Beyond Achieving ARC

By Mark Lentz, P.E. President, Lentz Engineering Assocs., Sheboygan Falls, Wis. February 1, 2006

Today, the HVAC industry faces a crisis that is growing by the day. We must find ways to significantly reduce energy use in buildings without making them uninhabitable. New solutions are desperately needed and there is enormous room for improvement.

While it will vary from building to building, the performance gains our firm has been able to achieve in facilities like Wausau East High School, the project which won CSE’s ARC award for HVAC, (see A+ for IAQ IQ ), have brought us to the conclusion that about 85% of the energy used in buildings today is just plain wasted—that’s almost 40% of the total energy used in this country. That alone is the difference between being dependent on foreign energy sources or being energy independent. Maintaining the “status-quo” is simply unacceptable from an ethical, environmental, health/safety and economic—and even a national security—perspective.

The HVAC design for Wausau East is a step in the right direction. It uses about half the energy of its twin, Bay Port High School, despite the fact that they share virtually identical floor plans and materials of construction. For the record, Bayport uses a conventional VAV reheat system with code minimum levels of ventilation. In fact, Bayport underwent an energy conservation program at the time of the utility cost comparison between the schools. This was accomplished by reducing ventilation rates below the minimum requirements of ASHRAE 62 and subsequent revisions. While noteworthy, Wausau East’s peak electric demand is 0.6 MW lower than Bayport—and it still meets or exceeds the requirements of standard 62.1.

Also, for the record, Wisconsin, for those not aware, is one of the few states, if not the only state, which has, to date, failed to adopt the ASHRAE 62-1989 ventilation rate procedure as the basis of its minimum code ventilation requirements.

But before anyone considers emulating the trademarked Regenerative Dual Duct System (RGDD) at the heart of Wausau East, there are several points engineers need to consider.

The RGDD system is physically simple in configuration, consistent from space to space and flexible to the point that the same system can be used to serve any mix of occupancies. Primary heating and cooling plants—hydronic and air distribution systems—are significantly smaller (cooling 8:1, heating 4:1), and most of the components are standard devices obtainable from multiple manufacturers. This makes the approach readily constructable at installed costs that have the advantage over other, far less capable systems, like VAV reheat or unit ventilator schemes. It also makes changing space function very simple.

While this will come as a major shock to most designers—and runs counter to conventional wisdom—the above can all be accomplished because the system provides 100% outdoor air to each space, and does not recycle internally generated contaminants. The widely held belief that 100% outside air systems cannot be cost-effective is simply wrong. A 100% outside air strategy opens up opportunities that recirculating systems simply cannot take advantage of—They are the future of HVAC. Recirculation is a thing of the past.

Because it is possible to monitor and control airflow to each space, a properly designed and controlled OA system can demonstrate real-time compliance with ASHRAE 62 under all conditions of operation—something few recirculating strategies can accomplish. At the same time, the RGDD application, while seemingly simple is actually, deceptively complex and requires extremely careful and competent engineering.

The system is configured using multiple air-to-air heat exchangers, which make for extremely complex psychrometrics and increase the number of “design conditions” that have to be satisfied from the usual two (cooling, heating) to six. In the process, it creates conditions that the engineer must account for that are never seen in other system applications.

Multitasking required

In most HVAC systems, each major system element serves a single function; a cooling coil is only used to provide cooling, a preheat coil preheats, etc. When not in active use, these elements accomplish little other than creating parasitic losses for the system. In an RGDD application, individual system elements may serve up to five or six different functions, and when not in active use, they are bypassed to eliminate their parasitic losses on the system.

Evaporative processes are used as the primary cooling processes. The systems are based on direct and enhanced indirect evaporative cooling, which, in spite of the fact that it uses 100% outdoor air, actually employs both air- and water-side economizers. This permits us to literally shed 80% to 85% of the refrigeration load required to provide full air conditioning. There are no cooling coils in the airstream.

In most HVAC systems, there is virtually no planned interaction between different system elements. RGDD design makes deliberate and effective use of interaction between system elements to “enhance” performance through the entire range of system operation. This interaction is deliberate, and must be thoroughly understood and quantified by the designer to properly size both primary heating and cooling systems, and by the commissioning agent.

Commissioning is not an option; it is an absolute necessity. Everything must be properly controlled and the system must be tuned so that it can be set up to achieve it’s design potential.

Must be taught

I have been repeatedly asked when I am going to publish on “the Lentz System.” This is a difficult question, as first, it’s not a “system” in that it does not lend itself to cookie-cutter design practices. It represents a radical departure from the underlying principles of HVAC as currently practiced in the United States. Because it is new—and controversial—the market acceptance of this technology could be quickly destroyed through misapplication. In my opinion, this is what happened to solar energy in the 1970s, and nearly happended to lab VAV systems in the 1980s. The wide applicability—and relatively low cost—of this strategy makes it too important for this to happen. Developing the necessary skills for its application will require significant training, much of it of a remedial nature, and a culture change in the industry before most practitioners will be able to apply these skills. I have been looking into this for several years, but I believe there is currently no mechanism available that is adequate to provide the necessary level of training. LEA is currently looking into the possibility of setting up a school for this very purpose.

LEA has successfully designed numerous high performance facilities, each different from the last. There have been numerous configurations, and many more are possible. And, there are definite principles involved. “High performance” HVAC design should really be considered an entirely new field because it has so little in common with classical HVAC design. Most enhanced HVAC systems are little more than classical configurations that have had some form of energy recovery added, often in a configuration that results in minimal benefits.

In the case of Wausau East, an entirely new concept in HVAC design was employed, one based on very different underlying principles and design objectives. It was derived from scratch by starting with the ultimate objectives to be achieved—how to minimize energy use at the space, how air is optimally delivered, what temperature is to be maintained, air quality objectives, humidity control, space pressurization, sepsis control, etc.—at the point of use (the space) and by identifying and systematically eliminating systemic inefficiencies from the system through to the primary plants.

The system design is the outcome of a methodology based in knowledge and skill, learned one step at a time. It takes time, study and effort to develop that knowledge. It takes practice and a total committment to quality to develop the necessary skills.

Those who wish to be the technological leaders of tomorrow need to understand and appreciate that this will require real corporate commitment to learning, continuous improvement, research and careful application of sound engineering principles. When developing new strategies, it is wise to start by learning each process, one at a time. They should be learned using demonstration projects to limit designer liability exposure. Application of combinations of processes should not occur until each process is mastered by the designer, or his supervisor, and new applications should be researched carefully before they are considered for application. When problems occur—and it should be anticipated that they will—it is necessary to analyze failures to identify why they occurred, what needs to be done to correct it, and how to avoid the same mistake in the future. Small errors or misconceptions, in concept or execution, can make very big differences when it comes to performance.

Scratching the surface

LEA has applied this practice to its basic business model since it was formed, and this is our secret. It is hard work, but it does not take many small steps forward to move a long way ahead of an industry that is for all intents and purposes stagnant. And, we have only begun to scratch the surface of what can be accomplished.