Replacement of HVAC Systems

O’Brien & Gere was retained by Cayuga County to replace the heating, ventilation, and air conditioning systems at the historic Cayuga County Courthouse and, in the course of replacing these systems, to identify and provide an abatement plan for asbestos-containing materials. Constructed in 1830 as a two-story building, the Main Courthouse was expanded in the 1880s to add a three-story annex to house the Police Department, District Attorney’s office, and other occupancies. In 1922, a severe fire resulted in the rebuilding of the Main Courthouse structure. At that time, a third story was added.

Background information on the courthouse indicated that the air conditioning equipment was approximately 21 years old, with two systems being older than 21 years. The cooling equipment had been in service beyond the median value of its estimated service life. Some terminal heating equipment was the same age as the air conditioning systems. The boilers, most of the heating piping, and some terminal heating equipment, were estimated to be at least 70 years old. The purpose of this project was to replace the existing equipment and systems with a functional, reliable system that is energy-efficient and economical to operate.

The principal design challenges were:

• Completing the renovations cost-effectively, given the physical restrictions of the building, which is massive and constructed of a variety of materials (stone, concrete and brick), in several architectural styles, with hip roofs, and walls and floors over 3 ft thick in some areas
• Accomplishing the work while the building is in partial use by the public on a daily basis
• Preserving the historic nature of the building and the surrounding site, by minimizing the architectural impact to the building for usage and aesthetics

Based on previous experience and known facts, O’Brien & Gere initially selected a water source heat pump system, based on its high energy efficiency, minimal architectural impact to the building, zoning flexibility, and simple, expandable controls. This recommendation required confirming five critical conditions:

1. that the building structure and architecture allowed installation of the new equipment and piping
2. that the gas and electric service had sufficient capacity for interconnection to the heat pump system
3. that there was adequate space for a central ventilation air handler and distribution ductwork
4. that mechanical exhaust would be provided for toilet and janitor rooms that don’t have it, and
5. that an implementation scenario could be developed that would minimize impact to the building occupants and meet budget constraints

O’Brien & Gere then conducted a site visit to assess capacities of existing equipment, verify equipment locations and zones, and evaluate space limitations for equipment and water loop installation. The assessment confirmed that boilers and associated piping systems were in poor condition, in some cases corroded; existing exhaust equipment and ductwork was in fair and serviceable condition; many incremental, through-the-wall units, and unit ventilators equipped with steam heating coils were inoperable. Many of these units also had leaking heat control valves, causing overheating. The ventilation air flows, as originally designed, no longer complied with Building Code requirements. Outside air for ventilation was supplied through unit ventilators for the courtrooms and interior occupied spaces in the Annex, but many of these units were not in service. Some windows could be opened to supply natural ventilation to supplement the mechanical ventilation.

Once the existing boilers were removed, the boiler room would have enough space to add new hot water boilers, heat rejection equipment, and main circulating pumps. Adequate space existed in the main building basement as well, for equipment and ductwork. However, due to the massive construction of the building, and the thickness of walls and floors, access for placement and areas for routing ductwork to different floors did not exist. Attic areas of the main courthouse and Annex buildings also had large areas to locate air handling equipment, but limited openings for equipment placement and service. Vertical routing of ductwork was limited to a few chases. Steam and condensate piping would need to be removed to provide a clear path for new heat pump water piping.

Preliminary HVAC load calculations were performed to verify the capacity of the heat addition and rejection equipment for use in a heat pump system. Heating and cooling loads for each building space were calculated, taking into consideration additional glazing and ventilation airflow, which would significantly increase building loads.

The findings of the site assessment and the preliminary HVAC load calculations confirmed the selection of a water source heat pump system. The heat of lights and people in the building would be reclaimed in the loop and used to heat the building exterior and ventilation air. The main piping would be uninsulated supply and return pipe. The only other possible alternative system (given the massive building construction) would be a four-pipe fan coil system with a central chiller and boiler. In this case, the main heat and chilled water lines must be insulated, which would more than double the cost of piping installation. There is no heat reclaim available with a fan coil system. Therefore, the water source heat pump system was concluded to be the most economical and was recommended.

Conceptual Design

O’Brien & Gere prepared the conceptual design for the new HVAC system as follows:

Conceptual Zoning
Individual zones for the heat pump system will be provided for each occupiable space and typically include one room sensor or thermostat per zone. Interior corridors and waiting areas will be cooled as individual zones. Toilet rooms will be heated with electric wall heaters and not air conditioned. The second and third floor courtrooms (which have perimeter steam heat) will have hot water radiant panels to supplement the horizontal, ducted heat pumps serving these spaces. Condensing units will be removed from the main Courthouse roof and the roof patched to match the existing roof. Central air handlers, located in the attics, supply ventilation air (heated and cooled with a glycol coil) to most areas of the main Courthouse and Annex. A new dormer will be constructed on the Annex roof to provide access and ventilation air for the building. Heating and cooling energy for the unit and supplementary heat for the courtrooms will be generated with water-to-water heat pumps. Additional exhaust systems will be installed for toilet areas and for building air balance.

Heat Pump Placement
Heat pumps will be located above the suspended ceilings. These units will serve interior and courtroom areas now served by unit ventilators. Console, floor-mounted, heat pump units will be placed in perimeter spaces beneath windows and outside walls and in interior corridor areas.

Closed Water Loop System
Closed water loop equipment, pumps and controls will be located in the existing boiler room. The existing boilers will be replaced by two or more smaller gas-fired boilers. A fluid cooler will provide loop cooling. Closed water loop pipe routing will reuse the existing pipe tunnel and basement areas, with supply and return main piping installed around the building perimeter with individual branches to core and perimeter heat pump units.

Asbestos Abatement
Materials found to contain asbestos included the following:

• flooring throughout much of the building
• boiler and piping system insulation primarily in the boiler house, basements, and attics
• insulation debris associated with damaged insulation
• HVAC piping wrap in the main courthouse attic, and
• acoustical blankets above the suspended ceilings of two courtrooms.

As part of this project, it was recommended that damaged pipe insulation and debris in the main building attic be removed, as well as asbestos-containing materials in the boiler house, tunnel and crawlspaces, basements and Annex attic, and above the suspended ceilings of the two courtrooms (total approximately 29,000 ft2). Such removal could be accomplished relatively cost-effectively as the HVAC work is performed in these areas. Undamaged asbestos-containing flooring, pipe insulation within walls, and pipe insulation in the main building attic could be left in place, except for removals necessary to accomplish the HVAC work.

A two-year, phased construction period was anticipated for installation of the complete heat pump system in a modular fashion to minimize disruption of building occupants and activities.