Commercial Aquatic Centres – Energy Efficiency Analysis & Operating savings

Following a request from a well-known Aquatic centre, Sondex were invited to carry out an energy efficiency assessment on possible waste heat recovery & in addition, if we could try & ascertain or explain why their energy bills have noticeably increased, year after year, but confusingly well above the energy price rises indicated on their statements. Sondex visited two (2) Council & YMCA AQC around Melbourne & were amazed at the findings. The aim was to establish a base line cost for the supply of both Gas & Electricity. As suppliers & rates varied from area to area we decided to take an average for these calculations.


A typical AQC plant room consists of heating boilers, pumps, filtration & Chlorination systems, a plate heat exchanger, valves / controls & heaps of pipe work. The first items we considered were where can energy be lost or inefficiently consumed & are they being maintained for optimum operation. We were able to quickly see that the boiler & plant rooms were actually contracted to a regular service regime & that the boilers were serviced & checked regularly, the filters/chlorination systems are maintained amazingly well, (& for a very good reason) however what we did observe was the absence of any attention to the heat exchangers or pumps. The pumps we can understand, as they will either leak or stop if there is a mechanical problem, but the heat exchangers have no cleaning or inspection regime whatsoever & yet that is the single most important piece of equipment tasked with transferring the energy produced in a boiler into the pool water as efficiently as is humanly possible. Any energy that does not get transferred from the “Heat Exchanger” into the pool water, is simply lost & passed out the flue of the boiler. It really is that simple.


It suddenly became apparent that pool operators assumed the boiler contractors would service the heat exchangers but nothing is further from the truth, that’s like a pilot hoping that the radar technician is also checking the brakes, boilers & heat exchangers are very different appliances & require very different servicing attention.


So, back to the wasted energy & the high bills….


The fact is that as the heat exchanger is a complex series of plates carefully designed, pressed & arranged into honeycomb like array that can super efficiently transfer the heat (energy) created by the boiler into the pool water through very thin layers of Titanium plate. Well certainly that’s the design on day one. The problem that follows is that unless you keep these heat transfer plates clean, they slowly & surely foul up & slowly over time silently stop working efficiently. Picture touching a BBQ plate that is hot (yes ouch!!), now put a layer of dirt or mud on it & suddenly you can touch it & no ouch. That’s what happens on the surface of a heat transfer plate. It builds up layers of human fats, dirt & other foreign bodies & it insulates heat from being transferred.


So when this fouling occurs (& yes it happens to 100% of heat exchangers in this service) the boiler sensors see the pool water is not achieving its required temperature & it fires up, the pool pumps start to receive less water flowing through the (blocking) heat exchanger & so they work harder. The boiler still sees no improvement in the pool temp. & so it stays on high fire for longer…. & thus energy is now being wasted every second of every minute of every day, & yes the numbers really do start to add up.


Unfortunately fouling is like emphysema of the heat exchanger, it is slow subtle & ever so deadly to your constant operating costs. Well now, if that sounds scary then read on as the actual numbers tell the real story.


So here is what really happens inside that little box called a heat exchanger


As it begins to foul up to five system components can be effected:

  1. The first, is the heat transfer through the titanium plates of the heat exchanger reduces. (Tech. terms its Watts per square metre of heat transfer)
  2. This has an immediate effect on the boiler run time. It will spend more time on high fire in an attempt to satisfy the pool temperature.
  3. As the fouling continues the HX is blocking & the pressure drop across the heat exchanger increases, this increases the resistance or back pressure on the pump head, in turn increasing the running cost of the pump (more energy used to achieve a flow).
  4. Over time & left unchecked, this effect will eventually occur on both sides of the heat exchanger effecting both pumps and their running costs.
  5. Eventually the desired pool temperature will begin to drop & not recover. The speed at which this occurs depends on many factors such as, is the pool inside or outside, how many people use the pool, is there a wind factor, the ambient temperature, what season you are in & so on

Increased running cost:


When clean, the average run time of the boiler was 20 minutes in the hour. The boiler output was 485 KW (1,746 MJ) at 75% efficiency the boiler input is 2,328 MJ at 0.6615c/MJ.

  • The boiler normal run time is 20 mins per hour during the 4 months of winter = $14,784.00
  • With a partially blocked plate heat exchanger the boiler run time is 40 mins/Hr = $29,568.00
  • In the event the boiler can no longer maintain pool temperature, run time is 100% = $44,351.19
  • If we take the same approach with the pool pumps at a rate of 5c/KWh the results are as follows. The pumps run continuously so all we need to consider is the cost increase caused by the higher pump head.


Once again based on the averages the pool pump increased its power consumption by approximately 1.0 KW per hour. Over the 4-month period this equates to an increased cost of $144.00 for both pumps during the winter period.

 
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