1、Brian Warwicker is a special professor of engineering at the School for the Built Environment, Nottingham University, UK. A consultant to Buro Happold Building Services, UK Dan Cash is a senior engineer at Buro Happold Building Services, UK. Energy Farming Professor Brian Warwicker Dan Cash Member A
2、SHRAE Affiliate Member ASHRAE ABSTRACT In most climates heating and cooling systems place large demands on the electrical power grid. This paper will discuss the concept of Energy Farming harvesting and storing as a method of reducing these demands and their impact on the global climate. Whilst Ener
3、gy Farming is of interest as a means to reduce the required capacity from the electrical infrastructure, the discussion will extend to reducing the total installed cooling capacity and energy demand. The paper will explore the relationship between mechanical cooling and electrical demand profiles an
4、d consider the benefits of storing energy. This will include traditional methods of thermal storage such as ice storage with unconventional operational regimes. The use of Energy Farming is of particular importance in countries with expanding populations, increased energy demand and consumption. The
5、 discussion will further extend to the increased use of renewable technologies such as wind power and solar power. A climate friendly building Farms Energy. INTRODUCTION It is only a matter of time before the electricity grid is completely redesigned to fully integrate widely distributed generation
6、and storage in a unified smart grid that is far more efficient, less costly and environmentally friendly than todays methods of distribution. Legal and regulatory frameworks surrounding electricity generation, storage, transmission and distribution can in some instances be more antiquated than the e
7、quipment. New smart legislation and regulation will therefore be required. The new architecture for distributed energy will embrace a variety of small modular power generating technologies. This technology is commercially available; but has been limited by a mismatch in some instances between the en
8、ergy supplier, building owner, the building operator and the building occupier who ultimately pays the operating cost. When owners, operators and occupiers pay attention to the design and construction process they can define the inclusion of energy saving technologies that will reduce the daily and
9、annual energy requirements. Moreover, if the customer pays a flat rate for electricity that obscures the cost differential between peak and off peak generation, there is a perception that there is no advantage for end users to take the benefits that energy farming technologies can provide, or is the
10、re? The economics that shape these decisions and reduce energy consumption are multi faceted; there is also a common misconception that there is a real time connection between electricity being generated and being consumed. A NEED TO STORE ENERGY Electricity is consumed in many ways, from industrial
11、 manufacturing processes to light bulbs in homes. The power demand of these can vary hourly, daily and annually. Some energy uses are simple to predict such as lighting being used predominantly when it is the night time. However other forms of energy use can be unpredictable and highly variable. Tec
12、hnologies which generate electricity currently include: LV-11-C072 2011 ASHRAE 5872011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution
13、, or transmission in either print or digital form is not permitted without ASHRAES prior written permission.x Thermal power plants which are fueled by non-renewable energy sources such as fossil fuels including oil and gas or Nuclear Power. x Renewable energy sources such as solar, wind, wave and ti
14、dal power. A countrys national electrical supply network must balance the energy supplied from its primary sources to the demand placed upon it. This balance is achieved through the delicate control of energy production to maintain the correct voltage and frequency of the electricity in the grid. Mo
15、st countries rely on this balancing act between supply and demand, with electricity system operators relying on energy stored in the form of fossil fuel, to reliably meet these changing loads. Energy is released from this storage as it is required to meet demand. In the future energy storage using m
16、ethods other than fossil fuel will be of paramount importance for the following two reasons: x Energy demand management x Increased integration of renewable energy sources, as illustrated in fig.(1) Demand Management It has been established that the energy demands of a country are constantly varying
17、 and in many cases increasing. The average energy demand for a country is lower than the peak instantaneous requirement. As the installed generating capacity of a network must be able to match demand at all times, IE the peak instantaneous demand, as well as built in redundancy. This means for a lar
18、ge portion of the year a significant proportion of the primary energy generation equipment will not be required and therefore be inactive. If it were possible to store electrical energy, for it to be generated and stored for future use, then the generation and demand of energy would not strictly nee
19、d to coincide. Generation equipment could therefore operate continuously and when demand does not exist, energy can be stored for use at a later time. When demand increases the stored energy can be discharged to supplement the generation equipment. Some countries currently have pumped hydropower sys
20、tems where water is pumped into a high reservoir when demand is low and excess generation capacity exists. This stored water is then released through a turbine when sudden increases in demand occur. This is generally a small proportion of total generation capacity as sites where these systems can fe
21、asibly be installed, are rare. Peak load reduction techniques are of particular importance. As the Worlds population is continually expanding, so too is the demand for energy. Managing demand by peak load reduction means that the increased power requirements may be provided by storage and or with a
22、minimal increase in generation. Storing Renewable Energy Most clean renewable electrical generation relies on a natural process to generate power. By its nature the energy generated is intermittent and in some cases difficult to predict. x Wind power is a primary example where although some predicti
23、on is possible sudden gusts or lulls in wind can cause sudden peaks or drops in power generated. x Wave power again ultimately depends on wind to generate waves and the variation between peak and average power generation can be very large. 588 ASHRAE Transactionsx Solar Power has an obvious dependen
24、ce on the sun which is predictable although weather and cloud movement can cause sudden drops in output. The Desertec g concept is that the world will eventually receive its power from solar plants in the worlds desserts. “Within 6 hours the worlds desserts receive more energy from the sun than mank
25、ind consumes in a year”. x Tidal power relies essentially on the orbit of the moon and earths orbit around the sun. This is very reliable although there is no control over when power output occurs in relation to demand. x Hydro-power on a large scale is very reliable although annual variations can o
26、ccur due to rainfall. The introduction of these technologies to an electrical network presents a problem in matching this constantly varying and uncontrollable generation to unpredictable and uncontrollable demand. These renewable technologies are generally easy to switch off when demand is not ther
27、e but this means that the opportunity to use clean, renewable electrical energy is lost. This problem will increase as the installed generating capacity of renewable energy increases as countries seek to meet the promises made in the Kyoto Agreement to reduce reliance on the energy generated by foss
28、il fuel. This problem has already been experienced in the UK with the national grid operator paying wind farm operators to shut down wind farms when energy demands are low. As they are easy to switch off unlike fossil and nuclear energy generation. It is therefore the demand side where we must take
29、the first steps, to ensure maximum use of clean energy. The supply side currently operates with no control of demand. We demand what we want, when we want it. The link between demand and supply has to be improved; this must take priority before we go ahead and build lots of new power generation stat
30、ions, in order to satisfy these demands. Energy farming is the process of storing energy when it is available for use at other times. This is analogous to growing food when rain and sun is readily available and then harvesting and storing it for future use. Energy storage is therefore set to be a ke
31、y element in the electrical networks of the future in order to provide flexibility of use between the patterns of energy demand and energy generation. The energy industry has recently realized this and many research exercises are being undertaken in this area. Electrical energy is not easy to store
32、and technologies such as redox flow batteries and pumped storage systems are expensive. Energy may be stored as hydrogen although this technology is still in its infancy and at the moment quite inefficient. Another option is to store thermal energy. One large scale example in the UK g proposes a sys
33、tem comprising two large gravel silos. Electricity to be stored is used to drive a heat pump which creates one hot reservoir and one cold reservoir. When the stored energy is required the heat pump reverses to act as a heat engine, thus re-generating the electricity. Electrical energy, thermally sto
34、red a can also be used on a smaller scale within the built environment. Buildings demand heating and cooling for air conditioning systems and heat for hot water. These requirements for thermal energy from electrical energy mean that electrical energy can be farmed and stored in the building as therm
35、al energy to be used when demanded. Thus thermal energy, heat and coolth is now gaining currency because of the growing awareness of its potential to store electrical energy, providing flexibility and adding efficiency as well as resilience. The important part is the interaction of the storage mediu
36、m with the system, how it behaves with the pattern of the demand and the generation, plus consideration of the input energy. Researchers are improving their understanding of thermal energy, in the context of energy storage, transfer materials and devices. A great deal of this research has been with
37、phase change materials k such as molten salt, fatty acids and liquid sodium for the storage of heat and historically with water and ice for the storage of heat and coolth. All these enable electrical energy to be stored as thermal energy and a delay in its use created, IE store the heat and or coolt
38、h and then discharge it later at a different rate. Flexible demand is about shifting the time of use of energy rather than focusing on reducing the overall consumption. This shift in demand will ideally lead to a potentially lower carbon generation 2011 ASHRAE 589mix b and more efficient electrical
39、energy supply system. The smart electrical grid of the future will control these thermal stores to manage the demand on the grid and implement energy farming to maximise the utilization of renewable energy generation. A climate friendly building should include thermal energy storage (TES) in order t
40、o facilitate the implementation of energy farming. With the new smart grid the electricity generators will be able to provide an appropriately attractive tariff for flexible energy users. This will be based on the capital cost saved in not building additional generating capacity and or the reduced c
41、ost of generation by the most efficient plant. The cost difference between the costs to build generation and costs to provide storage are demonstrated in table (1). An appropriate tariff and/or incentive structure could mean that both electrical generator and building operator benefit from the insta
42、llation of a thermal storage system. Technology Cost$/WGas Turbine 0.70-1.00Combined Cycle Plant 2.00-4.00New Coal Plant 3.00-5.00Clean Coal Plant 4.00Nuclear 4.00-8.00Wind 1.50-2.50PV (30% Cap Factor -15% Peak Red) 6.50Building Thermal Storage 0.5-1.0Table 1 Comparison of the cost of building therm
43、al storage with other power generation technologies. Source Federal Energy Regulatory Energy Commission (FREC). It could all be so simple and extremely efficient, thermal energy stores can provide a way of filling the intermittency gap that our increased requirement and dependence on renewable energ
44、y may leave us with, in the future. U.S. ELECTRICITY In general US energy demands are expected to reduce due to the implementation of more efficient technology although a significant increase in renewable energy production will affect the design of building systems to include demand management techn
45、ology. The annual energy outlook 2010 ef for the U.S. predicts growth in energy use linked to population growth through increases in demand for housing and commercial floor space, transportation, manufacturing and services. Energy consumption per person has declined sharply during the current econom
46、ic recession and is currently the lowest since 1968. Energy use per capita fig.(1) is predicted to increase slightly as the economy rebounds but then is predicted to begin declining in 2013 as higher efficiency standards for vehicles and lighting take effect. From 2013 to 2035, energy use per capita
47、 is predicted to decline by 0.3% per year on average. Concurrently, growth is predicted to occur in the commercial sector, 1.0% per annum from 2008 to 2035. It currently has the smallest share of end use energy demand but will surpass residential by the end of the period. Growth in commercial 590 AS
48、HRAE Transactionssector energy use is propelled by population growth (0.9% per annum) and commercial floor space (1.3% per annum), but will be constrained by efficiency standards fig.(1). 0.80.850.90.9511.051.11.15199020082035Year(Index,1990=1)2009 TechnologyReferenceHigh TechnologyBest AvailableTec
49、hnologyOffice equipment: otherOtherLightingHeating, cooling, ventilationOffice equipment: PCsCookingRefrigeration-0.500.511.522.53Average Annual Growth Rate (%)Figure 1: (Left) Commercial delivered energy consumption per capita. 1990-2035 (index, 1990 = 1). (Right) Average annual growth rates for selected end uses in the commercial sector, 2008-2035 (percent per year). Delivered commercial energy use per person fig.(1) remains virtually constant throughout the period, due to efficiency improvements largely offsetting the incre
