### Comparing CO2 emissions from different RHI technologies

Calculations were done to determine the CO2 emissions from different technologies. The calculations were based on a typical 4 -bedroom house whose energy requirements are 17000kWh on space heating and 3500kWh on water heating.

Based on the efficiencies of different technologies, the total energy input that yields this output energy (delivered heat) can be calculated.

This is done using the equation 4.1

In order to get the CO2 emissions in Kgs the total input energy is multiplied by the CO2 conversion factors of the different heating technologies as shown in equation 4.2.

These CO2 factors were obtained from

http://www.carbontrust.co.uk/cut-carbon-reduce-costs/calculate/carbon-footprinting/pages/conversion-factors.aspx

In order to calculate the amount of carbon emitted, the fraction of carbon in CO2 is obtained. This is done by taking into account the Relative Molecular Masses (RMM) carbon in the CO2 molecule and is given as
Hence Kgs of Carbon(C) will be given as

Using the equation above, carbon emissions for different fuel technologies were calculated as shown in the table below

### Comparing Annual Heating Bill Costs between Existing and New Technologies

The annual running costs of each of the heating technologies for a typical 4-bedroomed house with typical usage of 17000kWh for heating and 3500kWh for hot water. The approximate costs per kWh were obtained from

In order to get the cost per unit of delivered heat, the efficiencies of using the different technologies have to be taken into consideration. This is done using the formulae

Where η is the efficiency of the system (Heat lost across heat exchange. Pipe work and radiators are not considered for ease of calculation)

According to the data from table 5.1, the annual costs for running wood pellet technologies are cheaper than running the other technologies. Electricity is the most expensive technology to run annually. Running other renewable technologies on their own, such as GSHP and ASHP, is seen to be cheaper than most of the fossil fuel technologies apart from natural gas, which is seen to be relatively cheaper. Just as before, the COP of the GSHP and ASHP will vary with temperatures and, in the colder seasons, lower temperatures will lead to decrease in COP causing more electricity to be used and so increasing the cost of running these technologies.

The table above shows the potential annual savings and possible increase in costs of replacing current fossil fuel technologies with renewable ones. It is observed that replacing current technologies with wood pellet technologies will cause the greatest savings across all technologies.