A Cost Comparison for the Supply and Installation of Three High Rise Sewer Stack Systems

Transcription

1 A Cost Comparison for the Supply and Installation of Three High Rise Sewer Stack Systems Published by Studor Independent Foreword by John Turner MSc CEnv MCIWEM FIHEEM FCIPHE, Director of Britewater International Ltd.

2 Foreword Years of professional experience have taught me that it is a real challenge to provide a constructive and comprehensive cost comparison for any of the building engineering services; sewer stacks are no different. Nevertheless, the way in which this study has been developed in an impartial and detailed manner, using experienced independent quantity surveyors, designers and consultants, should give any reader confidence that the evidence presented is based on standard construction processes and a practical analysis of the actual costs applied to each system. In other words, it is a level playing field. The three systems analysed here are the three most commonly used approaches for sewer stack design: a Fully Vented Modified System using AAVs, a Reduced Velocity Aerator Stack System and a Studor Single Pipe System. However, there will be hybrids around the world which have been influenced by local preferences, regulations and experience, and by individual engineering design exponents. In an industry that is predominantly price driven it is encouraging to see what can be achieved by cooperation between component manufacturers and researchers within academic institutions. The Studor Single Pipe System incorporating AAVs and the P.A.P.A. device is the outcome of such cooperation, and represents a modern, economic, calculated and researched design approach that can be consistently reproduced for any building type or height. I would recommend that anyone presently engaged on a construction programme that requires sewer pipework design and performance assessment should at least consult Studor and compare for themselves both the economic and technical advantages inherent in the application and design of their products. BIOGRAPHY John Turner has over 40 years of experience in the field of building services engineering, including commercial, public sector and academic roles. He holds a Master s degree in Water and Waste Water Technology and began his professional career as a Senior Lecturer on the Building Services course at Salford University in the UK. Since then he has worked on a wide range of international projects for some of the most prestigious names in the fields of building services engineering and the built environment. His posts have included those of a consulting Senior Public Health Engineer, a Senior Hydraulics Engineer and a Mechanical, Electrical and Plumbing Engineer. His experience covers a comprehensive range of building types including hospitals, airports, shopping malls, academic institutions, residential complexes and office buildings. John is currently based in Manila, Philippines, and is the Director of Britewater International Ltd. He is a Fellow and past National President of the Chartered Institute of Plumbing and Heating Engineering, a Member of the Chartered Institute for Water and Environmental Management, a Fellow of the Institute of Healthcare Engineering and Estates Management and an Associate of the Chartered Institute of Building Services Engineers. In addition to his commercial work, he has been a National Examiner for the City & Guilds course in Plumbing and Mechanical Services, and for the Chartered Institute of Building Services Engineers technical paper in Plumbing and Public Health Engineering. John Turner August

3 Introduction In 2011 Studor Australia Pty Ltd commissioned an independent investigation into the costs associated with the supply and installation, of the three main types of high rise sewer stack systems currently utilised in Australia and New Zealand. The system designs were: 1) A Reduced Velocity Aerator Stack System (RVASS). 2) A traditional passive vented system, referred to in this paper as a Fully Vented Modified Stack System (FVMSS). 3) The Studor Single Pipe System (SSPS), which by contrast is an active vented system, incorporating Positive Air Pressure Attenuators (P.A.P.A.s) and Studor Air Admittance Valves (AAVs). The purpose of the investigation was to provide concrete evidence for something that Studor has long held to be true; the SSPS is the most cost-effective system on the market due to its reduced pipework requirements and quicker, easier installation. The FVMSS utilises a pipe network that carries air into the system in order to relieve negative transient pressure whilst providing a relief vent through which positive transient pressure can travel, thus directing the transients away from the water trap seals within the stack system. The FVMSS is the conventional passive ventilation system, and is the established requirement for all global plumbing standards. The SSPS is the only system that employs active ventilation principles, and uses the working combination of the Studor P.A.P.A. and Studor AAVs to intercept and alleviate both positive and negative pressure transients near their source of generation. This single pipe system was the result of 6 years of academic research carried out specifically to develop a remedial solution for the issues caused by transient pressures within high-rise building designs. The system has rapidly been accepted internationally by standard organisations and building code bodies, and is already installed in many of the world s tallest buildings. The unique advantage of the SSPS is its ease of installation. It also is a cost-effective solution for retro-fit, as there is no need to remove and replace existing pipework. In order to prove this, an independent hydraulics consultant was asked to design three different stack systems for the same high-rise apartment building. Each design was based upon one of the three common technologies (i.e. RVASS, FVMSS and the SSPS). A bill of quantities for each of the designs was created and supplied to two separate plumbing estimators, who were asked to produce estimates for the supply and installation of the systems. More about the three systems The RVASS is a single stack offset system that makes use of specially designed fittings on every floor to interrupt the downward flow at approximately 3 metre intervals, thus preventing the positive and negative transient pressures from affecting water trap seals in the system. However, it must be noted that Pressure Relief Lines (PRLs), must be installed at the base of the stack and at graded offsets. The RVASS was developed in the 1950s and has been produced under licence worldwide. Despite the appeal of having a single stack drainage system, the use of RVASS in tall buildings in Australia and New Zealand remains limited in comparison to other alternative systems. The Studor P.A.P.A., a component of the Studor Single Pipe System 3 STUDOR reserves the right to make changes to the product which may affect the accuracy of information contained in this document

4 Roof Roof Open Vent Mini-Vent AAV Aerator Fitting Maxi-Vent AAV Waste Stack Mini-Vent AAV Aerator Fitting P.A.P.A. Mini-Vent AAV Figure 1. Illustration of a typical RVASS system showing the aerator fitting at each branch and the pressure relief line at the base of the stack. FVMSS Figure 2. Illustration of the Studor Single Pipe System. Note the lack of both pressure relief line and vent direct to atmosphere. SSPS The Project The building used as the basis for this investigation was a high-rise apartment block of 22 storeys, referred to as Hamilton Harbour Apartments. An independent hydraulics consultant from Brisbane provided three different designs for the building s stack system, each utilising 24 separate stacks: 1) A RVASS system. 2) A conventional FVMSS, incorporating relief vents. In this case, the consultants designed the branch ventilation using AAVs, which is common practise in Australia for this type of system design. 3) An SSPS, which comprises of the Studor P.A.P.A. and Studor AAVs. A bill of quantities was created for each of the three designs and all relevant documents were passed to two plumbing estimation businesses located in Brisbane. The estimators were asked to produce estimates for the supply and installation of each system. To ensure accuracy, they were asked to provide a per metre / fitting rate which included the cost of the material and installation. This allowed for precise costing of each system down to individual component level. 4

5 The Estimates Figure 3. Top section of one of the FVMSS stack designs used in the study. Note the secondary vent stack to the left hand side. Figure 4. Top section of one of the RVASS stack designs from the study. The offsets of the aerator fittings are clearly visible. Each estimate is based on materials and labour costs for the installation of the stacks and branches. They do not include: Two estimates were created according to the following provisions: Estimate One Combination of merchant and generic pricing for materials 10% margin applied 3% margin applied for stock loss Labour rate of $75.00 per hour Material cost for HDPE risers with PVC for branch pipes (RVASS only) Material cost for PVC pipe (FVMSS and SSPS only) Estimate Two Combination of merchant and generic pricing for materials 15% margin applied Labour rate of $75.00 per hour Material cost for HDPE risers with PVC for branch pipes (RVASS only) Material cost for PVC pipe (FVMSS and SSPS only) Figure 5. Top section of one of the SSPS stacks used in the study. Note the location of the Studor P.A.P.A. device, just below floor level. 5 Delivery charges, crane hire or other costs associated with materials handling. Machinery, ladders, scaffolding or other items hired or used to manufacture or install the systems. Purchase or replacement of sundry items such as blades, drill bits or tools. The PRL at the base of the RVASS stack, which must also be taken into account when installing this system. No allowance has been made for design, drafting, fees or other ancillary costs prior to, during or upon completion of the project.

6 The Results The following table shows how the costs supplied by each estimator break down across the 24 stacks required for each system. Sovent Stack System Fully Vented Modified Stack System Studor Single Pipe System Stack No. Estimate 1 Estimate 2 Estimate 1 Estimate 2 Estimate 1 Estimate 2 1 $ 37, $ 37, $ 34, $ 32, $ 31, $ 31, $ 38, $ 38, $ 33, $ 33, $ 32, $ 32, $ 26, $ 25, $ 24, $ 23, $ 23, $ 23, $ 27, $ 26, $ 23, $ 22, $ 18, $ 18, $ 26, $ 25, $ 23, $ 22, $ 18, $ 18, $ 27, $ 26, $ 22, $ 22, $ 21, $ 21, $ 37, $ 37, $ 35, $ 34, $ 33, $ 33, $ 38, $ 37, $ 32, $ 31, $ 30, $ 30, $ 44, $ 44, $ 42, $ 41, $ 40, $ 40, $ 28, $ 27, $ 26, $ 25, $ 24, $ 25, $ 46, $ 45, $ 42, $ 40, $ 40, $ 39, $ 41, $ 41, $ 34, $ 34, $ 33, $ 33, $ 44, $ 44, $ 36, $ 36, $ 35, $ 35, $ 38, $ 37, $ 33, $ 32, $ 32, $ 32, $ 29, $ 29, $ 28, $ 27, $ 27, $ 27, $ 47, $ 46, $ 42, $ 42, $ 40, $ 41, $ 8, $ 8, $ 7, $ 6, $ 4, $ 4, $ 8, $ 8, $ 7, $ 6, $ 4, $ 4, $ 29, $ 29, $ 26, $ 25, $ 25, $ 25, $ 29, $ 29, $ 26, $ 25, $ 25, $ 25, $ 6, $ 6, $ 6, $ 5, $ 2, $ 3, $ 6, $ 6, $ 6, $ 5, $ 2, $ 3, $ 34, $ 34, $ 30, $ 29, $ 28, $ 28, $ 31, $ 31, $ 26, $ 25, $ 25, $ 24, SUB TOTAL $ 737, $ 728, $ 652, $ 635, $ 604, $ 604, GST $ 73, $ 72, $ 65, $ 63, $ 60, $ 60, TOTAL $ 811, $ 800, $ 717, $ 699, $ 665, $ 665, Average Price $ 805, $ 708, $ 665, Figure 6. Summary table showing breakdown of costs for each estimate by system and stack number. 6

7 The Conclusions 1) The Studor Single Pipe System is the most cost-effective of the three drainage systems. A quick analysis of the figures in the preceding section immediately shows that the SSPS offers the lowest overall combined costs for supply and installation. In ascending order, the average cost for each system was: 1. SSPS: $ 665, Traditional FVMSS: $ 708, RVASS: $ 805, This means that the cost of supplying and installing the SSPS would be 6.11% lower than the cost of the FVMSS and 17.46% lower than the cost of the RVASS. Furthermore, we can confidently state that the total cost for the installation of the RVASS would also be slightly higher, since neither estimate included the labour and materials to install the pressure relief line at the stack base as required. 2) Specifying the complete Studor Single Pipe System, including the P.A.P.A. device, creates additional savings on top of those offered by Air Admittance Valves. A point worth noting is that the traditional Fully Vented Modified Stack System (FVMSS) design, whilst incorporating a relief vent, utilises AAVs where required in place of traditional branch or group vents. This means that the additional savings offered by the SSPS are a direct result of specifying the P.A.P.A. device. This saving can be attributed to the P.A.P.A. alleviating the need for extra pipework required for relief, stack and header vents on the FVMSS, as well minimising the number of roof penetrations required, thereby reducing both labour and materials costs. An additional benefit of not having a relief vent with the SSPS is that the duct can be reduced in size, providing the possibility of increasing the habitable space of the building. 3) Although the Studor Single Pipe System offers differing levels of savings dependent on the load, a saving is always made. In every case, the SSPS, including the P.A.P.A. device, proved the most cost effective design for any of the 24 stacks. However, we can also see a relationship between the extent of the savings and the load on the stack. Please see Figure 7 at the bottom of the page. 4) The Studor Single Pipe System is the easiest system for contractors to cost accurately. Calculating the standard deviation for each set of estimates provides us with the following results: 1. SSPS: $ (0.04%) 2. RVASS: $ 7, (0.91%) 3. Traditional FVMSS: $ 13, (1.85%) As we can see, the estimates for the SSPS show the lowest standard deviation, followed by the RVASS and finally the FVMSS. The connotation is that, due to the straightforward system design and its ease of interpretation, the contractors were able to create more accurate and representative estimates for the supply and installation of the SSPS. This degree of consistency obviously has real-life advantages for contractors who install drainage systems based on Studor technology; the likelihood of projects running over-budget will be significantly lower than with the other passive drainage systems, and the provision of consistent and reliable quoting makes it easier for them to manage their own cash flow, as well as to secure long-term enhancements to both their profitability and their reputation. Average Cost of RVASS Average Cost of FVMSS Average Cost of SSPS Average SSPS Saving High Load $ 47, $ 42, $ 41, $ 4, Low Load $ 8, $ 7, $ 4, $ 3, Figure 7. Table showing relationships between SSPS savings and the load on the stack. 7

8 Summary The results of this investigation have demonstrated that the SSPS, including the P.A.P.A. device, is the most economical of the three drainage systems commonly utilised for high-rise developments in Australia and New Zealand. Whilst the extent of the savings that can be achieved is dependent upon the precise design of the stack, the SSPS is invariably the most cost-effective of the three options. Naturally, the costs associated with the investigation were estimated in Australian Dollars; however, the relative costs of the three systems are likely to be broadly similar across a number of other markets, including the UK and Europe. Furthermore, because of differing plumbing regulations, it is likely that in these territories an active drainage system based on Studor technology would require fewer P.A.P.A. devices, thereby creating even greater savings in comparison to the costs of the other passive drainage systems. Further Information Additional information in relation to this study, including a complete breakdown of all estimates, will be made available to interested parties upon request. Please contact the Studor Sales and Technical Support Centre on or by to info@studor.net. In addition to being the most cost effective of the three drainage systems investigated, the SSPS also offers a number of other benefits. The lack of roof penetrations makes it ideal for buildings requiring a strong external aesthetic appearance, the reduced pipework requirements make it a more sustainable choice in terms of raw materials used, whilst the reduction in duct size provides the possibility of generating additional income from an increased habitable space /112012