Green Solutions: Hybrid Chiller Plant Meets The Needs Of An Evolving Building

By Anne Cosgrove

Published in the March 2006 issue of Today’s Facility Manager

With electric capacity in Boston’s McCormack Building maxed out and utility rates rising, Bijan Mohammadipour, principal engineer for Massachusetts’ state office buildings, looked to improve the HVAC system. The installation of a hybrid chiller plant has lowered costs, reduced electric consumption, and improved occupant comfort.

Bijan Mohammadipour, principal engineer, State of Massachusetts

What is your position?
I am principal engineer for the Bureau of State Office Buildings (BSOB) for the Commonwealth of Massachusetts. Primarily, I have been managing all technical projects and HVAC operation of BSOB buildings for 20 years.

Please give a brief description of the facility involved in this project.
The department manages six buildings, four of which are in downtown Boston, including the historic State House. The McCormack building is 22 stories high, occupying 660,000 square feet.

What defines the green philosophy your organization would like to convey?
Understanding that we primarily manage buildings ranging in age from 35 years to more than 200 years, our green goals can not be as ambitious as we would like. Therefore, at every opportunity we aim for improvements.

From our experience, we have come to realize that, in the long term, the overall success of any project is dependent on achieving a sensible balance between cost, comfort, energy efficiency, and environmental concerns.

Why was the decision made to pursue this project for the facility?
The decision was prompted by the lack of adequate cooling capacity. Over the years, the whole character of the building had changed due to a number of factors. The electrical system was originally designed with steam-absorption systems, so the electrical capacity was less than it would have been had the building been designed for electric-drive chillers. The addition of electric-drive chillers in the 1980s to replace the original steam system, coupled with office automation and increased occupancy, resulted in a much higher electrical demand in a building designed and built based on 1975 standards.

At the same time, we faced an ever increasing cost of purchased steam for heating. In order to finance the heating and cooling project, we created a design-build performance contract, whereby the savings from the utility usage reduction financed the cost of the project. By converting from purchased steam to a fully automated heating and cooling plant and installing AERCO gas-fired high efficiency condensing hot water boilers with VFD hot water pumps, we generated a savings of over $500,000 dollars per year.

Please describe the decision making and research process for the facility.
Since we had neither the budget nor a practical way to increase electrical service into the building to operate all three chillers at the same time (let alone adding a fourth electric chiller to the load), we considered a steam absorption system only to find that it was not a viable solution. This was due to the high cost of purchased steam as well as having to cool down the steam condensate and discharge it into the sewage system. This led to the decision to use gas as the energy source for cooling.

Thus, the solution was to add two 400-ton, gas-drive absorption chiller-heaters from YORK.

At this point, we had two 450-ton electric centrifugal chillers, along with a newer 450-ton electric variable speed chiller. Because of the power limitation, we could only run two chillers at a time. So total available cooling capacity was 900 tons; however, the building load was nearly 1500 tons.

Next door, in one of our other buildings, a major renovation project had started, and the existing chillers in that building were to be scrapped. We seized the opportunity and replaced the two old 450-ton chillers in the McCormack Building with the newer CFC-free electric chillers (a 550-ton and a 650-ton). We kept the newer 450-ton electric variable speed chiller.

While the project didn’t increase electrical power capacity, it did increase cooling capacity.

The hybrid chiller plant enables us to switch between electric and gas according to utility rates. The demand cost is high in the summer for electricity especially during peak periods, and we can run electric chillers off peak when rates are lower. Before the peak starts, we put the gas-fired chillers on.

What was the vendor selection process like?
For this particular project, we put out a request for proposals (RFP) for a design-build contract. In the RFP, we specified our conceptual design with an intended savings of $500,000 per year.

The proposals had to identify the vendors and the type of equipment. A prime requirement was the equipment meet the rebate programs of our utility companies. The equipment also needed to be CFC-free and have the capability to communicate with our energy management system. There were also weight limits, because our mechanical room is located on the 22nd floor.

J.F. White Contracting Co. in Framingham, MA, was awarded the contract. The designer on the project, as part of the J.F. White team, was VAV International, Inc. located in Woburn, MA.

What was the reaction of upper management to the decision to embrace the principles of sustainable design?
Our high ranking managers and commissioners have been very supportive. The Division of Capital Asset Management has formed a team, with John DiModica as program manager, to review each project for inclusion of sustainable design concepts to the extent possible.

What economic benefits have you reaped as a result of this project?
The annual savings have been approximately $530,000 in utility costs. That figure increases when adding a savings of approximately $2 million in outside contractor manpower and maintenance and operation reductions.

What were some of the challenges?
One of the most challenging aspects was finding an uninterrupted vertical space to bring in a 6″ wide natural gas line from the street up to the mechanical room. There was no room in the building core. Ultimately, the mail chute, which runs along the core, was converted into a chase for the gas line.

As a green project, did this project cost more, less, or the same as a standard project of the same size?
The total project cost was $5.3 million. This included changing the entire heating system, the domestic hot water system, and the cooling system. We also added automation.

Our typical process (study, design, advertise, and construction phases), as opposed to the design-build project, would have taken three times longer. Another benefit of the design-build process was absence of potential change orders, since the contractor and the designer were on the same team.

Mitigating the costs were rebates from NSTAR and Keyspan, the local electric and gas companies, totaling over $250,000.

What has been the reaction to the project inside your organization?
It has been very positive. As the system was tweaked and balanced, the complaints decreased from 15 to 20 per week to one or two per week.

Why should facility professionals consider green solutions?
Facility professionals need to look at their buildings within a different context than they did in the 70s, 80s, or even early 90s. You can’t keep repeating the same types of projects.

What was the most professionally rewarding aspect of this project?
For my team, and me it was rewarding to witness our concept become reality in less than a year. It would have been extremely tough without the support of Vincent Cirigliano, first deputy superintendent of planning and engineering of BSOB, and John Killelea, our senior mechanical engineer. Tess Francisco with the operational services division and John DiModica were also greatly instrumental in this project.

Questions about this project can be sent to Bijan Mohammadipour at