Week 12 - Chapter 17 - Thermal Demand and Supply Flashcards
(24 cards)
Thermal energy system
The thermal energy system is the third of the major subsystems in the overall energy system. (Cooking, space heating, industrial processes)
Thermal energy use is the oldest and most basic form of human energy use, originating with the harnessing of fire to burn wood and other biomass for cooking and space heating.
Improved furnaces and fuels that could achieve higher temperatures allowed the melting and processing of metals and evolution of human society from the Stone Age to the Bronze Age to the Iron Age.
Today it is still the largest subsystem as measured by energy flows, representing 37% of final energy consumption in the OECD countries, and 47% worldwide due to a lower relative demand for electricity and transportation services in the developing world.
Final energy use for heat (FEH)
Breakdown of the fuels consumed in the production of heat as well as the end-use sectors to which the heat is applied.
In the industrialized OECD countries, natural gas is the primary source of energy for heat, followed by oil and coal, which collectively make up about 85% of the final energy use for heat (FEH). In the developing world, a substantially higher reliance on biomass for residential heating and cooking applications reduces, but does not eliminate, the relative contribution of fossil fuels to FEH.
As shown in the figure, end-use applications for this heat are primarily split between heat used for industrial purposes (such as smelting, process heat, etc.) vs. heat used in building applications (space conditioning, such as heating and air conditioning, cooking, and hot water).
Best available technology (BAT)
Also called best available techniques in Europe, is a defined standard established by governments to describe the state-of-the-art performance of a particular technology in the marketplace.
BAT performance must be defined precisely according to targeted impacts or outcomes being measured, such as environmental impacts, discharge of waste, or energy efficiency of the technology.
When setting regulatory requirements for the performance of devices, firms, or sector behavior along these impact dimensions, regulations often refer to the BAT as the benchmark against which realized (actual) performance will be measured. For this reason, correctly determining what the “best” technology is can influence behavior, cost of compliance, and overall outcomes.
Process heating
Industrial process heating is a category of material transformation processes that use thermal energy to refine materials, alter their properties, or remove unwanted moisture or other contaminants.
Three primary types:
- Fuel-based process heating
- Electric-based process heating
- Steam-based process heating
Thermoelectric
thermoelectric cells that can directly convert heat to electricity.
(in context of capturing waste heat to electricity)
Fuel switching
Using a different fuel for industrial thermal processes.
Where available and technically feasible, coal-to-gas switching may reduce pollution and emissions from cogeneration. Also, fossil fuel to renewable switching can improve emissions characteristics and dampen fuel price volatility and dependence, but it must also be evaluated for reliability and cost.
Submetering
When an occupant is billed directly for individual use.
To pay for energy consumption, the occupant either receives a direct bill for individual use (submetering) or receives a pro rata share of the total building’s bill based on some estimation method. Many principal-agent issues can arise in these situations in which the choice of energy consumption is separated between the building owner and the tenant, and either the choice of equipment installed in the apartment or the consumption of energy is invisible to the other party.
Triple net lease
Agreement in US where tenant is responsible for energy bill, among other things like taxes and insurance.
In the United States, for example, it is common for commercial landlords to lease space to their tenants under a triple net lease arrangement, which essentially means that the tenant is responsible for the energy bill (among other things, like taxes and insurance), despite having very little say over the construction or equipment choices that went into that building.
MUSH market
One of the main designations of institutional types of buildings and their owners.
M-municipal and state governments
U-universities and colleges
S-schools (K-12)
H-hospitals
HVAC
HVAC is the acronym representing heating, ventilation, and air conditioning.
Many methods condition the air in buildings, but the general strategy is to adjust the temperature so that it stays in a reasonable range for building occupants or storage and, secondarily, so that it maintains humidity within a comfortable range or provides filtration to improve indoor air quality.
Radiant heat
When heat generated is transferred to the rest of the house or building through direct radiation.
Steam heat
When heat generated is transferred to the rest of the house through the distribution of steam in pipes and radiators.
Heat pumps
Heat pumps comprise a vast range of technologies that can move heat (through the use of a liquid or gaseous refrigerant carrier) from one location (a source) to another (a sink).
Through various types of compression (electrically driven) or absorption (thermally driven), these technologies can even extract heat from a colder location to a warmer one, or vice versa, allowing heating in cold climates and air conditioning in warm ones.
The most commonly used systems are vapor-compression refrigeration units, which use a liquid refrigerant that expands into gas (a phase change) and back into liquid as it cycles through the unit.
Coefficient of performance (COP)
A common metric used to standardize the relative efficiency of heat pumps is the coefficient of performance (COP). Conceptually, the COP is the ratio of the heat supplied to or removed from the reservoir as a percentage of the work consumed by the pump.
Devices with a pure thermal in and thermal out cycle, such as stoves or boilers, naturally have a COP of less than 1 due to the laws of thermodynamics. Devices that tap into ambient heat sources, such as heat pumps, can have a COP of greater than 1.
Air source heat pumps
These heat pumps use ambient air outside the building as a source or sink of heat in their operation. They are the simplest to set up but may suffer from efficiency losses in extremely hot or cold ambient environments.
Ground source heat pumps
Also called geothermal heat pumps, these heat pumps require equipment to circulate water (or another refrigerant) in a closed or open loop under the ground, taking advantage of the natural temperature differentials between the ground and the ambient air. The systems tend to be very efficient (see Metrics Sidebar), but their initial setup can be expensive due to the excavation or drilling necessary to install the loops.
Building envelope
The building envelope is a set of features, common to all buildings, that determines the relationship between the building and the external conditions.
Ultimately, the efficiency of heating and cooling a building is determined by many factors beyond the choice of HVAC equipment. The main consideration for the thermal performance of a building has to do with how the building is designed, including a wide range of aspects of its building envelope.
Components of building envelope:
- Roofs
- Ventilation and air leakage
- Walls
- Windows and doors
- Floors and basements
Factors influencing thermal efficiency:
- U-factor
- Solar heat gain coefficient
- Air leakage
- Visible transmittance
- Light-to-solar gain
Combined heat and power (CHP)
Combined heat and power (CHP) was discussed in detail in Chapter 6 and represents the process whereby the waste heat from electricity generation can be captured and put to work for productive purposes.
Sometimes this productive use is to increase the efficiency of electricity generation itself, but more often the low-quality heat is targeted toward local thermal needs, such as space or water heating.
Passive design
Even without trying to capture and redirect the energy of the sun, many design features determine a building’s relationship to the sun, seasons, and ambient conditions, collectively referred to as the passive design of the house, or just passive design.
These passive design features include the orientation of the house, doors, and windows; building envelope material, color, and insulation choices; and awnings, airflow, and other engineering choices. The combination of these choices can have a dramatic impact on the overall heating, lighting, and cooling requirements of a building for a given environment. Due primarily to cost issues, many of these features are best embedded in the initial design and construction, though retrofits can help with some aspects of design as well.
District energy
District heating and cooling systems, collectively referred to as district energy, are not sources of energy themselves but instead are methods of capturing heat from a source and moving it to a sink using large integrated networks of delivery systems across multiple buildings and users. The usual justification for these systems is either having ample sources or sinks of excess heat or favorable economics for building a system large enough to capture and deliver heat with corresponding economies of scale.
A particular type of district heating system is called a municipal steam system, one of the most famous of which is in some of the more densely populated parts of New York City. One of the nice features of a steam system is that the temperature of the delivered steam is high enough to be useful for industrial as well as residential and commercial users.
Building management systems (BMS)
Intelligence control systems for heating and cooling, which can optimize electricity demand and energy use.
In addition to the smart energy management tools described in the electricity demand section in Chapter 9, smart controls for integrating thermal systems can have a substantial impact on building comfort and energy performance. Advances in technology and cost reduction for local metering, distributed programmable devices, and integration and communication protocols have allowed substantially more information and control on building performance for both residential and commercial buildings.
These modern intelligent control systems are typically referred to as building management systems (BMS), or building automation systems, the design of which can range from the simple to the complex, and they typically integrate both electrical and thermal aspects in their overall control schemes. Some of the features they might include are varying the energy load and temperature requirements of the building based on time of day, occupancy, or ambient outdoor conditions. A smart BMS may change the internal temperature and lighting requirements of an entire building, specific floors, or even a single room based on normal work flow patterns, reducing them during nights and weekends in an office building, for example, unless it detects an unexpected increase in occupancy.
Thermal storage devices
Thermal storage devices are designed to retain the heat (or lack of it) in place and to shift its availability to when the heating (or cooling) is more desirable.
For example, using a combination of storage media that can absorb and reemit thermal energy and an appropriate encasing layer of insulation, thermal storage devices can retain heat from the time it is generated to the time it is needed. Thermal storage devices for chilling need to do the same process in reverse.
Molten salt thermal storage
Molten salt thermal storage—This type of storage requires insulated tanks of salt solutions that melt above 131°C to store the captured heat from solar thermal installations.
Figure 17.25 shows how the system is arrayed with dual tanks, one at a higher 566°C to capture the input heat from the collector and one at a lower 288°C for waste heat that can be used to preheat fluids sent to the thermal collector. These technologies are well understood and are used in multiple solar thermal installations today, but building a storage device large enough to back up a solar thermal power plant and provide output for energy applications is costly, and long-term economics are still not well understood.
There are three primary methods of storing high-temperature heat: in molten salts, in solid media, and thermochemically.
Repowering
When the performance/economics of existing electricity generators or thermal plants are enhanced through new financial and physical capital.
Use existing assets or infrastructure and enhance their performance or economics through meaningful additions of new financial and physical capital.
Often, these opportunities arise long before the end of the useful life of an asset, but overhauling the aging equipment using state-of-the-art components (retrofits) might still make economic sense, depending on the circumstances. When this is done using electricity generators, thermal plants, or even engines, it is often referred to as repowering an asset.
