditioning, an incubator, a centrifuge and a microscope. (Photo: David Jones)

A fundamental part of energy management, and the first step in improving a health facility energy system, is an electrical load inventory.  An electrical load inventory is a listing of all electricity-consuming equipment in a facility, everything from light bulbs to expensive lab equipment to cell phone chargers. 

These electrical loads drive energy consumption and costs, but also facilitate the critical health services that take place in such facilities; understanding the best way to support, protect and expand those services starts with an analysis of those loads.

A basic electric load assessment involves creating a table showing power ratings, or loads (in Watts), of all electrical devices in the facility along with an estimate of the number of hours each device will operate on a daily basis.  This results in an estimate of facility consumption, the number of Watt-hours used by the facility per day, and the total facility electrical load, the sum of all inventoried loads.  These two basic metrics, load and consumption, form the basis for the design of energy supply and distribution systems, like PV panels, battery banks, inverters, generators, electrical circuits and UPS systems.  They are also used to track increases or reductions in energy usage, a key energy management activity.

When properly executed, a load analysis can yeild valuable insights into facility energy usage that can be used to save on energy costs, increase productivity and protect critical assets.  This article explains the basic methodology behind performing load analyses, inlcuding inventories, data logging, load categorization and energy indices.  Important best practices and lessons learned through experience in the field are conveyed.  Finally, a number of example load calculations are given for different types and sizes of health facilities.

 

IHFI Experience  

The Improving Health Facility Infrastructure (IHFI) project performs load analyses for all project installation sites.  The load analysis is the first step in determining a facility's backup power and power quality needs.  When sizing backup power systems in Haiti, or PV power systems in Guyana, IHFI uses load inventories and data logging to design appropriate and sustainable systems.

ihfi - loadshaiti
Average load distribution at IHFI project sites in Haiti.

While load analysis is a critical aspect of IHFI's interventions at individual facilities, it is also an important part of country-wide knowledge managment efforts.  By aggregating the data collected across all sites in Haiti, IHFI has produced benchmarks for Haiti's Ministry of Public Health and Population showing the average end use load distribution in health facilities.  IHFI has also performed a survey of backup generators to determine if these equipment have been appropriately sized to meet load demands.

The chart to the right presents the average end use load dristribution among 32 IHFI project sites throughout Haiti.  As a basic benchmarking tool, this chart allows for a quick comparison of average end uses to those of an individual facility.  These data, subject to deeper analysis, can also be used to benchmark average end use loads by facility area or number of beds.  This type of analysis is useful to managers at the facility or national level, to identify areas of improvement, both in terms of healthcare performance and energy efficiency.

The chart below compares backup generator capacity to maximum load at 12 IHFI sites in Haiti.  The figure demonstrates that many facilities have oversized generators, or more generators than necessary to meet their backup needs.  This kind of analysis is useful when allocating resources, and sizing backup systems - an oversized generator will not run as efficiently.

 

generators in haiti
Generator capacity as compared to maximum load at twelve sites in Haiti.

 

 

Load Characterization 

Backup Power and Power Quality Needs

When analyzing health facility energy systems and electrical loads, the difference between contact and no-contact loads is an essential concept.  Health facility loads can be characterized in one of three ways: non-critical loads, contact critical loads and no-contact critical loads.  

  • Non-critical loads are those loads which, if not supplied with power, will not put patients at immediate risk or substantially disrupt facility operations.  Air conditioners, in most cases, are an example of a non-critical load.  
  • Critical loads are normally defined as equipment that is crucial to the operation of the facility.  Some common examples include: lighting, laboratory equipment, emergency and operating rooms, and information systems and computers.  Critical loads are further categorized by their need for high-quality, uninterrupted power.  
    • Contact critical loads are those which can endure minor fluctuations in voltage and brief loss of power.  This type of critical load can include lighting or vaccination refrigeration.  
    • No-contact critical loads are loads for which any interruption in power will result in damage to the equipment or loss of data.  Sensitive laboratory instruments, medical equipment such as x-rays, and data acquisition systems are all no-contact critical loads.

Properly identifying what portion of a facility's total load is a contact or no-contact load is essential to estimating a backup power system.  Sizing backup power for non-critical loads inevitably leads to a larger, more costly system than necessary.  Similarly, uninteruptible power supplies must be sized to cover all no-contact loads, providing a UPS for contact loads will lead to a higher system cost, with little added benefit.

End Uses

loads - ac
Air conditioning often makes up a significant portion of facility load. (Photo: David Jones)

A load end use describes the general purpose or equipment type with which it is associated.  The goal of classifying loads by end use is to organize the load inventory and better understand what activies at the facility are most energy intensive.  Defining appropriate end use categories depends on the size of the facility, the diversity of loads found at a facility, the different healthcare activities that take place at the facility and the objectives of the load analysis.  End use categories can be very broad or very specific depending on the needs and interests of the energy management plan.

Examples of some typical end use categories include lighting, air conditioning and office equipment.  In these examples all lighting equipment (e.g. fluorescent tubes, CFL bulbs, exam lamps, security lighting) would be classified as lighting, all air conditioners, regardless of size or type, are classified under air conditioning, and any computers, printers, fax machines, or even UPSs for those loads, could be classified under the office end use.

These very basic categories can be broken down further.  Lighting can be classified as indoor or outdoor lighting, or by technology - fluorescent, compact fluorescent, incandescent, LED, high pressure sodium, etc.  Similarly, it is common to define air conditioners by type (e.g. window, mini-split, ducted units) and capacity (e.g. BTU/hr, tons, kW).  Office equipment can be subcategorized by specific equipment type, like computer, printer, etc.  Subcategorizing broad end use classifications makes a load inventory more versitile; it can be used to present a high level overview of energy consumption, or to estimate the energy savings from targeted measures like fluorescent lighting retrofits.

An end use category may also refer to a specific facility area or function.  For example, laboratory loads are often grouped together, although each peice of eqiupment may serve a very different purpose.  It may be useful to differentiate loads between areas used for administration, reception, storage or treatement.

 

Loads, Consumption and Energy Indices 

The primary products of a load inventory are quantified estimates of facility electricity load and consumption.  These two figures play a large role in choosing and sizing appropriate energy supply systems such as batteries and PV panels.  They can also be used to compare facility energy usage  to benchmarks, such as sector norms, or similar facilities elsewhere.  Creating energy indices allows for energy consumption to be tracked and compared by other performance indicators, such as the number patients served.

Loads

Electricity loads are measured in Watts, which is a unit of power, or the rate of energy use.  The load of a particular piece of equipment, then, is the amount of electricity it requires to operate at any given moment.  That electricity must be provided by the facility's energy supply system, which may be the grid, a generator, or an array of PV panels.  Understanding equipment loads is therefore very important to correctly sizing the facility energy system.

Load information can be gathered from multiple sources.  Some equipment types have standard Wattage values that can be assumed in most cases; for example, T12 fluorescent lamps consume about 44W, including their ballast.  Information of typical load values for a wide range of equipment can be found online.  All electrical equipment (air conditioners, refrigerators, computers, lighting, etc.) should, however, have some label indicating at least its voltage and current, and often other important information like Wattage or cooling capacity.  Finally, load can be measured using a voltmeter and ammeter.

loads - label
Equipment labels are a valuable source of load information.  In the case of this air conditioner label, the maximum and rated loads are given, but the voltage and current ratings can also be used to determine load. (Photo: David Jones)

Summing up the load values (in Watts) of all the equipment at a facility will yeild the total facility connected load, which is the maximum amount of power the facility would need to operate all equipment at once.  This figure can be broken down by load characteristics (end use or contact/no-contact), yeilding, for example, the total lighting load, or total no-contact load.

It is unlikely, however, that all electrical equipment at a facility will be turned on at the same time - different equipment operates at different times of the day.  For this reason, a load profile is created.  A load profile sums equipment loads not for the entire facility, nor by end use, but based on the time of day that the equipment operates.  An hourly load profile, for example, presents the total of all the loads operating during each hour of the day (it excludes any loads that are not operating).  The load profile approximates actual demand for electricity throughout the day.

During a facility's normal operating hours, the load profile should show higher total loads, because computers, lab equipment and other devices are being used.  In the evening, or during off-hours, loads are reduced because the facility is supporting less activity.  The load profile is an essential tool in analysing energy usage in that it indicates the actual demand placed on the energy supply and reveals the minimum and peak loads.

Consumption

Electricity consumption is measured in Watt-hours, a unit of energy, or the total energy used in a given amount of time (e.g. daily, annually).  Consumption is determined by multiplying each load by the number of hours it operates - the same information used to create the load profile. 

Energy consumption correlates directly to energy costs.  Most electricity bills are charged in $/kWh, a set cost per unit of consumption.  Likewise, diesel generator fuel use corresponds to the amount of electricity consumed.

Energy Indices

An energy index is a measure of energy intensity that facilitates tracking and comparison of facility energy usage to similar facilities of different size, or the same facility over time.  Energy indices are usually calculated by dividing the facility energy consumption by some other indicator of facility performance or size.  A common energy index is consumption per floor area, or kWh/m2; using this index, a facility can be benchmarked to other buildings, regardless of differences in size.

Other examples of useful energy indices for health care facilities include: kWh/number of beds, kWh/number of patients treated, kWh/local population, kWh/number of staff, or kWh/lab test completed.

An energy index is also very useful when tracking facility consumption over time, and allows for changes in activity level at the facility (e.g. patient visits, new treatment iniciatives) to be factored into the comparison. 

 

Data Logging 

Logging actual facility loads is an important part of load analysis as it provides real load data to compliment the estimates made through load inventories.  These data provide more accurate information on peak and minimum load values, operational hours and consumption.  Loads can be measured at the facility level, or for individual circuits.  Data should be logged for a number of days, and preferable for several weeks.  Longer data logging sessions add confidence to the results of the load analysis.  By tracking loads over multiple days or weeks, it is possible to distinguish between periods of facility operation and downtime, such as days, nights and weekends.

Futhermore, comparing meausred data to estimates based on load inventories provides insight into what equipment is being used and for how long.  If sufficient measured data is available, it is preferable to used actual data for analysis purposes, rather than estimated figures.

 

logged data
Generator and grid power logged at a site in Haiti, note the daily peaks in demand and the nightly baseline load.

 

Example Health Clinic Loads 

Small Rural Health Clinic

  • Low energy requirements, up to 10 kWh/day
  • 0 - 60 beds

A small health clinic may have the following characteristics:

  • Typically located in a remote setting with limited services and a small staff
  • Lights are used during evening hours and to support limited surgical procedures (e.g. suturing)
  • One or two refrigerators are used to maintain the cold chain for vaccines, blood, and other medical supplies
  • Basic lab equipment such as a centrifuge, hematology mixer, microscope, incubator, and hand-powered aspirator may be used

An example load inventory for a small rural health clinic is provided below.  Even these small loads can be difficult to support in remote settings where access to energy is limited.  Grid power is often not an option in such cases and diesel power can be very expensive and is subject to fuel shortages; while PV systems are often a sustainable option, their upfront cost is relatively high.

 

smclin - load
Load distribution by end-use.
EquipmentPower 
(watts)
Hours Used 
per Day
Energy Used 
(watt-hours)
Total Watt-Hours Used per Day 516-928
Vaccine Refrigerator 60 5-10 300-600
Lights (compact fluorescent) 11 6-8 66-88
Microscope 30 1-2 30-60
Exam Light 20 1-3 20-60
Radio 10 10-12 100-120

 

The table and chart above reveal that vaccine refrigeration is the most significant load and consumer at the facility.  This analysis suggests that a stand-alone, solar powered refrigerator may be a good option.  Such refrigerators are commercially available specifically for situations such as this.  Relieving the energy system of this refrigeration load would lower energy consumption and cost by about half.

Medium Rural Health Clinic

  • Moderate energy requirements, 10-20 kWh/day
  • 60 -120 beds

A medium health clinic may have the following characteristics:

  • Medical equipment similar to that of a small health clinic; frequency of use and number of devices are key factors of differentiation between small and medium health clinics
  • Separate refrigerators may be used for food storage and cold chain
  • Communication device, such as a radio, may be utilized
  • May accommodate more sophisticated diagnostic medical equipment and perform more complex surgical procedures

The following table is an example load inventory for a medium sized health clinic.  This inventory details equipment locations and quantities, day and night operational hours, and contact/no-contact loads as well as total load and consumption.  Such detail allows for an in-depth analysis into where and when energy is being consumed.

 

AreaQtyLoadWatts EachHrs/DayWatt-hoursTotal Conn WattsContact/No-contact
Day Night Day Night Total  
Grand Totals7,4928,47615,9685,888 
Lighting and Fans
Entry and Corridors 10 Fluorescent Light 22   12   2,640 2,640 220 Contact
PMTCT Lab Partial 2 Fluorescent Light 22 2 4 88 176 264 44 Contact
2 Fluorescent Light 22   2   88 88 44 Contact
Blood Lab 1 Fluorescent Light 22 2 4 44 88 132 22 Contact
Male Ward 3 Fan 22   4   264 264 66 Non-critical
1 Fluorescent Light 80 4 4 320 320 640 80 Contact
Exam Room 1 Fluorescent Light 22 1 4 22 88 110 22 Contact
Post Natal 2 Fluorescent Light 22   4   176 176 44 Contact
1 Fan 80 4 4 320 320 640 80 Non-critical
Maternity Dorm 5 Fluorescent Light 22   4   440 440 110 Contact
2 Fan 80 4 4 640 640 1,280 160 Non-critical
Delivery Room 4 Fluorescent Light 22   4   352 352 88 Contact
Kitchen 2 Fluorescent Light 22   2   88 88 44 Contact
Offices (5) 5 Fluorescent Light 22 4 4 440 440 880 110 Contact
Other Lights 4 Fluorescent Light 22   4   352 352 88 Contact
Security Lighting 4 Fluorescent Light 22   8   704 704 88 Contact
Total Lighting 1,874 7,176 9,050 1,310  
Lab Equipment
Blood Lab 3 Microscopes 30 2 2 180 180 360 90 No-contact
1 Radio 30 4 4 120 120 240 30 Contact
PMTCT Lab 1 Rotator 60 1   60   60 60 Contact
1 Refrigerator-Maytag 500 1 1 500 500 1,000 500 Contact
1 Centrifuge 600 1   600   600 600 Contact
1 Water Bath 400 1   400   400 400 Contact
1 Spectrophotometer 63 1   63   63 63 No-contact
1 Autoclave 630 1   630   630 630 Contact
Dental Suite 1 Chair 710 0.5   355   355 710 Contact
1 Compressor 370 2   740   740 370 Contact
1 Jet Sonic Cleaner 45 2   90   90 45 Contact
1 Amalgam Filling Mach. 80 1   80   80 80 Contact
1 X-Ray 200 0.5   100   100 200 No-contact
Total Lab Equipment 3,918 800 4,718 3,778  
Other Equipment
RHO Office 1 Refrigerator 500 1 1 500 500 1,000 500 Contact
Admin Office 2 Computers 150 4   1,200   1,200 300 No-contact
Separate Solar System 1 Dulas Solar Vaccine Refrigerator                
1 CB Radio                
Total Other Equipment 1,700 500 2,200 800  

 

The charts below summarize the load inventory data by end use, and reveal some interesting insights.  While the majority of the connected load is laboratory equipment, most of the estimated consumption is due to lighting.  An examination of the load inventory shows that operating hours for each piece of lab equipment are relatively low while lighting operates for long periods.  The day to night load profile highlights that most of that lighting is on only at night.

These insights should be considered when planing a facility energy system.  If this facility ran on diesel generation, for example, that generator would need to be sized to meet the maximum daytime load.  Much of the actual energy consumption, however, takes place at night, when the generator would be at half-load, resulting in inefficient operation.  In this case a battery bank may suppliment the generator, charging during the day and powering lighting at night.

Plugging this load inventory data into the HOMER energy tool allows the program to account for these day-to-night variations in energy load and consumption to size the most cost-effective PV/generator/battery hybrid energy system.

 

mdclin - legend
mdclin - load mdclin - consump mdclin - profilegraph
 Total load by end use.  Total consumption by end use. Day to night load profile by end use.

 

 

Large Health Clinic

  • High energy requirements, 20-30 kWh/day
  • over 120 beds

A large health clinic may have the following profile:

  • May serve as a regional referral center and coordinate communication between several smaller facilities and hospitals in large cities
  • May need to communicate with remote health centers and hospitals by way of telephone, fax, computer, and Internet
  • May contain sophisticated diagnostic devices (x-ray machine, CD4 counters, blood typing equipment, etc.) requiring additional power

 

Example Health Laboratory Loads 

These examples provide load calculations for some different sized facilities visited in Haiti and Zambia.  A basic laboratory and standard laboratory at presented in the following tables.  The equipment found in each are identical but the standard lab has larger quantities and longer operational hours for some; these differences are highlighted in the standard lab inventory.

 

Basic Laboratory Load Inventory
AreaQtyLoadWatts EachHrs/DayWatt-hoursTotal Conn WattsContact/No-contact
Day Night Day Night Total  
Grand Totals 18,140 840 18,980 2,855  
Lighting
Laboratory 4 Fluorescent Lamps 40 8 - 1,280 - 1,280 160 Contact
Total Lighting 1,280 - 1,280 160  
Equipment
Laboratory 1 CD4 Machine 200 4 - 800 - 800 200 No-contact
1 Hematology Analyzer 230 4 - 920 - 920 230 No-contact
1 Blood Chem. Analyzer 45 4 - 180 - 180 45 No-contact
2 Microscope 30 6 - 360 - 360 60 No-contact
2 Centrifuge 400 2 - 1,600 - 1,600 800 Contact
1 Fan 150 8 - 1,200 - 1,200 150 Non-critical
Total Equipment 5,060 - 5,060 1,485  
Refrigeration
Laboratory 1 Efficient Refrigerator 60 10 14 600 840 1,440 60 Contact
1 Air Conditioning Unit 1,000 10 - 10,000 - 10,000 1,000 Non-critical
Total Refrigeration 10,600 840 11,440 1,060  
Other
Office 1 Desk Top Computer 150 8 - 1,200 - 1,200 150 No-contact
Total Other 1,200 - 1,200 150  

 

 

Standard Laboratory Load Inventory
AreaQtyLoadWatts EachHrs/DayWatt-hoursTotal Conn WattsContact/No-contact
Day Night Day Night Total  
Grand Totals 23,090 1,680 24,770 3,405  
Lighting
Laboratory 6 Fluorescent Lamps 40 8 - 1,920 - 1,920 240 Contact
Total Lighting 1,920 - 1,920 240  
Equipment
Laboratory 2 CD4 Machine 200 6 - 2,400 - 2,400 400 No-contact
1 Hematology Analyzer 230 6 - 1,380 - 1,380 230 No-contact
1 Blood Chem. Analyzer 45 6 - 270 - 270 45 No-contact
4 Microscope 30 6 - 720 - 720 120 No-contact
2 Centrifuge 400 2 - 1,600 - 1,600 800 Contact
1 Fan 150 8 - 1,200 - 1,200 150 Non-critical
Total Equipment 7,570 - 7,570 1,745  
Refrigeration
Laboratory 2 Efficient Refrigerator 60 10 14 1,200 1,680 2,880 120 Contact
1 Air Conditioner 1,000 10 - 10,000 - 10,000 1,000 Non-critical
Total Refrigeration 11,200 1,680 12,880 1,120  
Other
Office 2 Desk Top Computer 150 8 - 2,400 - 2,400 300 No-contact
Total Other 2,400 - 2,400 300  

 

loads - labloads
 labbatt3

Top: The daytime and nighttime consumption of the basic and standard labs with and without air conditioning and the capacity of a set of batteries.

Bottom: The number of batteries necessary to acheive 10 hours of backup power at each lab.

The example laboratory loads in the tables above demonstrate the importance of distinguishing non-critical, contact and no-contact loads.  The non-critical air conditioning load increases total daily consumption considerably, at the basic laboratory it accounts for over half.  Compare this increased consumption to the difference between the standard and basic laboratories without air conditioning.  The increased consumption from basic to standard lab is due to additional laboratory equipment and longer operational hours, directly contributing to facility performance.

The chart to the right shows the daily consumption of the basic and standard sized labs with and without air conditioning, as well as the kWh capacity of a standard 8-battery battery bank.  In this scenario, a bank of eight, 6 Volt, 207 Amp-hour batteries are considered, discharged to 50% depth-of-discharge at 90% efficiency.

The daily facility consumption directly effects the size of the battery bank required to backup these laboratories.  The number of batteries needed to provide power over the 10-hour day considered in the this example are shown in the next chart.  Battery bank size reflects daytime consumption, thus connecting the air conditioning units to backup power greatly increases the size and cost of the system.

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