ASSUMPTIONS:
1. For both the case studies, tenement and high rise building, two scenarios were built up:
Scenario (a): CHP running throughout the year.
Scenario (b): CHP shut down during summer.
2. For tenement block, we did not use mini CHP (Baxi Dachs), as we fail to get payback period, though we meet the total heat demand. It is found for both the scenarios.
Therefore for our analysis, we used micro CHP, for tenement block.
3. For high rise building, we did not use micro CHP (Whisper Gen), as we get a payback period more than 11 years, meeting the total heat demand. It is found for both the scenarios.
Therefore for our analysis, we used mini CHP, for high rise building.
4. A minimum hour of operation of CHP is 5000 hours.
5. Summer period taken into account:
Start of Summer-130th day of the year.
End of Summer-290th day of the year.
6. Cost of Natural Gas- £0.04/ year / kWh
7.Cost of Electricity-£0.14/ kWh
8. Maintenance cost of CHP-£0.006 / kWh electricity
9. Boiler Efficiency-65%
10. Installation Cost for CHP
(a) For Tenement Block
Therefore the installation cost for tenement block = £925/ flat.
(b) For High Rise Building
Therefore the installation cost for High rise building = £ 4325/ flat.
METHODOLOGY ADAPTED FOR CALCULATIONS
1. Amount of Grid electricity = Total Electrical Demand- Total CHP supply
2. Cost of Electricity = Total Electrical Demand*Cost of Electricity
3. Boiler Fuel Cost = (Cost of Natural Gas* Total Heat Demand)/Efficiency of Boiler
4. CHP Fuel Cost = (Total CHP Electrical Demand*Cost of Natural Gas)/ Total Electrical Efficiency of CHP
5. CHP Maintenance Cost = Cost of Maintenance* Total CHP Power Supply
6. CHP Running Cost = CHP Fuel Cost + CHP Maintenance Cost
7. Total Running Cost (Old System using Boiler) = Boiler Fuel Cost + Cost of Electricity
8. Total Savings = Total Running Cost (Old System using Boiler)- CHP Running Cost
9. Payback Period = Installation Cost / Annual Cost Savings
10. Amount of Heat Wasted = Total Heat Demand – Total CHP Heat Supply
The above assumptions were considered and following the methodology we generated the results as shown below:
Old System (using Boiler)
Cost of Electricity- £10.23
New System (Using CHP)
Payback Period- 11 years
Cost of Electricity- £8.57
Annual Cost Savings- £690
Waste heat production- 5.7 %
Old System (using Boiler)
Cost of Electricity- £19.23
New System (Using CHP)
Payback Period- 14 years
Cost of Electricity- £13.14
Annual Cost Savings- £317 /flat
Waste heat production- 39%
The above results show that installing CHP can reduce our electricity bills, but the long payback period does not encourage us to invest in the system.
© University of Strathclyde 2009
