DISTRICT HEATING ASSESSMENT FOR ALEWIFE CAMBRIDGE

Transcription

1 DISTRICT HEATING ASSESSMENT FOR ALEWIFE CAMBRIDGE Project name District heating assessment for Alewife Project no Recipient Cambridge Community Development Department Document type Report Version 3 Date 24/08/2018 Prepared by SMT, JNF, TSR, SANH, CLABO, IMC Checked by JNF, SMT Approved by JNF CONTENTS 1. Introduction 1 2. Why district heating 2 3. Heat demand assessment 4 4. Hydraulic network analysis 5 5. Heat source technology options 7 6. Thermal tank storage 9 7. Summing up Next steps Introduction Alewife is an industrial and commercial district developed in the nineteenth century. The major part of the existing building mass is likely to replaced by new development. The district is changing fast and by % of the area will be developed under the Envision Cambridge Alewife district plan. This is a unique opportunity to come up with new solutions for energy production and distribution and to utilize the synergies between the local resources, thus increasing the efficiencies. Also, the risk of flooding should be considered in the new development of the city, and solutions that take these risks into account should be found. Within energy, the focus should be on environmentally friendly solutions which support a long-term goal of reducing carbon emissions and provide the district with a low-cost, resilient and efficient energy supply. Therefore, it is vital to find holistic solutions which address several of the challenges that the district is facing. Version 3 1/11

2 2. Why district heating As found in the Cambridge Low Carbon Energy Supply Strategy (LCESS) study, 1 Alewife can benefit from developing district heating, both in terms of costs and emissions. Building energy supply can be based on many different technologies. If a technology is applied on an individual basis, the building owner will typically be using the technology for many years, most likely until the end of the technical lifetime of the technology. In the coming period, the overall energy system will change rapidly from fossil fuels to an increasing share of sustainable fuels such as wind and solar PV. For the building owner, it will be too expensive to install several technologies. Therefore, the building will not be able to change the supply if the external conditions such as e.g. fuel prices or prices for electricity are changing. However, if a water-based thermal network is installed in the district with supply to each individual building, it will be possible to supply from several different technologies to the network, known as district heating. Since the necessary capacity of the district level technology is significantly higher than on an individual basis, the specific costs will be significantly lower. This is due to the economies of scale in the technologies. The district heating network will typically have a technical lifetime of more than 50 years, if it is installed properly. The district heating system consists of central energy production in the forms of hot water, a water pipe network distribution system of the energy and finally a heat exchanger unit (also called energy transfer system ETS ) located at the consumer s building. The ETS is installed instead of a boiler. The network functions as a carrier of the energy produced centrally. There is often a large thermal energy storage connected to the network to enable independent production of electricity and heat, if the production technology is based on cogeneration. The networks are usually district-wide and can supply several thousands of consumers with thermal energy. A prerequisite of district heating is a high energy density. Typically, in a district such as Alewife, smaller heating clusters can be identified in which it is economically viable to establish a network. From these clusters the network can be extended to neighbouring buildings. The network can be extended further, until it is no longer viable to establish a connection, compared to installing individual supply. The connection to a modern district heating system can provide energy savings for consumers when compared to individual alternatives. Connection to a district heating network also means that there is no need for building owners to invest in individual boilers or to maintain these individual boilers and auxiliaries. District heating provides the basis for centralized operation as well as maintenance by modern technology and by a staff of well-trained specialists, ensuring optimal operation and a long technical lifetime of the equipment, again reducing costs in the long run. The costs for maintaining one central energy unit is lower than the costs of maintaining many individual energy units. Compared to the traditional steam network, the lower temperatures in the waterborne system allow for lower operation and maintenance costs and for lower 1 Version 3 2/11

3 heat losses. A rule of thumb is that the lower the temperature of the system, the lower the losses. The heat losses in a steam-based network are often between 30 and 40 %, whereas the losses in a water-based system are between 5 and 10 %. This reduces primary fuel consumption. District energy is more environmentally friendly than conventional heating systems for many reasons: Firstly, it is possible to utilize lower grade energy sources in the network such as from industry; and secondly, it is possible to supplement the electrical grid through integration of alternative generation sources such as solar photovoltaics (PV) and wind. By using the excess electricity from wind and solar PV to produce heat and then store this for use at a time when there is no excess electricity, but a high demand for heat, the overall emissions from the system can be reduced and the excess renewable electricity can be used instead of becoming a problem. District heating facilitates the production of both heat and power from CHP plants, thus providing efficient energy generation. A CHP power plant uses approximately 30 % less fuel compared to producing heat and electricity separately. It is also possible to obtain synergies between district heating and cooling as heat is a by-product of the production of cooling and vice versa. Since cooling is produced during summer when the heat demand is low, a thermal storage is necessary to utilize the full potential. An aquifer thermal energy storage (ATES) system is a possibility. The heat pump may also be used to integrate low temperature waste heat sources. A district heating network is a solution that will ensure a stable and secure supply of heat. Instead of being reliant on one unit, a district heating network can have more than one unit connected, that operates with different costs. This ensures a stable supply, and if one unit breaks down, the other units can supply the demand. A challenge, however, with district heating is that it requires tight overall planning of the district, and that all buildings are made district heating ready and comply with a certain building code. In the next sections, we will touch upon the following: Evaluate data provided by City for the Alewife development area and develop heat and cooling demand for proposed development Complete high-level hydraulic sizing of piping and route for a district heating and cooling (DH&C) network, including cooling clusters Outline volume of thermal storage for both heating and cooling Outline capacity and footprint of heat source required to meet demand, but not what the heat source is as this requires further study with a scenario analysis Outline potential heat source scenarios which could be examined further We will wrap up with a short recommendation for next steps of the implementation of DH&C networks in Alewife and where a potential energy centre could be located. Version 3 3/11

4 3. Heat demand assessment The heating and cooling demand in the Alewife area used for the later hydraulic analysis is presented in this section. GIS shape files from the Alewife District Plan were used to estimate the energy demand in the Alewife development area. The data provided from the City of Cambridge held information on proposed land use and corresponding ground floor areas (GFA) for each building polygon. Energy use intensities (EUI) used for the Alewife development area in the Cambridge Study (based on the Low Carbon Energy Supply Strategy figures) were used to estimate heating and cooling demands for this study. As it is assumed that there will be a 60 % buildout by 2030, the benchmarks have been linearly interpolated to that year. Table 3-1: EUI for the Alewife DH Study values are used 2. Original land use/building use in the data Heating EUI [kbtu/sq ft/yr] Cooling EUI [kbtu/sq ft/yr] Land use Commercial 26,53 21,23 15,92 10,61 3,04 2,44 1,83 1,22 Industrial 26,53 21,23 15,92 10,61 3,04 2,44 1,83 1,22 Residential 29,72 23,78 17,83 11,89 2,00 1,60 1,20 0,80 In Table 3-2, the heat and cooling demand is calculated by multiplying each EUI with the corresponding GFA. As each data point can have more than one land use, the dominant land use, in terms of GFA, is used to classify the overall land use for the datapoint/building polygon. If approximately equal GFAs appear, the data point/building polygon is classified as Mixed-Use. The EUI data used in this study is based on data from the Kendall Square EcoDistrict Energy Study. In the subsequent phase, we suggest that we look further into the EUI numbers for the area. 3 Table 3-2: Estimated heat and cooling demand for the Alewife DH study Land Use Heat Demand [kbtu] Cooling Demand [kbtu] Total GFA Commercial Industrial Mixed-Use Residential Total The total heating demand correspond to approx. 45,000 MWh per year and the cooling demand correspond to approx. 4,000 MWh per year. 3 The EUI assumptions for cooling seem very low. This should be re-evaluated in the subsequent phase Version 3 4/11

5 Mixed-Use is assumed to be 40 % residential and 60 % commercial. 4. Hydraulic network analysis The hydraulic analysis is based on the heat demands found in the assessment in the previous section. Maps of the heat demand, cooling demand and land use are attached as PDFs. In Figure 4-1, the district heating network applied in the hydraulic analysis using TERMIS is shown. The results are shown in Table 4-1 alongside an estimated investment cost based on the pipe price estimates used in the LCESS study for the full installation. Because we must cross a railway to reach the small cluster of buildings in the northern part of Alewife, that cost might increase. However, in that case it must be investigated whether two separate DH networks with separate production facilities are more cost-efficient than one single DH network. This is a task for a subsequent phase. We do not conduct any further economic analysis of the most beneficial option for heat production. However, in the next section, we list some technologies for a possible scenario analysis. The overall investment cost of the DH network is also included in this analysis. Version 3 5/11

6 Figure 4-1: District heating (DH) network and location of the energy centre Version 3 6/11

7 Table 4-1: District heating network trench and investment Dimension Trench Pipe prices Investment Inch meter $/meter million $ , , , , Total 8, Based on the initial assessed cooling demand, we have not found that cooling clusters can be developed in the Alewife area as the expected cooling demands are too small we have found that cooling clusters cannot be developed in the Alewife area as the expected cooling demands are too small. However, this should be looked at further in a subsequent phase. 5. Heat source technology options Based on the peak heat demand, we estimate that the capacity of the base heat production will be around MW and have a requirement of m 2 of building space. We have made a list of production and storage technologies that may be combined to create the best solution in a scenario analysis: Water source heat pumps. This heat pump utilizes the nearby Fresh Pond as a heat source. The efficiency will likely be slightly better than an air source heat pump; however, excess heat sources can be a better alternative. The investment cost of a lake water intake can be high depending on location. Ground source heat pumps. This heat pump will use the heat from the ground as the heat source. The challenge will probably be that vertical boreholes are needed and that these can be expensive. There will also be a limit to how much heat can be extracted from each borehole. Ground source heat pumps can both be Version 3 7/11

8 an individual solution as well as a district level solution with ground source heat pumps supplying the heating network. Air source heat pumps. This heat pump utilizes the air as the heat source by using dry coolers. This heat source is probably the least efficient of the options considered. Furthermore, there can be restrictions on noise levels from the dry coolers, which limits potential locations. Heat pump utilizing waste heat sources. A heat pump that can use a local source of waste heat like wastewater or heat from industry can be more efficient than the previous heat sources. Using wastewater as the heat source may have some restrictions because the water is contaminated. Heat pumps with combined heating and cooling. The best heat source is a district cooling system if the cooling demand is adequate and the energy intensity is high. The EUIs used in this study will be assessed further in a subsequent phase. By producing both heating and cooling - and on top maybe have an aquifer thermal energy storage (ATES) system - the heat pump can be very efficient. However, this requires that district cooling is beneficial to establish. So far, this is not fully certain. Electric boiler. This unit can be used for peak load heat production, utilizing low electricity prices, which often relates to high renewable energy production. Solar thermal. Depending on available space, a solar thermal plant can be a costeffective alternative. At some percentage of the annual heat demand, the production must be stored in a tank or pit thermal storage, or otherwise cooled away. Biomass boiler. This technology is well known and has been in operation for many years. Either wood pellets or wood chips can be used as fuel. However, the carbon impact of biomass is not agreed upon. Biomass ORC. This technology has also been in operation for many years. Here, the plant will also produce electricity in a combined heat and power mode. The investment cost is higher than for a heat-only biomass boiler. Either wood pellets or wood chips can be used as fuel. Peak/back-up boiler. This boiler can use biooil, gas or oil as fuel. The unit will have very few operational hours but is available for back-up and peak production. We also believe that the following thermal storage technologies are relevant to investigate: Aquifer thermal energy storage (ATES). This storage technology is operated in district heating/cooling networks where excess heat is stored from summer to winter and excess cooling from winter to summer, significantly improving the efficiency of the heat pump system. Tank storage. Used to store heating and cooling over a period of up to a week. Version 3 8/11

9 In a scenario analysis in a subsequent phase, the first task would find the relevant technologies which should be looked at further. The long-term costs for the technologies (capital and operational expenditures) should be compared with a business-as-usual scenario. 6. Thermal tank storage With a thermal tank storage, it is possible to optimize the production of heating and cooling, and thereby lower the production costs. The tank storage will have hot water in the upper part of the tank and cooler water in the bottom of the tank. Hot and cold water is separated by the difference in specific density of hot and cold water; i.e. there is no mechanical separation. The function of the thermal tank storage is shown in Figure 6-1. Figure 6-1: Thermal tank storage (stratification) The figure shows that there is steam in the top of the tank. This is to prevent oxygen entering the tank storage and to prevent corrosion. More often, however, nitrogen is used as an alternative. The above principle is used in most Danish cogeneration plants, which counts for more than 400 units. The technology is well-proven. If the main production is based on cogeneration of heat and electricity, the heat can be produced during peak hours in the electrical system and the revenue will be maximized. When prices for electricity are low, the plant may not produce at all since the revenue from production of electricity will not be able to pay for the fuel consumption. If the heat production is instead based on heat pumps or electric boilers, the heat should be produced during off-peak hours in the electrical system. The volume of a thermal storage tank can be determined based on the hourly electricity prices or, alternatively, the electricity tariffs. We have not investigated these. Instead it is assumed that the tank storage must be able to supply base load for 8 hours. The peak heat demand is determined to be around 22 MW. Including diversity, the required base load capacity will be about 60 % of the peak load, which corresponds to a content of 105 MWh. The base load is the approximate capacity at which the production from the main production technology covers more than 90 % of the demand for heat. The remaining 10 % is produced Version 3 9/11

10 on peak/back-up boilers. With these assumptions, the thermal tank storage will be around 3,500 m 3. The height is 22 meters and the diameter 15 meter, based on the preliminary assumption of 8 hours operation in base load. The final design of the thermal tank storage will be investigated in the software EnergyPRO with hourly electrical prices on an annual basis as one of the inputs. 7. Summing up We have evaluated the data provided by the City for the Alewife development area and developed heating and cooling demands. Both are attached as PDFs in maps. We also completed a high-level hydraulic analysis sizing the district heating pipes from a predetermined trench and location of the new energy centre. This trench can be used in the subsequent economic analysis on the viability of district heating in Alewife. The capacity of the primary heat source is MW and will take up m 2 in building space. One potential location for such a facility has been indicated on the maps in the northwest part of the Alewife Quadrangle along the railroad tracks. This could facilitate delivery of fuel to the facility. More detailed site assessment would come in subsequent planning stages. The remaining part of the heat demand will be supplied from peaking and backup boilers. We also outlined the technologies we find best suited for a further feasibility study. The optimal volume of the thermal storage can be determined in a later study considering heat demand, electricity prices and electricity tariffs, as well as heat production capacity. The thermal tank storage will be around 3,500 m 3, based on a preliminary assumption of 8 hours operation in base load. Whether it is economically viable to cross the railway with a district heating pipe is also a task for a later and more detailed study. The buildings across the railway could alternatively have their own district heating system or none at all. 8. Next steps A more detailed feasibility assessment should be conducted to determine whether to proceed with district energy planning and implementation for the Alewife district. Such an assessment should include: Consideration of other potential connections to district energy systems nearby (e.g. Cambridgepark Drive, Cambridge Discovery Park, Rindge Corporation Apartments etc.). Re-evaluation of cooling EUI. Will district cooling be viable in Alewife? Location of potential cooling clusters. Confirm zoning of Alewife. Should some parts of Alewife be individually supplied? Model a Business-as-usual energy supply scenario for Alewife. Model alternative district energy supply scenarios with heating, cooling, electricity and thermal storage. Conduct techno / economic evaluation of different energy supply technologies and district energy facility locations also with consideration of flooding events. Model potential trenching costs for district heating and cooling (if found viable). Version 3 10/11

11 Evaluate thermal storage opportunities, including underground aquifer thermal energy storage? Develop district energy system design conclusions and recommendations, including stakeholder engagement and development/operation business planning. Version 3 11/11