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Arden Hills – City Hall Facility Assessment Mechanical & Plumbing Narrative 4075-001-00 Part 3, Page 1 of 2 MECHANICAL & PLUMBING NARRATIVE Overview Overall, the building’s HVAC and plumbing systems appear to be in good condition for their age. Occupants have not reported excessive equipment maintenance or failures, but they have complained about uncomfortable space conditions, both hot and cold, throughout the year. Energy performance is acceptable, but could be improved. Both issues comfort and energy performance could be due to reduced performance of the condensing units as noted below and/or improper control of the HVAC system. Investigation into both of these systems is recommended. Heating System The building was designed and constructed in 2000, and presumed to have opened in 2001. Overall building area is approximately 17,390 sf. The core of the mechanical system is comprised of three air handlers and two hot water boilers located in the mechanical room on the lower level. Air handling unit 1 (AHU-1) serves the office and lobby area of the first and second floors. It is a variable-volume Trane MCCA climate changer size 017 scheduled for 9,000 cfm of air flow, 25 tons of cooling and 324,000 Btu/hr of heating. Air handling units 2 and 3 (AHU-2, 3) serve the council chambers and lower level, respectively. They are both Trane MCCA climate changer size 006 scheduled for 3,000 cfm of air flow, 9/8 tons of cooling and 118,000/98,000 Btu/hr of heating, respectively. AHU-2 is variable-volume; AHU-3 is constant volume. AHU-1 and 2 utilize inline return fans (IF-1,2) to bring the space air back to the unit. All units appear to be original. Unit heaters provide conditioning in the lower level storage rooms and cabinet heaters serve the main entry vestibule as well as the secondary vestibule at the top of the stairs to the lower level. Heating water boilers 1 and 2 (B-1, 2) are Caravan Slant Fin model GG 350 HEC, each with 285,000 Btu/h output. Hot water is distributed to the AHU’s VAV boxes, unit heaters, cabinet heaters, radiators and convectors throughout the building via two inline 50 gallon-per-minute pumps. Air-cooled condensing units 1, 2 and 3 (ACCU-1, 2, 3) serving their respective air handling unit are located outside, on grade, along the south side of the building. ACCU-1 is a Trane model RAUCC25, (25 ton nominal capacity) and ACCU-2 and 3 are a Trane model TTA 120 (10 ton nominal capacity). Capacity of the units may be reduced due to the proximity to each other and the screen wall increasing short-cycling of the surrounding air. The office and lobby areas served by AHU-1 have VAV boxes with reheat for each HVAC zone with hot water radiators below the glazing in the northwest corner of both floors. AHU-2 serves the council chambers, AV room and projector room directly as a single zone, with the council office airflow modulated via a VAV box with reheat. An independent Carrier split system cooling unit has been installed in the AV room; the outdoor unit is assumed to be located on the roof. The lower level is one single zone served by AHU-3. HVAC control system is a Johnson Controls Metasys system. Energy Usage From October 2016 through September 2017, the building consumed 142,088 kWh of electricity and 10,263 therms of natural gas for a total cost of $21,157. This equates a specific energy cost of $1.22 per square foot per