The landmark Sage-Allen department store building was constructed in the 1800s as the first department store in Harford, CT. Over the years, it has been an historic part of downtown.
Its location, however, made it ripe for an improvement. Using that landmark building as an anchor, 18 Temple Street LLC decided to build loft apartments, townhomes, and a parking garage — all three of which required a different mechanical solution.
To handle this triple threat, the construction manager for the project, Bartlett, Brainard & Eacott, issued a request for Design/Build proposals to a select list of mechanical contractors. The RFP had an outline spec with some suggested HVAC systems. The bid also allowed for alternative systems proposals from the Design/Build contractors.
EMCOR Services/New England Mechanical, and sister EMCOR company, Tucker Mechanical, both recieved an RFP, and decided to partner and submit a single Design/Build proposal.
Initially, the EMCOR project team responded with just an HVAC system proposal — the unique nature of its proposed valance system design intrigued the construction manager and the owner.
EMCOR Services/New England Mechanical also prepared a preliminary operating cost comparison between a water source heat pump system and the proposed valance system. The analysis showed that even when excluding the electrical costs for each apartment’s water source heat pump compressor and fan, the valance system’s total energy and maintenance costs were projected to be less than the water source heat pump system.
The combined project team was awarded the plumbing, fire protection, and HVAC systems under a Design/Build contract.
EMCOR Services/New England Mechanical provided the design and engineering for the plumbing and HVAC systems, and was also responsible for the HVAC air-side systems and automatic temperature controls installation. Tucker Mechanical was responsible for the plumbing and HVAC water-side system installation, as well as the design and installation of the fire protection systems.
In addition to the tight urban site, significant aesthetic considerations created an overall project design challenge. The project consisted of three different occupancies, each requiring a different mechanical solution — the loft apartments, the townhouses, and the parking garage.
Rapid and significant cost escalation was experienced in materials and equipment between the time the proposal submission and when construction began. Working cooperatively with the construction manager and the owner, minor modifications to the project scope were allowed, in order to reduce the impact of the cost escalation. Construction of the mechanical systems for the loft portion began approximately six months after originally scheduled. Furthermore, the design did not allow for the construction of the townhouse portion until the parking garage had been completed — and the project completion date could not be extended.
“Design-wise, the loft apartments had significant constraints for the HVAC system,” says Dana Finnegan, president of EMCOR Services/New England Mechanical. “The building owner’s desire to maintain the existing Sage-Allen building facade for the new ‘bookends’ created large window areas with predominately eastand west-facing exposures.”
The deep apartments — 40 and 50 ft. in some cases — with narrow exposures, created narrow- feeling spaces that made for diverse thermal zones between the interior and exterior rooms.
The original Design/Build RFP required a separate air conditioning zone per apartment, and prohibited packaged units or through the wall air conditioning units, due to aesthetic concerns. EMCOR Services/ New England Mechanical believed any single system serving both interior and exterior spaces would not provide a uniform level of comfort in all spaces of the apartments.
With the comfort and maintenance issues in mind, EMCOR Services/New England Mechanical recommended a valance heating and cooling system to serve the entire perimeter of the building, and a dedicated outdoor air make-up air unit with a heat recovery wheel to condition interior spaces and provide mechanical ventilation to each apartment.
The valance heating and cooling system consists of a coil installed within an insulated metal cover mounted approximately 12-in. down from the ceiling, and 12-in. away from the exterior window covering or wall. This type of system conditions the space without the use of a fan, depending soley on natural convection to heat or cool the space.
The townhouse units are heated and cooled with packaged rooftop units to eliminate the need for the air handler closets, refrigeration piping, and flues that are typically required for townhouse split system air conditioning systems. The parking garage is ventilated by a variable volume exhaust system. Outdoor air is introduced from one end of the garage and exhausted at the remote other end of each parking level.
EMCOR Services/New England Mechanical’s valance system design provides each loft apartment perimeter room with its own independent section of valance and thermostat. A direct digital control (DDC) space thermostat controls a twopostion control valve for each of the approximately 160 valance sections.
“The valance system design and installation requires very close coordination,” Finnegan says. “Each valance section is custom-designed and selected for each room. To further compound the coordination issues on this project, the Sage-Allen building has varying glazing amounts on each floor. Therefore, there was not a typical floor with regard to the valance sizing. Each valance section required a unique label or tag.”
Each valance section had to be checked in the field to ensure the correct section was installed in the correct location — with more than 160 sections of valance — provided a daunting task for the Design/ Build team.
During the design phase of the project, it was decided to purchase a pre-fabricated mechanical penthouse to house the HVAC boilers, pumps, remote chiller barrel, and domestic hot water heaters. The penthouse was conceptually designed by New England Mechanical, with the final detailed layout by Epsilon Industries.
Air Quality and Efficiency
The constant volume ventilation system consists of a heat recovery unit on the roof. Fresh air is conditioned by a combination of enthalpy heat recovery wheel, direct expansion cooling coil, condenser reheat coil, and a natural gas burner for winter heating.
The unit is controlled to reset the leaving air temperature and leaving dew point based upon the ambient conditions and the space exhaust conditions. The conditioned ventilation air is ducted down through the building and distributed to each apartment.
Commissioning Made Easy
The valance system of the loft apartments was easy to commission, due to its simplicity. The packaged penthouse came with a progammable controller for control of the boilers, pumps, and chiller.
The controller was factory-programmed, supposedly in accordance with design sequence of control. During the commissioning, however, it was determined that the boiler control logic could cause accidental boiler trips and not properly sequence the boilers.
In addition, it was determined the scale for the pressure sensor used for the pump differential pressure control did not match the controller in the penthouse. All of these items were corrected by EMCOR Services/ New England Mechanical, and the systems have performed very well since.
The townhouse units were finished and turned over in groups for occupancy, with the thermostat for each unit located on the first level. When the first few units were turned over during a severe cold spell, it was discovered that the rooftop unit gas burners were shutting down on a high temperature limit.
After both weather stripping and wall insulation were installed, the space temperature equalized between the lower and upper floors, and the high temperature limit problems went away.
The parking garage, essentially below grade and capped with the townhouse plaza, eliminated the potential for any vertical ventilation. The exhaust fans were installed flush with the interior garage wall and extended into the exhaust areaways.
The solutions provided by EMCOR Services/New England Mechanical for all three facets of this project — the loft apartment, the townhouses, and the parking garage — are an outstanding example of how the Design/Build process can work.
The successful delivery of this project has taken into consideration the owner’s schedule and budget, as well as energy efficiency and ongoing costs to maintain.