Calculated

The TURNOVER time shall be calculated based on the total volume of water divided by the flow rate through the filtration process.

A new methodology is being proposed for use in the future that calculates the recommended minimum design recirculation flow rate, which is called the maximum sustainable BATHER LOAD (MSBL) calculation. The MSBL calculation is based on the values in MAHC Annex Table 4.7.1.10.2 (below) and adjusted by all applicable multipliers in MAHC Annex Table 4.7.1.10.3 (below) as the maximum TURNOVER time allowable based on the pathogen load and CHLORINE demand imparted by BATHERS. Whereas, the traditional TURNOVER time values (required in MAHC Table 4.7.1.10 above) are based on physical transport processes of CONTAMINANTS and disinfectant in the POOL. The MSBL design TURNOVER rates should use the adjustment factors provided. For mixed-use POOLS, each zone of the POOL should individually meet the recommended TURNOVER time for the zone based on the lesser TURNOVER time calculated by the procedures already described. All of the maximum TURNOVER times provided in MAHC Table 4.7.1.10 are required for AQUATIC VENUES as defined in the MAHC. The MSBL values calculated might help to identify POOLS that could be slightly over-designed to meet the demands placed on the AQUATIC VENUE. Furthermore, the MSBL approach actually identifies risk factors that might require higher or lower levels of treatment based on the actual system. * Zone Volume (ft3) = Zone Surface Area (ft2) x Average Depth (ft) * Zone Bather Load Factor (BATHERS/ft3) = 1 / {Surface Area per BATHER (ft2/BATHER)} x (Average Depth (ft)) * Estimated Maximum Number of Bathers Per Zone = Zone BATHER LOAD Factor (BATHER/ft3) x Zone Volume (ft3) * Raw Recirculation Flow Rate Per Zone (gal/min) = Estimated Maximum Number of BATHERS Per Zone x 5.34 (a constant) * Turnover Time (h) = Water volume (gal) / {Recirculation rate (gal/min) x (60 min / 1 hr)} Table 4.7.1.10.2: Bather Loading Estimates Water Depth Surface Area Per Bather Under 3 feet (0.9 m) 25 ft2 (2.3 m2) 3 to 6 feet (0.9 m to 1.8 m) 30 ft2 (2.8 m2) 6.1 to 10 feet (1.9 m to 3.0 m) 22 ft2 (2.0 m2) Over 10.1 feet (3.1 m) 16 ft2 (1.5 m2) Table 4.7.1.10.3: Recirculation Rate Multipliers (Adjustment Factors) Adjustment Reason Adjustment Factor Recommendation(s) Edge Loading (more bathers at edge of larger pools) 1.1 Pools must be greater than 100,000 gallons (378, 541 L) Spas must be greater than 10,000 gallons (37,854 L) Increased-Risk (diaper-aged patrons present) 0.75 Pool designed for at least 10% of patrons to be diaper-aged. Activity / Line (attractions increase bather density) 0.5 Any pool/spa with an associated ride or activity (besides swimming) or line to enter High-Temperature (increased sweat production) 0.5 Pool/Spa with water temperatures routinely exceeding 95 F. Indoor (protected from some environmental factors) 1.15 Pool/Spa must be located completely indoors year round. Limited-Use (pools that are frequently lightly loaded) 1.33 Pool must be at an Apartment, Condominium, or Hotel/Motel with no associated attraction or activity. Showering Recommended (showering reduces bather load) 1.15 Pool/Spa must recommend showering prior to entry. Example Calculation For example, here is a set of example calculations for an indoor POOL in a hotel that is 20 feet (6.1 m) wide by 30 feet (9.1 m) long with an even floor slope that goes from 4 feet (1.2 m) at the shallow end to 6 feet (1.8 m) at the deep end. * Zone Volume (ft3) = 20 ft x 30 ft x 5 ft = 3,000 ft3 * Zone Bather Load Factor (BATHERS/ft3) = 1/(30 ft2/BATHER) x (5ft) = 0.00666 BATHERS/ft3 * Estimated Maximum Number of Bathers Per Zone = 0.00666 BATHER/ft3 x 3,000 ft3 = 20 BATHERS * Raw Recirculation Flow Rate Per Zone (gal/min) = 20 BATHERS x 5.34 = 106.8 gal/min * Turnover Time (h) = 3,000 ft3 x 7.48 gal/ft3/(106.8 gal/min) x (60 min/1 hr) = 3.5 h * Adjustments for indoor pool and limited use pool: 3.5 h x 1.15 x 1.33 = 5.35 h Compare the MSBL value of 5.35 h to the value in Table 4.7.1.10.3 of 5 h and use the lower value = 5 h. Additional example calculations are provided in Table 4.7.1.10.4. Table 4.7.1.10.4: Recirculation Rate Calculation Examples by Pool Type Based on Bather Load Large Indoor Pool Wave Pool Activity Pool Spray Pad Kiddie Pool Spa Deep Diving Pool Small Pool Volume 322,000 gals. (1,218,902.6 L) 750,000 gals. (2,839,058.8 L) 50,000 gals. (189,270.6 L) 20,000 gals. (75,708.2 L) 1,000 gals. (3,785.4 L) 750 gals. (2,839.1 L) 100,000 gals. (378,541.2 L) 35,000 gals. (132,489.4 L) Average Depth 7.33 ft. (2.23 m) 4.98 ft. (1.52 m) 3.00 ft. (91.44 cm) 1.00 ft. (30.48 cm) 1.00 ft. (30.48 cm) 1.50 ft. (42.72 cm) 16.00 ft. (4.88 m) 5.00 ft. (1.52 m) Surf Area 5870.20 ft2 (545.36 m2) 20120.5 ft2 (1,869.26 m2) 2228.16 ft2 (207.00 m2) 2673.80 ft2 (248.40 m2) 133.69 ft2 (12.42 m2) 66.84 ft2 (6.21 m2) 835.56 ft2 (77.63 m2) 935.83 ft2 (86.94 m2) Square Side 76.62 ft. (23.35 m) 141.85 ft. (43.24 m) 47.20 ft. (14.39 m) 51.71 ft. (15.76 m) 11.56 ft. (3.52 m) 8.18 ft. (2.49 m) 28.91 ft. (8.81 m) 30.59 ft. (9.32 m) Factor 1 (bathers/ft3) 0.007346 0.025 0.02 0.04 0.04 0.02667 0.003906 0.00945 Factor 2 (bathers/ft3) 0.006011 0.00778 0.009445 0.04 0.04 0.02667 0.003906 0.00735 Factor 3 (bathers/ft3) 0.003821 0.00504 0.009445 0.04 0.04 0.02667 0.003906 0.00655 Total Bathers 219.09 797.52 78.81 106.95 5.35 2.67 52.22 34.93 K 5.34 5.34 5.34 5.34 5.34 5.34 5.34 5.34 gpm Q 1171 4261 421 571 29 14 279 187 Minimum Turnover 275 176 119 35 35 53 358 188 Raw Turnover 4.58 2.93 1.98 0.58 0.58 0.58 5.97 3.13 >100K gallons/Large Pool Edge Load Factor 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Small Pool High Risk Factor 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 Activity Pools Density/Line Factor 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 >90°F (32°C) Hot Water High Temp. Factor 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Indoor Pools Env. Protect Factor 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 Shower Required Bather Load Reduction 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 Plain Pools Only: Apartment/ Condo/Hotel Limited Use Factor 1.33 1.33 1.33 1.33 1.33 1.33 1.33 1.33 Final Turnover (Hours) 5.8 1.61 0.99 0.22 0.44 0.22 7.56 4.16 w/ a Required Shower 6.67 1.86 1.14 0.25 0.5 0.25 8.69 4.78 Standard Table Values 4.0-5.0 1.5-2 1-1.5 0.25 0.50 .25-.5 6.0-8.0 5.0 When POOL recirculation rate recommendations are broken down to their essential elements, it is essentially about removing suspended matter (including microbial contaminants) with the filters and effectively maintaining uniform FREE CHLORINE RESIDUAL at the proper pH. Both the FREE CHLORINE RESIDUAL and the microbial concentrations are a function of the number of BATHERS in a given volume of water. While it is not possible to always accurately predict the BATHER COUNT for a given POOL on a given day, it is generally possible to estimate the maximum number of BATHERS likely to be in any given type of POOL per unit surface area (since most batherS have at least their head above water most of the time and the primary activity in a pool often dictates the comfort level in regards to bathers per unit surface area and hence the likelihood of bathers entering or leaving the pool). After establishing a maximum sustainable bather load (MSBL) or maximum number of BATHERS expected in a POOL, it is possible to calculate the recommended flow of recirculated water necessary to be treated in order to handle the pathogen load and CHLORINE demand imparted by the BATHERS. An empirically-derived multiplier was used by PWTAG¹⁴¹ to convert the MSBL to the recommended recirculation rate. The empirical multiplier used in this code was derived independently using English units specifically for use in the U.S. The value of the U.S. multiplier is approximately 29% smaller than the PWTAG value using equivalent units because POOL design in the UK is more conservative than in the US.