One of the original drivers for the emergence of distributed power was the environmental and economic need for utilizing the ‘waste’ heat of on-site power generation. This could be achieved by bringing smaller power plants closer to the consumer’s heat demand area. The concept of distributed power grew, along with other factors like energy security and energy quality, but unfortunately, almost all subsequent studies, models and applications, grossly neglected this need for utilizing the ‘waste’ heat for distributed power.
Once the distributed power concept is truly coupled with its usefulness for satisfying heating (and cooling) demand in the constructed environment, then its potential contributions to the environment, energy, economy and quality of life, will become much more visible and real. By the same token, our studies at the Organized Industrial Region (OSTIM) in Ankara, Turkey, reveal that the actual virtues of distributed power will remain underestimated unless this technology is coupled with the concept of distributed heat.
This is particularly true in an era in which the sustainability and other efficiency measures are still based only on the quantity of energy. In fact, the quality of energy and how efficiently we are matching the supply quality with the demand quality are becoming the main players in determining the attributes of distributed power and heat. This is especially evident in the building sector, which demands low quality energy for heating and cooling, while fossil fuels provide a very high energy quality. This quality imbalance directly translates to additional, but avoidable, carbon emissions and higher operating costs.
The new administrative building of OSTIM in Ankara, Turkey, was commissioned on a preliminary basis in March 2009
The solution is to couple cogeneration or polygeneration systems with green and high-performance buildings which require even less quality of energy, in such a manner all players are optimally coupled with a correct balance of fossil fuels with alternative and waste energy resources.
The new OSTIM administrative building seems to prove this concept: an integrated polygeneration system with a steam bottoming cycle operating alongside solar and wind energy, a ground source heat pump, ground heat exchangers, biogas, thermal storage, passive solar systems, and other green mechanical systems and equipment. These systems represent an optimally green energy bundle with the highest degree of balance in energy supply and demand qualities.
The building itself exhibits many architecturally green and healthy building features, like Trombe walls (sun-facing walls that can act as a thermal mass combined with an air space, insulated glazing and vents, to form a solar thermal collector), maximum day-lighting, solar gain control, under floor heating and cooling, waste water management, green landscape with minimum water requirements, silver ion-coated ventilation and air-conditioning ducts and appliance surfaces. Thus, while the building itself becomes a low energy density building, both in energy quality (low-exergy) and quantity, the energy supply side copes with this low demand with a careful mix of high-quality fossil fuels (natural gas) with low, quality alternative and waste energy sources, including biogas from the district waste water system.
OSTIM ‘green’ building design
Man spends approximately 90% of his time in enclosed environments. Enclosed volumes namely buildings consume approximately 40% of all energy resources, 75% of the generated electrical energy and one-eighth of fresh water resources. Occupant health, welfare, and productivity are directly linked to micro-environmental quality and comfort conditions. Therefore commercial buildings, schools, hospitals and office buildings in particular have a very high energy density.
Satisfying this energy density in many forms, especially in heating, ventilating, and air-conditioning, has a negative impact on the environment, economy and our energy balance, and increases the burden of limited and depleting fossil fuels even more.
The OSTIM green administration building has been designed in accordance with the platinum grade of LEED (Leadership in Energy and Environmental Design) green building certification program of USGBC (United States Green Building Council) and high performance building criteria of ASHRAE (American Society for Heating, Refrigerating, and Air-conditioning Engineers Inc). The OSTIM building responds to all six LEED criteria for a platinum grade, as follows:
- characteristics of the area and site where the construction takes place
- water efficiency
- energy efficiency and greenhouse gas emissions to atmosphere
- construction materials and raw material resources used
- indoor air quality
- creativity and innovation in design process.
Energy efficiency and greenhouse gas emissions
This category provides eight sub-criteria regarding rational and efficient use of energy, as well as routine arrangements with regard to commissioning of the building. These are: performance thresholds for energy use; use and management of refrigerants; optimization of energy performance; use of embedded (fitted) energy systems; innovativeness in commissioning; use of new and harmless refrigerants; real-time monitoring of the building and measurements; and use of green energy.
This is the most important category in which cogeneration and polygeneration systems may play a vital role for green buildings by providing on-site high-quality, high-efficiency power and useful heat, together with large quantities of fuel savings as specified by EU directive EU 2004/8/EC. This also results in much reduced carbon emissions and a smaller overall environmental footprint of the building and the mechanical system. These all become much more effective and sustainable when a polygeneration system marries with a green, high performing building. A study made by an EU Sixth Framework Programme (FP6) polygeneration combined-cycle project named HEGEL, High Efficiency PolyGeneration Applications proved this.
According to the International Energy Agency (IEA) report ‘Energy Technology Perspectives: Scenarios and Strategies to 2050: In Support of the G8 Plan of Action,’ the impact of cogeneration on reducing carbon emissions until the year 2050, which only appears in the ‘Industry’ category, is projected to be only 300 tonnes per year. On the other hand, in the ‘Buildings and Appliances’ category, district energy applications have a projected potential of reducing carbon emissions by 2050 by 500 tonnes per year, increasing to 1100 tonnes per year for building heating and cooling technologies.
The latter two figures show that the overall potential of cogeneration, when coupled with buildings and district energy, has more environmental benefits when compared to industrial applications. This was phrased as: ‘When cogeneration applications shift from industry to buildings, cogeneration becomes much more meaningful, from a sustainability point of view.’
Some buildings, which are described as ‘green’ buildings in theory, might not be truly green and healthy. The green building concept is not only simply design but a closed-loop action that also covers implementation of the integrated building design, operation, and evaluation of the performance, continuous monitoring, preventive maintenance/repair, design refinements and improvement phases. Nineteen fundamental principles were identified by our design and consulting team to realize a truly sustainable, beyond-green, high-performance building, with minimum environmental footprint and carbon emissions, with the following design objectives:
- Energy efficiency exceeding 85% (First Law of Thermodynamics)
- Energy quality matching efficiency exceeding 60% (Second Law of Thermodynamics)
- Close to net zero-carbon emissions
- Minimum 50% contribution of alternative energy sources based on installed capacity (wind, solar, ground heat, waste heat, passive systems)
- Minimum 20% peak HVAC (heating, ventilating and air-conditioning) load shaving with thermal energy storage
- Low-exergy building (demanding very low quality of energy) with innovative HVAC systems
- Hygienic and clean indoor air quality
- Further reduction of energy quality demand with hybrid air conditioning systems
- Compliance with EU 2004/8/EC Directive in CHP systems, and minimum of 30% fuel savings.
The sustainable design
The new OSTIM administration building is a three-floor and 2700 m2 office building. The building is only 350 metres away from the electric sub-station and only 450 metres away from OSTIM’s own combined-cycle power station. The polygeneration system in this building is interconnected with this local grid so this is distributed energy within a distributed energy system.
In the selection of all construction elements and interior fittings, the environment, health, hygiene, air quality, regional procurement, sustainability, reuse and recycling were all fully considered. The overall window to wall ratio has been optimized in terms of cooling and heating loads, along with thermal insulation and visual comfort parameters, passive shadowing and Trombe wall applications, plus the advantage of natural lighting for a twelve month period.
During winter, air heated in the greenhouse during the day and heated by the stored heat in the Trombe wall during night, is distributed around the building using fans. On the greenhouse floor, there are heat storing natural stones and a decorative/functional solar pond. During the summer, air circulated within the Trombe wall greenhouse is bypassed outdoors, without distribution into the building.
In the main HVAC system, floor heating and floor cooling systems operate with the ceiling fan-coil system in tandem; and the risk of surface condensation in the cooling mode is eliminated by proper controls. With this arrangement, heating and cooling the ground-source heat pump and the absorption chiller, coefficient of performance (COP) values for cooling increase. Another important reason for the increase in COP values is the fact that the low-exergy HVAC system in the building requires energy at very moderate temperatures, both in heating and cooling. Besides these attributes, additional energy savings will be achieved by implementing a hybrid wall HVAC system in certain zones. This is a combination of radiant and forced convective heat transfer mechanism, all integrated and sandwiched into a single wall unit.
An overall optimization effort was carried out in order to determine the best collection of waste, alternatives, and polygeneration in the mechanical room. Figure 1 shows the mechanics for winter operation of the building. Figure 2 shows the summer operation mode. The high performance, multi-level green polygeneration system consists of three main components, all connected in functionality and energy balance in terms of both quality and quantity. The core polygeneration system consists of a combined heat and power system with an internal combustion engine that has dual fuel capability, namely natural gas and biogas, or a mixture of both.
Figure 1. Green mechanical system with polygeneration: winter operation
Figure 2. Green mechanical system with polygeneration: summer operation
This engine-generator unit delivers 120 kW electric power and 180 kW thermal power in the form of useful heat to the building. Total thermal efficiency is 89% at design conditions. The next important components of the polygeneration system in the building are the solar photovoltaic and wind turbine systems that provide additional electric power and complement the cogeneration system. Solar flat-plate collectors provide additional heat. Two separate thermal energy storage tanks provide peak-load shaving by storing heat at two different energy quality (exergy) levels, namely high-temperature and low-temperature.
The solar photovoltaic system is an innovative set of solar trigenerator modules, each consisting of a customary photovoltaic module, heat pipe energy recovery wafer, and a thermo-electric cooling wafer all sandwiched together. The heat exchanging module of the solar trigenerating module captures the solar heat absorbed by the photovoltaic module, while cooling it for better photoelectric efficiency. This thermal energy may be either used for additional useful heat supply to the building or may be used for additional electric power generation in a metal-hydride system.
The thermo-electric cooler wafer employs the same heat exchanger wafer as a thermal sink, thus adds more useful heat to the system while part of the electric energy from the solar photovoltaic module is utilized for cooling purposes by this wafer. Therefore, this innovative solar trigeneration module itself acts as a stand-alone polygeneration system and pushes the boundaries of the overall polygeneration concept of this building outward.
A wind turbine completes the second component of polygeneration.
The third component of the polygeneration is a bottoming cycle, in which part of the waste heat from the combined heat and power (CHP) unit is utilized to generate high pressure steam for additional power generation in the range of 15 kWe. In this bottoming-cycle mode, the maximum useful thermal power from the CHP that can be delivered to the green building drops to about 140 kW heat from 180 kWe. This means an ideal heat to power ratio of almost one is achieved. This heat is supplied to the building at 120ºC maximum by a closed-loop hydronic system.
Soil thermal response tests. In the background is the semi-completed building
The drop in useful heat supply to the building is off-set by the ground source heat pump (GSHP), which is driven by the electric power generated on-site by the polygeneration system. A careful set of soil thermal response tests were carried out in order to realistically design the vertical ground loops. The photo above shows this operation. In the background is the semi-completed building in September 2008. As a result of these analyses, seven vertical bores were drilled, each to a 75 metre depth.
A dedicated control unit optimizes the collective operation of the polygeneration system and the GSHP, and optimally diverts a certain amount of on-site electric power to the GSHP. Part of the useful heat supply is utilized by the absorption chiller in order to satisfy minor cooling loads from inner office zones. The GSHP system collectively satisfies heating and cooling loads of the building along with the useful heat delivered by CHP and the absorption chiller in winter and summer months. A waste water treatment system, which is coupled with a bio-gas generator, provides input energy to the dual-fuel CHP unit. On-site electric power shares a common grid with the OSTIM combined-cycle power plant nearby.
On the green building side, the lowest possible quality of heat is demanded thanks to an optimum combination of four different heating, cooling, ventilating and air-conditioning systems in an optimum cascade of supply and return temperatures. Starting from the highest quality to the lowest, these are; air-conditioning system, floor heating system, hybrid wall (radiant and forced convection porous wall), and ventilation system. A ground heat exchanger pre-conditions the fresh air intake, thus contributes to energy savings and efficiency.
The summer operation basics are almost identical to winter operation, except for the chilled-water storage tank for shaving off the peak summer cooling loads, optional chilled beams to complement radiant floor cooling, and a separate ground heat exchanging loop for CHP heat output that may exceed the demand in summer. GSHP may be called upon to provide some heat for domestic use if the CHP unit is off and solar energy is not sufficient.
Table 1 shows the components of the installed polygeneration system in the building. The ‘-’ symbol indicates demand, while ‘+’ sign indicates supply.
Waste water recycling
Grey and black water discharge from the building may be properly utilized after being recycled in a biological treatment system. Biogas to be produced in the second phase of the project will replace the natural gas input for the polygeneration system.
In the first phase of the project, biogas production will be tested on a laboratory scale. If this method proves to be feasible, biogas production will be extended to the OSTIM district waste collector. However, there is a small amount of carbon dioxide gas emission during biological treatment, and this production contradicts the entire philosophy of the application. However, our calculations showed the amount of carbon dioxide generated in the treatment and recycling unit of the green building, is approximately 200 g per day, and it is negligible compared to the reduction in carbon emissions generated from burning natural gas, which is to be replaced by biogas. However, separate studies are in progress to prevent this low-level emission during biological treatment as well. Analyses show that the annual carbon emissions reduction potential of this building will be in excess of 500 tonnes.
For any system that involves energy, its additional carbon dioxide emission responsibility due to exergy inefficiency in the building sector, is given by the following connected equation:
Here, c is the carbon equivalency per kWh heating value of the fuel, typically 0.2 kg CO2 per kWh for natural gas. This figure is about 0.6 for coal.
The term η is the thermal efficiency, ψR is the energy quality balancing efficiency, and P is the heat load. Per unit combined power and heat loads at a power to heat ratio of 1 (2P), the above equation shows that for a natural-gas condensing boiler (η = 0.95 and ψR = 0.06) avoidable carbon emissions is 0.38 kg/kWh.
In this respect, the OSTIM building had several unique achievements as summarized in Table 2. According to the values given in this table, the equation shows that the carbon emissions reduce to 0.17 kg/kWh. This 51% reduction in emissions is at the CHP level only. When the energy mix shown in Table 1 is considered and weighted on installed capacities, the overall carbon emission reduction potential becomes 90%. Even if parasitic power demand for biogas production in the second phase of the project is included, the building becomes a net zero-carbon building.
Table 2 also compares the OSTIM building with a business-as-usual case mentioned earlier; fuel savings are about 45% when the energy quality balancing efficiency is factored into the calculations.
M. Ali Kilicaslan is the Natural Gas O&M manager, OSTIM, Ankara, Turkey.e-mail: email@example.com
Orhan Aydin is chairman of the OSTIM Industrial Zone, and Adem Arici is regional manager of OSTIM Industrial Zone
The scientific and technical contributions of Dr Birol Kilkis, WADE’s (World Alliance for Distributed Energy) country manager for Turkey, have helped to make this project a success and design inputs were greatly appreciated.