The Board of Public Utilities presently provides District Heating service to the foundation of the customer's building and shut off valves to separate the building from the main distribution system. The building owner has the responsibility to install all necessary hydronic equipment to utility district heating. This would include heat exchanger, expansion tank, pumps, and control system. The BPU is responsible to install and monitor the BTU meter and the flow meter.
Engineering Design Criteria
- The district heating valve for each exchanger shall be located on the district return side and meet the following conditions:
- minimum turn down 30 to 1
- control valve to exceed HX pressure drop by 1 psi, but not greater then 4 psi for building heating or 5psi for district heat water, pool, etc.
- minimum inlet pressure and temperature for design of valve 232 psig/250°F.
- valve shall be capable of closing against a differential pressure of 100 psi
- valve type – two way, shall have a spring loaded Teflon V ring stem packing, shall be a single seated, plug type with a maximum leakage factor of .1% of the rated Cv
- valve shall fail in closed position for air, as is position for electricity
- temperature sensor located in district return line shall have authority, working through temperature controller, over building cooling control valve to limit district return water temperature to a maximum of 150 degree F. Unit may not be required if load is small, please check with BPU.
- The district heating water temperature leaving each exchanger shall not be greater than 150 degree F and shall be reduced by a minimum of 40 degree F from the incoming district heating water at all times.**
- A balancing valve (B & G circuit setter or equal) shall be installed for each control valve and if there is more than one control valve, another balancing valve shall be installed which is common to all control valves. The balancing valve shall be sized as small as possible using 3 ft of pressure drop across the readout ports at design flow. This will usually result in a balancing valve which is one size less than line size.
- A Y type strainer with monel screens with mesh of 1/16” opening shall be furnished and installed on the district cooling supply. This is to protect the flow meter for the BTU meter and the exchanger, if used.
- A plate and frame type unit shall be used. The following shall apply:
- Gasket should be peroxide cured (peroxide vulcanized material); nothing else should be acceptable.
- Gaskets should be crush proof at all temperatures within their operational range.
- Gaskets should not have more than 50% change in hardness when exposed to liquids at 212 degree F or a change in volume more than 10% when exposed at liquids at 212 degree F.
- Exchange plates shall be a minimum of .8 mm thick.
- Plate HX shall be design for 300 psi/350 degree F.
- Use a fouling factor = .0005 ftsqhrdegree F/BTU or 20% over dimension for building heating units, do not use plate type units for domestic hot water applications unless a water conditioner is installed.
- Each heat exchanger shall be designed for 350 psi/340 degree F on the district heating side, except as noted. Use a fouling factor = .001 for U tube type units.
- Pressure drop through exchanger shall not exceed 3.0 psig on the district side.
- The district heating piping and valves supplied by the owner shall be designed for 232 psi/250 degree F.
- Pressure gauges, valves and thermometers shall be provided generally as shown on Service connection Detail Drawing.
- The district heating piping and valves shall be 1.5” insulation for pipes size 2” and less, 2” of insulation for pipe sizes over 2”.
- Building Owner’s engineer shall submit to the BPU the maximum pressure drop that will occur in the building Owner’s district supply and return piping prior to installing the system
- The BTU flow meter must be installed with straight pipe upstream and downstream of flow meter. Length of strength pipe needed to be provided by the BPU
- Contractor shall test district cooling chilled water supply and return piping at 350 psig for a minimum of one hour and until all joints have been inspected
- Contractor supplied pipe is to be schedule 40 black steel; above 2” – weld, up to 2” – weld or screw. Use schedule 80 pipe if using screwed joints.
- Contractor may have to supply 150 lb flanges for flow meter, BPU to provide direction. Contractor to provide and install with a spool piece. Install BTU sensors in elbow facing into flow of water. Hydro prior to flushing lines.
- Owner/engineer to submit design calculations and proposed equipment cut sheets to the BPU for approval prior to hook up. It should be noted that designing the building heating heat exchanger for a 150 degree F return water temperature will result in a saving on the heat exchanger cost.
** If cascaded heat exchangers are use, this item shall apply only to the last downstream heat exchanger.