Commercial Pool Heating

For most centres, energy costs form the second highest operating cost after salaries/wages. Indeed, energy costs may be equivalent to around 15% of total operating costs. As each dollar reduction in energy costs through energy management returns a direct and recurring improvement in the operating bottom-line position, the management of energy costs is critical to efficient operation and future viability.

The complexity of efficient energy management depends on the nature of the pool centre. For large aquatic centres with indoor/outdoor wet and dry facilities, the optimal approach to energy management must include sophisticated energy management control, say through a Building Management System (BMS). At the other end of the spectrum, energy management at a part-season limited outdoor facility, may be confined to selection and operation of water heating plant, pump operation and adherence to sensible blanket cover routines.

Pool water heating is undertaken primarily by solar, gas, electric heat pump, electric element and heat recovery. Each of these heating sources have differing capital costs, running costs, heating characteristics, operating requirements, etc. The selection between heating source must be a balanced decision, weighing the importance of each of the above factors to the specific needs of the pool centre. No one technology is the correct choice in all cases.

EVALUATING THE CORRECT HEATING OPTION

Ultimately, the selection between heating technologies will be determined by a mix of the desired heating system performance and available/ongoing budget. In many cases, this will involve a compromise between these factors within the constraint of the available budget.

A full economic evaluation, preferably considering whole-of-life costs, should be fundamental to heating system selection. Various sources are available to provide detailed computer modelling of the heat load characteristics of swimming pools to determine these costs. These sources include consultants, industry associations and manufacturers. While this modelled data is fundamental, the selection of the heating system must also be made with a clear understanding of the pool manager's intentions for operation of the pool, based on the marketing plan.

The standard industry modelling facility has been developed by the University of New South Wales (Poolheat Program, Version 2.6 "Performance Evaluation of Swimming Pool Heating Systems".

HEATING CHARACTERISTICS OF INDOOR POOLS

The heating characteristics of indoor and outdoor pools vary quite markedly and present differing economics regarding heating system selection. The heat load an indoor pool is much flatter than an outdoor pool, ie. the peak winter heating load is less than twice the summer load. This occurs as the indoor pool does not get the benefit of direct solar gain in summer, whereas the outdoor pool may require little or no boost heating due to solar gain. The opposite applies in winter where the indoor pool is protected from extremes of outside air temperature.

The total energy requirements of the indoor and outdoor pool may be similar as the indoor pool has an ongoing requirement for heating throughout the year. This characteristic means that the indoor pool heating system has a higher monthly utilisation factor and significantly lower peak load requirement. The level of installed heating capacity for an indoor pool is much smaller and is matched more closely to the load. These factors suit a heat pump system. The use of solar is also suited to an indoor pool as virtually all of its' summer capacity is required by the pool, whereas this heat transfer is not needed by the outdoor pool in the peak of summer. The use of gas is feasible as the total heating cost will not be prohibitive.

HEATING CHARACTERISTIC OF OUTDOOR POOLS

The outdoor pool's heating requirement varies significantly over the year. The winter heating load may be more than four times the summer load. There is also more variability in the heat load profile of an outdoor pool, as the heating requirement varies dramatically depending on differing levels of sun and wind exposure and blanket routines. This factor means that anecdotal evidence regarding heating system performance or costs do not transfer well from one pool to another.

The expected heating profile of an outdoor pool is particularly important in considering solar installation. The cost-benefit of solar should not be assumed. The economic value of capital investment in solar heating should be based on the dollar value of the energy (either gas or heat pump) that it displaces. For an outdoor pool that is sheltered from the wind and in full sun, there may be no need for auxiliary heating system contribution. In this context, any solar heating system capacity would be redundant, except at the edges of the season. For outdoor pools, the solar system contribution in cooler months is also considerably less as a percentage of the total pool heat load than is the case for an indoor pool.

The capital cost of a heat pump system for an outdoor pool increases dramatically compared with an identical indoor pool. Likewise, the level of utilisation of this capital investment is reduced. This occurs as the heat pump system is designed to meet the maximum rate of heat loss in winter and consequently, the reduced heat load of the outdoor pool in milder months through direct solar gain makes much of this redundant for much of the year. This characteristic supports the installation of integrated heat pump and gas systems, with the level of heat pump capacity reduced by around one-third and replaced with gas boost. The running cost penalty of this approach is reasonable and the pool manager gains the benefit of heat pump efficiency with the rapid heating capability of gas. The use of gas alone at published tariff rates would appear uneconomic for full-year heating in all States over than Victoria. Final project economics will be determined by comparative installation costs and high costs for electricity supply upgrade can change the relative economics.

POOL BLANKETS

The benefit of blanket coverage in reducing the rate of heat loss for an outdoor pool is clearly evident. As with the use of solar in an integrated system, the heat retention benefit of the blanket should be translated to the energy value of heater operation avoided and this figure contrasted to the cost of the blanket. This analysis will support blanket use. For indoor pools, blankets provide the additional benefit of containing evaporative losses to the pool hall (reducing condensation).