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assessment of their effectiveness in meeting current and future needs. If there is some extra capacity available then it may be possible to reduce operating temperatures and flow rates in heating circuits, which will generally be of benefit to the CH scheme. It is also important to establish the method of control used for both time and temperature in order to predict accurately effects on the CH systems.

When details of existing systems are available it will be possible to propose a programme of works that will enhance existing systems and yet still be compatible with the proposed CH system. However, several options may have to be considered and cost estimates are prepared for use, in an overall option appraisal.

In some buildings, the provision of domestic hot water may represent a significant part of the demand, and there are a number of ways of generating domestic hot water from a CH system. The most energy-efficient schemes will involve taking advantage of the low temperature of the cold water feed so as to cool the community heating return as close as possible to this temperature. This leads to the use of non-storage calorifiers or additional coil surface in cylinders. In larger buildings, two-stage heating, utilising the return water from a space-heating circuit to carry out pre-heating of the cold water feed, is the best solution, provided it should be economical.

3.4: Central Plant

Once the heat demand assessment has been made, work can commence on examining the central plant options. The aspects to be covered are:

• prime mover choice

• fuel choice, contract flexibility, and security

• site location and topography, and interfaces with fuel, electricity and CH infrastructure

• balance between CHP heat and boiler heat

• provision of standby capacity

• building to house the plant.

It is likely that a number of options will present themselves and each will need to be analysed under similar assumptions to determine the optimum selection. Capital, operating and maintenance costs will need to be assessed for each combination of plant.

The CHP operating strategy needs to be developed to establish the most economical method of operation in relation to varying heat and power demand profiles and varying selling prices, e.g. following the heat demand at full output and dumping heat. A spreadsheet-based operating model is essential to ensure that the correct operating strategy has been made and to calculate the annual energy flows, and to permit rapid sensitivity analysis.

The optimum CHP plant capacity needs to be determined by considering a range of plant sizes and by carrying out an economic assessment of each. For single-site CHP projects it is important to have a reasonable match between the generated output and the electricity demand. For a CHP/CH system, electricity is often sold in bulk and the site demand must also be taken into account. However, there may be good opportunities for selling electricity to customers who are more directly linked to the scheme, by use of system arrangements. In this case, modelling the CHP plant in re本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。