Swimming Pool Water Temperature and Heating Costs Simulator

This interactive calculator performs an accurate and full heat loading cost calculation, comparable to AS 3634 Solar heating systems for swimming pools, for the three main types of heaters in Australia - solar, heat pump and gas (for full validation see here).

* Use a time and area average in shoulder times, hence if half the pool is shaded for half the day, the setting should be 25%. As another example, if half of the pool is shaded for the whole day use a 50% setting.
** Note: if you choose the south facing roof pitch, the compass direction North is now actually defined as South, NorthEast is SouthEast and NorthWest is SouthWest, while West is still West and East is still East.
§ Heat pumps need to be regularly maintained - even then they lose efficiency over their 10-year average lifetime. Condenser coils and air filters become dirty and clogged up, refrigerant levels may not be optimal all the time. This factor takes this into account; adjust it if you have an estimate from your heat pump manufacturer.
¥ Choosing a different pump to run the solar will affect both the system's thermal efficiency and COP factor (electrical efficiency). Pumps are ideally chosen to produce approximately 100% pool volume turnover per day, however this can be varied depending on what's important to you, i.e. thermal efficiency or electrical efficiency. With a 42m² PoolMasterPro (14 tube) system with 100% coverage, even at a pump power producing close to the minimum recommended AS 3634 flow of 2 L/min/m², we can get a solar COP of ~100 with a 6% collector loss over the 5 L/min/m² scenario. A low pressure loss OKU system running at 10 L/min/m² is both electrically and thermally efficient.
† See below for definitions.
^ 10-year running costs are calculated in wage earnings (hence are dependent on your tax bracket) and do not include unit replacement and maintenance costs. They include energy cost inflation, unit efficiency degradation (see "Data Used" section for factors), and interest.
‡ Please refer to our solar pool heating manuals on our download page for different types of plumbing arrangement. Note: manual systems have a 15% efficiency penalty factor over automatic systems, as people are not going to baby-sit their systems and turn them off manually every time it clouds over.

Assumptions and Data Sources Used by this Calculator

• This calculator performs full heat loss/gain balance calculations similar to AS 3634 to predict pool temperatures. It uses literature-updated evaporation, convection, and radiation heat loss factors. Where there is debate as to the exact magnitude of the loss factor in the literature, we use consensus average values. Predicted pool temperatures were validated by comparing to AS 3634 and PoolHeat program V 5.10.9 programmed by Prof. Graham Morrison.
• The predicted solar boosted pool temperatures given by the calculator were triple validated by comparing to experimental values given in: 1) the American SRCC solar collector database real-world efficiency testing reports for OKU collectors: http://www.solar-rating.org 2) "Testing of Solar Swimming Pool Heaters", Phase 1, by K.I. Guthrie, Victorian Solar Energy Council, report 237-P2/2/84-KG, September, 1984. Implemented in the solar simulation PoolHeat program V 5.10.9. 3) Czarnecki J.T. Swimming Pool Heating by Solar Energy, CSIRO Division of Mechanical Engineering, Technical Report No.TR19, 1978.
• Solar collector efficiency scaling factors for different roofs were taken and fitted to data supplied in "Testing of Solar Swimming Pool Heaters", Phase 1, by K.I. Guthrie, Victorian Solar Energy Council, report 237-P2/2/84-KG, September, 1984.
• The calculator performs a correction for East or West mounted solar collectors (collectors mounted on west facing roofs get the benefit of substantially warmer air and roof temperatures). 3pm and 9am average air temperatures and wind velocities taken from http://www.bom.gov.au/climate/data/ were used in these corrections, assuming a typical unglazed collector efficiency curve.
• Evaporation, convection, radiation loss and light transmission scaling coefficients for pool blankets were fitted to reproduce blanket covered pool temperature data given by Czarnecki J.T. Swimming Pool Heating by Solar Energy, CSIRO Division of Mechanical Engineering, Technical Report No.TR19, 1978. (Adjusted for the different weather data used in the Czarnecki work). With a mean absolute error in pool temps of 0.2°C.
• Minimum acceptable pool temperatures were set around 20°C, while desired temperatures were about 5°C higher. Source: Sheridan, N.R. "The Heating of Swimming Pools", Solar Research Notes No. 4, (1972) University of Queensland. However, this calculator adjusts these values slightly higher especially for modern times and northern states.
• Gas boiler efficiency, source: http://www.energyrating.gov.au
• Pool heat pump efficiencies are taken from all the actively manufactured units on the US AHRI Certification Directory Database (as of Nov 2018, out of manufacture unit data were discarded) source: https://www.ahridirectory.org
• Pool heat pump manufacturer specified performance data points are defined in the 2014 Standard for Performance Rating of Heat Pump Pool Heaters: ANSI/AHRI Standard 1160. Test points are at HAHH = High Air temperature High Humidity (27°C|80%|27°C), HAMH = High Air temperature Mid Humidity (27°C|63%|27°C), LAMH = Low Air temperature Mid Humidity (10°C|63%|27°C)
• In the calculator heat pump efficiency drop down definitions are as follows: "Least Efficient of the Modern Units" is the average LAMH, HAMH and HAHH specs of the bottom 10 units in the AHRI Database (as sorted by the LAMH value). "Typical Efficiency of Heat Pumps" is an average of the vast majority of units in the AHRI Database (approx. 250 units, excluding the top 10 worst and best). "Use Highest Efficiency Units" is the average specs of the top 10 best units. The drop-down "Older Generation Existing Unit" is approximated as 0.5 COP units less than the worst modern unit in the AHRI Database (this number is a guess and should be used with caution, as we could not find data on COP efficiencies of existing old units in Australia).
• A note of caution on the ANSI/AHRI 1160 standard and AHRI listings: it should be kept in mind that as of Nov 2018, this is a voluntary American Standard, as such it's expected that only heat pump manufacturers with good COP numbers have the motivation to voluntarily test their units. Hence the COP numbers used in this calculator may very well over-estimate COP efficiencies of "Typical" units sold in Australia. Regardless, the calculator has facilities to specify custom COP efficiencies.
• Electricity rate, source: https://reneweconomy.com.au/market-insight-residential-electricity-price-series-96026/
• Gas price rates, source: "Gas Price Trends Review 2017", Version 2.1 March 2018, source: https://www.energy.gov.au/publications/gas-price-trends-review-report
• Average max and min daily temperatures source: 1301.0 - Year Book Australia, 2012
• Average daytime humidity used for the heat pump humidity corrections was taken from http://www.bom.gov.au/climate/data/ using the 3pm data, while the average 9am data was used as the average nighttime humidity.
• Assumed 10-year loss in efficiencies are as follows: ~20% for heat pumps, ~10% for gas heaters, ~15% for PoolMasterPro strips, ~5% for OKU pool panels (HDPE is not subject to surface chalking).
• Term definitions given in "Data Used" section:
• Ta = mean monthly dry bulb air temperature (Source: Australian Solar Radiation Data Handbook, ASRDH v2, 1987)
• Ts = mean monthly effective sky temperature (Literature average sky temperature factors are used, corrected using BOM total number of cloudy vs clear days monthly data)
• Tw = mean monthly pool water temperature in an unshaded, uncovered, unheated pool (as calculated)
• V10 = mean monthly wind speed at 10 metres above the ground (m/s) (Source: Australian Solar Radiation Data Handbook, ASRDH v2, 1987, scaled to 95% due to climate change wind speed trends: Troccoli et al., 2012)
• Pa = mean monthly partial water vapour pressure in the air (kPa) (Source: BOM)
• Qh = mean monthly global solar irradiation on a horizontal plane, (MJ/m2.d) (Source: Australian Solar Radiation Data Handbook, ASRDH v4, 2006)
• Qi = mean monthly total solar irradiation on a north facing plane inclined at the latitude angle (MJ/m2.d) (Source: Australian Solar Radiation Data Handbook, ASRDH v4, 2006)
• Ave_Temp = mean day or night time dry bulb air temperature (Source: 1301.0 - Year Book Australia, 2012)
• Td = desired temperature of the pool, set on the Heating Options tab (and the Finer Max Desired Temp Adjustments on the Advanced Adjustments tab)
• R_Humidity = 3pm or 9am mean relative humidity used for heat pump COP corrections, depending on if the heat pump option is set at "Night Usage" or "Day Usage" (Source: BOM)