Heating and energy Flashcards
What is exergy?
Exergy: the amount of work a system can perform when it is brought intt thermodynamic equilibrium with its environment.
-Measures the quality of an energy flow or an energy source
-High temperature cooling and low temperature heating.
Describe the advantages and disadvantages of electrical heating.
Pros:
- Fast
- Practically no distribution losses
- No noise
- No pollutants
- Easy to control
- Cheap installation cost
- High exergy
Cons:
- Can overheat, some damage risk
- Expensive run costs
- Bad for heating large spaces
Why is it more difficult to cool an indoor space to a temperature below the ambient temperature than to heat it to a temperature above the ambient temperature?
It is because of the second law of thermodynamics, which state that heat naturally flows form a warmer to a cooler environment. Ex. so when you cool down a room you do the opposite against the natural flow - need more energy.
What are Thermally Activated Building Systems (TABS)?
Thermally Activated Building Systems (TABS) are a type of energy-efficient and sustainable heating and cooling technology used in commercial and residential buildings. They leverage the thermal mass of a building’s structure, such as concrete floors or ceilings, to store and distribute heating and cooling energy.
The thermally Activated Building System (TABS) is a combined heating and cooling system with pipes embedded in the structural concrete slabs or walls of multi storey buildings. In these piped you can run hot or cold water depending if you want heating or cooling
Why are heat pumps suitable as a source of heat for floor heating systems?
Heat pumps are well-suited as a source of heat for floor heating systems for several reasons:
- Efficiency. Heat pumps are highly efficient in converting electrical energy into heat.
- Even heating. Floor heating systems distribute heat evenly across the floor.
- Low operating temperatures. Heat pumps can generate low temperature heat required for underfloor heating without a significant decrease in efficiency.
Draw a graph comparing for different stages of a building project the cost of making project changes to the ability/possibility of making effective changes.
Se i anteckningar
Explain the concept of “Trias Energetica”.
The “Trias Energetica” is a concept and design philosophy used in sustainable building and energy management. It provides a framework for achieving energy efficiency and sustainability in the built environment.
Reduce energy demand
Utilize Renewable energy
Select energy source
Explain the passive space-conditioning concepts of “ground heating” and “ground cooling”. Illustrate both concepts with simple sketches.
This concept is based on a pipe buried in the earth 1,2-2 meters below the surface where the ground temperature is almost constant. The temperature in the ground at that depth is higher than the ambient temperature during the winter and lower than the ambient temperature during the summer. When fresh air draws down the pipe it will either preheat or pre cool depending on demand.
When using preheated air instead of cold air the heat pump doesn’t need to heat up as much → saving energy.
Explain the passive space-conditioning concepts of “cool roofs”. Illustrate the concept with a simple sketch.
Normal construction materials usually have:
High solar absorbance, and no reflection
Enhance high solar gains
Cool roofs uses instead cool materials sush as
have high solar reflectance
reduce solar gains
enhance emmittance
allow the building to remove stored heat by radiation
Discuss the advantages and disadvantages of the passive space-conditioning concept of “green roofs”.
Green roofs = vegetated roofs or living roofs are passive space-conditioning concept where plants, often grasses or other vegetation are grown on the roof.
+ Energy efficiency, improved air quality, absorb rainwater, extended roof lifespan, improve building insulation, cooling effect due to evaporation, aesthetic value, biodiversity
-Installation and maintenance costs (they require a waterproofing membrane, drainage layers, plants), structural load (heavy, stronger more expansive constructions needed), limited plant choices, leak risks, fire risk, seasonal variability (green roofs may not provide the same level of insulation and cooling in all seasons).
What are “thermal heating or cooling loads” and how do they impact indoor thermal comfort?
Thermal heating or cooling loads is the heat or coolth that is delivered to a system to achieve, restore and maintain a certain desired level of thermal comfort in indoor environments.
A thermal load is any heat flow that needs to be compensated for by heating or cooling in order to maintain the desired indoor thermal environments.
Using a simple sketch, identify the principal heat gains and losses in a building.
Se anteckningar
Describe the terms “sensible heat flow” and “latent heat flow”
They are two different types of heat flow
Sensible heat flow
You can refer it to temperature you can feel. It is the amount of energy required to change the temperature of a substance with no phase change. The temperature change can come from sun absorption or warmer air from ventilation etc.
Latent heat flow
Latent heat is energy absorbed by or released from a substance during phase change from a gas to liquid or vice versa. Boiling water is a good example, shen boiling over a stove, energy is being absorbed from the heating element (stove) and goes into expanding the water molecules into a gas, known as vapor instead of changing the temperature further.
Human comfort depends on providing acceptable levels of both sensible heat (temperature) and latent heat (humudity). Change in temperature in sensible heat flow and change in moisture content is latent heat flow. The total heat flow is the sum of these two.
