2018-425-E AMS - Sasser Companies Annex upfit

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DocuSign Envelope ID: 9826C043- 4C32- 49CD- A4CC- DC28ABAB7CE7 SECTION 238147 — DEDICATED OUTDOOR AIR SYSTEM door air shall be drawn through the bypass dampers to reduce the pressure drop of the outdoor air- stream. L. The rooftop unit DDC controller shall provide frost control for the energy recovery wheel. When a frost condition is encountered the unit controller shall stop the wheel. When in the frost control mode the wheel shall be jogged periodically and not be allowed to stay in the stationary position. 2.06 EXHAUST FAN A. Exhaust fan shall be a single width, single inlet (SWSI) airfoil centrifugal fan. The fan wheel shall be Class II construction with aluminum fan blades that are continuously welded to the hub plate and end rim. The exhaust fan shall be a direct drive fan mounted to the motor shaft. Belts and sheaves are not acceptable due to the additional maintenance. B. The fan motor shall be a totally enclosed EC motor that is speed controlled by the rooftop unit controller. The motor shall include thermal overload protection and protect the motor in the case of excessive motor temperatures. The motor shall have phase failure protection and prevent the motor from operation in the event of a loss of phase. Motors shall be premium efficiency. C. The unit DDC controller shall provide building static pressure control. The unit controller shall pro- vide proportional control of the exhaust fans from 25% to 100% of the supply air fan designed airflow to maintain the adjustable building pressure setpoint. The field shall mount the required sensing tub- ing from the building to the factory mounted building static pressure sensor. 2.07 FILTERS A. Unit shall be provided with a draw - through filter section. The filter rack shall be designed to ac- cept a 2" prefilter and a 4" final filter. The unit design shall have a hinged access door for the filter section. The manufacturer shall ship the rooftop unit with 2" MERV 8 construction filters. The con- tractor shall furnish and install, at building occupancy, the final set of filters per the contract docu- ments. 2.08 COOLING COIL A. The indoor coil section shall be installed in a draw through configuration, upstream of the supply air fan. The coil section shall be complete with a factory piped cooling coil and an ASHRAE 62.1 compliant double sloped drain pan. B. The direct expansion (DX) cooling coils shall be fabricated of seamless high efficiency copper tub- ing that is mechanically expanded into high efficiency aluminum plate fins. Coils shall be a multi - row, staggered tube design with a minimum of 3 rows. All cooling coils shall have an interlaced coil circuiting that keeps the full coil face active at all load conditions. All coils shall be factory leak tested with high pressure air under water. C. The cooling coil shall have an electronic controlled expansion valve. The unit controller shall con- trol the expansion valve to maintain liquid subcooling and the superheat of the refrigerant system. D. The refrigerant suction lines shall be fully insulated from the expansion valve to the compressors. E. The drain pan shall be stainless steel and positively sloped. The slope of the drain pan shall be in two directions and comply with ASHRAE Standard 62.1. The drain pan shall have a minimum slope of 1/8" per foot to provide positive draining. The drain pan shall extend beyond the leaving side of the coil. The drain pan shall have a threaded drain connection extending through the unit base. 2.09 HOT GAS REHEAT A. Unit shall be equipped with a fully modulating hot gas reheat coil with hot gas coming from the unit condenser B. Hot gas reheat coil shall be a Micro Channel design. The aluminum tube shall be a micro channel design with high efficiency aluminum fins. Fins shall be brazed to the tubing for a direct bond. The capacity of the reheat coil shall allow for a 20 °F temperature rise at all operating conditions. C. The modulating hot gas reheat systems shall allow for independent control of the cooling coil leaving air temperature and the reheat coil leaving air temperature. The cooling coil and reheat coil leaving air temperature setpoints shall be adjustable through the unit controller. During the dehumid- ification cycle the unit shall be capable of 100% of the cooling capacity. The hot gas reheat coil shall provide discharge temperature control within +/- 2 °F. Reece, Noland & McElrath, Inc. 238147-4 Orange County Board of Elections Orange Co., NC 05/04/18