TBC

TBC

Making Buildings Work Better

Presentation: Who Stole My High Performance Building?

I want to thank the Utah ASHRAE Chapter for inviting me to give my presentation called “Who Stole My High Performance Building?” on Friday December 3, 2010. It was a packed house with over 70 people in attendance. The audience participation and questions were great.  This presentation shares many of the lessons learned in the field and gives valuable feedback of how different designs are performing in the field. Read the rest of this entry »

Lessons Learned from a Building User

I received some feedback from a reader, Daryl,  the other day that was great and I’d like to share it with you.

From Daryl…

I would like to talk about HVAC air flow engineering with you some just for fun. I have some text book errors to share with you. Read the rest of this entry »

History of Commissioning

The Total Building Commissioning industry is relatively new and growing up as we speak.  It has been fun to be involved in the process and rub shoulders with many of the industry pioneers and experts.  A couple of years ago at a NCBC conference a “History of Commissioning” was presented as a display.  It was fascinating to see the information gathered together in one place.  PECI has posted this information on their website and kept it updated.

You never know if a website link will go bad someday so I will copy the information below (giving full credit to PECI).  I will also add a couple of things to the list which I have put in bold and italics.

I hope you enjoy looking back at and seeing just how far the commissioning industry has come. Read the rest of this entry »

Air Handler Supply Air Temperature Set Point (AH SAT StPt) Control Based on VAV Box Cooling Demand

In the Air Handler Supply Air Temperature Control post, we discussed a method of resetting the air handler supply air temperature set point based on the outside air temperature (OAT).  This post will discuss another method of resetting the air handler supply air temperature set point (AH SAT StPt) based on VAV box cooling demand.

The advantage of resetting the AH SAT StPt based on VAV box cooling demand is that the supply air temperature set point would actually track the building demand.  It sounds pretty simple on the surface, but there are some things that can derail this strategy and make it fail.

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Keys to making this strategy work:

  1. All zones must be able to be cooled most of the time by higher supply air temperatures.
    • A good rule of thumb is that the full cooling supply air flow delivered at the upper SAT reset limit should cool 50% of the design load.
    • Zones that are scheduled to turn off during unoccupied periods should be separated from zones that have a 24/7 cooling load.  This is often done by providing dedicated air conditioning units for the 24/7 rooms such as data closets, or grouping these zones together and serving them from separate air handlers.
    • Accurate, properly placed and calibrated temperature sensors are also key to making any control strategy work.

Conditions that will kill any supply air temperature reset strategy:

  1. One or more zones has a constant high cooling demand and always requires supply air temperatures near the lower end of the SAT reset range.  Typical applications are data and telecom rooms or any place that has equipment running.
  2. Failure to communicate how the reset control strategy works and the conditions necessary for it to work.  This is important to describe in the Basis of Design.

These items listed above point out good design practices that all designers know, but the designer needs to make some adjustments to the standard design in order to optimize any SAT reset strategy.

After determining each zone’s peak heating and cooling loads, the designer needs to then identify all of the zones that have high cooling demands that do not back off during non-peak conditions.  If there are cases where high cooling demand zones cannot be separated from intermittently occupied zones, the designer can design these high cooling demand zones for a higher supply air temperature.  This will increase the cooling airflow which will increase the size of the VAV box serving these zones.  For instance, a zone supplied by 55 degree air with 75 degree return air requiring 1000 CFM to cool the space would required 2000 CFM to cool the space with a 65 degree supply air temperature.  This will cost a little more up front for a larger VAV box and supply ductwork in this zone, but it will save significant amounts of reheat energy and increase comfort in the other system zones.  The argument could successfully be made that the air handler airflow would not need to be increased because during the cooling design load conditions the air handler SAT would be 55 degrees and so this zone would only require 1,000 CFM to cool this room.  The CFM would only increase during the periods of low cooling demand in the other zones.  As long as this is explained in the Basis of Design other people can quickly understand that the system has diversity and that the sum of the VAV box CFMs will be more than the air handler CFMs.

A real-world example of this strategy is the project that is located in Salt Lake City where the summer dry bulb design temperature is 97 degrees F.  The system resets the supply air temperature between 55 and 68 degrees.  The strategy has eliminated almost all of the reheating and reduces the overall system airflow and fan energy.  This was easy to see why, because before the reset strategy was implemented, 50 to 75% of the VAV boxes would be in reheat mode while about 2 – 5% of the VAV boxes would be in cooling mode when the outside air temperature was 70 degrees F.  By resetting the supply air temperature, the supply airflow is increased to the high cooling load zones while the other boxes that were in reheat are now operating at the minimum airflow set point which is significantly less than the heating airflow set points.

With that said, here is a Supply Air Temperature Reset Control sequence based on VAV box demand that could have been used in the project from the previous post.

  1. SUPPLY AIR TEMPERATURE SET POINT RESET CONTROL:

Reset the air handler SAT StPt of each air handler based on the VAV box cooling demand.  If the air handler enters a cooling mode that involves the evaporative cooling (Stage 3), then the SAT StPt shall be set to the evaporative cooling mode set point. Each air handler will have its own reset schedule as follows:

  1. If the maximum VAV cooling demand is below 85% for 5 minutes then the supply air temperature set point shall be raised by 0.5 degrees.
  2. If the maximum VAV cooling demand is above 100% for 5 minutes then the supply air temperature set point shall be lowered by 0.5 degrees.
  3. The initial supply air temperature shall be 60°F.
  4. If the air handler enters a cooling mode that involves the evaporative cooling (Stage 3), then the SAT StPt shall be set to the evaporative cooling mode set point.

Air Handler SAT Reset Based on VAV Box Cooling Demand

It should pointed out that this strategy is called “Trim and Respond” because the set point is “trimmed”, and then the system responds and is allowed to settle out before trimming again.  The reason for using this type of strategy instead of a PID loop is that there would be interactions with other PID loops and it would be very difficult to keep them stable.  When you change the supply air temperature, then the VAV box PID loop will respond by increasing or decreasing the cooling demand signal.  This is fed back to the SAT StPt control loop.  By using a trim and respond sequence with a significant time delay, the SAT StPt control will be stable.

As it is noted in this post that there are many details that need to be addressed to make the VAV box cooling demand reset method work, I believe that the extra effort is worth it and can pay huge dividends in energy savings and occupant comfort.

Sequence Notes: A safety in this sequence was to make sure that whenever the evaporative cooling mode was operating that the SAT StPt would be 55°F or below.  Graphic design was also addressed to provide the operators simple and intuitive access to monitor system operations and adjusting system settings.

 

Todd Rindlisbaker

 

Todd Rindlisbaker, P.E., QCxP, LEED AP, HBDP, CCP, has been in the HVAC/plumbing design and commissioning business since 1993. He has extensive experience in project management, HVAC design, and energy studies and specializes in hydronic heating and cooling systems, controls optimization for comfort and energy efficiency and in commissioning. He has been involved in the design, installation, and commissioning of mechanical, plumbing, and building management systems throughout the United States and internationally.

A “Game Changer” for Commissioning Providers, Constructors and Engineers

I recently attended the ACG Annual Conference on Total Building Commissioning in Las Vegas, NV. One presentation provided information that was categorized as a “game changer” for commissioning providers, constructors and engineers alike.

Signed into law and effective January 1, 2011, California has adopted the California High Performance Green Standards Building Code. What is significant about this is that ASHRAE, USGBC, IES and ICC have developed an almost identical document published this year–ASHRAE Standard 189, Design of High Performance Green Buildings.

What is ASHRAE 189? Simply put, it is an ANSI standard developed in model code language designed to provide code-enforceable mandatory minimum requirements for high-performance green buildings.

“Applicable to new commercial buildings and major renovation projects, it will address energy efficiency, a building’s impact on the atmosphere, sustainable sites, water use efficiency, materials and resources and indoor environmental quality. Standard 189P will become the benchmark for all sustainable green buildings in the United States because it is being developed for inclusion into building codes,” said ASHRAE President Terry Townsend.

The groups developing this standard–USGBC, ASHRAE, ICC, ICBO, BOCA and others–intend that this standard become an integral part of the next version of building codes published in the United States. Of course adoption of these codes in whole (or in part) is the prerogative of each municipality, yet the tenets of ASHRAE 189 will significantly impact the design and construction industry in the years to come.

Some highlights:

Many of the LEED components familiar to constructors and designers of commercial buildings will become code.

Comprehensive commissioning for buildings over 5,000 SF is required by code.
• All water-consuming elements must be commissioned including irrigation.
• The commissioning authority will verify all IAQ requirements through the construction process.
• Envelope commissioning is mandatory. Building envelope systems, components and assemblies to verify air tightness, thermal and moisture integrity.
• Measurement devices with remote communication capability shall be provided to collect energy consumption data. This requires that buildings be circuited segregating HVAC, lighting and process electrical loads so that energy can be monitored and projected energy performance can be verified.

Of course there are many other important elements to ASHRAE Standard 189 that affect all members of the design-build team. To learn more go to: www.ashrae.org/greenstandard

Raymond A. Dodd, P.E., CxA, LEED AP possesses a wide breadth of experience, totaling more than 25 years, in the mechanical facilities field with extensive knowledge of commercial, industrial, institutional and high-technology mechanical facilities systems. He is a skilled project manager proficient at handling the logistic, technical and communications challenges required in the commissioning, construction, design and sales process. He has been the owner of an HVAC service company, which has given him hands-on experience and provided him with additional insight into constructability of his designs as well as the issues faced by owners and facilities personnel throughout the commissioning process. He has worked as a consulting engineer and directed the engineering group for a large national mechanical design/build company and served as a LEED™ commissioning engineer.

rad@tbcxinc.com

Air Handler Supply Air Temperature Control

As noted in The Genesis post, we will be sharing a lot of stories from the field.  This example seems like a great place to start.

On a recent project, the Variable-Air-Volume (VAV) air handler controls sequence did not have supply air temperature reset control.  This is acceptable according to the local energy code (ASHRAE 90.1-2007) which only requires supply air temperature reset for constant volume air handler systems, but it uses additional energy. These air handlers are VAV-type systems with four stages of cooling; outside air economizer dampers (OA Econ), in-direct condenser water cooling coil (ICC), direct evaporative cooling (Evap), and a chilled water coil (CHW).  This system is commonly called an IDEC (In-Direct, Evaporative Cooling) system.  The cooling sequence is as follows;

Stage OA Econ ICC Valve Evap CHW Valve OAT
1 0 – 100% 0% Off 0% OA < DAT StPt
2 100% 0 – 100%

Off

0% OA > DAT StPt
3 100% 0 – 100% ON 0% OA > DAT StPt
4 100% 100% Off 0 – 100% OA > DAT StPt

At first glance, someone would look at this and be thinking that these are expensive air handlers, and they would be right that it does cost more to add the in-direct and direct evaporative sections to a regular air handling unit. So it is important to note that this project is located in Salt Lake City, UT which is a high mountain desert.  The design conditions are 97°F DB and 63°F.  If you do a BIN data plot on a psychometric chart,  it is fairly easy to see that this system will operate on mechanical cooling between 100-200 hours a year verses about 2000 hours a year on a traditional mechanical cooling only air handler.  The following BIN data plot shows the number of hours that the system will operate at each outdoor air condition throughout the year (based on a five-day work week).  The number of hours that the cooling will be reduced are the hours between the first and second lines.

Hourly BIN Plot on Psychrometric Chart - Salt Lake City, UT (created by TBC using Greenheck HDPsyChart)

An IDEC type cooling system requires the supply air temperature to be 55°F or lower whenever the evaporative cooling stage is on.  This constraint is meant to ensure that the indoor humidity will not rise above 40%. The engineer specified that the supply air temperature set point be set at 53°F.

Even though a constant supply air temperature set point is acceptable for a VAV system based on the local energy code (ASHRAE 90.1-2007) it was causing the system to use large amounts of reheat energy most of time, even when the outside air temperature is as high as 80°F.  It was also causing many occupant comfort complaints especially when the outside air temperature was cold or moderate.

There are multiple methods to provide Supply Air Temperature Set Point  (SAT StPt) Reset Control.  Two of the most common methods are based on Outside Air Temperature and on the maximum VAV box cooling signal.

Each reset method has its advantages and disadvantages:

Outside Air Temperature Reset Method

Advantages:

  • Relatively simple to program
  • Better than nothing

Disadvantages:

  • It is “open loop” control.  Open loop control does not provide feedback into the control loop and therefore does not adjust based on system response.  Open loop control is highly discouraged because of this.  An example of open loop control in your car would be speed control based on the type of street driven on.  This method would press down the accelerator a certain percentage based on the street type.  This control would not give any feedback to how fast the car was going, what the traffic was like, whether you were traveling downhill or uphill, or even, the actual speed limit.  It is easy to see how this would be very inaccurate and undesirable.
  • No very accurate.  A building operator has to watch the system over a year of two and try to adjust the reset parameters to get it to match the building characteristics.  Even when this is done right, it will only be a fair estimation.

VAV Box Cooling Demand Method

Advantages:

  • The system responds directly to the building load and is able to use less energy by using the highest supply air temperature as possible.

Disadvantages:

  • It is more complicated to program.

This particular project’s building owner operates well over 100 buildings and has a very knowledgeable, full-time control system engineer who monitors the buildings and can deal with building control issues as needed.  Based on this, the owner chose to use the outside air temperature reset control method, with the understanding that the controls engineer would need to monitor the building over the next one to two years and tweak the set points to get the supply air temperature set point (SAT StPt) reset adjusted for this building.

The following Supply Air Temperature Reset Control sequence was used for this project:

Reset the air handler SAT StPt of each air handler based on the outside air temperature.  If the air handler enters a cooling mode that involves the evaporative cooling (Stage 3), then the SAT StPt shall be set to the evaporative cooling mode set point. Each air handler will have its own reset schedule as follows:

Air Handler SAT Reset based on OAT

End of Sequence

Sequence notes: A safety in this sequence was to make sure that whenever the evaporative cooling mode was operating that the SAT StPt would be 55°F or below.  Another item addressed in this sequence was graphic design that would provide simple and intuitive access to the operators for monitoring system operations and adjusting system settings.

In my next post I will provide an example of the SAT StPt reset control based on VAV box cooling demand. Later blog posts will explore control system graphics design.

 

Todd Rindlisbaker

 

Todd Rindlisbaker, P.E., QCxP, LEED AP, HBDP, CCP, has been in the HVAC/plumbing design and commissioning business since 1993. He has extensive experience in project management, HVAC design, and energy studies and specializes in hydronic heating and cooling systems, controls optimization for comfort and energy efficiency and in commissioning. He has been involved in the design, installation, and commissioning of mechanical, plumbing, and building management systems throughout the United States and internationally.

Budgeting for Commissioning

Building owners from all over the country are finding that the energy, water and operational savings resulting from commissioning offset the cost of implementing the commissioning process. Recent studies indicate that on average the operating costs of a building that has been commissioned range from 8-20 percent below that of a non-commissioned building. An investment in commissioning at the beginning of a project often results in operating cost reduction that last the life of the building.

So how do you budget for commissioning? Can you just plug in a $/sq. ft. number and move on? Maybe or maybe not.
Is the project LEED™? If so, LEED™ views commissioning as a prerequisite with prescribed tasks covering the HVAC, lighting control, domestic hot water and renewable systems beginning at the construction phase of the project. LEED™ also offers an enhanced point for commissioning that brings the commissioning authority on during the design phase of the project with additional tasks (and an increased budget).

If the LEED™ measurement and verification point (M&V) is attempted, commissioning takes an additional role to verify the energy usage which begins in the design development of the project.

Another factor is the size and complexity of the building. Because some commissioning tasks are uniform for all projects,  smaller buildings have a higher cost per square foot.

Finally, what does the building require? In an office building,  HVAC, lighting control and domestic hot water commissioning may suffice. However, a clean room with tight control of humidification will require envelope commissioning. In a data center, commissioning of the electrical systems is critical.

Below are a few ranges for commissioning costs but as this article suggests, have a commissioning  professional budget the project based on building type, operational requirements, size and complexity so that your cost estimates for commission have you covered.

Note: In general, the cost of commissioning a new building ranges from 0.5 to 1.5 percent of the total construction cost, as shown in the table. For an existing building, never before commissioned, the cost of retro-commissioning can range from 3 to 5 percent of the total operating cost.

  • Entire building (HVAC, controls, electrical, mechanical): 0.5-1.5 percent of total construction cost
  • HVAC and automated control system: 1.5-2.5 percent of mechanical system cost
  • Electrical systems: 1.0-1.5 percent of electrical system cost

Raymond A. Dodd, P.E., CxA, LEED AP possesses a wide breadth of experience, totaling more than 25 years, in the mechanical facilities field with extensive knowledge of commercial, industrial, institutional and high-technology mechanical facilities systems. He is a skilled project manager proficient at handling the logistic, technical and communications challenges required in the commissioning, construction, design and sales process. He has been the owner of an HVAC service company, which has given him hands-on experience and provided him with additional insight into constructability of his designs as well as the issues faced by owners and facilities personnel throughout the commissioning process. He has worked as a consulting engineer and directed the engineering group for a large national mechanical design/build company and served as a LEED™ commissioning engineer.

rad@tbcxinc.com

The Genesis

In engineering school we are taught about Newton’s law of physics. One of those laws that quickly comes to mind is that an object at rest will stay at rest unless acted upon by an outside force. At Total Building Commissioning, Inc. (TBC) we have had many requests from clients, design engineers and fellow commissioning authorities for information about commissioning and how to make buildings work better.  These “outside forces” have set this blog in motion.

Our intent in providing this blog is to provide an online, searchable, content-rich resource. The majority of the blog posts will be “reports from the trenches”, “stories from the field” and other real-life experiences to help bring information to life with real world examples.  We welcome your constructive comments, information and input to increase the value to those who read this blog.

BEST PRACTICES, WAR STORIES AND LESSONS LEARNED

This Best Practices, War Stories, and Lessons Learned blog will provide inspiration and instructional content to building owners, design engineers, contractors and commissioning authorities alike.  Topics will cover the Total Building Commissioning process, design, troubleshooting and operations of building systems, including HVAC, DDC control, electrical and many others.  This blog will be an informal, fun, content-rich forum for exchanging information.

Email: info@tbcxinc.com

Todd Rindlisbaker

Todd Rindlisbaker, P.E., QCxP, LEED AP, HBDP, CCP, has been in the HVAC/plumbing design and commissioning business since 1993. He has extensive experience in project management, HVAC design, and energy studies and specializes in hydronic heating and cooling systems, controls optimization for comfort and energy efficiency and in commissioning. He has been involved in the design, installation, and commissioning of mechanical, plumbing, and building management systems throughout the United States and internationally.

Welcome to the Total Building Commissioning Blog

Welcome to the blog for Total Building Commissioning. This blog is a repository for information regarding commission and it’s value to the industry.

Total Building Commissioning (TBC) is a facility consulting firm that specializes in the commissioning of mechanical, electrical, controls and all other major building systems. TBC offers more than 28 years experience related to commissioning, energy-efficiency consulting and building automation and controls consulting. TBC also provides LEED™ certification consulting. A distinguishing characteristic of the TBC commissioning process is the emphasis we place on leaving clients with a building that works and operation and maintenance (O&M) personnel that are trained.

About TBC

As a leader in the building commissioning industry, Total Building Commissioning (TBC) is a facility consulting firm that specializes in the commissioning of mechanical, electrical, controls and all other major building systems as well as LEED™ certification consulting.

Contact TBC

info@tbcxinc.com

Phone: 801-401-8401
Toll Free: 877-822-9462

324 South State Street, Suite 400
Salt Lake City, Utah, 84111