Sometimes the best measure of a successful Design/Build project isn't found in a sophisticated software analysis or energy certification, but rather in the tenants' signatures on lease renewals. That was the happy result that EMCOR Services New England Mechanical, Vernon, CT, was able to provide for the Hampshire Companies, owners of an 11-story, 230,000 sq.ft. office building in Bridgeport, CT.
The Hampshire Companies purchased the building, known as 1000 Lafayette, in 2006. The need to upgrade the building's 17-year-old HVAC system soon became apparent, as tenants were beginning to report comfort issues throughout the building. As the leases for several of the building’s major tenants neared renewal, they asked the Hampshire Companies to provide assurances and evidence that the comfort issues were going to be addressed before they renewed their leases.
The Hampshire Companies consulted with two engineering firms, both of which recommended extensive changes, including replacement of the existing chiller plant. This option would require significant disruption in the building's operations, which now extended well beyond the original "weekday 9 to 5" design assumption. Curt Hurst, the Hampshire Companies' account director, turned to Contracting Business' 1998 Commercial Contractor of the Year, EMCOR Services New England Mechanical Services Inc. (NEMSI).
NEMSI had recently provided a mechanical infrastructure upgrade for another building owned by the Hampshire Group, and had completed many renovations for 1000 Lafayette’s previous owner. Based upon his company’s positive experiences with NEMSI and their familiarity with this building, Hurst asked NEMSI for recommendations.
"We provided the Hampshire Companies with a holistic approach to overcoming the problems at 1000 Lafayette," says Roderick Dapkins, P.E., NEMSI's vice president and general manager.
The original chilled water plant design consisted of two single-compressor, nominal 255-ton screw chillers and 24 thermal storage tanks. On weekdays, the chiller plant was designed to melt ice and produce chilled water from 8:00 a.m. to 10:00 a.m.; melt ice from 10:00 a.m. to 6:00 p.m.; and produce ice the rest of the time to recharge the tanks. However, the system was continually running out of ice, forcing both chillers to operate during peak electrical demand times.
First Step: Full Review of Building Operations
NEMSI surveyed the building's electrical and mechanical systems, monitored the building's conditions and operations using a monitoring system, and reviewed the building's energy consumption for the prior three years. As a result of this comprehensive review, NEMSI's team discovered several issues, including unbalanced make-up air for the first floor restaurant kitchen, variable air volume (VAV) terminal unit control problems, and lack of cooling in perimeter zones because of air leaks in the medium-pressure spiral duct and air handling units’ discharge plenums.
NEMSI ran cooling load calculations and determined that the existing screw chillers in the chiller-only operation couldn’t carry the load on most days, let alone design days. In addition, NEMSI's team found that many of the existing air terminal unit controllers weren’t working.
"We recommended retro-commissioning the VAV terminal units before we made a final decision on the chiller plant sizing," Dapkins says. "Once the retro-commissioning and subsequent VAV terminal repairs were completed, the building load appeared to fall in line with our calculated loads. More importantly, the retrocommissioning dramatically improved tenant comfort and energy efficiency."
Recommendations for Max Efficiency
After a detailed analysis of options, NEMSI's team recommended replacing the existing screw compressor with three oil-free compressors, and adding a chiller control on each existing chiller. This proposed system would maximize the chilled water production capability of each chiller bundle, and increase reliability dramatically. Even if a single compressor failed on a chiller, the remaining compressors would be able to provide slightly more than 200 tons of capacity due to the increased heat transfer available to the two compressors.
NEMSI's system design also included the installation of variable frequency drives for the building's distribution pumps. The building's original system was designed to simply ride the pump curves. By installing variable frequency drives on each pump, NEMSI’s design allows for the pumps to be staged on and off, or to be synchronized and function as one large pump.
Repair to VAV Terminal Units
NEMSI's crew surveyed the building’s 270 VAV terminal units and repaired 179 of them during normal business hours without disrupting the building' operation. The problems with the terminal units typically included calibration errors, failed DCC controllers, and jammed dampers. In addition, leaks in the spiral duct system and air handling units' discharge plenums were methodically located and repaired. Both of these steps enabled NEMSI to eliminate comfort problems in the building and reduce overall chilled water demand.
Simple Solution to Infiltration Problems
The kitchen make-up air unit for the restaurant located off the building's lobby caused extreme infiltration problems, and the lobby was never able to reach a comfortable level of warmth in the winter. After reviewing the make-up air unit, NEMSI found it to be perfectly functional, yet delivering much higher CFMs than necessary. NEMSI was able to effect an immediate improvement in comfort in the lobby by merely slowing down the supply fan. As a bonus, this also solved a major noise problem in the restaurant and kitchen.
The combination of retrocommissioning, duct leak repairs, and the retrofitted chilled water system brought about major improvement in energy savings. According to NEMSI, based on the first eight months of 2009 (of which the retrofitted chiller was only running from late April through August), the Hampshire Companies saved approximately $42,000 in electrical costs in the chiller plant alone.
"This project is a 'poster child' for how to holistically improve a building: scrutinize the building's existing operation, understand its issues and problems, apply methodical retro-commissioning to make sure the building systems are operating properly, and then upgrade the infrastructure using sound but creative engineering solutions," Dapkins says. "This project was a success because it kept the building fully operational, greatly improved the tenants' comfort, reduced operating costs, and improved the cooling system's reliability."
It was also a success in the most practical and important of ways to the building owner: all the tenants renewed their leases.