Define microgeneration?
The small-scale generation of heat and power
What are the main sources of microgeneration?
Solar PV
Wind
These are micro electricity technologies: Small devices capable of producing electricity:
Solar Thermal
Ground Source heat pumps
Biomass
These are micro heat technologies: Small devices that are capable of producing heat.
Explain the benefits of microgeneration - Reduced energy costs
The amount of energy used from fossil fuels decreases: (Less costs & Purchases)
Less electricity used from the National Grid
Less heating oil used to heat a develop
Less natural gas used if a gas pipeline is available locally
Less fuels purchased for heating eg logs & coal
Explain the benefits of microgeneration - Environmental
The use of microelectricity also aided NI in its ambitious target of 40% renewables from 2020. This target was reached in June 2019 when 44% of electricity was derived from renewables.
Explain the benefits of microgeneration - Security
Less reliant on fuels which are vulnerable to price hikes. Both Geopolitics and currency movements can cause these rapid changes.
Explain the benefits of microgeneration - Financial incentives
These make the project more viable from a financial perspective and reduces the repayment period for such projects considerably.
How does energy transfer with regards to temperature?
Energy Transfers naturally from a high temperature body to a low temperature body.
What does heat pump do?
A heat pump transfers energy from a low temperature region to a higher temperature region against the natural temperature gradient.
Where are heat pumps used?
Radiators, AC, fridges
Describe the changes of state from ice to steam?
Ice gains energy to become a mixture of ice and water up to 0 degrees, A significant amount of energy is needed to make the substance entirely water.
As more energy is added the liquid heats up and slowly becomes a mixture of a gas and a liquid.
An enormous amount of energy has been absorbed to covert all the water into steam.
What is compression of a gas?
The force applied to and end plate increases the pressure of the gas
Work is done on the gas giving it more internal energy making its molecules move with greater Ke increasing the temperature.
What are the four components in a heat pump?
1 - Expansion Valve
2 - Radiator
3- Compressor
4 - Radiator
What is the expansion of a gas?
The compressed gas exerts a force onto the moveable end plate making it move to the right.
The gas expands as the volume inside the cylinder increases, reducing gas pressure.
As the compressed gas has exerted a force over a certain distance, the compressed gas has done work. So the gas has less internal energy afterwards.
The molecules will move with a reduced average kinetic energy, the temperature of the gas will decrease.
What is important about the position of the expansion valve and compressor?
The expansion valve is on the LHS and the compressor is on the RHS of the external wall and both are secured to a concrete foundation.
Both are installed by the supplier & never move position.
Explain how the evaporator works?
The radiator located on the lower temp side is always required to absorb thermal energy from the lower temp side.
A HTF is passed through this component and HTF must be a lower temp than the external environment.
The HTF gains thermal energy and evaporates to a gaseous state. This occurs at a constant temperature and is too low of a temperature to be directly transferred from into the radiator inside the house.
Explain how the condenser works?
The radiator located on the higher temp side is always required to radiate energy to this location.
A HTF is passed through this component and this HTF must be a higher temp than the external environment.
The HTF in a gaseous state emits thermal energy to its surroundings losing thermal energy & decreasing in temperature. The gas condenses to a mixture of gas & liquid.
Explain Stage 1: The Evaporator of a heat pump
The refrigerant enters the evaporator and is cooler than the external environment. Energy transfers from the surroundings to the evaporator. The internal energy of the refrigerant increases and changes to a gas. While this gas has much more energy it still exists at a low temp. The temp must be increased to enter.
Explain Stage 2: The Compressor of a heat pump
Passes into the compressor in a gaseous state and is compressed to increases its pressure and temperature to a level above the inside of the house. The refrigerant can pass to the Condenser.
Explain stage 3: The Condenser of a heat pump
The refrigerant transfers thermal energy to the cooler external surroundings and its temp will decrease. It will condense into a mixture of a gas and a liquid.
Explain stage 4: The expansion valve of a heat pump
The mixture of gas & liquid is allowed to expand and the refrigerant does work. The pressure decreases & the refrigerant loses energy so its temp decreases and it condenses to a liquid. The liquid is a lower temp than the surroundings.
Explain Stage 5: Repeat the process of a heat pump
The refrigerant after leaving the expansion valve is a liquid and at a lower temp than the surroundings. It can be pumped to the evaporator for the cycle to continue.
What parts of the heat pump require electricty?
A pump is required to transfer this refrigerant from component to component. This pump and the compressor require electricity - must be provided & paid for.
How does the heat pump work in AC and fridges?
The radiator in the house now acts as the evaporator as it absorbs energy from the lower temperature side.
The radiator outside the house now acts as the condenser as it emits energy to the higher temperature side.
The evaporator & condenser changes sides
The direction of the flow of refrigerant changes.
