Heat pump vs electric heater for a UK pool

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tikigod19

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May 6, 2016
25
essex, uk
Hi all I have a 6000 galon outdoor pool in the uk used May-Sep (temps between 17-25 celcius)

Currently we have a 9kw heater which on first heat up this year took 48hrs (and cost me £60) to heat up. An air conditioning engineer friend came round the other day (and randomly went in the 20 degree c pool..) and said he'd heard good things about heat pumps that use the air to heat.

I've since looked and found a 14kw heat pump for £1300. If my assumptions are correct and it uses 1/5th of the electricity as stated then that will save me £440 based on 30 hours heating a week (is that unrealistic?) so within 3 years it will pay for itself (4 if I have to pay to have it fitted but it appears quite simple).

I was wondering what you guys would do. Living in the UK, the heater is one of the most important parts of our pool unlike lots of you lucky so and so's living in scorching USA.

The only disadvantage I can think of is the eyesore of the unit and also possibly the noise but I'd love to get your thoughts.

This is the model I am looking at:
Polytropic 14kw Advance M, Summer Use Single Phase Pool Heat Pump [Polytropic Advance M 14kw] - 1,350.00 :
 
I have an 18kW heat pump, probably similar style to the one you are looking at. It cost about £2k last year. In reality it adds approx 12 kW heat to the water, as calculated from flow rate and temp increase. so 1/5th is more like 1/3 to 1/4. This is still cheaper than gas and much cheaper than direct electric. It takes in 3 to 3.5kW

I made a trolley with castors for mine so that I can wheel it in the garage for the 7 months of the year it isn't being used. Hopefully it won't rust away quite so quickly!

We keep the pool between 30 and 35 degC. Opened 1st week of May this year. The heat pump ran timed from 8am to 7pm during May, but has now backed off because of the warm weather.

We have 10kW of solar PV which takes away most of the running cost and environmental guilt, but I also have a solar mat, and a heat exchanger on the central heating boiler for quick boosts if we're having guests.

It does make a noise, but we don't notice it.

I'd recommend getting the biggest heater you can, which means you can heat the pool quicker and closer to the time you are going to use it. Particularly if you don't use it every day. I'd expect your 14kW heater to take roughly the same amount of time to heat the pool as your 9kW direct heater.
 
With resistance heaters power in = heat out so when your heater is on its eating 9kw all the time. All the heat is supply by the electricity.

A heat pump on the other hand is power in x 6 = heat out. Because the heat pump is taking heat from the outside air and putting it into your pool it is much more efficient. So a 14kw output heat pump will only take roughly 2kw to run.

I can have a conversation standing next to my heat pump while its running and not have to raise my voice. From the other side of my pool I can barely hear it. Obviously though sound levels will vary depending on the make and model you buy.
 
thanks guys, seems like a sensible investment. Even if the 14kw only outputs 9kw (and I'd expect it to hopefully be nearer 12kw based on what you have all said) and it takes just as long, the 1/4 of the price is what attracts me.

I love the idea of removing it in the winter (I guess I could alternatively make a watertight boxing out of wood painted the same as the pool shed) I hadn't thought of that.

- - - Updated - - -

a34536 said:
We keep the pool between 30 and 35 degC
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Whoa! That would be a luxury! We just about got ours to 25 degrees when it was 20 outside and that took a good 48 hours so we left it there. We've actually braved it at 18/19 deg c since. Only for seconds admittedly.. that's not the way to enjoy a pool is it!!

a34536 said:
We have a heat exchanger on the central heating boiler for quick boosts if we're having guests.
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I'd love to have the luxury of something like this, the quick boost is something we'll never be able to achieve I fear whether we go heat pump or not!

So.. any disadvantages I might not be considering other than the manageable (from what you guys have said) noise?
 
You can cover it with a tarp or something if you want. But, it is designed to be outside. Get it serviced the same as you do a home heat pump/AC unit annually, check freon, etc, and it should last 10-20 years just like any other heat pump. As far as managing your water chemistry just keep PH at 7.2 or higher to prevent any damage to the heat exchanger.

Do you use a solar cover? An 8mil solar cover at night will keep in most of that heat you are paying for.
 
Definitely use a solar bubble cover, otherwise you'll lose all the heat overnight. Particularly in May and Sept when the air temperature is in single digits overnight. We lose 3 deg C overnight even with a solar cover.

The heater will draw around 2.5kW judging from the COP on the spec page, which is right on the limit for continuous operation with a 13A plug. So if you do use a normal plug on this heater, keep an eye on it - it will probably get very warm. Hardwiring or using blue 16a commando sockets would be better.

The Bowman boiler heat exchangers come up on ebay sometimes, which is where mine came from.
 

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Ok guys so I've decided on the 14kw Polytropic heat pump. I just need to decide location now.. Your thoughts?

Option 1 - outside pool shed right next to the pump but in clear view of every window in the house.

Option 2 - at the other end of the shed 8 meters away but hidden nicely away.

I'm not sure what the heat loss through friction would be. Have been advised I could use 2" pipes to reduce this but does anyone have any experience? If I'm losing 5% of the heat it may be worth avoiding the eye sore but if it's much more probably not..
 
Not only eyesore but ear-sore too. If you can see it then the sound is going straight to the window. Heat loss should be negligible. 8 meters of straight pipe will not add much head loss. I vote option 2
 
pooldv said:
Not only eyesore but ear-sore too. If you can see it then the sound is going straight to the window. Heat loss should be negligible. 8 meters of straight pipe will not add much head loss. I vote option 2
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good point. Ok I think option 2 is definitely the way to go. The garden is on a downward incline so unless I stick the heat pump on a high shelf which will be difficult, it means the pipes will drop down (and obviously go up hill on the return) about 1m in height. I assume this won't cause an issue with flow rate? (Cant give you spec of my pump off hand sorry but can find out if its an issue)
 
Height makes no difference in pool head loss because it's a circulation system. Work required to push water up is covered by energy gained when it comes down. Only the friction loss in the pipe and going through the heat exchanger will add to your head requirement (which won't be too much as mentioned previous).

The heat pump specs might (but seldom do) provide a friction loss figure. Also note that the heat pump will have a minimum and maximum flow spec, but this is very likely to be fine as well.
 
needsajet said:
Height makes no difference in pool head loss because it's a circulation system. Work required to push water up is covered by energy gained when it comes down. Only the friction loss in the pipe and going through the heat exchanger will add to your head requirement (which won't be too much as mentioned previous).

The heat pump specs might (but seldom do) provide a friction loss figure. Also note that the heat pump will have a minimum and maximum flow spec, but this is very likely to be fine as well.
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Thanks needsajet. The heat pump requires 5-8 m3/hr but I'm struggling finding a model number for my pump to check this. On the multiport valve it says Midas but that's as much info as I can get.. Do you think with a 6000 galon pool I'll have a pump that supplies between 5-8 m3/hr ?
 
dang metric. In agriculture, everything is in US gallons per minute, which is just so much handier and everyone knows it!

The conversion is 4.4 US gallons per minute per cubic metre per hour, so that's 22 to 35 US GPM. Good chance you're fine, but possibly above that. If you post your pump make/model and filter pressure we might be able to find a pump curve, which will give a rough estimate of your current flow. (if you have the pump curve, take a pic and post it. As long as your current flow meets the minimum for your heat pump, it can be readily solved with plumbing, so not a worry.
 
needsajet said:
If you post your pump make/model and filter pressure we might be able to find a pump curve, which will give a rough estimate of your current flow. (if you have the pump curve, take a pic and post it. As long as your current flow meets the minimum for your heat pump, it can be readily solved with plumbing, so not a worry.
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This is where I come unstuck. I can't see a model number on the multiport valve (am I looking at the right part?) Here are some photos of my setup

20160609_112219-2800.jpg20160615_160241-2800.jpg
 

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