Ultrasonic flowmeters are capable of accurately measuring low flows during off hours in a CHP environment. (Photo courtesy FLEXIM AMERICAS Corporation)
There has been an increasing interest in combined heat and power (CHP), also called cogeneration. The primary reason is energy cost savings. While a typical natural gas plant runs at 35 percent efficiency, a CHP system runs at more than 90 percent. Those most interested are owners of older buildings with inefficient heating and cooling systems.

CHP works by using modular turbines connected in parallel to generate electrical power on site, capturing the heat created, and using it to heat the facility in winter and to drive an absorption chiller in warm months. One of the beauties of CHP is that those who use it are no longer dependent on the power grid.

DSM Engineering Associates in Hauppauge, New York, specialize in CHP retrofits for large buildings including apartment buildings, office space, manufacturing plants, and education facilities among others. Over their 20-plus years they have successfully completed projects in many important buildings in the New York City area including three campuses of the State University of New York, the New York State Energy Research & Development Authority (NYSERDA), and Consolidated Edison Company.

“One thing that has made our job easier has been NYSERDA,” said Jim Armstrong, vice president at DSM. “They have not only been our good customer, they also provide extensive funding for CHP conversions that meet their qualifications. It makes a CHP conversion more affordable so, when you combine the energy savings with NYSERDA funding, our clients have a shorter return on investment.”

“The incentives for going co-gen aren’t just in New York,” said Brad Selmon, president of M. A. Selmon, a major East Coast rep firm. “I believe all states have similar programs. I recently helped a major Massachusetts sporting goods manufacturer convert to CHP by setting them up with a modular co-gen system with ultrasonic flowmetering. They got federal and state incentives in the hundreds of thousands of dollars. It worked so well, they are installing CHP units at another site and getting similar incentives. The metering was key to qualifying because they have to be able to verify to the State of Massachusetts how much they are reducing their carbon footprint.”
Monitoring Electric and Thermal
“We don’t see a lot of building owners in New York State properly monitoring their energy usage,” said Armstrong. “In most cases that would entail either installing building management systems (BMS) or energy management systems (EMS), both very expensive. So in recent years we have been working to identify a more affordable way to monitor energy use.

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“I used to work at the Con Edison Control Center for a number of years. We had access to a significant amount of interval and real-time data by which decisions were made regarding power purchase, generation, dispatches, and things like that. The value of having that kind of information in front of you was very well instilled into my mindset. In the world of consulting where I am now, a lot of our work centers on development and design and ultimately installation supervision of packaged co-gen systems in a variety of different types of buildings. One of the issues for co-gen, or any other energy efficiency measure, has always been that most older buildings do not have any monitoring of their actual energy use. The two most important are electrical and thermal. If you can get a picture of how much energy the building is using, what the consumption patterns are, what the real loads are, you can make adjustments to get the optimum efficiency out of your system.

“In the past a lot of the information has been derived from utility billing data, which means you have to take a monthly number for use and demand and try to derive an estimate of what the peak consumption of the building might be, of what the minimum consumption might be, so you can try to optimize your co-gen design—how many units should be installed, what their capacities should be. This also applies to optimizing a new boiler or chiller system as well as co-gen. The bottom line is that by using just the utility’s billing data, we were missing a lot of information that would enable us to be more precise in designing the optimum co-gen system for individual buildings.
An Ultrasonic Solution
“Our solution was to put in electric and thermal load profiling systems that we call Tru-Use because the idea behind these is to get a true picture of what the building actually uses. This way we can see accurately what the building’s consumption is going to be throughout a given day, and even longer periods. Ideally the system can collect data for up to a year or permanently log it. We came up with an electrical monitoring system that worked very effectively and we could remotely access the data. It’s an electrical box that takes four sets of circuit transformers so we can monitor four circuits and voltage input and it’s a logger that we can access remotely. It has a direct connection to the Internet for either permanent or longer-term temporary installation. In a shorter temporary situation we just download data to a laptop.
Finding the Right Flowmeter
“The thermal was more of an issue. We were trying to find a way that could see what was actually going on with facility heating and cooling on any given day in as close to real time as possible. Then we could collect this data remotely without having to go into the building to do it.

“The problem was finding the right meter for the job. We have used insertion meters, but the requirements for installation—typically a contractor being hired to open the piping system and install the meters—makes these costly. Accuracy at low flows and operational issues such as turbine failures and low flow inaccuracies are additional problems with insertion meters. I had heard about FLEXIM AMERICAS ultrasonic flowmeters from some managers of large facilities who had made the conversion to ultrasonic meters and we started to talk to them about how our Tru-Use could work with the meters and we both saw that it would be a good application for their equipment and would work well with the FLEXIM ultrasonic meters.”

Metering Slow Flow
“A few years ago a company named Coastal Monitoring Associates had come to us,” said Peter Chirivas, an engineer at FLEXIM. “They specialize in monitoring ground water contamination to keep clients within EPA standards. The meter they used in their patented technology had been discontinued and they wanted to know if our ultrasonic technology could do the job.

“It was a really interesting challenge. No one at FLEXIM had ever thought about measuring such slow flows. We had developed the capability to measure gasses, liquids, slurries, and all of them over a wide range of temperatures. But they had never tried extra slow flows. Ron Paulsen, a Coastal hydrologist, and I worked on the challenge after-hours. Coastal’s need was clear and we wanted to be of help. To our surprise one of our existing meters really did well. We made some adaptations to further improve accuracy and got down to the 1 to 2 percent range. It worked so well we now incorporate the technology in a variety of our other meters, so we were ready when DSM came calling.”

How Ultrasonic Flowmeters Work
“One of the major benefits of ultrasonic flowmeters is that, unlike traditional meters, they contain no moving parts and do not need frequent calibration and maintenance,” explained John Van Nostrand, FLEXIM AMERICAS’ southern regional manager. “Measurements are made using the transit-time difference method. It exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium. An ultrasonic signal moves slower against the flow direction of the medium and faster when it is in the flow direction.

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“For the measurement, two ultrasonic pulses are sent through the medium, one in the flow direction and the second against it. The meter’s transducers work alternately as transmitter and receiver. The transit time of the signal sent in the flow direction is shorter than that of the signal sent against the flow. The meter measures the transit time difference and calculates the average flow velocity. Since the ultrasound signals propagate in solids, the meter can be mounted directly onto the exterior of the pipe non-invasively. And the transducer paste problem was solved by Flexim engineers who developed solid-mounting pads that don’t need replacing and conform to the shape of the pipe.

Permanent Monitoring and Sizing
“What we’re doing right now, we have FLEXIM portable meters that we’re using to do short-term monitoring for sizing a system. That meets the criterion for providing data to the cogen vendors who have to prepare economic models for NYSERDA for applications for funding. NYSERDA wants an hourly model for the facility for a year based on a standard weather profile and how the machines are expected to perform based on load. That’s where your interval loading information comes in and you use that to build an hourly thermal model for the building. You also build the hourly electrical use for the year. Then you layer your co-gen system on top of that to see what its output will be.

“Now we are encouraging our clients to install permanent metering for both electrical and thermal for two reasons. First, they can use the data to optimize the efficiency of their co-gen systems. Second, they can use their metering capability to find areas in their operations where there is an opportunity for improved efficiency.”

“Our goal was to come up with a low cost system that would give both us and building management this vital information without the expense of retrofitting a BMS or EMS. On the co-gen side, most of this metering has to be part of the NYSERDA monitoring system, so we can leverage that as a way to saving them money on installation costs.

Independence—Staying off the Grid
“A final advantage for incorporating CHP technology either as the prime means of electrical power, heat and cooling or as a backup is that your business is no longer solely dependent on the power grid. If you haven’t actually experienced black outs and brown outs, you have read of their devastating effects. And now we have the added threat of terrorists. Nearly every day we hear of how vulnerable the grid is to terror attacks. CHP units can also provide standby power to facilities to maintain operation of selected equipment such as elevators and egress lighting. Generally, CHP units are not intended to replace required emergency or standby generators, but CHP can supplement them where installed as an added benefit to their primary function of reducing overall facility energy costs.”

It seems even older buildings can achieve energy efficiency savings at reasonable costs.

Jack Sine is a freelance writer specializing in environmental issues and the chemical, power, and HVACR industries. He can be reached at jack.sine@verizon.net or by phone at 845-831-6578.