HVAC Hydronic (chilled water) system

HVAC Hydronic (chilled water) system

  • Chilled water system shall be selected based on a 7 °C ±1 °C delta T operating temperature.
  • Chilled water return temperature shall not be greater than 13 °C ±1 °C.
  • Chilled water piping 50 mm (2 in.) diameter and above shall be sized for 1.2 to 2.1 m/s velocity maximum. Pipe under 50 mm (2 in.) diameter shall be sized for a 1.2 m/s velocity maximum.
  • Energy conservation systems are preferred to be utilized in refrigeration system to minimize the overall power consumption such as chilled water storage tank, variable refrigeration system,…etc.
  • Flow rate of chilled water from air cooled water chillers shall be efficient to allow an economical selection of heat transfer equipment. Chilled water pumps shall be provided to ensure a suitable circulation of chilled water between the water chillers and heat transfer equipment.
  • Pumping system configuration shall be selected based on life cycle cost analysis comparing primary variable pumping arrangement against primary-secondary pumping.
  • Chilled water pumps shall be upstream of chillers. An expansion tank shall be connected to the chilled water pump suction line. Chilled water systems shall be equipped with sight glass to provide indication of system water level. System shall be arranged for complete drainage, with drain valve at low point. Chilled water systems shall include water sample line connection, and another for adding chemical to the chilled water system.
  • Variable or constant chilled water pumping system shall be selected to conform with space/zone cooling  and  heating  load  profile.  Comparisons  between  different  pumping  configurations (primary variable  or  primary-secondary …etc)  to  select  optimum  pumping  layout.  Variable frequency drives shall be used as part of the system to modulate the chilled water rate load based on the space/zone load change.
  • Chilled water piping shall be in accordance with ASME B 31.9.
  • Chilled water piping shall be carbon steel insulated and covered with aluminum jacket. Copper tubing may also be used in small branch lines. Potable water shall be used for chilled water system.
  • All chilled water piping systems shall include a valve, potable water quality, make-up water connection. In addition to the shut-off valve, the make-up water connection shall include a reduced pressure type backflow preventer.
  • Connection between equipment and supply and return mains shall be flanged in sizes above 2 in. Connection 2 in and smaller shall be screwed.
  • Flexible connection shall be installed between rotating equipment and stationary element of the building to prevent the transmission of vibration.
  • Balancing valves shall be installed in the discharge of each water coil downstream of the control valve when 2-way control valve is used for variable water chilled system. When 3-way valves are used, there shall be a balancing valve in the bypass line. Isolation valves shall be installed on water supply to and return from coil. Manual bypass valves shall be provided around control valves and flow meters.
  • Pressure gages or gage cocks shall be installed on supply and return pipe branch to each water coil, control valve, pump, and flow meter. Thermometer wells (or insertion tap points) shall be installed on incoming supply pipe and on return pipe from each coil. Pipe strainers shall be installed immediately before flow meters and flow control valves. Valve flush connections shall be provided on supply and return pipes of chilled water cooling coils.
  • Dissimilar metal piping connections, for example valve connections, shall be  exposed and accessible, and shall be provided with insulating unions or insulating flange sets.
  • Relief valves shall be provided to protect chilled water systems. Relief valves shall be located downstream of pumps.
  • For each pump, a serviceable strainer shall be provided on the suction side, and a check valve on the discharge side.
  • A check valve shall be installed in the discharge line of each centrifugal and rotary pump. In services where hydraulic shock can occur, the check valve shall be of the quick response or non-slam type. Connection between equipment and supply and return mains shall be flanged in sizes above 2 in. Connections 2 in and smaller shall be screwed.
  • A block valve shall be provided in the suction and discharge side of each pump. The block valve on the suction side shall be located upstream of the serviceable strainer, and the block valve on the discharge side shall be located on the downstream side of the check valve.
  • Suction lines shall be designed to avoid pocketing of vapor or gas. Reducers in horizontal runs and at horizontal pump suction connections shall be eccentric with straight side up. A concentric reducer shall be used if the reduction occurs immediately adjacent to elbow on downcomer from overhead. Where practical, long radius reducing ells shall be used for carbon steel classes.
  • Elbows in horizontal suction piping to double suction pumps (split case) shall be at least 5 pipe diameters upstream of the pump suction flanges with the following clarification
    1. Where no reducer is employed between the pump flange and elbow, a straight run at least five pipe diameters long shall be provided.
    2. Where a reducer is located between the pump flange and the elbow, a straight run of at least 2 pipe diameters long (based on the larger pipe diameter) shall be provided. In effect, a reducer next to the pump flange shall be considered to be equivalent to 3 larger diameters.
    3. When a positive displacement pump is not equipped with a built-in relief valve, a relief valve shall be installed in the discharge piping between the pump nozzle and first block valve, and shall usually discharge into the pump suction line. In services where a serious heat build-up can occur at the pump during blocked discharge, or where the pressure breakdown will liberate gas, the relief valve discharge line shall be installed to relieve to a suction source, for example a tank or accumulator.
  • Centrifugal pump suction and discharge valves shall be sized as follows:
    1. Suction valves shall be full line size
    2. For line sizes 8 in and larger, check valves and discharge block valves may be a maximum of one size smaller than line size. For line sizes less than 8 in, the valve shall be line size. In no circumstances shall the valves be less than pump nozzle size.
  • Jacket and seal cooling water, packing flush, and similar flowing fluids from pumps, shall be piped to open drain funnels or into closed drains. They shall not be discharged onto pump bases. Drain piping and valves shall conform to the applicable line class specification.
  • A chemical treatment system shall be provided for the chilled water system. Closed chilled water systems shall be treated with a corrosion inhibitor, except where chemical costs due to water leakage rates are estimated to be higher than equipment life cycling costs. This corrosion inhibitor shall be a buffered, nitrite-based product, with sodium nitrite residual in the range of 700 to 1200 parts per million (ppm), or molybdate in the range of 250-350 ppm; both with a pH of 7 or higher. Chilled water shall be at least 10 percent glycol by weight. Chillers and coils shall be derated to reflect the addition of glycol.
  • Vibration spring isolators with defined deflection rate shall be installed per selection guide of vibration isolation in chapter 47 of ASHRAE HVAC Applications handbook or per manufacture recommendations.
  • See Piping and Equipment Insulation for chilled water piping materials, insulation and accessories.

 

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