Yes I thought I would do as you say and use a gas heater to heat up the pool quickly on days I want it any time of the year (keeping a pool blanket on of course). I would have preferred to use a heat pump as the cost would be off set by the solar panels. I heard though that heat pumps are quite noisy which I wouldn't like, nor would my neighbours. I dont know how true that is. Also, the ambient temperature in Sydney in winter would not enable the heat pump to heat the pool enough. Am I on the right track with my thought process? Gas the way to go in Sydney?

It's not a case of a heat pump not being able to do the job, it's the size of the equipment.

For example, if you got a small car with a 1.5L engine and found that it couldn't tow your boat, you might say "a car can't tow this boat." But a Holden Commodore with a V8 engine can tow the boat, so it depends on the size of the car and the engine.

To heat your pool in winter within a day might require a gas heater with around 25kW output. You should be able to get that installed for under $5k.

However, to install a heat pump with the same heat output will probably cost upwards of $20k. Heat pumps are much more complicated machinery than gas boilers, hence the higher costs.

So you could put in a smaller (cheaper) heat pump, but it won't heat you pool as quickly.

Generally heat pumps are not that noisy, although since they contain a fan they do produce some noise so if it's right by your bedroom then it might cause you problems.

One last thing - when I say gas I mean natural gas; ie, connected to the gas main in your street. If you have to use bottled gas (LPG) then that's much more expensive to run.

Thanks for the explanation. Think it's going to be gas heat pump for me.

Haha, I think you mean gas heater not "gas heat pump"?

I stand corrected lol

I'd definitely spend more time researching the time & cost to heat a pool with a heat pump. You want to make the best use of your solar PV system.

How big is your solar PV system? Do you produce a lot of excess electricity that is sent to the grid? A fairly large system (5kW) should produce an average of around 20kWh of electricity a day. Much more in summer, but just over half that amount in winter. So say you are exporting 8kWh of excess electricity a day in winter. A heat pump (COP of at least 3) could produce at least 24kW of heat a day for free. This is in mid-winter, you should have higher levels of excess power in the shoulder season, which could be used to heat you're pool for free. Plus a heat pump with a higher COP, that is efficiency (3 is a very conservative figure), will produce more heat. If you have 3 phase power & a much larger solar PV system you should have much higher levels of excess production.

So I would definitely be spending a lot of time investigating the running costs of both heat pump (using your solar PV) & gas heaters. The time the heater would need to run each day. Life cycle costs (install costs, maintenance costs & life expectancy).

There are quite a few online calculators to give you a basic idea, & I'm sure you'll get plenty more qualified advice (I'm no expert).

Hi ddaroch, yes making a decision isn't easy. I would LOVE to make use of my 'free electricity' and get a heat pump. I have a 5.7kW system and a single phase home. I don't know yet what sort of excess I have as I am waiting for my net smart meter to be installed (new PV system and home still under renovation). I do believe I will have enough excess electricity to run the heat pump.

I have used the on line calculators which show that the heat pump would cost about $3800 pa (doesn't factor in free PV electricity) and $8900 using gas. On that alone one would go with a heat pump, a no-brainer.

However, my concerns with a heat pump are 1. the noise of the pump disturbing neighbours and 2. whether the ambient temperature in Sydney in winter is enough to provide enough heat to the heat pump to heat the pool enough. I have heard that the heat pumps are quite noisy (and need to be placed outside to draw in the ambient heat) and the outside temperature in Sydney would enable the heat pump to work efficiently to allow you to swim in winter. Do you have any experience or thoughts on this?

My concern with a gas heater is with out a doubt its cost, but it supposedly will provide enough heat quickly on the days we want to swim, irrespective of the outside temperature.

Hi guys,

Let's take a look at the numbers.

The swimming pool is 55,000L in volume. To heat the water from 15C to 26C will require 704kWh (Volume x Heat capacity of water x 11C). Let's assume there's no heat loss while you're heating it, and if the pool has a decent cover then the losses will be minimal anyway.

To deliver this much energy in 24 hours will require a heater with output 29kW. (704kWh/24hours)

A gas boiler of this size could be installed for around $5,000 and will cost around 10c per kWh to run.

A heat pump with 30kW output is a huge beast. You'll be paying in the range of $20k-$30k to get it installed and it will require three-phase power. Of course you can get a smaller heat pump, but it won't heat the whole pool in under 24 hours.

A heat pump this size with an average COP of 3 will be drawing around 9-10kW. This is more than your solar system can provide, so you'll be paying to electricity from the grid. Also, if you're trying to heat your pool in one day then at least half the time will be at night which means your solar panels produce nothing.

If your electricity cost is 30c per kWh (seems typical in Sydney) then the heat pump (at COP 3) will produce 1 kWh for 10c (similar to gas!). In winter or at night when the temperature is colder the COP will reduce, so you'll then be paying more than 10c per kWh to run your heat pump.

On the subject of noise - a 30kW heat pump is a big unit with some big fans in it. This is really pushing into the boundaries of of a commercial-size heat pump, so it will produce some noticeable noise. It's hard to comment on whether your neighbours will get upset without knowing more about the layout of your property. A bigger concern would be where to actually put it, you're going to need some serious mounting to isolate the vibrations.

Alternatively you could install two smaller heat pumps. But they'll still produce some noise.

If you really wanted to heat your pool with solar energy then you'd be best with thermal solar panels (eg, evacuated tubes) which are much more efficient then photovoltaic panels. You could get 15kW-20kW solar thermal power with a few panels, and boost the rest with gas or a heat pump. But as you say you have no space for additional solar panels.

Please don't take this as a suggestion that solar energy isn't worthwhile. I'm all for using renewable energy, but you need the right tool for the job. If you want to heat your pool in a day then you'll need a big heat pump. Trying to get "free" solar energy to run it will require a huge number of panels, and if you want to run the heat pump on solar power at night then you'll need to install batteries to store the energy.

You could also investigate whether you need to heat the pool from cold each time you want to use it or whether it would be better to heat it up and keep it warm with a cover during winter. The second option is likely to be cheaper in the long run if you will use the pool frequently in winter.

Hope that helps!

Hi Luxury Home Heating....wow, that really helps! Love your number crunching as it was doing my head in trying to work it out and make sense of the on line calculators. I will now look at the feasibility of some solar tubing on my north facing roof to see if there is enough space to run some to support the gas heater (probably not enough space but worth asking). I very much appreciate your time in helping me through this maze.

You're welcome, feel free to get in touch any time if I can help you with more information.

As you say Luxury Home Heating, if the pool is cold (at ambient temperature) the gas boiler will get it up to temperature much quicker, unless the heat pump is an absolute beast!

But, as you also said, watchedpoppy may not want to let the pool cool down substantially, between swims. This is a much more sensible idea. Use every single bit of excess power to heat the pool. Every day the sun is shining, have the heat pump heat the pool. If the pool status at a reasonably constant temperature, the heat pump won't have to be over sized. Saving on the capital install costs, & ensuring that the heat pump doesn't have a large power draw, that may be higher than the excess power produced by the solar PV.

Oh, & watchedpoppy, I'm not sure about the quality of heat pumps for pools. Yes, heat pumps become less efficient at colder temperatures. But some heat pumps can work in extremely cold temperatures, such as Canadian Winter's (RC AC, which are air-sourced heat pumps). In warmer temperatures, some RCAC's have COP's of 7.0. Meaning they produce 7kW of heat for every 1kW of electricity used.

So have a look at the spec sheets of the heat pumps you're looking at. I'd expect COP's will be at a bare minimum 3.0, but more likely substantially higher than that during a Sydney winter day (especially if you are coastal). So if your 5.7kW system produces an excess of 5kWh a day (it could be more), you'd have a minimum of 15kWh of heat a day that could be dumped in your pool for free, most probably substantially more.

More food for thought, just when I thought I had figured it out.... I'll look into those Canadian heat pump too. Thank you for information.

Interesting information there ddarroch. Do you have any more information on these heat pumps with COP 7.0? Make and model?

My experience (10+ years in this industry) is that air-sourced heat pumps will generally operate with a COP around 3 under typical conditions. If it's cold outside, they'll be down at around COP 2.5.

Here in Australia, Mitsubishi Heavy Industries have recently released their Q-Ton heat pump, with a two-stage CO2 compressor that they're advertising as an "industry leading" COP of 4.3.

Stiebel-Eltron have a heat pump available (WPL25) with a COP 5.09, which is about the best I've ever seen on the market.

Those are both expensive units and at the high end of the range. Of course those numbers are both under ideal conditions, and generally they will be less efficient than that.

Hi Luxury Home Heating, sorry, I confused the COP with the star rating. I was thinking of the 7 star Daikin Ururu Sarara (US7). It has a COP of 5.8 for the 2.5kW unit. So not bad, but not 7 :) As you say, top of the line, under lab conditions.

watchedpoppy, here's something about heat pumps designed for cold temperatures. Note, these are reverse cycled air conditioners (air-to-air), not pool heat pumps (air-to-water). I don't know how heat pumps stack up. It's an American site, so FYI -13F equals -25C.

http://www.mitsubishicomfort.com/benefits/hyper-heating

On a side note, temperature is just the product of the motion of atoms & molecules (kinetic energy). These are in motion all the way down to zero Kelvin (-273C). So although it may feel cold outside, there's still energy available in the site, although heat pumps do become much less efficient when it's cold (the difference in input & output temperatures is important).

One thing that has made heat pumps very inefficient in the past is that the condensing coil would ice up at around zero C. This would have to be thawed out with a plain old electric element (COP of 1). Greatly reducing the overall COP in temperatures around our below zero C.

But the modern heat pumps, which use the CO2 compressors Luxury Home Heating has talked about don't have an electric element to thaw them out, greatly increasing their efficiency.

As for the noise issues. Some modern heat pumps (but not all) are very quiet. So just pay close attention to the decibels they produce, listed on their spec sheets.

FYI, here's a good read. Though it doesn't mention solar PV, which would be advantageous for a heat pump.

https://www.pooledenergy.com/blog/choosing-a-pool-heater-what-are-the-relative-performances-of-solar-gas-electric-pool-heaters/

sorry, predictive text. I meant that there is energy available in the air. I'm sure there's other typos in the too. Swype typing, without proof reading, is not a good mix :)

oh, & by the way. I'm not saying that you need a heat pump for those frigid conditions. I'm just saying that the technology is available, so don't be scared that that can't operate efficiently in winter. Just look for something that is appropriate for Sydney's conditions, & will remain energy efficient in our climate.

Daikin US7 is a wall-mounted air conditioner, not a water heater, so not really applicable here.

Also a 2.5kW unit is probably the smallest heat pump on the market, much smaller than what OP is looking for in this case.

According to Daikin's website here, the 6kW version only has a COP of 4.6 so the efficiency drops off pretty quickly as you go up to larger units.

The typical COP for air-to-water heat pumps operating in Sydney is around 3.0.

Yep LHH, I know it's a wall mounted air conditioner (air-to-air heat pump) of minimum size, I made these points above.

Good to know that an air-to-water heat pump should operate at a COP of 3 in Sydney.

ddarroch, good physics lessons again for me, takes me back. Good article on the different heating methods.

ddaroch and Luxury Home, you both talked about COP. I came across Australian Energy Systems website that said they have a inverter heat pump with a COP of 16.1. Does this sound realistic? http://www.poolheating.com.au/heat-pumps/residential-inverter-heat-pumps/

This heat pump sounds pretty good.

I'm pretty skeptical about a 16.1 COP. Could be a typo.
If they're going to stand by that I'd be interested to see an independent testing report from a reputable testing facility.

Yes it does seem quite high given the numbers you and ddarroch were talking about.

I'm meeting another pool renovation company next week and see what they recommend. Is there another type of company/field I should discuss this with to help make a decision?

A pool company should be able to give you a reasonable quote. Maybe shop around a couple of places and see what you get offered.

I expect you'll be offered 3 options: 1. Solar, 2. Gas, 3. Heat Pump.

As we've discussed, solar isn't an option for you, but see what they say about the gas or heat pump options.