Abstract – January 17, 2000



“Band Aid” solutions often

cause more problems without overall systems review

AUTHORS

Hemant R. Mehta, P.E.

Christopher Tso, P.E.

WM Group Engineers, P.C.

New York, NY

Abstract

This paper will discuss several case studies where “Band Aid” solutions have led to more problems than solutions with overall systems review. Several case studies are as described below:

1. Bristol-Myers Squibb (BMS)

At the BMS facility in Lawrenceville, New Jersey, a portion of the system was not getting enough cooling. The “Band Aid” solution was to install booster pumps to serve this portion of the system. Some troubleshooting and an overall systems review indicated that old abandoned orifice type flow meters were chewing up a substantial amount of system pressure just outside the plant. Removing the orifices negated the need for new booster pumps. This paper will discuss how to find problems in large district cooling systems.

2. The Pennsylvania Capitol Complex

The chilled water systems at the Pennsylvania Capitol Complex present a good lesson in learning what not to do. Over the years, with improper consulting advice, the State has installed control valves in their chilled water system to throttle down the system pressure, inducing as much as 60 psig of pressure drop at these control valve stations. This case study will discuss how the client was convinced to install these pressure reducing valves in the system and then to over-pump to overcome the added system resistance. The paper will also discuss simple solutions to make systems reliable and cost effective.

3. Hospital for Special Surgery

This case study will discuss how a desperate client consulted two well known vendors for solutions to their chilled water system problems. One vendor’s recommendation was to remove the newly installed chillers and replace them with larger chillers. The other vendor thought that system balancing was the problem. Our review of the overall system indicated that removal of unnecessary pumpsets would fix the system. This case history will discuss systems analysis.

4. Brown University

At Brown, lack of an overall Master plan for expansion of the systems resulted in modifications that where implemented over several years which degraded the utilization of an originally well designed system. The system design philosophy was not followed as chillers were replaced, and now the University cannot operate their Cogeneration system during the summertime without significant penalty. In addition, this paper will discuss additions to a heating hot water system that were implemented without keeping the overall system in perspective. These modifications resulted in unnecessary pumping stations and multiple expansion systems. Both systems were victims of multiple “Band Aid” solutions which were implemented without considering the impact on the overall system.

The cases described above represent what happens when multiple consultants modify different portions of the same system and only focus on their own project without an overall review of the whole system. As a result, these “Band Aid” solutions create systems which are more and more complex and which become unable to provide the required capacity. In almost all cases, an overall system review indicated that simple piping modifications would solve the problems and would enable the systems to satisfy their loads while saving substantial operating costs.

Keywords

Band Aid solutions, consulting engineering, system troubleshooting, case studies, district heating, district cooling, chilled water, high temperature hot water

Bristol - Myers Squibb (BMS)

The Architectural profession is very unique. Generally, Architects are given the opportunity to build their “dream building”. Engineers, on the other hand, often work with existing systems and do whatever it takes to make the systems perform. Our profession is not as glamorous and certainly not as glorious. As an engineer in 1988, I was given an opportunity to build my “Taj Mahal Central Utility Plant”. E.R. Squibb, now know as Bristol-Myers Squibb, was going through a major expansion of their pharmaceutical research facility in Lawrenceville, New Jersey. In 1988, the facility was 700,000 square feet. Today the facility is near its maximum FAR at about 1.6 million square feet.

[pic] [pic]

Figure 1 – BMS Site (1998) Figure 2 – BMS Site (2003)

The original complex had a chilled water plant in the basement of Building C which served the entire site. This plant was replaced by a new central utility plant at the other end of the complex. Figure 1 and Figure 2 indicate the site in 1988 (Building C plant) and the current site (new central utility plant). The new central plant was designed to meet heating, cooling and power requirements for the ultimate site build-out. The chilled water system designed in 1988 was based on a variable volume all primary pumping system.

In the summer of 2003, I got a call from the facility director advising me that they were not getting enough chilled water flow to the front portion of the complex and that they were planning to install booster pumps to serve this portion of the complex. Many clients in our industry provide what they perceive as the solution to their problems to the consultant and expect the consultant to simply provide a design to implement that solution. Most of the time this ends up as a “Band Aid” approach to fixing system problems. My advice to the client was to give me some time to find out exactly why there was a chilled water flow shortfall in that area of the complex and then design the optimum solution. My gut instinct was that there was some restriction in the system. A flow diagram of a portion of the distribution system is shown in Figure 3 below.

[pic]

Figure 3: BMS - MER 9

I advised the client to install pressure gages at each building takeoff on each of the supply and return lines and to record the readings. The review of the pressure readings for the supply and return lines indicated that the pressure drop in the return line between MER 9 and Buildings A & B was almost twice the pressure drop in the corresponding supply line.

This indicated that there was some sort of blockage in the return pipe between MER 9 and Buildings A & B. The piping configuration of this segment forms a loop as shown in the flow diagram above. The main reason for the loop was that the existing mains serving the air handling units in MER 9 were too small. So rather than removing the lines and replacing them with larger lines, we ran another set of mains parallel to the existing lines and created a loop. The site survey indicated that a valve on one branch of the loop was closed. Upon inquiring, we were told that the valve was closed by a contractor to isolate the piping in order to install a new air handling unit. The contractor simply forgot to open the valve after his work was complete. The second problem was that the old plant in Building C had two abandoned orifice type flow meters on the system mains leaving the old plant. The flow meters were disconnected, however the orifice plates were never removed from the pipe. After opening the valve in the loop and removing the orifices, the restrictions in the system were eliminated and the existing pumps had no difficulty in delivering plenty of flow to all of the buildings. Our review of the overall system resulted in finding simple solutions which negated the need for the installation of new booster pumps.

The Pennsylvania Capitol Complex

At the Pennsylvania Capitol Complex, chilled water is generated at the chiller plant and distributed to the buildings through a network of tunnel and underground piping. The chilled water pumping system is configured for primary/secondary/tertiary pumping. The primary and secondary pumps are located in the plant and the tertiary pumps are located at each of the buildings.

The secondary pumps used for site distribution are sized for 288 feet of head. Taking the expansion tank pressure into account (~70 psig), the total system pressure is about 450 feet of head (195 psig) at design conditions. However, the building chilled water systems are only rated for 125 psig maximum working pressure. At peak cooling conditions, the maximum working pressure of the building systems are exceeded. In order to reduce the system pressure in the buildings, the client installed control valves to throttle down the system pressure at each of the buildings. Immediately downstream of these control valve stations, the building pumps (tertiary pumps) are used to boost the pressure back up and circulate the chilled water through the buildings. In fact, a pressure reducing station was installed on the chilled water system at a newly constructed building to limit the maximum system pressure to 90 psig. The building pumps, located downstream of this pressure reducing station, are then used to pump the chilled water through the building.

This is a classic case of the application of a “Band Aid” solution without considering the overall system. When the building systems were experiencing problems due to high pressures, control valve stations where installed to reduce the pressure at the entrance to the buildings. The building pumps, downstream of the control valve stations, were still used to circulate water through the buildings. Even the engineer designing the new building systems included a pressure reducing station and a pumpset as a part of the building design to supply chilled water to the new building. Little or no thought was given to the overall system dynamics when these modifications were made. As a result, the system distributes chilled water at a high pressure, then the pressure is throttled down at the building control valve stations and then more pressure is added to the system by the building pumps. All the energy used to pump the water through the distribution system is wasted by throttling down the pressure at the control valve stations, and then more energy is added by the building pumps. This is an extreme example of wasted energy use and over-pumping. A pressure diagram of the system is shown in Figure 4, below.

[pic]

Figure 4: PA Capitol Complex Pressure Diagram

Our recommendations included removal or replacement of the building control valve stations and conversion of the system to an all primary variable volume system. The secondary pumps (288 feet TDH design) have more than enough capacity to circulate the water through the plant, site distribution, the building systems and back. There is no need for any other pumps in the system. We recommended the removal or bypassing of about 800 hp of pumping throughout the system which would result in a projected annual energy cost savings of over $300,000 per year with the existing loads and almost $100,000 per year with the projected future loads.

The Hospital for Special Surgery (HSS)

At the Hospital for Special Surgery (HSS) in New York city, chilled water is provided to the hospital from the East plant and the West plant. The East plant has two 250 ton chillers which were installed in 1995. These chillers provide chilled water for the surgical area air handling units and the patient room fan coil units. Ever since the chillers were installed, the client had complained that the surgical area was too warm. HSS contacted two major chiller vendors in an effort to solve this problem. One vendor made an impressive presentation with the conclusion that the original chillers were not big enough and recommended replacing the chillers with larger units at an estimated cost of over $600,000. At this time, the client went to another large chiller vendor for their advice. This chiller vendor hired a balancing contractor.

The report from the balancing contractor was that the air handling units were getting lower than design flow, and the cooling coils could not satisfy their loads. After finding no real solution to their problem, and living with this problem for about five years, the client hired us to examine the system. The existing system flow schematic showing our recommendations is shown in Figure 5 below.

[pic]

Figure 5: HSS – East Plant

As shown in the flow schematic above, the pumping system was all primary for the air handling units and primary with booster pumps for the fan coil units. Our analysis of the system indicated that the primary with booster pumping systems serving the fan coil units not only robbed water from the air handling units, it also created very high pressure for the fan coil units. In order to relieve this high pressure in the fan coil unit systems, the building engineer had provided a “Band Aid” solution by installing pressure relief valves and bypasses.

Our analysis indicated that the fan coil system booster pumps were not required and the pressure relief valves and bypasses were unnecessary. We bypassed the booster pumps serving the fan coils, converting the system to an all primary pumping configuration and provided equal pressure differentials to the air handling unit risers and the fan coil risers. The problem was solved, and the surgical area and patient rooms now receive adequate chilled water flow and can now satisfy their loads.

Brown University

Brown University’s original central utility system, in my judgment, was a very well thought-out system and excellent design. The central plant generated high pressure steam at 900 psig. The high pressure steam was used to produce electric power with a backpressure turbine. The backpressure steam from the turbine generator was used to make high temperature hot water (HTHW) with cascade heaters. The HTHW is distributed to the site and used in each building for heating in the wintertime and for cooling in the summertime utilizing local HTHW absorption chillers.

Over the years, due to lack of a Master Plan and without an overall system perspective, when the absorption chillers at the various buildings required replacement, most of them were replaced by electric centrifugal chillers. The conversion of these absorption chillers to electric chillers eroded the summertime HTHW demand to such a point that there is now virtually no need for HTHW during the summertime. Therefore, the backpressure steam for the power generator cannot be utilized and subsequently, the HPS turbine generator is shutdown during the summertime to avoid near continuous venting of the backpressure steam. Instead of utilizing the turbine generator to minimize the electric power purchased from the local utility company year-round, the University is currently paying higher electric bills for electric chiller operation in the summertime while the turbine generator sits in the plant severely under-utilized. Over the years, the effectiveness of this system was destroyed by replacing the absorbers without stopping to examine the overall effect these replacements would have on the entire system.

The central plant at Brown also provides heating hot water at 180(F to the Smith Swim athletic center. Since the plant is shutdown during the summertime, the athletic center has its own local boilers for summer use. Over the years, the 180(F hot water system was expanded at the Smith Swing center with very little planning. This resulted in a system with multiple expansion tanks and pumpsets. Oftentimes new pumps will be installed to serve new or renovated systems without any thought about the overall system. The project managers or engineers put on “blinders” and focus on their own project and not the overall system. As shown in the following flow diagram (Figure 6), several pumps as well as an expansion tank were removed from the existing system.

[pic]

Figure 6: Brown University – Smith Swim Center

Conclusion

Oftentimes, when portions of existing systems are retrofitted or modified, the overall system is not considered and is often neglected. This results in “Band Aid” solutions that attempt to fix local problems that can in turn cause system-wide problems which have far-ranging consequences. In extreme cases, implementation of these “Band Aid” solutions results in straying from the overall system design philosophy. It is imperative that the impact on the entire system be reviewed whenever modifications are made to the systems. Sometimes even a seemingly innocuous change to a small portion of the system may cause significant system problems. A Master plan detailing the phased system expansion, spelling out the system design philosophy and providing design standards for the future is an extremely useful tool. Facilities implementing a district energy or central distribution system must have a plan in place which is followed to ensure all future systems are compatible with the existing systems and in line with the overall system design philosophy to maximize system performance and minimize operating costs.

Hemant Mehta, P.E. is the President of WM Group Engineers, P.C., an engineering consulting firm headquartered in New York City. In his more than 25 years in the industry, Mr. Mehta has managed more than 100 central utility projects throughout the United States as well as in Germany, Saudi Arabia and Japan. His expertise is in optimizing performance and improving efficiencies of existing facilities through simple modifications. Mr. Mehta can be reached at HMehta@.

Christopher Tso, P.E. is an Associate at WM Group Engineers, P.C., an engineering consulting firm headquartered in New York City. Mr. Tso specializes in system modeling and hydraulic analysis as well as chilled water system design. He has performed system-wide hydraulic analyses for the Pennsylvania Capitol Complex, the University of Connecticut, Amgen, Foxwoods Casino, New York Presbyterian Hospital, MIT and others. In addition, Mr. Tso has completed chiller plant expansion projects for Rockefeller Center, Brown University and the College of New Jersey. Mr. Tso can be reached at CTso@.

For additional case histories and technical papers please visit our website at .

-----------------------

[pic]

Insufficient CHW flow for the buildings in this area

Building L (New)

Building C

Plant Decommissioned

New CUB

Location of New Plant

Building C

Location of Original Plant

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download