CHP for Existing Buildings

Transcription

1 A BSRIA Guide CHP for Existing Buildings Guidance on design and installation By Arnold Teekaram, Anu Palmer and James Parker BG 2/2007

2 ACKNOWLEDGEMENTS BSRIA would like to thank the following sponsors for their contribution which has led to the production of this report: Department for Business, Enterprise and Regulatory Reform. (Formally known as the Department of Trade and Industry) Ian C. Davis Birmingham City Council Joe Knowles Brotherhood Aircogen Graham Meeks CHPA (Combined Heat and Power Association) Chris Wilcox EA Technology Jim Hibbert HB Energy Consultants Ltd John Amos Hoare Lea Consulting Engineers Don Lack Leicester City Council Martin Wager Cogenco Ltd (Formerly Nedalo (UK) Limited) Brian Latham Dept of Health (formerly NHS Estates) William Orchard Orchard Partners Brian Cave Poolsbrook Heating Development Ltd John Forte Private Consultant R H Pearson Shepherd Engineering Services Bob Martindale Turbomach Ltd Alan Breeze University of Portsmouth George Henderson Atkins Consultants The contributing authors were John Amos, Jim Hibbert, Joe Knowles, and William Orchard. Dr Arnold Teekaram, Dr Anu Palmer, James Parker and Reginald Brown contributed from BSRIA. This publication has been produced by BSRIA as part of a contract placed by the Department of Trade and Industry. The contract was let under the Partners in Innovation programme, which provided part funding of collaborative research. Any views expressed are not necessarily those of the Department. The authors have sought to incorporate the views of the steering group, but final editorial control of this document rested with BSRIA. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic or mechanical including photocopying, recording or otherwise without prior written permission of the publisher. BSRIA November 2007 ISBN Printed by ImageData Group CHP FOR EXISTING BUILDINGS 05/12/07 CHP FOR Existing Buildings

3 CONTENTS 1 INTRODUCTION 1 2 FEASIBILITY AND DESIGN 4 3 THERMAL INTERFACING OF CHP PLANT Heat rejection from CHP Interfacing chp with boiler circuits The effect of mixing on flow temperature settings for boilers and CHP Items for consideration for effective control of CHP 18 4 FURTHER DESIGN CONSIDERATIONS Introduction Schematic of a typical CHP unit Retrofitted CHP unit interface with boilers and heating systems Retrofitted chp control options 22 5 DESIGN EXAMPLES Circuits used by Cogenco Circuits used by AirCogen 24 6 PRACTICAL INSTALLATION GUIDANCE Introduction Off-loading and positioning Secondary water system Intercooler water system (when fitted) Exhaust system Gas supply Heat rejection circuit Cold water top-up Combustion and ventilation air requirements Electrical Earthing system Insulation Noise and vibration control Health and safety Testing and commissioning 44 7 NEW RETROFIT SITES Airbus UK s Manufacturing Facility, Broughton, Cheshire Baltic Centre for Contemporary Art, Gateshead Time Capsule, Coatbridge 52 8 POST-INSTALLATION AUDITS Post-installation checklist Royal Mail, Peterborough St Matthew s, Leicester Whiteabbey Hospital, Northern Ireland Heathrow Marriott Hotel 74 CHP FOR EXISTING BUILDINGS 05/12/07 CHP FOR Existing Buildings

4 TABLES Table 1: Technical and operational constraints and solutions 4 Table 2: Effect of two-way and three-way valve control 8 Table 3: An example of effect on CHP performance and heat rejection as load varies 11 Table 4: Calculation of boiler temperature rise 14 Table 5: Required flow temperature off the boiler to achieve a flow temp of 82 2 C 15 Table 6: CHP details at Stringers 46 Table 7: CHP details at the Airbus Skin Mill 48 Table 8: CHP details at the Airbus West Factory 49 Table 9: CHP details at Baltic Centre for Contemporary Art 50 Table 10: Details of the CHP system at the Time Capsule 52 Table 11: Emission measurements at the Time Capsule 59 Table 12: CHP details at mail centre in Peterborough 62 Table 13: Emissions from the Royal Mail CHP units at Peterborough 70 Table 14: Emissions from Royal Mail CHP units at Greenford 70 Table 15: CHP details at St Matthew s 71 FIGURES Figure 1: Typical Gas Engine CHP (courtesy of Brotherhood Air Cogen) 2 Figure 2: Examples of the most common types of heating systems 8 Figure 3: Examples of heating system connections deemed unsuitable for CHP 13 Figure 4: Boiler circuit to illustrate the effect of mixing on flow temperatures 14 Figure 5: CHP circuit taken from literature which is deemed unsuitable see text 16 Figure 6: Example of a heat recovery system for CHP engine linked to a dry air-cooler 17 Figure 7: Schematic of a typical CHP unit 20 Figure 8: Typical CHP System Schematic 21 Figure 9: Example of the heat recovery system for CHP unit 27 Figure 10: Example of CHP with system heat rejection circuit 28 Figure 11: Example of CHP unit with intercooler heat rejection circuit 29 Figure 12: Example of CHP with absorption chilling 30 Figure 13: Example of a heat recovery system to air and water in air-chp 31 Figure 14: Schematic of air-chp 32 Figure 15: Secondary water circuit 34 Figure 16: Intercooler water system 35 Figure 17: Exhaust system 37 Figure 18: CHP condensate drains 38 Figure 19: Gas supply 39 Figure 20: Heat rejection circuit 40 CHP FOR EXISTING BUILDINGS

5 FIGURES Figure 21: Installation of two 407 kwe AirCogen air-chp units at the Stringers Facility 47 Figure 22: Total heating and electrical demands of the Stringers building (design condition) 47 Figure 23: Total energy demands of the Stringers building 48 Figure 24: Installation of three 1020 kwe air-chp units at the West Factory 49 Figure 25: Baltic Centre for Contemporary Art, Gateshead (courtesy of Aircogen Ltd) 50 Figure 26: Time Capsule overview 52 Figure 27: Schematic of CHP installation at Time Capsule (courtesy of HB Energy Consultants) 54 Figure 28: Schematic of the heat recovery systems for IVECO CHP engine 54 Figure 29: Example data of the CHP unit at Time Capsule 57 Figure 30: Power management 58 Figure 31: Heat output 59 Figure 32: CHP cumulative efficiencies 59 Figure 33: Front view of the CHP unit 60 Figure 34: Side view of the CHP unit 60 Figure 35: Peterborough mail centre 62 Figure 36: Electrical connection schematic 65 Figure 37: Gas connection schematic 66 Figure 38: Daily efficiency in the first year of operation 67 Figure 39: Weekly energy use in the first year of operation 68 Figure 40: First year cost savings, net of maintenance 68 Figure 41: CHP at Royal Mail Peterborough 69 Figure 42: Whiteabbey Hospital, Northern Ireland 72 Figure 43: CHP installation at Whiteabbey Hospital, Northern Ireland 73 Figure 44: The Heathrow Marriott Hotel 74 CHP FOR EXISTING BUILDINGS 05/12/07 CHP FOR Existing Buildings

6 SYMBOLS CHP FOR EXISTING BUILDINGS

7 INTRODUCTION INTRODUCTION INTRODUCTION Combined Heat and Power (CHP), also known as co-generation, is the simultaneous generation of both usable heat and electrical power from the same source. CHP has developed into an established technology and has become a key part of the UK government s strategy to reduce CO 2 emissions. The government has set a target of MWe (Megawatt electrical) of good quality CHP capacity to be installed by This includes industrial plants, district heating and CHP in buildings. The quality is being monitored by the CHP Quality Assurance programme (CHPQA), which began in CHP systems are most suitable for applications where there is primarily a significant year-round demand for heating as well as the electricity generated by the CHP unit. These are typically applications such as hospitals, leisure centres and hotels, although CHP is installed at a wide range of sites. The CHP systems installed for hospitals represent the largest generation capacity, with a total electrical capacity of MWe and a heating capacity of 220 8MWth (Megawatt thermal). This is compared with CHP in the leisure sector (44 7 MWe and 68 1 MWth) and hotel schemes (37 4 MWe and 58 8 MWth). CHP systems are usually categorised according to the size of the electrical output. The terminology for the different sizes is as follows: 1 Micro CHP: Mini CHP: Small scale CHP: Medium scale CHP: Large scale CHP: <5 kwe 5 to 500 kwe 500 kwe to 5 MWe 5 to 50 MWe <50 MWe. CHP uses a variety of different technologies for the prime mover, as well as a variety of fuels. Technologies include reciprocating engines, steam turbines, gas turbines, and combined cycle systems. Reciprocating engines (see Figure 1) dominate the smaller end of the market (micro, mini and small scale CHP). The majority of reciprocating engines used in CHP are automotive or marine engines that have been adapted to run on natural gas. These CHP systems produce two grades of heat, high grade from the engine exhaust, and low grade from the engine cooling circuits. Steam turbines are generally used for the medium and large scale CHP applications and include back-pressure steam turbine systems and pass-out condensing steam turbine systems. In both systems the steam is generated in a boiler before entering the turbine. In the back-pressure system all the steam is used in the turbine before being exhausted at the required pressure. In the pass-out condensing system, some of the steam is extracted at an intermediate pressure from the turbine with the remainder being fully condensed before being exhausted. 1 DEFRA, The Government s Strategy for Combined Heat and Power to 2010, Department for Environment, Food and Rural Affairs, London, 2004 CHP FOR EXISTING BUILDINGS 1

8 1 INTRODUCTION Gas turbine systems are available for mini CHP applications upwards. They are often developments of aero-engines with the exhaust gases used to produce the usable heat, normally in the form of steam. In combined cycle systems the plant has more than one prime mover, for example a gas turbine and steam turbine. These gas turbine exhaust gases are used in a steam generator, with the steam in turn passing through a steam turbine. This is known as a combined cycle gas turbine plant (CCGT) and is suited to large installations. Figure 1: Typical Gas Engine CHP (courtesy of Brotherhood Air Cogen). In addition to the environmental and energy benefits, CHP systems are being installed because of their electrical supply benefits. They can improve the quality of power supply by stabilising supply currents and voltages. They can also black start (automatic start if power is lost) in island mode (disconnected from the grid) for when the grid goes down. CHP units are rarely installed as the exclusive provider of hot water and electricity. Commonly, CHP units are sized to provide a base heat load for a building, with supplementary boilers to meet the higher levels of thermal load. Correct integration and control of the CHP unit with the boilers and with the building s electrical system is the key for maximum energy efficiency. However, problems arise when the CHP unit is controlled in the same way as boilers running on partial load. When this occurs the return temperature rise, causing the CHP unit to trip out due to over-heating. This problem is alleviated by setting the control so that the CHP is the lead unit, taking the heat load in preference to the boilers at all times. These integrated systems provide security of supply for both electrical and thermal requirements. In the UK, the procedures for designing and installing CHP plant may differ between CHP providers. Systems are implemented based on past experience and individual perception of what constitutes good practice. In this study, the main objective has been to encourage uptake of small scale CHP by assessing the practical problems and devising solutions 2 CHP FOR EXISTING BUILDINGS

9 INTRODUCTION 1 when retrofitting existing installations. The solutions that are presented here are based upon the current practice by some of the main CHP providers. The purpose of this publication is not to fuel the debate on which schemes are designed correctly or incorrectly, but mainly to give examples of schemes that have been successfully installed, together with pertinent guidance. While this publication provides guidance on the retrofitting of small-scale CHP systems, many of the issues are the same for a first time installation. Included is guidance on the issues, both technical and operational, involved with the practical installation of such systems. This includes thermal interfacing with existing plant, effective control, and heat rejection. In addition to the practical guidance there are case studies that illustrate sites with retrofitted CHP plant. CHP FOR EXISTING BUILDINGS 3

10 2 2 FEASIBILITY AND FEASIBILITY DESIGN AND DESIGN 2 FEASIBILITY AND DESIGN Good planning and the ability to foresee potential problems are essential to any retrofitting project. Table 1 lists the main issues to be considered with respect to feasibility, design, installation and operation. This guidance should be used to produce an installation plan. Table 1: Technical and operational constraints and solutions. Constraints Solutions Feasibility Obtaining accurate information on the actual electrical, heating and cooling loads of the existing systems. The original installation may have had a degree of over-specification or change in use has led to lower loads than original Lack of knowledge of the existing installation and the control strategy of the existing heating system Obtaining accurate information on the age, quality and suitability of the existing installation for CHP retrofit Connection to electricity networks (A potential problem with old installations.) Commercial arrangement for the import and export top up and spill power Arrangements for export sales of heat and linking with energy networks to optimise the economies of scale for plant Cost of installing equipment to lower emissions (Reducing NOx can lower efficiency thus increasing CO 2 emissions.) Sizing of CHP plant Thermal interfacing of CHP with an existing heating system Operation of CHP at a partial load (the same way as boilers) CHP tripping out on high jacket temperatures Review utility bills for the previous two years Carry out an initial feasibility audit on the site Implement pre-design monitoring period using temporary instrumentation Identify the largest electrical transient demand Use data loggers over three or six month periods. Data logging for two months in both summer and winter is desirable Analysis of swimming pool evaporation rates is important for leisure centres. This will determine the base heating load for the swimming pool Carry out detailed site assessment survey Assess the condition of plant items and pipework using non destructive testing Identify the condition of reusable items, such as flue systems Discuss with gas and electricity companies as soon as possible in the planning stage Ensure the electricity company local requirements are fully understood and addressed Discuss with electricity companies at the feasibility stage and before project commitment Invite potential partners to discuss possibilities early in the planning stage Carry out a separate optimisation study In gas turbines, dry low NOx results in a slightly higher capital cost but this is lower than the through life costs associated with water or steam injection. Dry low NOx running costs are zero Design Size the CHP for the base heat-load requirement (not the electrical load) The base heat load should equal the CHP minimum output typically 50 percent of the maximum Consider the value and implications of a heat-dump system, if any Include part-load operation in the economic model Design for CHP to operate at constant load as this requires less complicated connections and control arrangements compared to a situation where the CHP works with the boiler, where the heat load demands fluctuate Design for CHP to take the heat load at all times in preference to boilers Consider practicalities of using low grade (normally waste) heat to maximise efficiency Whatever variations in load are allowed for, when the system heat load is below the CHP unit design load, the temperature of the water reaching the CHP unit must be below the maximum allowable CHP return temperature Consider the way CHP is connected in relationship to boilers Consider the way CHP is controlled in the connection Modulate CHP off on rising building water return temperature or Transfer heating controls to building water return temperature. Note that this could result in lower flow temperatures than is allowable 4 CHP FOR EXISTING BUILDINGS