As an example, my 3.5kW heat pump consume up to 900W (normally around 850W) and it takes about 45 min to heat the 150L tank. Bit less in summer (water is warmer and warmer outside temps) and more in winter. In the cold days of winter it can take up to 60min to heat the tank. (now there is a nice round number to divide by 
)
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Heatpump aircons are great, in winter you get almost free heat, well not really free but its like using 3 heaters and only paying for oneās consumption and in summer the cooling and more so you get dehumidification. You may not need any thoā¦.
Groetnis
Is Phil maybe referring to an aircon that can heat your room using a heat pump? So an aircon (reverse heatpump) functionality as well as a heater (heatpump) functionality. That would work well, because we end up using our aircon for heating often.
Using an aircon to double up as a water heater will probably not be feasible. Firstly your room inside is unlikely to have enough āhotā air (I think these heatpumps need to be installed in an open air environment) and secondly, you will freeze in the winter.
To find out if someone is serious ask if they have a workshopā¦
If (like myself) you are also into second hand stuff then you must visit the Milnerton Flea Market on Marine Drive CT. Itās a hardware market only (no food, art or any trivia!)
Aaah yes, thatās possible. Iām sure heāll swing by to clarify. I assumed he meant water heating since thatās the overall context of the discussion (despite the many useful and humourous diversions ). It makes perfect logical sense that pumping heat from inside the house (where you donāt want it) into a water tank (where you do want it).
Iām not sure it is practical though. This arrangement works about 3 months in the year. The rest of the time I donāt need the house to be cooled. Also, when I do need the house cooled, the AC runs up to 5 hours a day, sometimes more. At this time of the year, your showers are adjusted towards the cooler side and you generally spend less time showering too (unlike winter when we add that extra minute to warm up a bit). So I have 5 times more heat than I can put into a water tank tooā¦
What would work is some kind of combination system, where I can choose where to absorb the heat from (inside or outside). Iām sure it would cost an arm and a leg though
Re Air conditions that can also heat the room: I think that is pretty much standard now with most split-type units. In the last two decades I have not come across one that couldnāt do both.
This brings back happy memories, of visiting my parents in Cape Town and going to the flea market each Saturday. The car guards knew my dad by name and always made sure they āreservedā a spot for him. Bought quite a lot of nice tooling which I had to fly back home.
One time even bought a 4 tier oak barrel wine rack, which I had to leave there untill the next time we came up by train. In those days, around ten years ago, the Premier Classe train trip was still worthwhile.
That is indeed what I was imagining. After some googling such units do exist, and I saw a COP (Coefficient of Performance) quoted at 6.4 somewhere.
I have no idea how they overcome different seasonal demands, but that sounds to me like an universal issue that will have been long since resolved.
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I think Iām making at least one mistake here.
A dedicated heat pump (like my ITS) runs around two hours to heat the tankā¦ but that is from completely cold, and it runs at 100% utilisation.
An air-conditioner does not run at 100% utilisation. Itās main job is to keep the house cool, and if you size the thing right (and use proper insulation on the roof), it would probably run at a 50% duty cycle. So immediately I have 4-hours of hot water budget.
It is also not going to run at the same duty cycle the whole day. At around 3PM it is going to work harder than it will at 11AM.
In other words, I may be underestimating the practicality of this.
There is also nothing that prevents you from fitting a simple radiator, pump and fan to the geyser, should you need to get rid of excess heat.
I suppose there is also no reason why you cannot open doors and windows to let in warm air (with the AC running!) should you have a lack of heat.
The argument is going to break down somewhat in winter though
So a quick follow-up on the consumption of power.
Usage for the last 7 days 5.74KWh (as measured by my sonoff POW)
I have done 2 experiments. Heating and not using any water to see how much energy is lost (Needs 0.6KWh heatpump power to reheat after about 1 day of losses) vs 0.8-1 KWh to heat the water when it has been used for 2 showers. Roughly 60-80% of the re-heating power is losses.
A heatpump makes total sense if you use a lot of water as it is cheap to heat large volumes of water. Unfortunately I am not measuring my water usage (yet), but from the usage I gather that my losses are more than my usage. I should have installed the best insulated geyser I could find on the market as the price difference vs losses is a drop in the ocean.
Costs over 10 years
R16K + (R500 * 10 Services) + installation ?? R5K + power consumed (same geyser same losses and assume you already have a geyser installed)
VS normal geyser already installed + power consumed (same geyser same losses)
So heatpump = R26K + usage (low rate)
Vs Geyser = usage (high rate)
So how many litres would you need to use to offset the R26K price difference?
R26K / R2.50 (electricty price) = 10400KWh / 10 years = 1040 KWh / year ~= 86.6KWh / month or R216
If your water heating cost is below R216 then a heat pump does not make sense. I still need to add some actual usage for the heatpump so let us assume 30KWh * R2.50 so roughly R75 which mean that under R291 it does not make sense.
I was a bit shocked with the conclusion of my calculation. Maybe someone can check if they agree.
So if I can add some margin for error my conclusion: If you spend less than R300/month heating water then a heatpump is not for you as you are unlikely to break even.
Edit: Also assuming the price of electricity stays the same over 10 years which we all know is not the case. The more expensive power gets the lower your monthly spends needs to be to not break even
Edit: Changed the calc to only pay for the heatpump, and I assume we all have a geyser already installed
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Assuming a COP of 3.5, that means you have a standing loss of 0.6 times 3.5, thatās 2.1kWh, which is bang on what youād expect of a 150 liter tank.
Again, then I assume you use 0.4kWh (the difference) times 3.5 = 1.4kWh worth of electricity to reheat the water. Dude, you should at least wash the soap off before getting out of the shower! 
It takes 1.16Wh to heat one liter by one degree. 1400/1.16 ~= 1200 liter-celsius (I made up that unit), assuming ambient at 15 and fully heated at 55 (delta = 40), that means 30 liters of hot water. Of course that is an estimate based on the mentioned assumptions. And you mix it down with colder water too, so closer to 50 liters actual consumption.
At such low volumes, you are right that the heat pump makes no sense. In fact, this is the one place I would suggest using LPG (or natural gas if that is available in your area). Water heating with LPG is slightly more expensive per liter, but at very low volumes, when traded against the standing loss (which you donāt have anymore), it absolutely wins.
mmm, very interesting. Googled a bit
B rated geyser have a standing heat loss of approx. 50-60 watts per hour so about 1.5KWh p/day
vs 105 -115 achieved on the older 150l D rated geyser closer to 2.5KWh p/day
That probably means I have an older D rated geyser installed.
I have gotten used to the regime. Apply water till wet, close water, apply soap, scrub, rinse, dry.
In summer we use very little water. In winter swambo (sy wat altyd met besem opstyg) switches from the shower to the bath and tops up everytime it gets cold. The heatpump will pay for itself during winter
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