THURSDAY, FEB 2, 2023: NOTE TO FILE
Module 4-5
Energy Efficient Technologies
Often the greatest gains in the design of energy systems come from energy conservation methods. This can mean the super-insulation of buildings, reducing the weight of vehicles and efficiency in the use of energy and so on. Many energy-consuming appliances have an energy rating, which leads to intelligent choices (eg: European Union Energy Label).
More and more industries concentrate on the security of their energy supply, which often means a private grid with some in-house generating capacity, along with connection to the national grid. For example, in 2015 Apple announced their plan to build a massive 130MW solar farm in California (more). Industries also work at achieving ongoing system efficiencies. This involves looking at industrial processes from first principles to reduce energy and waste. It also means smaller actions, such as replacing electric motors with more efficient models and smarter controls.
5.1. Combined Heat and Power (CHP)
CHP is the cogeneration of electricity and heat from the same system. It is particularly suitable for municipalities, where district heating is energised from the heat generated as a “byproduct” of producing electricity. Industrial processes also frequently need both heat and electrical power on the same site. Most large systems use conventional fuels; however, there is a growing use of methane from landfills powering gas engines and distributing heat where practical.
Non-fossil fuels for CHP can be methane from an anaerobic biodigestor or biomass from a local forest. Above about ~1 MW the wood fuel can be gasified (more on gasification). Smaller systems generate steam, which is used in a steam turbine. This reduces electrical generating efficiency to about 25%. Heat is often distributed through a district heating system.
“Decentralising a quarter of London's energy supply could help the capital reduce carbon emissions by 3.5m tonnes according to a study published by London First. The report, Cutting the Capital’s Carbon Footprint - Delivering Decentralised Energy, calls for collaboration between central Government, the Mayor and his agencies, energy companies, developers and boroughs to decentralise a quarter of London’s energy. Linking large heat users such as housing estates, leisure centres and hospitals to locally-placed electricity plants can deliver massive efficiency gains, instead of centralised generation with its huge waste heat losses and losses from many miles of high voltage cables. Some local energy centres may produce power from renewable sources such as unrecyclable waste.” - UK CHP Association, 2008 (now Association of Decentralized Energy)
Combined heat and power plant |
5.2. Micro CHP
There are now micro-CHP plants available, powered by natural gas or diesel.
The principle is that a gas or oil-fueled engine drives a generator that produces electricity. The heat from the engine block, oil cooler and exhaust, which would normally be wasted, is absorbed by coolant water through a high efficiency heat exchanger. This energy, stored as hot water, is then used directly for central heating, domestic hot water, or indirectly for air conditioning. In general, the production of 1 kilowatt of power creates 2 kilowatts of usable heat energy. These co-generation units are powered by natural gas or diesel and have a heat storage system and advanced computer management (example). A wood pellet micro-CHP model based on the sterling engine has been created by an Austrian company called OkoFen.
5.3. Ground Source Heat Pump
Ground source heat pump technology can be used in large buildings, clusters of buildings or in a house. Generally, the larger systems have lower costs per kWh delivered.
A ground-source coupled (or geothermal) heat pump works like a refrigerator. If heat is required, a large amount of ground is cooled slightly and heat delivered in a “concentrated” or high temperature form to provide the central heating in a building.
In the cooling cycle, the system works in reverse – heating the ground and cooling the house. In the summer, the air conditioning is energised by the heat pump and in the winter the heated earth is cooled. In some regions, both heating and cooling (or dehumidification) are required, which is ideal for this technology.
For the heating cycle, the energy taken from the ground during the winter to heat a residence is replaced by solar energy, which falls on the ground throughout the year. The energy moved, or “pumped”, from the ground is natural “renewable” energy. This ground, or “earth” energy is tapped by circulating water from the well or coil in the ground.
The cooling of the circulating water by the heat pump causes heat energy to flow from the warmer earth surrounding the well or coil to the circulating water. The heat pump then transfers this heat energy into the building’s heating system, which in turn warms the house.
What makes this process of recycling stored solar energy from the ground so economical is that little electricity in the heat pump compressor is used to transfer considerable heat energy from the ground to the house. Heat pumps can deliver up to four times the energy used by the compressor.
5.4. Geothermal Energy
There are two different types of geothermal heat pumps, identified as:
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Water–to-air heat pump, which takes heat from water in a heat exchanger and transfers it to air in another heat exchanger to distribute heat by air ducts in the house.
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Water-to-water heat pump, which takes heat from water in one heat exchanger and transfers it to water in a second heat exchanger. These water-to-water units then distribute heat to the house, typically by radiant floor heating.
Steps Required In the Geothermal System Decision Process:
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Selection of the heating or cooling distribution system is the most important first step, because it determines the type of heat pump required (water-to-water, or water-to-air) and impacts the efficiency of heating or cooling distribution, in a tightly constructed building.
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The second step is to specify the required heating & cooling levels to give the best long-term investment for the space-conditioning infrastructure in the building.
Where there is room around the building and the ground is suitable, a horizontal loop is normally the most economical. Where there is an aquifer, or a close pond, a horizontal loop is normally the most economical. Where there is an aquifer, the borehole method should be investigated. Water to water is the most efficient system. There are also air source heat pumps (which are not geothermal).
The US EPA has carried out in-depth research on heat pumps |
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The Heat Pump Association (HPA) is the UK's leading authority on the use and benefits of heat pump technology. |
The technology is reliable, and although the capital investment is higher than conventional alternatives, the running cost is typically 30-50% less. The following are useful YouTube videos:
Video 1:https://www.youtube.com/watch?v=asg0Uova7Xk
Module 4, lesson 6
