Low Carbon Pool Heating: Getting the Temperature Right with Geothermal and Cogeneration

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1 Sustainability in Public Works Conference July 2014 Low Carbon Pool Heating: Getting the Temperature Right with Geothermal and Cogeneration C. Heal 1 1 City of Fremantle, Local Government craigh@fremantle.wa.gov.au ABSTRACT: This article details the project approach, technologies used, key lessons learnt and results, supported by detailed figures in order to provide conference participants with information and recommendations on how best to conduct similar low carbon pool heating projects. Councils pool leisure centres are typically the biggest source of greenhouse gas, consuming 10% to 30% of Council s greenhouse profile and are a major expense. When the Fremantle Leisure Centre was slated for major renovations in June 2013, it was the ideal opportunity to optimise the electrical and heating demand for a facility that accounts for 15% of Council s total greenhouse gas profile. The pool heating project provided an innovative solution to a need for sustainability and energy conservation by implementing the first of its kind low carbon technology arrangement, primarily led by a 300kW geothermal heat pump, supported by a 76kW cogeneration unit, electrically led and operating on peak periods and supplemented by a wing of instantaneous natural gas boilers. These elements were integrated with new supporting piping and plant room equipment, BMS automation, flow and temperature monitors and housed in a new custom mechanical plant room. This is the first time these technologies have been incorporated within an Australian Local Government. KEYWORDS: Local Government, geothermal, cogeneration, natural gas boilers, pool, leisure centre. 1 Introduction The City of Fremantle has a policy to be a carbon neutral city. As part of this commitment, abatement measures and energy efficiency projects are frequently conducted. When Council decided to upgrade its premier leisure and swimming centre, the forty year old Fremantle Leisure Centre (FLC), it naturally researched low-carbon options. This heating project was part of a 10 month, $6 million overhaul of the centre which concluded in April This project included a geothermal heating system, cogeneration plant, resurfaced pools, upgraded change and restrooms, aquatic playground area and access ramps to all pools. 2 Objectives The project s key objectives were: To heat the FLC s two main pool bodies independently to different temperatures in a sustainable, cost effective manner. Improve the operation and automation of pool heating and chemical dosing equipment. Improve the pool amenity, operations, safety and functionality for all stakeholders. Reduce greenhouse gas emissions at the FLC, as it is the City s largest single source of emissions. Implement the project to be consistent with the City s Strategic Direction report and the Low Carbon City Plan, which calls for a 40% reduction in greenhouse gas emissions by Determining the ideal pool heating technology mix The City evaluated the site s electricity and gas consumption data to determine the thermal and electrical energy load requirements. This was modelled against 12 technologies to determine the optimal solution against a number of sustainability and financial criteria including capital, maintenance and replacement cost, energy efficiency and greenhouse gas profile. The technologies were then deployed on a merit basis, with the best technology applied first as determined by the weighted criteria. In this fashion, once a preferred technology s capacity was expended and if energy was still required, the next best technology was selected until all thermal energy needs were met and an operating strategy could be developed [1].

2 This process identified that the ideal technology mix was a 75kW cogeneration system electrically led, a 300kW heat pump extracting heat from a 160m geothermal borefield supplemented by a wing of instantaneous natural gas boilers. exclusively. The geothermal heat pump supplies primary heat energy throughout the year and is designed for steady constant use. The cogeneration unit supplies a steady supply during peak times throughout the year; some heat rejection in summer occurs, a minor amount in the winter. The boiler supplies top up during cold weather months, and in peak use and maintenance events. Figure 1: View of the plant room showing all heating units installed. Left to right: cogeneration unit, geothermal heat pump and gas boiler wing. FLC already has a 30 kw solar PV system installed. This is sizing limit before reverse power protection is required to protect the grid. Additional PV s were not considered as the cost to comply with this protection requirement made them non-competitive against the weighted criteria. Modelling and determining optimal solution Modelling of the FLC s energy consumption for heating over 2011 and 2012 was analysed with respect to predicted future energy requirements. This informed the request for tender process, seeking the provision of geothermal heat pumps, cogeneration and boiler units. The preferred tender respondent s technical characteristics were then modelled to evaluate if they could be utilised within the expected operating strategy to meet the required thermal load. Figure 2: Monthly average contribution to thermal load [1]. Drilling down to average daily profiles for different months reveals the FLC s very different hourly thermal heating requirements and the specialisation of the different heating units, and determines the features of the overall heating operating strategy. Examples from January and July are provided below in Figures 3 and 4 for consideration. January s high ambient heat means little thermal load is required to heat the FLCs. The facility s high relative HVAC energy consumption makes it more profitable to run the cogeneration unit for its electrical contribution and reject nearly all the heat load to the atmosphere than heat the pools through other sources. The heat load was examined in greater depth because it drastically affects the pool s heating operating strategy, financial viability and greenhouse abatement potential. Figure 2 details how each heating element contributes to the required average monthly thermal load. Little heat energy is required in summer months; the heat pump supplies base load augmented by the cogeneration unit almost

3 A number of pools in Perth have used aquifers approximately 1,000 metres deep; however, the City opted for a shallow bore as it greatly reduces both risk and capital outlay. Figure 3: Daily average contribution to thermal load in January [1]. In July, the FLC s heating requirements are much greater, such that a fully loaded heat pump cannot supply the full heat required. In this case, the boiler is preferentially used during the off-peak period and the cogeneration unit kicks in at peak periods as it is now cheaper to produce energy through the cogeneration unit than by using the boiler. A much lower amount of heat from the cogeneration unit is rejected to the atmosphere as it is required by the pools. Greater greenhouse gas abatement could be achieved by running the cogeneration unit all the time, but the financial cost is excessive compared to the implemented alternatives. A 300 kw closed geothermal heat pump draws water from the Leederville aquifer 160m below the ground. The water, which exits the aquifer at 27 C, is passed through the heat pump and then re-injected back into the aquifer via a separate injection bore. The bore water is passed through a heat plate exchange and is applied to the FLC s swimming pool. The water is reinjected at 22 C into the borefield. Though the water only transfers 5 C of heat energy to the pool water, it is significant because it is being circulated at 12L/s. See figure 5 for a schematic. Figure 5: Closed loop shallow geothermal energy schematic [1] based on [4]. The system is designed to provide primary heating to the FLC s pools at all times. It is the most cost effective and has the lowest greenhouse gas profile per unit of heat energy produced. The heat pump operates at an impressive COP of over 6.0 all year round, heating the pools efficiently. That is, for every 1 unit of energy applied to the heating components it generates 6 units of energy. Figure 4: Daily average contribution to thermal load in July [1]. 4 Heating technologies employed Each heating technology s project characteristics are explained in turn, to detail how they benefit the FLC s heating operating strategy. Although the temperature was greater at the maximum depth of 264m ( C) than at the final bore depth selected of 160m ( C), the geology at this depth made it a more favourable reservoir to obtain the necessary water flow into the long term [2]. Geothermal Heat Pump

4 Figure 6: Geothermal bore construction The actual pumped groundwater temperature is about 0.5 C lower due to heat losses through the bore casing and headworks. The City was fortunate in that bore yielded water that was hotter than preliminary investigations projected. This increased the amount of geothermal heat energy recoverable from the system and improved overall efficiency. Having a clear understanding of the borefield geological composition at construction is vital for determining the reinjection rate and overall operating strategy of the geothermal heat pump. C Murphy s Hydrogeological Masters thesis report determined that the FLC s borefield has a service life of 50 years before reaching thermal equilibrium [3]. The localised cone of depression over time is negligible, as the system is closed, this positively contributes to the sustainability of the groundwater resource use. This means there is projected to be a viable hot groundwater resource at the required depth to justify a complete replacement to the current heat pump at end of life. Figure 7: Comparison of temperature prediction models for the borefield over fifty years [3]. The City s strategic plan for another pool at the FLC in the longer term meant that the diameter of the hole drilled for the bore was larger than is currently required to heat the pools. The bore can produce 18 L/s but will only use 12 L/s for the time being. Once the new pool is built, the bore will then be fully utilised and should achieve a coefficient of performance of around 7.3. This bore design was selected as an optimisation of the FLC s long-term heating needs, flow rate against borefield longevity and present needs. The cost to drill a larger diameter hole is not significantly greater. The heat pump has a projected 25 year service life and requires just a weekly visual inspection and annual maintenance. Cogeneration The City has decided to deploy cogeneration to reduce the FLC s use of grid electricity and to use waste heat from this process to heat the swimming pools. Cogeneration produces two forms of usage energy, in this case heat and electrical. The system selected is a reciprocating engine fuelled by natural gas. It has an efficiency of 85% and has the benefit of on-site power providing energy security, lower greenhouse gas and greater cost certainty.

5 Gas instantaneous boilers A supplementary wing of gas instantaneous boilers were also installed to provide heat topup during the middle of winter, at peak events and to supply heat during the heat pump and cogeneration units maintenance events. Figure 8: Schematic of a typical cogeneration system [1] based on [5]. The cogeneration unit will generate 75 kw of electricity for the facility and 120 kw of heat for the FLCs. The cogeneration system will only operate in peak electricity times to improve financial return. Modelling showed operating the cogeneration system to meet the thermal demand resulted in the highest greenhouse gas savings. The system will be slightly undersized to limit excess electricity created as export of electricity to the Perth grid is presently not allowed. In this case, it will pass through protection resistance or will be throttled back as required. Figure 9 details the cogeneration unit s operating strategy by month against grid electricity. Using the cogeneration facility solely during peak increases the system s long service life. Supporting technologies All technologies operate through an advanced Building Management System (BMS) which can manage fine heating characteristics including diverting 100% of each unit s heating capacity to either the 50m or 25m pools via three-way valves and a pool piping manifolds. Figure 10: Heating system manifolds, pumps and heat exchangers for both pool bodies. The BMS unit also controls the entire plant room including main filter pumps, all gas boilers, bore pumps and monitoring equipment, heat pump, electricity grid connection and the CHP system. The BMS system can be monitored remotely via PC or smartphone and includes a centralised control console. Figure 9: Electricity source for pool heating by type and month [1]. Figure 11: Upgraded electrical motor control board and BMS.

6 5 Results Since commencing operation in April 2014, this mix of low carbon technologies will save Council annually, over $100,000 in decreased operating cost, a facility energy reduction of around 25%. Abate 250 tonnes of greenhouse gas and shave 5% off the City s total greenhouse gas profile. While the total amount of energy required to heat the Centre s pools will remain the same, it will now come from cheaper sources, with lower operating, staffing and maintenance requirements that also produce fewer emissions. The pools will now be heated with greater levels of control and specialisation. The cost savings are achieved through lower gas use to power the bore, and onsite generation of electricity rather than purchasing off the grid. The cogeneration system is expected to supply about 273 MWh of electricity annually and approximately 390 MWh of heat per year. Simple payback cost recovery will occur in year 12. Complex payback including ongoing costs will occur around year 15. The project s return on investment rapidly improves in years 20 to 30 as maintenance costs are lower and life of the equipment is much greater than the previous boiler system. 6 Recommendations Recommendations for other parties considering undertaking a similar project are listed by order of where they appear in a heating project s progression: 1. To ensure the long term operation of heating elements it is vital to have at least two years of detailed time of use electricity and energy data for the facility and have it interpolated by energy engineering experts to define renewable energy needs. The Australian Local Government pool cogeneration experience could be reasonably summarised as being oversized, leading to overheating and suboptimal usage and performance issues. 2. Business cases for these projects are more favourable when including nett present value, discount or internal rate of review calculations rather than just simple payback due to the long product life of equipment and improved financial return in later years against higher initial capital outlay. This will allow decision makers to more completely evaluate the full financial worth of a proposed project. 3. Determine all costs and project particulars prior to commencement. Costs to repair underground services or rehabilitate grass are expensive and often unexpected. Other costs like equipment ventilation and detailed piping design cannot be reasonably anticipated at the planning stage and costs must be sourced from an allocated contingency budget. Keeping a close eye on project creep is required. 4. Consider whether an equipment performance contract or acquiring an Owners Engineer will achieve the City s quality assurance and project expertise needs. 5. Clearly define performance levels expected, redundancy in design, equipment calibre and operating schedule to ensure a tailored response from tenderers. 6. Take time to develop tender and contract documentation for supply and implementation of capital equipment. Conduct detailed quality assurance, change control register and signoff to ensure promised outcomes are achieved. 7. Obtain integration approvals with electricity network provider as soon as equipment specifics are known and advise as changes occur as this process is lengthy. The requirements in Western Australia are particularly lengthy compared to the eastern states. 8. Pay special attention to all stakeholders. Like all Local Government projects, community consultation and information was vital. It was important to manage community s perception and expectations against the larger pool upgrade. A detailed communication plan is advisable.

7 7 Conclusion The City is pleased with the outcome of the project. It has achieved all project objectives and an overall operational efficiency of around 5.5 coefficient of performance for all pool heating components [1]. This is an especially favourable result compared to a typical pool heating system utilising a gas boiler and prior base case which has a coefficient of performance of less than 2. Figure 13: City of Fremantle Project Councillors, Staff and drilling contractors at borefield commencement. Figure 12: Final operational mechanical plant room. Acknowledgements The project received $356,048 in Community Energy Efficiency Program funding under the Commonwealth Government s Clean Energy Future program, Improving Australia s Energy Efficiency. The City of Fremantle would like to acknowledge the following principal consultants and contractors listed by contract size for their invaluable contribution to the project. Consultants Energy Made Clean Rockwater Contractors EvoHeat WellDrill Shenton Aquatics WESCO Figure 14: Principal heating technology contractors and Project Manager on site preconstruction. References 1. Energy Made Clean, 2014, Fremantle Leisure Centre Heating Design Review, Perth. 2. Rockwater, 2013, H2 Level Hydrogeological assessment and bore completion report for the Fremantle Leisure Centre Geothermal Borefield, Perth, pp C Murphy, 2014, Evaluation of the effect of different analytical, conceptual and numerical models on predictions of impact of a geothermal doublet system in the Perth Basin, Masters of Hydrogeology Research Thesis, University of Western Australia, pp Sonic Samp Drill Company referenced in Energy Made Clean, 2014, Fremantle Leisure Centre Heating Design Review, Perth, pp Gandras Energy Company referenced in Energy Made Clean, 2014, Fremantle Leisure Centre Heating Design Review, Perth, pp 5.