The building commissioning design review process provides opportunities to see how HVAC designers apply efficiency to pumping systems. There are outstanding designs and, unfortunately, some not so excellent applications.

Over many years of design review of dozens and dozens of projects on the east coast, some fundamentals of energy efficient pumping system design become apparent.

Get the Most from Every Gallon

Hands down, the single most important element for efficient and sustainable hydronic system operation is this: Try to get as much energy as possible out of each gallon of fluid pumped to the building.

For most HVAC systems, this means selecting terminal equipment to use a high temperature difference (TD) between the entering supply water and return water. A goal of a 40F TD in heating hot water systems is achievable without having to jump through hoops.  Chilled water systems can use a 16F TD or greater.

There are still designers using the old 20F TD for hot water heating and 10F TD for chilled water. These were state of the art circa late 1970’s, when as a junior designer, I was taught these standard design practices. ASHRAE has been advocating the use of high TD’s since the 1980’s.

High TD permanently reduces the building owner’s operating cost.  And it reduces the initial construction costs since with high TD everything becomes smaller including pumps, piping and electrical service to support the hydronic system.

Move only what is needed

The second fundamental gleaned from design review as well as from observing system performance for commissioning: Move only the amount of fluid required to condition the building at any given time. This, of course, means variable flow pumping. Applying VFD’s to pumps results in the pump motor using only a fraction of full load power, typically less than 25%. That’s impressive.

Most of the designs these days incorporate variable flow, even for small 1 horsepower pumps. It’s difficult to think of a situation where variable flow can not be used. Variable flow exploits Pump Laws, to the client’s advantage.

One example of a high performance, cost effective design is avoidance of differential pressure (DP) by-pass valves (to maintain minimum pump flow). By-pass valves are expensive and add a lot of complexity. DP by-pass is never correctly specified; such “details” are left to the installing contractor. Thus, DP by-pass often creates unnecessary flow demands on pumps because they are rarely set up correctly.

Good designs use several three port constant flow control valves for terminal units at the ends of piping runs and avoid the by-pass rig penalty. Another design approach that eliminates by-pass valves is to operate unit heaters without a control valve. A similar approach is applied for water source heat pumps by allowing water to flow continually for a limited number of units without control valves. Eliminating DP by-pass valves enables pumps to operate under low load allowing the pumps to live long and happy lives moving only a small percentage of the design flow.

Our colleagues in the design build world have been telling us for years that it is less expensive to install a VFD on a new fan or pump than a motor starter. No one is better at sharpening their pencils than a design build contractor.

Minimize the Pressures

The third fundamental aspect applies to both design and operation: Minimize the system pressure that the pumps need to overcome.

Size piping for friction rates below 4 feet per equivalent 100 feet of pipe. Designers can do that without breaking the bank.

Another design feature is to avoid bullhead tees which provide for a head on collision of return water.

Bullhead Tee diagram

Designers who really know stuff display a clear understanding of what happens during part load operation. The best of the best never use manual balancing valves … they have no place in a variable flow system, and under certain conditions, are detrimental to temperature control.

Triple duty valves at pump discharge are a taboo. Why put a permanent resistor in your piping circuit?  Better to use a static venturi flow meter in the common supply piping. This allows an accurate flow measurement, and only one device has to be purchased.

For pumping operations, the experienced designers state an initial estimated differential pressure (DP) control setpoint on the drawings, which controls the pump speed and capacity. This avoids the chronic problems of excessive DP setpoints.

The best of the best designers specify automatic reset for the DP setpoint (see my previous blog) to further dramatically reduce part load power use.

Probably the single most important item for persistence of high performance pumping is simply displaying the pump kW captured from the VFD and displaying it on the BMS graphic panels.

Have I missed any essentials? What elements do you see contributing to a high efficiency hydronic system design?

The post Fundamentals of Energy Efficient HVAC Pumping appeared first on Building Energy Resilience.

Fun and profit can come in unexpected ways to energy efficiency engineers. A couple of months ago while at a jobsite conducting central air handler control testing, there was the inevitable wait-around time. So I stopped to take a look at a central heating hot water plant we commissioned a couple of years ago. It’s a basic system – an all-primary layout with two boilers and variable flow 7.5 horsepower pumps, controlled by a piping differential pressure (DP) control sensor located in a remote section of the distribution piping. The plant serves a few dozen single duct VAV box reheat coils. A pretty typical system.

Central Heating Hot Water Plant Diagram

The DP Reset Test

It was a moderate 50°F day with hot water supply (HWS) temperatures in the low 140°F range, holding a relatively low 5.0 PSI fixed differential pressure control setpoint. The pump was running at about 58% speed and using about .70 kW of power.  To see what would happen, I changed the DP setpoint to 2.0 PSI. Two hours later, the pump power dropped from .70 kW to a remarkable .30 kW. Yet the system was easily meeting the low-load thermal needs of the terminal reheat coils.

Savings Seen Before

A year earlier, while commissioning the heating hot water plant controls for a major building renovation, we discovered the control technician had increased heating hot water pump DP setpoint from 4.0 PSI to 8.0 PSI. The technician made the change because a few zones were having heating problems. The weather was cool, in the 40°F range. The heating HWS temperature was found with a reset schedule which was too aggressive (HWS temperature was too cool during moderate weather). So the HWS reset was adjusted to be warmer and the DP setpoint changed back to the original 4.0 PSI setpoint. That solved the heating problems.

What really caught our attention was the pump power reduction from 4.5 kW to only .80 kW, fifteen minutes after adjusting the DP setpoint lower. This wasn’t a fair power vs. setpoint test; a system really needs an hour or so to stabilize and truly settle down, so the savings would probably be a little lower. But the quick and dirty savings calcs we did on the fly were impressive: about 22,000 kWh per year. That’s worth about $2,600 per year, using Vermont’s average commercial electrical rate of about $ .12 kWh.

pipes (Photo credit: uberculture)

And by the way, further functional testing identified the pump variable speed drive (VFD) was setup with a 20% minimum speed, which created piping over-pressurization during low demand, with actual pressures greater than the 4.0 PSI setpoint. Changing the VFD min speed from 20% to 10% resulted in dropping the pump power even further, from .80 kW to only .30 kW.

The magnitude of these casual, very simple DP “what if” tests made me wonder why we, as an industry, have continued to use a practice of maintaining a constant, fixed high pressure setpoint. A high pressure setpoint is only needed during a full load “design day” as we say in this business.

Resetting variable flow pumping pressure setpoints lower during moderate weather allows the pump to work much easier, as the pump motor power reductions indicated. The cumulative annual savings can be significant because there are a LOT of annual hours with temperatures in the 30°F to 65°F range where resetting the DP setpoint lower can readily be applied. For example, in the Burlington, Vermont region, there are about 5,500 hours per year with temperatures in this 30°F to 65°F range where DP reset can be applied.

Uncommon Practice

Yet, to my knowledge, there is only one engineering firm in our region that applies this DP reset practice. Applying DP reset is neither expensive nor complicated. No additional hardware is needed, just some additional programming, which my guess is can be done for probably less than $500.

DP Reset Methods

What methods can be applied for resetting a pump DP setpoint?  Outside air temperature based reset, where the DP setpoint becomes higher as outside temperatures become colder is a very common reset algorithm used in our industry. This is perhaps the simplest method and a method likely to persist.

There are other methods, such as looking at terminal equipment control valve positions. When a terminal control valve modulates to greater than 90% open, increase the DP setpoint .1 PSI higher. Reverse the sequences as the valve modulates towards closed. Having said that, the sequence will never work in the real world. Inevitably, there will be a few “rogue” zones – problem zones which, for a variety of reasons, are always “calling.” Providing the building operator with the capability to easily ignore such rogues will enhance the persistence.

New ASHRAE Standard Requires DP Reset

This past weekend I was sitting around the living room reading the newest version of the primary energy code in the US, ASHRAE Standard 90.1-2010, “Energy Standard for Buildings Except Low-Rise Residential Buildings.” Yes, I really do have a life, but sometimes, as happened over the weekend, “work” and “fun” comingled. And I was pleasantly surprised to find pumping DP reset is now required. So in a few years, as various states update their state energy codes, we’ll see DP reset as business as usual.

That makes sense to me – the economics clearly indicate this is economically viable. Low hanging fruit – so low you’ll bump into it.

Hanging Fruit (Photo credit: Albert’s Images)

Your Experience?

Have you ever applied pumping DP reset? What techniques worked well for you, and were there any that did not work so well? What kind of power savings did you find? Please join the conversation in our comments section below or find us on Twitter – @CxAssociates.

The post Testing Differential Pressure Reset For Fun and Profit appeared first on Building Energy Resilience.

A recent Test and Balance (T&B) report for a central air handler made me really question the value of some of our current T&B practices. The system was a conventional variable air volume (VAV) air handler with a return air fan and single duct reheat terminal VAV boxes. The purpose of the T&B process is to adjust and record air handler performance to achieve the specified maximum flow rates.

VAV Air Handler Schematic

The report stated the return fan was unable to achieve design flow rates because the fan had an undersized motor. The air flow was below spec and the motor amps were at the maximum rating.

There were two items in the final T&B report which caught my eye.

Carrying Its Load

First, the return fan discharge pressure, with the fan operating under full load conditions, was a negative value, which means the return fan was operating in series with the supply fan. This forced the supply fan to do some of the return fan’s work, so the test did not represent real-world full load conditions.

The correct method is to test maximum return air flow by putting the system in 100% outside air mode. This inherently creates a positive return fan discharge pressure (the pressure required to overcome resistance of the relief air path, relief damper and relief louver).

Not All Amps are Created Equal

The report listed the return fan variable frequency drive (VFD) operating at 50 Hz (below max speed of 60 Hz) and the VFD display indicated 8 amps, the motor’s max rating. Instead of adjusting the fans’ sheaves (pulleys) to achieve design flow at full speed, the T&B tech simply told the control technician to limit the fans’ max speed to 50 Hz.

In the field a few weeks later, the T&B tech and I looked in to this deficiency together. When I mentioned my check calcs indicated the return fan should have plenty of motor capacity, the response was, “No way, see… the 8 amps on VFD display are already at max rating.”

An amp at 460 line voltage is not the same as an amp measured downstream of a VFD operating at 50 Hz (383 volts output).  I was surprised to find that the technician was unaware of this fact.  The tech adjusted the sheaves, tested the fan in 100% outside air mode (with positive discharge pressure) and recorded amps at line voltage entering the VFD.   The fan, now having to work harder than before (more discharge pressure to overcome), achieved design flow, and even had a little room (amperage) to spare.

A VAV box during installation

Why Are We Doing This?

The purpose of T&B is to ensure a system has the capacity to operate at max design flow. It seems to me current T&B procedures are not providing the basic information we need to evaluate a system’s performance. Nor do accepted T&B procedures address modern, variable flow system performance.

In the VFD amperage example, fundamental questions remain unanswered. For instance, how much power is the motor using? Fan power consumption is an important part of code compliance and operating efficiency.  Can air flow be increased if needed for future building use changes?

Our industry uses outdated, pre-variable flow testing procedures. For example, tests typically assess individual VAV box design flow rates by setting all terminal units to max flow concurrently. This approach does not address system diversity, nor will it ensure an individual VAV box will be able to achieve design flow while the air system operates in the normal part load mode.

We still test outside ventilation air volume with a VAV central air handler at max flow. But air flow pressure gradient profiles tell us 20% outside air at max fan flow actually results in less than 20% outside air when the fan operates at its normal 60% to 70% part load capacity.

Our industry needs to review our T&B procedures relative to our real objectives with modern variable flow air and hydronic systems. We certainly need full load testing procedures.  However, with VAV systems part load testing is at least as important as full load testing since the system is at part load for the vast majority of its operating life. There should be more focus on system power measurement, especially at part load because part load is where the real operating cost reductions are.

What are you seeing in T&B reports for your projects? How do you think we can improve our methods and procedures?

The post Testing and Unbalancing Variable Air Flow System Performance appeared first on Building Energy Resilience.

As an industry, we provide building operators with efficient heating, ventilation and air conditioning (HVAC) systems as well as powerful building management control systems. Then we expect the operators to run the high-tech HVAC equipment efficiently.

But we don’t give them the tools to answer the fundamental question: “How many ‘miles per gallon’ is my central air handing system getting?” The expectations are implicit, but the tools and basic information for management are lacking. We are not providing energy use feedback in our designs.

Providing such information does not have to be complex or expensive. In fact, the most basic energy use parameter for a fan or a pump, which are commonly fitted with variable frequency drives (VFD) nowadays, is motor power consumption: kW. Every VFD has a “free” built-in kW meter. With over a decade of conducting design reviews, I have yet to see a design engineer call for the motor power to be displayed on the system graphics panel. There is no incremental cost to do so. Why not?

Simply displaying kW next to the fan graphic display provides useful feedback. We can take it one step further for a central variable air volume (VAV) air handler by providing a meaningful performance metric such as kW per 1,000 Cfm (kCFM). This is quite simple: sum the dynamic supply, return (and relief, if applicable) fan kW using the supply air volume. Most VAV air handlers have air flow measurement stations to capture supply air flow. If not, the next best option is to totalize the terminal VAV box air flows.

This kW per kCFM is akin to miles per gallon we use for our cars. Something we all understand. Just like modern cars that display real time mpg, which enables us to learn how to drive more economically, feedback from building systems will enable facilities staff to operate their buildings more economically.

Empowering Building Operators

Now a building operator has information to immediately know the impact of changing a setpoint such as a colder supply air temperature (because the boss in the corner office is complaining).

And other questions in the building operator’s mind can be answered such as:

A graphic from a DDC system displaying fan speed.

• How does my air handler compare to other similar systems?
• Am I using what is expected?
• Has anything changed?
• Am I improving over time?

This is important because according to the Lawrence Berkeley National Laboratory, building energy use depreciates about 2% to 3% annually. Simply providing performance information, even if operators are not actively engaged in reducing air handler energy use, reduces energy use by about 2%.

Real World Answers

I often read articles in technical publications such as ASHRAE Journal, where the author says something like, “We determined changing the supply air temperature increased fan energy by conducting computer building simulation modeling.”

Why simulate? Why not answer the question using a real air handler with its performance metrics displayed? A real system and real answers.

Quick Answers Enable a Faster Response

Operator empowerment from performance metrics enables quick answers to optimizing strategies such as:

• Is static pressure setpoint reset really worth the effort?
• Did the recent change out to cog type fan belts actually improve my air handler performance?

Trending and archiving such performance data can answer other questions such as, “Why is my system using more power than it did three years ago?”

And there are other benefits. For example, a utility offering efficiency rebates for retrocommissioning (RCx) of an air handler will have available a pre-RCx baseline and post-RCx actual benefit. No fancy complex evaluations or calculations – just real world, believable answers.

Isn’t this really management 101? “You cannot manage what you cannot measure.”

Related Articles

Building Performance Monitoring And Metrics: Putting Building Data To Work [Thomas Anderson and Jennifer Chiodo, Engineered Systems Magazine]

Summary Monitoring-Based Commissioning Study [Evan Mills, PhD, Lawrence Berkeley National Labs]

Performance Metrics Research Project – Final Report [National Renewable Energy Laboratory]

The post Building Performance Metrics: Why Building Energy Use Feedback Is Essential appeared first on Building Energy Resilience.

One of the biggest challenges in conducting a building commissioning design review is to get the designer to seriously consider a design review suggestion. Designers will naturally be defensive, as would any of us. Having been an HVAC designer myself, I know one of the designer’s biggest fears is seeing comments that make the designer “look bad” to the client (building owner).

Some Fundamentals

To avoid a defensive reaction and get serious consideration from a designer plan carefully for the way in which a design review comment will be presented; it’s really no different than having a sensitive discussion in a meeting or on the phone. Always maintain a positive and respectful tone. Avoid sounding too authoritative. And never, ever make the designer look bad.

A comment should state the issue clearly, then present a solution or opportunity. One of the best approaches is to present the issue and then offer a solution in a question format. A question format is highly effective and it is a non-threatening approach. Here’s an example: “The specs call for glass “stick” type piping thermometers, which are difficult to read in the field. Could easy to read, round dial-type thermometers be specified?”

“In My Opinion”

Using the phrase “in my opinion” as part of a review comment is ineffective. Opinions don’t matter; and besides, everybody has one. Opinions are subjective. But engineering is objective.

However, using the phrase “in our experience” carries much more weight. The experience of a commissioning (Cx) service provider is viable and valid. Relating problems encountered from other projects is informative and useful. A designer will seriously consider an experienced-based comment because most designers have minimal startup and field testing experience. Experience is more objective, thus much more acceptable.

Good Design Practice

Using the phrase “good design practice” is subjective and by itself is ineffective. Referencing “good design practice” in a comment works only if it can be supported with an authoritative document to support the otherwise subjective phrase.

Design Conflicts

It is not unusual to see blatant errors and conflicts in a design that has been poorly executed. A piping detail may seriously conflict with a control schematic diagram or the specifications, and you know the problem is fundamentally sloppy or careless design. In these cases, the use of review phrases in your comment solution such as “…as the design progresses”, “…as the design is finalized” or “…suggest reconciling conflicts when final checking occurs” can work very well. The phrase is non-threatening because the reviewer acknowledges final checking is part of the process and no one expects an error free design when the design is only partially completed.

Heavy Ammunition

It’s not uncommon for a designer to be less than familiar with a critical code or industry standard and often the design will reflect that lack of knowledge. Using a code or industry standard, as well as the specific chapter and verse to convince the designer almost always works. Cite the specifics, such as Section 6.5.4.1, ASHRAE Standard 90.1-2007, Energy Standard for Buildings Except Low-Rise Residential Buildings. Including a sentence or two of the exact code language in a review comments can be powerful.

Energy Efficiency Opportunities: Hidden Veins of Gold

There are very few designs which capture all of the possible efficiency opportunities.  Most designers are in a mindset focused on design day conditions — extreme winter and summer conditions — and little attention is applied to part load operation. Part load opportunities are where the real gold resides because systems operate at part load 99% of the time. But to convince the designer, one has to provide calculated energy and operational cost-saving figures. Such savings estimates can quickly and accurately be created using spreadsheets. A precise estimate is not necessary to “sell” the opportunity; an average annual estimate will usually suffice. The order of magnitude of the savings is what is really important.

Reducing operating costs demonstrates the value of building commissioning to the owner.

Could I be Wrong?

Always keep an open mind to the designer’s response to a comment. There is always the possibility you could be flat wrong. If you think about what you have learned with each new project — sometimes you’ll wonder how you have survived and avoided big trouble all these years without that new knowledge.

Your goal is to get the very best building possible for the building owner. Carefully planning how you present your commissioning design review comments to the designer will make it more likely your recommendations will be accepted — and that you, the designer, and the building owner will all feel successful at the conclusion of the project.

Related articles

• Why You Need a Design Review (buildingenergy.cx-associates.com)
• Building Retrocommissioning: What Is It and Why Should You Care? (buildingenergy.cx-associates.com)

The post How to Present Your Commissioning Design Review Comments Convincingly appeared first on Building Energy Resilience.

We often hear a question that goes something like this from building owners: “Why do I need an independent design review? I hire the best architects and engineers.” It’s a reasonable question — asked so often in my opinion because those of us in the architecture, engineering and construction industries have done such a poor job answering.

First, A Definition

Although design review is a term used in many fields, it consistently includes two elements — independent review of the design against the project’s requirements. A definition that works across fields looks something like this: “A design review is a milestone within a product or building development process whereby a design is evaluated against its requirements in order to verify the outcomes of previous activities and identify issues before committing to, –and if need be re-prioritizing– further work. The ultimate design review, if successful, therefore triggers the product or building launch. By definition, a review must include persons who are external to the design team.”

More than LEED Design Review

In the building construction industry, design review emerged as part of the commissioning process in the late 1990’s. Both the California Commissioning Collaborative and ASHRAE are advocates of design review. It is widely recognized that design review earns credit for Enhanced Commissioning in the LEED green building certification process, but what are the advantages of a design review if yours is not a LEED project? I see four key benefits to including a design review in your commissioning process.

1. One Firm’s Practices or Proven Best Practices?

An independent design review differs from one engineering firm’s internal checking. An independent set of eyes can look beyond the design firm’s internal design practices and office culture by presenting a different method to consider, based on successful implementation of previous projects from designs by multiple firms.

The architecture and engineer (AE) community (just like the construction industry) is slow to change: misapplications from one generation of engineer or project seem to continue to the next. In recent decades, the design fee as a percentage of construction costs has decreased significantly. Engineers now have far less time in their fees for time on job site. And time in the field, especially during startup and operational testing, is where one learns very quickly what works very well and what can be done better during the next design project.

2. Reduced Construction Costs

A design review can add value to the design by reducing construction costs. Here’s an example: Consider the design of a new 10 HP pump, initially designed as a constant speed/constant flow pump. The design engineer assessment concluded: “It’s too small and not worth the cost of adding variable frequency drives (VFD)”. A third party design review would point out it is less expensive to install a VFD than a traditional motor starter. The reviewer would note annual pump operating costs would be cut 62%, avoiding 31,000 kWh a year, while dropping operating costs by $3,700. per year. And that’s not just one year; it’s every year going forward, for compounded savings.

This is true added value by reducing construction costs while concurrently reducing the owner’s overhead for the next 20 years.

Sometimes a reviewer may observe a design may not be in compliance with say, a ventilation code. While the remedy will likely increase construction costs, and possibly operating costs, the high level of indoor environmental air quality can be assured. And that may have a positive impact on productivity. This is a choice the building owner wants to at least be aware of.

3. Varied Perspectives

We each have our unique, individual blinds spots. An independent third party can point these out to a design team. It is a desire to add this varied perspective that drives the use of design review in the new product process in most industries, the software development system around the world, and in the building industry. A third party with significant commissioning and operational experience adds the perspective of installation and operations from multiple projects designed by multiple firms. A third party can suggest successful solutions from other previous projects. This institutional knowledge is shared with the entire team and adds value to the project.

4. Communication Means Fewer Errors

The least acknowledged benefit of a third party design review is fostering communication between designers, owners, and builders. Better communication reduces errors and omissions. When you think about it, aren’t most problems fundamentally due to a lack of communication?

Related articles

WBDG, National Institute of Building Sciences

ASHRAE Guideline 0, The Commissioning Process

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