2019-12-03-PBC-min - Laserfiche WebLink

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A cfiscuss0on was Aso hdd based on the wO fidd desogn and capacoty. A rnerno was re0ewed that S11MA/ed 30 Wells With a load of 28 tons. It Was stated that at 5(.0' We should 1,,..)e designing at 3 tons per wO. Thus Iead to a cfiscussuon that we may be aUe to reduce the number of w0s by hAf thus akWng for the costs between the 2 system to be negVogUe. See below for Clarifications from 1213 meeting with regards to the Geothermal System. Fhe next secflon of thus document darffies and detaoVs the approach and process for the cornpVoance woth the Red Lost and on finAzong a system sdecflon for the I]VAC equ#-nent. Geothermal Summary *Pending review of well data from Hastings school and confirmation on well design loads the Permanent Building Committee (PBC) approved the design team to proceed with the following recommendation (PBC final recommendation scheduled at the next meeting on 12/12/19: This also requires o recommendation to the Board of Selectmen (BOS)for final approval on 12116119 The committee tentatively approved to move forward with the air source VRF and to utilize a responsible portion of the difference in cost for Geothermal for appropriate resiliency considerations to the design, electrical system and HVAC system. Additional information required for a final decision to be rendered are as follows: 1) —Town of Lexington to get the design team data on the Hastings School geothermal capacity and efficiency. 2) — New Ecology to clarify the Life Cycle duration used to calculate the cost comparisons between air source VRF and GSHP. 3) — New Ecology to generate a comparison of capital replacement costs over the life expectancy of the geothermal well field. 4) — Design team to is generate a list of comparisons on the two systems with regards to their intrinsic resiliency characteristics. It was noted that both systems will meet and /or exceed the Town of Lexington sustainability standards and that the determination for selection is predominantly based on resiliency and cost. Clarifications from 12/3 meeting with regards to the Geothermal System Geothermal well field capacity and design. It was stated by the design team that the well field is comprised of 30 wells at 28 tons. The potential to reduce the well field by half was discussed based on the presumed design capacity of the Hastings School at 3 tons per well instead of 2 ton as noted in the Police HQ narrative. This was not a correct statement. Matt S clarified with the Engineer of Record (EOR) that the designed cooling load for the building is 68 tons and the heating load is 78. This would equal approximately 2.5 tons per well. Pending a test well to prove the potential well field's efficacy we cannot come to a final determination of how many wells may be eliminated. However, the EOR stated that at best, and under ideal circumstances, we may be able to eliminate 1 or 2 wells. That would not equal the savings needed to level to initial costs for geothermal versus air source VRF. PBC Meeting 12.03.19 5