characteristics of energy-efficient swimming facilities – a case study
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Energy 75 (2014) 508e512
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Energy
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Characteristics of energy-efficient swimming facilities e A case study
Wolfgang Kampel a, *, Bjørn Aas a, Amund Bruland b
a SIAT - Centre for Sport Facilities and Technology, Department for Civil and Transport Engineering, Faculty of Engineering Science and Technology,Norwegian University of Science and Technology (NTNU), Trondheim, Norwayb Department for Civil and Transport Engineering, Faculty of Engineering Science and Technology, Norwegian University of Science and Technology (NTNU),Trondheim, Norway
a r t i c l e i n f o
Article history:Received 8 April 2014Received in revised form31 July 2014Accepted 2 August 2014Available online 22 August 2014
Keywords:Energy efficientSwimming facilitiesSwimming poolsSavingsEnergyPools
* Corresponding author. Tel.: þ47 45134270; fax: þE-mail addresses: [email protected] (W.
(B. Aas), [email protected] (A. Bruland).
http://dx.doi.org/10.1016/j.energy.2014.08.0070360-5442/© 2014 Elsevier Ltd. All rights reserved.
a b s t r a c t
The European Union has introduced a directive with the aim to reduce primary energy production. With40% of energy consumption connected to buildings there is a particular need of understanding the en-ergy consumption profile and determine measures to achieve the agreed targets. Swimming facilities is abuilding category with particularly high energy consumption. The aim of this paper is to identify energy-efficient facilities and do an in-depth analysis to be able to determine their characteristics and further todescribe how they achieve this low energy consumption. In order to find the most energy-efficient fa-cilities, questionnaires were sent to all Norwegian swimming facilities. The results were screened and afollow up questionnaire, making a deeper analysis possible, was sent to the facilities with the lowestenergy-use. The in-depth analysis showed that the facilities with the lowest energy consumption useheat exchangers and heat pumps to recover energy from the outgoing water and air. The energy is thenused to warm up incoming air, pool water and tap water. However, it can be seen that even the bestswimming facilities have room for improvement.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
In Europe, there is an overall target of energy savings in primaryenergy production of 20% within 2020 [1]. Around 40% of energyconsumption is related to buildings [2] and there is a considerableneed of action in order to reach the mentioned targets. Within thebuilding sector, sports facilities may be described as high-levelenergy consumers [3], where swimming pools and ice rinks areon top [4]. This paper describes a case study on Norwegian swim-ming pools.
In order to meet the requirements of different user groups thereis a considerable variety of swimming facilities in Norway. While alittle shallow pool is enough for pupils to learn swimming, thefeatures of the largest facilities (leisure pool facilities) arecompletely different. Their offer often includes a pool of interna-tional size, a pool with artificial waves, a diving platform, differentwater attractions and relaxation areas like a restaurant, spa orsauna. Opening hours reflect the variety of size where small school
47 73597021.Kampel), [email protected]
pools are open for 20 h per week and the largest facilities for up to80e90 h per week for.
These different concepts result in different building envelopes,HVAC (heat, ventilation and air-conditioning) systems and watertreatment systems [5] which is expected to lead to equal variationin energy-use. Some data about energy-use in swimming facilitiesare published [4e10] but little is stated on why facilities achievelow energy consumption. Further, several papers deal with specificsubjects related to the water and energy aspects of swimming fa-cilities, like evaporation [11e13], heat pumps [14e18] and buildingenvelope [19].
The publications about evaporation from Shah [11,13] focusalmost exclusively on the calculation while Asdrubali [12] includeda chapter about energy consumption. However, no solutions orsuggestions are given.
The publications concerning heat pumps [14e18] conclude thatthis investment leads to savings in energy consumption. Sun et al.[16] calculated the payback period to be 1.1 year for a pool inShanghai when investing in using a ventilation system with a heatpump dehumidifier. Additionally, it must be mentioned that in-vestment in energy saving measures is closely related to the pricestructure for energy in each country, in particular price differencesin electric and thermal energy [20].
W. Kampel et al. / Energy 75 (2014) 508e512 509
Trianti-Stourna et al. [5] state that the energy-use for swimmingfacilities in Mediterranean climate is about 4300 kWh/m2 watersurface (WS) and up to 5200 kWh/m2 WS for buildings in thecontinental European zone. There is no indication about wherethese numbers originate from. The authors suggest architecturaland electromechanical interventions to improve the energy-efficiency of swimming facilities.
A Finnish publication [6] deals with one swimming facility inFinland calculating the energy-use to be 2784 kWh/m2WS per year.This number is much lower than the one presented by Trianti-Stourna et al. [5] but it represents only one swimming facility ona theoretical basis.
Data from Germany [7] and Norway [8] include swimming fa-cilities from the whole country and show a large spread in energy-use. The papers include only statistics and no more informationabout what makes the difference between swimming facilities withhigh and low energy consumption.
In a publication by Swedish public authorities [4] the numbersare presented in kWh/m2 useable area (UA) and it is not stated fromwhere these numbers originate. The only known fact is that nomulti-purpose facilities are included. The publication reports thedistribution of energy to the different subsystems but there is nodistinction between the swimming facilities with high and lowenergy consumption.
British authorities [9] distinguish between “typical practice” and“good practice” without defining criteria for the categories.
The study published by Kampel et al. [8] divides the facilities ingroups based on their WS and analysed their final annual energyconsumption (FAEC). Considerable variations were found withinthe groups leading to the research question for this paper. How canthe most energy-efficient swimming facilities be described? Whatmakes the difference between facilities with high and low energyconsumption?
2. Methods
A questionnaire was used to collect data from Norwegianswimming facilities. In total, more than 250 data sets (one data setis defined as the FAEC for one year for one swimming facility) werecollected where a bit more than a third (37%) could not be used dueto inaccuracy, missing data or the lack of energy measuring devices
Table 1Overview over the collected data for all swimming facilities.
Category 1
Facility 1 Facility 2
Building year 1966 1969Annual opening hours 1404 2904Annual visitors 55,000 44,700Air temperature [�C] 30 32Water temperature [�C] 27.5 28e32Humidity [%] 55 55WS [m2] 281 312.5Water consumption [m3] 3563 6500Water consumption per person [l] 65 145FAEC [kWh/m2 WS/hour opened] 2.93 1.40Automatic water quality control ✓ ✓
Water quality within regulations ✓ ✓
Heat pump for filter cleansing (pool refill)Heat exchanger for grey water (showers) ✓
Heat pump for grey water (showers)Heat exchanger in HVAC ✓
Heat pump in HVAC ✓
Energy from HVAC distributed to air ✓ ✓
Energy from HVAC distributed to pool water ✓
Energy from HVAC distributed to tap water ✓
at the facilities. The questionnaire was processed by senior staff atthe facilities.
The swimming facilities were divided into three categories. Thebuildings in category one are characterized by containing one pool.The second category includes facilities with two or three pools.Typically, a sports pool and a therapy pool that is slightly warmer.The third category consists of the biggest swimming facilities withseveral pools and water attractions. These categories differ slightlyfrom the ones used by Kampel et al. [21] and the Danish Techno-logical Institute [10]. The central change is the shift of facilities witha sports pool of 25 m � 12.5 m (WS of 312.5 m2) from the second tothe first category.
The termWS used in the article is equal to the pool surface area.The attractions are not included, but an overview can be found inTable 2.
The facilities were evaluated concerning their energy con-sumption and a follow up questionnaire was sent to those using thelowest amount of energy in each category to learn more about theircharacteristics. As benchmark for energy consumption kWh/m2
WS/opening hour was used as suggested by Kampel et al. [21]. Inthe analysis, delivered energy [22] is studied while primary energyis not discussed. The whole questionnaire with all included ques-tions can be found in the Appendix A. Further information wascollected by personal communication with plant representatives.
The original intention was to investigate three pools in eachcategory, which was not possible under the given circumstances.The authors met the greatest challenges concerning swimmingfacilities in category one as this building type is often combinedwith other sports halls or facilities and have no separate measuringdevices installed. In general, some of the swimming facilities,which seemed to show good energy performance, turned out to benot so energy-efficient after a deeper analysis, and had to beexcluded. Another reason to exclude answers was a general lack ofunderstanding of the energy systems by plant operators, leading toinaccurate responses.
Climate correction was applied, as the FAEC of the differentswimming facilities is dependent on the location and annual climatevariations. Referring to Enova [23], 40% of the FAEC in swimmingfacilities are influenced by the climate and needs to be adjusted. Alldata was corrected, using the Oslo climate of 2010 (degree-days ofOslo in 2010) as reference, with the following formula [24]:
Category 2 Category 3
Facility 3 Facility 4 Facility 5 Facility 6
1995 1982 2008 20073682 3294 4328 4114100,000 130,000 365,000 210,00028 30e33 31 3128.5 29.6 28 28.955 55 55e60 60548.5 637.5 1467 117013,278 11,817 48,418 16,250133 91 133 770.86 0.78 0.89 0.47✓ ✓ ✓ ✓
✓ ✓ ✓ ✓
✓ ✓
✓
✓ ✓ ✓
✓ ✓ ✓ ✓
✓ ✓ ✓ ✓
✓ ✓ ✓ ✓
✓ ✓
Fig. 1. Energy flux for the swimming facilities the most advanced technology (facilities4 and 6).
Table 2Water attractions in different facilities.
Category 1 Category 2 Category 3
Facility 1 Facility 2 Facility 3 Facility 4 Facility 5 Facility 6
Small children slide 1 m Springboard Slide (55 m)Diving platformSaunaSolarium
Slide (42 m)Diving platformWhirlpoolSpraysFlow channelSteam bathSaunaSolarium
Small children slide2 Slides (63 m & 67 m)Diving platformWhirlpoolSpraysFlow channelSteam bathSaunaSolarium
2 Slides (60 m)Diving platformWhirlpoolSpraysFlow channelSteam bathSaunaSolariumCounter current system
W. Kampel et al. / Energy 75 (2014) 508e512510
Energy useOslo ¼ Energy useactual facility
ð1� 0:4Þ
þ 0:4*
Degree daysOslo
Degree daysactual facility
!!
The Norwegian degree-days for the calculations originate fromEnova's website [25] and where recalculated to fit with the actualopening period of the facilities during the year.
2.1. Error analysis
The authors are dependent on the quality of the reported dataand therewith on the staff in the different swimming facilities.Quality control was applied but is only applicable to a certain de-gree and cannot eliminate the uncertainties completely.
The degree-day method is an acknowledged procedure [26] andwidely used by EU member countries [27]. Enova [23] suggests toapply climate correction to 40% of FAEC which is based on experi-ence. This percentage is hard to verify as it is expected to vary be-tween different facilities. Variations in the age of the facilities,energy management and usage patterns may change the climatedependent share.
3. Results
All facilities fulfill the requirements concerning water quality.Chlorine is used for disinfection and all facilities use pressurizedsand filters. Additionally, some use an activated carbon filter inpartial flow and UV (ultraviolet) equipment for disinfection. Facil-ities 1, 2 and 4 are closed during the summer (school holidays)while the other facilities are open during the whole year.
With respect to filter cleansing, different concepts are identified.Filter backwash may be manual or automatic. The cleansing pro-cedure varies from all filters being backwashed during the openinghours to automatic backwash of filters during night time.
The facilities in category 1 are older than 40 years but only fa-cility 2 went through major refurbishment in 2003 (ventilation andwater treatment) and 2009 (renovated poolroom and improvedinsulation of the outer walls). Facilities 4 and 6 had minor reno-vation of the building (civil works) while facilities 3 and 5 are un-changed since they were built.
In addition, Table 1 shows a relationship between the usedtechnology for water and energy management and the FAEC. Fa-cilities equipped with the whole range of systems for energy re-covery are the ones with the lowest FAEC. Table 1 shows that theselection and configuration of technology has a strong impact onannual water and energy consumption. The technologies describedinclude products from European suppliers and are commonly usedin Norwegian swimming facilities.
The categories show a significant spread concerning water at-tractions (Table 2) with facilities 1 and 2 offering few attractionswhile facilities 4, 5 and 6 provide a wide variety of features. Theitem “sprays” includes attractions like water mushrooms, water-falls, fountains, water cannons, etc. The heat loss due to evaporationincreases energy consumption but most of it can be recovered bymodern technology. The bigger contributor to FAEC is electricity,which is needed for the rotating equipment to operate theattractions.
The flow chart in Fig.1 shows the energy flux in a plant using themost advanced concepts for energy recovery (facilities 4 and 6). Theflow chart illustrates a short loop (pool water) and a long loop(poolroom ventilation). All the pool water, tap water and air areenergy carriers. The flow chart shows only the energy flux insidethe building.
The embedded heat pump in the air-handling unit recoversenergy from exhaust air from poolroom, and delivers energy forpreheating of incoming air, pool water and tap water. The grey
W. Kampel et al. / Energy 75 (2014) 508e512 511
water heat pump collects energy in grey water from showers andfilter cleansing. The warm side of the heat pump delivers energy totap water, used for refilling pools, or further heated for use inshowers.
4. Discussion
Table 1 shows that even some of the most energy-efficientswimming facilities in Norway differ significantly consideringtheir performance data. The significant difference between thestudied facilities in category 1 has different reasons. Both facilitiesare approximately equally old but facility 1 did not have any re-furbishments. Besides that, facility 2 has a modern HVAC systembut does not recover any energy from wastewater. Another inter-esting aspect is water consumption, especially proportional tovisitors. The substantial variation of water consumption can beexplained by the showers, where 9.75 L per minute (l/min) passthrough the shower heads in facility 1 compared to 15 l/min infacility 2. Another influencing factor is the grey watermanagement.Facility 1 achieves good water quality when exchanging only thewater from filter cleansing. In facility 2 an additional 4m3water perday have to be exchanged in order to achieve good water quality.
The difference in energy consumption of the two facilities incategory 2 is approximately 10%. Facility 4 uses significantly lesswater per person than facility 3 which can be partly explained bythe shower heads (10 l/min versus 9 l/min). Concerning energyconsumption facility 4 uses more advanced technology recoveringenergy from the wastewater of the showers and the HVAC systemrecovers excess energy also for preheating of tap water.
The buildings included in category 3 show a substantial differ-ence in FAEC, Facility 5 uses almost the double amount of energy asfacility 6. The reasons are a more advanced HVAC system in facility6, which recovers energy also to tap water, and energy recoveryfrom the backwash of filter cleansing. Facility 5 has a considerablehigher water consumption compared with facility 6. This maypartly be described by shower properties (10 l/min vs 6 l/min flowrate) and partly by the extra feeding of bleed water (4.4 m3/day) inorder to maintain water quality within limits. Further, the filterconfiguration in facility 5 with horizontal sand filters requires morefrequent backwash, increasing water consumption.
In general, the flow rates of the used shower heads needs to bediscussed as water for the showers represents a big share of thetotal water consumption.While the flow rate is easy tomeasure thebehaviour of the visitors is uncertain. It is unclear if all of the vis-itors take a shower before and after entering the pool and for howlong they use the showers. An average value for the shower dura-tion based on experience is 7 min [28].
Another interesting observation is that facilities 2 and 5 usehorizontal sand filters, which are known to be designed with lowersurface load and more frequent backwashing. Still the plants reporta need of additional feeding of tap water to the pools for keepingthe water quality within the regulations.
The total energy demand is mostly dependant on the usedtechnology for energy and water management, with the buildingenvelope being not as important [29]. Kampel et al. [21] showedthat FAEC, amongst others, is highly dependent on water con-sumption. This finding could be confirmed for the facilities in cat-egories 2 and 3 meaning that an energy analysis always has toinclude an equal analysis of water balance.
The facilities redirecting recovered energy from the ventilationsystem to pool and tap water show a better energy performance(FAEC). Especially in the summer months, there is a substantialsurplus of energy in the air from the swimming hall [16,29] and it isimportant that this surplus is not wasted. Sun et al. [16] show intheir case study from Shanghai that the recuperated energy from
the ventilation is enough to heat pool water for more than eightmonths per year. Facility 1 has a significant unused potential, asthey do not distribute the recovered energy from the air to pool andtap water. Facilities 3 and 5 have an unused capacity too, as they donot recover energy to the tap water.
A possibility to use the energy surplus [16,29] is combiningwater and energy systems by using holding tanks for grey waterand pre-heated tap water. Two storage systems are necessary forthe system to work. The heat pump recovering energy from greywater has to be operational as long as possible. Therefore, thestorage tank is needed to store energy in form of grey water andmake it available for the heat pump to use. Typically, the storagetank is filled with grey water caused by the visitors during the day.Flushing the filters during the night makes it possible for the heatpump to run around the clock. Further, it is important to transferthe recuperated energy to a newmedium tomake it available whenneeded. A logic choice for swimming facilities is to save pre-heatedwater in storage tanks. As tap water is mainly used for showers andrefilling pools after backwash, refilling should only be done duringnight time to reduce the need of storage volumes.
An interesting observation is that the used technology is notnew and most of it is described in the literature. Waterewater heatrecovery in swimming facilities is well described in the paper fromChan and Lam [14]. Energy recovery from air to air has been knownsince the 1960s. During the last decades this technology has beenimproved. Sun et al. [16] and Johansson and Westerlund [15]describe an HVAC system where energy is recovered fromexhaust air and applied to incoming air and pool water. The mostadvanced solutions identified in this study show a slightly moresophisticated system. To the knowledge of the authors, this systemis not described in the literature yet. The recovered energy is usedto heat the incoming air, pool water and tap water. For this solutionto work, it is essential that the condensers for air and pool water arearranged parallel and not in series. After the condensers, an after-cooler for preheating of tap water is essential to achieve the bestresult.
5. Conclusion
Good energymanagement in swimming pools requires recoveryof energy from air and water and distribution of recovered energyto air and water, features that were found in all investigated facil-ities. The ones using the most advanced technology used leastenergy. The relationship between water and energy consumptionwas found to be inconsistent. Low water consumption does notnecessarily result in a low FAEC but the two facilities with lowestFAEC use very little water, too. Partly explanations for the signifi-cant differences in water consumption are the flow rates of theshower heads and the use of bleed water to keep water qualitywithin regulations. However, these two factors do not account forall of the differences found, leaving some of the triggers for lowwater consumption unexplained. With Norwegian climate andenergy prices, energy recovery is best achieved using heat pumps.The most efficient swimming facilities have established storagevolumes for greywater as well as pre-heated tapwater tomaximizethe heat pump's operation time. It is essential that HVAC systemsare designed to recover energy from air and distribute it to theincoming air, pool water and tap water.
Most of the facilities among the best in Norway in terms ofenergy management show potential for improvement.
Appendix A
The questionnaire used for in-depth analysis of the selectedswimming facilities.
W. Kampel et al. / Energy 75 (2014) 508e512512
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