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Design Tips - Building and Site Requirements

This section describes the requirements involved in interfacing modular integrated energy systems (IES) with conventional building systems. This document is not intended to be a design guide for these building and site interfaces (which is the responsibility of the cognizant design engineer who is applying a Reference Design to a particular building). The Reference Designs are based on 2MW to 5MW Solar gas/diesel turbine generators, heat recovery boiler(s) with duct firing, and Broad USA heater/chiller(s) serving a variety of load scenarios and generic facilities. As such, the focus of this document is on identifying the kinds of conventional systems that are compatible with the Reference Designs, and provides a list of design resources that practitioners can use in applying modular IES technology. An illustration of key building interfaces is shown below. Additional discussion is presented in each section.

Utility Loads Siting Codes and Standards Waste Mechanical Electrical Instrumentation


Background

Introduction

The information presented here is the results of technical work being performed for developing packaged system designs for large (2 to 5 MW) building cooling, heating, and power (BCHP) Systems, also known as Integrated Energy Systems (IES). This work is funded by the U.S. Department of Energy and is being administered by Oak Ridge National Laboratory (ORNL Subcontract 4000011476). Honeywell and its team members, Broad USA, I.C. Thomasson, and the Chelsea Group, are developing a set of CAD-based packaged IES system designs and a supervisory control and optimization capability for these systems. This section covers the work performed under Task 2.1: Building & Site Requirements.

Project Overview

The objective of the program that developed the information in this section was to develop large (2 to 5 MW) BCHP packaging technologies and field-test a prototype system. These technologies include a set of “reference” CAD designs and an optimizing supervisory control system. Installation scenarios for these systems can vary widely, so packaging is dependent on modularity, namely, the ability to construct a system by choosing from a selection of compatible components with standardized interfaces. This is especially important for larger BCHP systems, where the physical size of the equipment prohibits the manufacture and shipment of the entire system in one enclosure. Packaging in this way still simplifies the design and installation process by reducing the amount of site-specific engineering and site preparation required.

This project was focused on BCHP packaged systems in the 2- to 5-MW size range, with 500 to 2000 tons of cooling, intended for central plant and district energy applications serving multiple buildings. The major modules are a turbine-generator, a heat recovery steam generator, and an absorption chiller. The set of “reference” packaged designs to be developed will allow these modules to be applied to a variety of customer sites.

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Codes and Standards

The purpose of this section is to provide the reader with a overview of the codes and standards that will generally apply to a CHP plant. By no means is this list comprehensive.

1.
Building Codes
 
International Building Code (IBC), developed as a model code for model code organizations:BOCA, UBC, SBC
State & local codes
 2. Mechanical Codes & Standards 
   2.1  ANSI Standards
   
Flanges and piping B16.5, B16.1, B16.47, etc.
 
2.2
ASHRAE Standards
   
Guideline 1-1996 The HVAC Commissioning Process
Std 15-2001 Safety Standard for Refrigeration Systems
Std 62-2001 Ventilation for Acceptable Indoor Air Quality
Std 114-1986 Energy Management Control Systems Instrumentation
Std 135-2001 BACnet - A Data Communication Protocol for Building Automation and Control Networks
Std 147-2002 Reducing the Release of Halogenated Refrigerants from Refrigerating and Air-Conditioning Equipment and Systems
   2.3  ASME Standards
   
Boiler Power Piping 31.1
Chemical Process Piping 31.3
Boiler and Pressure Vessel Code
Pipe Flanges and Flange Fittings B16.5
  2.4 ASTM Standards
    These are generally equipment standards and pertain to individual components of the CHP system
  2.5  UL Standards
  2.6  State & Local Code 
    A number of large municipalities (Chicago, New York City) maintain their own codes
 3. Electrical Codes & Standards
  3.1 IEEE
   
Interconnection Standard 1547
DG Standard 1589
IEEE Standards 519-1992, 929-2000, 84 (Harmonic Limits and Voltage Fluctuations, Waveform)
  3.2 National Electric Code (NEC)
  3.3 ASTM Standards
    These are generally equipment standards and pertain to individual components of the CHP system
  3.4 UL Standards
  3.5  State & Local Codes
    A number of large municipalities (Chicago, New York City) maintain their own codes
  3.6 State & Local Codes
 4. National Fire Protection Agency (NFPA) Codes
 
Gas-Fired Equipment Code 8501
Oil/Diesel-Fired Eqipment Code 31
National Gas Fuel Code (NFPA 54)
Liquid Fuel Storage Tanks Code (NFPA 30)

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Electrical Interconnections

The electrical equipment of the CHP facility, though not the most expensive part of the construction, is vital in the operating success of the facility, and is probably the most complicated and diverse part of the design. In most facilities there are two major areas of focus, the utility interface point and the CHP construction itself. We will consider these two points as separate parts of the design and in many cases may be remote from each other by a substantial distance.
1.
Utility Interface Point
 

The interface point is usually located close to or within the distribution substation for the facility. The following upgrades are usually considered in the design of this point of intersection. 

2.
Low-Med Voltage/Station Power Capacity
 
The CHP facility consumes power itself to operate. Although supplied by the CHP equipment itself through transformers, often an additional feed is used to provide this power from the utility during startup. A new standby generator may also be used.
3.
High Voltage-Substation
 
The CHP plant connects to the grid at the substation; sufficient space must be present for the switchgear and transformers required.
 
3.1
Over / Under Voltage Protection
 
 
It is usually critical for the cogeneration facility. The utility normal mode of design is to avoid voltage drop so they operate their distribution system at a higher than nominal level so that nominal levels can be maintained on the extended reaches of the distribution system. Cogeneration equipment removes load or may even export power removing voltage drop or creating voltage rise thereby driving the site into higher than normal voltage levels. Some utilities take an unrealistic, bureaucratic approach with mandatory trip requirements while operating at very high voltage levels. To avoid nuisance tripping of the interface breaker a fast acting, over voltage relay (ANSI Device 59) is required.
 
 3.2
Under Voltage Relaying
 
 
Under voltage relaying (ANSI Device 27) also required is usually not as critical as over voltage control.
 
 3.3
Out of Frequency - Over/Under Frequency Protection 
 
 
Out of frequency / over/under frequency protection (ANSI Device 81 O/U) is also important. The first signs of system instability occur in the system operating frequency. For a cogeneration plant operating in parallel the frequency is set by the utility. The system frequency protection should be set outside the utility trip points and set for on site equipment protection only. In the unlikely event of utility grid instability the cogeneration equipment should stay on line to avoid placing the facility load on a utility tending toward instability. Utility guidelines may be obtained to assist in making these determinations.
 
 3.4
Out of Step Protection
 
 
Normally any breaker interfacing between the utility and the cogeneration must be equipped with a Sync-check relay, (ANSI Device 25). This relay will be capable of monitoring the voltage via potential transformers (PT) on the line and load side of the device. The protective relay will prevent closing the breaker unless the voltages levels are the same and the both systems are in phase. If the co generation plant were accidentally connected to the utility out of phase, the two systems would attempt to instantly align themselves with other. This would cause major stress on the mechanical and electrical equipment operating on the site. 
 
 3.5
Reverse Power Protection
 
 
Reverse power protection may be required on facilities, which have not negotiated a power sell agreement with the utility. The reverse power relay (ANSI Device 32) monitors the direction of power flow and will, after a time delay, initiate a trip when power flows from the site to the utility grid. There is an option to either trip the site-interconnecting breaker or trip the generating equipment causing the reverse power. It is usually less disruptive to trip the generating equipment and suffering the impact of the increased power use penalties from the utility than to take the entire site off line. This however is not always the case, and must be analyzed for each site.
 
3.6
Detecting Unintentional Island Operation
 
 
The condition of unintentional island operation may occur when the facility load is approximately equal to the output of the cogeneration equipment. Under this condition, if a utility breaker upstream opens it may be difficult for the relaying at the interface point to detect that the utility is no longer connected. As long as the load is closely matched to the generators output the facility will continue to operate until a load change pushed the generator voltage or frequency out of the protection zone provided by the interconnecting relaying. Under this condition the facility may remain energized for several minutes creating the possibility of the upstream breaker reclosing on the facility out of phase or a possibly unsafe condition for utility maintenance workers. This condition does not occur during a fault since the fault energy would pull the generation equipment down, taking the CHP off line.
 
3.7
Power Import / Export Power Control
 
 
One feature that becomes vital in cogeneration facilities is the use of feed back control to limit the amount of power purchased from the utility. This is accomplished by sending a signal from the utility interface breaker to the CHP. Based on this feed back signal the turbine controls continually adjust the governor to maintain a fixed amount of power flowing through the utility interconnect breaker. This is modified only by the limits of the CHP generator.
 
3.8
Reactive Power Import / Export Power Control
 
 
A similar control function may be accomplished by monitoring the amount of reactive power purchased from the utility. The feed back signal from the interface breaker to the CHP allows the voltage regulator to be continuously adjusted to maintain a constant power factor across the utility main breaker. Protective features must be supplied for the generator controls to prevent over exciting the generator. The additional cost for this control feature may be recovered from utility charges against reactive power purchases.
4.
The CHP Electrical Design Considerations
 
4.1
Distribution System Configuration
 
 
The first consideration for a new CHP is the configuration of the distribution system to which it is connected. The presence or absence of a neutral in the distribution system will determine how the cogeneration equipment is connected to the system. Another consideration is to whether the system will be operated as an island or not. The presence of a neutral indicated that transformers are connected wye on the primary side. If this is the case an Isolating transformer will be required since the generator is not a good source for generating neutral currents.
 
4.2
The Isolating Transformer
 
 
The isolating transformer for the CHP cogeneration equipment allows an exact match between the site distribution and the generator output. It also provides a level of isolation between the generator and exposed distribution. Typically the wye connection faces the distribution system to supply ground faults and neutral currents, and the delta faces the generators to provide isolation. The generator is typically connected wye and grounded through a reactor or resistor that establishes the ground reference on the generator side.
 
4.3
Generator Bus
 
 
The generator can operate on an electrically isolated bus or can supply auxiliary CHP loads. If the generator bus is used to supply other loads a grounding bank to establish the generator bus ground reference must be installed for those situations when the CHP auxiliary loads are operating and the turbine generator is not in operation.
 
4.4
Underground Distribution System
 
 
If the cogeneration equipment is connected to an underground distribution system, not exposed to lightning flash over events, and the system has no neutral the turbine generator can be connected to the distribution system without an isolating transformer. When this is the design care must be taken to properly ground the generator or specify the proper generator construction to avoid harmonic currents circulating between the distribution system and the utility distribution system. The pitch of the generator windings must match those of the utility system, typically 2/3. This type of construction is more expensive for this size alternator. Another option is to purchase a standard alternator and mitigate the harmonic currents that can result by increasing the impedance in the generator neutral connection. This should be carefully considered since the installation can impact the performance of lightning arresters in the distribution system.
 
4.5
Synchronizing Switchgear Requirements
 
 
4.5.1 Synchronizing Switchgear
 
 
  Synchronizing switchgear is a piece of electrical switchgear constructed in such a manner to interface the generation equipment to the electrical distribution system. This gear contains the synchronizing breaker and all of the protective relaying required for protecting the alternator from electrical disturbances that occur on the distribution system. The location of this equipment in the electrical configuration for the CHP is between the generator and the first distribution bus upstream. In some cases the isolating transformer cam be placed between the synchronizing breaker and the alternator.
 
 
4.5.2 Synchronizing
 
 
  Synchronizing is the operation of adjusting the generator voltage to match the line voltage, aligning the generator phase angle to match the utility and closing the synchronizing breaker. The turbine control equipment performs this operation automatically. Provision is also provided for manual override in the event that the automatic system fails. The manual system consist of volt meters with selection for line and generator voltage comparison; sync-scope for monitoring each system phase relationship; sync-lights which are not illuminated when the two systems are in phase; manual voltage and speed switches, raise and lower; and a manual switch to close the synchronizing breaker.
 
 
4.5.3 Protective Relaying
 
 
  Protective relaying for the typical generator protection package may consist of the following. Presently many of these functions are housed in a multifunction, microprocessor protective relay.
 
 
  4.5.3.1 Sync-check relay
 
 
    Sync-check relay, (ANSI Device 25). This relay will be capable of monitoring the voltage on the line and load side of the device. The protective relay will prevent closing the breaker unless the voltages levels are the same and the both systems are in phase.
 
 
  4.5.3.2 Voltage restrained overcurrent (ANSI Device 50/51V)
 
 
    This feature protects against generator overload and faults in the generator and the distribution system. If the voltage in the generator collapses during a fault the voltage restrained feature decreases the trip point value by seventy five percent.
 
 
  4.5.3.3 Ground overcurrent (ANSI Device 50/51G)
 
 
    This feature protects against ground faults in the generator and the distribution system.
 
 
  4.5.3.4 Differential overcurrent protection (ANSI Device 87)
 
 
    Current transformers (CT) monitor the currents entering and leaving the zone of protection and trips if the values differ more than the set point value. CTs are located on the load side of the synchronizing breaker and the neutral side of the alternator.
 
 
  4.5.3.5 Reverse power (ANSI Device 32)
 
 
    This device monitors the direction of power flow and will, after a time delay, initiate a trip when power flows from the distribution system to the generator.
 
 
  4.5.3.6 Over / under frequency protection (ANSI Device 81 O/U)
 
 
    This function trips if the generator frequency is outside the relay set point range of protection.
 
 
  4.5.3.7 Over under voltage protection (ANSI Device 27 / 59)
 
 
    This function trips if the generator voltage is outside the relay set point range of protection.
 
 
  4.5.3.8 Loss of excitation (ANSI Device 40)
 
 
    This function trips if the generator power factor is outside the relay set point range of protection.
 
 
  4.5.3.9 Volts / hertz protection (ANSI Device 24) and inadvertent generator energization (ANSI Device 50 / 27)
 
 
    These features provide off line protection features that protect against generator voltage regulator malfunction with the generator running but not synchronized to the utility.
5.
Possible Utility Power Requirements
 
IEEE 519-1992, 929-2000, 84 (Harmonic Limits and Voltage Fluctuations, Waveform)
Power Factor, Voltage, Frequency, Harmonic Distortion, Voltage Flicker, Waveform Distortion, Phase Imbalance Limitations
IEEE 1547 Standards for DC Injection, Immunity Protection, Surge Capability
6.
Island Mode
 
The installation of an on-site electric generating facility requires an interconnection agreement between the facility operator and the local electric utility before a generator can be connected with the electrical service. When electric power from the on-site facility is substantial enough, the interconnection facility and supporting agreement may enable the operator to function in “island mode,” delivering a number of significant advantages. Island mode involves removing a piece of equipment or the entire facility’s electrical load from the electrical grid and serving it directly from the engine-generator, with no interconnection or ability to take power from the electric utility. This is vital when the industrial facility or commercial/institutional operation cannot afford even momentary outages, or when it requires exceptionally high-quality electric power. Firms engaged in high-quality electro-plating, for example, may require an hour or more downtime before production can resume after a power outage of just a few seconds duration. For them, island operation represents insurance against unforeseen and expensive production downtime. At its most basic, island mode requires no interconnection equipment or switchgear to access the power grid. This is rarely a practical option, however, since power from the utility must be available when the engine generator is down for maintenance or when the facility’s load exceeds that produced by the generator. An improperly sized engine-generator, for example, may be unable to handle demand spikes caused by certain types of equipment such as motors that can draw three times their rated electrical demand during startup. While reliability and power quality are primary drivers in selecting a natural gas-fueled electric generating or CHP (Combined Heat & Power) installation, sufficient bottom-line savings may add to the appeal and reduce the payback time
7.
Black Start
 
Black start is the procedure for recovery from total or partial shutdown of electrical supplies throughout the country’s national transmission system or supplier distribution network. A little additional outlay on capital cost to ensure back-up for potential systems failure can prove to be a time and money-saving option. All power stations, with the possible exception of small hydro-electric generating stations, need an electrical supply to start up. To be able to black start, a station must have some form of independent auxiliary supply with sufficient capacity to supply the unit auxiliaries while a main generator is prepared for operation. This additional power source is usually provided by a smaller peripheral black start generating plant, which is started from a battery or other energy storage device. Once operational, the power plant can then be used to energize part of its local network, providing supplies for other plant within the area to enable them to start-up. For partial or total shutdown of the transmission system, the general principle of recovery includes re-establishment of isolated power stations to provide ‘power islands’; these are then integrated into larger sub-systems eventually allowing the re-instatement of the whole national grid system. By having this capability at a number of strategically located sites, electrical supplies can be rapidly restored. Back-up diesel or turbine sets for black starting the main generating plant used to be a common occurrence at power stations. The reasons for the lack of these facilities at most modern plants can be technical, but more often than not they are commercial - the extra capital costs for black starting can be prohibitive. Plant and grid failures are few but power companies and plant managers need to bear in mind that accidents and systems failures do occur. Without black starting, re-establishing the supply system can be difficult, severely delayed and therefore costly. Investing in a secure back-up is essential to minimize the consequences of system failure.
8.
Meeting Local Utility Standards
  Every local power utility has their own set of interconnection requirements which must be researched and met. While utilities are currently developing uniform standards to guide CHP interconnection (California rule 21 for example), facilities currently must design unique equipment scenarios for each plant. Major power utility requirements include grid connection, condition of power, switchgear and transformer access, and meter access.

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Instrumentation

1.
Supervisory Control
  Evaluate existing control system for ability to expand and supervise new equipment packages. Data links may be established to new controls furnished with packaged system for data acquisition and supervisory set points.
 2.

Possible New Plant Steam Master for Brownfield Sites

  For plants with existing steam producing boilers, consider integrating the new HRSG into existing coordinated boiler control strategies. Coordination of some type will be required to allow the units to share steam loads without causing instability between the units.
    Option No. 1 – Expand existing controls to include new requirements including steam master and new balance of plant (BOP) auxiliaries
    Option No. 2 – Replace all plant controls if outdated
    Option No. 3 – Relatively few interconnect points required for coordinated control. Hardwire necessary interconnections.
    Option No. 4 – For coordinated control and more extensive data acquisition, investigate options and implement communication interface.
3.
Major Control Components
 
Major equipment is normally furnished with controls as part of the package including:
Burner Management (NFPA required compliance) if supplemental firing
Gas turbine and generator control
Gas Compressor (if required)
Chiller
HRSG, Chiller, and BOP equipment controls
Feed water control to HRSG
Management of Diverter (if equipped)
Supplemental firing rate of HRSG (if burner equipped)
Chiller start/stop operation
Chilled water set point and load management
Operation of various pumps, makeup water systems, cooling towers and other plant auxiliaries
Plant water chemistry measurement and control for cooling tower and boiler system
4.
Remote Monitoring
 5.
Safety
 
Gas Leak Detection Interrupt
Start building exhaust fans
Provide visual and audible alarms in building and at every entrance
6.
Emission and Environmental Monitoring 
 
CEM as required by local or federal regulation.
Blowdown monitoring as required by local authority
Blowdown monitoring as required by local authority

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Mechanical Interconnections

Mechanical interfaces represent the bulk of the connections required with turbine generator-based CHP systems.
1.
Natural Gas
 
Turbine generators may operate on a variety of fuels: natural gas, diesel or distillate oil, landfill or waste gas, hybrid fuels, bio-fuel and high hydrocarbon fuel, are among the most prevalent.
 
 1.1
Natural Gas Specification
    Many CHP equipment manufactures provide a natural gas specification. Performance may only be guaranteed if the specification criteria are met. A gas analysis, usually obtained from the natural gas utility, should be compared with the specification. Additional equipment may be required to meet the utility’s gas specification requirements. For example, a pressure reducing station may be required to lower the gas pressure, and heaters may be required to remove any non-condensable particulate formed by this temperature drop and pressure reduction
 
1.2
Gas Compressors
    Turbine generator sets in the size range between 2 MW and 5 MW typically require medium to high pressure gas (175 psi to 325 psi) for operation. If proper gas pressure is not available locally, a new high pressure line(s) may be run from the gas utility. If this new gas line is cost prohibitive, gas compressor(s) may be installed. Redundant gas compressors and associated maintenance may be a costly item, and should be evaluated on a site by site basis. Multiple smaller gas turbine generator units which require lower gas pressure may indeed be a better investment in place of a new high pressure gas line or installing several gas compressors.
 
1.3
Leak Detection
    Many regulations, and good engineering practice, dictate that natural gas leak detection be utilized when working with high pressure gas systems. The leak detection system is typically tied in with the plant control system, and will automatically close the gas shut off valve in the event that gas is detected.
2. 
Diesel
 
 
Diesel and natural gas are by far the two most common fuels for turbine generator CHP systems. Higher emissions and diesel fuel cost usually prescribe natural gas as the fuel of choice, but diesel burning capability may allow a facility to leverage natural gas by buying from cheaper interruptible tariffs. A second fuel capability will further provide a solid back up fuel option incase a primary fuel is unavailable or not economical. On site diesel fuel will require storage tanks and any associated air/groundwater permitting. Secondary containment will been to be addressed if required, as well as the filing of any storm water pollution prevention plan (SWP3) or spill prevention control and countermeasure (SPCC) plans required by the regulator. Proper siting is required for filling access by the diesel supplier. Many turbine manufactures require an additional air compressor to start a turbine on diesel. 
3.
Chilled / Hot Water
 
The Broad USA unit converts hot gas exhaust from the gas turbine into chilled or hot water. The interface to these systems is typically a simple welded pipe connection. Hot tapping may be utilized to avoid interruption of an existing system. Additional control devices may be required if the new CHP equipment works alongside existing chilling and/or heating equipment. Chilled water systems will require cooling water systems, which include cooling towers, city water makeup, chemical treatment, blowdown, and freeze protection. Hot water systems also have simple chemical treatment.
4.
Steam
 
CHP equipment can often be integrated into an existing plant with no additional requirement for steam auxiliaries. Typical steam auxiliaries include condensate storage tanks, condensate return pumps, water treatment equipment, deaerator, blowdown and boiler feed pumps. If the CHP steam production is similar to the existing plant’s steam production, most of these auxiliaries may continue to be used.
5.
City Water
  Existing heating plants probably use city water for makeup, and treat the water with additional chemicals and equipment accordingly. Turbine compressor blades foul after a certain operational time, and require washing at regular intervals. Washing may be on-line or offline, and requires a specific water quality. Additional equipment may be required to remove impurities and/or hardness of the city water supply, and additional pumps may be required to increase water pressure.

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Siting

1. Permiting
  Permits for construction and operation of a CHP facility will be required from federal, state, and local jurisdictions. The following list (adopted from Spiewak) represents a good starting point.
  1.1 Federal
   
Federal Aviation Administration Notification of Proposed Construction
NEPA Certification
U.S. Army Corps of Engineers Section 10 Permit
U.S. Army Corps of Engineers Section 404 Permit
U.S. EPA NPDES Permit
  1.2 State
   
Coastal