Services whole-life costs Heating

Heating is one of the most common engineering services elements. Unless a specific use precludes the need for heating, almost every building requires some form of heated environment to maintain comfortable conditions for the occupants.

The key to an effective heating design is to stick to the concept of a basic, well-engineered design solution, which should maximise the use of form and fabric to control the internal environment, and meet the varying requirements of use, operating times and internal conditions. Ideally, the system should be able to fulfil each of the following criteria: adaptability, variable operating range, ease of installation, simple operation, low maintenance, low capital cost, low running costs and good energy efficiency.

Unfortunately, no one heating system can meet all of these requirements. Inevitably, different systems will perform well in different areas, and this latest article in the series on whole-life costs assesses how four alternative heating installations perform over 25 years.

The building used for the cost model is a naturally ventilated community centre designed for a range of uses, from small offices to larger spaces suitable for communal activities.

A number of different heating solutions would be appropriate for a building of this nature. The four examined in this article are:

• Option 1 Low-temperature hot-water heating with pressed steel panel radiators
• Option 2 Low-temperature hot-water heating with continuous sill-line perimeter heating
• Option 3 Electric heating via peak-time wall-mounted radiant panel heaters
• Option 4 Electric heating via off-peak night storage heating and fan-assisted daytime boost facility.

There are advantages and disadvantages to each of these systems, and the decision on which to use may depend on a number of issues. If minimal maintenance and low capital costs are key factors, the electrical options may suit.

Alternatively, if low energy costs and good temperature control are essential, one of the low-temperature hot-water options would be ideal. However, with the cheapest capital cost option being the most expensive over the life cycle, considering whole-life costs at the outset of the design process is once again critical to the end user.

Capital costs for the heating systems

The capital costs shown below are based on the community centre's design criteria in the table). The costs comprise the cost of the complete heating installation, including supplies to mechanical plant and equipment, builder's work in connection, main contractor's preliminaries, overhead and profit and attendance, and an apportionment of professional fees. For the electrical heating options, the additional costs for a larger electrical supply and additional mains and low-voltage distribution are also included. It is assumed that the client would not be eligible to claim capital allowances, and these have therefore been excluded.

Whole-life costs

The whole-life cost for each option has been calculated over a 25-year period and is expressed in terms of its net present value. The life-cycle calculation for each system consists of four primary elements:

• Major asset replacement Major items of plant and equipment, such as boilers, pumps, flues and heat emitters
• Sundry replacement and repairs An allowance for the periodic replacement of faulty system components such as fans in night storage heaters, control valves and so on
• Planned preventative maintenance The annual cost of employing a specialist contractor to undertake full preventative maintenance tasks
• Energy costs The annual cost for consumption of electricity and gas.

The life expectancy of individual items of plant and equipment is generally based on the Chartered Institution of Building Services Engineers' Economic Life Factor Codes and Schedules, published in the Guide to Ownership, Operation and Maintenance of Building Services. Where available, manufacturers' data on guaranteed life expectancy has also been used.

The discount rate used to calculate the net present value for each element of the life cycle is about 4%. The whole-life cost model also makes allowance for replacement of the heat emitters for every option once during the life cycle.

Cost analysis

Both electric options perform well on capital cost, with the electric radiant panel option (option 3) providing by far the lowest initial cost. It is less than half the cost of the low-temperature hot-water perimeter heating (option 2) and considerably cheaper to install than the low-temperature hot-water radiator (option 1) and electric night storage (option 4).

The night storage system, despite being more expensive than electric panel heating, is still 18% cheaper than the low-temperature hot-water radiator and 35% cheaper than the perimeter heating.

The whole-life cost analysis tells a different story, with option 1 (low-temperature hot-water radiators) performing the best, followed by the night storage heaters (option 4), perimeter heating (option 2), and finally electric radiant panels (option 3).

Option 3 performs particularly badly because of its high annual energy consumption. The panel heaters use peak electricity, which means a large energy cost in comparison with the three other systems.

The low-temperature hot water options, which use gas as the main heating medium, are particularly cost-effective in terms of energy spend, although they do require more annual maintenance than the electrical systems. This is because of the need to regularly service boilers, pumps and so on, and the requirement for water treatment.

Despite the use of cheap off-peak electricity, option 4 (electric night storage heaters) is still expensive to run, with energy costs about double those of the low-temperature hot-water options.

Overall, despite being more expensive to install, the low-temperature hot-water radiator performs the best of the four options, although the night storage heater option runs a close second.