0.25 degrees C an hour is very slow. I need a heater for 1-2 degreec C an hour.
Then you need a heater of roughly 36-72 kW.
Is this too much to ask? even if I buy Pentair UTHP-9-HX for $3K AUD, still that will give the same resutls as the ebay cheap one since both are 9Kw.
It will give the same results, but will be a lot easier on your pocketbook to operate. ?
Heating times always correlate to heater output power. That said, the cheap eBay heater is a resistive heater. Resistive heaters output in heat exactly what they draw in power. So a 9 kW resistive heater outputs 9 kW of heat and uses 9 kW of electricity. This is usually always the
most expensive way to heat a pool. What do you pay per kWh of electricity? I pay $0.11 per kWh, so that ebay heater would cost me $0.99 per hour to run.
The Pentair UTHP-9-HX is a heat pump. Heat pumps are a lot different than resistive heaters. They output
more heat than the power they draw! This particular Pentair can output a maximum of 9.5 kW of heat, while drawing only 1.5 kW of heat. So essentially the same heating performance, but because it draws so much less power, it costs only 1/6th as much to run!
Heat pumps output more heat than the power they draw because they are not
producing heat, they are moving it, hence the name "heat pump". They draw heat from the air around your pool and put that into your pool. They can even do this when the air temp is lower than the pool temp, just like an air conditioner takes heat from the cool inside of your house and puts it into the much hotter air outside your house. In fact, an air conditioner is a heat pump, though the name
heat pump in common usage is usually reserved for devices that heat things rather than cool them.
Now, while it will pretty much always draw 1.5 kW, it won't always put
out 9.5 kW. How much it outputs depends on the ambient and pool temps. That 9.5 kW is peak performance, at an ambient of 24 °C and pool water temp of 27 °C. If the ambient temp was cooler or the pool water temp was hotter the output would be lower than 9.5 kW.
If you can afford it, a heat pump is much preferable to a resistive heater (such as the eBay one), although you need a much bigger one to get the temp rise times you desire.
will NG gas heater do better?
Generally, yes, at least for temp rise (perhaps not operating cost though). In the USA, the biggest NG heaters you can get are rated at 400,000 Btu/hr input and 80% efficiency, so they output 320,000 Btu/hr. This is 94 kW output heating power, so a NG heater with this rating would give 0.0286*94 = 2.7 °C/hr temp rise in your pool.
How much do you pay for NG in Australia? Here in the USA, natural gas prices are pretty cheap, and so a NG heater is usually about on par with a heat pump in terms of operating cost. This depends on location and desired length of use, as in hot places heat pumps usually win out but in cooler places or extending the swim season into spring and fall a lot NG heaters win out.
