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Saving energy in swimming pools

Heated swimming pools are operated by schools, universities and hotels as well as dedicated sports and leisure organisations - even hospitals have hydrotherapy pools. They are expensive to run, with energy costs being a major factor. This is not surprising, as the demands of the energy intensive processes are often exacerbated by very inefficient standards of operation. Improvements in the operating regime will not only reduce energy costs and carbon emissions but can sometimes improve both water quality and the user’s experience as well.

This article explains how pools use energy and what you can do to reduce running costs.

It covers the following topics:

  • How is energy used?
  • Pool hall ventilation
  • Pool circulation
  • Heating plant
  • Combined heat and power
  • Other opportunities

You might also like to read these related articles:

Boiler Plant – Beasts in the Basement

Are boiler controls a good idea?

Is your BMS Wasting Energy?

How is energy used?

In addition to heating the water, swimming pools use energy for circulating the water through the filtration system in order to maintain water quality, and to achieve appropriate conditions in the pool hall. In most swimming pools the main cause of heat loss is the ventilation and the electrical demands of fans and pumps may also be considerable.

Pool hall ventilation

This is usually the most significant energy cost, involving not only electricity use in fans but the substantial thermal input necessary to maintain temperatures. The critical first step to reducing costs must be to use a pool-cover. This prevents evaporation and the associated heat loss when the pool is unused, and the reduction in humidity will allow reduction in both ventilation rate and temperature when the cover is in place. Ideally, the pool cover should be put in place whenever the pool is unused for any length of time, not just overnight, and a mechanical reel is recommended in order to facilitate this. It should be possible to drop the pool hall temperature to about 22-25oC overnight with the cover in place, although this will vary according to the construction of the pool hall, external temperatures etc. A pool cover will reduce humidity, water use, and the consumption of volatile chemicals in the pool water.

The ventilation3450_jt13-nuff-nottingham - - becky rate may be reduced using “inverter” drives on the supply and extract fan motors. Ideally, the ventilation rate should be controlled on humidity, with the temperature being maintained 1-2oC higher than the temperature of the pool water when the cover is in place. It is important that this temperature is maintained at the air/water interface in order to reduce evaporation, and care should be taken with ventilation rates to ensure that increased stratification does not result in lower air-temperatures at the interface. The majority of pool halls are heated only by their ventilation systems, and although the installation of additional heating within the hall may be mechanically challenging, the evidence of a small number of installations suggests that this can result in much greater efficiency as well as improved comfort, and may well be worth the investment. Under-floor heating and additional radiators may both improve comfort conditions and reduce energy use.

Due to3450_1pic2-insight15 - - becky the requirement for a high ventilation rate and the high pool hall temperature when the pool is uncovered, heat-recovery on the ventilation system is essential. There are a number of methods of achieving this, with most pools having either a “plate” heat-exchanger within the air handling unit (AHU) or a system of run-around coils. Occasionally, heat-pumps are used, but these installations are not always successful, usually due to engineering or maintenance limitations. The heat-recovery should be capable of achieving an efficiency of about 50%, and an approximate figure may be obtained by measuring the supply, ambient air and extract air temperatures.

Pool circulation

This is 3450_1pic3-insight15 - - beckyoften a fruitful source of energy savings, as it tends to be neglected and attract much less maintenance and management attention than it should. All pool circulation systems should be fitted with flow meters and these should be checked periodically. In usual circumstances a volume equivalent to the capacity of the pool should be circulated every three hours, and the flow-meter will show whether this is being achieved, or over-achieved as is often the case. It should be borne in mind that it may not be necessary to achieve this circulation rate continuously. If there are long periods of inactivity in the pool some reduction may be appropriate and this may be beneficial for filter efficiency. Circulating pumps should therefore be inverter-driven, as through the operation of these devices a small reduction in circulation rate can result in a big reduction in electricity use.

Ideally, the circulation system should have pressure gauges fitted on the flow and return, and if the power input to the pumps can be determined (which may be done either using an energy analyser or from the inverter drives) and the circulating rate is known it is possible to calculate the pumping efficiency. Poor figures may indicate that the pumps need attention or that there are other hydraulic issues. A common problem is “leakage” back through the stand-by pump or pumps in a multiple pump installation, and stand-by pumps should be manually isolated.  Another common problem is blocked strainers and those fitted with clear plastic lids make checks straightforward. Pool circulation systems are often out of sight and out of mind, but an 18-kW pump might use over 150,000 kWh/year costing £10,000 or more, and a 20% saving will often be achievable, although the savings may be much greater than this.

Heating plant

Heated 3450_1pic4-insight15 - - beckyswimming pools will require an almost continuous thermal input. This will usually be provided through the operation of boiler plant either alone or in conjunction with combined heat and power (CHP). Ideally, separate plant should be used for the generation of domestic hot-water (DHW) and the boiler installation should be both condensing and capable of operating efficiently at low outputs – i.e. have a good turn-down ratio. All too often boiler plant is massively over-sized – no more than about 400kW should be required for a normal-sized pool, although installations in excess of 2,000 kW have been seen. Boiler operation is often very inefficient and should be thoroughly investigated (see Boiler Health Check below).

Combined heat and power

CHP 3450_1pic5-insight15 - - beckyinstallations are often regarded as an obvious choice for swimming pool installations due to the alleged scale of their thermal demands. However, in many cases CHP is both over-sized and inadequately controlled. Analysis indicates that there is no correlation between the presence of CHP and the efficiency of “wet” leisure centres.

The removal or curtailment of the CHP is often the first step towards achieving reductions in energy use and carbon emissions of 30% or more. CHP units are not a “tick-the-box” energy saving measure and do not automatically result in carbon or financial savings. For CHP to achieve a net carbon reduction, beneficial use must be made of about 60% of the thermal output. Whether or not it is financially viable will depend on the relative costs of gas and electricity.

Other opportunities

In addition to the main opportunities identified above, there will often be savings to be made in lighting, ventilation of changing-rooms and other areas, comfort-cooling and other aspects of the operation of a swimming pool although, if major savings are to be made, the ventilation and circulation systems are usually the areas to prioritise.

Your Independent RISK FREE Solutions

We have extensive experience of reducing the energy consumption of pools and leisure centres. A Green Consultancy Investment Grade Energy Efficiency Audit will identify and prioritise all cost-effective energy saving opportunities. To ensure that the energy consumption of your boilers and associated equipment is minimised we suggest a Boiler Health Check. For an investigation of all equipment controlled by your building management system you might like to consider a BMS Health Check or a BMS Audit.

Put us to the test NOW! To discuss your requirements please call John Treble on 01761 419081 or email John@GreenConsultancy.com

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Energy Management Training for Sporta

“The Green Consultancy provided training for Sporta members in London and Sheffield – covering all aspects of energy management in wet and dry leisure centres, including CHP and voltage management.

These workshops were greatly appreciated by our members and it was clear that The Green Consultancy has a comprehensive understanding of energy management in the leisure sector and a rigorous energy efficiency methodology for identifying the most cost-effective opportunities for reducing energy costs and carbon emissions.”

Brian Leonard, Chief Executive

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Multisite Energy Efficiency Survey for Nuffield Health Fitness & Wellbeing

“The work undertaken by The Green Consultancy, particularly the energy surveys and recommendations, allowed us to develop an energy strategy and capital investment plan to achieve savings & reduce our carbon emissions - £2.3M invested, with a payback period of under two years, yielding savings of £1.2M pa.”

Dale Sheppard, Former Group Energy & Environment Manager

See case history of our work for Nuffield Health


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Energy Efficiency Audit Sports Leisure Management Ltd

"A very helpful and worthwhile service - identifying opportunities to reduce energy costs by 28% with a payback period of under two years. I would recommend it to anyone who wants their business to be at the forefront of environmental practices not only for ethical reasons but also for cost saving ideas to help your business save money."

Adam East, Operations Manager, Watford Leisure Centre Central