Net Zero Energy Buildings

This is a recent article from HPAC Engineering that describes the history of one of the most famous Zero Energy Buildings (ZEB) in the country.  The Adam Joseph Lewis Center (AJLC) on the campus of Oberlin College in Oberlin, Ohio was designed in 1998 and put into operation in 2000.  This 13,600 ft² building has been widely publicized as the first and most significant net zero energy building in the US. The article describes just how difficult it is to design and operate a low energy building and moreover how very difficult (I mean approaching impossible) it is to design a ZEB if the energy production systems remain within the footprint of the building.  It also indicates just how “optimistic” energy use simulations can be when the designers are charged with reaching an unreachable goal.  As such, it is a commentary on human nature and the desire of many in our industry to make our work seem better than it really is.  As you will read, the devil is always in the details.
Download: Adam Joseph Lewis Center - A Paler Shade of Green
Source URL: http://hpac.com/air-conditioning/adam-joseph-lewis-center-paler-shade-green

Blog Post Written By: Jerry Williams
jwilliams@8760engineering.com
Blog Post Posted By: Michael Mosbacher
mmosbacher@8760engineering.com

Fan Heat Its Source Significance - Part 2

Download: Fan Heat: Its Source and Significance - Part 2

Fan Heat Its Source Significance - Part 1

Download: Fan Heat: Its Source and Significance - Part 1

Fan Heat and Pump Heat

I originally became interested in fan heat in about 1975.  As a young engineer of 27, I found myself assigned to do testing work on an existing high-rise office building in downtown St. Louis.  I was attempting to determine why the design discharge air temperature of 55°F could not be achieved on the leaving side of a certain air handling unit.  The unit was a high pressure draw-thru unit with roll filters, heating coil, cooling coil, and supply fan serving a two-pipe induction system with induction terminals in the building perimeter offices.  While I was making temperature readings to quantify the problem, the chief engineer at the facility saw me working and stated bluntly that he already knew the source of the problem.  However, since he had no degree in engineering (or as he put it – no sheepskin), no one would believe him.

Though I was not in the mood for his advice, I had no choice but to listen since at this point, I was a captive audience.  The chief engineer proceeded to tell me that the source of the problem was the high pressure drops across the filters and coils.  These pressure drops, because of the friction taking place, was causing the air to heat up in transit through these devices, raising the supply air temperature.  Though this argument was not correct, I had neither the patience nor the inclination at the time to try to explain why.

As an instructor in the ASHRAE Professional Development Seminar “Air System Design and Retrofit” starting in 1982, many questions arose with regard to the source of fan heat and where in the duct system this heat appears.  These questions were asked by competent mechanical engineers, thus indicating the confusion on this issue in our industry.  After I grew weary from presenting the same explanation at seminar after seminar, I published the first paper on the topic in the January 1989 issue of Heating Piping and Air Conditioning magazine entitled “Fan Heat: Its Source and Significance”.  Now I could simply use it as a handout at each seminar.

The articles to follow were printed again in HPAC Engineering magazine (the new name of the same publication) in August and September of 2005 with the title “Fan Heat and Pump Heat: Sources and Significance”.  Pump heat was added here because although the processes seem quite similar, the end results are not.  One thing good about articles like this is they are relatively timeless; the physics and thermodynamics of a process simply do not change over time.  Enjoy!

Article Author: Jerry Williams
jwilliams@8760engineering.com
Blog Post: Michael Mosbacher
mmosbacher@8760engineering.com

The Case For and Against TES for Campus Chilled Water Systems

As defined by ASHRAE, thermal energy storage (TES) systems are systems that remove heat from a storage medium (like water or ice) for use at another time.  The primary objective of a TES system is to reduce the on-peak electrical demand charges and therefore the cost of system operation.  A TES system can significantly reduce the cost of energy by allowing power intensive, electric driven cooling equipment to be predominantly operated during utility off-peak hours when utility electrical demand charges are reduced.  A TES system can theoretically shift all or part of the demand charges for the generation of cooling energy to utility non-peak hours, dependent only on the arrangement and physical size (capacity) of the storage vessel.  Thus these systems are principally designed to reduce energy cost.

Over the years, TES systems have been credited with saving energy as well.  Energy is equal to power (kW) multiplied by time (hours) or for electricity, kilowatt-hours (kWh).  For cooling energy, the equation is still power (tons) multiplied by time (hours) to yield ton-hours of cooling energy.  The TES system has the capability of shifting the generation of these ton-hours from peak to non-peak utility times thus saving cost, but not energy.  Any slight energy savings that may be available from operating a chiller at full load for more hours or operating at night with lower condensing temperatures will generally be offset by tank temperature losses and inefficiency in operation of the control system storing and releasing chilled water to the loads.

In addition, TES systems have also been considered as a substitute for redundant chiller capacity.  Whether or not this is true depends on one’s definition of a redundant chiller. All TES systems are designed based on a time component, back to cooling energy in ton-hours.  Consider a three chiller plant with no redundant chiller capacity.  Adding a storage tank that is used principally for the peak shaving of electrical demands to provide redundant capacity only makes sense if excess chiller capacity was available the day before.  If the true design load was three chillers, by the evening of the first day, the capacity of the tank has certainly been depleted and if the design load continues with two chillers, no other mechanism is available to make the excess chilled water for the TES system.  Even if the tank is just kept cold and kept in reserve (not used for peak shaving) until one of the three chillers fail, it could only be considered a redundant chiller for one day.

The concept of storing chilled water in the volumes required for a campus TES system has a disadvantage that is concerning from a redundancy and safety standpoint.  The typical campus cooling system is a closed, pressurized chilled water system with very little leakage over time and therefore very little make-up water introduced into the system.  Since the storage tank sizes required for a TES system cannot be constructed as pressure vessels, the connection of the TES storage tank converts the closed chilled water system into an open system.  The obvious issue here is that controls and control valves must be relied upon to maintain the level of water in the tank even when the supply and return line connections both have the capability of quickly overflowing the tank and disabling the chilled water system.  A less obvious issue is that the tank must be vented, putting air above a very large surface of chilled water.  Such water readily absorbs oxygen, making the chilled water system and its piping significantly more prone to corrosion with the oxygenated water.  Neither of these are insurmountable issues but they are further considerations in the desirability of a TES system.

The chilled water system could remain closed if a heat exchanger were inserted at the union of the storage system and the closed chilled water system.  However even with extremely effective plate frame heat exchangers, there must be some temperature difference between the stored chilled water and the chilled water in the closed system, thus further complicating the operation of the storage system.

Lastly, since the system saves only energy cost, it is completely dependent on the local electrical rate for on-peak vs. off-peak power.  Some Owners may find that relying on a 10 year payback based on the current electrical rate schedule more risky that competing energy cost reduction techniques.

Author:  Jerry Williams

Engineers Without Borders - 8760 Style

I have always looked for a good challenge, to travel, and to be able to help other people.  With Engineers without Borders (EWB), I found a great outlet for all of these and more.  Engineers without Borders has been a life changing experience for me. My name is Ryan Hoff, and I am an intern at 8760 Engineering. My experience with Engineers without Borders of Missouri University of Science and Technology (EWB-S&T) has helped me in many aspects of my life, but I feel that for all the good that it does not enough people know about it. 

I have been involved with EWB-S&T for three years at Missouri S&T, formerly University of Missouri-Rolla.  Our chapter has four projects working in Bolivia (2), Guatemala, and Honduras.  We focus on providing sustainable engineering projects to improve the standard of living in developing countries.  Since I have been most involved in the Guatemala project, I will discuss this project the most. We work in Nahualate, Guatemala a village of 2200 people, who have requested for us to help them with their potable water project.  To accomplish this we will construct a 15,000 gallon water tower, 8 miles of PVC piping, a 430 ft. deep well, and a chlorine sanitation system.  All of the analysis and design are done by the student team and approved by professional engineers. The project began five years ago with a feasibility study.  The project continued with several assessment trips where the team surveyed the whole community, met with contractors, and worked with the community to gauge the community’s needs and wants.  The well was successfully completed (after the second try) in September 2012.  The team and I are returning this month to begin the construction of the distribution system.  We will focus on teaching the community on how to read and understand our designs, and we will teach proper construction techniques.  The community will be responsible for completing the pipe construction in our absence. We will also be teaching the Water Committee and community about the operation, maintenance, and management of their large system. EWB-USA focuses on not only providing a large capital project, but also being able to create a sustainable project.  EWB-S&T donates their time and the initial capital cost to the community, but the community will be responsible for paying for running costs such as electricity cost and replacement parts.  

This is just one project of one chapter of EWB-USA. Engineers without Borders-USA has over 250 student and professional chapters across the United States. Missouri has five student chapters and two professional chapters.   

After I return from my trip, I will go into greater detail of how EWB has helped me on both the professional and personal level.  I will discuss a few lessons I learned that have applied to work I have done at 8760 Engineering.  I may also tell a few good stories about my trip, and what I have learned from living in a developing country.  Until then, you can check out the links below, look at the pictures below, or send me an email if you have any questions.

For more information you can see some of the following links:

http://www.youtube.com/watch?v=oH-tsu_Vck4

http://www.ewb-mst.org/

http://www.ewb-usa.org/?gclid=CIbJz-3LkbgCFWhp7AodLScAMg

Article Author: Ryan Hoff

rhoff@8760engineering.com

Fan Efficiency Grade: New Tool or Just Another Example of Relearning Something We Already Knew

I know last time I promised that my next contribution would be an explanation of why the supply air temperature wasn’t necessarily going to be 55°F.  I’ll get back to that later – I promise.  But right now, my thoughts seem to be heading in a new direction.  I just reviewed an excellent paper for HPAC Engineering Magazine on the concept of Fan Efficiency Grade (or FEG as it is being referred to).  Within a few days of that review, I heard an excellent talk at the St. Louis ASHRAE Chapter meeting by the President of AMCA, Mr. Vic Colwell, on the same topic.  For those of you looking to learn about one more constraint on your air handling systems design, ANSI/AMCA 205-12 Energy Efficiency Classification for Fans will provide some good bedtime reading (www.amca.org/feg/codes-and-standards.aspx). 

The idea of selecting fans of high efficiency is a concept that every engineer doing air systems design is fully aware of and embraces as a cornerstone of reducing energy use in these systems.  The idea of mandating an efficiency that is “acceptable” may slice against your grain but all would agree it’s a good and noble idea.  But it seems to me that fan efficiency really is a pretty small part of the overall picture.  Going back to the basics, the theoretical fan power (and therefore energy as it operates) to circulate air in an air duct system is given by the equation:
 

Fan Power = [(cfm)(FTP)]/[(6356)(η_T)]

Where  Fan Power =       Fan power needed not counting drive or motor losses (HP)

                cfm =                     Volumetric airflow rate (ft³/min)
                FTP =                     Fan total pressure (in wg)
                η_T =                        Fan total efficiency (decimal)               
                6356 =                   Constant to convert to horsepower

So obviously, the higher the fan efficiency, the lower the HP required.  So the FEG concept makes sense.  But there are still two more terms in the equation, the airflow required in cfm and the pressure required to overcome the air handling unit and duct system losses that establish the FTP.  The air quantity is set by the thermodynamics of the design and the load that is to be offset.  The designer has some leeway with this term but not a great deal.

That leaves the last factor, the fan total pressure.  And while the configuration of the building and the application may vary, this is a parameter that is almost totally established by the design of the system – and therefore, the designer.  Time to wake up - that’s us!  Though ASHRAE 90.1 has tried to weigh in on the topic of maximum fan pressure allowed, few designers understand it and even fewer code officials enforce it.  The next edition of ASHRAE 90.1 in 2013 will include prescriptive requirements for fan efficiency grade so get ready.  But the problem is really more fundamental than that.  This time we’ll look at just the system of ductwork and its design.  On another installment, we’ll look at how air handling unit design can also have an impact on that fan total pressure term.  But for now, let’s stick to ductwork.

With the types of projects we work on, we get to see lots of air system designs that are done by other engineering firms.  And although the drawings today are done in AutoCAD and are very professional looking, the thought that went into them has often not kept pace with the technology that produced them.  One of our partners has referred to duct designs that appear to be “puked up” on the page.  That may be a little too graphic (or too gross) for some but it does convey the meaning pretty clearly – the duct systems meander around the building so randomly that you wonder if there was any planning in the overall duct layout at all.

Sure, I can hear you saying it now … duct layouts, air distribution, layout organization and planning, it all sounds so 1970’s, it’s a waste of time - we’ve moved on to much more important stuff now.  We do have a lot more to think about now.  But I just want to remind you that some of that boring stuff makes your systems work better and save energy.  Please don’t forget that the basics are still important!

I’m going to proceed now to give you what I believe to be the five laws of air distribution and duct layout.  There will be some naysayers in the group who want to argue about these but I’m willing to take my chances.

Law No. 1 – KEEP IT SIMPLE

·         The shortest distance between two points is still a straight line; the shortest possible route requires less ductwork (less cost) and the lowest pressure drop (less fan power required)

·         There is nothing inherently wrong with a 45° elbow

·         An experienced sheet metal contractor I remember from when I was a pup told me “Engineers almost always get themselves in trouble when they run air past itself”

Law No. 2 – KEEP IT SYMMETRICAL

·         Attempt to use the duct geometry to provide an inherently balanced design

·         Terminal boxes (VAV boxes, mixing boxes, reheat boxes) should be located on the same side of the trunk duct as the area they serve

·         Terminal boxes should be centered with respect to the diffusers served to be more self-balancing

Law No. 3 – MAKE THE SYSTEM BALANCEABLE

·         Provide volume dampers to balance runouts with differing pressure needs (which always exist)

·         Avoid diffusers mounted to the side of ductwork to avoid noise and drafts

·         Design the ductwork so that the total supply airflow can be measured with a pitot tube traverse at one or two locations

·         Locate volume dampers as far from the supply diffusers as possible; avoid the use of registers for supply or return

Law No. 4 – LET THE AIR DISTRIBUTION DESIGN CONTROL THE DUCT DESIGN, NOT VICE VERSA

·         Don’t blow (or throw) from a ceiling diffuser in any direction further than the ceiling height

·         For selecting diffusers for VAV systems, look at diffuser performance at minimum flow as well as maximum flow

·         It may seem trivial but there is a lot to know about air distribution; take some time to study Chapter 20 in the 2009 ASHRAE Handbook of Fundamentals

·         For each new air distribution situation you encounter, test at least one space with the Air Diffusion Performance Index (ADPI – calculation described in Chapter 20)

Law No. 5 – BE CAUTIOUS WHEN MIXING AIR STREAMS OF DIFFERENT TEMPERATURES

·         Air streams of different densities caused by their temperature difference have no intention of mixing unless they are encouraged to do so; use direction and velocity to promote mixing

·         When mixing cold outdoor air and warm return air streams, introduce the cold outdoor air from the top of the duct at a 90° angle to the direction of the warm return air stream

·         Fans are not effective air mixing devices; an entering stratified air stream will produce a stratified outlet air stream (though it may be rotated or flipped in orientation)

If I can keep my brain pointed in the right direction, next time we’ll talk about air handling units.

Article Author: Jerry Williams
jwilliams@8760engineering.com
Blog Post: Michael Mosbacher
mmosbacher@8760engineering.com