Rightsizing Electrical Power Systems In Large Commercial Facilities

Transcription

1 Page 1 of 7 Rightsizing Electrical Power Systems In Large Commercial Facilities Michael A. Anthony, Member IEEE, Thomas L. Harman, Life Member IEEE James R. Harvey, Senior Member IEEE Abstract: For decades, application of National Electrical Code (NEC) rules for sizing services, feeders and branch circuits has resulted in unused capacity in almost all occupancy classes. US Department of Energy data compiled in 1999 indicates average load on building transformers between 10 and 25 percent. More recent data gathered by the educational facilities industry has verified this claim. Recognizing that aggressive energy codes are driving energy consumption lower, and that larger than necessary transformers create larger than necessary flash hazard, the 2014 NEC will provide an exception in Section that will permit designers to reduce transformer kva ratings and all related components of the power delivery system. This is a conservative, incremental step in the direction of reduced load density that is limited to lighting systems. More study of feeder and branch circuit loading is necessary to inform discussion about circuit design methods in future revisions of the NEC. Index Terms: branch circuits, building premises wiring, electric services, energy conservation, feeders, flash hazard, lighting power density, load diversity, National Electrical Code, sustainability, transformer loading, I. INTRODUCTION There has been a belief, for many years that the electrical power systems in many large commercial systems have been designed, specified, and installed with more electrical power systems capacity than necessary. If this proved to be the case, the negative implications would include higher installation costs, higher maintenance costs, increased energy consumption from losses, possibly higher arc-flash levels, and an excessive use of critical resources. Because of these many negative implications, a data gathering effort was undertaken by the educational facilities industry during 2010 and This data gathering effort was organized under the auspices of APPA.ORG: Leadership in Educational Facilities and it revealed that building electrical systems in these studied facilities have very often been designed to provide and distribute 15 watts per square foot, for at least the past 50 years; when, in fact, the operational electrical load in these facilities has proven to be rarely above 5 watts per square foot. This is statistically significant for owners of all large commercial facilities like colleges and universities because contrary to expectation with respect to classrooms, laboratories, and athletic facilities -- most of the square-footage in US colleges and universities can be classified by the building codes as office space. Energy codes promulgated by American Society of Heating and Refrigeration Engineers (ASHRAE) [1] and the International Code Council (ICC) [2] are driving down the electrical load allowed by lighting and HVAC systems. Also, historic electrical load growth assumptions of 4 to 5 percent per year coupled with NEC Section 90.8 requirements for future expansion and convenience in most cases no longer are being proven correct as the US economy grows less than 1 percent annually; or at least is growing differently from an electrica power standpoint.. Changes in the nature of electrical load itself (e.g., LED versus incandescent lighting, VSD s versus across-the-linestarters, etc.) have also exerted downward pressure on electrical load densities in commercial buildings. This oversizing of branch-circuits and feeder-circuits can result in inflated installation costs, excessive material use, and energy waste. Simultaneously, occupant availability demands increase the likelihood that electricians will be working on live equipment with higher than necessary flash hazard. Figure 1 is taken from a 1999 US Department of Energy study on transformer loading. [3]. The study includes medium voltage service substation transformers as well as downstream /120V distribution transformers and reinforces the findings of the 2010/2011 APPA data

2 Page 2 of 7 gathering effort that supplied substantiation for proposals presented to NEC Code-Making Panel 2 (CMP-2) densities asserted by the two dominant energy codes in the US set against the NEC requirement for supply circuit design [Figure 1] While the building premise service equipment is sized according to NEC fire safety requirements the load that is actually metered by the utility is significantly different and confirms the 1999 DOE findings and the 2010/2011 APPA.ORG findings. Utility service planners will usually take a load letter prepared by the Owner requesting, for instance, a utility-owned 1500-kVA exterior pad-mounted transformer, but install a 1000-kVA transformer instead because metering data from similar customer classes reveal that load computed according to NEC Article 220 methods for interior transformers will likely never be seen. Overloading of their units is rare but tolerated by the design of the transformers themselves, or avoided altogether with protective devices. II. NEW 2014 NEC LANGUAGE Due to the APPA.ORG data gathering results, and for other reasons, a number of proposals were submitted to the technical committees preparing the 2014 revision to the NEC. The acceptance of two key proposals will provide engineers with an exception that permits circuit sizing based upon power densities that track energy code limitations on lighting loads. The proposal that was approved was derived from numerous safety concepts presented by many others in the past four NEC cycles such as the American Chemistry Council, the State of Wisconsin, for example. The successful proposal merely offered a statistically significant data set to prove the reasonableness of concepts advanced by others. The disparity between the current NEC rules in Table and the new energy code requirements is not small, as can be seen in Figure 2 which is a tabulation of lighting power [Figure 2: Comparison of lighting power densities in VA (watts) per square foot] The new exception underlined below -- permits designers another way to compute the lighting load for a building. Table from the NEC (Figure 3) is also included here for reference Lighting Load for Specified Occupancies. A unit load of not less than that specified in Table for occupancies specified therein shall constitute the minimum lighting load. The floor area for each floor shall be calculated from the outside dimensions of the building, dwelling unit, or other area involved. For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use. Informational Note: The unit values herein are based on minimum load conditions and 100 percent power factor and may not provide sufficient capacity for the installation contemplated. Exception: Where the building is designed and constructed to comply with an energy code adopted by the local authority, the lighting load shall be permitted to be calculated at the values specified in the energy code where the following conditions are met: a. A power monitoring system is installed that will provide continuous information regarding the total general lighting load of the building. b. The power monitoring system will be set with alarm values alert the building owner or manager if the lighting load exceeds the values set by the energy code. c. The demand factors specified in are not applied to the general lighting load.

3 Page 3 of 7 service substation for example; designed according to the 3.5 VA/Square-Foot guidance given in Table , the lighting load may be computed according to either 0.82 VA/Square- Foot (ASHRAE 90.1) or 0.90 VA/Square-Foot (IECC) contingent upon the presence of an energy monitoring system that controls lighting load. These systems are being installed in most new buildings anyway. In the case of an office building where lighting was 30 percent of the load, that estimated 300 kva demand load would be permitted to be reduced 75 kva. When reflected into the service substation kva sizing, the calculation will likely result in the specification of a 750 kva service substation transformer instead of rounding up to the 1000 kva transformer. The following benefits accrue: a See (J) b See (K) [Figure 3: NEC Table ] National Fire Protection Association. Both the International Energy Conservation Code and ASHRAE 90.1 derived their values from the Illumination Engineering Society (IES) guidance [4]. The lighting requirements are specified in terms of foot-candles and lumens but the energy codes translate them into watts.. The designer must determine the multiplier that translates footcandles requirements into lighting power densities. New requirements in both the ASHRAE and IECC documents are trending toward expanding LED lighting; though the first cost of LED lighting is significantly more expensive at the present time Despite the very specific conditions under which the Section exception is permitted this change in the 2014 NEC revision is significant. For a 1000 kva office building 1. Lower kva nearly always results in reduced flash hazard 2. Lower kva reduces the size of switchgear and switchgear rooms 3. Lower kva means lower heat losses and smaller HVAC systems and cooling ductwork. 4. While relatively rare, 150 kva dedicated lighting transformer may now be specified at 50 kva requiring a smaller electrical closet. 5. Farther up on the grid, avoided no-load losses at medium voltage represents about a $43,860 savings (0.5% x 8760 hrs/year x $0.10 kwhr x 10,000 kva ) for every 10,000 kva of connected transformers. 6. Owners and operators of district energy systems (such as hospitals and universities) may see a reduction in reactive (kilovar) load. One or two percent higher power factor on a 100 MVA grid could save hundreds of thousands of dollars per year. III. COUNTERARGUMENTS The existing NEC calculation methodologies that lead to transformer oversizing has been difficult to handle politically, technically and economically. [5] Until arguments were presented that flash-hazard safety was undermined by bringing in too much energy into a building in the first place, the NEC panel that deals with Chapter 2 of the NEC was not going to move on arguments based of energy economics alone. The core mission of the NFPA suite of documents is safety. Without doubt, there are installations where transformers with redundant capacity are necessary. Double-ended

4 Page 4 of 7 substations are common in health-care facilities, laboratories, athletic venues and critical process areas. In high-rise facilities large fire pumps may require larger transformers to continue operation in emergencies. These are a minority of cases, however, and many of those transformers already have significant overload capability. The under-utilization of transformers was one of the drivers for the federal legislation directed at transformer manufacturers through the Energy Policy Act of The US Department of Energy understood, correctly, that it would likely be easier to mandate that manufacturers make their products more efficient -- as opposed to convincing experts on National Electric Code committees to change the calculation methods that determined their kva rating. Thus, the transformer efficiency standards set forth in NEMA TP were written into public law making it a requirement for all transformer manufacturers to meet or exceed these efficiencies in all non-exempt units built on or after 1 January The Department of Energy further addressed lowvoltage transformer design by defining varying levels of transformer efficiencies (CSL-1 through CSL-5) with CSL-3 being voluntarily adopted by a number of manufacturers through the NEMA Premium Efficiency Transformer Program [6]. In the proposal stage of the 2014 NEC revision (the so-called Report on Proposals stage, or ROP stage), the proposal that is the topic of this paper (Proposal 2-228, Log #2914) received three negative votes from Code Making Panel 2. One committee member rejected the need for a power monitoring system. A second committee member rejected the proposal over a concern that task lighting supplied from receptacles not controlled by the power monitoring system -- would result in overloading receptacle-only, or mixed-use branch circuits. A third committee member rejected the need for more exceptions to the general methods of Article 220. Many industries schools, restaurants, farms, multi-family dwelling builders have exceptions that add to the complexity of Article 220. In the ROP stage, Proposal passed with a narrow 8-3 majority. In the second, comment stage of 2014 NEC development (the so-called Report on Comments, or ROC stage), Proposal picked up two additional affirmative votes (with only 1 dissenting vote regarding the requirement for the power monitoring system). With no dissenting comments coming from public review; this demonstrated significant industry acceptance of the concept. Proposal was approved with a final 10-1 vote IV. RELATED PERMISSIVE STATEMENTS It is instructive to understand the evolution of Article 220 in terms of general rules and in terms of exceptions to general rules that have evolved over many revisions of the NEC. There are three sections where designers have been permitted relief from prescriptive design requirements. Section (Determining Existing Loads) The calculation of a feeder or service load of an occupancy can be based on the actual measured load if the designer wants to add electrical load to expand the occupancy in square-footage for example. Designers are permitted to use actual metered data of the existing load when determining the allowable increase in the service or feeder loads. Section (Feeder Demand Factor). Where reduced heating of the conductors results from motors operating on duty-cycle, intermittently, or from all motors not operating at one time, the authority having jurisdiction may grant permission for feeder conductors to have an ampacity less than specified in , provided the conductors have sufficient ampacity for the maximum load determined in accordance with the sizes and number of motors supplied and the character of their loads and duties. It is noteworthy that this section contains a reference to IEEE Color Books -- documents that are soon to be superseded which have traditionally been relied upon to contain best practice for the electrical power industry. Section (Engineering Supervision). Relaxation of Article 220 rules are permitted for information technology rooms. As an alternative to the feeder and service load calculations required by Parts III and IV of Article 220, feeder and service load calculations for new or existing loads are permitted to be used if performed by qualified persons under engineering supervision. With the exception of Section which was new to the 2008 NEC to accommodate data center design -- none of these performance clauses seemed to have an effect upon design overcapacity. A careful look at Section 220 and Annex D reveals industries such as farms and residences and restaurants getting exceptions but the largest occupancy class of them all -- large commercial facilities have not been permitted an occupancy-specific method to narrow the disparity between calculated and measured load. Several possible contributing factors to the persistent evidence of

5 Page 5 of 7 overcapacity in building premise switchgear may be as follows: a) If HVAC equipment circuit ampere requirements are based upon Article 440 methods, intended for field installation of multiple motors, the application of NEC diversity concepts for UL-listed, packaged products where internal controls result in lower ampere requirements may not be appropriate. b) There are no regional, or climate-based exceptions to NEC demand factors. Furthermore, organizations such as ASHRAE, AHRI and ASME have not yet captured in their leading practice documents, the economies of scale in buildings with multiple HVAC units. Electrical engineers inherit a long conversation about the competing requirements of safety and economy in large commercial buildings. That conservation needs to be informed with as much data as possible; and put in front of the organizations and technical professionals in the best position to understand all dimensions of the problem as soon as possible. V. JOINT IEEE-IAS/NFPA PROJECT NEC committees have always worked well with IEEE committees and many IEEE members have votes on NEC committees. There are currently over 15 references to IEEE standards in the 2011 NEC. There were a like number of in the 2008 version. Many of the IAS color books are included in these numbers. These 2011 references include the (former) Green Book [7], the Gold Books [8] among possibly others. The 2008 NEC also had specific reference to the Gray [9] and Red [10] books. Section of the 2011 NEC references Feeder Demand Factors. In prior years there were two, possibly more Red Book and Gray Book references to like subjects. Unfortunately, the tables that were referred to, initially, have not been in either the Red or Gray Books for many years. There are no copies of the book version having this information that is readily available. Given the expertise now concentrated in the Industrial and Commercial Power Systems Department (I&CPS) it is in the best position to assist agencies like the NFPA Research Foundation in the identification of thought leaders and to work collaboratively with any NEC workgroups during the 2017 revision cycle and present more data to support (or refute) a case for the following concepts: a) Relaxing the requirement for the energy management system in the new exception for the use of Table b) Reduction in the NEC per-outlet design requirement to 120 VA from the present 180 VA. c) The need to revisit the demand factors of Section for sizing supply switchgear for buildings with multiple HVAC units The assistance of IAS/I&CPS is needed in and of itself, and also to assist in the following proposed research project now requesting funding through the NFPA Research Foundation in January That request has the following goals: Research Objective. Provide updated data for a variety of occupancy and loading types that will inform National Electrical Code feeder and branch circuit design requirements in Articles 210 through 230 to size a building power system for safety and economy as well as efficiency. Another objective is to provide data to inform the assumptions about load diversity in Article 220. Project Description. It is more difficult to collect feeder and branch circuit data as compared to service load data, but this information is exactly what the electrical industry needs in order to inform technical discussions to keep the 2017 National Electrical in Code in step with energy codes. Estimated Funding Required for Project. The estimated cost is $1.5 million for a staff of 8 working full-time for 18 months. This estimate is based upon a data gathering effort of similar scale performed for the US Army Corps of Engineers. A scaled-down version of this study could involve only the loading of 480/208 volt building transformers that supply a mixture of lighting, receptacle and HVAC loads for general commercial occupancies. This might cut the cost of the research in half but would limit the applicability of the results. Project deliverables would be necessary before the deadline for proposing changes to the 2017 National Electrical Code. A completion date of October 2015 would be a reasonable target. This project could draw from recent findings in the new IEEE 3000 Series Collection [11] and could also contribute to our understanding of electrical demand characteristics in large commercial buildings in an economic environment which is driving power densities aggressively downward; coupled with heightened concern for safety and reliability.

6 Page 6 of 7 VI SUMMARY About 80 percent of commercial building power systems are using less than half their installed capacity. By permitting engineers the option of trimming back about 30 percent on Article 220 design rules, we have set the stage for running about 80 percent of building power systems above the 50% mark with offsetting I 2 R heat losses. Is the industry comfortable with this? Running our systems closer to capacity may raise the levels of required maintenance. It may also mean that we need to revisit how we actually rate electrical apparatus. We recognize that many safety concepts, widely scattered in many documents, or in unwritten "rules of thumb", may have to move together for a while until the practical effect of this change comes into view. It is possible in rare cases that this reduction in service capacity may result in fire accidents in improperly designed and operated systems where overheated equipment is not first de-energized by overcurrent devices. Proper designs would eliminate this problem. The gains--$10 s of billions per year in avoided cost in the US alone should be worth it if the offsetting gain is in electrician safety. VII. CONCLUSION For the first time in the history of the NEC we are seeing energy codes in the deliberation process about design in Article 220 where so many assumptions affect safety and cost. There is a large class of rehabilitation possibilities in which a single reason is not sufficient for a total upgrade of an electrical service but several reasons taken together -- reduction in the size of a transformer, reduction in flash hazard, removal of workspace violations, a desire for smart metering, on-site generation and distributed resource energy supplies -- can define a new "package" of electrical upgrades than can be financed, safely built, and economically run. Perhaps the result of agreement on updated guidelines for circuit design will set in motion a wave of development in which transformer retrofits have attractive payback periods. Such would be the case in building additions or rehabilitation when old, over-sized and lossy transformers can be economically replaced with newer, smaller, cooler transformers where architectural space permits. Medium voltage transformers installed in the 70 s and 80 s, for example, that were never loaded to more than 25% of rated capacity would be good candidates for replacement with an 800-ampere, 480V service that reflects the reality of 5 watts per square foot for most commercial facilities. Designing similar electrical systems to closer fit the loads that experience and measurement has shown actually exist in many installations will increase safety, save money, and increase efficiency. This new approach to design is a solid, measured step in the right direction. The NEC has succeeded as one of the most widely used technical standard in the world. It is wise to move slowly to see how this change in design methods proves itself and is integrated into the culture of the electrical industry. REFERENCES [1] Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE [2] International Energy Conservation Code 2010, International Code Council [3] Study of Transformer Loading in Northeast Region, US Department of Energy 1999 [4] Lighting Handbook 10th Edition Illumination Engineering Society [5] M. A. Anthony, J.R. Harvey, J. Sanguinetti, Driving New Concepts into the National Electrical Code, Facilities Manager, March-April 2012 [6] US Department of Energy Transformer Efficiency Guide TP-1 [7] IEEE Std Recommended Practice for Grounding of Industrial and Commercial Power Systems [8] IEEE Std Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems [9] ANSI/IEEE Std. 241, Recommended Practice for Electric Power Systems in Commercial Buildings. [10] ANSI/IEEE Std. 141, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants [11] IEEE 3000 Dot Standards: ks.html Michael A. Anthony Mike Anthony has been employed at the University of Michigan since 1982 and has had the longest career of any electrical engineer in the facilities division at the University of Michigan -- first planning and designing the build out of the Ann Arbor campus power distribution system from 50 MVA to 125 MVA up to year 2002 and more recently as Regulatory Advisor to the University of Michigan Plant Operations. As co-founder of the $200 billion US education facilities industry s advocacy capability through APPA.ORG Leadership in Educational Facilities -- he has been advancing safety and sustainability concepts in national and international technology standards since He is an advisor to the State of Michigan Electrical Advisory Board; he holds APPA's vote on the National Electrical Code and is the US technical liaison for the new International Facility Management Standard (ISO 267). He is the sole author of two textbooks by McGraw-Hill and a co-author on a third textbook Sustainable Combined Heat & Power Systems, also published by McGraw-Hill in He holds a seat on the NFPA Research

7 Page 7 of 7 Foundation on behalf of the education facilities industry. He holds a BSE degree from the University of Michigan and is a registered professional engineer in the State of Michigan. : [email protected] Thomas L. Harman. Tom Harmon is chairman of one the NEC Task Groups that advise NEC committees. He is a profession at the University of Houston Clear Lake, Houston, TX. He is an electrical engineer with a Ph.D. in Electrical Engineering from Rice University. He has held Master Electrician s Licenses in many cities and states around the US and has been a Master Electrician since 1973 in Houston, Texas. He has also had considerable practical experience in industrial, commercial and residential electrical design and installation. The experience includes industrial construction in hazardous locations. Dr. Harman has been called as an expert witness in numerous cases involving electrical accidents and faulty electrical designs. He is a member of the National Electrical Code Panel Number 2 that deals primarily with branch-circuit, feeder and service calculations. This is one of the panels that write the National Electrical Code published by the National Fire Protection Association. In 2005, he was given a 25-year award for his membership. As a result of his experience, he has written the popular textbook Guide to the National Electrical Code, published by Prentice Hall. This book is now in its 11 th edition. In private classes, Dr. Harman has used this textbook to train many electricians to prepare for their Master's examination. [email protected] James R. Harvey. Jim is Manager of Electrical Engineering for the University of Michigan Health Systems, and has worked in similar capacities at the University of Michigan for over 25-years. Prior to the University of Michigan he was a Senior Project Engineer, and Vice-President at Moylan Engineering of Dearborn Michigan. And in the early 1970 s he was a substation project engineer at the Detroit Edison Company. He is a registered professional engineer in Michigan, and has an Electrical Engineering degree from the University of Cincinnati. Jim is a Senior Member of IEEE, and has been a member of the Industrial and Commercial Power Systems Department of the Industrial Application Society for over 30-years. During this time he has worked on IEEE standards extensively, with a great emphasis on the White Book, the Red Book, and the Gray Book. Just recently he chaired the P working group. He is currently chair of the Power Systems Design sub-committee, of the Power System Engineering (PSE) Committee. The PSE is a part of the Industrial and Commercial Power Systems Department, of the Industrial Applications Society of IEEE. Besides IEEE, he is also a member of NFPA and AEE. Under AEE auspices he is recognized as a Certified Energy Manager [email protected]