Microgeneration

Question 1

What is microgeneration?

Answer 1

Small-scale generation of heat and power.

Question 2

What are microelectricity technologies?

Answer 2

Small devices capable of producing electricity.

Question 3

What are some examples of microelectricity technologies?

Answer 3

Solar PV
Wind

Question 4

What are microheat technologies?

Answer 4

Small devices capable of producing heat.

Question 5

What are some examples of microheat technologies?

Answer 5

Solar thermal
Ground source heat pumps
Biomass

Question 6

What are the benefits of home / community microgeneration?

Answer 6

Reduced energy costs.
Contribution to environmental targets.
Enhanced security of supply.
Financial incentives.

Question 7

How does home / community microgeneration lead to reduced energy costs?

Answer 7

1. Less electricity used from National Grid.
2. Less heating oil used to heat development.
3. Less natural gas used if gas pipeline available locally.
4. Less fuels purchased for heating.

Question 8

How does home / community microgeneration lead to a contribution to environmental targets?

Answer 8

Reduces use of fossil fuels so reduces emission of GHG.

Aided NÍ in meeting 40% target from renewables by 2020.

Question 9

How does home / community microgeneration lead to enhanced security of supply?

Answer 9

1. Require less electricity from National Grid.
2. Require less natural gas.
3. Required less heating oil.
4. Require less miscellaneous fuels.

Not vulnerable to energy price hikes.

Question 10

How does home / community microgeneration lead to financial incentives?

Answer 10

Significant financial incentives for installation by home owners or local communities.

Makes project more viable from financial perspective and reduced repayment period.

Question 11

What is a heat pump?

Answer 11

Technology designed to transfer thermal energy from low temp region to higher temp region, against natural temp gradient.

Question 12

What are 2 examples of a heat pump?

Answer 12

Fridge-freezer
Air conditioning system

Question 13

How does a heat pump work in a fridge-freezer?

Answer 13

Takes thermal energy from lower temp fridge interior and transfers to higher temp kitchen to keep food cool and reduce rate of decay.

Question 14

How does a heat pump work in an air conditioning system?

Answer 14

Transfers energy from lower temp interior to higher temp outside.

Question 15

What are all the components of a heat pump?

Answer 15

Expansion valve
Evaporator
Compressor
Condenser

Question 16

What are the 5 stages of the operation of a heat pump?

Answer 16

1. Evaporator
2. Compressor
3. Condenser
4. Expansion valve
5. Repeat process

Question 17

What is involved in the first stage of the operation of a heat pump?

Answer 17

Refrigerant enters evaporator in liquid form cooler than outside temp.

Energy transfer from outside to evaporator, increasing internal energy of refrigerant and changing into gas.

Question 18

What is involved in the second stage of the operation of a heat pump?

Answer 18

Refrigerant in gas form integers compressor.

Gas compressed which increase internal energy further to level above temp inside house, required electricity.

Question 19

What is involved in the third stage of the operation of a heat pump?

Answer 19

Refrigerant passes to condenser where thermal energy of gas transfers to inside of house.

Temp of refrigerant decrease as loses energy and condense into mixture of gas and liquid.

Question 20

What is involved in the fourth stage of the operation of a heat pump?

Answer 20

Refrigerant passes to expansion value when expands and loses energy.

Condenses back into liquid with temp lower than temp outside.

Question 21

What is involved in the fifth stage of the operation of a heat pump?

Answer 21

Refrigerant pumped to evaporator where cycle continues for as long as pump turned on.

Question 22

What are the 2 types of heat pumps?

Answer 22

Air source
Ground source

Question 23

What is the function of an air source heat pump?

Answer 23

Located outside building.

Has fan that maximises convection current through to evaporator, ensures max thermal energy transferred per second and increases effectiveness.

Question 24

What are the advantages of an air source heat pump?

Answer 24

Easily installed in existing and new buildings.

Lower cost than ground source.

Does not require large area of ground around building.

Question 25

What are the disadvantages of an air source heat pump?

Answer 25

Air temp varies more than ground temp during year, lower air temp contains less thermal energy so limits COP to lower than ground source. Makes humming noise.

Question 26

What is the function of a ground source heat pump?

Answer 26

Extracts thermal energy from refrigerant that circulates in loop in ground. At depth over 0.5m, ground has temp throughout heat between 6-12oC, allows fluid to absorb energy. When pumped back to heat pump, transfers thermal energy to evaporator through heat exchanger.

Question 27

What are the advantages of a ground source heat pump?

Answer 27

More consistent higher range of temp, higher COP. Repayment period smaller.

Question 28

What are the disadvantages of a ground source heat pump?

Answer 28

Large upfront costs. Larger area of ground required to install pipework loops.

Question 29

What is the equation for calculating the COP of a heat pump?

Answer 29

COP = QH / W

Question 30

What are the quantities involved in the equation COP = QH / W?

Answer 30

COP = Coefficient of performance for heat pump (no unit). QH = Thermal energy leaving system at hot end (J). W = Electrical energy supplied to heat pump (J).

Question 31

Why is the value for COP using the equation COP = QH / W incorrect?

Answer 31

Does not take into account energy taken from air or ground.

Question 32

What are the 3n those of ground source heat pumps?

Answer 32

Horizontal loop Vertical loop Pond loop

Question 33

Which type of ground source heat pump is the most expensive?

Answer 33

Vertical loop.

Question 34

Which type of ground source heat pump is the least expensive?

Answer 34

Pond loop