23 57 00 HEAT EXCHANGERS FOR HVAC

.01 Owner General Requirements

1. Summary:  Section includes requirements for shell-and-tube andplate type heat exchangers in HVAC applications.
2. General Requirements:
1. Professional shall design each heat exchanger application for optimal operating efficiency, reliability, flexibility, and ease of maintenance with the lowest life cycle cost. 
1. Design for efficient and stable system operation:  Professional shall determine the anticipated minimum and maximum loads for each system and evaluate most appropriate number, combination and arrangement of exchangers for optimal system efficiency and stable operation over entire operating range.
1. In variable flow pumping systems, minimum velocities to avoid laminar conditions to maintain adequate heat exchange capacity shall be maintained with minimum anticipated hydronic system flows.
2. Maximum velocities shall not be exceeded to avoid erosion of tube surfaces.
3. Ensure only dry steam enters the control valve and heat exchanger inlet to avoid water hammer or damaging tubes due to wet steam impingement.
2. Reliability/Redundancy:  Professional shall determine the consequences of system failure and provide for adequate system redundancy for each application.  
1. Install fully redundant (N+1) stand-by units for extremely critical applications (such as critical research laboratories and computer centers) and/or as otherwise defined specifically in the Owner’s Project Requirements. 
2. For non-critical applications (such as general office spaces, general purpose classrooms, general commercial type spaces) full redundancy/complete standby is typically not required.  In such cases two (2) units in parallel, each sized for a minimum of approximately 75% of maximum load may be considered.  This arrangement offers greater flexibility and turndown and still provides majority of capacity when one of the units is out of operation for any reason.
3. On applications with a single heat exchanger assembly, install a manual bypass assembly with globe valve around the temperature control valve(s) and strainer to allow emergency servicing of control valve(s) or strainer without complete shutdown.
3. Flexibility: Consider potential future expansion. Extent of expansion will be determined on a case-by-case basis. Consult with the University Project Leader and Engineering Services.
4. Controls: 
1. Select arrangement of control valve(s) for each heat exchanger for most appropriate turndown for anticipated operating range.
2. Coordinate control devices and operational sequences with Section 25 00 00 INTEGRATED AUTOMATION and 25 90 00 GUIDE SEQUENCES OF OPERATION
5. Maintenance:  
1. Locate in safe and convenient area and provide convenient means for frequently inspecting and cleaning.
2. Provide valves and bypasses in the piping so unit may be bypassed when required to permit isolation for inspection and repairs with interrupting main systems.
2. Equipment Layout:  
1. Comply with all Space Planning Requirements indicated in 01 05 05.02 Planning for Engineered Building Systems.  
2. Maintain minimum recommended service clearances of 36” around service ends of heat exchangers and 24” in general. 
3. Maintain minimum clearances for tube pull and/or cleaning of tubes as recommended by the equipment manufacturer, typically no less than the length of the heat exchanger.  
4. Coordinate structural reinforcements and other provisions for rigging of tube bundles for future removal and replacement.
5. Dimensions, sizes, weights and locations of heat exchangers must take into account how they can be easily moved in and out of building both during and after initial construction for installation and/or replacement.
6. For hot water applications, install pumps on the cooler return water side of the heat exchanger.  The lower operating temperature helps to extend mechanical seal life.
3. Seismic Performance:  Coordinate project specific seismic restraint requirements with structural engineer.  
3. Types, Applications and Selection Criteria: 
1. General:  Heat exchangers for HVAC applications shall be rated for minimum of 150 psig working pressure at 375ºF, or higher if otherwise required to provide rated working pressure of at least 1.5 times maximum operating pressure. 
1. A relief valve sized at not greater than 90% of the heat exchanger's maximum working pressure shall be installed on the water side of each steam/hot water heat exchanger and on both sides of water to water units.  The relief valves must be installed at the heat exchanger and prior to the isolation valves.  
2. Since PA L&I currently considers chilled water heat exchangers to be unfired pressure vessels, provide relief valves on both the building chilled water side and campus chilled water side.
3. The relief valves selection parameters shall be determined and scheduled by the design professional.
2. Shell and Tube “Converter” type: 
1. Applications include: 
1. Steam to hot water HVAC systems. 
2. Water to water with design approaches typically greater than 15ºF. 
3. Special high temperature and/or pressure separation requirements of parts of a system or systems with large differences or fluctuations in temperature or pressures between fluid sides. 
2. Selection Criteria
1. Converters shall have steam in the shell and water in the tubes.  For high temperature difference water to water systems, lower temperature water to heated shall be in the tubes. 
2. Converters shall typically be selected at 2 psig steam pressure operating in the shell for most efficient operation heating fluids up to 200 ºF.  Otherwise select a steam pressure that has a saturation temperature approximately 30 ºF higher than the required outlet temperature of the fluid being heated in the tubes. 
3. Do not oversize the control valve or else temperature overshooting and excessive control hunting will result in unstable operation and premature valve/actuator failure.  
1. For University Park campus steam characteristics refer to 33 63 00 STEAM ENERGY DISTRIBUTION.
2. For buildings served by campus low pressure steam, system pressures can vary seasonally between 5-12 psi, with 5 psi as the winter design condition.  Coordinate selection of control valve and heat exchanger accordingly.  Review with OPP Engineering Services. 
4. Maximum Velocity limits:  (confirm with manufacturer per application)
1. Tubeside Nozzle Velocity:  8 fps
2. Shellside Nozzle Velocity:  4 fps
3. Shellside Condensate Velocity:  2.5 fps

4. Maximum tube velocity shall not exceed the following, but may be less to keep water pressure drop low.

   Material	Max. Tube Velocity
   Stainless Steel:	10 ft/sec
   90-10 Cupronickel:	10 ft/sec
   Copper:	6 ft/sec

5. Minimize water pressure drop while maintaining effective heat transfer:  select to minimize pumping energy, typically 8 feet (3.5 psi) max. 
6. Fouling factor:  Shall be determined based on specific application and local water quality and Professional judgment.  Refer to manufacturer’s recommendations and/or Standards of Tubular Exchanger Manufacturers Association.  Typical listed value for low pressure steam heating medium (approximately 230-250ºF) to recirculated hot water application with “treated boiler feedwater” (temp. greater than 125ºF and velocity over 3 ft/sec) is 0.001 ft2 ºF/Btu. [Note:  This is higher than the previous value in the OPP standard of 0.0005 (the value for distilled water per table from TEMA).]
7. Refer to Equipment Requirement Piping Connection options to avoid excessive velocity and impingement erosion on the tubes. 
8. Steam Traps:  Provide properly sized and installed steam traps for complete condensate drainage. Inadequate drainage of condensate can result in significant loss of capacity and even in mechanical failure. 
1. The trap should be sized based on a 0.5 psig differential pressure, assuming 2 psig inlet pressure, 0 psig outlet pressure and a minimum 18” fill leg from the shell outlet to the trap inlet.  \
2. Allow a minimum 1.5 safety factor times the anticipated full load capacity for start-up conditions.
3. A float and thermostatic trap is typically the best selection for heat exchanger with modulating temperature control.
9. Mounting Height:  Always allow enough mounting height of heat exchanger to allow gravity drainage of the condensate from the steam trap to a vented gravity return line or a condensate return pump if gravity return is not feasible.  Avoid any lift in condensate return line above trap.
3. Gasketed Plate and Frame type:
1. Applications include:  
1. Closed Water to water systems with design approaches typically less than 15ºF and small fluctuations of temperatures and pressures. (i.e. - Process Cooling Water, Segregated loops requiring anti-freeze solution). 
2. Fluid separation between open and closed systems. (Open cooling tower to closed loop condenser water or water-side economizer).
3. Heat transfer between systems with fluids that require routine cleaning of heat exchanger surfaces due to fouling conditions.
4. Special temperature and/or pressure separation requirements of parts of a system with relatively low pressure and temperature differences and fluctuations.
5. Specialized industrial or food processes with steam (non-HVAC applications).
1. Selection Criteria
1. Minimize water pressure drop while maintaining effective heat transfer:  select to minimize pumping energy, typically 8 feet (3.5 psi) max. 
2. Fouling factor:  Shall be determined based on specific application and local water quality and Professional judgment.  
4. BRAZED-PLATE HEAT EXCHANGERS
1. Applications could include:
1. Closed, very clean systems that would not require routine opening for cleaning of heat exchanger.
2. Refrigeration.
2. Review potential application with OPP.
5. Other specialty heat exchangers for special applications:  Review with OPP.
1. Spiral
2. Helical tube
6. Additional Resources:
1. ASHRAE Systems and Equipment Handbook:  Heat Exchangers
2. Standards of Tubular Exchanger Manufacturers Assciation
3. Bell Gossett Article Steam Control and Condensate Drainage for Heat Exchangers, http://completewatersystems.com/2011/04/steam-control-and-condensate-drainage-for-heat-exchangers  
4. Related Standards Section
1. 23 00 01 Owner General Requirements and Design Intent
2. 23 00 10 Systems Selection and Application
3. 23 01 00 OPERATION AND MAINTENANCE OF HVAC SYSTEMS
4. 23 05 01 Mechanical General Requirements
5. 23 05 19 Measuring Instruments for HVAC
6. 23 05 93 Testing, Adjusting, and Balancing for HVAC
7. 23 07 00 HVAC INSULATION
8. 23 21 13 Hydronic Piping
9. 23 22 00 STEAM AND CONDENSATE PIPING AND PUMPS
10. 25 00 00 INTEGRATED AUTOMATION
11. 25 90 00 GUIDE SEQUENCES OF OPERATION
    
    
5. Documentation:  The Professional shall schedule all heat exchanger selection and performance data and project/application specific requirements on the drawings (not within project specifications).  Schedules shall indicate identification tag, system served, location, operation (Duty/Standby or Lead/Lag), type (i.e. end suction, double suction), service fluid (i.e percentage of glycol), entering and leaving temperatures, heat exchange capacity, fouling factor, minimum and maximum flow rates, maximum fluid velocities, minimum rated working pressure, inlet steam pressure, water pressure drops, number of passes, number of plates, manufacturer and model number (basis of design), maximum dimensions, operating weight, options/remarks.
1.  It is imperative to define all parameters to optimize selection for efficient heat transfer, achieving low pressure drop, and keeping velocities in range to avoid failures due to erosion.
2. Professional shall follow University Equipment Acronym List and Equipment numbering policy defined in Mechanical Identification in developing equipment tags and schedules.

3. Professional shall carefully review and edit the guideline installation details below, adapting them as needed to achieve application-specific, fully developed details for each project.

   Document	Version Date	Description
   23 57 00 D01.dwg                                        23 57 00 D01.pdf	August 30, 2018	Guideline detail:  Typical low pressure steam to hot water shell and tube heat exchanger with extended shell and high performance v-ball control valve.

.02 Guide Specifications

1. Design Professional shall carefully review and edit the guideline specifications below, adapting them as needed to achieve application-specific, fully developed specifications for each project.
2. These shall be edited using the process described in the instructions contained at the beginning of the document. Proposed modifications shall be reviewed with OPP staff.
3. Finalized version shall be included in the project contract documents. Use of other specifications is not acceptable.