Pool Heat Pump - Sizing

Swimming Pool Heat Pump Sizing Calculator

This interactive pool heat pump sizing calculator performs an accurate and full heat load calculation, comparable to the AS 3634-1989: Solar Pool Heating Standard , so you can size your heat pump and get an idea of your season (for full validation see here).

Tab 1: Situational Details

Specify your pool's water surface area; note, this must be accurate. Then specify your particular pool's heat loading scenario, and choose if you want solar to offset heating costs or just use a heat pump. Note: Your pool's unheated temperature is shown as a light blue line; this takes into consideration all the heat loading factors you've specified. The dark blue line represents an average Australian swimming pool in the state. The red chart shows your pool with the hypothetical standalone heat pump, or solar boosted. The horizontal dark line represents the minimum acceptable temperature you'd be willing to swim in, while the light orange line represents the maximum desired temperature.

Tab 2: Heating Options

This tab is used to specify your desired season length and the pool temperatures to strive for. Note, the longer the season and the higher the temperatures, the more it'll cost to heat your pool. This tab also allows you to specify heater efficiencies - it is used for the solar and auxiliary heating cost calculations.

Tab 3: Capacity Required

In this tab, you can set if you want to allow longer than recommended run times to lower the heat pump capacity required. Note, your heat pump will work harder if you go outside the recommended hours, as it'll have to work in the evening and morning when air temperatures are cooler. On this tab, you'll also have heat-up times for an unheated pool with your heat loading specifications. Note, if the average temperature doesn't reach the desired temperature, there is still a chance it could touch the desired temperature after a warm spell or day.

Tab 4: Advanced Adjustments

In this tab, you can adjust specific AHRI† COP factors for a particular heat pump if your manufacturer has supplied them. You can also specify and compare various solar pump sizes for solar pool heating systems, as this will impact both the solar system's heating efficiency and COP factor (electrical efficiency).

Tab 5: Financials

Finally, this tab shows the 10-year heating cost comparison for all the heating types. If required, you can override the average energy costs for your state and use your own rates. This tab also shows energy savings from a solar pool heater.

Notes on Heat Pump and Gas Heater Cost Predictions

Please be aware, compared to the industry standard PoolHeat (V 5.10.9) program, our calculator predicts lower year-round heating costs for heat pumps for the capitals Hobart, Canberra, and Adelaide by 15% and Melbourne by 10%. To our knowledge, PoolHeat does not use a humidity corrective factor for the heat pump calculations, while our calculator corrects for high humidity, which can improve COP factors. This calculator also predicts slightly lower auxiliary heating costs overall, possibly due to the lower wind speeds used, as the calculator incorporates recent work on 30-year wind speed climate trends by CSIRO.

* 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.
§ 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 consideration, adjust if you have an estimate from your heat pump manufacturer.
¥ Choosing a different pump to run the solar will effect both the systems 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. A 42m² PoolMasterpro (14 tube) system with 100% coverage, even at a pump power producing close to the minimum recommended AS 3634-1989 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 it off manually every time it clouds over.

About This Calculator

This calculator was developed by EcoOnline.com.au since there was no existing online tool were Australian pool owners could accurately and easily estimate and compare pool temperatures and heating costs, under various scenarios at the level of precision specified in the pool heat/loss loading standards AS 3634-1989 and ISO TR 12596 1995. It's free to use, links to this page are encouraged and welcome. For full validation and comparison to standards AS 3634-1989 and ISO TR 12596 1995 see here. For a brief summary of the assumptions, see below.

Assumptions and Data Sources Used by this Calculator

  • This calculator performs full heat loss/gain balance calculations similar to AS 3634-1989 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 3634-1989 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 valves 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 on in 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 (caution 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 manufactures 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 Australian. Regardless, the calculator has facilities to specify custom GOP efficiencies.
  • Electricity rate, source: https://reneweconomy.com.au/market-insight-residential-electricity-price-series-96026/
  • Gas prices 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 were 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 meters above the ground (m/s) (Source: Australian Solar Radiation Data Handbook, ASRDH v2, 1987, scaled to 95% due to climate change wind speed trends: Troccoil et.al, 2012)
  • Pa = mean monthly partial water vapor 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 under the Finer 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)

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