Transformer energy efficiency The article “Calculating the 'real' cost of ownership for transformers” in the Spring 2009 issue of Pure Power should be paid advertising, not editorial. It is little more than a blatant promotion for selling more expensive transformers. Just because Congress now mandates the use of National Electric Manufacturers Assn.


Transformer energy efficiency

The article “Calculating the 'real' cost of ownership for transformers” in the Spring 2009 issue of Pure Power should be paid advertising, not editorial. It is little more than a blatant promotion for selling more expensive transformers. Just because Congress now mandates the use of National Electric Manufacturers Assn. (NEMA) Standard TP-1 transformers does not mean they are any more efficient or economical than standard transformers. What it really means is that the congressional lobbying by NEMA (and others) was effective. The NEMA standard is neither ANSI approved nor a consensus standard.

Since NEMA TP-1 transformers are more expensive than standard transformers, good engineering practice justifies loading them higher than the 40% shown in the article—note that no comparisons with standard transformers are shown, nor are there comparisons at loads over 40%. What the article neglects to show is that at more than 50% loading, most NEMA TP-1 transformers, excepting those with 30% less losses, will have higher losses than standard transformers, and thus will waste energy.

Furthermore, the economic justification for more expensive transformers should be based on the incremental cost of electricity, not the average cost. For example, with the current 2009 PECO Energy Company Rate HT, while the average cost of electricity may be $0.10 or $0.12 per kWh, all electric use over 300 hours costs $0.12 per kWh per month—which is where most transformer losses take place. This makes the economic justification even more difficult or impossible.

If transformers are in cooled spaces, there will be reductions in cooling energy in the summer. However, during the heating season, lower losses from transformers in buildings will be offset by increased energy use for heating, thus further reducing or eliminating cost savings, depending on the relative cost of heating energy and electricity.

Finally, the article shows some of the flawed engineering, economics, and inconsistencies in the ASHRAE Advanced Energy Design Guides. The recommendation for energy-efficient transformers is not in any of the guides, except the guide for schools.

Larry Spielvogel , PEL. G. Spielvogel inc. King of Prussia, PA

Author's response:

Spielvogel contends that though Congress mandates NEMA-approved TP-1 transformers, they are not any more efficient or economical than standard transformers in some applications and loading levels. The manufacturers of TP-1-compliant transformers removed the losses from core and usually have equivalent coil losses compared to the old standard transformers. That being the case, they are more efficient than standard transformers at all loading levels. The economic impact of TP-1 transformers compared to standard units was never finalized by the Dept. of Energy; thus, we can only compare job-by-job based on loading and bill of material.

Spielvogel also notes that there were no comparisons with standard transformers or comparisons with loads of more than 40%. There was no comparison because they are no longer available for purchase in the U.S. market. Public Law 109-58, perhaps better known as the Energy Policy Act of 2005 (EPAct 2005), prevents the manufacturing and sales of units built after Jan. 1, 2007. The point of the article was to illustrate that when comparing transformers, engineers need only three pieces of information: core loss, coil loss, and load percentage. We agree that loads on transformers exceed what was in the example, but since the average loading of low-voltage transformers is 15% to 20% for the year, we provided the example on the lighter loading and increased hours. The same 15% to 20% can be done with 65% to 70% peak loading, but the hours of the loading become greater, without much change in the comparison.

Spielvogel also posits that the economic justification for more expensive transformers should be based on the incremental cost of energy, not the average cost. If we were trying to use the energy flowing through the transformer, the more complex calculations would add value.

Since we compared two interchangeable low-voltage transformers, the differences between the losses—which are less than 5% of the energy flowing through the transformers using the average cost (or total revenue by utilities divided by total W sold)—can suggest the approximate impact of interchanging the product. This single value removes the differences between utilities, differences between sizes of customers, the change between on-peak and off-peak use, and summer and winter utility rates. The only portion of the losses not given in this example is demand charges, but since the difference in losses is 2% to 3% of the entire flow, the impact on the example would be less than $20.

Finally, we agree with Spielvogel that transformer choice should include an HVAC evaluation, not just air conditioning. However, the HVAC portion of transformers is more complex than the cost for kWh; to complete a true evaluation one would need to take into account several variables.

Thomas Patzner Staff Product Specialist LV Transformer Business Schneider Electric Nashville, Tenn.

Wendell Leisinger Customer Segment Manager Consulting Engineers Schneider Electric Nashville, Tenn.

Comment on certification

I cannot agree more after reading the Editor's Viewpoint, “Are you Cx certifiable? Who isn't?” , in the March 2009 issue.

The requirement of these certifications is a slap in the face to the professional engineer or registered architect who is an actual licensee.

The Cx certification, if administered or written by ASHRAE and properly reviewed by LEED APs, would make sense as it would test one's knowledge of what the standards truly are, what is expected, and what to do when the numbers do not add up.

As a construction project manager, most people I have run into recently have little to no idea of what a full Cx and question-and-answer (Q&A) planning entails. The Q&A process begins before the equipment is brought on-site and extends through the final installation, prior to Cx. If it is not designed and installed properly, all the Cx in the world means nothing.

With the emerging push by Congress for a reduction in energy use and green design, those conducting energy audits for old buildings should understand that software and building plans alone do not create an energy auditor or a proper disaggregation study.

We have become a nation of software users. We have forgotten that one needs to get out of the office to truly understand how to:

  • Compute a U-value of a wall section

  • Compute loads

  • Understand the effects of solar gain

  • Test for infiltration and exfiltration

  • Compute and understand electrical demand and kWh use

  • Understand the effects of reduced lighting load versus increased heating or reduced cooling requirements.

All of this requires an understanding of the ASHRAE handbooks, and the formulas that one needs to use.

Ronald J. Asche CMDS Inc. New York

Comment on certification

Editor-in-Chief Michael Ivanovich raises a valid point in his blog/Editor's Viewpoint “Are you Cx certifiable? Who isn't?” regarding the number of certification programs currently on the market. It certainly can be challenging to figure out which certification to pursue and which to look for when hiring certified Cx providers.

On the flip side, each of these programs offers value to the industry. If nothing else, these different certification programs demonstrate the importance of certification to the building community. While ASHRAE supports the other Cx-related certification programs in the field, I'd like to clarify what sets ASHRAE's new program apart. While existing certification programs certify individuals to be Cx providers, ASHRAE focuses on the Cx process. ASHRAE's program targets the individuals who serve as the building owner's Cx project manager. These are the people who represent the owner in communicating with the Cx provider and the rest of the Cx team. These are the people, likely already on your staff, to which responsibility for the Cx process falls once the provider has left the building.

Further, this certification is focused on the management of the whole building Cx process, which may require management of several certified Cx service providers—HVAC&R, electrical, envelope, and building specialty systems. We believe this to be the unique characteristic of the ASHRAE certification. ASHRAE recognizes that Cx is more than the process—it's the people who carry out that process who can make or break the proper operation of your building.

David Underwood , PE, FASHRAE Chair ASHRAE CX Certification Subcommittee


Send your letters to Michael Ivanovich, editor-in-chief, Consulting-Specifying Engineer , 2000 Clearwater Drive, Oak Brook, IL 60523, or via e-mail to michael.ivanovich@reedbusiness.com .

Letters should be no longer than 200 words, and may be edited for space, style, spelling, and grammar.

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